JP2018038220A - Active filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output compensation currents following up the change of request power of a load with high responsiveness without restricting the output of the compensation currents.SOLUTION: An adder 751 adds a power value pdc for maintaining a capacitor voltage Vdc at a target capacitor voltage Vdc_ref, a power value ploss indicating the variation of instantaneous power requested by a load 120 and a power value pa for cancelling AC components of instantaneous effective power p to calculate target instantaneous effective power p'. A multiplier 752 multiplies instantaneous reactive power q by -1 to calculate target instantaneous reactive power q' for cancelling the instantaneous reactive power. A pq inverse conversion part 76 calculates target currents Iref of an inverter 20 by using the target instantaneous effective power p' and the target instantaneous reactive power q'. An inverter control part 77 calculates a voltage command value Vo for causing the inverter 20 to generate a compensation voltage Vc by using the target currents Iref.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an active filter that outputs a compensation current that cancels a harmonic component of a power supply current output from an AC power supply.

  If a harmonic component is included in the AC current output from the AC power supply, it adversely affects the load connected to the AC power supply and induces power loss, which is not preferable. Therefore, an active filter that removes this harmonic component is known.

  The active filter is, for example, a capacitor, an inverter that converts a DC voltage accumulated in the capacitor into an AC voltage, and generates a compensation voltage for removing harmonic components, and a compensation voltage output from the inverter as a compensation current. It is comprised by the reactor which converts and superimposes on the alternating current output from alternating current power supply, and the control circuit which controls an inverter.

  FIG. 6 is a diagram showing a configuration of a conventional active filter control circuit described in Patent Document 1. In FIG. The three-phase to two-phase converter (1) calculates instantaneous active power and instantaneous reactive power included in AC power supplied to the load. The first low-pass filter (2) extracts a direct current component of instantaneous active power. The first subtracter (3) extracts the AC component of the instantaneous active power by subtracting the extracted DC component from the instantaneous active power.

  The second low-pass filter (5) extracts a DC component of instantaneous reactive power. The second subtracter (6) extracts the AC component of the instantaneous reactive power by subtracting the extracted DC component from the instantaneous reactive power.

  The two-phase / three-phase converter (9) converts the AC component of the instantaneous active power obtained by the first subtracter (3) and the AC component of the instantaneous reactive power obtained by the second subtracter (6). Based on the three-phase target current value.

  In the conventional active filter, when the required power of the load changes abruptly, the power component that should be removed cannot be removed due to the time delay of the first and second low-pass filters (2) and (5), and is output. There was a problem of outputting unnecessary power components.

  Therefore, the active filter disclosed in Patent Document 1 monitors the output fluctuation of the first low-pass filter (5) and the first fluctuation monitoring section (4) that monitors the output fluctuation of the first low-pass filter (2). 2 monitoring units (7). The output adjustment unit (8) sets the output of the two-phase / three-phase converter (9) to zero if the output fluctuation of the first or second low-pass filter (2) or (5) is larger than a predetermined value, Limit the output of the active filter.

Japanese Patent No. 3715135

  As described above, Patent Document 1 has a problem in that the harmonic component included in the power supply current cannot be removed because the output of the active filter is limited when the required power of the load changes greatly. Moreover, since control which maintains the voltage of a capacitor | condenser is not performed, patent document 1 has the problem that the compensation electric current which tracks the change cannot be produced | generated rapidly when the required electric power of a load changes.

  An object of the present invention is to provide an active filter that outputs a compensation current following the change with high responsiveness without limiting the output of the compensation current with respect to a change in required power of a load.

An active filter according to an aspect of the present invention is an active filter that is connected in parallel with an AC power supply and a load, and generates a compensation current that cancels a harmonic component of a power supply current output from the AC power supply.
A capacitor,
An inverter that converts a capacitor voltage stored in the capacitor into an AC voltage and generates a compensation voltage;
A reactor for converting the generated compensation voltage into the compensation current and superimposing the power supply current;
A first voltage sensor for detecting a power supply voltage output from the AC power supply;
A first current sensor for detecting a load current input to the load;
A second voltage sensor for detecting the capacitor voltage;
A second current sensor for detecting the compensation current;
A first power calculation unit for calculating a first power value for maintaining the detected capacitor voltage at a predetermined target capacitor voltage;
A second power calculation unit that calculates a second power value indicating the amount of change in the required power of the load by feedforward control using the detected power supply voltage and the detected compensation current;
A first converter that converts the detected power supply voltage and the detected load current into instantaneous active power and instantaneous reactive power;
A third power calculation unit that calculates a third power value that cancels the alternating current component of the converted instantaneous active power;
A target power calculating unit that calculates a target instantaneous reactive power by adding the first to third power values to calculate a target instantaneous reactive power and cancels the instantaneous reactive power converted by the conversion unit;
A second converter for converting the calculated target instantaneous active power and the calculated target instantaneous reactive power into a target current of the inverter;
An inverter control unit that calculates a voltage command value that causes the inverter to generate the compensation voltage based on the converted target current, the detected compensation current, and the detected power supply voltage;

