JPH0928040A - Method for starting and operating system interconnection inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for starting and operating a system interconnection inverter device which can effectively suppress a rush current from an inverter side without increasing the cost remarkably. SOLUTION: In a method for starting and operating a system interconnection inverter device in which the AC output terminal of a system interconnection inverter 2 is connected to a system 7 through an output filter containing at least a shunt-connected filter capacitor 4 and a switch 6, interconnection operation is performed by turning on the switch 6a after the voltage value and phase of the capacitor 4 are made equal to those of a system voltage by charging the capacitor 4 with a current advanced in phase by about 90 deg. from that of the system voltage by means of the inverter 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a start-up of a grid-connected inverter device in which the AC output terminal of the grid-connected inverter is connected to the system via an output filter including at least a shunt-connected filter capacitor and a switch. Related to driving method.

[0002]

2. Description of the Related Art As a DC power supply for an inverter, a grid-connected inverter device that uses a DC power supply such as a solar cell or a fuel cell and connects the DC power supply to a system via an inverter has been proposed. FIG. 6 shows such a conventional system interconnection inverter device.

In FIG. 6, an output terminal of a DC power source 1, for example, a solar cell is connected to a DC input terminal of a PWM control system interconnection inverter 2, and an AC output terminal of the inverter 2 is connected to an inverted L-shaped filter reactor 3 And an output filter including a filter capacitor 4, a connection reactor 5 and a switch contact 6a, and are connected to the system 7. The switch contact 6a is operated by the operation coil 6. The operation coil 6 is controlled by the starting circuit 15. As the DC power supply 1, a fuel cell can be used in addition to a solar cell.

In order to extract the maximum output from the DC power source 1, the output voltage V ₁ of the DC power source ₁ and the voltage reference V _s corresponding to the system voltage
In accordance with the difference, the output voltage of the inverter 2 is controlled at a constant voltage via current control by a current control minor loop.
That is, the output voltage V ₁ of the DC power source 1 as compared to the voltage reference V _s, and inputs the difference to (= V _s -V ₁₎ to the voltage control amplifier 9. The voltage control amplifier 9 calculates an output signal for reducing the voltage difference, and inputs it to a first input terminal of the multiplier 11. The output signal of the transformer 10 for detecting the system voltage V _ac is input to the second input terminal of the multiplier 11. Multiplier 1
1 computes a current reference proportional to the product of both input signals. On the other hand, the output current I ₃ of the inverter 2 is detected by the current detector 12. A signal corresponding to the difference between the current reference thus obtained and the detected current, that is, a current deviation is input to the current control amplifier 13. The current control amplifier 13 forms a control signal for eliminating the current deviation and gives it as a current control signal to the inverter 2 via the PWM circuit 14 and the switch auxiliary contact 6b. The auxiliary contact 6b is a contact that operates in conjunction with the switch contact 6a.

The starting circuit 15 operates at the time of system interconnection control. By activating the operation coil 6 through the activation circuit 15, the contact 6a is turned on to achieve the system interconnection and the contact 6b is closed. Then, the inverter 2 is driven to enable the current control loop and start the voltage control.

In the main circuit shown in FIG. 6, an output filter connected to the output side of the inverter 2 removes harmonics contained in the output of the inverter 2 which is PWM-switched and controlled at a high frequency of several kHz to several tens kHz. It is arranged for the purpose. On the other hand, interconnection reactor 5
The first purpose is to limit the rush current to the filter capacitor 4 when the contact 6a is turned on.
The purpose of the present invention is to prevent a situation in which when the harmonics of the system 7 increase, a harmonic current flows to the capacitor 4 and the capacitor 4 is overheated. Here, regarding the second purpose,
The impedance of the system to which the small-to-medium-capacity inverter 2 is connected is relatively high, and the capacity of the capacitor 4 is switched from several kHz to about several tens of kHz due to the recent increase in the speed of the power switching element used in the inverter. Since a capacitor having a sufficient capacity is sufficient, there is almost no need to worry about overheating of the capacitor 4. However, for the first purpose, when the contact 6a is turned on, the capacitor 4
It is difficult to prevent a rush current that can flow through the interconnecting reactor 5 without connecting the interconnecting reactor 5, and thus the interconnecting reactor 5 is required.

