JP2016111876A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce excessive purchase power by preventing the supply of power from a DC power source from being excessively suppressed while avoiding excessive operation of a reverse power relay due to reverse power.SOLUTION: In a power converter (3), control target values (Pt) for controlling operation of a power conversion part (31) are set to differ from each other when the unbalance degree representing the degree of unbalance of load current of an L1 phase and an L2 phase formed between voltage lines (L1, L2) and ground points so as not to actuate a reverse power replay (32) for stopping output from the power conversion part (31) during generation of reverse power is less than a predetermined threshold (D), and when the unbalance degree is the threshold (D) or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power converter that is connected to a commercial power system (single-phase three-wire system or three-phase three-wire system).

  In a system equipped with a DC power source such as a power storage facility, the power converter operates in an interconnected manner with the commercial power system by converting the power stored in the storage battery into a specification suitable for the load and supplying the load to the load. . In the operation of such a power converter, the installation of a reverse power relay (RPR) that stops the output of the power converter when reverse power occurs is a requirement for interconnection. Here, the condition for stopping output is that reverse power of 5% or more of the rated output power is detected for about 0.5 seconds.

  In Patent Document 1, it is determined whether or not a reverse power state is generated based on a value obtained by adding the power of each phase, and when the reverse power state is continuously generated, the relay is disconnected. A grid-connected inverter that stops output is disclosed.

Japanese Patent No. 5117687 (issued on January 16, 2013)

  When supplying power with a single-phase three-wire system, in order to prevent the RPR from being interrupted, the power received and received with each commercial power system for each phase (power receiving point power) is usually measured. Then, the output of the power converter is controlled so that the combined power in anticipation of each measurement error is in a power purchase state. Specifically, even if the measured power value of each phase is small and power can be measured with high precision by high-magnification amplification, the detected power of the power-receiving point power is large and power measurement cannot be performed with high precision by high-magnification amplification. In the same manner as in the case, the output of the power converter is controlled so that the total power at the power receiving point is in a power purchase state in consideration of the measurement error. However, even when electric power can be measured with high magnification amplification with high accuracy, if the power supply from the power storage facility is restricted in accordance with such control, the purchased electric power increases, resulting in an increase in the electricity bill. There is an inconvenience.

  The same applies to the grid-connected inverter described in Patent Document 1. In order to prevent the relay from being interrupted, there is a possibility that extra power is purchased so that reverse power is not generated.

  The present invention has been made in view of the above-described problems, and avoids excessive operation of the reverse power relay due to reverse power while preventing excessive power supply from the DC power source. The purpose is to reduce purchased electricity.

  In order to solve the above problems, a power converter according to an aspect of the present invention converts a DC power output from a DC power source into an AC power and is supplied with a commercial power from a commercial power system. A power conversion unit that controls an alternating current at a power receiving point, and is formed between the wiring and a grounding point so as to supply alternating current power in conjunction with the commercial power system to a load connected to AC power supplied by the power conversion unit when the unbalance representing the degree of unbalance of the load current of each phase is less than a predetermined threshold and when the unbalance is greater than or equal to the threshold. A control unit configured to set a control target value having a different AC current at the power receiving point for controlling and instructing the power conversion unit to operate based on the control target value.

  According to one aspect of the present invention, it is possible to prevent excessive power supply from a DC power source while preventing excessive operation of a reverse power relay due to reverse power, and to reduce excess purchased power. There is an effect that can be done.

It is a block diagram which shows the grid connection system which concerns on Embodiment 1, 3-5 of this invention. It is a block diagram which shows the structure of the control part of the power converter in the grid connection system shown to FIG. 1 and FIG. It is a block diagram which shows the grid connection system which concerns on Embodiment 2-5 of this invention. It is a figure which shows the correlation with the output electric current of the said power converter in Embodiment 3 of this invention, and the electric current bought and sold with respect to the commercial power grid. It is a figure which shows the correlation with the output electric current of the said power converter, and the electric current bought and sold with respect to the commercial power grid | system in the modification of Embodiment 3 of this invention. It is a figure which shows the correlation with the output electric current of the said power converter in Embodiment 4 of this invention, and the electric current traded with respect to the commercial power grid. It is a block diagram which shows the grid connection system which concerns on Embodiment 5 of this invention. It is a block diagram which shows the grid connection system which concerns on Embodiment 6 of this invention. In Embodiment 6, it is a figure which shows the correlation with the output electric current of the said power converter, and the electric current sold and sold with respect to the commercial power grid. In Embodiment 6, it is a figure which shows the other correlation of the output electric current of the said power converter, and the electric current traded with respect to the commercial power grid.

Embodiment 1
The following describes Embodiment 1 of the present invention with reference to FIG. 1 and FIG.

  FIG. 1 is a block diagram illustrating a grid interconnection system 11 according to the first embodiment.

<Configuration of grid interconnection system 11>
As shown in FIG. 1, the grid interconnection system 11 is operated in linkage with the commercial power grid 1. The grid interconnection system 11 includes a DC power source 2, a power converter 3, and a current detector 4.

  The commercial power system 1 is a single-phase three-wire system (AC 200 V), and supplies single-phase AC power to a power receiving point. Specifically, the commercial power system 1 applies a voltage of AC 100 V to the L1 phase formed between the voltage line L1 and the neutral line N that is grounded (connected to the ground point), and the voltage line An AC voltage of AC100V is applied to the L2 phase formed between L2 and the neutral line N, and a voltage of AC200V is applied between the voltage line L1 and the voltage line L2. Further, loads LD1 to LD3 are connected to these three wires, that is, the voltage lines L1 and L2 and the neutral wire N. Specifically, a load LD1 is connected to the L1 phase, a load LD2 is connected to the L2 phase, and a load LD3 is connected between the voltage line L1 and the voltage line L2.

  The DC power source 2 is a device serving as a DC power source that outputs DC power. The DC power source 2 is configured by a storage battery, but may be configured by a generally popular DC power source including power generation equipment such as a solar cell.

  The power converter 3 is a single-phase two-wire converter that converts DC power output from the DC power source 2 into single-phase AC power (AC 200 V) and outputs the AC power to the voltage line L1 and the voltage line L2. In addition, the power converter 3 has a function of stopping output when the commercial power system 1 is in a specified reverse power state. Further, the power converter 3 outputs the output current (or power reception) in accordance with the degree of imbalance indicating the degree of imbalance (bias) of the load current (load consumption current) between the L1 phase and the L2 phase (each phase). It has a function of changing the control target value of the summed current at the point. The power converter 3 will be described in detail later.

  In addition, although the power converter 3 is a single phase two-wire type, it is not limited to this, A single phase three-wire type may be sufficient. The same applies to the power converter 3A (see FIG. 3) in the grid interconnection system 12 of the second embodiment described later.

  The current detector 4 is a detector that detects a current at the power receiving point (current flowing through the voltage lines L1 and L2), and detects the current in the form of a voltage. The current detector 4 includes a narrow range detector 41 (first current detector) and a wide range detector 42 (second current detector) that have different current detection ranges. For example, when the rated output of the power converter 3 is 5000 [W], the narrow range detector 41 has a detection range (first detection range) of 0 to 5 [A] (0 to 500 [W]) in one phase. Current is detected (less than 5 [A] is effective), and the wide-range detector 42 has a detection range of 0 to 25 [A] (0 to 2500 [W]) in one phase (upper limit value from the first detection range). (Second detection range having a high value) is detected (between 5 [A] and less than 25 [A] is effective). Of course, the detection ranges of the narrow range detector 41 and the wide range detector 42 are not limited to the above ranges.

  The narrow range detector 41 and the wide range detector 42 are configured to detect the same current as different voltage values by making the number of coil turns and the coil material different. Although the efficiency of converting the current value [A] of the narrow range detector 41 and the wide range detector 42 into the voltage value [V] may be changed as appropriate, in the case of the narrow range detector 41, the current value I [A] is converted into the voltage. The efficiency of conversion to the value [V] is preferably I / 1.5 [V] to I / 4 [V]. In the case of the wide range detector 42, the current value [A] is converted to the voltage value [V]. The efficiency is preferably I / 8 [V] to I / 13 [V]. Hereinafter, the narrow range detector 41 of the present embodiment converts the current value I [A] into a voltage value I / 2 [V] and detects it, while the wide range detector 42 detects the current value I [A] as a voltage. It is detected by converting to the value I / 10 [V]. In this case, for example, when the detection limit of both detectors is 2.5 [V], the narrow range detector 41 detects 5 [A] as 2.5 [V], while the wide range detector 42 detects 5 [A] as 0.5 V and 25 [A] as 2.5 V.