  In this aspect, the compensation current is determined in consideration of the third power value for canceling the AC component of the instantaneous active power indicating the harmonic component of the AC power output from the AC power source and the target instantaneous reactive power for canceling the instantaneous reactive power. The generated compensation current is superimposed on the AC current output from the AC power supply. Thereby, in this aspect, the harmonic component is removed.

  However, this alone cannot generate an appropriate compensation current when the required power of the load changes greatly. Therefore, in this aspect, a first power value for maintaining the capacitor voltage at the target capacitor voltage is calculated, and the compensation current is generated in consideration of the first power value. Therefore, even if the required power of the load changes greatly, it is possible to prevent an appropriate compensation current from being generated due to a shortage of energy stored in the capacitor.

  Furthermore, in this aspect, the compensation current is generated in consideration of the second power value indicating the amount of change in the required power of the load. Therefore, even with this configuration, fluctuations in the capacitor voltage can be suppressed, and it is possible to prevent an appropriate compensation current from being generated due to a lack of energy stored in the capacitor. Furthermore, since the second power value is calculated by feedforward control using the detected power supply voltage and the detected compensation current, the power shortage of the capacitor can be compensated with high responsiveness.

  Furthermore, since the present embodiment can generate an appropriate compensation current with high responsiveness even if the required power of the load changes significantly, when the required power of the load changes drastically as in Patent Document 1, compensation is performed. There is no need to limit the current output.

In the above aspect, based on the power supply voltage detected in a cycle earlier than the current cycle, the power supply voltage amplitude of the current cycle and a phase corresponding to the amplitude are calculated, and the calculated amplitude and phase Further comprising a predicting unit that generates a predicted power supply voltage in which a pulsation component is removed from the power supply voltage of the current cycle,
The inverter control unit may calculate the voltage command value based on the predicted power supply voltage instead of the detected power supply voltage.

  According to this aspect, since the voltage command value is calculated based on the predicted power supply voltage from which the pulsating component is removed, a more appropriate compensation current can be generated.

  In the above aspect, the first power calculation unit calculates the first power value by feedback control that makes a deviation between the energy of the capacitor in the detected capacitor voltage and the energy of the capacitor in the target capacitor voltage zero. May be.

  According to this aspect, the first power value is obtained by the feedback control that makes the deviation between the capacitor energy calculated based on the detected capacitor voltage and the energy of the capacitor calculated based on the target capacitor voltage zero. Since it is calculated, the capacitor voltage can be more accurately maintained at the target capacitor voltage. Moreover, since the deviation of the capacitor energy proportional to the square of the voltage is observed, the deviation can be observed sensitively.

  Note that, by applying feedback control, the responsiveness of the first power value is reduced, but the second power value is calculated by feedforward control and has high responsiveness. Therefore, even if this aspect is adopted, the decrease in the responsiveness of the first power value is compensated by the second power value, so that the power fluctuation of the capacitor can be suppressed with high responsiveness.

In the above aspect, the AC power source is a three-phase AC power source,
The feedforward control may be a control for calculating a value obtained by adding a multiplication value of each phase of the detected power supply voltage and the detected compensation current as the second power value.

  According to this aspect, the second power value can be accurately calculated with high responsiveness.

  According to the present invention, it is possible to output a compensation current following the change with high responsiveness without limiting the output of the compensation current with respect to a change in the required power of the load.

It is a block diagram which shows the whole structure of the active filter which concerns on Embodiment 1 of this invention. It is a block diagram which shows the detailed structure of a controller. It is a flowchart which shows the process of the active filter which concerns on Embodiment 1 of this invention. It is a block diagram which shows the detail of the controller of the active filter which concerns on Embodiment 2 of this invention. It is a wave form diagram for demonstrating the process of an estimation part. It is a block diagram which shows the conventional active filter.

