JPH0296815A - Reactive power compensator - Google Patents

Abstract

PURPOSE:To facilitate design for precisely suppressing a higher harmonic and standardization by detecting reactive current components and high frequency current components in a load current, injecting a compensation higher harmonic current from an inverter circuit to a power system and suppressing the outflow of a higher harmonic current to the power system. CONSTITUTION:The reactive current components and the higher harmonic current components in the load current flowing from the power system to a load are respectively detected in an reactive current/higher harmonic current detection circuit 6. A firing angle operation circuit 7 calculates the firing angles of thyristors 3B and 3C for causing the compensation reactive current cancelling the reactive current components in the load current to flow as the synthesis current of a lagging circuit 3 and a phase advancing capacitor 4, and energizes the thyristors 3B and 3C by the calculated firing angle. Consequently, the reactive current components in the load current are cancelled by the compensation reactive current flowing as the synthesis current of the lagging circuit 3 and the phase advancing capacitor 4, and the outflow of the reactive current to the power system is suppressed. Thus, the automatic and optimum suppression of the higher harmonic is performed and design for precisely suppressing the higher harmonic is facilitated, whereby standardization is facilitated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a reactive power compensator that also serves as an active filter for performing harmonic compensation. The present invention relates to a reactive power compensator that compensates for current as well as harmonics generated by a load and harmonics generated due to reactive power compensation.

[Traditional techniques]

In the conventional reactive power compensator, as shown in FIG. 3, a phase delay circuit 53 and a phase advance circuit 54 that perform phase control are connected in parallel to a load 52 that is supplied with power from a power system 51.

Slow homology B53 includes reactor 53A and thyristor 53B
, 53C is configured in series with an anti-parallel circuit of thyristor 53B.
, 53C, it is possible to increase or decrease the slow phase reactive current. Further, the phase advance circuit 54 includes phase advance capacitors 54A and 54B with fixed capacitance.

54C and each connected in series with each other or the accelerator 54
D, 54B, and 54F, and a constant phase-advanced reactive current flows through the power system 51.

Therefore, the sum of the slow phase reactive current flowing through the slow phase circuit 53 and the phase advancing reactive current flowing through the phase advancing circuit 54 flows as a reactive current in the power system 51, and the absolute value of the slow phase reactive current increases. If the absolute value of the phase reactive current is smaller than the absolute value of the phase reactive current, a phase leading reactive current flows as a composite ti*, and conversely, if the absolute value of the phase lag reactive current is larger than the absolute value of the phase leading reactive current, a phase lag reactive current flows as a composite current, If the absolute values of the lagging reactive current and the advancing reactive current are the same, no reactive current will flow at all. As a result, thyristors 53B, 53
By controlling the firing angle of C; n, either a leading phase reactive current or a slowing phase reactive current can be arbitrarily output as a compensating reactive current that cancels out the reactive current flowing through the load 2.

At this time, the reactive current detection circuit 55 detects the load current IL via the current transformer 56, and also detects the grid voltage V via the transformer 57, and based on the load tffl I L and the grid voltage V, Invalid i in load current IL! Current component (current component whose phase is shifted by 190 degrees with respect to the system voltage V)
Compensation invalidation 1 that cancels the detected reactive current component
The firing angles of the thyristors 53B and 53C are controlled so that afL flows as a combined current of the phase delay circuit 53 and the phase advance circuit 54.

When the phase delay circuit 53 and the phase advance circuit 54 generate a desired compensation reactive current, a harmonic current necessarily flows through the phase delay circuit 53 due to the relationship of phase control in the phase delay circuit 53, and in addition to this, a harmonic current flows through the phase delay circuit 53. A harmonic II current also flows. In order to suppress the outflow of such harmonic currents to the power system 51, the phase advance circuit 54 does not use a single phase advance capacitor, but uses divided phase advance capacitors 54A, 54B, 54.
reactors 54D, 54E, and 54F are connected in series to each of them to act as a passive harmonic filter.

[The invention tries to solve ii! ! the law of nature This reactive power compensator device includes a phase advance capacitor 54A.

54B, 54C and reactors 54D, 54E, 54
A power system 51 with a high JJ single wave current generated from a slow phase circuit 53 and a load 52 using a passive harmonic filter consisting of F.
Since the configuration suppresses the outflow to the power system, the harmonic state of the power system 51 and the generation of harmonics from the load 52! If the circuit constants of the harmonic filter are not set with a thorough understanding of 1 (including the correlation with reactive power), the harmonics may not be suppressed sufficiently, or the harmonic filter may generate excessive harmonic current. may flow and cause damage to the harmonic filter.

