JP2006223023A - Active filter for power - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the switching loss at control of voltage variation by switching the switching frequency. <P>SOLUTION: This active filter has a compensating command signal generating means 50B which generates a harmonic compensating current command for compensating harmonic components contained in set point voltage and an reactive current command for compensating the voltage variation of set point voltage, and a pulse width modulating means 50C which converts the compensating command signal into voltage and also modulates the pulse width. The pulse width modulating means is provided with a carrier signal switching means 80 to a carrier signal for a pulse width modulation signal, and in harmonic control mode, a carrier signal Sc high in frequency is used, while in voltage variation control mode, a carrier signal Sc<SB>2</SB>low in frequency is used. The switching loss in the voltage variation control mode is mitigated by lowering the frequency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an active filter for electric power. Specifically, when the harmonic compensation current command value generation system provided to compensate for harmonics generated in the distribution system is combined with the reactive current command value generation system provided to suppress voltage fluctuation of the supply voltage By switching the switching frequency (PWM modulation carrier frequency) for the switching means provided in the main circuit to suppress harmonics and voltage fluctuations generated in the distribution system, the entire active filter can be reduced in size and power The loss can be reduced.

  Many power devices such as high-voltage consumer load devices are connected to the power system, for example, the distribution system. When these power devices operate, waveform distortion (distortion due to harmonics) occurs in the system voltage. To do. In addition, harmonic components (particularly fifth-order and seventh-order odd-order harmonic components) superimposed on the power supply frequency included in the waveform distortion generated in the special high-order system that is a higher-order system of the distribution system are consumers in the distribution system. May increase due to the resonance phenomenon between the phase-advancing capacitor installed in and the leakage inductance of the distribution substation transformer.

  Since such harmonic distortion causes heating and burning of the power equipment, an active filter for power for the purpose of suppressing power supply harmonics is provided in the distribution system (for example, Patent Document 1).

  The power active filter disclosed in FIG. 1 and FIG. 2 of Patent Document 1 is an example of a parallel power active filter AF installed in parallel to a power distribution system (distribution line). The harmonic component of the installation point voltage v is extracted by the detection means connected to the installation point, and this is supplied to the control means to generate a compensation current command value proportional to the harmonic component. This compensation current command value is supplied to the harmonic removal means that functions as the main circuit of the active filter.

The harmonic elimination means is composed of a DC capacitor having a DC voltage v _dc , an inverter employing a PWM modulation method, and a three-phase reactor, and is PWM modulated with a control signal that is a compensation current command value, thereby being the same as the harmonic component A voltage (current) corresponding to a compensation current command value having a magnitude and a phase is generated, and the generated compensation current is injected into a distribution system (installation point). By injecting this compensation current, the current flowing through the distribution system becomes only the fundamental wave component, and harmonic distortion can be compensated.

  On the other hand, a reactive power compensator is known in order to stabilize the voltage in the distribution system. This reactive power compensator stabilizes the voltage of the power distribution system by adjusting the reactive power of the leading and lagging phases. In addition to voltage fluctuations due to the operation of load equipment, recently, distributed power sources such as solar power generation, wind power generation, and fuel cell power generation have also been linked to this power system. Sex is increasing more and more.

JP 2002-320329 A

  By the way, the basic circuit of the active filter for power described above is a voltage source power converter, and the reactive power compensator is also a voltage source power converter based on the basic configuration, both of which are connected in parallel to the power distribution system. Is done. Therefore, it can be considered that this power active filter having a function of compensating harmonics is also configured as a power active filter having a reactive power compensation function.

  However, when considering a configuration in which a power active filter is shared as a reactive power compensator, the following problems are caused.

(1) Since harmonic countermeasures deal with reactive currents of harmonics, a high-speed response is required. Therefore, it is necessary to use a relatively high frequency as the carrier frequency (same as the switching frequency supplied to the switching means) used for PWM modulation (pulse width modulation). On the other hand, since the current value of the harmonic current is relatively small, a conversion capacity of about 50 kVA is sufficient as the reactive power compensator.

(2) On the other hand, when the voltage is stabilized, the controlled object is a reactive current of the power supply frequency (fundamental wave). However, since the current to be handled is a large current because it is a fundamental reactive current, about 300 kVA is required for the conversion capacity that must be prepared as an active filter for power.

