JP3519760B2 - 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 an islanding operation detecting device in a system interconnection system using a voltage type current control type inverter.

[0002]

2. Description of the Related Art In recent years, several kW for solar cells, fuel cells, etc.
Various grid-connected systems have been proposed that connect (connect) a distributed power supply system equipped with a DC power supply of a certain degree and an inverter that converts its output to AC with a commercial power grid to supply power to loads such as home appliances. There is.

In the grid interconnection system, in order to ensure the safety of maintenance work of the commercial power system, the operation of the inverter is immediately stopped or the switch is immediately opened at the time of an unexpected power failure and a work power failure of the commercial power system. The function of disconnecting the inverter from the commercial power system by operating it to release the interconnection, that is, the function of preventing independent operation of the inverter circuit is essential.

A conventional system interconnection system is configured to detect a system power failure due to output voltage fluctuations and output frequency fluctuations of the inverter and disconnect the inverter from the commercial power system. However, in such a system interconnection system, when the output power of the inverter and the power consumption of the load are substantially equal to each other in the load balanced state, the output voltage and the output frequency of the inverter hardly change, and therefore, the system outage cannot be detected. There was a problem.

Therefore, in order to ensure detection of a system power failure due to frequency fluctuations, fluctuations of several hertz are given to the control target value during feedback control in the inverter, and the output frequency of the inverter is positively set at the time of power failure. A varying active detection method has been proposed.

[0006]

Since noises such as various harmonic components and low frequency components due to load fluctuations are superimposed on the interconnection points, it is difficult to detect frequency fluctuations due to system power failure without error. There was a problem.

An object of the present invention is to improve detection accuracy.

[0008]

In order to solve the above-mentioned problems, the device according to the invention of claim 1 is for interconnection of a voltage type current control system for outputting a current superposed with a low frequency component lower than a commercial frequency. An islanding operation detection device for an inverter, wherein the voltage waveform extraction means extracts the low frequency component of the voltage at the interconnection point between the inverter and the commercial power system, and the low frequency component of the output current of the inverter. A current waveform extracting means, a multiplying means for obtaining a product of respective outputs of the voltage waveform extracting means and the current waveform extracting means, and a comparing means for outputting an islanding operation detection signal when the product exceeds a threshold value.

According to a second aspect of the invention, a full-wave rectifier circuit for inputting the absolute value of the voltage at the interconnection point to the voltage waveform extracting means, and the absolute value of the output current of the inverter for extracting the current waveform. A full-wave rectification circuit for inputting to the means.

According to a third aspect of the present invention, the voltage waveform extracting means and the current waveform extracting means each include a second-order or higher-order filter circuit.

[0011]

In the interconnection operation, the change in the output current of the inverter is absorbed by the commercial power system, and the voltage frequency at the interconnection point is maintained at the commercial frequency.

At the time of system power failure, the load voltage also changes with the change of the output current of the inverter, and the low frequency component in phase with the output current of the inverter is superimposed on the voltage at the interconnection point. By extracting and multiplying the low-frequency component of the inverter output current and the low-frequency component of the voltage at the interconnection point, the in-phase component is emphasized and appears as a large signal change, so the effects of current noise and voltage noise Therefore, the output change of the inverter due to the power failure can be detected with high accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a photovoltaic power generation system 1 equipped with an islanding operation detecting device 40 according to the present invention, and FIG.
3 is a block diagram of the inverter 20 of FIG.

In FIG. 1, the solar power generation system 1 is
A solar cell 10 having a rated voltage of about 200 V, a voltage source current control type inverter 20, a system protection switchgear 30,
And the islanding operation detection device 40, and is connected to the commercial power system 2 via a transformer or the like (not shown). A load Z such as various home appliances is connected to the distribution line L.