However, it is not easy to understand the harmonic state of the above-mentioned power system 51 and the amount of harmonics generated from the load 52.
It has been difficult to design the circuit constants of a harmonic filter, and it has been difficult to design a design for accurately suppressing harmonics.

In addition, since the harmonic state of the power system 51 and the amount of harmonics generated from the load 52 are not constant, the harmonic filter capacity differs depending on the installed reactive power compensator, making it difficult to standardize the harmonic filter. It was hot.

Therefore, an object of the present invention is to provide a reactive power compensator that is easy to design and easy to standardize for accurately suppressing harmonics.

Means for Solving Problem C] The reactive power compensator of the present invention connects a slow-phase circuit consisting of a series circuit of a reactor and a thyristor in parallel to a load supplied with power from an electric power system, and connects a phase-leading capacitor to the slow-phase circuit. are connected in parallel. Further, a series resonant circuit whose resonant frequency matches the power system fundamental wave frequency is inserted between the neutral point side terminal of the phase advance capacitor and the power system neutral point.

Then, a reactive current/harmonic type fL output circuit is provided to detect reactive current components and harmonic current components in the load current flowing from the power system to the load, and the load detected by the reactive current/harmonic current detection circuit is installed. A firing angle calculation circuit that calculates the firing angle of the thyristor to flow compensation reactive current that cancels the reactive current component in the current as a composite current of the phase delay circuit and the phase advance capacitor, and conducts the thyristor at the calculated firing angle. has been established.

In addition, an inverter circuit is installed that injects a compensating harmonic current into the power system from the connection point between the phase-advancing capacitor and the series resonant circuit, and the content of A harmonic calculation circuit that calculates harmonic current components with different values is provided, and the harmonic current components in the negative rt1 current detected by the invalid 1t2It/harmonic '[nagarashide circuit and the delay calculated by the harmonic calculation circuit] An adder is provided to add the harmonic current components in the current of the phase circuit.

Furthermore, a command value that determines the on/off timing of the switching element of the inverter circuit is calculated in accordance with the output of this adder, and the switching element of the inverter circuit is controlled on/off according to the calculation result of the command value. An inverter command value calculation circuit is provided that cancels the harmonic current components of the current component and the harmonic current component in the current of the slow phase circuit with a compensation harmonic current injected from the inverter circuit into the power system.

[For production]

In the configuration of the present invention, the zero firing angle calculation circuit detects the reactive current component and the harmonic current component in the load current flowing from the power system to the load in the reactive current/harmonic current detection circuit. The firing angle of the thyristor is calculated so that a compensating reactive current that cancels out the reactive current component inside the circuit flows as a composite current of the phase delay circuit and the phase advance capacitor, and the thyristor is made conductive at the calculated firing angle. As a result, the reactive current component in the negative r@'lIi current is canceled by the compensating reactive current flowing as a combined current of the phase delay circuit and the phase advance capacitor, and the outflow of the reactive IT current to the power system is suppressed. .

On the other hand, the harmonic current components in the load current and the harmonic current components in the current of the slow phase circuit are suppressed from flowing into the power system by the active filter function described below.

The content of the harmonic energized 2it component contained in the current of the slow phase circuit differs depending on the firing angle of the thyristor, but the harmonic current component is calculated by the harmonic calculation circuit, and this harmonic current component and The harmonic current component in the negative current detected by the reactive current/harmonic current output circuit is added by the adder.Then, the inverter command value calculation circuit corresponds to the output of the adder. Then, a command value that determines the on/off timing of the switching element of the inverter circuit is calculated, and the switching element of the inverter circuit is controlled on/off according to the result of the calculation of the command value.As a result, harmonic current components in the load current and The harmonic current component in the current of the slow phase circuit is canceled out by the compensation harmonic current 1i that is injected from the inverter circuit into the power system through the phase advance capacitor.

At this time, a series resonant circuit is inserted between the neutral point side terminal of the phase advance capacitor and the power grid neutral point, and l*i current is injected from the inverter circuit into the connection point between the phase advance capacitor and the series resonance circuit. Therefore, the phase advance capacitor and the series resonant circuit act as an injection circuit for blocking the application of the fundamental wave voltage component of the power system to the inverter circuit.