(3) As a result, if the shared configuration is adopted, it must be configured as a device having a large current capacity and high-speed response characteristics. For this reason, the switching frequency is high particularly when the voltage is stabilized, so that the switching loss in the PWM modulation unit having the switching means increases, and the common device (the power conversion device which is an active filter for power) is increased in size and reduced. It also causes problems such as heat generation with efficiency.

  Therefore, the present invention solves such a conventional problem, and when a device for suppressing harmonics and a device for voltage stabilization are combined, generation of harmonics and voltage fluctuation are particularly remarkable. By switching the switching frequency for power conversion between harmonic suppression and voltage stabilization, the loss can be reduced and the device can be reduced in size and weight. The present invention proposes an active filter for electric power that can be achieved.

  In order to solve the above-mentioned problem, an active filter for power according to the present invention described in claim 1 includes a voltage detection means for detecting a voltage at a load installation point of a distribution system, and an installation point detected by the voltage detection means. A compensation command for generating and outputting a harmonic compensation current command value for compensating for a harmonic component contained in the installation point voltage and a reactive current command value for compensating voltage fluctuation of the installation point voltage from the voltage, respectively. Based on the signal generation output means, the pulse width modulation means for converting the voltage of the compensation command signal and performing pulse width modulation, and the harmonic compensation current command value and the reactive current command value generated by the compensation command signal generation output means. And control means for controlling fluctuations in the harmonic component of the distribution system and fundamental voltage, and the control means includes a pulse width modulation signal from the pulse width modulation means. Switching means is provided, and the pulse width modulation means is provided with carrier signal switching means used as a carrier signal of the pulse width modulation signal. In the harmonic suppression mode and the voltage fluctuation suppression mode, The carrier signal switching means is controlled so that carrier signals of different frequencies are supplied to the pulse width modulation means.

  In the present invention, attention is paid to the difference between the time zone in which the fluctuation of the power supply voltage is remarkable and the time zone in which the harmonics are generated. During times when multiple load devices and distributed power supplies do not operate (night time), voltage fluctuations in the distribution system are reduced, but resonance due to distribution line inductance and phase-advancing capacitors installed in high-voltage consumers Occurs and the harmonics are easily expanded (harmonic expansion phenomenon). Therefore, in this time zone, the mode is switched to the harmonic suppression mode.

  Since the current to be handled is a harmonic component (especially fifth-order and seventh-order harmonic components) of the power supply frequency, the current value is much smaller than the fundamental current. Therefore, the current capacity may be relatively small, and about 50 kVA is sufficient.

  In the harmonic suppression mode, the switching frequency in the switching means for switching the PWM modulation carrier frequency and the harmonic component is switched to a higher frequency. By doing so, high-speed response is possible, and harmonic distortion can be effectively and reliably suppressed. Moreover, even if the switching frequency is high, the controlled object is a harmonic, which is much lower than the current value of the fundamental wave. Therefore, the switching loss generated at this time is small. The carrier frequency and the switching frequency are the same.

  On the other hand, in a time zone where a plurality of load devices and distributed power sources are operated (usually, a daytime time zone), voltage fluctuations in the distribution system become severe, and voltage stabilization control is performed during this time zone. That is, the mode is switched to the voltage fluctuation suppression mode. In order to stabilize the voltage, a large fundamental wave current is to be controlled, so a large current capacity (about 300 kVA) is required. In the case of the shared configuration, there is no problem with respect to the current capacity because it is originally designed to cover a large current capacity.

  Since the current to be controlled is a fundamental wave, the carrier frequency for PWM conversion for voltage conversion and the switching frequency in the switching means to which the PWM modulated signal is supplied may be low. Because of the low frequency, the switching loss (power loss) in this switching means can be greatly reduced compared to the case where the switching frequency at the time of suppressing harmonics is used. This is because, when switching a large current, if the switching frequency is high, the switching loss is remarkably increased accordingly.

Several detection methods for switching the carrier frequency are conceivable.
(1) The voltage at the installation point of the distribution system is detected and its harmonic component is extracted, and when this is equal to or greater than the specified value, the mode is switched to the harmonic suppression mode. For example, when this harmonic component (total harmonic current) becomes a specified value (5%) or more, the harmonic is suppressed.
(2) The variation of the installation point voltage is detected, and when it exceeds the specified value, the mode is switched to the suppression mode for voltage stabilization. For example, when the installation point voltage exceeds ± 0.5% of a specified value, the mode is switched to the voltage stabilization mode.
(3) Focusing on the fact that voltage fluctuations occur mainly during the daytime and harmonics occur at night when the operation of the large-scale factory stops, the harmonic switching mode and the voltage stabilization suppression mode are switched by the timer circuit. The switching time can be selected as appropriate.

