JPH07336898A - Interconnection device for distributed power supply - Google Patents

Abstract

PURPOSE:To control an inverter under an optimum state at both the time of system interconnection and the time of system service interruption by operating the inverter in a current control mode at the time of interconnection with a system power supply, changing over the inverter from the current control mode to a voltage control mode at the time of the generation of service interruption and starting self-sustaining operation. CONSTITUTION:An inverter 12 is operated normally in a current control mode when a system power supply 16 is under a normal state at the time of interconnection with the system power supply 16. Even when the inverter 12 is brought to a single operation state by the generation of service interruption in the system power supply 16 and frequency is fluctuated with the rise and drop or distortion of the output voltage of the inverter 12, the frequency fluctuation is corrected by the PLL circuit 22 of digital processing mounted at the pre-stage of a current control circuit 18, and a stable output-current command value is output from the current control circuit 18 by the self-sustaining oscillatory waves of the PLL circuit 22. Accordingly, the inverter 12 can be controlled under an optimum state at both the time of system interconnection and the time of system service interruption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection device for distributed power sources, and more particularly, it is used in a solar power generation system or the like in which distributed power sources are interconnected with the system power source, and when the system power source fails, the inverter is The present invention relates to a system interconnection device for distributed power sources, which is controlled separately from the system power source so as to operate independently.

[0002]

2. Description of the Related Art For example, as shown in FIG. 3, a solar power generation system includes a distributed power source 3 including a solar cell unit which is a direct current power source 1 and an inverter 2 which converts direct current power generated from the direct current power source 1 into alternating current. The system power supply 5 is interconnected via the system interconnection switch 4, and the distributed power source 3 or the system power source 5 selectively supplies power to the load 6.

In general, the inverter 2 of the distributed power source 3 uses a current control mode in which the output current is feedback-controlled so that the output current reaches the target current value, and the output so that the output voltage reaches the target voltage value. There is a voltage control mode in which the voltage is feedback-controlled.
Conventionally, the inverter 2 in one of the current control mode and the voltage control mode has been used, and in particular, since the system voltage by the system power supply 5 is stabilized, the inverter in the current control mode is used to obtain a stable current waveform. Two
Has been prized.

[0004]

However, if the system power supply 5 fails for some reason, power cannot be supplied even to the in-house load 6 in which the DC power supply 1 is installed. Therefore, when a power failure occurs in the system power supply 5, the system interconnection switch 4 is cut off at that time, and the inverter 2 is independently operated by the DC power supply 1 of the solar cell unit to supply power to the load 6 in the site. There is a need to.

However, conventionally, the inverter 2 is controlled by either the current control mode or the voltage control mode in both the normal operation of the system power supply 5 when it is normal and the self-sustained operation when it is abnormal. There was such a problem.

That is, the inverter 2 in the current control mode
Then, when the system power supply 5 is normally operating during normal operation, there is no problem because a stable current waveform can be obtained, but when a power failure occurs in the system power supply 5 and the system power supply 5 is in an independent operation state, When the system voltage by the system power supply 5 disappears, the output current command value in the inverter 2 becomes unstable and becomes uncontrollable, and finally the inverter 2 stops.

On the contrary, the inverter 2 in the voltage control mode
If there is a power failure in the system power supply 5 and it is operating independently, there is no problem because a stable output voltage can be obtained, but if the system power supply 5 operates normally during normal operation, distortion due to harmonics will occur. Therefore, it is difficult to obtain a stable current waveform, and it is difficult to realize optimum control of the inverter 2.

As a means for solving this problem, when the inverter 2 is normally operated in the current control mode during the interconnection with the system power supply and a power outage occurs in the system power supply 5, at the time of the outage. It is conceivable that the control mode is switched to operate the inverter 2 independently in the voltage control mode.

However, when a power failure of the system power source 5 occurs,
When the inverter 2 is in the independent operation state, the system voltage disappears, the output current command value to the inverter 2 becomes unstable, and the voltage in the independent operation and the voltage in the next independent operation can be synchronized. Therefore, the inverter 2 must be stopped once, switched to the voltage control mode, and then restarted to start the self-sustaining operation. As a result, when the inverter 2 is once stopped, the load 6 in the local site is out of power.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to optimize the inverter for both normal operation during grid interconnection and self-sustaining operation during grid interruption. Another object of the present invention is to provide a system interconnection device for distributed power sources, which realizes various controls and can switch the inverter from the current control mode to the voltage control mode when the load in the site is uninterrupted when a system power supply power failure occurs.