  Note that the power at the power receiving point is calculated by the product of the current detection value and the voltage detection value at the power receiving point, but since the voltage detection value is substantially constant, it is determined predominantly by the current detection value. Therefore, in each embodiment including this embodiment, the current is detected indirectly by detecting the current with the current detector 4, the current detector 6 (see FIG. 3), and the current detector 6A (see FIG. 8). be able to.

<Configuration of power converter 3>
The power converter 3 includes a power converter 31, a reverse power relay (described as RPR in FIG. 1) 32, an amplifier circuit 33, an AD converter 34, and a controller 35.

  The power converter 31 is a main part of the power converter 3 that converts DC power into single-phase AC power. This power conversion unit 31 is connected to the commercial power grid 1 for loads LD1 to LD3 connected to the three voltage lines L1 and L2 and the neutral line N (wiring) supplied with commercial power from the commercial power grid 1. As a result, the AC power (AC current) at the power receiving point is controlled by controlling the supplied AC power (AC current) by turning on / off the switching element so as to supply AC power in an interconnected manner. Specifically, the power conversion unit 31 controls the AC power to be output based on a control instruction given by a control instruction unit 354 described later. For example, the control instruction is a switching operation pattern (switching command) of the switching element based on a control target value and a rated output current described later.

  The reverse power relay 32 is a protective relay that cuts off the output circuit of the power converter 3 so as to stop the output of the power converter 31 when the reverse power is detected. The reverse power relay 32 is provided in the power converter 3, but may be provided independently of the power converter 3.

  The amplifier circuit 33 amplifies the current detection value output as a voltage from the current detector 4. More specifically, the amplifying circuit 33 uses an analog voltage to increase the accuracy when the analog voltage output from each of the narrow range detector 41 and the wide range detector 42 is converted into a digital value by the AD converter 34. Is the input limit to the AD converter 34 (for example, the detection limit of both detectors 41 and 42 with respect to the analog voltage value is 2.5 [V], and the input limit value is 3 [V]. ).

  The AD converter 34 converts the analog voltage amplified by the amplifier circuit 33 into digital. As a result of the conversion, the AD converter 34 detects a current detection value Id1 that is a digital value of the current detected by the narrow range detector 41 and a current detection value Id2 that is a digital value of the current detected by the wide range detector 42. Is output. Here, as the current detection value Id1, the current detection value Id1L1 of the current flowing in the voltage line L1 (L1 phase current) and the current detection value Id1L2 of the current flowing in the voltage line L2 (L2 phase current) are output. The Further, as the current detection value Id2, a current detection value Id2L1 of the current flowing through the voltage line L1 and a current detection value Id2L2 of the current flowing through the voltage line L2 are output. In both detectors 41 and 42, the L1 phase current is a positive value for the flow from the power converter 3 to the commercial power system 1, and the opposite is a negative value. The flow from the converter 3 to the commercial power system 1 is detected as a negative value, and the reverse is detected as a positive value.

  The control unit 35 controls the operation of the reverse power relay 32 based on the detected current, and the sum of the alternating current at the power receiving point is the control target value so that the reverse power relay 32 does not operate when reverse power is generated. The operation of the power conversion unit 31 is controlled as much as possible. The controller 35 will be described in detail next.

<Configuration of control unit 35>
FIG. 2 is a block diagram illustrating a configuration of the control unit 35 in the power converter 3.

  As illustrated in FIG. 2, the control unit 35 includes a current determination unit 351, an RPR control unit 352, an unbalance degree calculation unit 353, and a control instruction unit 354.

  The current determination unit 351 determines which one of the current detection values Id1 and Id2 is valid, calculates a sum value (total current) of the L1 phase current and the L2 phase current at the power receiving point, This is given to the RPR control unit 352. Specifically, the current determination unit 351 determines an effective value of the current detection values Id1 and Id2 based on the values of the current detection values Id1 and Id2, and outputs the effective one to the unbalance degree calculation unit 353. To do. In addition, the current determination unit 351 calculates the total value of the current at the power receiving point by adding the determined current detection values Id1 and Id2. Thereby, for each of the L1 phase and the L2 phase, it is determined which of the current detection values Id1 and Id2 is valid, and it is determined that the current detection value Id1L1 and the current detection value Id2L1 of the L1 phase are valid. The detected value and the detected value determined to be valid among the L2 phase current detection value Id1L2 and the current detection value Id2L2 are added.

  The RPR control unit 352 determines whether or not the above-described combined current calculated by the current determination unit 351 is in a specified reverse power state, and controls to open and close the reverse power relay 32 according to the determination result The signal S is output. Specifically, the RPR control unit 352 controls the reverse power relay 32 to be in a closed state when the combined current is not in the specified reverse power state, while the combined current is in the specified reverse power state. If so, the reverse power relay 32 is controlled to be in the open state. As a result, the power converter 3 is interrupted and does not output an alternating current in a prescribed reverse power state.

  The unbalance degree calculation unit 353 includes the L1 phase value and the L2 phase value output from the current determination unit 351, the L1 phase of the power converter 3 and the control unit 35 grasping or detecting separately. The unbalance degree is calculated by using the output current value to the L2 phase. The degree of unbalance is the degree of current unbalance between the L1 phase and L2 phase consumed by the loads LD1 to LD3, that is, the degree of unbalance between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase. For example, the degree of unbalance is the difference between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase, that is, the output current value to the L1 phase of the power converter 3 and the L1 phase at the power receiving point. The difference between the detected current value) and the difference between the output current value of the power converter 3 to the L2 phase and the detected current value of the L2 phase at the power receiving point.

  The control instruction unit 354 sets and holds the control target value Pt as the control target value Pt1 when the degree of imbalance is less than a predetermined threshold value, so that the total current at the power receiving point becomes the control target value Pt. The power conversion unit 31 is instructed by giving a control instruction (the aforementioned switching command). Further, when the degree of imbalance is equal to or greater than the threshold value, the control instruction unit 354 sets and holds the control target value Pt at a control target value Pt2 that is larger than the control target value Pt1, and the total current at the power receiving point is the control target value. A control instruction is given to the power converter 31 so as to be the value Pt2. Furthermore, the control instruction unit 354 gives a control instruction to the power conversion unit 31 so as to output the rated output current as necessary.

  Here, the control target value Pt is a target value that the sum of the L1 phase current and the L2 phase current (total current) at the power receiving point should reach as a result of the control of the output current by the power conversion unit 31. It is set to a value that does not cause a reverse power state. The power converter 31 controls the output current so that the total current reaches the control target value Pt.

  Moreover, said threshold value is defined in the positive range which does not exceed the rated output current (1/2 of rated output current) in the single phase of the power converter 3, for example.

<Operation of grid interconnection system 11>
The setting operation of the control target value Pt by the grid interconnection system 11 configured as described above will be described.

  First, a case will be described in which it is determined that the currents detected by the narrow range detector 41 in both the L1 phase and the L2 phase are effective because both the currents flowing through the power receiving points of the voltage lines L1 and L2 are small. In this case, in the power converter 3, the amplifier circuit 33 includes the current detection value from the narrow range detector 41 (first detection value, L1 phase current value and L2 phase current value) and the wide range detector 42. The current detection values (second detection value, L1 phase current value, and L2 phase current value) are amplified. For example, when a current of 4 [A] flows and the current detection value from the narrow range detector 41 is 2 [V], the amplifier circuit 33 amplifies to 2.4 [V] with an amplification factor of 1.2. To do. Further, when a current of 4 [A] flows and the current detection value from the wide range detector 42 is 0.4 [V], the amplifier circuit 33 has a gain of 1.2 times 0.48 [V]. ] Is amplified.

  The AD converter 34 converts the current detection values from the narrow range detector 41 and the wide range detector 42 amplified by the amplifier circuit 33 into digital current detection values Id1 and Id2, and outputs the current detection values.