  As the high carrier frequency (high switching frequency), a frequency band of 5 to 20 kHz can be used. In this example, 8 kHz was used as the high switching frequency. As the low frequency, a frequency obtained by decreasing the frequency to ½ or less, for example, ½ can be used.

  In the present invention, a harmonic suppression function and a power stabilization function can be achieved by switching a carrier frequency (switching frequency) for power conversion.

  In addition to the effect of reducing the number of equipment parts used due to sharing, the high frequency fundamental is handled during voltage stabilization, and the switching frequency used during voltage stabilization is the switching frequency used during harmonic suppression. The switching loss is greatly reduced accordingly. This loss reduction not only brings about an energy saving effect, but also greatly contributes to heat dissipation and cooling measures for the entire apparatus, and as a result, the entire apparatus can be reduced in weight and size.

  Subsequently, a preferred embodiment of the power active filter according to the present invention will be described in detail with reference to the accompanying drawings when applied to a power distribution system.

  FIG. 1 shows a conceptual diagram including a power distribution system. The distribution system (feeder) between the power source 10 and the load 12 can be equivalent to the inductance L and the resistance component R of the distribution line DL. The distribution line DL includes the distributed power source 14 and the current flowing through the distribution line DL. A phase advance capacitor C for advancing the phase is connected in parallel. The output current of the distributed power source 14 is injected into the distribution line DL. Moreover, the active filter 20 for electric power which concerns on this invention is connected in parallel with the terminal of the distribution line DL which is a feeder trunk line. The compensation current is injected into the distribution line DL. The compensation current here is a concept that combines a compensation current based on a harmonic compensation current command value and a compensation current based on a reactive current command value for compensating for voltage fluctuation of the installation point voltage.

  With such a series-parallel connection to the distribution line DL, the voltage of the distribution line DL fluctuates due to the operation of the distributed power source 14 and the load 12 during the daytime, and the operation of the load 12 stops at nighttime. Since the operation of some of the distributed power sources 14 is stopped, the voltage harmonics are expanded by the resonance of the inductance L and the phase advance capacitor C.

  FIG. 2 shows a schematic configuration of the power active filter 20 according to the present invention. The power active filter 20 includes a voltage transformer 22 that functions as voltage detection means for detecting the voltage v at the installation point p. The voltage transformer 22 is a transformer for stepping down the high installation point voltage v to a voltage suitable for control. The step-down voltage obtained on the output side of the voltage transformer 22 (same as the installation point voltage v for convenience) is supplied to the compensation command signal generation output means 50.

  The compensation command signal generation output means 50 suppresses (compensates) the voltage fluctuation of the installation point voltage v and the harmonic compensation current command value for compensating the harmonic component generated in the installation point voltage v, thereby stabilizing the voltage. This is for generating and outputting the reactive current command value after voltage conversion for the purpose of achieving the above.

  The compensation current command value and the reactive current command value after voltage conversion are supplied to the active control means 30 connected to the distribution line DL. The control means 30 constitutes the main circuit of the active filter, and can suppress harmonics in the installation point voltage v and stabilize the voltage. Therefore, the three-phase voltage type PWM control unit 36 is connected via the boosting three-phase matching transformer 32 and the three-phase reactor 34 connected to the distribution line DL side. The three-phase reactor 34 is used as an interconnecting reactor because the AC side of the control means 30 that is the main circuit is also a voltage source with respect to the voltage source on the system side.

The three-phase voltage type PWM control unit 36 includes a switching means 38 connected to the three-phase reactor 34 side and a DC capacitor 39 connected to the switching means 38 as shown in the figure. _dc is supplied to the compensation command signal generation output means 50 described above.

  A specific example of the three-phase voltage type PWM control unit 36 is shown in FIG. One end (input side) of the three-phase reactors 34u, 34v, 34w is connected to the primary side of the three-phase matching transformer 32, and the other end (output side) is connected to the switching means 38. In this example, the switching means 38 is configured as a self-excited inverter.

