JP2929466B2 - Illegal current detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illegal current detection circuit, and more particularly to an illegal current detection circuit, for example, in a system interconnection operation when a private power generation system such as a photovoltaic power generation system is connected to a commercial power system for operation. The present invention relates to a current detection circuit.

[Background of the Invention] Power generation equipment typified by photovoltaic power generation using solar energy is expected to be introduced because of the advantages that a huge amount of energy can be used and that it is clean energy. In addition, it is expected that a so-called reverse power flow system interconnection system in which surplus power is supplied to the system by performing interconnection with a commercial system will be widely used in the future.

[0003] However, in the case of performing grid-connected operation, if an illegal current (hereinafter referred to as “cross current”) flows from the commercial power system to the photovoltaic power generator side, it adversely affects the operation of the grid-connected system.

[0004] In order to avoid the adverse effect of the cross flow, it is required to reliably detect the occurrence of the cross flow flowing from the commercial power system on the photovoltaic power generator side when performing the grid interconnection operation.

[0005]

2. Description of the Related Art Conventionally, a photovoltaic power generator in a system interconnection system generally includes a solar cell, an inverter device for converting DC to AC, a system interconnection protection device, and a distribution board.

Here, when a cross current is generated from the commercial power system in the inverter device of the photovoltaic power generation device, the cross current becomes regenerative power to the inverter device, and destroys an electric field capacitor provided at an input stage of the inverter device. Since the overcurrent protection circuit provided in the inverter device operates and leads to the stoppage of the operation of the inverter device, it is necessary to detect the occurrence of the cross current in order to cope with the trouble due to the cross current.

FIG. 5 is a block diagram showing a cross current detection circuit 101 in a conventional system interconnection system.

In FIG. 5, the detection of the cross current is performed by a PLL (Phas
e Locked Loop (PC): Phase Comp
By inputting the reference waveform signal from the commercial power system and the detection waveform signal from the inverter device to the arater) 102, the phase comparator 102 detects the leading / lagging of the phase of the detection waveform signal with respect to the reference waveform signal. The phase difference is constantly compared, and the output voltage from the phase comparator 102 generated by the phase difference is compared with the cross current determination circuit 10 comprising a comparator.
3 and a cross current is detected based on a difference voltage between the output voltage and the reference voltage of the cross current determination circuit 103.

[0009]

However, in such a cross current detection circuit as a conventional illegal current detection circuit, a phase comparator using a PLL is used to detect the cross current. There were serious problems.

That is, a PLL has various characteristics excellent in electrical characteristics and high precision. However, a large number of elements and parts are required to assemble a PLL circuit, and a discrete
Even if it is assembled with a screte, not only the circuit becomes very complicated, but also the price becomes high.

[Objective] In view of the above problems, the present invention provides
An object of the present invention is to reliably detect a cross current without using LL.

[0012]

As shown in FIG. 1, the present invention relates to a fraudulent current detection circuit 1 for detecting a fraudulent current flowing from a commercial power system to an inverter device 2 in a system linked operation system, The unauthorized current detection circuit 1 includes an inverter device 2, a first differentiating circuit 3, and a second differentiating circuit 4.
And a first comparison circuit 5, a second comparison circuit 6, and an AND circuit 7. The inverter device 2 converts DC to AC and outputs the converted AC voltage to the first differentiating circuit 3. And outputs the converted AC current to the second differentiating circuit 4. The first differentiating circuit 3 converts the differential waveform voltage of the AC voltage input from the inverter device 2 into the first comparing circuit 5. The second differentiating circuit 4 outputs a differentiated waveform voltage of the alternating current input from the inverter device 2 to one input terminal of the second comparing circuit 6. The first comparing circuit 5 compares the differentiated waveform voltage input from the first differentiating circuit 3 with a first reference voltage input from the other input terminal, and outputs a pulse voltage, which is a comparison result, as the logical product Output to one input terminal of circuit 7 And than, the second comparison circuit 6
Compares the differentiated waveform voltage input from the second differentiating circuit 4 with a second reference voltage input from the other input terminal, and outputs a pulse voltage as a comparison result to the other input terminal of the AND circuit 7. And the AND circuit 7 outputs
On the other hand the output voltage of the first comparator circuit 5 which is inputted from the input terminal, and outputs a logical product signal of the output voltage of the second comparator circuit 6 inputted from the other input terminal, the theory
The logical product output signal output from the logical product circuit 7 is
The AC voltage input from the barter device 2 is converted into the first differential circuit.
By differentiating on the road 3, the inverter device
2 is input to the second differentiating circuit 4.
The output signal of the AND circuit 7 is
Phase of voltage and current signal input from inverter device 2
"H" (normal) when the difference is less than 90 degrees, "L" when the difference is 90 degrees or more
(Illegal current) and can detect the illegal current and achieve the above purpose
Has formed.

In this case, for example, an AND signal output from the AND circuit 7 is fed back to the inverter device 2, and the inverter device 2 is output based on the logic of the AND signal. It is effective to control the phase of the AC voltage output from.