  In the control unit 35, the current determination unit 351 determines that the current detection value Id1 is an effective value within the first detection range because the magnitude of the current detection value Id1 is less than the maximum value (5 [A] in the example). The current detection value Id2 is not used. The current determination unit 351 outputs the detected current values Id1L1 and Id1L2 of the L1 phase and the L2 phase of the adopted current detection value Id1 to the unbalance degree calculation unit 353, and obtains the sum of the values. The unbalance degree calculation unit 353 uses the current detection values Id1L1 and Id1L2 and the output current values to the L1 phase and the L2 phase of the power converter 3 that are grasped by the control unit 35 or separately detected, Find the degree of imbalance. When the control instruction unit 354 determines that the unbalance degree is less than the threshold value by comparing the unbalance degree from the unbalance degree calculation unit 353 with the threshold value, the control instruction value 354 sets the control target value Pt1 as the control target value Pt, A control instruction based on the control target value Pt1 is given to the power converter 31. On the other hand, when the control instruction unit 354 determines that the degree of imbalance is equal to or greater than the threshold, the control target value Pt2 is set as the control target value Pt, and a control instruction based on the control target value Pt2 is given to the power conversion unit 31.

  When receiving the control instruction from the control instruction unit 354, the power conversion unit 31 switches the switching operation pattern of the switching element so that there is no difference between the control target value Pt and the current total value calculated by the current determination unit 351. Is appropriately changed to control the output current.

  Next, a case will be described in which it is determined that the current flowing through the power receiving points of the voltage lines L1 and L2 is large and the current detected by the wide range detector 42 is effective in both the L1 phase and the L2 phase. In this case, since the detected current exceeds the detection range of the narrow range detector 41 (overrange), the narrow range detector 41 cannot be detected, but outputs the maximum value of the detection range. In the power converter 3, the amplifier circuit 33 amplifies the current detection values (second detection value, L1 phase current value and L2 phase current value) from the wide range detector 42, but from the narrow range detector 41. The maximum current detection value is also amplified. For example, when a current of 20 [A] flows and the current detection value from the wide range detector 42 is 2 [V], the amplifier circuit 33 is 2.4 [V] with an amplification factor of 1.2. Amplify to. Further, when a current of 20 [A] flows and the current detection value from the narrow range detector 41 is 2.5 [V], the amplifier circuit 33 has an input limit value of 3 [ V].

  When the wide range detector 42 detects a current of 5 [A] to 25 [A], the narrow range detector 41 detects 5 [A] which is the maximum detection value. In this case, both detection values are amplified by the amplifier circuit 33 and then converted into digital values by the AD converter 34, but the current detection value Id1 is always 5 [A]. In such a case, the current determination unit 351 determines that the current detection value Id2 is valid.

  The AD converter 34 converts the current detection value (maximum value) from the narrow range detector 41 amplified by the amplifier circuit 33 into a digital current detection value Id1 and outputs the converted current detection value Id1. The current detection value from the range detector 42 is converted into a digital current detection value Id2 and output.

  In the control unit 35, the current determination unit 351 has a maximum current detection value Id1 (including a negative minimum value) and a maximum current detection value Id2 (25 [A] in the example). Therefore, the current detection value Id2 is adopted as an effective value within the second detection range. The current determination unit 351 outputs the detected current values Id2L1 and Id2L2 of the L1 phase and the L2 phase of the adopted current detection value Id2 to the unbalance degree calculation unit 353, and also calculates the total value thereof. By using the current detection values Id2L1 and Id2L2 and the output current values to the L1 phase and the L2 phase of the power converter 3 that are detected or separately detected by the control unit 35, the unbalance degree calculation unit 353 Find the degree of imbalance. When the control instruction unit 354 determines that the unbalance degree is less than the threshold value by comparing the unbalance degree from the unbalance degree calculation unit 353 with the threshold value, the control instruction value 354 sets the control target value Pt1 as the control target value Pt, A control instruction based on the control target value Pt1 is given to the power converter 31. On the other hand, when the control instruction unit 354 determines that the degree of imbalance is equal to or greater than the threshold, the control target value Pt2 is set as the control target value Pt, and a control instruction based on the control target value Pt2 is given to the power conversion unit 31.

  When receiving the control instruction from the control instruction unit 354, the power conversion unit 31 switches the switching operation pattern of the switching element so that there is no difference between the control target value Pt and the current total value calculated by the current determination unit 351. Is appropriately changed to control the output current.

  Note that one of the currents flowing through the power receiving points of the voltage lines L1 and L2 is small, the current detected by the narrow range detector 41 is determined to be effective, and the other of the currents flowing through the power receiving points of the voltage lines L1 and L2 is large. Even when the current detected by the wide range detector 42 is determined to be effective, the unbalance is calculated using the current values determined to be effective, and the control target value setting and output current control are performed. Are performed in the same manner as described above.

<Effect of grid interconnection system 11>
The grid interconnection system 11 according to the present embodiment controls the output current of the power converter 3 as described above, so that the total value of the L1 phase current and the L2 phase current at the power reception point is in the reverse power state. Not. Thereby, it can avoid operating the reverse power relay 32 to an open state.

  In the grid interconnection system 11, the current-voltage conversion magnification (for example, the above-mentioned 1/2) by the narrow range detector 41 is the current-voltage conversion magnification (for example, the above-mentioned 1/10) by the wide range detector 42. Bigger than. Thereby, it can be said that the current detection value of the narrow range detector 41 is more accurate than the current detection value of the wide range detector 42.

  Further, the control unit 35 reduces the control target value Pt1 when the difference between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase is small and the unbalance is less than the threshold value. Set to. On the other hand, the control unit 35 sets the control target value Pt from the control target value Pt1 when the difference between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase is large and the unbalance degree is equal to or greater than the threshold value. A large control target value Pt2 is set. In other words, when the current flowing through the voltage lines L1 and L2 such that the narrow range detector 41 detects current is small, the control target value Pt1 is easily adopted as the control target value Pt, and the wide range detector 42 is When the current flowing through the voltage lines L1 and L2 that detect current is large, the control target value Pt2 is likely to be adopted as the control target value Pt.

  Thus, when the current at the power receiving point is detected with low accuracy (with a large error) using the wide range detector 42, the control target value Pt is set to a large control target value Pt2 that allows for a large error. . In this case, the output current of the power converter 3 is controlled so as to be in a power purchase state from the commercial power system 1. On the other hand, when the current at the power receiving point is detected with high accuracy (with a small error) using the narrow range detector 41, the control target value Pt is suppressed to the control target value Pt1 that allows for a small error. In this case, since the output current of the power converter 3 is controlled based on the control target value Pt1 that is small, power purchase from the commercial power system 1 can be suppressed while securing power supply from the DC power source 2. . Therefore, excessive power purchase can be suppressed.

  The amplifier circuit 33 is commonly used for amplification of the current detection values of the narrow range detector 41 and the wide range detector 42. Thereby, it is not necessary to provide a dedicated amplifier circuit for each of the narrow range detector 41 and the wide range detector 42.

[Embodiment 2]
Embodiment 2 of the present invention will be described below with reference to FIGS. 2 and 3. For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those of the constituent elements in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 3 is a block diagram illustrating the grid interconnection system 12 according to the second embodiment.

<Configuration of grid interconnection system 12>
As shown in FIG. 3, the grid interconnection system 12 includes a DC power supply 2 as in the grid interconnection system 11 in the first embodiment. The grid interconnection system 12 includes a power converter 3A and a current detector 6 instead of the power converter 3 and the current detector 4 in the grid interconnection system 11, respectively.

  The power converter 3A is a single-phase two-wire converter similar to the power converter 3 in the grid interconnection system 11, and has a function of stopping output when a specified reverse power state is obtained, and a load LD1. It has a function of changing the control target value of the output current in accordance with the degree of unbalance between the phases of LD3. The power converter 3A will be described in detail later.

  The current detector 6 is a detector that detects the current at the power receiving point (current flowing through the voltage lines L1 and L2), and the wide range detection used in the current detector 4 in the grid interconnection system 11 of the first embodiment described above. A vessel 42 can be used.

<Configuration of power converter 3A>
Similarly to the power converter 3, the power converter 3 </ b> A includes a power conversion unit 31, a reverse power relay (described as RPR in FIG. 3) 32, and a control unit 35. The power converter 3A includes a high-magnification amplification circuit 36 (first amplification circuit) and a low-magnification amplification circuit 37 (second amplification circuit) instead of the amplification circuit 33 of the power converter 3. Here, as the low-magnification amplifier circuit 37, the amplifier circuit 33 in the power converter 3 described above can be used. The AD converter 34 can be the same as the AD converter 34 in the power converter 3 described above, and converts the analog output voltages of the high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 into digital values.