  A three-phase reactor 34u is connected to a midpoint of connection between a pair of semiconductor switching elements (self-excited power switching elements such as IGBTs) 42u and 42u connected in series, and similarly to the midpoint of connection of the semiconductor switching elements 42v and 42v. The three-phase reactor 34v is connected, and the remaining three-phase reactor 34w is connected to the connection midpoint between the semiconductor switching elements 42w and 42w. Then, for example, switching signals Gu to Gw that are sequentially turned on (turned on) so that current flows sequentially in the order of u phase, v phase, and w phase are supplied to the corresponding semiconductor switching elements 42 u to 42 w. The switching signals Gu to Gw are all PWM-modulated.

The PWM modulation and the three-phase reactor 34 generate a compensation current i _C having the same phase as the harmonic component of the distribution system and the same magnitude, and this is injected into the installation point p of the distribution system to suppress the harmonic. Is done. In addition, a reactive current corresponding to a compensation voltage that suppresses voltage fluctuation of the installation point voltage is generated, and the voltage of the distribution system is stabilized.

  FIG. 4 shows a configuration of a compensation command signal generation / output means 50 which is a main part of the power active filter according to the present invention.

  This compensation command signal generation output means 50 includes a compensation means signal generation means for generating a harmonic compensation current command value and a reactive current command value for voltage fluctuation compensation, including a detection means 50A for detecting the installation point voltage v and the like. 50B, and a pulse width modulation means 50C for converting the compensation command signal into voltage and performing pulse width modulation.

  More specifically, in addition to these means 50A to 50C, a reactive current generating means 50D for generating a reactive current command value and a DC current command value for stabilizing the DC voltage with respect to the DC capacitor 39 are shown. DC current generating means 50E for generating, and further carrier signal switching means 80 for pulse width modulating means 50C.

I will explain in order. For convenience of explanation, the compensation command signal generation unit 50B will be described below. The configuration requirements of the compensation command signal generation unit 50B are as follows.
(1) It has a dq converter 52 for converting a three-phase AC voltage into a two-phase component.
(2) In this example, a high-pass filter 56 (56d, 56q) for detecting the harmonic component from the dq conversion output is provided.
(3) It has operational amplifier 58 (58d, 58q) which carries out current conversion of a harmonic output and produces | generates a harmonic compensation current.
(4) A dq inverse converter 70 is provided.
(5) It has the adder 72 (72u-72w) for outputting as a harmonic compensation current command value.
(6) Furthermore, it has mode switching means 60 which switches and outputs a harmonic compensation current and a compensation reactive current.

The above configuration will be sequentially described.
The three-phase AC voltage v = (v _u , v _v , v _w ), which is the installation point voltage detected by the voltage transformer 22 in FIG. 2, is converted to the fundamental positive phase component of the power supply voltage in the dq converter 52. It is converted into an instantaneous voltage (v _d , v _q ) represented by two components (d, q) of the rotating coordinate system with the d axis. The d component corresponds to the effective component (instantaneous active current) of the three-phase power, and the q component corresponds to the reactive component (instantaneous reactive current). This conversion is performed according to the following equation.

This instantaneous voltage is hereinafter simply referred to as installation point voltage. This dq conversion processing is performed in synchronization with the fundamental wave components (sin component and cos component) obtained from the fundamental wave component generation circuit 54 of the power supply voltage. Here, ωt is a basic angular frequency of the power supply voltage.

The dq converted installation point voltage (v _d , v _q ) is supplied to a high-pass filter (HPF) 56 (56d, 56q) functioning as a harmonic extraction means and the installation point voltage (v _d , v _q ). Are extracted. When waveform distortion occurs in the installation point voltage v, the d component and the q component include an alternating current component in addition to the direct current component. This AC component is not corrected and becomes a harmonic component of the power supply voltage. In this example, the fifth-order and seventh-order odd harmonic components V _dh and V _dq are mainly extracted by the high-pass filters 56d and 56q.

The voltage harmonic components V _dh and V _dq extracted by the high pass filters 56d and 56q are supplied to the harmonic compensation current generating means 58d and 58q. The harmonic compensation current generators 58d and 58q are both operational amplifiers, and are multiplied by a harmonic suppression gain K _V that functions as a damping resistor, thereby converting the harmonic compensation current (i ^* _Chd , i) converted into a current. ^* _Chq ) is generated. This harmonic compensation current (i ^* _Chd , i ^* _Chq ) is used as a command value (target value) for suppressing harmonics.

This harmonic compensation current (i ^* _Chd , i ^* _Chq ) is supplied to the mode switching means 60. The mode switching means 60 is used for switching between the harmonic suppression mode and the voltage fluctuation suppression mode. This will be described later.

Of the harmonic compensation current (i ^* _d , i ^* _q ) that has passed through the mode switching means 60, an adder 62 is provided in the fundamental wave component (d component) system corresponding to the effective component of the installation point voltage v. Here, a direct current (target direct current) Δi ^* _Cd related to the charging voltage v _dc of the direct current capacitor 39 is supplied and an addition process is performed.

This addition processing system is constituted by DC current generating means 50E for stabilizing the voltage v _dc charged in the DC capacitor 39. The direct current generating means 50E will be described.

In this example, a DC voltage setting circuit 64 is provided as shown in FIG. 4, and a target DC voltage v ^* _dc is output from the setting circuit 64. This DC voltage v ^* _dc is supplied to the adder 66. The adder 66 is supplied with the voltage v _dc across the DC capacitor 39, and the adder 66 obtains the difference DC voltage (v _dc −v ^* _dc ). The DC voltage difference (v _dc −v ^* _dc ) of the difference is supplied to the operational amplifier 68 for current conversion and is multiplied by a predetermined DC gain K _dc . The operational amplifier 68 acts as a resistance component on the difference DC voltage component (v _dc −v ^* _dc ), and the target DC current Δi ^* _Cd , which is the multiplication result, is converted into the effective component supplied to the adder 62 described above. It is added to the corresponding harmonic compensation current i ^* _d .

On the other hand, the reactive current generating means 50D supplied to the mode switching means 60 is configured as follows. The reactive current generating unit 50D includes a voltage amplitude calculating unit 92, and the above-described amplitude calculation process (square root process of sum of squares) of the voltage (v _d , v _q ) is performed.

The amplitude calculation output | v | is supplied to the adder 96 together with the voltage command value V ^* _f from the voltage command value setting circuit 94, and the difference (| v | −V ^* _f ) is calculated. The calculation output (| v | −V ^* _f ) is supplied to the fundamental wave reactive current control circuit 98 and converted into a reactive current i ^* _Cfq corresponding to the difference. Since this reactive current i ^* _Cfq is automatically adjusted so that its value becomes zero, this reactive current i ^* _Cfq is supplied to the mode switching means 60 as a reactive current command value.

The mode switching means 60 is composed of two switchers that are switched in conjunction with each other, and the a terminal (effective component side) has a harmonic compensation current i ^* associated with the d component V _d and q component V _q described above ^. _Chd , i ^* _Chq is supplied. Of the other b terminal (ineffective component side), the d component system is set to zero input “0”, and the q component system (corresponding to the invalid component) is the reactive current command value i ^* from the reactive current generating means 50D described above ^. _Cfq is supplied.

  Therefore, switching to the a terminal is in the harmonic suppression mode, and switching to the b terminal is in the voltage fluctuation suppression mode. The timing at which the suppression mode is switched will be described below.

In this example, the harmonic component V _dh related to the d component and the calculation output | v | of the voltage amplitude calculation means 92 are supplied to the detection means 50A, and the detection means 50A uses either or both of the modes. A switching signal Sm (Sn) is generated.

Therefore, this detection means 50A detects whether or not the input harmonic component V _dh is equal to or greater than a specified value, and whether or not the input voltage fluctuation is equal to or greater than the specified value. When the harmonic component V _dh exceeds a predetermined value (for example, 5%), a harmonic mode switching signal Sm is generated, and the mode switching means 60 is switched to the harmonic suppression mode (a terminal side). Alternatively, when the variation of the installation point voltage v is detected and the installation point voltage exceeds a specified value (for example, ± 0.5%), the stabilization mode switching signal Sn is generated, and the mode switching means 60 is set to the voltage. The mode is switched to the fluctuation suppression mode (b terminal side).

  The detection means 50A does not need to include both a harmonic component detection system and a voltage fluctuation detection system at the same time. Any one of the detection systems may be provided, and the mode switching means 60 may be switched and controlled only by the mode switching signal Sm or Sn from there.

  Further, the detection means 50A can be constituted by only a timer circuit. This is because voltage fluctuations occur mainly during the daytime, and harmonics occur mainly during the night when large-scale factories stop operating. The built-in timer circuit (not shown) counts the time and switches to voltage fluctuation suppression mode to suppress voltage fluctuation during daytime hours (for example, from 7:00 am to 7:00 pm) to stabilize the voltage of the distribution system Plan. On the other hand, the other time zone (night time zone) is switched to the harmonic suppression mode to reduce the waveform distortion of the distribution system. Thus, even if the switching timing is fixed by the timer circuit, the intended purpose can be achieved.

As shown in FIG. 4, each of the harmonic compensation current including the voltage stabilizing DC current Δi ^* _Cd for the DC capacitor 39 and the voltage stabilizing reactive current i ^* _Cq for the distribution system is expressed by the following equation: Can be expressed as

i ^* _Cd = i ^* _Chd + [ _Delta] i ^* _Cd (3)
i ^* _Cq = i ^* _Chq (4)
From (| v | −V ^* _f ), in the voltage fluctuation suppression mode, the fundamental wave reactive current i ^* _Cfq from the fundamental wave reactive current control circuit 98 becomes the compensation reactive current i ^* _Cq .
i ^* _Cd = Δi ^* _Cd (5)
i ^* _Cq = i ^* _Cfq (6)

The DC current Δi ^* _Cd for voltage stabilization and the reactive current i ^* _Cq for compensation are supplied to the dq inverse converter 70 and inversely converted into three-phase compensation signals (currents) i ^* _Cu , i ^* _Cv , i ^* _Cw. Is done. The inversely transformed three-phase compensation currents i ^* _Cu , i ^* _Cv , i ^* _Cw are respectively the three-phase current i (iu to iw) on the power source side fed back from the distribution system in the adder 72 (72u to 72w). Is added. Actually, a process of subtracting the three-phase current i from the three-phase compensation signals i ^* _Cu , i ^* _Cv , i ^* _Cw is performed. This subtracted current becomes the final compensation current command value i ^* _{Cu0 to} i ^* _Cw0 .

The compensation current command values i ^* _{Cu0 to} i ^* _Cw0 are supplied to the pulse width modulation means 50C as compensation command signals. The pulse width modulation means 50C includes a three-phase operational amplifier 74 (74u to 74w) that functions as voltage conversion and pulse width modulation (PWM modulation), and a three-phase operational amplifier 76 (76u to 76w) that functions as a gate circuit. The operational amplifiers 74 and 76 are commonly supplied with the carrier signal Sc. The voltage conversion coefficient Kc of the operational amplifier 74 acting as a resistance component can be selected to an appropriate value.

The output of the carrier signal switching means 80 is used for the carrier signal Sc. The carrier signal switching means 80 includes an oscillation circuit for the carrier signal Sc, a sawtooth wave oscillation circuit 82 in this example, and a reduction circuit for decreasing the frequency of the carrier signal Sc obtained thereby to 1/2 or less, in this example 1/2. 84 and a switching unit 86 to which the carrier signal Sc and the decreasing carrier signal Sc ₂ are respectively supplied.

Since harmonics generated in the power distribution system are fifth-order and seventh-order odd-order harmonics with respect to the power supply frequency, in order to be able to suppress these harmonics, the carrier signal Sc is several times more than that. A frequency, in this example a frequency of 5-10 kHz, is used. When 8 kHz is used as the carrier frequency, the decreasing circuit 84 outputs a 4 kHz decreasing carrier signal Sc ₂ . The carrier signal Sc having a high frequency is a carrier signal used when the harmonic suppression mode is used, and the decreasing carrier signal Sc ₂ having a low frequency is used as a carrier signal when the voltage variation suppression mode is used.

The switching unit 86 is a simple changeover switch and is controlled by mode switching signals Sm and Sn. Therefore, when the harmonic distortion of 5% or more is detected by the detection means 50A, the mode is switched to the harmonic suppression mode (a terminal side) and the 8 kHz carrier signal Sc is output. The operational amplifier 74 outputs this carrier signal Sc. Thus, the compensation current command value is pulse width modulated. 5 and 6 both show basic conceptual diagrams of PWM modulation, and when the compensation current command values i ^* _{Cu0 to} i ^* _Cw0 are low (eg, Sa) and high (eg, Sb) as shown in FIG. 5A. And the pulse width modulation output differs (see FIGS. 5B and 5C).