[0011]

As a technical means for achieving the above object, the present invention provides a distributed power source in which a distributed power source including a DC power source and an inverter is connected to a system power source through a system interconnection switch. In a system interconnection device for use, a current control circuit that normally operates an inverter in a current control mode during system interconnection, a voltage control circuit that independently operates an inverter in a voltage control mode when a system power failure occurs, and the current control circuit or voltage control A gate control circuit for switching the inverter based on a command value selectively input from the circuit through the changeover switch; and an abnormality detection circuit for detecting the islanding operation of the inverter after a system power failure and switching the changeover switch. , A single transformer connected to the system power supply side of the system interconnection switch, and the current control circuit and voltage control The output current command value, which is provided in the previous stage of the circuit, corrects the frequency fluctuation of the inverter output voltage in the islanding operation after the system power failure detected by the transformer is generated by the free-running oscillating wave, and after the system power failure occurs. A single PLL circuit that generates a voltage waveform synchronized with the inverter output voltage in an isolated operation is provided.

Further, the present invention is a system interconnection device for distributed power sources in which a distributed power source including a DC power source and an inverter is connected to the system power source via a system interconnection switch, and the inverter is operated in a current control mode during the system interconnection. Is normally operated, a voltage control circuit for independently operating the inverter in the voltage control mode when a system power failure occurs, and the current control circuit or the voltage control circuit is selectively input via the first changeover switch. A gate control circuit for switching the inverter based on a command value, an abnormality detection circuit for detecting the islanding operation of the inverter after the occurrence of a system power failure and switching the first changeover switch, an inverter side of a system interconnection switch and a system Of the first and second transformers respectively connected to the power source side, and the current control circuit and the voltage control circuit The output current command value, which is provided in the stage, corrects the frequency fluctuation of the inverter output voltage in the islanding operation after the system power failure detected by the first transformer is generated by the free-running oscillation wave, and after the system power failure occurs. Of a single PLL circuit that generates a voltage waveform that is synchronized with the inverter output voltage in the islanding operation, and that generates a voltage waveform that is synchronized with the system voltage detected by the second transformer when the system is restored, and the preceding stage of the PLL circuit. And a second changeover switch which is connected to the first and second transformers and which is changed over by the detection output of the abnormality detection circuit.

[0013]

The device of the present invention normally operates the inverter in the current control mode when it is connected to the grid power supply, and switches the inverter from the current control mode to the voltage control mode when a power failure occurs in the grid power supply and then starts independent operation. Thus, the inverter can be controlled in the optimum state both during the grid interconnection and during the grid power failure, and the present invention exhibits the following actions.

When a power failure occurs, the PLL circuit
By correcting the frequency fluctuations of the inverter output voltage during islanding, even if the inverter goes into islanding mode,
A stable output current command value can be given to the inverter by the free-running oscillation wave of the PLL circuit.

With the PLL circuit, it is possible to generate a voltage waveform that is synchronized with the inverter output voltage in the islanding operation after the occurrence of the system power failure, and the overcurrent does not occur.
The inverter can be switched to self-sustaining operation.

From the above, the control can be switched in the uninterrupted state of the load in the site without temporarily stopping the inverter when switching from the current control mode to the voltage control mode.

When the system is restored, a voltage waveform synchronized with the system voltage can be generated by the PLL circuit based on the system voltage after the system is restored, and an overcurrent is generated when the system interconnection is started. Without, the inverter can be switched to normal operation.

By the second transformer connected to the inverter side of the system interconnection switch, it is possible to feedback control the inverter while detecting the inverter output voltage during the self-sustaining operation of the inverter after the system power failure. Become.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a grid interconnection device for distributed power sources is applied to a solar power generation system will be described below with reference to FIGS.