  The high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 AD-convert the analog voltage value in order to increase the accuracy when the analog voltage output from the current detector 6 is converted into a digital value by the AD converter 34. (For example, the detection limit of the current detector 6 with respect to the value of the analog voltage is 2.5 [V], and the input limit value is 3 [V]). The high magnification amplification circuit 36 and the low magnification amplification circuit 37 amplify the current detection values output as voltages from the current detector 6 with different amplification factors. For example, the high magnification amplifier circuit 36 has an amplification factor (first amplification factor) of 6 times (= 3 / 0.5), and the low magnification amplifier circuit 37 has an amplification factor of 1.2 times (= 3 / 2.5). It has an amplification factor (second amplification factor). Thereby, the high-magnification amplification circuit 36 amplifies the current detection value up to 5 [A] (= 0.5 [V]), and the low-magnification amplification circuit 37 is 25 [A] (= 2.5 [V]. ] Is amplified. Therefore, the low magnification amplification circuit 37 amplifies a wider range of current detection values than the high magnification amplification circuit 36.

<Operation of grid interconnection system 12>
The setting operation of the control target value Pt by the grid interconnection system 12 configured as described above will be described.

  First, a case will be described in which it is determined that both the currents flowing through the power receiving points of the voltage lines L1 and L2 are small and the current amplified by the high-magnification amplification circuit 36 is effective in both the L1 phase and the L2 phase. In this case, in the power converter 3A, the high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 amplify the current detection values (the current value of the L1 phase and the current value of the L2 phase) from the current detector 6. For example, when the current detection value from the current detector 6 is 0.4 V (4 [A]), the high-magnification amplification circuit 36 sets the current detection value to 6 in the first amplification range (first amplification range). Amplify to 2.4 [V]. Further, the low-magnification amplification circuit 37 amplifies the current detection value to 0.48 [V] that is 1.2 times in the second amplification range (second amplification range).

  The AD converter 34 converts the current detection values from the current detector 6 amplified by the high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 into digital current detection values Id1 and Id2, respectively, and outputs them. The current detection values are the same as those in the first embodiment, but here, the current detection values are distinguished by the output amplification circuits 36 and 37.

  In the control unit 35, the current determination unit 351 adopts the current detection value Id1 as an effective value within the first amplification range when the magnitude of the current detection value Id1 is less than the maximum value (in the example, 5 [A]). The current detection value Id2 is not adopted. The current determination unit 351 outputs the detected current values Id1L1 and Id1L2 of the L1 phase and the L2 phase of the adopted current detection value Id1 to the unbalance degree calculation unit 353, and also calculates the total value thereof. By using the current detection values Id1L1 and Id1L2 and the output current values to the L1 phase and the L2 phase of the power converter 3A, which are grasped by the control unit 35 or separately detected, the unbalance degree calculation unit 353 Calculate the degree of imbalance. When the control instruction unit 354 determines that the unbalance degree is less than the threshold value by comparing the unbalance degree from the unbalance degree calculation unit 353 with the threshold value, the control instruction value 354 sets the control target value Pt1 as the control target value Pt, A control instruction based on the control target value Pt1 is given to the power converter 31. On the other hand, when the control instruction unit 354 determines that the degree of imbalance is equal to or greater than the threshold, the control target value Pt2 is set as the control target value Pt, and a control instruction based on the control target value Pt2 is given to the power conversion unit 31.

  When the power conversion unit 31 receives a control instruction from the control instruction unit 354, the power conversion unit 31 performs the same as in the first embodiment so that the difference between the control target value Pt and the current total value calculated by the current determination unit 351 is eliminated. To control the output current.

  Next, a case will be described in which it is determined that both the currents flowing through the power receiving points of the voltage lines L1 and L2 are large and the current amplified by the low-magnification amplification circuit 37 is effective in both the L1 phase and the L2 phase. In this case, the detected current exceeds the input limit value (for example, 0.5 V) to the high-magnification amplification circuit 36 (overrange), and the maximum value of the input range is input. In the power converter 3A, the high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 amplify the current detection value from the current detector 6 with each amplification range and amplification factor. For example, when the current detection value from the current detector 6 is 2 [V] (20 [A]), the high-magnification amplification circuit 36 sets the current detection value to 3 [V] which is the maximum value of the output range. The low-amplification amplifier circuit 37 amplifies the current detection value to 2.4 [V] with an amplification factor of 1.2.

  When the current detector 6 detects 0.5 [V] to 2.5 [V] (5 [A] to 25 [A]), the high-magnification amplification circuit 36 has a maximum value of 3 [V]. Is output. In this case, the current detection value Id1 is always 5 [A]. In such a case, the current determination unit 351 determines that the current detection value Id2 is valid.

  The AD converter 34 converts the current detection values from the current detector 6 amplified by the high-magnification amplification circuit 36 and the low-magnification amplification circuit 37 into digital current detection values Id1 and Id2, respectively, and outputs them.

  In the control unit 35, the current determination unit 351 determines that the magnitude of the current detection value Id2 is the maximum value (in the example, 25 [A]) when the magnitude of the current detection value Id1 is the maximum value (including the negative minimum value). ), The current detection value Id2 is adopted as an effective value within the second amplification range, and the current detection value Id1 is not adopted. The current determination unit 351 outputs the detected current values Id2L1 and Id2L2 of the L1 phase and the L2 phase of the adopted current detection value Id2 to the unbalance degree calculation unit 353, and also obtains the sum value thereof. By using the current detection values Id2L1 and Id2L2 and the output current values to the L1 phase and the L2 phase of the power converter 3 that are detected or separately detected by the control unit 35, the unbalance degree calculation unit 353 Calculate the degree of imbalance. When the control instruction unit 354 determines that the unbalance degree is less than the threshold value by comparing the unbalance degree from the unbalance degree calculation unit 353 with the threshold value, the control instruction value 354 sets the control target value Pt1 as the control target value Pt, A control instruction based on the control target value Pt1 is given to the power converter 31. On the other hand, when the control instruction unit 354 determines that the degree of imbalance is equal to or greater than the threshold, the control target value Pt2 is set as the control target value Pt, and a control instruction based on the control target value Pt2 is given to the power conversion unit 31.

  When receiving the control instruction from the control instruction unit 354, the power conversion unit 31 controls the output current so that there is no difference between the control target value Pt and the current total value calculated by the current determination unit 351.

  Note that one of the currents flowing through the power receiving points of the voltage lines L1 and L2 is small, and it is determined that the current amplified by the high-magnification amplification circuit 36 is effective, and the other of the currents flowing through the power receiving points of the voltage lines L1 and L2 is Even when it is determined that the current amplified by the low-magnification amplification circuit 37 is valid, the degree of imbalance is calculated using each current value determined to be effective, and the control target value setting and output current are calculated. Control is performed in the same manner as described above.

<Effect of grid interconnection system 12>
The grid interconnection system 12 according to the present embodiment controls the output current of the power converter 3 as described above, so that the total value of the L1 phase current and the L2 phase current at the power receiving point is in the reverse power state. Not. Thereby, it can avoid operating the reverse power relay 32 to an open state.

  Further, the control unit 35 reduces the control target value Pt1 when the difference between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase is small and the unbalance is less than the threshold value. Set to. On the other hand, the control unit 35 sets the control target value Pt from the control target value Pt1 when the difference between the total load current consumption of the L1 phase and the total load current consumption of the L2 phase is large and the unbalance degree is equal to or greater than the threshold value. A large control target value Pt2 is set. In other words, when the current flowing through the voltage lines L1 and L2 is small (eg, 0 [A] or more and less than 5 [A]), the control target value Pt1 is easily set as the control target value Pt, and the voltage line L1 , L2 is large (for example, 5 [A] or more and less than 25 [A]), the control target value Pt1 is easily set as the control target value Pt.

  As a result, when the current at the power receiving point is amplified with low accuracy (with a large error) by the low-magnification amplification circuit 37, the control target value Pt is set to a large control target value Pt2 that allows for a large error. In this case, the output current of the power converter 3 </ b> A is controlled so that the power is purchased from the commercial power system 1. On the other hand, when the current at the power receiving point is amplified with high accuracy (with a small error) by the high-magnification amplification circuit 36, the control target value Pt is suppressed to the control target value Pt1 that allows for a small error. In this case, since the output current of the power converter 3 is controlled based on the control target value Pt1 that is small, power purchase from the commercial power system 1 can be suppressed while securing power supply from the DC power source 2. . Therefore, excessive power purchase can be suppressed.

