JP3186430B2 - System interconnection device for distributed power supply - Google Patents

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 a distributed power source, and more particularly, to a power generation system in which a distributed power source is connected to a system power source. The present invention relates to a system interconnection device for a distributed power supply that performs switching control so as to operate independently from a system power supply.

[0002]

2. Description of the Related Art For example, as shown in FIG. 3, a photovoltaic power generation system includes a distributed power supply 3 comprising a solar cell unit as a DC power supply 1 and an inverter 2 for converting the DC power generated from the DC power supply 1 into an alternating current. The power supply 5 is connected to a system power supply 5 via a system connection switch 4, and power is selectively supplied to the load 6 from the distributed power supply 3 or the system power supply 5.

In general, the inverter 2 of the distributed power source 3 operates in a current control mode in which the output current is feedback-controlled so that the output current becomes a target current value, and its output is output so that the output voltage becomes a target voltage value. There is a voltage control mode in which voltage is feedback controlled.
Conventionally, the inverter 2 in either the current control mode or the voltage control mode is used. 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. 2
Has been awarded.

[0004]

However, if the system power supply 5 fails for some reason, power cannot be supplied even to the load 6 in the own place where 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 shut off at that time, and the inverter 2 is operated independently by the DC power supply 1 of the solar cell unit to supply power to the load 6 in the own place. There is a need to.

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

That is, the inverter 2 in the current control mode
In normal operation of the system power supply 5, there is no problem because a stable current waveform can be obtained. However, when a power failure occurs in the system power supply 5, the system power supply 5 enters an isolated operation state. When the system voltage from the system power supply 5 disappears, the output current command value in the inverter 2 becomes unstable, the control becomes impossible, and the inverter 2 finally stops.

On the contrary, the inverter 2 in the voltage control mode
Then, when the system power supply 5 is operating independently due to a power failure, there is no problem because a stable output voltage can be obtained. Therefore, it is difficult to obtain a stable current waveform, and it is difficult to realize optimal control of the inverter 2.

As a means for solving this problem, the inverter 2 is normally operated in a current control mode during interconnection with a system power supply, and when a power failure occurs in the system power supply 5, It is conceivable to switch the control mode so that the inverter 2 operates independently in the voltage control mode.

However, when a power failure occurs in the system power supply 5,
When the inverter 2 enters the islanding operation state, the system voltage is lost, the output current command value to the inverter 2 becomes unstable, and the voltage in the islanding operation is synchronized with the voltage in the next independent operation. 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 stopped once, there is a problem that the load 6 in the own place is out of power.

Therefore, the present invention has been proposed in view of the above-mentioned problems, and an object of the present invention is to optimize an inverter in both normal operation during grid connection and independent operation during system blackout. It is another object of the present invention to provide a system interconnection device for a distributed power supply that can switch the inverter from the current control mode to the voltage control mode in a state where the load in the local power supply is not interrupted when a power failure occurs in the system power supply.

[0011]

[0012]

As a technical means for achieving the above object, the present invention provides a distributed power supply in which a distributed power supply composed of a DC power supply and an inverter is connected to a system power supply via a system interconnection switch. A power control circuit for normally operating an inverter in a current control mode during a power grid connection, a voltage control circuit for autonomously operating an inverter in a voltage control mode when a power failure occurs, and the current control circuit or the voltage control. A gate control circuit for switching the inverter based on a command value selectively input from the circuit via a first changeover switch; and detecting the first operation of the inverter after a system power failure occurs by detecting the first operation of the inverter.
Detection circuit for switching a changeover switch, and a first transformer connected to a system power supply side of a system interconnection switch
And connected to the inverter side of the grid connection switch,
A second transformer input-connected to the voltage control circuit, and an inverter output provided in a preceding stage of the current control circuit and the voltage control circuit and operated in an isolated operation after the occurrence of a system power failure detected by the first transformer. A self-propelled oscillation wave is used to generate an output current command value in which the frequency fluctuation of the voltage is corrected, and a voltage waveform synchronized with the inverter output voltage in the isolated operation after the occurrence of the system power failure is generated. A single PLL circuit that generates a voltage waveform synchronized with the system voltage detected by the transformer, and is connected to the first and second transformers provided before the PLL circuit and switched by a detection output of the abnormality detection circuit. And a second changeover switch.