Note that the compensation harmonic current output from the inverter circuit is divided into the phase advance capacitor side and the series resonant circuit side, so the transfer function calculation of the injection circuit is performed together in the inverter command value calculation circuit. . Furthermore, since there is no series resonant circuit for the phase-advanced reactive current flowing from the power system through the phase-advanced capacitor, there is no adverse effect on reactive current compensation.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 and 2. As shown in FIGS. 1 and 2, this reactive power compensator has a load 2 supplied with power from the power system connected in parallel with a slow phase circuit 3, and a phase advance capacitor 4 connected in parallel with the slow phase circuit 3. are doing.

Further, a series resonant circuit 5 is inserted between the neutral point side terminal of the phase advancing capacitor 4 and the power system neutral point X. In this case, the delay circuit 3 includes the reactor 3A and the thyristors 3B and 3.
It consists of a series circuit with an anti-parallel circuit of C. The series resonance port 15 is made up of a series circuit of a reactor 5A and a capacitor 5B, and the resonance frequency is set to the power system fundamental frequency (5
0Hz or 60Hz). Further, the phase advancing capacitor 4 and the series resonant circuit 5 constitute an injection circuit 12 for harmonic compensation.

A reactive current/harmonic current detection circuit 6, a firing angle calculation circuit 7, an inverter circuit B8, a harmonic calculation circuit 9, an adder IO, and an inverter command value calculation circuit 11 are provided.

The above-mentioned reactive current/harmonic current detection circuit 6 includes a current transformer 14
The reactive current component and the harmonic [wave component] in the load current fL flowing from the power system 1 to the load 2 via the transformer 15 are detected. In addition, the firing angle calculation circuit 7 converts the compensating reactive current that cancels the reactive first current component in the load current IL detected by the reactive current/harmonic current detection circuit 6 into a composite current of the phase delay circuit 3 and the phase advance capacitor 4. The firing angles of the thyristors 3B and 3C are calculated to cause the current to flow, and the thyristors 38.3C-t- are made conductive at the calculated firing angles.

Further, the inverter circuit 18 injects a compensation harmonic current into the power system 1 from the connection point between the phase advance capacitor 4 and the series resonant circuit 5 in the injection circuit 12 through the reactor 13 .

The harmonic calculation circuit 9 calculates wave components of harmonics included in the xi of the phase delay circuit 3 and having different contents depending on the firing angles of the thyristors 3B and 3C. The adder 10 calculates the harmonic current component in the load current IL detected by the reactive current/harmonic current detection circuit 6 and the 'r! of the slow phase circuit 3 calculated by the harmonic calculation circuit 9. The harmonic current components in the L current are added. The inverter command value calculation circuit 11 calculates a command value that determines the on/off timing of the switching elements of the inverter circuit 8 according to the output of the adder 10, and operates the switching elements of the inverter circuit 8 according to the calculation result of the command value. By controlling the on/off illumination, harmonic current components in the load current IL and harmonics T4 in the current of the phase delay circuit 3 are reduced. The color of the current component is canceled by the compensation harmonic current injected from the inverter circuit 8 into the power system I.

Next, the operation of this reactive power compensator will be explained. In this reactive power compensator, the reactive current/harmonic current detection circuit 6 detects a load tlJ flowing from the power system l to the load 2.
The zero firing angle calculation circuit 7, which detects the reactive current component and harmonic current component in LIL, cancels out the reactive current component in the load current LL. The firing angles of the thyristors 3B and 3C are calculated to cause the i-ineffective tl current to flow as a composite current of the phase delay circuit 3 and the phase advance capacitor 4, and the thyristors 3B and 3G are made conductive at the calculated firing angles.

As a result, the reactive current component in the load current
The power system V
Outflow to ci is suppressed.

On the other hand, the harmonic 1i current component in the load current IL and the harmonic current component in the current of the slow phase circuit 3 are suppressed from flowing into the power system 1 by the active filter function described below.

The harmonic current component contained in the current of the slow phase circuit 3 differs in content depending on the firing angle of the thyristors 3B and 3C.
The harmonic current component is calculated by the harmonic calculation circuit 9, and the adder 10 calculates the harmonic current component and the harmonic current component of the load current detected by the reactive current/harmonic current detection circuit 6. will be added. Then, in the inverter command value calculation circuit II, a command value that determines the on/off timing of the switching elements of the inverter circuit 8 is calculated in accordance with the output of the adder 10, and a command value that determines the on/off timing of the switching elements of the inverter circuit 8 is calculated in accordance with the output of the adder 10. The switching element is controlled to be turned on or off. As a result, a harmonic current component in the load current IL and a harmonic current component in the current of the phase-lag circuit 3 are combined into a compensation harmonic current that is injected from the inverter circuit 8 into the power system 1 through the reactor l3 and the phase-advanced capacitor 4. will be canceled out.