As shown in FIG. 7, a transformer 51 may be interposed between the filter capacitor 4 and the switch contact 6a. In this case, an exciting rush current of the transformer 51 is generated when the contact 6a is closed. Therefore, after controlling the voltage of the capacitor 4 to a value close to the same voltage and the same phase as the system 7,
A method of introducing a is also used. In this case, the impedance of the transformer 51 fulfills the function of the interconnection reactor to some extent, and all or a part of the interconnection reactor 5 can be omitted. However, in this case, it is necessary to separately provide a voltage detection circuit and a voltage control loop.

Further, as shown in FIG. 8, a series circuit of another contact 16a and a resistor 17a is connected in parallel with the contact 6a, and the relay coil 16 is first excited by the output signal of the starting circuit 15. The two-stage operation of turning on the contact 16a, charging the capacitor 4 with the system voltage via the resistor 17a by current limiting, and then energizing the operating coil 6 to turn on the contact 6a performs the inrush current of the capacitor 4 Restrictions have also been made.

[0009]

The circuits and methods shown in FIGS. 6 to 8 exemplified as the prior art have the following disadvantages.

In the case of the circuit shown in FIG. 6, especially in an inverter having a small capacity, the main purpose of the interconnection reactor 5 is to limit the rush current when the contact 6a is turned on. Has become. In the case of the circuit of FIG. 7, the capacitor voltage is controlled in advance for the purpose of suppressing the inrush current of the transformer 51. In this case, there is no problem that the efficiency decreases during the steady operation. It is necessary to provide a separate control loop, which causes a problem of cost increase. In the case of the circuit shown in FIG. 8, the number of circuit components increases, which causes a problem of cost increase.

Therefore, it is an object of the present invention to provide a start-up operation method for a grid-connected inverter device which can achieve the effect of suppressing the inrush current seen from the inverter without significantly increasing the cost.

[0012]

In order to achieve the above object, according to the present invention, an AC output terminal of a grid interconnection inverter is connected to a grid through an output filter including at least a shunt-connected filter capacitor and a switch. A method for starting operation of a system interconnection inverter device, wherein a filter capacitor is charged with a current which is advanced by about 90 ° from the system voltage by an inverter in a state where a switch is opened, and the filter capacitor has a voltage value substantially equal to the system voltage. -The feature is that after the phases are set to the same phase, the switches are turned on to operate the interconnection.
By controlling in this manner, the inrush current of the circuit can be suppressed without additionally connecting the circuit components such as the interconnection reactor.

The value of the charging current supplied from the inverter to the filter capacitor should be changed substantially in proportion to the frequency of the system voltage. This method is effective for charging the filter capacitor so as to almost match the system voltage without DC charging.

It is desirable to connect a resistor in parallel with the filter capacitor when the switch is open, and to disconnect the resistor when the switch is open. By doing so, the direct current of the filter capacitor current control loop can be consumed by the resistor, and the voltage rise due to the direct current component of the filter capacitor can be prevented.

The value of the charging current supplied from the inverter to the filter capacitor is preferably controlled so as to be substantially proportional to the system voltage. By doing so, the filter capacitor voltage can be made to match the system voltage even when the power supply fluctuates, and smooth system interconnection can be achieved.

A control loop for controlling the current of the filter capacitor is formed, and after starting the current control near the system voltage zero, the filter capacitor is connected to the system via the switch within a short time so that the DC capacitor does not charge too much. It is desirable to set it up.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an apparatus for carrying out the present invention, and the same parts as those in FIG.