(Embodiment 1)
FIG. 1 is a block diagram showing an overall configuration of an active filter 1 according to Embodiment 1 of the present invention. The active filter 1 generates a compensation current Ic that cancels the harmonic component of the power supply current output from the AC power supply 110.

  The AC power supply 110 and the load 120 are connected via a three-phase AC power supply line L1. The power supply line L1 includes three power supply lines L1u, L1v, and L1w corresponding to the phases u, v, and w. The active filter 1 is connected to the power supply line L1 via the output line L2. The output line L2 includes output lines L2u, L2v, and L2w corresponding to the phases u, v, and w. The output lines L2u, L2v, and L2w are connected to power supply lines L1u, L1v, and L1w through connection points Pu, Pv, and Pw, respectively. Thereby, the active filter 1 is connected in parallel with the AC power supply 110 and the load 120.

  The AC power supply 110 is, for example, a system AC power supply, and supplies a power supply current Is, which is a three-phase AC current having a predetermined frequency component as a fundamental frequency component, to the load 120 via the power supply line L1. As the frequency of the fundamental frequency component, for example, 50 Hz and 60 Hz are adopted in Japan. The power supply current Is includes a plurality of harmonic components in addition to the fundamental frequency component. These harmonic components adversely affect the load 120 and induce power loss. Therefore, the active filter 1 superimposes the compensation current Ic on the power supply current Is to remove harmonic components contained in the power supply current Is.

  The load 120 is, for example, an electric device that is driven by the power supply current Is. The power supply current Is input to the load 120 is referred to as a load current IL.

  The active filter 1 includes a capacitor 10, an inverter 20, a reactor 30, and a controller 70. The capacitor 10 is composed of, for example, an electrolytic capacitor. Hereinafter, the DC voltage generated in the capacitor 10 is referred to as a capacitor voltage Vdc.

  The inverter 20 converts the capacitor voltage Vdc into an AC voltage under the control of the controller 70, and generates a compensation voltage Vc for removing harmonic components. The inverter 20 is a three-phase inverter and includes six switches SW1 to SW6. The switches SW1 and SW2 correspond to the U phase, the switches SW3 and SW4 correspond to the V phase, and the switches SW5 and SW6 correspond to the W phase. The switches SW1, SW3, and SW5 constitute the upper arm of the inverter 20, and the switches SW2, SW4, and SW6 constitute the lower arm of the inverter 20.

  The switch SW1 and the switch SW2 are connected via the connection point Ou, the switch SW3 and the switch SW4 are connected via the connection point Ov, and the switch SW5 and the switch SW6 are connected via the connection point Ow. Output lines L2u, L2v, and L2w are connected to the connection points Ou, Ov, and Ow, respectively.

  Each of the switches SW1 to SW6 includes a transistor Q and a diode D. The transistor Q is composed of, for example, an IGBT. In the example of FIG. 1, the transistor Q is configured by an npn type IGBT, but may be configured by a pnp type IGBT. The transistor Q may be a field effect transistor such as a MOSFET other than an IGBT, or may be a bipolar transistor.

  The transistor Q has a gate connected to the controller 70 and is turned on and off in accordance with a PWM signal supplied from the controller 70. The diode D is a freewheeling diode, and has an anode connected to the emitter of the transistor Q and a cathode connected to the collector of the transistor Q.

  The reactor 30 includes reactors 31, 32, and 33 corresponding to the phases u, v, and w. Reactors 31, 32, and 33 are provided on output lines L2u, L2v, and L2w, respectively. Reactor 30 converts compensation voltage Vc output from inverter 20 into compensation current Ic and supplies it to power supply line L1. Thereby, the compensation current Ic is superimposed on the power supply current Is, and the harmonic component included in the power supply current Is is removed.

  The active filter 1 further includes a current sensor 40, a voltage sensor 50, a current sensor 60, and a voltage sensor 65.

  The current sensor 40 detects compensation currents Icu, Icv, and Icw, which are compensation currents Ic for the phases u, v, and w. Here, the current sensor 40 includes two current sensors corresponding to any two of the u, v, and w phases. In this case, the current sensor 40 detects the compensation current Ic of each phase of u, v, and w by calculating the remaining one-phase compensation current Ic from the two-phase compensation current Ic detected by the two current sensors. do it. The current sensor 40 may be composed of three current sensors corresponding to the phases u, v, and w. The same applies to the current sensor 60.

