JP2020096450A - Self-excitation reactive power compensation device - Google Patents

Abstract

To improve responsiveness of unbalanced voltage suppression control of a high-voltage distribution system by detecting negative sequence voltage at high speed.SOLUTION: When negative sequence voltage is detected using αβ conversion and reverse γδ conversion, a ripple component (second harmonic component) which is generated by conversion of positive sequence voltage is removed with an FIR type filter, and then harmonic is removed with an IIR type low pass filter, and a dc component (the negative sequence voltage is converted into the dc component) is extracted. Higher cut-off frequency of the IIR type low pass filter can be achieved by using the FIR type filter, and thus high-speed detection of the negative sequence voltage is enabled.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technique for suppressing unbalance of three-phase voltage in a distribution system by using a self-excited reactive power compensator.

A reactive power compensator that compensates reactive power using a self-excited converter is called a self-excited SVC, SVG, or STATCOM. The self-excited converter is composed of a semiconductor device such as an IGBT, and can rapidly suppress a rapid voltage fluctuation in the distribution system by high-speed reactive power output control.

The SVG described in Patent Document 1 below has a function of suppressing the three-phase unbalanced voltage of the power distribution system by itself, thereby installing a three-phase unbalanced power output converter in addition to the SVG which is a voltage adjusting device. It has the effect of eliminating the need and reducing equipment costs.

As a method of suppressing the three-phase unbalanced voltage, a reverse-phase component is calculated and detected from the system voltage, and an output capable of canceling the reverse-phase voltage is calculated. Then, it is realized by outputting the calculated amount of electric power to the distribution system.

Patent No. 3830095

However, in the above-mentioned Patent Document 1, as a calculation method of the above-mentioned reverse-phase voltage, only the calculation of the reverse-phase voltage from the voltage of each phase detected by the current/voltage sensor is described, and a specific calculation method is described. Not listed.

Therefore, in the present invention, while presenting a specific method for calculating the reverse-phase voltage, by detecting the reverse-phase voltage at high speed, the responsiveness of the three-phase unbalanced voltage suppression control of the distribution system, and In this paper, we present a self-excited reactive power compensator that can realize unbalanced voltage suppression control that is robust against system frequency fluctuations.

The invention according to claim 1 is a self-excited reactive power compensator for suppressing a voltage imbalance of a system by detecting a reverse phase component of a system voltage and outputting a reactive power for reducing the negative phase component to 0 to the system. In the device, the positive phase voltage that appears as a ripple component when the system voltage is αβ-converted and the reverse γδ-converted to detect the negative-phase voltage is removed by the FIR type filter, and the harmonics contained in the system voltage are removed by IIR. It is characterized in that the negative-phase voltage can be detected at high speed by removing the negative-phase voltage by a low-pass filter of the type.

According to a second aspect of the present invention, in the reactive power compensator according to the first aspect, the frequency of the system voltage is detected, the sampling frequency is synchronously varied with the frequency of the system voltage, and the system voltage is sampled. It is characterized by enabling unbalanced voltage suppression control that is robust against frequency fluctuations.

According to the first aspect of the present invention, the reverse phase voltage can be detected at high speed, and as a result, the reactive power that sets the reverse phase voltage to 0 is output to the grid to quickly eliminate the voltage imbalance of the three-phase distribution line. It becomes possible to do.

According to the second aspect of the present invention, it is possible to detect the reverse phase voltage that is robust against the fluctuation of the system frequency.

FIG. 3 is a control block diagram of a self-excited reactive power compensator according to the present invention. FIG. 6 is a control block diagram of a self-excited var compensator according to another embodiment of the present invention. It is a control block diagram in the case of adding the three-phase distribution line voltage imbalance suppression control function robust with respect to system frequency fluctuation to the self-excited var compensator according to the present invention.

An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a control block diagram of a self-excited reactive power compensator A according to the present invention.

Since the implementation of the FIT system, a large number of household solar power generation facilities have been connected to the distribution system. Since household solar power generation facilities are single-phase, when a large number of such distributed power sources are connected to each other, there is a concern that three-phase voltage imbalance may increase due to voltage rise due to reverse power flow.