At this time, a series resonant circuit 5 is inserted between the neutral point side terminal of the phase advance capacitor 4 and the power system neutral point Since the configuration is such that a compensating harmonic current is injected, the phase advance capacitor 4 and the series resonant circuit 5 act as an injection circuit 12 for blocking the application of the fundamental voltage component of the power system I to the inverter circuit 8. become.

Note that the compensation harmonic current output from the inverter circuit 8 is divided into the phase advance capacitor 4 side and the series resonant circuit 5 side, so the transfer function calculation of the injection circuit 12 is performed by the inverter command value calculation circuit 11. We are doing it together. Also, it is the same as if there is no series resonant circuit 5 for the phase advancing reactive current flowing from the power system 1 through the phase advancing capacitor 4.
There is no adverse effect on reactive current compensation.

Next, reactive current/harmonic current detection circuit 61 firing angle calculation circuit 7, harmonic calculation circuit 9. The configuration and operation of the adder 10 and the inverter command (a calculation circuit 11) will be explained in detail.

First, reactive current/harmonics 1121i! The L detection circuit 6 is
It is configured to detect reactive current components and harmonic t'/JL components in load current IL by performing fast Fourier transform,
By detecting the system voltage Vs of the power system 1 by the transformer 15 and the voltage detection circuit 21, and inputting this system voltage ■s to the phase locked circuit (PLL circuit) 22, the system voltage Vs is detected by the transformer 15 and the voltage detection circuit 21.
A reference clock is created by multiplying the frequency of .

On the other hand, the load current ■ is detected by the current transformer 14 and the load current detection circuit 23, and the load current ■ゎ is sampled by the sample-hold/A/D conversion circuit 24 using the above reference clock. D conversion and memory (RAM)
25. In this case, the sampling operation is performed for one cycle of the fundamental wave, for example, at 256 points or 512 points.
Data such as points and the like are stored in the memory 25 at regular intervals. The CPU and digital signal processor (DS)
The processing circuit 26 consisting of P) performs Fourier transform on the data stored in the memory 25 according to the fast Fourier transform program etc. stored in the memory (ROM) 27 to obtain the amplitude of the reactive current component and the amplitude of each harmonic current component. The amplitude of the reactive current component and the amplitude and phase of each harmonic current component are stored in memory (RAM)2.
Note that the timing controller 29 writes to B.
The timing of the sample-hold/A/D conversion circuit 824 and the memory 25 is controlled based on the reference clock obtained from the phase synchronization circuit 22 according to instructions from the processing circuit 26 .

Next, the firing angle calculation circuit 7 calculates the amplitude of the reactive current component in the load current IL and the firing angle of the thyristors 3B and 3C for supplying a complementary reactive current to cancel out the reactive current component. The memory 28 of the reactive current/harmonic 1i current detection circuit 6 has a built-in load reactive current-firing angle correspondence table showing the relationship between
The firing angles of the thyristors 3B and 3C corresponding to the amplitude of the reactive current component in the load 'WL flow IL read out from the fL load reactive current-firing angle correspondence table are read out from the phase synchronization circuit 2.
Based on the reference clock No. 2, a firing pulse is generated at the timing of the read firing angle. This ignition pulse is amplified by the thyristor ignition amplifier 30 and the thyristor 3B,
3C, and the thyristors 3B and 3C become conductive at the timing of the firing angle.

Next, the harmonic calculation circuit 9 calculates the difference between the amplitude of the reactive current component in the load current IL and the amplitude and phase of each harmonic current component generated when creating a reactive compensation current that cancels out this reactive current component. relationship, in other words, thyristor 3B, 3
Negative rfI reactive current-harmonic IT flow correspondence table showing the relationship between the firing angle of C and the amplitude and phase of each harmonic current component generated by the firing of thyristors 3B and 3G C firing angle-
It has a built-in harmonic current correspondence table), and loads each harmonic current component corresponding to the amplitude of the reactive current component in the load current IL read out from the memory 28 of the reactive current/harmonic current detection circuit 6. Read from the reactive current-harmonic current correspondence table.

The adder 10 calculates the amplitude and phase of each harmonic current component output from the harmonic calculation circuit 9 and the amplitude and phase of each harmonic current component read from the memory 28 of the reactive current/harmonic current detection circuit. Each harmonic current component is added vectorially based on the phase.

