JPH07336897A - Inverter device for distributed power supply and control method thereof - Google Patents

Abstract

PURPOSE:To improve safety and reliability by a method wherein reactive power output from an inverter is detected, a phase-difference measured value based on the detection and a phase-difference command value transmitted over the inverter are compared, the single operation of the inverter after the generation of system service interruption is detected and the single operation is stopped. CONSTITUTION:The phase-difference measured value of output currents to reactive power, output voltage, actually output from an inverter 12 is computed by a single-operation decision circuit 22. On the other hand, a phase-difference command value transmitted over the inverter 12 is transmitted over the single- operation decision circuit 22 from a current control circuit 20. The single- operation decision circuit 22 compares the phase-difference measured value and the phase-difference command value, decides the inverter 12 as single operation when the absolute value of the difference of the phase-difference measured value and the phase-difference command value is larger than a tolerance, and stops the inverter 12. Accordingly, safety and reliability are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for a distributed power source and a control method thereof, and more specifically, it is used in a solar power generation system or the like in which a distributed power source is connected to a system power source. The present invention relates to an inverter device for a distributed power source that detects and stops an isolated operation, and a control method thereof.

[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.
Particularly, since the system voltage by the system power supply 5 is stabilized, the inverter 2 in the current control mode is favorably used to obtain a stable current waveform.

[0004]

By the way, if the system power supply 5 fails for some reason, the inverter 2 will be in the independent operation mode. If left in this state, since the inverter 2 is operating independently despite the power failure of the system power supply 5, the line that should be the power failure area will be in a charging state, so that the operator will get an electric shock. There are various problems such as the risk of In order to solve this problem, when a power failure occurs in the system power supply 5, it is necessary to detect the islanding operation of the inverter 2 after the power failure and stop it immediately.

Therefore, as means for detecting the above-mentioned islanding operation of the inverter 2, there are three methods including a voltage phase jump detection method, a third harmonic voltage distortion rapid increase detection method, and a frequency change rate detection method. The voltage phase jump detection method is a method of detecting a sudden change in the voltage phase due to an imbalance between the power generation output and the load when shifting to the isolated operation. The third harmonic distortion sudden increase detection method is a method of detecting a sudden increase in the third harmonic voltage that depends on the transformer at the inverter output stage when shifting to the islanding operation. Furthermore, the frequency change rate detection method is a method of detecting a sudden change in frequency due to an imbalance between the power generation output and the load when shifting to islanding. All of these three detection methods focus on transient changes in the output voltage of the inverter.

The detection of the isolated operation is one of the most important items in terms of security as a measure for preventing the isolated operation, and
Since technical difficulties are involved, in order to improve the safety and reliability, it is the current situation that an islanding operation detecting means other than the above-mentioned three methods is required.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to provide a new method capable of quickly and reliably detecting the isolated operation of the inverter after the occurrence of a system power failure. The purpose is to

[0008]

As a technical means for achieving the above object, the method of the present invention detects fluctuations in the output voltage of a distributed power source inverter connected to a system power source,
The current phase is controlled based on this voltage fluctuation to generate a phase difference (reactive power) command value that causes the current to have a predetermined phase difference with respect to the inverter output voltage, while the phase difference command value and the inverter actually It is characterized in that the phase difference [reactive power] actually output is compared with the actual measured value, and based on the comparison result, the isolated operation of the inverter due to the occurrence of the system power failure is detected and stopped.

Further, the device of the present invention detects the fluctuation of the output voltage of the distributed power inverter connected to the system power supply, and a voltage fluctuation judging circuit for the inverter output voltage based on the output of the voltage fluctuation judging circuit. Control circuit that controls the current phase so that the current has a predetermined phase difference, a current control circuit that outputs a phase difference [reactive power] command value based on the output of the phase control circuit, and the current control circuit The phase difference command value output from the inverter is compared with the phase difference [reactive power] actual measurement value obtained by detecting the output voltage and output current of the inverter, and an isolated operation determination circuit that outputs an inverter stop signal from the comparison result Is provided.