  In addition, the grid interconnection system 12 includes a high-magnification amplification circuit 36 and a low-magnification amplification circuit 37, thereby replacing the current detector 4 (the narrow range detector 41 and the wide range detector 42) in the grid interconnection system 11. A simplified current detector 6 is employed. Thereby, the configuration of the grid interconnection system 12 is complicated as an amplifier circuit, but the configuration of the current detector 6 that is more expensive than the amplifier circuit is simplified, so that the cost is lower than that of the grid interconnection system 11. Can be configured.

[Embodiment 3]
Embodiment 3 of the present invention will be described below with reference to FIGS. For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those of the constituent elements in the first and second embodiments are denoted by the same reference numerals and description thereof is omitted.

<Setting of control target value Pt>
In the present embodiment, details of determination of the control target value Pt in the grid interconnection system 11 (see FIG. 1) according to the first embodiment and the grid interconnection system 12 (see FIG. 3) according to the second embodiment will be described. .

  FIG. 4 is a diagram showing a correlation between the output current of the power converter 3 and the grid current purchased and sold for the commercial power grid 1.

  In the present embodiment, the control instruction unit 354 of the control unit 35 shown in FIG. 2 sets the above-described threshold as follows.

  First, the detected current values in the L1 phase and the L2 phase at the power reception point adopted by the current determination unit 351 of the control unit 35, and the L1 phase of the power converter 3 that the control unit 35 grasps or detects separately. Of the total load currents (consumption currents) of the L1 phase and the L2 phase calculated from the output current value to the L2 phase and the L2 phase, the larger one is A [A] and the smaller one is B [A] (0 ≦ B ≦ A), the rated output current of the power converter 3 is C [A] (C / 2 [A] for each of the L1 phase and the L2 phase), and the threshold is D [A] (0 <D <C / 2).

[1] 0 ≦ A + B ≦ C (total current consumption is 0 or more and C or less)
(1) 0 ≦ A−B <D (the degree of imbalance is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
In this case, current is exchanged as shown in FIG. In the L1 phase, when the current of (A + B) / 2 is output from the power converter 3 (power conversion unit 31), the power of (A−B) / 2 is purchased from the commercial power system 1, that is, the power A [A] is obtained by adding the converter output current and the power purchase current. In the L2 phase, when (A + B) / 2 power is output from the power converter 3, the (A−B) / 2 current is sold to the commercial power system 1, that is, from the power converter output current. B [A] is obtained by subtracting the current selling current.

(2) D ≦ A−B ≦ C (the degree of imbalance is not less than D and not more than C)
Control target value Pt = Pt2 = C * 0.05 [A] (power purchase)
0.05: Maximum value of error in current detection (current measurement) that is assumed [2] C <A + B
In this case, since the total current consumption exceeds the rated output current C, even if the power conversion unit 31 outputs the rated output current C, it does not become reverse power, so that the rated output current C [A] is output. The power converter 31 is controlled.

<Effect by setting control target value Pt>
When the total current consumption is 0 or more and C or less, if the unbalance is 0 or more and less than the threshold D, the control target value Pt1 is set to 0 [A], while the unbalance is more than the threshold D and rated If it is equal to or less than the output current C, the control target value Pt2 is set to C * 0.05 [A] (power purchase). As a result, as shown in FIG. 4, when the degree of unbalance is 0 or more and less than the threshold value D, the sum of the trading currents of the L1 phase and the L2 phase at the power receiving point becomes 0. it can. In addition, when the degree of imbalance is not less than the threshold value D and not more than the rated output C, it is possible to purchase power so as to avoid reverse power.

<Modification>
A modification of this embodiment will be described.
FIG. 5 is a diagram showing a correlation between the output current of the power converter 3 and the grid current that is bought and sold for the commercial power grid 1.

  In this modification, the threshold value D is set as follows.

D = Dp × 2
Here, Dp represents a current detection range change threshold value. The current detection range change threshold is expressed by a boundary value between the range of the current detection value Id1 (low range) and the range of the current detection value Id2 (high range) adopted by the current determination unit 351 in the grid interconnection systems 11 and 12. It is determined by the upper limit value (for example, 5 [A]) of the range of the detection value Id1.

  When the aforementioned control target value Pt = 0, as shown in FIG. 5, in a state where 0 ≦ (A−B) / 2 <Dp, that is, 0 ≦ A−B <D, the power converter 3 outputs With respect to the output current of (A + B) / 2, the current of buying and selling is obtained while obtaining A [A] and B [A] by buying and selling the current of (A−B) / 2 from the commercial power system 1. Offset.

  Also, at the moment when (A−B) / 2 becomes equal to or greater than the current detection range change threshold Dp, the moment when Dp = (A−B) / 2, that is, 2Dp = A−B, the current detection range is changed from the low range to the high range. The Therefore, by setting D = Dp × 2, when the current detection range is changed, switching is performed in the case of (2) D ≦ A−B ≦ C, and the control target value Pt (Pt2) is changed to the power purchase. Is done. Thereby, the timing which changes an electric current detection range, and the timing which changes control target value Pt synchronize.

  In the configuration of the above-described third embodiment, at the time when the current detection range is changed (when the current detection value Id1 exceeds the current detection range change threshold Dp), the control unit 35 has a current that is less accurate than the current detection value Id1. The total current is calculated by switching to the detection value Id2. For this reason, even if the control unit 35 attempts to control the power conversion unit 31 so that the summed current at the power receiving point is 0 [A] (control target value Pt = 0 [A]), in reality, the power sale (reverse) There is a possibility that it is in a tidal current state.

  On the other hand, by synchronizing the timing for changing the current detection range and the timing for changing the control target value Pt, the control target value Pt is changed from 0 to a value in a power purchase state at the synchronized timing. As a result, even if the total current is calculated using the current detection value Id2 with low accuracy, the control target value Pt is changed according to the current detection value Id2, so that the reverse power flow can be avoided more reliably.

[Embodiment 4]
The following description will discuss Embodiment 4 of the present invention with reference to FIGS. 1 to 3 and FIG. 6. For convenience of explanation, in the present embodiment, constituent elements having functions equivalent to those in the first to third embodiments are denoted by the same reference numerals and description thereof is omitted.

<Setting of control target value Pt>
In the present embodiment, details of determination of the control target value Pt in the grid interconnection system 11 (see FIG. 1) according to the first embodiment and the grid interconnection system 12 (see FIG. 3) according to the second embodiment will be described. .

  FIG. 6 is a diagram showing a correlation between the output current of the power converter 3 and the grid current purchased and sold for the commercial power grid 1.

  In the present embodiment, the control instruction unit 354 of the control unit 35 shown in FIG. 2 sets the above-described threshold as follows.

  First, as in the above-described third embodiment, among the total load currents (consumption currents) of the L1 phase and the L2 phase, the larger one is A [A] and the smaller one is B [A] (0 ≦ B ≦ A) The rated output current of the power converter 3 is C [A] (C / 2 [A] for each of the L1 phase and the L2 phase), and the threshold is D [A] (0 <D <C / 2). To do. The threshold value D is D = Dp × 2.

[1] 0 ≦ A + B ≦ C (total current consumption is 0 or more and C or less)
(1) 0 ≦ A−B <D (the degree of imbalance is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
(2) D ≦ A−B ≦ C (the degree of imbalance is not less than D and not more than C)
Control target value Pt = Pt2 = (A−B) * Er [A] (power purchase)
Er: Assumed current detection (current measurement) error (range 0.02-0.05)
In this case, current is exchanged as shown in FIG. In the L1 phase, when the current of (A + B) / 2− (A−B) * Er / 2 is output from the power converter 3 (power conversion unit 31), the commercial power system 1 outputs (A−B) / 2 + ( A-A) A [A] is obtained by purchasing a current of * Er / 2. Further, in the L2 phase, when the power of (A + B) / 2− (A−B) * Er / 2 is output from the power converter 3, (A−B) / 2− (A−B) to the commercial power system 1 ) B [A] is obtained by selling a current of * Er / 2. In this way, by setting the control target value Pt to (A−B) * Er [A], both of the output currents of the power converter 3 are (A−B) * for the L1 phase and the L2 phase. The value is obtained by subtracting Er / 2. In addition, for the L1 phase, (AB) * Er / 2 power purchase increases, while for the L2 phase, (A-B) * Er / 2 power sale decreases.