The inverter 20 has an inverter circuit 21 composed of a plurality of switching elements and a control system 22 thereof. As shown in FIG. 2, in the inverter 20, the output voltage V of the solar cell 10 that changes according to the amount of solar radiation.
1 is detected by an isolation amplifier or the like,
The output voltage V1 of the solar cell 10 is controlled by the differential amplifier 220.
Of the input error signal S that is the difference between the voltage command value Vref and the voltage command value Vref
a is generated. The input error signal Sa becomes one input signal of the multiplier 221. At this time, the voltage command value Vref
As, a value near the optimum operating point of the solar cell 10 is set. However, in order to detect the islanding operation of the inverter 20, fluctuations are given to the voltage command value Vref by superimposing a low frequency of about 4 Hz.

The fundamental frequency component of the interconnection point voltage V3 extracted by the transformer 24 and the bandpass filter 224 is input to the multiplier 221 as the other input signal. Then, by multiplying the input error signal Sa by the fundamental frequency component, the current command value signal Si indicating the control target value is generated. That is, the magnitude (amplitude) of the output current of the inverter circuit 2 is set by the input error signal Sa, and the phase of the output current is set by the system voltage at the interconnection point.

The current command value signal Si and the actual output current value detected by the current transformer 23 or the like are input to the operational amplifier (error amplifier) 222, and the current error signal SΔi is generated. This current error signal SΔi is applied to the PWM control unit 2
23 is input.

In the PWM control section 223, the current error signal S
By comparing Δi with the reference triangular wave signal of about 20 kHz, a switching signal whose pulse width is adjusted so that the current error signal SΔi becomes zero is generated, and the inverter circuit 2
It is output to 1.

By such feedback control, as a normal operation, the current value is set so as to extract the maximum power from the solar cell 10, and the AC power with a power factor of 1 whose current phase is the same as the system voltage is the inverter circuit. It will be output from 21.

Now, returning to FIG. 1, the islanding operation detecting device 4
0 is a full-wave rectification circuit 41, 42, a waveform extraction unit 43, 4
4, a multiplier 47, and a 16-bit microcomputer 48. The waveform extraction units 43 and 44 are
High-order (for example, 8th-order) low-pass filter 45
And a high pass filter 46, and extracts a low frequency component corresponding to the fluctuation of the voltage command value Vref from the input signal.

One full-wave rectification circuit 41 includes a transformer 24
The interconnection point voltage V detected by is input, and the signal indicating the absolute value of the interconnection point voltage V is input from the full-wave rectifier circuit 41 to the waveform extracting unit 43. The other full-wave rectification circuit 42
The output current I of the inverter 20 detected by the current transformer 23 is input to the, and a signal indicating the absolute value of the output current I is input from the full-wave rectifier circuit 42 to the waveform extraction unit 44.

The low frequency components extracted by the waveform extracting sections 43 and 44 are respectively added to the multiplier 47 and multiplied by the change component signal S47 which is the product of the low frequency component of the voltage V and the low frequency component of the current I. It is output from the device 47.

During operation of the commercial power system 2, the power capacity of the commercial power system 2 is orders of magnitude larger than the power capacity of the solar cell 10 and the frequency is stable, so that the output current I of the inverter 20 is stable. The current is supplied to the load Z in a form of compensating for the minute fluctuation of That is, the fluctuation of the output current I of the inverter 20 is absorbed by the commercial power system 2, and the frequency of the interconnection point voltage V is maintained at the commercial frequency. as a result,
The output of the waveform extraction unit 43 becomes 0 level.

On the other hand, at the time of system power failure, the load voltage also changes with the change of the output current I of the inverter 20, and the low frequency component in phase with the output current I is superimposed on the interconnection point voltage V.

By extracting and multiplying low frequency components from the output current I of the inverter 20 and the interconnection point voltage V, respectively, the in-phase change component is emphasized and appears in the change component signal S47 as a large signal change.

In the solar power generation system 1, the microcomputer 4 is based on such a change component signal S47.
The isolated operation state is detected by 8. That is, the microcomputer 48 compares the A / D converted value of the change component signal S47 input to the analog port with the threshold data stored in advance. Then, the microcomputer 48 outputs the islanding operation detection signal SD to the switchgear device 30 when the change component signal S47 exceeds the threshold value.

The switchgear 30 operates in response to the islanding operation detection signal SD to release the interconnection between the inverter 20 and the commercial power system 2. As a result, the solar power generation system 1 is disconnected from the commercial power system 2.