The solar power generation system shown in FIGS. 1 and 2 will be roughly described. It comprises a solar cell unit which is a DC power supply 11 and an inverter 12 which converts the DC power generated from the DC power supply 11 into AC power. Distributed power 13
The system interconnection switch 14 and the circuit breaker 15
Is connected to the system power supply 16 via the power supply, and the distributed power 13 or the system power supply 16 selectively supplies power to the in-house load 17. The system interconnection switch 14 is a magnet switch, and the inverter 1
2 and the in-house load 17 are disconnected from the system.

The basic embodiment of the present invention shown in FIG.
A current control circuit 18, a voltage control circuit 19, a gate control circuit 20, an abnormality detection circuit 21, and a PLL circuit 22, which is a feature of the present invention, constitute a main part, which will be described later.

In the figure, reference numeral 23 is a changeover switch which is inserted and connected between the outputs of the current control circuit 18 and the voltage control circuit 19 and the input of the gate control circuit 20.
The current control mode or the voltage control mode is selected and switched by the output of. Reference numeral 24 is a current transformer provided on the system bus 25 and connected to the current control circuit 18 and the abnormality detection circuit 21, and 26 is a transformer connected to the system power supply side of the system interconnection switch 14 of the system bus 25. Detection circuit 21 and P
It is connected to the LL circuit 22.

The current control circuit 18 normally operates the inverter 12 in the current control mode based on the amplitude and phase of the inverter output current detected by the current transformer 24 during the interconnection with the system power supply 16. The output current command value calculation circuit unit 27 is included. The output current command value calculation circuit unit 27
For example, it is composed of a BPF (band pass filter) circuit, an operational amplifier circuit, etc., and when the inverter output voltage fluctuates during grid interconnection, the current phase with respect to the inverter output voltage is controlled and calculated in order to suppress the fluctuation. Generates an output current command value. Based on the output current command value output from the output current command value calculation circuit unit 27, the reactive power of the inverter 12 is controlled so that the inverter 12 outputs the reactive power component. When operating the inverter 12 at a power factor of 1, the output current command value calculation circuit unit 27 is not necessary.

Further, the voltage control circuit 19 uses the system power supply 16
When a power failure occurs, the output voltage command value by the free-running signal is set based on the inverter output voltage detected from the transformer 26, and the inverter 12 is operated independently by the voltage control mode based on the output voltage command value. Gate control circuit 20
Switches the inverter 12 based on a command value selectively input from the current control circuit 18 or the voltage control circuit 19 via the changeover switch 23. When a system power failure occurs, the abnormality detection circuit 21 detects, by the transformer 26, voltage fluctuations due to rise / fall or distortion of the system voltage due to the independent operation of the inverter 12.

The current control circuit 18 and the voltage control circuit 1
The single PLL circuit 22 provided in the preceding stage of 9 is based on the detection signal output from the abnormality detection circuit 21, and the frequency accompanying the rise / fall or distortion of the inverter output voltage in the isolated operation after the occurrence of the system power failure. A stable output current command value is generated by correcting the fluctuation by the free-running oscillating wave, and this is sent to the gate control circuit 20 via the changeover switch 23 as an output current command value in islanding operation, and after a system power failure occurs. The voltage waveform synchronized with the inverter output voltage in the independent operation is generated and is sent to the gate control circuit 20 via the changeover switch 23 as the output voltage command value in the independent operation.

The operation of the device of the present invention will be described in detail below.

First, when the system power supply 16 is in a normal state at the time of interconnection with the system power supply 16, the inverter 12 is normally operated in the current control mode. At this time, the system interconnection switch 14 and the circuit breaker 15 are in the ON state. Further, the changeover switch 14 is in a state of being connected to the current control circuit side. In this state, the current control circuit 18 generates an output current command value based on the inverter output current detected by the current transformer 24 of the system bus 25, and based on the output current command value output from the current control circuit 18. Then, the inverter 12 is normally operated in the current control mode by the gate control circuit 20 via the changeover switch 23.

Here, when a power failure occurs in the system power supply 16, the system voltage is lost and the inverter 12 is in the independent operation state in the current control mode. This system power supply 1
The abnormality detection circuit 21 detects an increase / decrease or distortion of the inverter output voltage in the isolated operation state after occurrence of a power failure of 6 through the transformer 26.