In the reactive power compensator A shown in FIG. 1, the system voltage detection unit 1 detects the three-phase voltage (vofu, vofv, vofw) of the distribution system via the voltage detection transformer VT, and outputs it to the αβ conversion unit 2. ..

The αβ conversion unit 2 performs coordinate conversion of the input three-phase voltage (vofu, vofv, vofw) into a two-phase voltage (α-phase voltage vofa, β-phase voltage vofb) equivalent to the three-phase voltage, and converts it into the γδ conversion unit 3. Output to the inverse γδ conversion unit 4.

In the γδ conversion unit 3, the two-phase voltage (α-phase voltage vofa, β-phase voltage vofb) is γδ-converted to convert the positive-phase voltage into a DC component and the negative-phase voltage into a double harmonic component of the system frequency. Convert and output.

The γ-phase voltage vofg and the δ-phase voltage vofd output from the γδ converter 3 are input to the FIR filters 5 and 6, respectively. This FIR type filter is a finite impulse response type filter, and its feature is that it outputs the DC component as it is and makes the second harmonic component zero.

Therefore, the FIR filters 5 and 6 output the positive phase voltage, which is the DC component of the input γ-phase voltage vofg and the δ-phase voltage vofd, as they are, and zero the negative-phase voltage that is the second harmonic component.

The outputs of both FIR type filters 5 and 6 are input to IIR type low pass filters 7 and 8, respectively. The IIR low-pass filter is an infinite impulse response type filter and can remove harmonics of the system voltage.

Therefore, by passing the output of the FIR type filter 5 through the IIR type low-pass filter 7, it is possible to output the γ-phase component vofpg of the positive phase voltage obtained by removing harmonics from the positive phase voltage. By passing the output through the IIR type low-pass filter 8, it is possible to output the δ-phase component vofpd of the positive phase voltage obtained by removing harmonics from the positive phase voltage.

On the other hand, in the α-phase voltage vofa and the β-phase voltage vofb input to the reverse γδ conversion unit 4, the conversion unit 4 converts the negative-phase voltage into a DC component, and the positive-phase voltage is a double harmonic component of the system frequency. Is converted to.

The γ-phase voltage vofig and the δ-phase voltage vofid output by the inverse γδ converter 4 are input to the FIR filters 9 and 10, respectively, and the reverse-phase voltage is directly output by the filters 9 and 10, and the positive-phase voltage is It becomes zero.

By inputting this output to the IIR type low-pass filters 11 and 12, harmonic components are removed from the γ-phase voltage vofig and the δ-phase voltage vofid, and the γ-phase component vofng and the δ-phase component vofnd of the anti-phase voltage are output. be able to.

The γ-phase component vofpg and the δ-phase component vofpd of the positive phase voltage are input to the positive phase voltage calculation unit 13, and the current positive phase voltage value of the distribution system is calculated by the positive phase voltage calculation unit 13. The output of the positive phase voltage calculation unit 13 is one input of the addition point 14, and the addition point 14 calculates the difference from the positive phase voltage target value which is the other input, and the positive phase voltage control system compensator 15 Output to.

The positive phase voltage control system compensator 15 generates the output current command value iorpd so that the current positive phase voltage value matches the target value, and outputs it to the decoupling unit 16. The output iorpg of the direct current (capacitor) voltage control unit 17 is input to the decoupling unit 16 as the other input.

The output iorpg is output for the purpose of keeping the voltage of a DC-side capacitor (not shown) forming the reactive power compensator A constant. In other words, due to the loss of the reactive power compensator A shown in FIG. 1, the capacitor (not shown) supplies energy corresponding to the loss, and the capacitor voltage decreases.

Therefore, it is necessary to charge the capacitor with energy for the loss by taking in the active power from the grid to keep the capacitor voltage constant. The output iorpg of the direct current (capacitor) voltage control unit 17 is output for this purpose.

The decoupling unit 16 performs processing to prevent interference from occurring in the current output unit, which will be described later, due to the conversion performed by the inverse γδ conversion unit 18, and the output of the decoupling unit 16 is inverse γδ conversion. The inverse γδ conversion is performed in the unit 18, and the output is output to the addition point 19 as the α-phase positive phase compensation current command value iorpa and the β-phase positive phase compensation current command value iorpb.

On the other hand, the γ-phase component vofng of the negative phase voltage is input to one of the addition points 20, and 0 [V], which is the γ-phase target value of the negative phase voltage, is input to the other of the addition points 20. Similarly, the δ-phase component vofnd of the negative phase voltage is input to one of the addition points 21, and 0 [V], which is the δ-phase target value of the negative phase voltage, is input to the other of the addition points 21.

The addition point 20 calculates the difference between the γ-phase component vofng of the negative-phase voltage and the target value of the γ-phase of the negative-phase voltage, 0 [V], and outputs the difference to the negative-phase voltage γ-phase control system compensator 22. At the addition point 21, the difference between the δ-phase component vofnd of the negative phase voltage and 0 [V] which is the δ-phase target value of the negative phase voltage is calculated and output to the negative phase voltage δ phase control system compensator 23.

The anti-phase voltage γ-phase control system compensator 22 and the anti-phase voltage δ-phase control system compensator 23 output so that the γ-phase component and the δ-phase component of the current anti-phase voltage become 0 [V] which are the target values. The current command values iorng and iornd are generated and output to the decoupling unit 24.

The decoupling unit 24 performs processing for preventing interference from occurring in the current output unit, which will be described later, due to the conversion performed by the γδ conversion unit 25, and the output of the decoupling unit 24 is the γδ conversion unit 25. Is converted into γδ, and the output is output to the addition point 19 as the α-phase anti-phase compensation current command value iorna and the β-phase anti-phase compensation current command value iornb.

The addition point 19 is the α-phase positive-phase compensation current command value iorpa and the β-phase positive-phase compensation current command value iorpb, and the α-phase anti-phase compensation current command value iorna and the β-phase anti-phase compensation current command. The value iornb is added and output to the inverse αβ converter 26.

The inverse αβ conversion unit 26 inversely αβ-converts the input and outputs the output current command values ioru, iorv to the current output unit 27. The current output unit 27 includes an output current control and PWM control inverter, an LC filter, and a step-up transformer, and has three-phase (U-phase, V-phase, W-phase) currents according to the output current command values ioru and iorv. Outputs iou, iov, iow. That is, the reactive power (output currents iou, iov, iow) at which the positive phase voltage is the target value and the negative phase voltage is zero is output. By setting the reverse-phase voltage to zero, voltage imbalance in the high-voltage distribution system can be suppressed.

In the above-described first embodiment of the present invention, in obtaining the γ-phase component vofpg and the δ-phase component vofpd of the current positive phase voltage, by combining the FIR type filters 5 and 6 and the IIR type low pass filters 7 and 8, Considering that the negative phase voltage is converted into the second harmonic component when the positive phase voltage is detected by using the αβ conversion and the γδ conversion, the double harmonic component (the negative phase voltage ) Is removed, and the harmonics contained in the system voltage are removed in the IIR low-pass filters 7 and 8.

Further, in the first embodiment of the present invention, when the γ-phase component vofng and the δ-phase component vofnd of the current negative-phase voltage are obtained, by combining the FIR filters 9 and 10 and the IIR low-pass filters 11 and 12, αβ In consideration of the fact that the positive phase voltage is converted into the double harmonic component when the negative phase voltage is detected by using the conversion and the reverse γδ conversion, the double harmonic component (the positive phase voltage ), and the IIR low-pass filters 11 and 12 remove harmonics contained in the system voltage.

In this respect, it is conceivable that the FIR type filter and the IIR low-pass filter are not combined, but only the IIR type low-pass filter is used. However, normally, the negative phase voltage is as small as about 3% of the positive phase voltage. If the harmonic component (positive phase voltage) is to be removed only by the IIR low-pass filter, the filter is designed so that the allowable value of the removal level is 1/10 or less (0.3%) of the negative phase voltage. There is a need.

Therefore, when it is attempted to reduce the second harmonic component to 0.3%, the cutoff frequency is about 0.3 [Hz] when the system frequency is 50 [Hz] and the IIR first-order low-pass filter is used. As a result, the detection of the reverse phase voltage is delayed. As a result, there arises a problem that the response of the unbalance suppression control of the high voltage distribution system becomes slow.

Therefore, in the present invention, not only the IIR type low-pass filter but also the FIR type filter is used to increase the cut-off frequency of the IIR type low-pass filter (about 30 [Hz]) so that the anti-phase voltage can be detected at high speed. As a result, the response of the unbalance suppression control of the distribution system could be improved.

FIG. 2 is a control block diagram showing a self-excited reactive power compensator B according to a second embodiment of the present invention. When the three-phase voltage imbalance is eliminated in the reactive power compensator B and the system voltage is adjusted to the target value, the three-phase voltage of the distribution system is detected by the system voltage detection unit 31 via the voltage detection transformer VT. (Vofu, vofv, vofw) is detected and output to the αβ converter 32.

The αβ conversion unit 32 performs coordinate conversion of the input three-phase voltage (vofu, vofv, vofw) into a two-phase voltage (α-phase voltage vofa, β-phase voltage vofb) equivalent thereto, and the αβ conversion unit 33 and It outputs to the inverse γδ converter 34.

In the γδ converter 33, the two-phase voltage (α-phase voltage vofa, β-phase voltage vofb) is γδ-converted, thereby converting the positive-phase voltage into DC components of the γ-phase and the δ-phase, and the negative-phase voltage of each. It is converted into a double harmonic component and output as a γ-phase voltage vofg and a δ-phase voltage vofd.

The α-phase voltage vofa and the β-phase voltage vofb input to the reverse γδ conversion unit 34 are converted by the conversion unit 34 into the DC components of the γ-phase and the δ-phase, respectively, and the positive-phase voltage of each of the two components is It is converted into a harmonic component and output as a γ-phase voltage vofig and a δ-phase voltage vofid.

The γ-phase voltage vofg and the δ-phase voltage vofd output from the γδ conversion unit 33 are output to the positive-phase voltage calculation unit 35, and the calculation unit 35 calculates the current positive-phase voltage value of the distribution system. However, this calculated value contains a harmonic component including a reverse phase voltage. The output of the positive phase voltage calculation unit 35 is one input of the addition point 36, and the difference between the addition point 36 and the positive phase voltage target value which is the other input is calculated and output to the FIR type filter 37. It

In the FIR filter 37, the positive phase voltage of the input differential voltage is output as it is, and the negative phase voltage which is the second harmonic component becomes zero.

Further, the IIR type low-pass filter 38 in the latter stage removes harmonics from the positive phase voltage and outputs the positive phase voltage control system compensator 39.

The positive phase voltage control system compensator 39 generates the output current command value iorpd so that the current positive phase voltage value matches the target value, and outputs it to the decoupling unit 41. The output iorpg of the direct current (capacitor) voltage control unit 40 is input to the decoupling unit 41 as the other input.

The output iorpg is output for the purpose of keeping the voltage of a DC-side capacitor (not shown) forming the reactive power compensator B constant. That is, due to the loss of the reactive power compensator B shown in FIG. 2, the capacitor (not shown) supplies energy corresponding to the loss, and the capacitor voltage decreases.

Therefore, it is necessary to charge the capacitor with energy for the loss by taking in the active power from the grid to keep the capacitor voltage constant. The output iorpg of the direct current (capacitor) voltage controller 40 is output for this purpose.

The decoupling unit 41 prevents the current output unit, which will be described later, from causing interference due to the coordinate conversion performed by the inverse γδ conversion unit 42, and the output of the decoupling unit 41 is inverted by the inverse γδ conversion unit 42. γδ conversion is performed, and the output (iorpa, iorpb) is input to the addition point 43.

The γ-phase voltage vofig and the δ-phase voltage vofid output by the inverse γδ conversion unit 34 are output as one input of the addition points 44 and 45, respectively. To the other input of the addition points 44 and 45, 0 [V], which is the γ-phase target value and the δ-phase target value of the negative phase voltage, is input, and both addition points 44 and 45 show the difference between the inputs. The calculated value is output to the FIR filters 46 and 47.

In the FIR filters 46 and 47, the negative phase voltage of the differential voltage is output as it is, and the positive phase voltage that is the second harmonic component becomes zero.

The outputs of the FIR filters 46 and 47 are input to the IIR low-pass filters 48 and 49, respectively, and the low-pass filters 48 and 49 remove harmonic components.

The outputs of the low-pass filters 48 and 49 are input to the anti-phase voltage γ-phase control system compensator 50 and the anti-phase voltage δ-phase control system compensator 51, respectively, and the compensators 50 and 51 cause the γ-phase component of the current anti-phase voltage. And output current command values iorng and iornd are generated such that the δ-phase component becomes 0 [V], which is the target value, and they are output to the decoupling unit 52.

The decoupling unit 52 performs a process of preventing interference from occurring in the current output unit, which will be described later, due to the conversion process of the γδ conversion unit 53 in the subsequent stage. The output after the γδ conversion by the γδ conversion unit 53 becomes the other input of the addition point 43.

The addition point 43 is the input α phase positive phase compensation current command value iorpa and β phase positive phase compensation current command value iorpb and α phase anti-phase compensation current command value iorna and β phase anti-phase compensation current command. The value iornb is added and output to the inverse αβ converter 54.

The inverse αβ conversion unit 54 inversely αβ-converts the input and outputs the output current command values ioru, iorv to the current output unit 55. The current output unit 55 outputs currents iou, iov, iow of three phases (U phase, V phase, W phase) according to the output current command values ioru, iorv.

As a result, reactive power (output currents iou, iov, iow) with the positive-phase voltage as the target value and the negative-phase voltage as zero is output, and the voltage of the high-voltage distribution system is adjusted to the target value and Suppress equilibrium.

Also in the reactive power compensating apparatus B according to the second embodiment shown in FIG. 2, as in the reactive power compensating apparatus A shown in FIG. 1, a reverse phase voltage can be detected at high speed by combining the FIR type filter and the IIR type low pass filter. Therefore, the response of the unbalanced voltage suppression control of the distribution system can be improved.

FIG. 3 is a control block diagram in the case where a function for realizing unbalanced voltage suppression control that is robust against frequency fluctuation is added to the self-excited reactive power compensators A and B shown in FIGS. 1 and 2.

In FIG. 3, 60 is a system frequency detection unit (PLL), and 61 is an A/D conversion start signal generation unit. The A/D conversion start signal generation unit 61 gives the A/D converter a timing signal when three-phase simultaneous sampling is performed on the system voltage using the A/D converter.

In the configuration shown in FIG. 3, the system frequency detection unit 60 always detects the system frequency fo to detect the fluctuation of the system frequency fo, and outputs it to the A/D conversion start signal generation unit 61.

The A/D conversion start signal generation unit 61 variably controls the sampling frequency fs of the A/D converter so as to be N·fo, following the detected system frequency fo. For example, when the system voltage is sampled at 3° intervals, the sampling frequency fs is made to follow the system frequency fo, and the A/D conversion start signal is supplied to the system voltage at time intervals of 1/fs=1/(120·fo). Output to the detection units 1 and 31.

The frequency characteristic of the FIR filter changes due to the influence of system frequency fluctuations. As an example of the FIR filter for removing the second harmonic component, a filter whose input/output relationship is expressed by the following equation will be briefly described.
y(n)=(x(n)+x(n-m))/2
y(n): Filter output value at n time (current time) x(n): Filter input value at n time (current time) x(n-m): Filter input value at nm time (m time before current time) (This is 90 degrees ago
Set as the filter input value of. When sampling at 3° intervals, m=30
)

If the second harmonic expressed by the following equation is input to this filter,
x(n)=sin(2ωo·nTs+φ)
ωo=2πfo, Ts: sampling interval

The input value 90° (=π/2 [rad]) before is
x(n−m)=sin(2(ωo·nTs−π/2)+φ)
=-sin(2ωo·nTs+φ)
Becomes At this time, the output of the filter is
y(n)=0
And the second harmonic component is completely removed.

When the system frequency fo changes, if the sampling interval Ts is fixed, x(n−m) is not the input value 90° before, so x(n−m)≠−sin(2ωo·nTs+φ), and y( n) ≠ 0. That is, the second harmonic component remains without being completely removed.

However, if the sampling interval Ts is changed so as to follow the system frequency fo, x(n−m) becomes the input value 90° before, so the second harmonic component is removed even if the system frequency fo changes. It will be possible.

Although only the second harmonic component has been described above, the same applies to other frequency components, and the frequency characteristics of the FIR filter change due to the influence of system frequency fluctuations.

By varying the sampling frequency fs of the A/D converter in synchronization with the system frequency fo, the system voltage detection units 1 and 31 can accurately perform phase synchronization and sample the system voltage. As a result, the FIR type The frequency characteristics of the filters 5, 6, 9, 10, 37, 46, 47 are robust against system frequency fluctuations.

That is, even if the system frequency fluctuates, the gain characteristic of the FIR filter is not affected, and the gain for the second harmonic component can always be zero. Therefore, even if the system frequency fluctuates, it is possible to completely remove the second harmonic component after γδ conversion by the γδ conversion units 3 and 33 or after inverse γδ conversion by the inverse γδ conversion units 4 and 34.

As a result, the self-excited reactive power compensator shown in FIGS. 1 and 2 can reliably suppress the imbalance of the three-phase voltage even when the system frequency fo changes.

As described above, according to the self-excited reactive power compensator of the present invention, the reverse-phase voltage can be detected at high speed, so that the response of the unbalanced voltage suppression control of the high-voltage distribution system can be speeded up.

In addition, unbalanced voltage suppression control that is robust against fluctuations in the system frequency becomes possible.

INDUSTRIAL APPLICABILITY The present invention can be used for a reactive power compensator installed in a power distribution system.

1,31 System voltage detection unit 2,32 αβ conversion unit 3,33 γδ conversion unit 4,34 Inverse γδ conversion unit 5,6,9,10,37,46,47 FIR type filter 7,8,11,12, 38,48,49 IIR type low-pass filter 13,35 Positive phase voltage calculation unit 14,19,20,21,36,43,44,45 Addition point 15,39 Positive phase voltage control system compensator 16,24,41 , 52 Decoupling unit 17,40 Direct current (capacitor) voltage control unit 18,42 Reverse γδ conversion unit 22,50 Reverse phase voltage γ phase control system compensator 23,51 Reverse phase voltage δ phase control system compensator 25,53 γδ conversion unit 26,54 Inverse αβ conversion unit 27,55 Current output unit 60 System frequency detection unit (PLL)
61 A/D conversion start signal generator A, B Self-excited reactive power compensator

Claims (2)

When suppressing the voltage imbalance of the system by detecting the opposite phase component of the system voltage and outputting the reactive power that makes the opposite phase component 0 to the system, the system voltage is converted to αβ and reverse γδ. The positive phase voltage that appears as a ripple component when the negative phase voltage is detected is removed by the FIR type filter, and the harmonics contained in the system voltage are removed by the IIR type low pass filter, thereby reducing the negative phase voltage. A self-excited reactive power compensator characterized by being configured to detect at high speed. By detecting the frequency of the system voltage, changing the sampling frequency in synchronization with the frequency of the system voltage, and sampling the system voltage, it is possible to perform unbalanced voltage suppression control that is robust against frequency fluctuations. The self-excited reactive power compensator according to claim 1.

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