[0013]

The device of the present invention normally operates the inverter in the current control mode when the power supply is connected to the system power supply, and starts the self-sustained operation after switching the inverter from the current control mode to the voltage control mode when a power failure occurs in the system power supply. The inverter can be controlled in an optimal state both at the time of system interconnection and at the time of system power failure, and the present invention exhibits the following operation.

When a system power failure occurs, the PLL circuit
By correcting the frequency fluctuation of the output voltage of the inverter in the islanding operation, even if the inverter enters the islanding state,
A stable output current command value can be given to the inverter by the free-running oscillation wave of the PLL circuit.

[0015] The PLL circuit can generate a voltage waveform synchronized with the inverter output voltage in the isolated operation after the occurrence of a system power failure, and without generating an overcurrent.
The inverter can be switched to independent operation.

As described above, the control can be switched in a state where the load in the own place is uninterrupted without temporarily stopping when switching the inverter from the current control mode to the voltage control mode.

At the time of system restoration, a voltage waveform synchronized with the system voltage can be generated by the PLL circuit based on the system voltage after the system restoration, and an overcurrent occurs at the start of system interconnection. And the inverter can be switched to normal operation.

It is to be noted that the second transformer connected to the inverter side of the system interconnection switch makes it possible to perform feedback control of the inverter while detecting the inverter output voltage during the self-sustaining operation of the inverter after the occurrence of a system power failure. Become.

[0019]

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

The photovoltaic power generation system shown in FIGS. 1 and 2 is roughly described first. The photovoltaic power generation system comprises a solar cell unit as a DC power supply 11 and an inverter 12 for converting DC power generated from the DC power supply 11 into AC. Distributed power supply 13
The system interconnection switch 14 and the circuit breaker 15
The power supply is connected to the system power supply 16 via the power supply, and power is selectively supplied from the distributed power supply 13 or the system power supply 16 to the local load 17. The system interconnection switch 14 is a magnet switch, and the inverter 1
2 and the in-house load 17 are separated from the system.

The embodiment which forms the basis of the invention shown in FIG.
A main part is configured by 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, which will be described later.

In the figure, reference numeral 23 denotes a change-over switch inserted between the outputs of the current control circuit 18 and the voltage control circuit 19 and the input of the gate control circuit 20.
And the current control mode or the voltage control mode is selected and switched. 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; 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
Connected to LL circuit 22.

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

The voltage control circuit 19 is connected to the system power supply 16.
When a power failure occurs, an output voltage command value based on a free-running signal is set based on the inverter output voltage detected from the transformer 26, and the inverter 12 is operated independently in a voltage control mode based on the output voltage command value. Gate control circuit 20
Causes the inverter 12 to perform a switching operation 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 uses the transformer 26 to detect a voltage fluctuation based on a 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
9, a single PLL circuit 22 provided on the basis of a detection signal output from the abnormality detection circuit 21 operates based on a detection signal output from the abnormality detection circuit 21. A fluctuation is corrected to generate a stable output current command value by the free-running oscillating wave, and this is sent to the gate control circuit 20 via the switch 23 as the output current command value in the isolated operation. A voltage waveform synchronized with the inverter output voltage in the stand-alone operation is generated and sent to the gate control circuit 20 via the switch 23 as the output voltage command value in the stand-alone operation.

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

First, at the time of interconnection with the system power supply 16, if the system power supply 16 is in a normal state, 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 an 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. 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 enters the isolated operation state in the current control mode. This system power supply 1
In step 6, the abnormality detection circuit 21 detects a rise, fall, or distortion of the inverter output voltage in the isolated operation state after the occurrence of the power failure through the transformer 26.

On the other hand, even if the inverter 12 enters the isolated 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 detected by the current control circuit 18. Is corrected by a digital processing PLL circuit 22 provided at the preceding stage of
The current control circuit 18 outputs a stable output current command value by the free-running oscillation wave of the LL circuit 22. 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 eventually stopping.

On the other hand, when the inverter 12 operates alone,
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. Thereby, the voltage control circuit 1
In No. 9, the output voltage command value having a voltage waveform synchronized with the inverter output voltage in the isolated operation can be generated by the PLL circuit 22.

As a result, when a power failure occurs in the system power supply 16, after detecting the independent operation state of the inverter 12, the changeover switch 23 is switched to the voltage control circuit side based on the detection signal output from the abnormality detection circuit 21. As described above, even when shifting from the current control mode 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. The switching from the current control mode to the voltage control mode can be performed smoothly without causing any overcurrent.