The pulse width modulation outputs Gu to Gw (= vCu ^{* to} vCw ^* ) are supplied as gate signals (switching signals) to the corresponding gate terminals of the semiconductor switching elements 42u to 42w shown in FIG. 3 through the gate circuits 76u to 76w. The As a result, the conduction angle of the semiconductor switching elements 42u to 42w is controlled by the pulse width modulation outputs Gu to Gw, and the amount of compensation current i _C flowing through the three-phase reactors 34u to 34w via these semiconductor switching elements 42u to 42w is reduced. Be controlled. As a result, the harmonic component of the current flowing through the distribution line DL at the installation point p is controlled.

Similarly, when the variation of the voltage is equal to or greater than the default value, together with the mode switching means 60 is switched to the voltage stabilization mode side, the carrier signal is also switched to the decreasing carrier signal Sc _2. As a result, the controlled object becomes a reactive current in relation to voltage fluctuations, also becomes slow (1/2) as compared to FIG. 5, as the pulse width modulation processing is also FIG 6A~C using this degressive carrier signal Sc ₂ . Since is not required fast response when suppressing the fluctuation in voltage, a sufficient processing speed even in this degressive carrier signal Sc _2. The conduction angle of the semiconductor switching elements 42u to 42w is controlled by the pulse width modulation outputs Gu to Gw processed at low speed, and the amount of compensation current i _C flowing through the three-phase reactors 34u to 34w via these semiconductor switching elements 42u to 42w Is controlled. As a result, the voltage v of the distribution line DL at the installation point p is stabilized.

The compensation reactive current generating means 50D can be configured as shown in FIG.
This reactive current generating means 50D includes a positive / negative (sign) detector 102 that outputs a positive or negative signal according to the positive / negative of the output (| v | −V ^* _f ) of the adder 96, and its output sqn. An up / down counter 104 is provided. Furthermore, the output of the adder 96 (| v | −V ^* _f ) is multiplied by a predetermined gain K _P to be converted into a current command value i ^* _CP , and the count output of the up / down counter 104 is expressed. And an adder 108 for adding the current value i ^* _CI and the current command value i ^* _CP .

The adder 108 functions as a current command value calculation unit that generates the fundamental wave reactive current command value i ^* _Cfq . As the up / down counter 104, a hexadecimal counter is used. If the sampling period of the up / down counter 104 is 60 μs, the output i ^* _CI changes from the minimum value (for example, −5 amperes) to the maximum value (for example, +5 amperes) in about 3.9 seconds.

According to the reactive current generating means 50D, the voltage amplitude value | v | is compared with a predetermined target value V ^* _f, and when | v |> V ^* _f , the value of the up / down counter 104 is compared. Since i ^* _CI increases, the value of the installation point voltage v is lowered so that the voltage amplitude value | v | becomes the target value V ^* _f . When | v | <V ^* _f , the value i ^* _CI of the up / down counter 104 is decreased, and the voltage amplitude value | v | is controlled to become the target value V ^* _f. By controlling the DL voltage fluctuation to be reduced, voltage fluctuation is suppressed.

In FIG. 4, the carrier signal Sc (or step-down carrier signal Sc ₂ ) is supplied to both the operational amplifiers 74 and 76 as the pulse width modulation means 50C in FIG. 4, but the operational amplifier 76 for the gate circuit at the subsequent stage is provided in this configuration. Omitted, the gate signals Gu to Gw obtained by the operational amplifier 74 may be directly supplied to the switching means 38.

  With the above configuration, it is possible to control harmonics and control voltage fluctuations in the distribution system with the same configuration. A high frequency carrier signal is used as a switching signal (gate signal) when suppressing harmonics, and a low frequency carrier signal (decreasing carrier signal) is used as a switching signal when controlling voltage fluctuations. Compared with the case where a frequency carrier signal is used as it is as a switching signal when controlling voltage fluctuation, the switching loss when controlling voltage fluctuation can be greatly reduced. As a result, it has features such as contributing to downsizing of equipment.

  The present invention can be applied to a power active filter having a shared configuration as a harmonic suppression device and a voltage stabilization device connected to a power system, particularly a power distribution system.