The circuit of FIG. 1 is based on the circuit configuration of FIG. 6, but on the one hand, the interconnection reactor 5 and the contact 6b are omitted therefrom, and on the other hand, the 90 ° advance circuit 20, the current setting circuit 21 and the discharge resistor 22 are provided. Is attached. The discharge resistor 22 is connected in parallel to the filter capacitor 4 with a normally closed contact 6e operated by the operation coil 6 in the main circuit in series. The output signal of the voltage control amplifier 9 is applied to the multiplier 1 via a normally open contact 6h operated by the operation coil 6.
1 is input to the first input terminal. A signal representing the current set by the current setting circuit 21 is also input to this input terminal via the normally closed contact 6i operated by the operation coil 6. The current setting circuit 21 determines the magnitude of the charging current of the capacitor 4. The system voltage detected by the transformer 10 is not directly input to the second input terminal of the multiplier 11, but one is input through the normally open contact 6f and the other is It is input through the 90 ° advance circuit 20 and the normally closed contact 6g. The 90 ° advance circuit 20 uses the input system voltage as a reference, and outputs a 90 ° advanced phase capacitor current reference. When the operation coil 6 is not excited, the normally closed contacts 6e, 6g, 6i are closed,
The normally open contacts 6a, 6f, 6h are open. Conversely, when the operation coil 6 is energized, the normally open contacts 6a, 6f, 6h
Is closed, and the normally closed contacts 6e, 6g, 6i are open.

Immediately after the start-up when the operation coil 6 is not excited, the contacts 6e, 6g and 6i are closed and the contacts 6a, 6f and 6h are open. In this state, the current setting circuit 21 sets the current amount of the capacitor 4, while the 90 ° advance circuit 2 is set.
A system voltage detected by the transformer 10 via 0 is used as a reference to obtain a sine wave advanced by 90 °, and a signal corresponding to the product of the two is obtained by the multiplier 11. This serves as a current reference for the capacitor 4. The capacitor current detected by the current detector 12 is compared with a current reference, and the difference, that is, the current deviation is input to the current control amplifier 13, and the output current I of the inverter 2 is reduced via the PWM circuit 14 so as to reduce the deviation.
_3, that is, the charging current of the capacitor 4 is controlled, and the voltage across the capacitor 4 is controlled to match the system voltage. Thereafter, by energizing the operation coil 6 through a command from the starting circuit 15, the main circuit closes the contact 6a to start the interconnection operation. At this moment, the rush current does not flow because the voltage of the capacitor 4 substantially coincides with the system voltage. At the same time when the contact 6a is closed, the other contacts 6f and 6h are also closed, resulting in the same circuit state as the conventional circuit shown in FIG. it can.

The operation of the series circuit of the resistor 22 and the contact 6e in parallel with the filter capacitor 4 will be described. Generally, the current of the capacitor 4 is about several percent of the rated current of the inverter 2. Therefore, when the capacitor current is controlled, the capacitor current is about several% (0.1 to 0% of the rated current of the inverter 2) due to drift of the current detector 12, errors in the amplifier of the current control loop, and transient components. .01%
), The capacitor 4 is charged by the DC component, and when the contact 6a is turned on, a large difference occurs between the capacitor voltage and the system voltage, so that an inrush current flows when the contact 6a is closed. There is. The resistor 22 is inserted to discharge the DC component. Although the loss is small even if the resistor 22 is connected at all times, a rated inverter of 50% is used for an inverter for interconnection using a solar cell as a power source.
% In order to reduce the loss in this state as well, by closing the contact 6a and opening the contact 6e, control is performed so that no resistance is connected during interconnection.

As described above, according to this embodiment, the filter capacitor is charged with a current 90 ° ahead of the system voltage before the time of system interconnection, and the direct current component is discharged through the discharge resistor. However, since the interconnection operation is started in a state where the capacitor voltage is substantially equal to the system voltage, the inrush current becomes extremely small and no disturbance is given to the system.
Moreover, it is possible to provide a stable grid-connected inverter device without lowering the efficiency by disconnecting the discharge resistor during grid-connected.