On the other hand, even if the inverter 12 goes into an independent operation state due to the occurrence of a power failure in the system power supply 16 and a frequency fluctuation occurs due to a rise / fall or distortion of the inverter output voltage, the frequency fluctuation is caused by the current control circuit 18 This is corrected by the digital processing PLL circuit 22 provided in the front stage of
The free-running oscillation wave of the LL circuit 22 outputs a stable output current command value from the current control circuit 18. As a result, a stable output current command value can be secured during the independent operation of the inverter 12, and it is possible to prevent the inverter 12 from becoming uncontrollable and finally stopping.

On the other hand, when the inverter 12 is operated independently,
The same voltage waveform as the inverter output voltage detected by the transformer 26 is generated by the PLL circuit 22 and input to the voltage control circuit 19. As a result, the voltage control circuit 1
In 9, the PLL circuit 22 can generate an output voltage command value having a voltage waveform synchronized with the inverter output voltage in the isolated operation.

As a result, when the power failure of the system power supply 16 occurs, the independent operation state of the inverter 12 is detected, and then the changeover switch 23 is switched to the voltage control circuit side based on the detection signal output from the abnormality detection circuit 21. Even when the current control mode is switched to the voltage control mode, the voltage control circuit 19 outputs the voltage waveform completely synchronized with the inverter output voltage in the isolated operation state as described above, so that the inverter 12 is stopped. It is possible to smoothly switch from the current control mode to the voltage control mode without causing an overcurrent.

In this way, the gate control circuit 20 starts the independent operation of the inverter 12 in the voltage control mode via the changeover switch 23. At the same time,
By turning off the system interconnection switch 14, the inverter 12 and the load 17 in its own place are disconnected from the system power supply 16. The independent operation of the inverter 12 is PLL
This is performed in the voltage control mode by the voltage control circuit 19 by the free-running oscillation wave of the circuit 22.

When the system power supply 16 is restored, the system interconnection switch 14 is in the OFF state as described above. At this time, the system voltage due to system recovery is detected by the transformer 26, and the PLL circuit 22 generates a voltage waveform synchronized with the system voltage to generate the voltage control circuit 19 and the current control circuit 1.
Enter in 8. As a result, the output voltage of the inverter 12 operating independently in the voltage control mode and the system voltage can be completely synchronized, and in this state, even if the system interconnection switch 14 is turned on, overcurrent does not flow. The inverter 12 can be connected to the system power supply 16, and then the changeover switch 23 is switched to the current control circuit side to shift from the voltage control mode to the current control mode, and the normal operation in the current control mode is started.

In the embodiment shown in FIG. 1, the load 17 is not distorted, so that the present invention is applied to the inverter 12 having no voltage feedback system. However, the present invention is not limited to this. As an application example of the example, it can be applied to the inverter 12 having a voltage feedback system because the load 17 has distortion.

The application example shown in FIG. 2 is a transformer 26 provided on the system power supply side of the system interconnection switch 14 of the above-described embodiment.
Separately from the [first transformer], a grid interconnection switch 1
The other transformer 28 [referred to as a second transformer] is connected to the inverter side of the No. 4 inverter, and in addition to the changeover switch 23 [referred to as a first changeover switch] of the above-described embodiment, the front stage of the PLL circuit 22 is provided. Is provided with a changeover switch 29 [referred to as a second changeover switch]. The output of the second transformer 28 is input-connected to the abnormality detection circuit 21, the voltage control circuit 19, and one terminal of the second changeover switch 29. On the other hand, the output of the first transformer 26 is input-connected to the other terminal of the second changeover switch 29.

As in this application example, the system interconnection switch 14
By input-connecting the second transformer 28 connected to the inverter side to the voltage control circuit 19, during the grid power failure, in the independent operation in the voltage control mode of the inverter 12,
The inverter output voltage can be detected by the second transformer 28, and the voltage control circuit 19 can perform feedback control based on the detection signal, and voltage distortion and control delay can be corrected. Further, by detecting the islanding operation of the inverter 12 after the occurrence of the system power failure by the abnormality detection circuit 21, the first changeover switch 23 is switched to the voltage control circuit side to shift to the self-sustained operation. The changeover switch 29 is also changed over to the voltage control circuit side. With this configuration, when the system is restored, the system voltage can be detected via the first transformer 26 and the second changeover switch 29, and the output voltage of the inverter 12 and the system voltage during the self-sustained operation can be detected. It is possible to synchronize.

