JP3108282B2 - Islanding detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system for supplying power to a load by a parallel operation of a distributed power supply system equipped with an inverter and a commercial power system, and more particularly to a photovoltaic system that supplies power to the load when the commercial power system fails. The present invention relates to an islanding detection device.

[0002]

2. Description of the Related Art In recent years, a distributed power supply system having a DC power supply of about several kW composed of a solar cell and an inverter for converting the output into an AC is interconnected with a commercial power system to supply power to loads such as home electric appliances. Various photovoltaic power generation systems have been proposed.

[0003] In a photovoltaic power generation system, in order to ensure the safety of maintenance work of a commercial power system, at the time of an unexpected power outage and work power outage of the commercial power system, the operation of the inverter is immediately stopped or the switch is immediately operated. A function of disconnecting the inverter from the commercial power system by operating and disconnecting the interconnection, that is, a function of preventing the independent operation of the inverter is indispensable.

For this reason, various active detection methods and passive detection methods have been proposed as the islanding detection methods.
Typical examples of the detection method include a rapid increase detection method in the passive detection method and an output fluctuation detection method in the active detection method.

The method of detecting a sudden increase in harmonics focuses on the fact that the third harmonic component increases sharply due to the excitation characteristics of a pole transformer during a power outage, and detects the harmonic component of the voltage at the interconnection point with the system. Then, the independent operation state of the inverter is detected by determining the degree of increase of the harmonic component with respect to the normal state.

On the other hand, in the output fluctuation detection method, a fluctuation component whose amplitude is modulated at a frequency lower than the commercial frequency of about several Hz is included in the inverter output, and this fluctuation component which appears at an interconnection point in the event of a system power failure is taken. This is to detect the isolated operation state of the inverter.

[0007]

However, according to the above-described method for detecting a sudden increase in harmonics, when the output power of the inverter is smaller than the load capacity connected to the interconnection point, as shown in FIG. There is a case where the third harmonic component temporarily increases at the time of a power failure and immediately decreases, and it is difficult to distinguish the sudden harmonic noise from a sudden noise, so that there is a possibility that a system power failure cannot be reliably detected.

In recent years, from the viewpoint of protection of a commercial power system, it has been considered to detect a system power failure by using both the above-described method of detecting a sudden increase in harmonics and the method of detecting fluctuations in output to prevent the independent operation of the inverter. . By adopting this combined method, the problems caused by the above-described method of detecting a sudden increase in harmonics can be solved.However, during normal interconnection operation, the active power or the reactive power output from the inverter fluctuates. Could not always be sent from the inverter, resulting in a decrease in system efficiency.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and uses a combination of a method of detecting a sudden increase in harmonics and a method of detecting an output fluctuation to change the state of the load capacity and the output power of the inverter. Regardless of whether the system power outage is detected,
The purpose is to prevent a decrease in system efficiency during normal interconnection operation.

[0010]

According to the present invention, there is provided a solar cell, an inverter for converting DC power generated from the solar cell into AC power, and an output of the inverter having an amplitude modulated at a frequency lower than a commercial frequency. A fluctuation component generating unit that includes a fluctuation component, wherein the inverter is connected to a commercial power system to supply power to a load, and a solar power generation system is provided at a connection point with the commercial power system. A harmonic sudden increase detecting unit that detects a rapid increase in a high frequency component of a voltage or a current, an output fluctuation detecting unit that detects an increase in the fluctuation component at the interconnection point, and detection by the harmonic sudden increase detecting unit and an output fluctuation detecting unit based on the results anda isolated operation determination unit for detecting the islanding state of the inverter, the isolated operation determination unit, harmonic by the higher harmonic wave surge detector
If the wave component does not continue to increase for a certain period of time
Only when the fluctuation component generating section is operated,
Harmonic surge detector detects a rapid increase in harmonic components for a fixed time
If the output is detected
If an increase in the fluctuation component is detected at the output, the
It determines that converter islanding is isolated operation detecting apparatus according to claim and this <br/> to detect the islanding state.