Next, another embodiment will be described. In the circuit of FIG. 1, if the power loss of the resistor 22 does not need to be much of a problem, the contact 6 e is short-circuited or removed, and the resistor 22 is always connected to the capacitor 4 in parallel. Good. The reduction in efficiency due to the power loss of the resistor 22 is, for example, 0.
It is about 2 to 0.3%, which is not a problem in practical use in many cases.

The functions of the contact 6e and the resistor 22 of FIG. 1 can be replaced by the posistor 23 of FIG. Here, the posistor is a thermistor having a positive temperature coefficient of resistance, and as shown in FIG. 3, when the temperature reaches a certain value T _s or more, the resistance value rapidly increases by 10 ² to 10 ³ times. It has the property of increasing. When the inverter 2 is started, a relatively small current according to the voltage of the capacitor 4 flows through the posistor 23. In this state, the temperature of the posistor 23 is low.
Therefore, since the resistance value is also small, the DC component is not integrated in the capacitor 4 but is discharged through the posistor 23. For this reason, when the contact 6a is turned on, the capacitor voltage is substantially in the same phase and the same voltage as the system voltage, so that the inrush current can be ignored. The contact 6a is turned on, the temperature of the posistor 23 rises a few seconds, and when it reaches a constant value T _s , its resistance value increases sharply and the power loss decreases in inverse proportion to the resistance value. Because it can be ignored in relation to the power of the entire system,
It can be used even when connected.

FIG. 4 shows an example in which only the control circuit portion of FIG. 1 is changed. In this main circuit, a vector adder 26 is inserted in the input stage of the current control amplifier 13 and an AND circuit 27 is added in the output stage of the PWM circuit 14 in comparison with the main circuit of FIG. In the control circuit, a zero-cross detection circuit 28 is provided at the input stage of the operation coil 6.
A synchronization circuit 29 has been added, and the contacts 6f, 6g, 6i have been removed. Instead, the voltage detection circuit 24, the frequency detection circuit 25, and the second multiplier 11b (the first multiplier is 11
a) is added.

The transformer 10 detects the system voltage, and the voltage detection circuit 24 and the frequency detection circuit 2 are detected based on the detection result.
5, the voltage and frequency are detected, and the magnitude of the current I flowing through the capacitor 4 is calculated by an arithmetic circuit as I = 2πfCV based on both detection results. Here, f is the system frequency, V is the system voltage, and V is the capacitance of the capacitor 4. The value of the current I is set as a set current value to be output from the current setting circuit 21 and is input as a first input of the multiplication circuit 11b. The second input of the multiplication circuit 11b is 90
This is the output of the advance circuit 20. The output signal of the multiplier 11a (corresponding to the multiplier 11 of FIG. 1) is provided as a first input of the adder 26 provided at the input stage of the current control amplifier 13 to the contact 6
The current component I _{rc of the} capacitor 4 advanced by 90 ° from the system voltage, which is input via h and is generated as a second input of the adder 26 by the multiplier 11b corresponding to the product of both inputs, is input as a reference. It The output of the adder 26 becomes a current reference and is compared with the inverter current I ₃ detected by the current detector 12 to reduce the resulting current deviation,
The current control loop described above controls the capacitor current.

When the start-up circuit 15 outputs a start signal, the zero-cross detection circuit 28 detects the zero-cross point of the voltage from the system voltage, and the current control is started from the voltage zero-cross point through the synchronizing circuit 29 and the AND circuit 27. The output of the synchronization circuit 29 simultaneously drives the operation coil 6 and
a, 6h (see FIG. 1) indicate the operation time of the relay (10 to 40).
It closes after ms). At this time, a current reference having the same phase as the system voltage is created in the multiplication circuit 11a, and the effective current reference I _r is added via the contact 6h in the addition circuit 26 to the capacitor current reference I.
_Vectorically added to _rc to create a new current reference. According to this new current standard, the current control of the inverter 2, that is, the current control of the capacitor 4 is performed.