  The voltage sensor 50 detects power supply voltages Vsu, Vsv, and Vsw, which are power supply voltages Vs of each phase of u, v, and w. The voltage sensor 50 includes two voltage sensors that detect a voltage between two phases, such as a uv phase and a vw phase. And the voltage sensor 50 should just detect the power supply voltage Vsu, Vsv, Vsw of each phase of u, v, and w by calculating the voltage of one phase remaining from the voltage between two phases which both voltage sensors detected. . Alternatively, the voltage sensor 50 may be composed of three voltage sensors corresponding to the phases u, v, and w.

  The current sensor 60 detects load currents ILu, ILv, and ILw that are load currents IL of the respective phases u, v, and w. Voltage sensor 65 detects capacitor voltage Vdc.

  The controller 70 is composed of a computer including a CPU and a ROM, and controls the active filter 1.

  FIG. 2 is a block diagram showing a detailed configuration of the controller 70. The controller 70 includes a capacitor controller 71 (an example of a first power calculator), a change amount calculator 72 (an example of a second power calculator), a pq converter 73 (an example of a first converter), and an extractor 74 ( An example of a third power calculation unit), a target power calculation unit 75, a pq inverse conversion unit 76 (an example of a second conversion unit), and an inverter control unit 77.

  The capacitor control unit 71 calculates a power value pdc for maintaining the capacitor voltage Vdc at a predetermined target capacitor voltage Vdc_ref. Specifically, the capacitor control unit 71 includes energy calculation units 711 and 712, a subtracter 713, and a PI control unit 714. The energy calculation unit 711 calculates a target electrical energy E1 that is an electrical energy of the capacitor 10 when the capacitor voltage Vdc is the target capacitor voltage Vdc_ref. The energy calculation unit 712 calculates the current electrical energy E2 of the capacitor 10 using the capacitor voltage Vdc detected by the voltage sensor 65.

Energy calculating unit 711 receives the target capacitor voltage Vdc_ref to u in formula C · u ^2/2, by entering the capacitance of the capacitor 10 and C, may be calculated target electric energy E1. Also, the energy calculator 712 receives the capacitor voltage Vdc which is a voltage sensor 65 detects the u in formula C · u ^2/2, by entering the capacitance of the capacitor 10 and C, by calculating the electrical energy E2 That's fine.

  Note that the energy calculation unit 711 may read the target electrical energy E1 calculated in advance from the memory and output it to the subtracter 713. As the target capacitor voltage Vdc_ref, for example, considering the rated voltage of the power supply voltage Vs and the rated voltage of the capacitor 10, even if the required power of the load 120 changes greatly, the inverter 20 generates an appropriate compensation voltage Vc. A predetermined voltage value that can be used can be adopted. The appropriate compensation voltage Vc refers to a compensation voltage Vc that can remove a harmonic component contained in the power supply voltage Vs.

  The subtractor 713 calculates a deviation e1 of the electric energy E2 with respect to the target electric energy E1 by subtracting the electric energy E2 from the target electric energy E1. The PI control unit 714 calculates a power value pdc (an example of a first power value) that sets the deviation e1 to 0 by PI control (proportional / integral control). That is, the PI control unit 714 calculates a power value pdc that makes the deviation e1 zero by feedback control.

  The change amount calculation unit 72 calculates the change amount of the capacitor voltage Vdc due to the change in the required power of the load 120 by feedforward control using the compensation current Ic detected by the current sensor 40 and the power supply voltage Vs detected by the voltage sensor 50. The indicated power value ploss (an example of the second power value) is calculated. Here, the change amount calculation unit 72 calculates the power value push using the following equation (1).

ploss = Icu · Vsu + Icv · Vsv + Icw · Vsw (1)
That is, the change amount calculation unit 72 calculates the power value ploss by adding the multiplication value of each phase of the compensation current Ic and the power supply voltage Vs. The amount of power change of the capacitor 10 depends on the loss of the active filter 1, and the power value “loss” in Expression (1) indicates the loss of the active filter 1. Therefore, the power value plus indicates the amount of change in the power of the capacitor 10 due to the change in the required power of the load 120.