In a specific configuration, the harmonics
The component is the third harmonic component.

Further, in a specific configuration, the fluctuation
The amplitude component generator modulates the output current of the inverter by amplitude modulation.
To change the active power flowing from the inverter.
Things.

[0013]

[0014]

According to the present invention, based on the detection of a sudden increase in the harmonic component of the voltage or current at the interconnection point occurring at the time of a power outage and the detection of the increase in the fluctuation component of the output at the interconnection point, the independent operation determination unit determines the inverter. Is detected.

Further, by using the third harmonic component as the harmonic component, more accurate islanding detection can be performed. Further, the isolated operation determining unit detects that the rapid increase state of the harmonic component has continued for a predetermined time or more by the harmonic sudden increase detection unit, detects the independent operation state of the inverter, and sets the fluctuation component generation unit to detect the harmonic component. By operating only when the rapid increase state does not continue for the predetermined time or more, the system blackout can be reliably detected regardless of the state of the load capacity and the inverter output power, and the normal interconnection operation is performed. The system efficiency at the time can be improved.

Alternatively, when the fluctuation component generating section does not keep the abrupt increase of the harmonic component for a certain period of time or more, the amplitude modulation ratio is increased to thereby increase the amplitude modulation during normal interconnection operation. In addition, it is possible to prevent a decrease in system efficiency as much as possible, and to further improve the accuracy of the detection of the isolated operation of the inverter.

In addition, the output current of the inverter is amplitude-modulated by the fluctuation component generating section and the active power flowing from the inverter is varied, so that only the active power is always supplied from the inverter during the normal interconnection operation.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an islanding detecting apparatus according to the present invention. FIG. 1 is a block diagram of a photovoltaic power generation system 1 having an islanding detection device 40 to which the present invention is applied, and FIG. 2 is a flowchart of the islanding detection process.

In FIG. 1, a solar power generation system 1 includes:
A solar cell 10 having a rated voltage of 200 V, a voltage-type current control inverter 20 that converts a DC output of the solar cell 10 into an AC output and supplies a predetermined AC voltage, a switching device 30 for system protection, and islanding detection Device 40,
The commercial power system 2 via a switchboard or wattmeter (not shown)
Has been interconnected to.

The inverter 20 has an inverter circuit 21 composed of a plurality of switching elements, and a control unit 22 therefor. The control unit 22 controls the solar cell 1 as described later.
Based on the output current and the voltage of 0 and the output current and the voltage of the inverter circuit 21, the PWM control signal is sent to the switching element of the inverter circuit 21 so that the operating power factor becomes 1 and the maximum power is drawn from the solar cell 10. To control the output current of the inverter circuit 21.

Here, reference numeral 23 denotes first current detecting means comprising a current transformer for detecting the output current of the solar cell 10, 24 denotes first voltage detecting means comprising a transformer for detecting the output voltage of the solar cell 10, 25 Is a second current detecting means comprising a current transformer for detecting the output current of the inverter circuit 21, and 26 is a second voltage detecting means comprising a transformer for detecting the output voltage of the inverter circuit 21, ie, the interconnection point voltage.

The switching device 30 operates in response to the input of the disconnection signal from the isolated operation determination unit 43 of the isolated operation detection device 40 described later, and releases the interconnection between the inverter 20 and the commercial power system 2. Thereby, the solar power generation system 1 is disconnected from the commercial power system 2.

The islanding detection device 40 comprises a harmonic sudden increase detection section 41, an output fluctuation detection section 42, and an islanding operation determination section 43 composed of a microcomputer. The harmonic surge detection unit 41 is extracted with a third harmonic component extraction unit 411 including a bandpass filter that extracts a third harmonic component of the interconnection point voltage detected by the second voltage detection unit 26. An absolute value circuit 412 for performing full-wave rectification of the third harmonic component, and an integration circuit 413 for inputting a signal Sh having a level corresponding to the amplitude of the third harmonic component to the isolated operation determination unit 43. Have been.