[0014]

According to the first aspect of the present invention, in the system interconnection operation system, the output voltage and the output current from the inverter device are differentiated by the first and second differentiating circuits, and each differentiated waveform is generated by the first and second differentiating circuits. The first comparison circuit and the second comparison circuit convert the square wave pulse of the output voltage and the output current into a square wave pulse. Based on the logical product of the converted square wave pulses, it is detected whether or not an illegal current (cross current) is flowing. .

Thus, without using a PLL,
Unauthorized current (cross current) is reliably detected.

In this case, according to the second aspect of the present invention,
The AND signal output from the AND circuit is fed back to the inverter device, and based on the level of the AND signal.
Can determine the illegal current, and control the phase of the AC voltage output from the inverter device. For example, when the illegal current (cross current) is detected, the phase of the output voltage is advanced, so that the illegal current (cross current) can be controlled. ) Can be prevented from flowing.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to FIGS.
This will be described with reference to FIG. 2 to 4, FIG.
The same reference numerals are given to the same parts.

First, the configuration of this embodiment will be described.

FIG. 2 is a block diagram showing a configuration of a main part of the unauthorized current detection circuit according to this embodiment. In FIG.
The unauthorized current detection circuit 1 includes an inverter device 2, a CR filter 3 as a first differentiation circuit, a CR filter 4 as a second differentiation circuit, a comparator 5 as a first comparison circuit, a comparator 6 as a second comparison circuit, and a logic circuit. It comprises an AND gate 7, a transformer 8, a current transformer 9, a commercial power system 10, and an interconnecting reactor 11 which are integrated circuits. In FIG. 2, 2
0 is a load that supplies electric power during the system interconnection operation.

The inverter device 2 is an inverting device for converting a direct current into an alternating current. In the present embodiment, for example, the inverter device 2 is an inverter device for converting a direct current obtained from a solar cell or the like into an alternating current, and is used for system interconnection. The developed grid-connected operation inverter is used.

FIG. 3 is a circuit diagram of the CR filters 3 and 4 and a diagram showing output waveforms.

The CR filter 3 and the CR filter 4 are, as shown in FIG. 3A, composed of a capacitor (C) and a resistor (R), and are differentiating circuits having both ends of the resistor as output terminals. Binary changes in the waveform (for example,
The change appears only on the output side when it suddenly increases and suddenly decreases. The output waveform changes depending on the amplitude of the input pulse waveform and the time constant τ as shown in FIG. 3 (b). Come.

Incidentally, in the waveform diagram shown in FIG.
Although a square wave pulse is input as an input waveform to the CR filters 3 and 4, the input waveform of the CR filters 3 and 4 in the present embodiment is a sine curve input, so the output waveform is shown in FIG. As shown. Further, the amount of differentiation by the CR filters 3 and 4 in this embodiment is set to an amount having a width of about 1/4 cycle with respect to the reference clock cycle, so that there is no malfunction due to noise and the circuit can be simply constructed. Can be.

The comparator 5 and the comparator 6 provide a comparison voltage (CR filter 3 and C
Each output of the R filter 4 is compared with a reference voltage applied to the other input terminal, and a difference voltage as a result of the comparison is output.

The AND gate 7 receives the output from the comparator 5 and the output from the comparator 6 as inputs, and outputs the logical product of the outputs to the inverter device 2, that is, the output of the comparator 5 and the output of the comparator 6. When the phase of each output is the same, the output of the AND gate 7 becomes "H", and when the phase of each output differs by 90 degrees or more, the output of the AND gate 7 becomes "L". By the way,
In this embodiment, when the output of the AND gate 7 becomes "L", it is determined that there is a cross flow.

The transformer 8 detects the output voltage of the inverter device 2 and supplies the output voltage from the inverter device 2 to the CR filter 3, while the current transformer 9 detects the output current of the inverter device 2. And supplies an output current from the inverter device 2 to the CR filter 4.

The commercial power system 10 is a power system for interconnection, and supplies power to the load 20 via the interconnection reactor 11.

In this case, the interconnection reactor 11 in the present embodiment has a function of controlling the phase of the output voltage of the inverter device 2 based on the feedback signal from the AND gate 7 to the inverter device 2.

Next, the operation (operation) of this embodiment will be described.

First, the circuit operation shown in FIG. 2 will be described with reference to FIG.

FIG. 4 is a timing chart for explaining the operation of this embodiment.

First, the inverter 8 is operated by the transformer 8.
After the output voltage from the inverter 8 is detected, the output current from the inverter device 2 is detected by the current transformer 9 and the output waveform is half-wave rectified.
While being input to the filter 3, the output from the current transformer 9 is input to the CR filter 4.

Next, the output of the CR filter 3 is input to one input terminal of the comparator 5 and compared with a reference voltage, and the output of the CR filter 4 is output from the comparator 5.
Is input to one input terminal and compared with a reference voltage. In each of the comparators 5 and 6, a difference voltage as a result of comparison with the reference voltage is output as a square wave pulse, and each output is input to the AND gate 7. .