It is a systematic diagram using the active filter for electric power which concerns on this invention. It is a conceptual diagram which shows schematic structure of the active filter for electric power which concerns on this invention. It is a connection diagram which shows schematic structure of the control means which functions as a main circuit of the active filter for electric power. It is a block diagram which shows an example of the harmonic suppression and voltage fluctuation suppression circuit used for the active filter for electric power which concerns on this invention. It is a wave form diagram with which it uses for the operation | movement description (the 1). It is a wave form diagram with which it uses for operation | movement description (the 2). It is a block diagram which shows an example of a fundamental wave reactive current production | generation means.

Explanation of symbols

DL ... distribution line 12 ... load device 20 ... active filter 22 for power ... voltage transformer 30 ... control means (main circuit)
34 ... Three-phase reactor 36 ... PWM converter 38 ... Switching means 39 ... DC capacitor 50 ... Compensation command signal generation output means 50A ... Detection means 50B ... Compensation command signal generation Means 50C ... Pulse width modulation means 50D ... Reactive current generation means 50E ... DC current generation means 60 ... Mode switching means 80 ... Carrier signal switching means

Claims (9)

Voltage detection means for detecting the voltage at the load installation point of the distribution system;
From the installation point voltage detected by the voltage detection means, a harmonic compensation current command value for compensating for a harmonic component contained in the installation point voltage and a reactive current command for compensating voltage fluctuation of the installation point voltage. Compensation command signal generation output means for generating and outputting values respectively;
A pulse width modulation means for converting the voltage of the compensation command signal and modulating the pulse width; and
Based on the harmonic compensation current command value and reactive current command value generated by the compensation command signal generation output means, the control system is configured to control the harmonic component of the distribution system and the fluctuation of the fundamental voltage,
The control means is provided with switching means for supplying a pulse width modulation signal from the pulse width modulation means,
The pulse width modulation means is provided with carrier signal switching means used as a carrier signal of the pulse width modulation signal,
The power active filter, wherein the carrier signal switching means is controlled so that a carrier signal having a frequency different between the harmonic suppression mode and the voltage fluctuation suppression mode is supplied to the pulse width modulation means. The compensation command signal generation output means, harmonic detection means for extracting the harmonic component,
Harmonic compensation current generating means for generating a harmonic compensation current by multiplying the harmonic component by a predetermined gain;
Mode switching means provided at the subsequent stage of the harmonic compensation current generating means,
This mode switching means is supplied with the above-described harmonic compensation current and a compensation reactive current that is a current conversion output of a compensation voltage used as voltage fluctuation suppression.
The mode switching means is controlled to be switched so that the harmonic compensation current and the compensation reactive current can be selected in relation to the harmonic suppression mode and the voltage fluctuation suppression mode. Active filter for power. 2. The active filter for electric power according to claim 1, wherein when the distribution system is a three-phase AC signal, a dq conversion output is supplied to the harmonic extraction means. In the carrier signal switching means, switching to a high frequency carrier signal in the harmonic suppression mode,
2. The power active filter according to claim 1, wherein control for switching to a carrier signal having a low frequency is performed in the voltage suppression mode. 2. The power active filter according to claim 1, wherein the carrier signal switching means includes an oscillation circuit for the carrier signal, a decreasing circuit for decreasing the frequency of the carrier signal, and a switching unit thereof. 3. The active filter for electric power according to claim 2, wherein the harmonic detection means detects the presence or absence of a harmonic on the basis of a fluctuation rate of odd harmonics of the installation point voltage. Instead of the harmonic detection means, a voltage fluctuation detection means for detecting the fluctuation of the installation point voltage is provided,
3. The active filter for electric power according to claim 2, wherein when there is a voltage fluctuation exceeding a specified value, the mode is switched to a voltage fluctuation suppressing mode. Along with the harmonic detection means, a voltage fluctuation detection means for detecting the fluctuation of the installation point voltage is provided,
When harmonics exceeding the specified value are detected, switch to harmonic suppression mode,
3. The power active filter according to claim 2, wherein when a voltage fluctuation exceeding a specified value is detected, the mode is switched to a voltage fluctuation suppression mode. Instead of the harmonic detection means, a timer circuit is provided,
3. The active filter for electric power according to claim 2, wherein, based on the output of the timer circuit, the mode is switched to the voltage fluctuation suppression mode at daytime and the harmonic suppression mode at nighttime.

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