The output fluctuation detecting section 42 includes a peak detecting section 421 for detecting a peak value of each cycle of the interconnection point voltage detected by the second voltage detecting means 26, and a peak detecting section 42.
Frequency analysis of a plurality of peak values detected in 1
Frequency fluctuation section 422 for extracting a fluctuation component of Hz, and 10H of interconnection point voltage extracted by frequency analysis section 422.
a level comparison unit 423 that compares whether the level value of the fluctuation component of z is equal to or higher than a preset reference level, and inputs an islanding operation detection signal to the islanding operation determination unit 43 if the level value is equal to or higher than the reference level; It is configured.

The reference level in the level comparing section 423 is set based on a voltage fluctuation value of a fluctuation component of 10 Hz that appears in the interconnection point voltage when the inverter 20 operates independently as described later.

The isolated operation judging section 43 takes in the output of the harmonic sudden increase detecting section 41 to detect a sudden increase of the third harmonic component, and sends a fluctuation component generation signal to the control section 22 in accordance with the detection time. Alternatively, a disconnection signal is sent to the switching device 30. In addition, the islanding operation determination unit 43 sends a disconnection signal to the switching device 30 in accordance with the input of the islanding operation detection signal from the output fluctuation detection unit 42.

More specifically, the islanding operation judging section 43 detects the sudden increase of the third harmonic component of the interconnection point voltage based on the input of the signal Sh from the harmonic sudden increase detecting section 41 over a certain period of time. If a power failure occurs, it is determined that
A disconnection signal is sent to the switching device 30. In addition, when the third harmonic component sudden increase of the interconnection point voltage is temporarily detected, the isolated operation determination unit 43 sends a fluctuation component generation signal to the control unit 22, and outputs the fluctuation signal from the output fluctuation detection unit 42. According to the input of the islanding operation detection signal, it is determined that the system is in a power failure state, and a disconnection signal is transmitted to the switchgear 30.

Next, the configuration of the control unit 22 will be described. The control unit 22 includes a power command unit 221 and a multiplication unit 2
22, a fluctuation component generator 223, and an error amplifier 224.
And a PWM comparator 225 (pulse width modulation means).

In the power command section 221, the current detected by the first current detecting means 23 and the voltage detected by the first voltage detecting means 24 are determined by a predetermined sampling period (50 μm in this embodiment).
s) and the solar cell 10 based on the input value.
Is calculated, and the direction of change of the voltage command value Vsb, which is the control target value of the operating voltage of the solar cell 10, is determined based on the sign of the power change amount ΔPs, and the constant change width The voltage command value Vsb is changed by ΔV (1.5 V in this embodiment), and a current command value Ib serving as a control target value of the output current I of the inverter circuit 21 is calculated based on the voltage command value Vsb, The current command value Ib is input to one end of the multiplying means 222.

Then, the power command unit 221 first sets the voltage command value Vsb of the solar cell 10 to a voltage value higher than the output voltage at the maximum power point of the solar cell 10 (210 in this embodiment).
V) in the above-described sampling cycle, and the current command value I is reduced based on the voltage command value Vsb.
b is set. During this time, the power change amount ΔPs takes a positive value, and the output power Ps of the solar cell 10 increases.

When the sign of the power change ΔPS changes from positive to negative, that is, when the voltage command value Vsb exceeds the maximum power point voltage, the direction of change of the operating point is reversed to change the voltage command value Vsb. The current command value Ib is set based on the voltage command value Vsb by increasing the width ΔV. Similarly,
The change direction of the operating point is reversed based on the change in the sign of the power change amount ΔPs. By repeating the above operation, the operating voltage of the solar cell 10 is maintained near the maximum power point, and the operating point of the solar cell 10 always follows the maximum power point.