In this way, the gate control circuit 20 starts the self-sustaining operation of the inverter 12 in the voltage control mode via the changeover switch 23. At the same time,
Turning off the system interconnection switch 14 disconnects the inverter 12 and the load 17 in the own location from the system power supply 16. Independent operation of the inverter 12 is performed by a PLL
The operation 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 power of 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 detected by the system restoration is detected by the transformer 26, and a voltage waveform synchronized with the system voltage is generated by the PLL circuit 22 to generate the voltage control circuit 19 and the current control circuit 1.
Enter 8 As a result, the output voltage of the inverter 12 and the system voltage that are operating independently in the voltage control mode can be completely synchronized with each other. In this state, even when the system interconnection switch 14 is turned on, no overcurrent flows. Then, 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, thereby starting the normal operation in the current control mode.

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

An 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.
Apart from [referred to as the first transformer], the system interconnection switch 1
4 and another transformer 28 [referred to as a second transformer] is connected to the inverter side of the PLL circuit 22 in addition to the switch 23 [referred to as the first switch] of the embodiment. Is provided with a changeover switch 29 (referred to as a second changeover switch). The output of the second transformer 28 is connected to the abnormality detection circuit 21 and the voltage control circuit 19 and to one terminal of the second switch 29. On the other hand, the output of the first transformer 26 is connected to the other terminal of the second switch 29.

As shown in this application example, the system interconnection switch 14
Is connected to the voltage control circuit 19 by the input of the second transformer 28 connected to the inverter side.
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, so that voltage distortion and control delay can be corrected. In addition, by detecting the isolated 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 independent operation. The changeover switch 29 is also switched to the voltage control circuit side. In this way, when the power 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-sustaining operation can be detected. It is possible to synchronize.

In the above embodiment, the photovoltaic power generation system has been described, but the present invention is not limited to this.
The present invention is also applicable to a system having a DC power source other than the solar cell unit.

[0038]

According to the present invention, since a single PLL circuit is provided before the voltage control circuit and the current control circuit, a stable output current can be obtained even if the inverter enters an isolated 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 is used when switching control from standalone operation to independent operation after a system power failure occurs, and when switching control from independent operation to normal operation when the system is restored. Since the control can be switched in this manner, no overcurrent occurs. Thus, control switching can be performed without interrupting the load in the own location without temporarily stopping the inverter when switching the control mode. Further, since only a single PLL circuit needs to be provided, it is easy to reduce the cost and size of the device.

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, feedback control of the inverter during self-sustained operation can be performed. Control delay can be corrected, and optimal control can be realized even when the load has distortion.

[Brief description of the drawings]

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 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 Unit] 28 Transformer [second transformer] 29 Changeover switch [second changeover switch]

Continuation of the front page (72) Inventor Toshihiko Shikata 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Nissin Electric Co., Ltd. (56) References JP-A-2-7832 (JP, A) JP-A-62-155732 ( JP, A) JP-A-4-190634 (JP, A) JP-A-3-196207 (JP, A) JP-A-60-216727 (JP, A) JP-A-59-153426 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H02J 3/06-3/46 H02J 7/35 H02M 7/48

Claims (1)

(57) [Claims] 1. A system in which a distributed power supply including an inverter is interconnected 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 voltage control circuit for independently operating the inverter in a 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 a first switch. Detecting the isolated operation of the inverter after the occurrence of the system power failure, and
Detection circuit for switching a changeover switch, and a first transformer connected to a system power supply side of a system interconnection switch
And connected to the inverter side of the grid connection switch,
A second transformer input-connected to the voltage control circuit, and an inverter output provided in a preceding stage of the current control circuit and the voltage control circuit and operated in an isolated operation after the occurrence of a system power failure detected by the first transformer. A self-propelled oscillation wave is used to generate an output current command value in which the frequency fluctuation of the voltage is corrected, and a voltage waveform synchronized with the inverter output voltage in the isolated operation after the occurrence of the system power failure is generated. A single PLL circuit that generates a voltage waveform synchronized with the system voltage detected by the transformer, and is connected to the first and second transformers provided before the PLL circuit and switched by a detection output of the abnormality detection circuit. And a second changeover switch.