Here, as described above, the output of the AND gate 7 is "H" when the phases of the voltage and the current are equal.
When the phases of the voltage and the current differ by 90 ° or more, the output becomes “L” and it is determined that there is a cross current. Ma
Also, in other words, the load has a capacitive load or an inductive load
If the phase difference between the voltage and the current is less than 90 °,
The output of the gate 7 becomes "H" (normal) and is judged to be normal.
You.

That is, by feeding back the output of the AND gate 7 to the inverter device 2,
When the output of the AND gate 7 is “H”, the normal operation is performed. On the other hand, when the output of the AND gate 7 is “L”, the cross current is blocked by advancing the phase of the output voltage of the inverter device 2, Can be prevented from occurring.

As described above, in the present embodiment, the cross current can be detected by a simpler circuit as compared with the cross current detection circuit 101 using a PLL which has been conventionally used. In the system, the inverter device 2
Of the output voltage and output current from the comparators 3 and 4, and differentiated waveforms from the comparators 5 and 6
Converts it into a square wave pulse of output voltage and output current,
Whether or not the cross current is flowing can be detected by the logical product of the converted square wave pulses.

Therefore, the presence or absence of a cross current can be reliably detected without using a PLL.

In this case, the output from the AND gate 7 is fed back to the inverter device 2 to detect the cross current from the system, and then the phase of the output voltage of the inverter device 2 is controlled using the interconnection reactor 11. , Cross flow can be prevented.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, For example, the time constant τ of the CR filter constituting the differentiating circuit can be arbitrarily set.

In the above description, the invention mainly made by the inventor has been described as applied to a system interconnection operation which is a background of application, but the invention is not limited to this. For example, the present invention can be applied not only to a system interconnection operation system but also to an inverter parallel operation system, which is an inverter system having a function of operating inverter devices in parallel.

[0041]

According to the first aspect of the present invention, in the system interconnection operation system, the output voltage and the output current from the inverter device are differentiated by the first and second differentiation circuits, and each of the differentiated waveforms is differentiated. The first comparison circuit and the second comparison circuit convert the output voltage and the output current into a square wave pulse, and the logical product of the converted square wave pulses can detect whether or not an illegal current (cross current) is flowing. .

Therefore, an unauthorized current (cross current) can be detected without using a PLL.

In this case, according to the second aspect of the present invention,
By feeding back the AND signal output from the AND circuit to the inverter device and controlling the phase of the AC voltage output from the inverter device based on the logic of the AND signal, for example, illegal current (cross current) can be reduced. By advancing the phase of the output voltage when it is detected, it is possible to prevent an illegal current (cross current) from flowing.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an unauthorized current detection circuit according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a main part of an unauthorized current detection circuit according to the embodiment.

FIG. 3 is a diagram illustrating a circuit diagram and an output waveform of a CR filter.

FIG. 4 is a timing chart for explaining the operation of the present embodiment.

FIG. 5 is a block diagram showing a cross current detection circuit in a conventional system interconnection system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 unauthorized current detection circuit 2 inverter device 3 CR filter (first differentiation circuit) 4 CR filter (second differentiation circuit) 5 comparator (first comparison circuit) 6 comparator (second comparison circuit) 7 AND gate (logical product circuit) Reference Signs List 8 transformer 9 current transformer 10 commercial power system 11 interconnection reactor 20 load 101 cross current detection circuit 102 phase comparator 103 cross current determination circuit

Claims (2)

(57) [Claims] An unauthorized current detection circuit for detecting an unauthorized current flowing from a commercial power system to an inverter device in the system operation system, wherein the unauthorized current detection circuit includes an inverter device, a first differentiation circuit, and a second differentiation circuit. A differentiation circuit, a first comparison circuit, a second comparison circuit, and an AND circuit, the inverter device converts DC to AC, and outputs the converted AC voltage to the first differentiation circuit, Outputting the converted AC current to the second differentiating circuit, wherein the first differentiating circuit outputs a differential waveform voltage of the AC voltage input from the inverter device to one input terminal of the first comparing circuit. Wherein the second differentiating circuit outputs a differentiated waveform voltage of an alternating current input from the inverter device to one input terminal of the second comparing circuit. The path compares a differentiated waveform voltage input from the first differentiating circuit with a first reference voltage input from the other input terminal, and outputs a pulse voltage as a comparison result to one input terminal of the AND circuit. The second comparing circuit compares the differentiated waveform voltage input from the second differentiating circuit with a second reference voltage input from the other input terminal, and outputs a pulse voltage as a comparison result. The AND circuit outputs the output voltage of the first comparison circuit input from one input terminal and the second comparison circuit input from the other input terminal. An AND signal with an output voltage is output, and an AND output signal output from the AND circuit is
The AC voltage input from the inverter device is subjected to the first differentiation.
By differentiating the circuit, the inverter device
Is differentiated by the second differentiating circuit.
Thus, the output signal of the AND circuit is
The phase difference between the voltage and current signals input from the
"H" (normal) below 90 degrees, "L" (90% or more)
And a detection method that can judge illegal current.
Illegal current detection circuit. 2. The method according to claim 1, wherein a logical product signal output from said logical product circuit is fed back to said inverter device, and a phase of an alternating voltage output from said inverter device is controlled based on a logical value of the logical product signal. The unauthorized current detection circuit according to claim 1.