The multiplying means 222 multiplies the output from the power command section 221 by the voltage waveform detected by the second voltage detecting section 26, and outputs the multiplication result to the fluctuation component signal generating section 2.
23. In the multiplication means 222, the current command value Ib set in the power command section 221 and a reference waveform corresponding to the system voltage are input and multiplied by both, so that an amplitude corresponding to the current command value Ib is obtained. And a signal having a sine waveform of a commercial frequency synchronized with the system voltage waveform is output from the multiplication means 222.

When the fluctuation component generation signal is input from the isolated operation determining unit 43, the fluctuation component generation unit 223 modulates the amplitude of the output signal from the multiplying unit 222 at 10 Hz.
A signal including the fluctuation component is output. On the other hand, when the fluctuation component generation signal is not input from the isolated operation determination unit 43, the output signal from the multiplication unit 222 is output as it is.

The error amplifier 224 includes a fluctuation component generator 2
After amplifying the difference between the output from 23 and the current detected by the second current detecting means 25, it is input to the PWM comparator 225.

The PWM comparator 225 compares the error signal from the error amplifier 224 with a preset reference triangular wave, and switches the switching element of the inverter circuit 21 so that the error signal from the error amplifier 224 becomes zero. Supply control signals.

Next, the processing operation of the islanding detection performed by the islanding operation determination unit 43 of the photovoltaic power generation system 1 configured as described above will be described with reference to the flowchart of FIG.

First, the third harmonic extraction signal Sh from the integration circuit 413 is sampled at a fixed period (set to 10 ms in this embodiment), and is sampled a plurality of times (3 in this embodiment).
The average value of the sampling values (set for the batch) is obtained, and the average value is taken in as the detected value Vin of the third harmonic component (S1). That is, execution of this step S1 results in 3
The third harmonic component is detected at a period of 0 (= 10 × 3) ms.

Next, the difference (= Vin−Vref) between the detected value Vin and a preset reference voltage value Vref is determined by a predetermined threshold value eo.
It is determined whether it is greater than (S3). If YES, the process proceeds to the next step S5.
Go to 15. The reference voltage value Vref is set based on the voltage level of the third harmonic component generated at the interconnection point during normal operation. Further, as the threshold eo, when the system voltage of the commercial power system 2 is 101 V (effective value),
The value is set to be about 1 V in terms of the voltage level at the interconnection point.

In step S5, it is determined whether or not a counting operation is being performed by a counter provided as a timed timer.
In the case of ES, the process proceeds to step S9, and in the case of NO, the counting operation is started (S7) and the process proceeds to step S9.

Then, in step S9, it is determined whether or not a count operation has been performed for a predetermined time T1 (T1 = 240 ms in this embodiment) by the timed timer. If YES, the process proceeds to step S11, and if NO, the process proceeds to step S11. Step S1
Return to

It is determined whether or not the rapid increase of the third harmonic component has continued for a certain period of time T1 by the processing of the above steps S1 to S9, that is, whether or not a similar result has been obtained in a plurality of successive difference determinations. Since the third harmonic component abrupt increase due to the system power failure is determined, the independent operation of the inverter 20 can be reliably detected while suppressing the influence of noise.

In step S11, an islanding operation detection flag is set, a disconnection signal is output to the switchgear 30, and the photovoltaic power generation system 1 is disconnected from the commercial power system 2, and the process proceeds to step S13.

In step S13, the count operation of the timed timer is stopped, the count value is reset, and the islanding detection process is terminated. On the other hand, in step S3, N
In the case of O, the process proceeds to step S15, and it is determined whether or not the counting operation by the timed timer is being performed. In the case of YES, the process proceeds to step S17. In the case of NO, that is, when the system is normal, the process returns to step S1.