[0010]

When a power failure occurs in the system power supply, the reactive power on the power generation side and the reactive power on the load side become unbalanced, and the inverter outputs the amount of reactive power required by the load side. In the present invention, the reactive power actually output from this inverter is detected, and the phase difference measured value based on the reactive power detection,
The phase difference command value given to the inverter is compared. Based on the result of comparison between the phase difference command value and the phase difference actual measurement value, it is possible to detect the isolated operation of the inverter after the occurrence of the system power failure, and to quickly stop the isolated operation.

[0011]

EXAMPLE An example in which the present invention is applied to a solar power generation system will be described with reference to FIGS.

The solar power generation system shown in FIG. 1 will be briefly described first. A distributed power source 13 including a solar cell unit which is a direct current power source 11 and an inverter 12 which converts direct current power generated from the direct current power source 11 into alternating current. Is connected to the system power supply 15 via the system connection switch 14 so that the distributed power 13 or the system power supply 15 selectively supplies power to the in-house load 16. The system interconnection switch 14 is a magnet switch, and is for disconnecting the inverter 12 and the in-house load 16 from the system.

The control unit 17 of the inverter device of the present invention is
A voltage fluctuation determination circuit 18, a phase control circuit 19, a current control circuit 20, a gate control circuit 21, and an isolated operation determination circuit 22, which will be described later, constitute a main part. In the figure, 23 is a current transformer provided on the system bus 24 and connected to the current control circuit 20 and the islanding operation determination circuit 22, and 25 is a transformer connected to the inverter side of the system interconnection switch 14, Phase control circuit 19, voltage fluctuation determination circuit 18, and isolated operation determination circuit 2
Connected to 2.

The voltage fluctuation judging circuit 18 detects the fluctuation of the output voltage of the inverter 12 through the transformer 25 and sends the detection signal to the phase control circuit 19. The phase control circuit 19 uses the inverter output voltage directly input through the transformer 25 as a reference based on the detection signal output from the voltage variation determination circuit 18, and sets a predetermined current for the inverter output voltage. The current phase is controlled so that the phase difference becomes. The current control circuit 20 has a phase difference [reactive power] such that the current has a predetermined phase difference with respect to the inverter output voltage based on the output of the phase control circuit 19.
The command value is output to the gate control circuit 21 and the islanding operation determination circuit 22. The gate control circuit 21 is a current control circuit 2
The inverter 12 is switched based on the phase difference command value from zero.

On the other hand, the islanding operation determination circuit 22 includes the transformer 2
Phase difference [reactive power] based on the current detected by the current transformer 23 with respect to the inverter output voltage detected by
The measured value, that is, the actually measured phase difference value from the inverter 12, and the phase difference command value output from the current control circuit 20, that is, the current has a predetermined phase difference with respect to the inverter output voltage. The phase difference command value is compared, and it is determined whether the inverter 12 is operating alone based on the comparison result. When the inverter 12 is operating independently, an inverter stop signal is sent.

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

First, when the system power supply 15 is in a normal state at the time of interconnection with the system power supply 15, the inverter 12 is normally operated in the current control mode. That is, the phase control circuit 19 controls the current phase so that the current has a predetermined phase difference based on the inverter output voltage detected by the transformer 25, and the current control circuit 20 outputs the phase control circuit 19 based on the output of the phase control circuit 19. Outputs a phase difference [reactive power] command value and controls the inverter 12 through the gate control circuit 19 based on the phase difference command value.

Here, when a power failure occurs in the system power supply 15, the system voltage is lost and the inverter 12 is in the independent operation state in the current control mode. Inverter 12
When the power generation side becomes a stand-alone operation state after the occurrence of a system power failure, the reactive powers on the power generation side and the load side become unbalanced, and the inverter 12 outputs the reactive power required by the load side. As a result, the amount of reactive power actually output by the inverter 12 and the amount of reactive power commanded by the control unit 17 to the inverter 12 do not match.