Inverter command 4i11 performance) E circuit 11 includes a processing circuit 31 consisting of a CPU and a DSP, a memory (ROM) 32 storing various programs, and a DC voltage detection circuit 3 that detects the voltage of a DC power supply 16 that supplies power to the inverter circuit 8.
It consists of 3. Then, the processing circuit 31 calculates the transfer function of the injection circuit 12, the reactor 13, etc. for each harmonic electric color component based on the amplitude and phase of each harmonic current component given from the adder 10. , outputs a square wave signal for turning on and off the switching elements of the inverter circuit 8 according to the calculation results. This square wave signal is amplified by the inverter driving amplifier 34 and applied to the switching element of the inverter circuit 8. Note that since the output voltage of the inverter circuit 8 varies depending on the level of the voltage of the DC power source 16, the processing circuit 31 also performs calculations to correct changes in the voltage of the DC power source 16.

As a result of the above, the compensation harmonic current injected from the inverter circuit 8 into the power system l through the reactor 13 and the injection circuit 12 is negative tyt? The harmonic current component in the XIL and the harmonic current component in the current of the slow phase circuit 3 are exactly canceled out, and the outflow of the harmonic current to the power system 1 is suppressed.

This reactive power compensator detects reactive current components and harmonic current components in a load current I with a reactive current/harmonic current detection circuit 6, and detects harmonics in the load current IL as wave components and a phase delay circuit 3. A compensating harmonic current is injected from the inverter circuit 8 into the power system 1 to cancel the harmonic current generated by controlling the firing angles of the thyristors 3B and 3C.
Power grid 1
Harmonics are automatically and optimally suppressed without having to know in advance the harmonic status of the load and the harmonic status of the load, making it easy to design for accurate harmonic suppression and easy to standardize. be.

Also, the injection circuit 12 for injection of the compensation harmonic TM, current
Since the phase advance capacitor 4 is also used as the phase advance capacitor 4, the number of parts can be reduced.

〔Effect of the invention〕

According to the reactive power compensator of the present invention, the reactive current/harmonic current detection circuit detects the reactive current component and the harmonic current component in the load current, and detects the harmonic current component in the load current and the lagging phase circuit. A compensation harmonic current is injected from the inverter DI into the power grid to cancel out the harmonic current generated by controlling the firing angle of the thyristor, thereby suppressing the outflow of harmonic current into the power grid. Harmonics are automatically and optimally suppressed without having to know in advance the harmonic status of the load and the harmonic status of the load, making it easy to design for accurate harmonic suppression and easy to standardize. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing a specific configuration of the main part of FIG. 1, and FIG. 3 is a block diagram showing the configuration of an example of a conventional reactive power compensator.

Claims (1)

[Claims] A slow phase circuit consisting of a series circuit of a reactor and a thyristor connected in parallel to a load supplied with power from the power system;
A phase advance capacitor connected in parallel to this phase delay circuit, and a series resonant circuit whose resonance frequency matches the power system fundamental wave frequency and which is inserted between the neutral point side terminal of the phase advance capacitor and the power system neutral point. a reactive current/harmonic current detection circuit that detects reactive current components and harmonic current components in a load current flowing from the power system to the load; and the load current detected by the reactive current/harmonic current detection circuit. A firing angle of the thyristor is calculated so that a compensating reactive current that cancels out the reactive current component in the thyristor flows as a composite current of the phase delay circuit and the phase advance capacitor, and the firing angle of the thyristor is made conductive at the calculated firing angle. an arithmetic circuit; an inverter circuit that injects a compensation harmonic current into the power system from a connection point between the phase advance capacitor and the series resonant circuit; and an inverter circuit included in the current of the phase lag circuit and corresponding to the firing angle of the thyristor. a harmonic calculation circuit that calculates harmonic current components with different contents; and a harmonic calculation circuit that calculates harmonic current components in the load current detected by the reactive current/harmonic current detection circuit and the harmonic current components that are calculated by the harmonic calculation circuit. an adder that adds the harmonic current components in the current of the slow phase circuit; and a command value that determines the on/off timing of the switching elements of the inverter circuit corresponding to the output of this adder; The harmonic current components in the load current and the harmonic current components in the current of the slow phase circuit are transferred from the inverter circuit to the power system by controlling the switching elements of the inverter circuit on and off according to the calculation result of A reactive power compensator including an inverter command value calculation circuit that cancels the injected compensation harmonic current.