  If no harmonic component is included in the power supply current Is, ideally, the loss of the active filter 1 is zero, that is, the power value push is zero. However, in reality, power loss occurs due to the resistance component included in the circuit. Therefore, even if the harmonic component is not included in the power supply current Is, the power value “ploss” does not actually become zero.

  The pq conversion unit 73 converts the load current IL into the instantaneous active power p and the instantaneous reactive power q using the power supply voltage Vs detected by the voltage sensor 50 and the load current IL detected by the current sensor 60. Here, the pq converter 73 may calculate the instantaneous active power p and the instantaneous reactive power q using the same method as the three-phase two-phase converter of Patent Document 1.

  The extraction unit 74 calculates a power value pa (an example of a third power value) that cancels the AC component of the instantaneous active power p. Specifically, the extraction unit 74 includes a low-pass filter 741 and a subtracter 742. The low-pass filter 741 extracts the DC component pd included in the instantaneous active power p. The subtractor 742 calculates the power value pa by subtracting the instantaneous active power p from the DC component. Here, since the subtracter 742 subtracts the instantaneous active power p from the DC component pd, the power value pa is a value obtained by multiplying the AC component included in the instantaneous active power p by -1. Therefore, the power value pa indicates a power value that cancels the AC component included in the instantaneous active power p.

  The target power calculation unit 75 includes an adder 751 and a multiplier 752. The adder 751 adds the power value pdc, the power value ploss, and the power value pa to calculate the target instantaneous active power p ′. The target instantaneous active power p ′ maintains the capacitor 10 at the target electrical energy E1, and compensates for the power loss of the active filter 1, that is, the amount of change in the required power of the load 120, and the instantaneous effective power AC. Indicates the power value that cancels the component.

  The multiplier 752 multiplies the instantaneous reactive power q by −1 to calculate a target instantaneous reactive power q ′ that cancels the instantaneous reactive power.

  The pq inverse conversion unit 76 calculates the target current Iref of the inverter 20 using the target instantaneous active power p ′ and the target instantaneous reactive power q ′. Here, the pq inverse conversion unit 76 may calculate the target current Iref using the same method as the two-phase three-phase converter disclosed in Patent Document 1. The target current Iref includes target currents Iref_u, Iref_v, and Iref_w corresponding to the phases u, v, and w.

  The inverter control unit 77 uses the target current Iref, the compensation current Ic detected by the current sensor 40, and the power supply voltage Vs detected by the voltage sensor 50 to cause the inverter 20 to generate the compensation voltage Vc. The command value Vo is calculated.

  The inverter control unit 77 includes a subtractor 771, a P control unit 772, and a PWM generation unit 773. The subtractor 771 calculates the deviation e2 between the two currents by subtracting the compensation current Ic detected by the current sensor 40 from the target current Iref. Specifically, the subtractor 771 calculates the deviation e2 by calculating (e2_u, e2_v, e2_w) = (Iref_u−Icu, Iref_v−Icv, Iref_w−Icv).

  The P control unit 772 calculates the compensation voltage Vc necessary for making the deviation e2 zero (the target current Iref is set as the compensation current Ic) by P control (proportional control). Specifically, the P control unit 772 calculates a compensation voltage Vc (Vcu, Vcv, Vcw) for each phase necessary to make the deviation e2 (e2_u, e2_v, e2_w) for each phase zero.

  The PWM generator 773 calculates the voltage command value Vo by adding the power supply voltage Vs to the compensation voltage Vc. Specifically, the PWM generation unit 773 calculates the voltage command value Vo by (Vou, Vov, Vow) = (Vcu + Vsu, Vcv + Vsv, Vcw + Vsw). The PWM generation unit 773 generates a PWM signal for each phase of u, v, and w according to the voltage command value Vo (Vou, Vov, Vow).

  The PWM generation unit 773 outputs the generated u-phase PWM signal to the switch SW1, and outputs a PWM signal obtained by inverting the generated u-phase PWM signal to the switch SW2. The PWM generator 773 outputs the generated v-phase PWM signal to the switch SW3, and outputs a PWM signal obtained by inverting the generated v-phase PWM signal to the switch SW4. Also, the PWM generation unit 773 outputs the generated w-phase PWM signal to the switch SW5, and outputs a PWM signal obtained by inverting the generated w-phase PWM signal to the switch SW6.