The use of the microcomputer 48 facilitates arbitrary setting of detection resolution, control timing of the opening / closing device 30, and the like. Further, the microcomputer 48 can also be used for controlling the inverter 20.

According to the above-mentioned embodiment, the waveform extracting section 43,
Since the low pass filter 45 of 44 has a higher order to increase the selectivity, it is possible to cut the sideband component of the fluctuation and extract only the basic component. Therefore, the fluctuation is set as low as possible and the operating efficiency of the inverter 20 is reduced. Can be increased.

According to the above embodiment, the full-wave rectifier circuit 4
Since 1, 42 are provided, the detection is speeded up and the waveform extraction unit 4 is provided.
The cost can be reduced by lowering the breakdown voltage of 3,44. That is, in principle, the change in voltage at the time of system power failure is in phase with the current, but depending on the characteristics of the voltage and current detection means, a phase difference may occur between the voltage and current after detection. There are cases. In this case, if the full-wave rectification circuits 41 and 42 are omitted, when the polarity of the voltage and the polarity of the current are different, the multiplication result of these becomes negative, and the microcomputer 48 outputs a positive polarity signal of 0 to 5V, for example. Since the level is determined, the period in which the multiplication result is negative becomes a dead period for detection and the detection is delayed. Further, when the half-wave rectifier circuit is provided, even if the voltage and the current are in phase, the dead period occurs when the polarity is negative.

[0031]

According to the present invention, since the in-phase change component is emphasized by multiplication, it is possible to realize highly accurate detection while suppressing the influence of noise.

According to the second aspect of the present invention, it is possible to realize rapid and highly accurate detection by using a processor that handles a signal of a single polarity, and to reduce the cost of the waveform extracting means.

According to the third aspect of the invention, the active change in the output current of the inverter can be detected more reliably.

[Brief description of drawings]

FIG. 1 is a block diagram of a photovoltaic power generation system including an islanding operation detection device according to the present invention.

FIG. 2 is a block diagram of the inverter of FIG.

[Explanation of symbols]

2 Commercial power system 20 Inverter (Inverter for interconnection) 40 islanding operation detector 43 Waveform Extraction Unit (Voltage Waveform Extraction Means) 44 Waveform Extraction Section (Current Waveform Extraction Means) 47 multiplier (multiplication means) 48 microcomputer (comparison means) SD islanding detection signal 41,42 Full-wave rectifier circuit 45 Low-pass filter (higher-order filter circuit)

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-57-40373 (JP, A) JP-A-62-71428 (JP, A) JP-A-62-89429 (JP, A) JP-A-62- 95933 (JP, A) JP 62-110166 (JP, A) JP 5-244717 (JP, A) JP 6-332553 (JP, A) JP 7-131937 (JP, A) Dingji, Yasuhiro Makino, Yukinori Kuwano, Prevention of islanding operation of grid-coupling inverter with bimodal bandpass filter, Transactions of the Institute of Electrical Engineers of Japan B, Japan, The Institute of Electrical Engineers of Japan, April 20, 1994, Vol. 114, No. 4, p. 425-426 (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 23/00-23/20 H02J 3/38

Claims (3)

(57) [Claims] 1. An islanding operation detection device for a voltage-type current control type interconnection inverter that outputs a current in which a low-frequency component lower than a commercial frequency is superposed, wherein an interconnection operation point of the inverter and the commercial power system is provided. A voltage waveform extracting means for extracting the low frequency component of the voltage, a current waveform extracting means for extracting the low frequency component of the output current of the inverter, and a product of outputs of the voltage waveform extracting means and the current waveform extracting means. And a comparing means for outputting an isolated operation detection signal when the product exceeds a threshold value. 2. A full-wave rectification circuit for inputting the absolute value of the voltage at the interconnection point into the voltage waveform extraction means, and a full-wave rectification circuit for inputting the absolute value of the output current of the inverter into the current waveform extraction means. The islanding operation detection device according to claim 1, further comprising: 3. The islanding operation detecting device according to claim 1, wherein the voltage waveform extracting means and the current waveform extracting means each include a second-order or higher-order filter circuit.