[2] C <A + B
In this case, since the total current consumption exceeds the rated output current C, the power converter 31 does not become reverse power even if the rated output current C is output, so that the rated output current C [A] is output. The power converter 31 is controlled.

<Effect by setting control target value Pt>
When the total current consumption is 0 or more and C or less, if the unbalance is 0 or more and less than the threshold D, the control target value Pt1 is set to 0 [A], while the unbalance is more than the threshold D and rated If it is equal to or less than the output current C, the control target value Pt2 is set to (A−B) * Er [A] (power purchase). Thereby, when the degree of imbalance is not less than the threshold value D and not more than the rated output current C, it is possible to purchase power so as to avoid reverse power. Specifically, in both the L1 phase and the L2 phase, when the trading current includes an error component of (A−B) * Er / 2 with respect to (A−B) / 2, in the worst case, in the L1 phase, ( While only A-B) / 2- (A-B) * Er / 2 is purchased, the L2 phase sells (A-B) / 2 + (A-B) * Er / 2. In that case, even if we intend to control the total value of trading current to 0, we sell (A−B) * Er as a result of adding the two-phase trading current. It will be. Therefore, by setting this value as the control target value Pt2, reverse power can be avoided while obtaining the load currents A and B.

<Modification>
A modification of this embodiment will be described.

  In this modification, by introducing the auxiliary threshold value E (D <E <C) and the coefficient α (0 <α <1), the case of 0 ≦ A + B ≦ C (total current consumption is 0 or more and C or less) The control target value Pt is set as follows.

(1) 0 ≦ A−B <D (the degree of imbalance is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
(2) D ≦ A−B <E (the degree of imbalance is not less than D and less than E)
Control target value Pt = Pt2 (second control target value) = (A−B) * Er * α [A] (power purchase)
(3) E ≦ A−B ≦ C (the degree of unbalance is E or more and C or less)
Control target value Pt = Pt2 (first control target value) = (A−B) * Er [A] (power purchase)
In this way, by introducing the auxiliary threshold value E, when the degree of imbalance is not less than D and less than E, the error Er itself is reduced, so that the error Er is multiplied by a coefficient α smaller than 1. . As a result, the amount of power purchase can be further reduced within a range where the error Er is reduced.

[Embodiment 5]
The following describes Embodiment 5 of the present invention with reference to FIG. 2, FIG. 4, and FIG. For convenience of explanation, in this embodiment, components having functions equivalent to those of the components in the second embodiment are denoted by the same reference numerals and description thereof is omitted.

  FIG. 7 is a block diagram illustrating the grid interconnection system 13 according to the fifth embodiment.

<Configuration of grid interconnection system 13>
As shown in FIG. 7, the grid interconnection system 13 includes a DC power supply 2, a power converter 3 </ b> A, and a current detector 6, similar to the grid interconnection system 12 in the above-described second embodiment. The grid interconnection system 13 further includes a surplus power absorption device 7.

  The surplus power absorbing device 7 is a device that absorbs surplus power of either the L1 phase or the L2 phase, and includes an auxiliary battery, an adjustment load, and the like. Of the power lines connecting the surplus power absorbing device 7 to the voltage lines L1, L2 and the neutral line N, the power lines connecting the surplus power absorbing device 7 and the voltage lines L1, L2 are provided with switches SW1, SW2, respectively. It has been.

  In the present embodiment, the control unit 35 is configured as follows, unlike the other embodiments.

  When the total consumption current of the L1 phase and the L2 phase at the power receiving point is equal to or lower than the rated output current of the power converter 3, the control unit 35 controls the power conversion unit 31 with the control target value Pt1 as 0 [A]. Further, in this case, when the degree of imbalance is equal to or greater than the threshold value D, the control unit 35, based on the current adopted by the current determination unit 351 shown in FIG. The opening and closing of the switches SW1 and SW2 is controlled so that the surplus power absorbing device 7 is connected to the connected one.

  Further, when the total consumption current is larger than the rated output current of the power converter 3, the control unit 35 controls the power conversion unit 31 so that the power converter 3 outputs the rated output current.

<Setting of control target value Pt>
As in the third embodiment, among the total load currents (consumption currents) of the L1 phase and the L2 phase, the larger one is A [A] and the smaller one is B [A] (0 ≦ B ≦ A). The rated output current of the power converter 3 is C [A] (C / 2 [A] for each of the L1 phase and the L2 phase), and the threshold is D [A] (0 <D <C / 2).

[1] 0 ≦ A + B ≦ C (total current consumption is 0 or more and C or less)
(1) 0 ≦ A−B <D (the degree of imbalance is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
(2) D ≦ A−B ≦ C (the degree of imbalance is not less than D and not more than C)
Control target value Pt = Pt2 = 0 [A] (here, Pt1 = Pt2)
In the cases of (1) and (2), as in the case of 0 ≦ AB <D in the third embodiment, current is exchanged as shown in FIG. In the L1 phase, when the current of (A + B) / 2 is output from the power converter 3, A [A] is obtained by purchasing the current of (A−B) / 2 from the commercial power system 1. Further, in the L2 phase, when the current of (A + B) / 2 is output from the power converter 3, B [A] is obtained by flowing the current of (A−B) / 2 in the direction of the commercial power system 1. .

[2] C <A + B
In this case, the power converter 31 is controlled so as to output the rated output power C [A].

<Effect of grid interconnection system 13>
As described above, the grid interconnection system 13 sets the control target value Pt2 to 0 [A] so that the total current at the power receiving point becomes 0 [A] even when the unbalance between the phases of the load is large. Set to. Even if surplus power is generated due to an error in current detection, the surplus power is absorbed by the surplus power absorbing device 7, so that reverse power flow can be avoided. Therefore, the purchased power can be further reduced by not operating the reverse power relay 32 by the reverse power regardless of the current detection error.

  The grid interconnection system 13 according to the present embodiment basically has the same configuration as that of the grid interconnection system 12 according to the second embodiment, but the grid interconnection system 11 according to the first embodiment has the same configuration. You may apply.

[Embodiment 6]
The fifth embodiment of the present invention will be described below with reference to FIGS. 2 and 8 to 10. For convenience of explanation, in this embodiment, constituent elements having functions equivalent to those in the second and third embodiments are denoted by the same reference numerals and description thereof is omitted.

  FIG. 8 is a block diagram illustrating the grid interconnection system 14 according to the fifth embodiment.

<Configuration of grid interconnection system 14>
As shown in FIG. 8, the grid interconnection system 14 is operated in linkage with the commercial power grid 1A. Further, the grid interconnection system 14 includes the DC power supply 2 as in the grid interconnection system 12 in the second embodiment. Furthermore, the grid interconnection system 14 includes a power converter 3B and a current detector 6A instead of the power converter 3A and the current detector 6 in the grid interconnection system 12, respectively.

  The commercial power system 1A is a three-phase three-wire system (AC 200V), and supplies three-phase AC power to a power receiving point. Specifically, the commercial power system 1A includes a voltage line U and a ground point (U phase), a voltage line V and a ground point (V phase), and a voltage line W and a ground point ( AC voltage of AC 200V is applied to each of the W phase. For example, a load LD11 is connected to the U phase, a load LD12 is connected to the V phase, and a load LD13 is connected to the W phase. The load LD 14 that consumes the three-phase AC power is connected to the voltage lines U, V, and W.

  The power converter 3B is a three-phase, three-wire converter, and has a function of stopping output when a reverse power state occurs and a load current consumption bias between the U phase, the V phase, and the W phase. A function of changing the control target value of the output in accordance with the degree of unbalance to be expressed. The power converter 3B replaces the two-wire power conversion unit 31 and the reverse power relay 32 included in the power converter 3A in the grid interconnection system 12 with a three-wire power conversion unit 38 and a reverse power relay 39, respectively. Have. The power conversion unit 38 and the reverse power relay 39 handle three-phase AC power, respectively, but basically have functions equivalent to those of the power conversion unit 31 and the reverse power relay 32.

  Similarly to the power converter 3A in the grid interconnection system 12, the power converter 3B includes a high-magnification amplification circuit 36, a low-magnification amplification circuit 37, an AD converter 34, and a control unit 35. . The high-magnification amplification circuit 36, the low-magnification amplification circuit 37, the AD converter 34, and the control unit 35 according to the present embodiment handle three-phase AC power unlike the case of handling single-phase AC power in the second embodiment. Basically, it has a function equivalent to the function in the second embodiment.