Next, a method of charging the capacitor 4 which does not transiently generate a DC component in the circuit of FIG. 4 will be described with reference to FIG. If the capacitor current I _c is passed at the zero cross point t ₁ of the system voltage V _ac , the capacitor voltage V ₄ rises almost in synchronization with the system voltage V _ac as shown in the figure. In this case, since the capacitor current I _c is proportional to the power supply frequency and the voltage, respectively, this is calculated by the calculation circuit 30.

The contacts 6a and 6h are closed at the time point t _{2 so as} to be connected to the grid and at the same time the active power reference I _r is added to the adder circuit 26.
And the current is controlled according to the result. If the time period between t _{1 and} t ₂ is short, the integrated value of the DC component of the capacitor 4 can be ignored. When the operation of the operation coil 6 is slow, the operation coil 6 may be excited earlier than the signal of the capacitor current control ON.

Since the rise time of the capacitor current I _c is necessary, it is desirable to start the current control of the capacitor 4 at time t _0, which is slightly earlier than time t _1, but such a technique should be used appropriately. You can

[0030]

As described above, according to the present invention, after the current of the filter capacitor is supplied so that the integration of the DC component can be ignored, the interconnection contact is closed.
Even if the interconnection reactor is omitted, the inrush current can be prevented. Therefore, it is small, lightweight, highly efficient and economical,
In addition, it is possible to provide a starting operation method of the system interconnection inverter device that does not cause disturbance to the system.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an apparatus for implementing a start-up operation method of the present invention.

FIG. 2 is a circuit diagram of a main part of another device for carrying out the startup operation method of the present invention.

FIG. 3 is a diagram showing a characteristic of resistance value with respect to temperature of a posistor used in the device of FIG.

FIG. 4 is a circuit diagram of still another apparatus for performing the start-up operation method of the present invention.

5 is a voltage / current waveform diagram for explaining a startup operation method by the circuit of FIG. 4;

FIG. 6 is a circuit diagram of an apparatus for performing a conventional startup operation method.

FIG. 7 is a circuit diagram of a main part illustrating another conventional startup operation method.

FIG. 8 is a circuit diagram of a main part illustrating still another conventional startup operation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Inverter 3 Filter reactor 4 Filter capacitor 5 Reactor for interconnection 6a to 6i Switch contacts 6 Switch operating coil 7 System 9 Voltage control amplifier 10 System voltage detection transformer 11 Multiplier 12 Current detector 13 Current control amplifier 14 PWM circuit 15 startup circuit 20 90 ° advance circuit 22 resistance 24 voltage detection circuit 25 frequency detection circuit 26 addition circuit 27 AND circuit 28 zero-cross detection circuit 29 synchronization circuit 30 arithmetic circuit

Claims (5)

[Claims] 1. A start-up operating method for a grid-connected inverter device, wherein an AC output terminal of the grid-connected inverter is connected to the grid via an output filter including at least a shunt-connected filter capacitor and a switch, After the switch capacitor is opened, the filter capacitor is charged by the inverter with a current that is advanced by 90 ° from the system voltage, and the filter capacitor is made to have substantially the same voltage value and the same phase as the system voltage, and then the switch device. A start-up operation method for a grid-connected inverter device, which is characterized in that the inverter is connected to perform a grid-connected operation. 2. The start-up operation method according to claim 1,
A start-up operation method for a grid interconnection inverter device, characterized in that a value of a charging current supplied from the inverter to the filter capacitor is changed substantially in proportion to a frequency of the grid voltage. 3. The start-up operation method according to claim 1,
A startup operation method for a grid-connected inverter device, comprising connecting a resistor in parallel with the filter capacitor when the switch is in an open state, and disconnecting the resistor when the switch is in a closed state. 4. The start-up operation method according to claim 1,
A startup operation method for a grid-connected inverter device, wherein the value of a charging current supplied from the inverter to the filter capacitor is controlled so as to be substantially proportional to the grid voltage. 5. The start-up operation method according to claim 1,
A control loop for controlling the current of the filter capacitor is configured, and after starting the current control near the system voltage zero, the filter capacitor is connected to the system via the switch within a short time so as not to be overcharged with the DC component. A method for starting up a grid-connected inverter device, comprising: