JP2005245117A - Power active filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active filter for automatically adjusting a control gain when a circuit constant of a distribution system changes and always compensating high frequency components included in system voltages by the accurate control gain. <P>SOLUTION: After the three-phase system voltages Vu, Vv, Vw detected by a system voltage detecting section 2 are converted into two-phase AC voltages Vd, Vq by a dq converting section 3, DC components are extracted and n-th order harmonic voltage components Vnd, Vnq included in the system voltages are found. n is an odd number of 3 or more. After three-phase high frequency compensating current Iau, Iav, Iaw detected by a compensating current detecting section 7 are converted into two-phase AC currents Id, Iq by a dq converting section 8, DC components are extracted and n-th order harmonic current components Ind, Inq included in the high frequency compensating currents are found. A control gain determining section 10 detects fluctuations of the n-th order harmonic current components, and determines the control gain K so as to maintain the fluctuations within a range without an influence on the system voltages. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an active filter for power connected to a distribution system in order to suppress harmonic distortion of system voltage.

  In the distribution system, a phenomenon may occur in which the harmonics generated from the harmonic generation source expand due to resonance caused by the phase advance capacitor and the distribution line impedance. When the harmonic expansion phenomenon occurs, an accident may occur in which the phase advance capacitor is overloaded and burned out due to the influence of the harmonic voltage.

As a power active filter installed in a distribution system in order to suppress harmonic distortion of a system voltage, a voltage detection type active filter as shown in Patent Document 1 is known. The voltage detection type active filter includes a system voltage detection unit that detects the system voltage of the distribution system, and an n-order (n is an odd number of 3 or more) harmonic component Vaf included in the system voltage detected by the system voltage detection unit. A harmonic voltage component detection unit for detecting the control gain, a control gain setting unit for setting the control gain K, and the control gain K set by the control gain setting unit as shown in the following equation (1): A compensation current output unit that outputs a harmonic compensation current Iaf obtained by multiplying the nth-order harmonic voltage component Vaf detected by the detection unit, and distributes the harmonic compensation current Iaf output by the compensation current output unit Injecting into the system suppresses harmonic distortion of the system voltage.
Iaf = K × Vaf (vector operation) (1)
This active filter operates as a 1 / K [Ω] resistor that acts only on the harmonic voltage.

  In order to quickly detect the harmonic component, the harmonic voltage component detection unit uses a rotating coordinate system that rotates the three-phase system voltage detection signal at the same angular velocity as the angular velocity of the harmonic component to be detected. A method of converting to a two-phase AC signal and detecting a harmonic component from the two-phase AC signal is employed. When a three-phase system voltage detection signal is converted into a rotating coordinate system signal that rotates at the same angular velocity as the harmonic component angular velocity, the harmonic component is stationary and detected as a DC component in the rotating coordinate system. The harmonic component can be obtained by performing an averaging process on the output of the coordinate conversion unit and extracting a direct current component.

  In this case, the harmonic voltage component detection unit converts the three-phase AC voltage detection signal obtained from the system voltage detection unit into the same angular velocity as the angular velocity of the nth harmonic component having two axes, d-axis and q-axis. The dq conversion unit converts the rotation coordinate system into a two-phase AC voltage signal rotating at nωt, and the low-pass filter extracts a DC component from the two-phase AC voltage signal obtained from the dq conversion unit. When the harmonic voltage component detection unit is constituted by a microprocessor, the filter calculates an average value of an average value of the two-phase AC voltage signal obtained from the dq conversion unit (DC component included in the two-phase AC voltage signal). Consists of. As the average value calculating means, a means for performing a moving average calculation over the period of one cycle of the fundamental component of the system voltage on the digital value of the two-phase AC voltage signal obtained from the dq converter is often used.

When the harmonic voltage component detection unit is configured as described above, the compensation current output unit multiplies the harmonic voltage component obtained from the DC component extraction unit by the control gain K to thereby obtain a two-phase harmonic compensation current. A multiplication means for generating a command, a dq reverse conversion unit that outputs a three-phase harmonic compensation current command by performing a reverse conversion to the conversion by the dq conversion unit on the two-phase harmonic compensation current command, an inverter, , An inverter that controls the inverter in response to the three-phase harmonic compensation current command so that the harmonic compensation current having the magnitude and phase commanded by the harmonic compensation current command output by the dq inverse conversion unit is output from the inverter. And a control unit.
JP 2002-320329 A

  From the superposition theorem, the system voltage Va at the installation point of the active filter AF is based on the voltage Va1 caused by factors other than the harmonic compensation current Iaf output by the active filter AF, the harmonic compensation current Iaf output by the active filter, and the active filter. This is the vector sum of the voltage Va2 determined by the system impedance as seen from FIG. Therefore, the harmonic voltage compensation control by the active filter has a control loop as shown in FIG.

  In an active filter, the harmonic compensation effect increases as the control gain K is increased within a range that does not exceed the limit gain (the maximum value of the control gain K that causes the active filter to operate stably and varies depending on the load condition of the distribution system). Becomes higher. However, if the control gain K is increased, the load situation of the distribution system does not change, and even if the limit gain does not change, the control delay caused by the detection delay of the harmonic voltage component Vaf, etc. The control system may become unstable, and the harmonic components may be amplified. In particular, if the control loop shown in FIG. 5 includes a mode in which the system voltage Va at the installation point increases due to the harmonic compensation current Iaf output from the active filter AF, the harmonic compensation current Iaf becomes infinite (actually the rated current). And the harmonic distortion of the system voltage increases.

  In addition, when the load status of the distribution system changes, the limit gain changes from moment to moment. Therefore, if the control gain K is increased, the control gain is likely to exceed the limit gain, and the control system becomes unstable. There is a risk of increasing harmonic components.

  As described above, if the control gain is too large and the control of the active filter becomes unstable, the harmonic component contained in the system voltage may be increased, which will adversely affect the system. It is not preferable.

  In the conventional active filter as shown in Patent Document 1, since the above problems are not taken into consideration, it is difficult to obtain a high harmonic suppression effect by increasing the control gain.

  Further, according to the prior art, in order to determine the optimum control gain for obtaining the maximum harmonic suppression effect within a range in which the control is not unstable, detailed prior examination or complicated Since it was necessary to conduct a field adjustment test, preparations for installing the active filter became troublesome, and there was a problem that the cost required for installation increased.

  It is an object of the present invention to provide a power active filter that can obtain a high harmonic compensation effect by increasing the control gain as much as possible within a range that does not adversely affect the power distribution system.

  Another object of the present invention is to provide a power active filter that can be installed in a power distribution system without performing complicated preparations for setting a control gain.

  The present invention relates to a system voltage detection unit that detects a system voltage of a distribution system, and a harmonic that detects an nth-order (n is an odd number of 3 or more) harmonic component included in the system voltage detected by the system voltage detection unit. Outputs harmonic compensation current obtained by multiplying the nth harmonic voltage component detected by the harmonic voltage component detector by the control gain set by the voltage component detector, control gain setting unit, and control gain setting unit. And a compensation current output section that injects a harmonic compensation current into the distribution system to suppress a harmonic distortion of the system voltage.

  In the present invention, the control gain setting unit detects a harmonic compensation current output from the compensation current output unit, and an nth order (n of harmonic compensation current detected by the compensation current detection unit. Is an odd number of 3 or more) A harmonic current component detector for detecting a harmonic current component and a range in which the fluctuation range of the n-th harmonic current component detected by the harmonic current component detector does not affect the system voltage. And a control gain determination unit that determines the control gain so as to maintain the control gain.

  In a preferred aspect of the present invention, the control gain determination unit is configured to increase the maximum value of the n-th harmonic current component included in the harmonic compensation current detected by the compensation current detection unit during one period of the fundamental component of the system voltage. The harmonic current component fluctuation range calculation means that calculates the difference between the minimum value and the minimum value as the fluctuation range of the harmonic current component, and the upper limit value in the range where the calculated fluctuation range of the harmonic current component does not affect the system voltage When the value is equal to or greater than the set first determination value, the control gain is decreased by a value obtained by multiplying the fluctuation range of the harmonic current component by the first constant, and the fluctuation range of the harmonic current component is the first determination value. Control gain calculation for calculating the control gain by increasing the control gain by the second constant multiplied by the fluctuation range of the harmonic current component when the value is equal to or smaller than the second determination value set to a smaller value than Part.

  In the above configuration, the control gain determining unit keeps the fluctuation range of the nth harmonic current component included in the harmonic compensation current output from the compensation current output unit within a range that does not affect the system voltage. However, the control gain determination unit determines the control gain so as to keep the fluctuation range of the nth harmonic voltage component detected by the harmonic voltage component detection unit within a range that does not affect the system voltage. It may be.

  In this case, the control gain determination unit determines the difference between the maximum value and the minimum value of the nth-order harmonic voltage component detected by the harmonic voltage component detection unit during one period of the fundamental component of the system voltage as the harmonic voltage. Harmonic voltage component fluctuation width calculating means for calculating the fluctuation width of the component, and a first determination value that is set to an upper limit value in a range in which the calculated fluctuation width of the harmonic voltage component does not affect the system voltage When the control gain is decreased by a value obtained by multiplying the fluctuation width of the harmonic voltage component by the first constant at a certain time, the fluctuation width of the harmonic voltage component is set to a value smaller than the first determination value. It is preferable that the control gain is configured by a control gain calculation unit that calculates the control gain by increasing the control gain by the second constant multiplied by the fluctuation range of the harmonic voltage component when the value is equal to or less than the determination value.

  The harmonic voltage component detection unit has a rotating coordinate system that rotates the three-phase AC voltage detected by the system voltage detection unit at the same angular velocity as the angular velocity of the n-th harmonic component having the d axis and the q axis. A first dq converter (3-phase / 2-phase converter) for converting into a two-phase AC voltage, and a fundamental component of the system voltage in the digital value of the two-phase AC voltage obtained from the first dq converter The second phase n-th harmonic component contained in each of the two-phase AC voltages is obtained by performing a moving average operation over a period of one cycle and extracting a DC component contained in each of the two-phase AC voltages. 1 DC component extraction unit. When the harmonic voltage component detection unit is configured as described above, the harmonic voltage component fluctuation range calculating means is configured to calculate the two-phase n-order harmonic voltage component obtained during one period of the fundamental wave component of the system voltage. The larger one of the differences between the maximum value and the minimum value is adopted as the fluctuation range of the harmonic voltage component.

  Further, the harmonic current component detection unit has a rotating coordinate system that rotates the three-phase alternating current detected by the system current detection unit at the same angular velocity as the angular velocity of the n-th harmonic component having the d axis and the q axis. A second dq conversion unit (3-phase / 2-phase conversion unit) that converts to a two-phase alternating current, and a digital value of the two-phase alternating current obtained from the second dq conversion unit, 1 of the fundamental component of the system voltage A second calculation is performed to obtain a two-phase n-order harmonic current component included in each of the two-phase AC currents by performing a moving average operation over a period of the period and extracting a DC component included in each of the two-phase AC currents. And a direct current component extraction unit. When the harmonic current component detection unit is configured in this way, the harmonic current component fluctuation range calculation means is configured to calculate the two-phase n-order harmonic current component obtained during one period of the fundamental wave component of the system voltage. The larger one of the differences between the maximum value and the minimum value is adopted as the fluctuation range of the harmonic current component.

  Further, the compensation current output unit multiplies the two-phase harmonic voltage component obtained by the DC component extraction unit by the control gain to obtain the two-phase harmonic compensation current, and the two-phase harmonic compensation current. By applying a conversion opposite to the conversion by the dq conversion unit, the three-phase harmonics giving the magnitude and phase of the three-phase harmonic compensation current injected into the distribution system in order to reduce the harmonic voltage component contained in the system current. The dq reverse conversion unit (2-phase / 3-phase conversion unit) that generates the harmonic compensation current command, the inverter, and the magnitude and phase commanded by the three-phase harmonic compensation current command generated by the dq reverse conversion unit An inverter control unit that controls the inverter in accordance with a three-phase harmonic compensation current command so as to output the three-phase harmonic compensation current from the inverter can be provided.

  Here, the “range that does not affect the system voltage” means a range in which the fluctuation range of the system voltage and the distortion rate of the waveform do not deviate from the standard. That is, when the fluctuation range of the n-order harmonic current component included in the harmonic compensation current or the fluctuation range of the n-order harmonic voltage component included in the system voltage is in the “range that does not affect the system voltage”, To prevent fluctuations in the system voltage from deviating from the standard and fluctuations in the system voltage waveform from deviating from the standard due to fluctuations in the harmonic compensation current injected into the system, “No range” shall be set.

  As described above, the control gain is determined so as to keep the fluctuation range of the n-order harmonic current component included in the harmonic compensation current or the n-order harmonic voltage component included in the system voltage within a range that does not affect the system voltage. Then, when the circuit constants of the power distribution system change, the control gain is automatically adjusted to a value that can keep the control stable. The maximum harmonic compensation effect can always be obtained by adjusting to.

  In addition, the above configuration facilitates the installation of the active filter because it is not necessary to carry out a detailed preliminary study for setting the control gain to an appropriate value according to the system conditions and a complicated field adjustment test. be able to.

  As described above, according to the present invention, the fluctuation range of the n-order harmonic current component included in the harmonic compensation current or the n-order harmonic voltage component included in the system voltage is maintained within a range that does not affect the system voltage. Thus, when the circuit constants of the distribution system change, the control gain is automatically adjusted to a value within a range where the control is stably performed, and the maximum harmonic compensation effect can always be obtained. .

  Further, according to the present invention, it is not necessary to carry out a detailed preliminary study for setting the control gain to an appropriate value according to the system condition and a complicated field adjustment test, so that the active filter can be easily installed. Can do.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
First Embodiment FIG. 1 shows an overall configuration of a first embodiment of the present invention. In FIG. 1, 1u to 1w are U, V, W3 phase distribution lines provided in a distribution system. Reference numeral 2 denotes a system voltage detection unit for detecting the voltage of the distribution lines 1u to 1w, and 3 denotes conversion of the three-phase system voltages Vu, Vv, Vw detected by the system voltage detection unit 2 into two-phase AC voltages Vd, Vq First dq converter (3-phase / 2-phase converter) 4 is a two-phase AC voltage by extracting DC components contained in two-phase AC voltages Vd and Vq obtained from the first dq converter, respectively. The first DC component extractor 5 and 6 are obtained from the first DC component extractor for obtaining two-phase nth-order (n is an odd number of 3 or more) harmonic voltage components Vnd and Vnq included in Vd and Vq, respectively. Two-phase harmonic compensation by multiplying the two-phase n-order harmonic voltage components Vnd and Vnq by the control gain K A multiplying means for calculating the flow Iad and IAQ.

  Reference numeral 7 denotes a compensation current detection unit for detecting harmonic compensation currents Iau, Iav, and Iaw output from a compensation current output unit described later. Reference numeral 8 denotes a three-phase harmonic compensation current Iau, detected by the compensation current detection unit 7. A second dq conversion unit 9 converts Iav and Iaw into two-phase AC currents Id and Iq, and 9 extracts DC components contained in the two-phase AC currents Id and Iq obtained from the second dq conversion unit, respectively. The second DC component extractor 10 for obtaining the d-axis component Ind and the q-axis component Inq of the n-order harmonic current contained in the two-phase AC currents Id and Iq, respectively, is obtained from the second DC component extractor. A control gain determination unit that determines a control gain K by performing arithmetic processing on the n-th harmonic current components Ind and Inq, a compensation current detection unit 7, a second dq conversion unit 8, and a second DC component extraction The control gain setting unit 11 includes the unit 9 and the control gain determination unit 10. It is configured.

  Further, 12 is a dq inverse conversion unit for converting the harmonic compensation current command values Iad and Iaq into three-phase harmonic compensation current command values Iau ′ to Iaw ′, 13 is an inverter control unit, 14 is an inverter, and multiplication means 5 6, the dq inverse conversion unit 12, the inverter control unit 13, and the inverter 14 that is controlled by the inverter control unit 13 and outputs a predetermined compensation current Iau-less Iaw constitutes a compensation current output unit 15.

  In the active filter shown in FIG. 1, the system voltage detection unit 2 and the compensation current detection unit 7 are configured by hardware including sensors that respectively detect voltage and current, and the inverter 14 is configured by a bridge circuit of semiconductor switch elements. Yes. The inverter control unit 13 includes an on / off command generating means for generating an on / off command for a switch element constituting the inverter 14 and a driver circuit for supplying a drive signal to the switch element constituting the inverter according to the on / off command. Yes.

  First dq conversion unit 3, first DC component extraction unit 4, multiplication means 5 and 6, second dq conversion unit 8, second DC component extraction unit 9, control gain determination unit 10, and dq inverse conversion unit 12 and the on / off command generation means of the inverter control unit 13 are configured by causing a microprocessor to execute a predetermined program.

  More specifically, the system voltage detector 2 is connected to the three-phase distribution lines 1u to 1w and outputs PT (instrument voltage) that outputs system voltage detection signals Vu, Vv and Vw proportional to the three-phase system voltage. A transformer) and an A / D converter that converts the output of the PT into a digital value. Digital values of the system voltage detection signals Vu, Vv, and Vw obtained from the system voltage detection unit 2 are given to the first dq conversion unit 3.

The first dq converter 3 has the three-phase AC voltages Vu, Vv, Vw detected by the system voltage detector 2 using the following conversion equation (Equation 1), and has a d-axis and a q-axis. Then, an arithmetic process is performed to convert the two-phase AC voltages Vd and Vq of the rotating coordinate system that rotates at the same angular velocity nωt as the angular velocity of the n-th harmonic component. Since the two-phase AC voltage Vd, Vq of the rotating coordinate system that rotates at the same angular velocity nωt as the angular velocity of the n-order harmonic component includes the n-order harmonic component as a DC component, the two-phase AC voltage Vd, By extracting a direct current component from Vq, an nth-order harmonic component can be detected.

  The signal obtained from the first dq conversion unit 3 is given to the first DC component extraction unit 4. The first DC component extraction unit 4 is a low-pass filter (LPF) that extracts a DC component from the two-phase AC voltages Vd and Vq obtained from the dq conversion unit 3. The DC component extraction unit 4 of the present embodiment samples the digital value of the two-phase AC voltage obtained from the first dq conversion unit 3 at a constant sampling frequency (6 [kHz] in the present embodiment) It consists of an average value calculation means for performing a moving average calculation of sampling values over a period of one cycle of the fundamental wave component of the voltage (20 [msec] when the frequency of the system voltage is 50 [Hz]). By calculating an average value of the voltages Vd and Vq, a direct current component is extracted from both signals to obtain n-order harmonic voltage components Vnd and Vnq included in the system voltage. The nth-order harmonic voltage components Vnd and Vnq are given to the multipliers 5 and 6 together with the control gain K given from the control gain setting unit described later. In the present embodiment, the first dq conversion unit 3 and the first DC component extraction unit 4 constitute a harmonic voltage component detection unit.

  The compensation current detection unit 7 includes a CT (current transformer) that detects the output current of the compensation current output unit 15 and an A / D converter that converts the output of the CT into a digital value. The digital values of the compensation currents Iau, Iav and Iaw detected by the compensation current detection unit 7 are given to the second dq conversion unit 8. The second dq conversion unit 8 uses the conversion formula obtained by replacing the voltage of the conversion formula (Equation 1) with a current, and uses the three-phase harmonic compensation currents Iau, Iav, Iaw is converted into a two-phase alternating current Id, Iq of a rotating coordinate system having a d-axis and a q-axis and rotating at the same angular velocity nωt as the angular velocity of the n-order harmonic component.

  The output of the second dq conversion unit 8 is given to the second DC component extraction unit 9. The second direct current extraction unit 9 samples the digital value of the two-phase alternating current obtained from the second dq conversion unit 8 at a constant sampling frequency (6 [kHz] in this embodiment), and generates a harmonic. It consists of an average value calculation means for performing a moving average calculation of sampling values over one period of the fundamental component of the compensation current, and both AC currents are calculated by calculating the average value of the two-phase AC currents Id and Iq. The n-th harmonic current components Ind and Inq included in the signal are obtained. In the present embodiment, the second dq conversion unit 8 and the second DC component extraction unit 9 detect harmonics included in the harmonic compensation current detected by the compensation current detection unit 7 in the n-order harmonic component. A current component detection unit is configured.

  The harmonic current components Ind and Inq obtained from the second DC component extraction unit 9 are given to the control gain determination unit 10. As will be described later, the control gain determination unit 10 applies a predetermined calculation process to the harmonic current components Ind and Inq to influence the fluctuation range of the n-th harmonic component of the harmonic compensation current on the system voltage. The control gain K is determined so as to keep it in a non-existing range. The control gain K determined by the control gain determination unit 10 is given to the multiplication means 5 and 6.

The multiplying means 5 and 6 perform a vector operation of multiplying the harmonic voltage components Vnd and Vnq by the control gain K to obtain two-phase harmonic compensation currents Iad and Iaq, and supply these to the dq inverse conversion unit 12. The dq inverse conversion unit 12 converts the two-phase harmonic compensation currents Iad and Iaq into three-phase harmonics by performing the inverse conversion to the conversion performed by the dq conversion unit using the following arithmetic expression (Equation 2). The wave compensation current commands Iau ′, Iav ′ and Iaw ′ are converted.

  Three-phase harmonic compensation current commands Iau ′ to Iaw ′ obtained from the dq inverse conversion unit 12 are given to the inverter control unit 13. The inverter control unit 13 controls the inverter 14 so that the harmonic compensation currents Iau, Iav and Iaw having magnitudes and phases commanded by the three-phase harmonic compensation current commands Iau ′ to Iaw ′ are output from the inverter 14. To do. The three-phase harmonic compensation currents Iau to Iaw output from the inverter 14 are injected into the distribution lines 1u, 1v and 1w. This compensation current reduces the nth-order harmonic component included in the system voltage and improves the waveform distortion of the system voltage.

  In the present embodiment, the basic operation of the active filter is the same as that of the conventional one. However, in the present invention, the control gain determination unit 10 outputs the nth-order harmonic current component output from the harmonic compensation current output unit. The control gain is determined so as to keep the fluctuation range in the range that does not affect the system voltage. In the present embodiment, the control gain determination unit 10 calculates the difference ΔInd between the maximum value and the minimum value of the d-axis component Ind of the n-order harmonic current component detected during one period of the fundamental wave component of the system voltage. Harmonic current fluctuation width calculating means for calculating the fluctuation width ΔI of the n-th harmonic current component, and the calculated fluctuation width ΔI of the n-order harmonic current is set to an upper limit value that does not affect the system voltage. When the value is equal to or greater than the first determination value, the control gain is decreased by the amount obtained by multiplying the fluctuation width of the n-order harmonic current component by the first constant, and the fluctuation width ΔI of the n-order harmonic current component is The control gain is increased by increasing the control gain by an amount obtained by multiplying the fluctuation range ΔI of the nth-order harmonic current component by the second constant when the value is equal to or smaller than the second determination value set to a value smaller than the determination value. And a control gain calculating section for calculating. The second determination value is preferably set to a lower limit value that can be taken within a range in which the fluctuation range of the n-th harmonic current component included in the harmonic compensation current does not affect the system voltage.

  A flowchart showing an algorithm of a program executed by the microprocessor to constitute the control gain determining unit is shown in FIG. In the example shown in FIG. 2, the case where the fifth harmonic component is compensated is taken as an example. The microprocessor executes the routine of FIG. 2 at a constant control cycle. In the present embodiment, the routine of FIG. 2 is executed at the same cycle as the sampling cycle when the first DC component extraction unit 4 samples the output of the first dq conversion unit 3.

  In the case of the algorithm shown in FIG. 2, first, in step 1, the two-phase fifth harmonic current components I5d and I5q obtained from the second DC component extractor 9 are read. Next, in step 2, the maximum value (I5dmax, I5qmax) and the minimum value (I5dmin, I5qmin) of the d-axis component I5d and the q-axis component I5q of the two-phase fifth harmonic current are determined, and the newly determined maximum Replace the value and minimum value with the already determined maximum and minimum values (update the maximum and minimum values).

  Next, at step 3, it is determined whether or not one period (20 ms) of the system voltage (50 Hz in this example) has elapsed. As a result, when the period of one cycle has elapsed, the routine proceeds to step 4 where the absolute value of the difference I5dmax-I5dmin between the maximum value and the minimum value of the d-axis component of the fifth harmonic current is calculated. Fluctuation ΔId of the d-axis component of the second harmonic current is calculated, and the absolute value of the difference I5qmax−I5qmin between the maximum value and the minimum value of the q-axis component of the fifth harmonic current is calculated, and the fifth harmonic is calculated. The fluctuation range ΔIq of the q-axis component of the wave current is calculated. Thereafter, in step 5, the larger one of the fluctuation width ΔId of the d-axis component and the fluctuation width ΔIq of the q-axis component of the fifth harmonic current is adopted as the fluctuation width ΔI of the harmonic current component. After obtaining the fluctuation range ΔI of the harmonic current component in this way, the first determination value in which the fluctuation range ΔI of the harmonic current component is set to the upper limit value that does not affect the system voltage in step 6. If it is determined whether or not the fluctuation range ΔI of the harmonic current component is equal to or larger than the first determination value, the process proceeds to step 7 to change the control gain K to the fluctuation range of the fifth harmonic current component. Is reduced by a value ΔI × G1 multiplied by the first constant G1. For example, the first determination value is set to 1.0% of the rated value of the fifth harmonic compensation current of the active filter.

  When it is determined in step 6 that the fluctuation range ΔI of the fifth harmonic current component is smaller than the first determination value, the process proceeds to step 8 where the fluctuation width ΔI of the fifth harmonic current component is It is determined whether or not it is equal to or less than a second determination value set to a value smaller than the determination value of 1, and when the fluctuation range ΔI of the fifth harmonic current component is equal to or less than the second determination value, Proceeding to step 9, the control gain K is increased by a value ΔI × G2 obtained by multiplying the fluctuation width ΔI of the fifth harmonic current component by the second constant G2. Here, the second determination value is a lower limit value (a non-zero value) in a range that does not affect the system voltage, and is set to, for example, 0.3% of the rated value of the fifth harmonic compensation current of the active filter. The

  After decreasing or increasing the control gain in step 7 or step 9, the process proceeds to step 10 to clear the maximum value (I5dmax, I5qmax) and minimum value (I5dmin, I5qmin) of the fifth harmonic current component, After outputting a new control gain K in step 11, this routine is finished.

  If it is determined in step 3 that the period of one cycle of the system voltage has not elapsed, the process proceeds to step 11 to output the original control gain K, and then this routine is terminated.

  As described above, when the fluctuation range ΔI of the n-th harmonic current component included in the harmonic compensation current output from the compensation current output unit is equal to or larger than the upper limit value in the range that does not affect the system voltage, the control gain When the control gain setting unit is configured to decrease K and increase the control gain when the fluctuation range ΔI of the n-th harmonic current component falls below the lower limit of a range that does not affect the system voltage, When the circuit constant changes, the control gain is automatically adjusted to an appropriate value within the range in which the control is stably performed, and the maximum harmonic compensation effect can always be obtained.

  In addition, the above configuration facilitates the installation of the active filter because it is not necessary to carry out a detailed preliminary study for setting the control gain to an appropriate value according to the system conditions and a complicated field adjustment test. be able to.

  The first constant G1 and the second constant G2 are set to G1 = 5 and G2 = 0.1, for example. These constants are for adjusting the response of the control. When the first constant G1 is increased, when the fluctuation range ΔI of the harmonic current component exceeds the upper limit value, the fluctuation range ΔI is less than the upper limit value. Control to return to can be performed quickly. In addition, when the second constant G2 is increased, when the fluctuation range of the harmonic current component becomes smaller than the lower limit value, the control for returning the fluctuation range ΔI to the lower limit value or more can be quickly performed.

  It should be noted that there is a dead band between the first determination value and the second determination value, and when the fluctuation range ΔI of the nth harmonic current component is between the first determination value and the second determination value, the control gain No adjustment is made.

  In the case of the algorithm shown in FIG. 2, the difference between the maximum value and the minimum value of the nth-order harmonic current component detected during one cycle of the fundamental wave component of the system voltage is calculated by steps 2 to 5 as harmonics. Harmonic current component fluctuation width calculating means for calculating the fluctuation width of the current component is configured. In addition, when the calculated fluctuation range of the harmonic current component is greater than or equal to the first determination value set to the upper limit value in the range that does not affect the system voltage in steps 6 to 9, the fluctuation range of the harmonic current component When the control gain is decreased by the amount multiplied by the first constant, and the fluctuation width of the harmonic current component is equal to or smaller than the second determination value set to a value smaller than the first determination value, the harmonic current A control gain calculation unit is configured to calculate the control gain by increasing the control gain by an amount obtained by multiplying the fluctuation range of the component by the second constant.

Second Embodiment FIG. 3 shows the configuration of the second embodiment of the present invention. In FIG. 3, the dq conversion unit 3 and the DC component extraction unit 4 are the first dq conversion shown in FIG. This is the same as the unit 3 and the first DC component extracting unit 4, and the harmonic component component detecting unit is configured by the dq converting unit 3 and the DC component extracting unit 4.

  In the present embodiment, the control gain determination unit 10 determines the control gain so that the fluctuation range of the nth-order harmonic voltage components Vnd and Vnq detected by the harmonic voltage component detection unit is kept in a range that does not affect the system voltage. 'Is provided, and this control gain determination unit 10' constitutes a control gain setting unit 11 '. Other configurations are the same as those of the embodiment shown in FIG.

  In the embodiment shown in FIG. 3, the control gain determination unit 10 ′ includes the d-axis component Vnd of the nth-order harmonic voltage component detected by the harmonic voltage component detection unit during one period of the fundamental wave component of the system voltage. The difference ΔVnd between the maximum value and the minimum value and the maximum value and the minimum value of the q-axis component Vnd of the nth-order harmonic voltage component detected by the harmonic voltage component detector during one period of the fundamental wave component The difference ΔVnq is calculated, and the higher one of ΔVnd and ΔVnq is used as the fluctuation width ΔV of the harmonic voltage component, and the fluctuation width of the calculated harmonic voltage component is the system. When the value is equal to or higher than the first determination value set to the upper limit value of the range that does not affect the voltage, the control gain is reduced by the amount obtained by multiplying the fluctuation range of the harmonic voltage component by the first constant, and the harmonic voltage The fluctuation range of the component is set to a value smaller than the first judgment value. And a control gain calculating unit that calculates the control gain by increasing the control gain by the second constant multiplied by the fluctuation range of the harmonic voltage component when the value is equal to or less than the second determination value. . The second determination value is preferably set to a lower limit value that can be taken within a range in which the fluctuation range of the n-th harmonic current component included in the system voltage does not affect the system voltage.

  FIG. 4 is a flowchart showing an algorithm of a program executed by the microprocessor at a predetermined control period in order to configure the control gain determination unit 10 ′. In the case of the algorithm shown in FIG. 4, first, in step 1, the two-phase fifth harmonic voltage components V5d and V5q obtained from the second DC component extractor 9 are read. Next, in step 2, the maximum values (V5dmax, V5qmax) and minimum values (V5dmin, V5qmin) of the d-axis component V5d and q-axis component V5q of the fifth harmonic voltage are obtained, and the newly obtained maximum values and minimum values are obtained. Replace the values with the already determined maximum and minimum values (update the maximum and minimum values).

  Next, at step 3, it is determined whether or not one period (20 ms) of the system voltage (50 Hz in this example) has elapsed. As a result, when the period of one cycle has elapsed, the routine proceeds to step 4 where the absolute value of the difference V5dmax−V5dmin between the maximum value and the minimum value of the d-axis component of the fifth harmonic voltage is calculated. Fluctuation ΔVd of the d-axis component of the second harmonic voltage is calculated, the absolute value of the difference V5qmax−V5qmin between the maximum value and the minimum value of the q-axis component of the fifth harmonic voltage is calculated, and the fifth harmonic is calculated. The fluctuation range ΔVq of the q-axis component of the wave voltage is calculated. Thereafter, in step 5, the larger one of the fluctuation width ΔVd of the d-axis component and the fluctuation width ΔVq of the q-axis component of the fifth harmonic voltage is adopted as the fluctuation width ΔV of the harmonic voltage component. After obtaining the fluctuation range ΔV of the harmonic voltage component in this way, in step 6, the first determination value in which the fluctuation range ΔV of the harmonic voltage component is set to the upper limit value that does not affect the system voltage. If it is determined whether or not the fluctuation width ΔV of the harmonic voltage component is equal to or larger than the first determination value, the process proceeds to step 7 to change the control gain K to the fluctuation width of the fifth harmonic voltage component. Is reduced by a value ΔV × G1 multiplied by the first constant G1. For example, the first determination value is set to 0.1% of the rated value of the fifth harmonic compensation current of the active filter.

  If it is determined in step 6 that the variation width ΔV of the fifth harmonic voltage component is smaller than the first determination value, the process proceeds to step 8 where the variation width ΔV of the fifth harmonic voltage component is It is determined whether or not it is equal to or less than a second determination value set to a value smaller than the determination value of 1, and when the fluctuation range ΔV of the fifth harmonic voltage component is equal to or less than the second determination value, Proceeding to step 9, the control gain K is increased by a value ΔV × G2 obtained by multiplying the fluctuation width ΔV of the fifth harmonic voltage component by the second constant G2. The second determination value is a lower limit value (a non-zero value) in a range that does not affect the system voltage, and is set to 0.03% of the rated value of the fifth harmonic compensation voltage of the active filter, for example.

  After decreasing or increasing the control gain in step 7 or step 9, the process proceeds to step 10 to clear the maximum value (V5dmax, V5qmax) and minimum value (V5dmin, V5qmin) of the fifth harmonic voltage component, After outputting a new control gain K in step 11, this routine is finished.

  If it is determined in step 3 that the period of one cycle of the system voltage has not elapsed, the process proceeds to step 11 to output the original control gain K, and then this routine is terminated.

  As described above, when the fluctuation width ΔV of the nth-order harmonic voltage component included in the system voltage becomes equal to or larger than the upper limit value in the range that does not affect the system voltage, the control gain K is decreased, and the harmonic voltage component Even when the control gain setting unit is configured to increase the control gain when the fluctuation range ΔV is less than or equal to the lower limit value of the range that does not affect the system voltage, when the circuit constant of the distribution system changes, By automatically adjusting the control gain to an appropriate value within the range where the control is stably performed, the maximum harmonic compensation effect can always be obtained. In addition, since it is not necessary to perform detailed preliminary examination for setting the control gain to an appropriate value in accordance with the system condition and a complicated field adjustment test, it is possible to easily install the active filter.

  In the embodiment shown in FIG. 3, the first constant G1 and the second constant G2 are constants for adjusting the control response, and are set to G1 = 1 and G2 = 0.02, for example.

  In the case of the algorithm shown in FIG. 4, the difference between the maximum value and the minimum value of the nth-order harmonic voltage component detected during one period of the fundamental wave component of the system voltage is calculated by steps 2 to 5 as harmonics. Harmonic voltage component fluctuation width calculating means for calculating the fluctuation width of the voltage component is configured. In addition, when the calculated fluctuation width of the harmonic voltage component is greater than or equal to the first determination value set to the upper limit value in the range that does not affect the system voltage in Steps 6 to 9, the fluctuation width of the harmonic voltage component When the control gain is reduced by the amount multiplied by the first constant, and the fluctuation width of the harmonic voltage component is equal to or smaller than the second determination value set to a value smaller than the first determination value, the harmonic voltage A control gain calculation unit is configured to calculate the control gain by increasing the control gain by an amount obtained by multiplying the fluctuation range of the component by the second constant.

  Since the system voltage detected by the system voltage detection unit 2 includes harmonics and fundamental waves, when the system voltage is configured as shown in FIG. When A / D conversion is performed on Vu, Vv, and Vw, an error tends to occur in the digital value of the nth-order harmonic component. On the other hand, in the case of the configuration shown in FIG. 1, the compensation current detection unit 7 detects only the n-th harmonic current component, so that when the output of the detection unit is A / D converted, n Errors that occur in the digital value of the second harmonic component can be reduced.

  In the above embodiment, the fifth-order harmonic component is compensated. However, the present invention is generally applied to the case where the n-order (n is an odd number of 3 or more) harmonic component included in the system voltage of the distribution system is compensated. can do.

It is the block diagram which showed the structure of the 1st Embodiment of this invention. It is the flowchart which showed an example of the algorithm of the program which makes a microprocessor perform in order to comprise the control gain determination part used in embodiment of FIG. It is the block diagram which showed the structure of the 2nd Embodiment of this invention. It is the flowchart which showed an example of the algorithm of the program which makes a microprocessor perform in order to comprise the control gain determination part used by embodiment of FIG. It is a block diagram for demonstrating the structure of the control system of an active filter.

Explanation of symbols

1u to 1w Distribution line 2 System voltage detection unit 3 First dq conversion unit 4 First DC component extraction unit 5 Multiply unit 6 Multiply unit 7 Compensation current detection unit 8 Second dq conversion unit 9 Second DC component extraction Unit 10 Control gain determination unit 11 Control gain setting unit 12 dq inverse conversion unit 13 Inverter control unit 14 Inverter 15 Compensation current output unit

Claims (4)

A system voltage detection unit that detects a system voltage of the distribution system, and a harmonic voltage component that detects an n-order (n is an odd number of 3 or more) harmonic voltage component included in the system voltage detected by the system voltage detection unit Outputs the harmonic compensation current obtained by multiplying the control gain set by the detection unit, the control gain setting unit, and the control gain setting unit by the nth harmonic voltage component detected by the harmonic voltage component detection unit A power active filter that suppresses harmonic distortion of the system voltage by injecting the harmonic compensation current into the distribution system.
The control gain setting unit includes a compensation current detection unit that detects a harmonic compensation current output from the compensation current output unit, and an n-order harmonic current component of the harmonic compensation current detected by the compensation current detection unit. The control gain is determined so that the harmonic current component detection unit to be detected and the fluctuation range of the n-th harmonic current component detected by the harmonic current component detection unit are kept within a range that does not affect the system voltage. A control gain determining unit;
Active filter for power.   The control gain determination unit is configured to calculate a maximum value and a minimum value of the n-th harmonic current component included in the harmonic compensation current detected by the compensation current detection unit during one period of the fundamental component of the system voltage. Harmonic current component fluctuation range calculating means for calculating the difference as a fluctuation range of the harmonic current component, and a first limit value set in a range in which the calculated fluctuation range of the harmonic current component does not affect the system voltage. The control gain is decreased by an amount obtained by multiplying the fluctuation range of the harmonic current component by a first constant when the determination value is equal to or greater than 1, so that the fluctuation range of the harmonic current component is greater than the first determination value. Control for calculating the control gain by increasing the control gain by a value obtained by multiplying the fluctuation range of the harmonic current component by a second constant when the value is equal to or less than the second determination value set to a small value. And gain calculation unit And power active filter according to claim 1 and. A system voltage detection unit that detects a system voltage of the distribution system, and a harmonic voltage component that detects an n-order (n is an odd number of 3 or more) harmonic voltage component included in the system voltage detected by the system voltage detection unit Outputs the harmonic compensation current obtained by multiplying the control gain set by the detection unit, the control gain setting unit, and the control gain setting unit by the nth harmonic voltage component detected by the harmonic voltage component detection unit A power active filter that suppresses harmonic distortion of the system voltage by injecting the harmonic compensation current into the distribution system.
The control gain setting unit determines the control gain so as to keep the fluctuation range of the nth harmonic voltage component detected by the harmonic voltage component detection unit within a range that does not affect the system voltage. Having a part,
Active filter for power. The control gain determination unit calculates a difference between a maximum value and a minimum value of the nth-order harmonic voltage component detected by the harmonic voltage component detection unit during one period of the fundamental wave component of the system voltage. Harmonic voltage component fluctuation width calculating means for calculating the fluctuation width of the component, and a first determination value set to an upper limit value in a range in which the calculated fluctuation width of the harmonic voltage component does not affect the system voltage When the above is satisfied, the control gain is decreased by the amount of fluctuation of the harmonic voltage component multiplied by the first constant, and the fluctuation width of the harmonic voltage component is smaller than the first determination value. A control gain calculation unit that calculates the control gain by increasing the control gain by a value obtained by multiplying the fluctuation range of the harmonic voltage component by a second constant when the value is equal to or less than a set second determination value; Claims consisting of Power for the active filter according to.

Images