Therefore, by detecting the output voltage of the inverter 12 with the transformer 25 and detecting the output current with the current transformer 23, the reactive power actually output from the inverter 12 in the isolated operation determination circuit 22, That is, the actual phase difference [reactive power] of the output current with respect to the output voltage is calculated. On the other hand, the phase difference command value output from the current control circuit 20 and to be applied to the inverter 12 is used as the islanding operation determination circuit 22.
Send to. As a result, the actual phase difference value obtained by the islanding operation determination circuit 22 and the phase difference command value sent from the current control circuit 20 to the islanding operation determination circuit 22 are compared by the islanding operation determination circuit 22.

In the isolated operation judging circuit 22, as shown in FIG. 2, the phase difference measured value θm is fetched at a predetermined sampling interval and the phase difference command value θo is fetched at an inverter control time interval by the current control circuit 20. , The difference Δ between the measured phase difference θm and the phase difference command value θo
The absolute value | Δθ | of θ is calculated. The result of this comparison, namely
If the absolute value | Δθ | of the difference Δθ between the phase difference measured value θm and the phase difference command value θo is larger than the allowable range α, it is determined that the inverter 12 is operating independently and the inverter stop signal is output. The independent operation of the inverter 12 is stopped. On the contrary, if the absolute value | Δθ | is smaller than the allowable range α, it is determined that the inverter 12 is not in the independent operation but is in the normal operation state during the grid interconnection, and the operation of the inverter 12 in the current control mode is performed. Let it continue.

The sampling interval of the phase difference measured value θm is set shorter than the inverter control time interval of the phase difference command value θo. This makes it possible to compare the measured phase difference value θm with the latest phase difference command value θo.
In addition, the allowable range α to be compared with the absolute value | Δθ | is set based on the actual measurement error and the control error, and thus the erroneous determination of the isolated operation of the inverter 12 may be made due to the actual measurement error and the control error. It can be prevented.

In this way, the islanding operation determination circuit 22 detects the islanding operation of the inverter 12 after the occurrence of the system power failure, and after stopping the inverter 12, the system interconnection switch 14 is opened or the inverter 12 becomes independent. Move to operation.

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.

[0024]

According to the present invention, it is possible to provide a new islanding operation detection method focusing on the reactive power based on the phase difference of the output current with respect to the output voltage of the inverter, which is generally technically difficult. One new means will be added to the detection of isolated operation, which makes it easier to more reliably detect the isolated operation of the inverter after a system power outage, greatly improving safety and reliability. Improve to.

[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 flow chart for performing islanding detection according to the method of the present invention.

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

[Explanation of symbols]

 12 Inverter 15 System power supply 18 Voltage fluctuation judgment circuit 19 Phase control circuit 20 Current control circuit 22 Individual operation judgment circuit θo Phase difference command value θm Phase difference actual measurement value

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01L 31/04 H02M 7/48 D 9181-5H (72) Inventor Ikuchi Natsuta Ukyo, Kyoto City, Kyoto Prefecture 47 Umezu-Takaune-cho, Niishin Electric Co., Ltd.

Claims (2)

[Claims] 1. A change in the output voltage of an inverter for a distributed power supply connected to a system power supply is detected, the current phase is controlled based on this voltage change, and the current has a predetermined phase difference with respect to the inverter output voltage. While generating such a phase difference [reactive power] command value, the phase difference command value is compared with the phase difference [reactive power] actually measured value actually output from the inverter,
A method for controlling an inverter device for a distributed power supply, characterized in that an independent operation of an inverter due to a system power failure is detected and stopped based on the comparison result. 2. A voltage fluctuation judging circuit for detecting fluctuations in the output voltage of a distributed power inverter connected to a grid power supply,
A phase control circuit that controls the current phase so that the current has a predetermined phase difference with respect to the inverter output voltage based on the output of the voltage fluctuation determination circuit, and a phase difference [reactive power] based on the output of the phase control circuit. ] Comparing the current control circuit that outputs the command value, the phase difference command value output from the current control circuit and the phase difference (reactive power) measured value obtained by detecting the output voltage and output current of the inverter, An inverter device for a distributed power supply, comprising: an isolated operation determination circuit that outputs an inverter stop signal from the comparison result.