Although the solar power generation system has been described in the above embodiment, the present invention is not limited to this.
It is also applicable to a system having a DC power supply other than the solar cell unit.

[0038]

According to the present invention, a single PLL circuit is provided in front of the voltage control circuit and the current control circuit, so that a stable output current can be obtained even when the inverter is in the independent operation state after a system power failure occurs. A command value can be given to the inverter, and a voltage waveform synchronized with the inverter output voltage can be used when switching control from independent operation to independent operation after a system power failure, and when switching control from independent operation to normal operation when the system is restored. Since the control can be switched over, no overcurrent is generated. As a result, it is possible to switch the control of the internal load without interruption during the switching of the control mode. Further, since it is sufficient to provide a single PLL circuit, cost reduction and downsizing of the device can be easily realized.

If a transformer is also connected to the inverter side of the system interconnection switch and its output is connected to the voltage control circuit, the inverter in the self-sustaining operation can be feedback-controlled, so that voltage distortion or It becomes possible to correct the control delay, and optimal control can be realized even when the load has distortion.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of an inverter device for distributed power supply according to the present invention.

FIG. 2 is a circuit block diagram showing an application example of the present invention.

FIG. 3 is a schematic configuration diagram showing a state in which an inverter device for distributed power supply is connected to a system power supply.

[Explanation of symbols]

 12 inverter 13 distributed power supply 14 system interconnection switch 16 system power supply 18 current control circuit 19 voltage control circuit 20 gate control circuit 21 abnormality detection circuit 22 PLL circuit 23 changeover switch [first changeover switch] 26 transformer [first transformer Vessel] 28 transformer [second transformer] 29 changeover switch [second changeover switch]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiko Shikata 47 Umezutakaunecho, Ukyo-ku, Kyoto City, Kyoto Prefecture Nissin Electric Co., Ltd.

Claims (2)

[Claims] 1. A distributed power source including an inverter, which is interconnected with a system power source via a system interconnection switch, wherein a current control circuit for normally operating the inverter in a current control mode during system interconnection and a system power failure occurs. A voltage control circuit for independently operating the inverter in a voltage control mode, a gate control circuit for switching the inverter based on a command value selectively input from the current control circuit or the voltage control circuit via a changeover switch, and a system An abnormality detection circuit that switches the changeover switch by detecting the independent operation of the inverter after the occurrence of a power failure, a single transformer connected to the system power supply side of the system interconnection switch, and the current control circuit and the voltage control circuit The inverter output voltage frequency change in the stand-alone operation after the grid power failure detected by the transformer And a single PLL circuit that generates a voltage waveform that is synchronized with the inverter output voltage in the islanding operation after the occurrence of the system power failure, while generating the output current command value in which the dynamics are corrected by the free-running oscillation wave. A system interconnection device for distributed power sources. 2. A distributed power supply including an inverter connected to a system power supply via a system interconnection switch, wherein a current control circuit for normally operating the inverter in a current control mode at the time of system interconnection and a system power failure occurs. A voltage control circuit for independently operating the inverter in the voltage control mode, and a gate control circuit for switching the inverter based on a command value selectively input from the current control circuit or the voltage control circuit via the first changeover switch. And an abnormality detection circuit for detecting the islanding operation of the inverter after the occurrence of a system power failure and switching the first changeover switch, and a first and a second connected to the inverter side and the system power supply side of the system interconnection switch, respectively. A transformer and a system interruption detected by the first transformer, which is provided in the preceding stage of the current control circuit and the voltage control circuit. Generates an output current command value that corrects the frequency fluctuations of the inverter output voltage in isolated operation after power is generated, and generates a voltage waveform that is synchronized with the inverter output voltage in isolated operation after a system power failure occurs. A single PLL circuit that generates a voltage waveform that is synchronized with the system voltage detected by the second transformer when the system is restored.
A system interconnection device for a distributed power supply, comprising: a second changeover switch, which is provided in a preceding stage of the circuit, is connected to the first and second transformers, and is changed over by a detection output of the abnormality detection circuit. .