In step S17, it is determined whether or not the count operation for the fixed time T1 has been performed by the timed timer.
In the case of ES, the process proceeds to step S19, and in the case of NO, the process returns to step S1. In this step S17, the count operation by the timed timer is started by the detection of the sudden increase of the third harmonic component.
It is determined whether or not the next higher harmonic component is in a reduced state. That is, it is determined whether or not there is a possibility that a sudden increase in the third harmonic component may be detected due to a system power failure in a state where a load having a larger capacity than the output power of the inverter circuit 21 is connected. .

If YES is determined in step S17, that is, a sudden increase in the third harmonic component caused by a system power failure in a state in which a load having a larger capacity than the output power of the inverter circuit 21 is connected to the load is detected. If it is determined that there is a risk of the occurrence, the process proceeds to step S19, and a fluctuation component generation signal is transmitted to the fluctuation component generation unit 223.

According to the input of the fluctuation component generation signal from the isolated operation determination unit 43 to the fluctuation component generation unit 223, the fluctuation component generation unit 223 modulates the output signal from the multiplying means 222 at 10 Hz, and modulates the fluctuation component. Is output. Thereby, the inverter circuit 2
An inverter output current including a fluctuation component of 1 to 10 Hz is transmitted, and the active power supplied from the inverter circuit 21 is changed at a cycle of 10 Hz.

In the next step S21, it is determined whether or not an islanding operation detection signal has been input from the output fluctuation detecting section 42. If YES, the flow advances to step S11 to set an islanding operation detection flag and A disconnection signal is output, and the process proceeds to step S13.
Proceed to 23.

In the event of a system power failure, the inverter circuit 2
The change in the active power from 1 causes the load voltage to fluctuate,
On the other hand, at the time of system interconnection, the fluctuation of the active power is absorbed by the commercial power system 2, and therefore, the presence or absence of a system power failure is determined by using the fact that the load voltage hardly fluctuates.

In step S23, it is determined whether or not a count operation has been performed for a predetermined time T2 (T2 = 300 ms in this embodiment) by the timed timer. If YES, the process proceeds to step S25, and if NO, the process proceeds to step S19. Return.

In step S25, the counting operation of the timed timer is stopped, the count value is reset, and the process returns to step S1. By performing the above-described islanding operation detection processing, even when the output power of the inverter circuit 21 is smaller than the load capacity and the third harmonic component temporarily increases at the time of a system power failure, it is caused by sudden noise. It is possible to reliably distinguish the third harmonic component from a sudden increase, and it is possible to reliably detect the isolated operation of the inverter 20 due to a system power failure.

Also, during the normal interconnection operation, the output from the inverter is not changed for the detection of the isolated operation.
Since the maximum power obtained from the solar cell is always sent out from the inverter, system efficiency during grid-connected operation can be improved. A power outage can be reliably detected.

In the above-described embodiment, the harmonic sudden increase detecting section 4
In the case where the rapid increase of the third harmonic component is temporarily detected by step 1, the fluctuation component generation unit 223 is operated to slightly oscillate the magnitude of the inverter current from the inverter circuit 21 to periodically reduce the active power. However, the reactive power may be periodically changed by slightly oscillating the phase of the inverter current.

Further, in order to further improve the accuracy of the detection of the independent operation of the inverter, the fluctuation component generation section 223 is always operated, and the fluctuation range of the output from the inverter circuit 21 by the fluctuation component generation section 223 is reduced during the normal interconnection operation. However, when the sudden increase in the third harmonic component is temporarily detected by the harmonic sudden increase detection unit 41, the value may be increased. However, in this case, the system efficiency during the normal interconnection operation is slightly reduced as compared with the above embodiment.

Further, in the above embodiment, the case where the independent operation of the inverter is detected by detecting the rapid increase of the harmonic component of the interconnection point voltage has been described. I do not care.

[0055]

As described above, according to the present invention, when the output power of the inverter is larger than the load capacity, the state in which the harmonic component rapidly increases at the interconnection point due to the power outage continues for a certain period of time. By detecting this, the isolated operation of the inverter is detected. On the other hand, when the output power of the inverter is smaller than the load capacity, the state of rapid increase of the harmonic components at the interconnection point due to the system blackout does not continue for a certain time, but the fluctuation component in the output appearing at the interconnection point increases. Is detected, the isolated operation of the inverter is detected. Therefore, irrespective of the state of the load capacity and the output power of the inverter, erroneous detection due to sudden increase of harmonic components caused by sudden noise is prevented, the detection accuracy of the system power failure is increased, and Independent operation of the inverter can be detected.

Also, at the time of normal interconnection operation, the output from the inverter is not changed for the detection of the isolated operation.
The output is fluctuated in a minute cycle only when the harmonic component does not rapidly increase for a certain period of time, so the maximum power obtained from the solar cell is always sent from the inverter during normal interconnection operation, and the system efficiency is reduced. Can be improved.

Further, during the normal interconnection operation, the amplitude modulation width of the output of the inverter is reduced, and the amplitude modulation width is increased only when the rapidly increasing state of the harmonic component does not continue for a certain period of time. It is possible to prevent a decrease in system efficiency during system operation as much as possible, and to further improve the accuracy of detection of independent operation of the inverter.

[Brief description of the drawings]

FIG. 1 is a block diagram of a photovoltaic power generation system having an islanding detection device to which the present invention is applied.

FIG. 2 is a flowchart illustrating the content of an islanding detection process according to the present invention.

FIG. 3 is a diagram illustrating a change in a third harmonic component of an interconnection point voltage due to a system power failure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photovoltaic power generation system (distributed power supply equipment) 2 Commercial power system 10 Solar cell 20 Grid connection inverter 21 Inverter circuit 22 Control part 23 1st current detection means 24 1st voltage detection means 25 2nd current detection means 26 2nd voltage Detecting means 30 Switchgear 40 Islanding operation detecting unit 41 Harmonic sudden increase detecting unit 42 Output fluctuation detecting unit 43 Islanding determining unit 221 Power commanding unit 222 Multiplying unit 223 Fluctuation component generating unit 224 Error amplifier 225 PWM comparator (pulse width modulating unit)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masahiro Maekawa 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-61-92131 (JP, A) JP-A-61-92129 (JP, A) JP-A-64-12823 (JP, A) JP-A-6-141470 (JP, A) JP-A-62-114435 (JP, A) JP-A-7-20041 (JP, A) , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H02J 3/38

Claims (3)

(57) [Claims] 1. A solar cell, an inverter for converting DC power generated from the solar cell into AC power, and a fluctuation component that includes a fluctuation component whose amplitude is modulated at a frequency lower than a commercial frequency in an output of the inverter. And a generator.
A photovoltaic power generation system that interconnects the inverter with a commercial power system and supplies power to a load, wherein a harmonic surge that detects a rapid increase in a high-frequency component of a voltage or a current at a point of interconnection with the commercial power system. A detecting unit, an output fluctuation detecting unit that detects an increase in the fluctuation component at the interconnection point, and an independent detecting unit that detects an independent operation state of the inverter based on detection results of the harmonic sudden increase detecting unit and the output fluctuation detecting unit. has a operation determination unit, wherein the isolated operation determination unit, the
When the rapid increase of the harmonic component is constant by the harmonic sudden increase detector
The fluctuation component generation section only when the measurement has not been continued for more than
Is operated, and harmonics are detected by the
Detects that the wave component has rapidly increased for a certain period of time.
The fluctuation component increases in the output fluctuation detection unit.
Is determined to be the stand-alone operation of the inverter when
And an islanding operation detection device for detecting an islanding operation state . 2. The isolated operation detection device according to claim 1, wherein the harmonic component is a third harmonic component. 3. The islanding operation detection device according to claim 1, wherein the fluctuation component generator modulates an amplitude of an output current of the inverter to change an active power flowing from the inverter.