  The current detector 6A is different from the two-wire current detector 6 in the grid interconnection system 12 in that the current at the receiving points of the voltage lines U, V, and W is different, but basically the current detector 6 has the same current detection function.

<Setting of control target value Pt>
FIG. 9 is a diagram illustrating a correlation between the output power of the power converter 3B and the grid power purchased and sold for the commercial power grid 1A.

  In the present embodiment, the control instruction unit 354 of the control unit 35 shown in FIG. 2 sets the above-described threshold as follows.

  First, the power converter employed by the current determination unit 351 of the control unit 35, the current detection values of the U phase, V phase, and W phase at the power receiving point, and the control unit 35 grasps or is separately detected. The total load current (current consumption) of each of the U phase, V phase, and W phase calculated from the output current values to the U phase, V phase, and W phase of 3B is expressed as U [A], V [A], W [A] (Here, the case of 0 ≦ U ≦ V ≦ W will be described), and the rated output power of the power converter 3B is C [A] (for each of the U phase, the V phase, and the W phase, C / 3 [ A]) and the threshold value is D [A] (0 <D <C / 3). Further, the threshold value D is D = Dp × 3.

[1] 0 ≦ U + V + W ≦ C (total current consumption is 0 or more and C or less)
<< 1 >> 0 ≦ V <(U + W) / 2 (⇔V−W <U−V)
(1) 0 ≦ 2U−V−W <D (2U−V−W is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
(2) D ≦ 2U−V−W ≦ C (2U−V−W is not less than D and not more than C)
Control target value Pt = Pt2 = 2 (2U−V−W) / 3 * Er [A] (Buy power)
<< 2 >> (U + W) / 2 ≦ V (⇔U−V ≦ V−W)
(1) 0 ≦ U + V−2W <D (U + V−2W is 0 or more and less than D)
Control target value Pt = Pt1 = 0 [A]
(2) D ≦ U + V−2W ≦ C (U + V−2W is not less than D and not more than C)
Control target value Pt = Pt2 = 2 (U + V-2W) / 3 * Er [A] (electric power purchase)
In the case of << 1 >> (1) or << 2 >> (1) above, current is exchanged as shown in FIG. In the U phase, when outputting the current of (U + V + W) / 3 from the power converter 3B (power converter 38), by purchasing the current of (2U−V−W) / 3 from the commercial power system 1A, U [A] is obtained. In the W phase, when (U + V + W) / 3 current is output from the power converter 3B, W [A] is obtained by selling (U + V-2W) / 3 current to the commercial power system 1A. It is done.

  In the V phase, when the current of (U + V + W) / 3 is output from the power converter 3, in the case of << 1 >> (U + W-2V> 0), the current of (U + W-2V) / 3 is supplied to the commercial power system 1A. V [A] is obtained by selling power. In the case of << 2 >> (U + W−2V ≦ 0), V [A] is obtained by purchasing (2V−U−W) / 3 current from the commercial power system 1A.

  In the case of << 1 >> (2) or << 2 >> (2) above, current is exchanged as shown in FIG. By setting the control target value Pt at the power receiving point to (U−W + | U + W−2V | / 3) * Er [A], the output current from the power converter 3B is U phase, V phase and In the W phase, both decrease by (U−W + | U + W−2V | / 3) * Er / 3. On the other hand, the grid current will increase by purchasing electricity (U-W + | U + W-2V | / 3) * Er / 3, and selling power (U-W + | U + W-2V | / 3) * Er / 3. Electricity decreases.

[2] C <U + V + W
In this case, since the total current consumption exceeds the rated output current C, even if the power conversion unit 38 outputs the rated output current C, it does not become reverse power, so that the rated output current C [A] is output. The power converter 38 is controlled.

<Effect of grid interconnection system 14>
The grid interconnection system 14 according to the present embodiment is applied to the three-phase three-wire commercial power system 1A, but basically has the same configuration as the grid interconnection system 12 according to the second embodiment. Therefore, it is a matter of course that the same effect can be obtained when obtained by the grid interconnection system 12. And since the grid connection system 14 may be applied to the structure of Embodiment 1, 3-5, it is also possible to acquire the effect equivalent to the effect acquired by each embodiment.

  Further, when (2U−V−W) / 3, | U + W−2V | / 3 and (U + V−2W) / 3 shown on the right side in FIG. 9 exceed the current detection range change threshold Dp, the current detection range is Changed from low range to high range. For example, in the case of 0 ≦ V <(U + W) / 2, (2U−V−W) / 3 is maximized in the three phases, so that when Dp ≦ (2U−V−W) / 3 is satisfied, U The current detection range changes as described above. Further, when (U + W) / 2 ≦ V described above, (U + V−2W) / 3 is maximized in the three phases. Therefore, when Dp ≦ (U + V−2W) / 3 is satisfied, the current detection is performed in the W phase. A range change occurs. Therefore, by setting D = Dp × 3, when the current detection range is changed, switching is performed between the case of [1] << 1 >> (2) and the case of [1] << 2 >> (2), and the control target value Pt It is changed so that (Pt2) is purchased. Thereby, the effect equivalent to the modification of Embodiment 3 is acquired.

  In addition, for (2U−V−W) / 3, | U + W−2V | / 3 and (U + V−2W) / 3 shown on the right side in FIG. ) / 3 * Er, | U + W−2V | / 3 * Er, and (U + V−2W) / 3 * Er. For this reason, when the control target value Pt is 0 [A], in the worst case, there is a possibility that a total of three current detection errors (U−W + | U + W−2V | / 3) * Er power sales (reverse power flow) may occur. There is.

  Therefore, in the case of [1] << 1 >> (2) and [1] << 2 >> (2), the total current at the power receiving point is (U−W + | U + W−2V | / 3) * Er Control as electricity purchase. By the way, the value of this combined current is expressed as in the cases of [1] << 1 >> (2) and [1] << 2 >> (2), depending on the magnitude relationship of U, V, and W. .

[Summary]
The power converter which concerns on aspect 1 of this invention converts the direct-current power output from the direct-current power source (DC power supply 2) into alternating current power, and the three-wire wiring (commercial power is supplied from the commercial power system 1, 1A ( AC power is connected to the commercial power systems 1 and 1A for the loads LD1 to LD3 and LD11 to LD14 connected to the voltage lines L1, L2, neutral line N, voltage lines U, V, W). The power conversion units 31 and 38 that control the alternating current at the power receiving point and the reverse power relays 32 and 39 that stop the output from the power conversion units 31 and 38 when reverse power is generated are not operated. In addition, when the unbalance degree representing the degree of unbalance of the load current of each phase formed between the wiring and the ground point is less than a predetermined threshold D, the unbalance degree is equal to or greater than the threshold D. In some cases, the power converters 31 and 38 are provided. A control target value Pt that is a different target of the alternating current at the power receiving point for controlling the AC power to be set is set, and the power conversion units 31 and 38 are instructed to operate based on the control target value Pt. And a control unit 35.

  According to the above configuration, the control target value Pt is made different depending on whether the degree of imbalance is less than the threshold value D or more than the threshold value D. As a result, the control target value Pt is set small in a range where the unbalance degree in which the load current detection error is small is small, and the control target value Pt is set large in a range in which the unbalance degree is large where the load current detection error is large. It becomes possible. Therefore, it is possible to suppress power purchase from the commercial power systems 1 and 1A while securing power supply from the DC power source in a range where the degree of unbalance is small.

  In the power converter according to aspect 2 of the present invention, in the above aspect 1, the first detection value in which the first current detector (narrow range detector 41) detects the current at the power receiving point within a predetermined first detection range, And an amplifying circuit 33 for amplifying a second detection value in which the second current detector (wide range detector 42) detects the current at the power receiving point in the second detection range whose upper limit value is higher than the first detection range. The controller 35 determines which one of the first detection value and the second detection value amplified by the amplifier circuit 33 is valid, and the first determined to be valid. The degree of imbalance may be calculated based on a detection value or the second detection value.

  In the above configuration, even if the first detection value and the second detection value are amplified by the common amplification circuit 33, it is determined whether or not each detection value is valid based on whether or not each detection value is an overrange. In this case, it is not necessary to use a dedicated amplifier circuit.

  A power converter according to Aspect 3 of the present invention is the power converter according to Aspect 1, wherein the current detector amplifies the detection value obtained by detecting the current at the power receiving point with a predetermined first amplification factor (high magnification amplification). Circuit 36) and a second amplification circuit (low magnification amplification circuit 37) for amplifying the detection value in a wider range than the first amplification circuit with a second amplification factor, and the control unit 35 includes the first amplification circuit. It is determined which of the detected values amplified by the circuit and the second amplifier circuit is effective (current determination unit 351), and the unbalance degree is determined based on the detected value determined to be effective. May be calculated.

  In the above configuration, whether or not the amplified output value of the first amplifier circuit is overrange even if amplified by the first amplifier circuit and the second amplifier circuit having different detection values. Therefore, it is not necessary to use dedicated current detectors corresponding to the first amplifier circuit and the second amplifier circuit.

  A power converter according to aspect 4 of the present invention is the power converter according to any one of aspects 1 to 3, wherein the control unit 35 has a total value of the load currents equal to or less than a rated output current of the power conversion units 31 and 38. The control target value Pt is set to 0 when the unbalance degree is less than the threshold D, while the control target value Pt is set to the commercial power system when the unbalance degree is equal to or greater than the threshold D. If the sum of the load current is larger than the rated output current, the control instruction is given to the power converters 31 and 38 so as to output the rated output current. Good.

  According to said structure, the electric power purchase from the commercial power grids 1 and 1A can be suppressed more by setting a control target value to 0 when an imbalance degree is less than the threshold value D.

  The power converter which concerns on aspect 5 of this invention WHEREIN: The said threshold value D may be determined based on the boundary value of the detection range from which the electric current detected by the said receiving point differs in the said aspect 4. FIG.

  According to the above configuration, since the threshold value D is determined based on the boundary value, the timing at which the current detection range changes can be associated with the timing at which the control target value Pt is changed, and can be preferably synchronized. As a result, a large control target value Pt is set based on the degree of imbalance based on the current detected in the detection range with low accuracy, and a small control target value Pt based on the degree of imbalance based on the current detected in the detection range with high detection accuracy. Can be set. Therefore, the amount of electricity purchased can be reduced while avoiding the reverse power flow more reliably.

  The power converter according to aspect 6 of the present invention is the power converter according to any one of the aspects 1 to 5, wherein the commercial power system 1 is a single-phase three-wire system, and the unbalance is a difference in load current of each phase, When the total value of the load current is less than or equal to the rated output current of the power converters 31 and 38, the control unit 35 purchases from the commercial power system 1 when the unbalance is greater than or equal to the threshold D. The control target value Pt may be set so that electricity is supplied.

  According to the above configuration, since the degree of unbalance is determined by the difference in load current of each phase, the control is performed when the difference in load current increases, that is, when the detection error of the receiving point current of each phase increases. The target value Pt is set to purchase power. Thereby, the amount of power purchase can be reduced while avoiding a reverse power flow more reliably.

  The power converter according to Aspect 7 of the present invention is the power converter according to Aspect 6, wherein the control unit 35 has an auxiliary threshold E greater than the threshold D when the imbalance is greater than or equal to the threshold D. In the above range, a first control target value is set as the control target value Pt, and a second value smaller than the first control target value is set as the control target value Pt in the range where the unbalance is less than the auxiliary threshold E. A control target value may be set.

  According to the above configuration, in the range below the auxiliary threshold E where the degree of imbalance is equal to or greater than the threshold D, the error in detecting the current at the power receiving point is small, and accordingly, the control target value Pt is set to a small value. Two control target values can be set. Thereby, the amount of power purchase can be further reduced.

  The power converter according to the aspect 8 of the present invention converts a DC power output from a DC power source (DC power source 2) into an AC power, and a three-wire wiring (commercial power is supplied from the commercial power system 1, 1A ( AC power is connected to the commercial power systems 1 and 1A for the loads LD1 to LD3 and LD11 to LD14 connected to the voltage lines L1, L2, neutral line N, voltage lines U, V, W). The power conversion units 31 and 38 that control the alternating current at the power receiving point and the reverse power relays 32 and 39 that stop the output from the power conversion units 31 and 38 when reverse power is generated are not operated. In addition, when the total value of the load currents of the respective phases formed between the wiring and the ground point is equal to or less than the rated output current of the power converters 31 and 38, the AC supplied by the power converters 31 and 38 The power receiving point for controlling power The control target value Pt is set to 0, and the power converters 31 and 38 are instructed to operate based on the control target value Pt, while the unbalance representing the degree of unbalance of the load current of each phase. When the balance is equal to or greater than a predetermined threshold value, a control unit 35 is provided that connects the surplus power absorbing device 7 that absorbs surplus power to the wiring in the phase where the load current is small.

  According to the above configuration, even if the control target value Pt is set to 0 when the sum value of the load currents is equal to or less than the rated output current of the power converters 31 and 38, the surplus power due to the current detection error is not increased. When generated, the surplus power is absorbed by the surplus power absorbing device 7. Thereby, reverse power flow can be avoided. Therefore, the purchased power can be reduced by not operating the reverse power relays 32 and 39 by the reverse power regardless of the current detection error.

  In the power converter according to aspect 9 of the present invention, in any one of the above aspects 1, 2, 3, 4, 5 or 8, the commercial power system 1A and the power conversion unit 38 may be a three-phase three-wire type. Good.

  According to the above configuration, the power conversion unit can be controlled so as not to operate the reverse power relay while suppressing power purchase, corresponding to the three-phase three-wire commercial power system 1A.

  A grid interconnection system according to aspect 10 of the present invention includes the power converter according to any one of aspects 1 to 9 and the DC power source.

  According to said structure, in a grid connection system, a power converter can be controlled so that operation of a reverse power relay is not performed, suppressing power purchase.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

1,1A Commercial power system 2 DC power supply (DC power source)
3, 3A, 3B Power converter 4 Current detector 7 Surplus power absorption device 31, 38 Power conversion unit 32, 39 Reverse power relay 33 Amplifier circuit 35 Control unit (connection control unit)
36 High magnification amplifier circuit (first amplifier circuit)
37 Low magnification amplifier circuit (second amplifier circuit)
41 Narrow range detector (first current detector)
42 Wide range detector (second current detector)
351 Current determination unit 353 Unbalance degree calculation unit 354 Control instruction unit D Threshold Dp Current detection range change threshold E Auxiliary threshold (threshold)
L1, L2 Voltage line (wiring)
U, V, W Voltage line (wiring)
LD1 to LD3 load LD11 to LD14 load

Claims (5)

DC power output from a DC power source is converted into AC power, and AC power is connected to the commercial power system and connected to the three-wire wiring supplied with commercial power from the commercial power system. A power converter for controlling an alternating current at a power receiving point to supply,
When the unbalance degree representing the degree of unbalance of the load current of each phase formed between the wiring and the ground point is less than a predetermined threshold, and when the unbalance degree is equal to or greater than the threshold. Control for setting the control target value for different AC current at the power receiving point for controlling the AC power supplied by the power conversion unit and instructing the power conversion unit to operate based on the control target value And a power converter. A first detection value in which a first current detector detects a current at the power receiving point in a predetermined first detection range, and a second current detector has an upper limit value for the current in the power receiving point from the first detection range. An amplifying circuit for amplifying the second detection value detected in the high second detection range;
The control unit determines which one of the first detection value and the second detection value amplified by the amplifier circuit is valid, and the first detection value or the The power converter according to claim 1, wherein the unbalance is calculated based on a second detection value. A first amplification circuit for amplifying a detection value obtained by detecting a current at the power receiving point with a predetermined first amplification factor;
A second amplifying circuit for amplifying the detection value in a wider range than the first amplifying circuit with a second amplification factor;
The control unit determines which one of the detection values amplified by the first amplification circuit and the second amplification circuit is effective, and based on the detection value determined to be effective The power converter according to claim 1, wherein an unbalance is calculated. The commercial power system is a single-phase three-wire system,
The unbalance degree is a difference in load current of each phase,
When the total value of the load current is less than or equal to the rated output current of the power conversion unit, the control unit is configured to purchase power from the commercial power system when the unbalance is greater than or equal to the threshold value. The power converter according to any one of claims 1 to 3, wherein a target value is set.   The control unit sets a first control target value as the control target value in a range where the unbalance degree is equal to or greater than an auxiliary threshold value greater than the threshold value when the unbalance degree is equal to or greater than the threshold value. 5. The power converter according to claim 4, wherein a second control target value smaller than the first control target value is set as the control target value in a range where the degree of balance is less than the auxiliary threshold.

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