  Referring to FIG. 1, a power supply voltage Vs is applied to connection points Pu, Pv, and Pw, and a voltage (Vc + Vs) corresponding to a voltage command value Vo is applied to connection points Ou, Ov, and Ow. Therefore, the voltage difference (= Vc) between the power supply voltage Vs and the voltage (Vc + Vs) corresponding to the voltage command value Vo is applied to the reactors 31, 32, and 33, so that the compensation voltage Vc is output from the inverter 20. Will be.

  FIG. 3 is a flowchart showing processing of the active filter 1 according to Embodiment 1 of the present invention. This flowchart is executed at predetermined time intervals in a predetermined control cycle.

  First, the pq converter 73 generates the instantaneous active power p and the instantaneous reactive power q using the power supply voltage Vs and the load current IL (S301).

  Next, the extraction unit 74 calculates a power value pa that cancels the AC component included in the instantaneous active power p (S302). Next, the capacitor control unit 71 calculates a power value pdc for maintaining the capacitor voltage Vdc at a predetermined target capacitor voltage Vdc_ref (S303).

  Next, the change amount calculation unit 72 substitutes the power supply voltage Vs and the compensation current Ic into the above equation (1), and calculates the power value ploss (S304).

  Next, the adder 751 calculates the target instantaneous active power p ′ by the power value pdc + power value ploss + power value pa, and the multiplier 752 calculates the target instantaneous reactive power q ′ by the instantaneous reactive power q × (−1). Calculate (S305).

  Next, the pq inverse conversion unit 76 calculates the target current Iref using the target instantaneous active power p 'and the target instantaneous reactive power q' (S306).

  Next, the inverter control unit 77 calculates a voltage command value Vo for setting the compensation current Ic to the target current Iref, and generates a PWM signal for the switches SW1 to SW6 using the calculated voltage command value Vo.

  As described above, the compensation current Ic is output from the active filter 1, the compensation current Ic is superimposed on the power supply current Is, and the harmonic component included in the power supply current Is is removed.

  Thus, according to the first embodiment, the target instantaneous active power p ′ for canceling the AC component of the instantaneous active power p indicating the harmonic component of the AC power output from the AC power supply 110 and the instantaneous reactive power q are canceled. The compensation current Ic is generated in consideration of the target instantaneous reactive power q ′, and the generated compensation current Ic is superimposed on the power supply current Is output from the AC power supply 110. As a result, harmonic components are removed.

  However, this alone cannot generate an appropriate compensation current Ic when the required power of the load 120 changes greatly. Therefore, in the first embodiment, a power value pdc for maintaining the capacitor voltage Vdc at the target capacitor voltage Vdc_ref is calculated, and the compensation current Ic is generated taking this power value pdc into consideration. Therefore, even if the required power of the load 120 changes greatly, it is possible to prevent the appropriate compensation current Ic from being generated due to the shortage of energy stored in the capacitor 10.

  Further, in the first embodiment, the compensation current Ic is generated in consideration of the power value ploss. Therefore, also with this configuration, fluctuations in the capacitor voltage Vdc can be suppressed, and it is possible to prevent an appropriate compensation current from being generated due to a lack of energy stored in the capacitor 10. Further, the power value ploss is calculated by feedforward control using the detected power supply voltage Vs and the detected compensation current Ic. Therefore, even if the required power of the load 120 changes significantly, the compensation current Ic that follows the change in the capacitor voltage Vdc can be generated with high responsiveness.

(Embodiment 2)
FIG. 4 is a block diagram showing details of the controller 701 of the active filter 1 according to Embodiment 2 of the present invention. The active filter 1 according to the second embodiment generates a predicted power supply voltage Vs ′ that is a power supply voltage Vs obtained by removing a pulsating component from the power supply voltage Vs detected by the voltage sensor 50. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The controller 701 shown in FIG. 4 is different from the controller 70 in that a prediction unit 80 is newly added.

  In general, the power supply voltage Vs includes a pulsation component (ripple). Therefore, the prediction unit 80 determines the amplitude of the power supply voltage Vs in the current cycle and the phase corresponding to the amplitude based on the waveform of the power supply voltage Vs detected by the voltage sensor 50 in a cycle earlier than the current cycle. Based on the calculated amplitude and phase, a predicted power supply voltage Vs ′ is generated by removing the pulsating component from the power supply voltage Vs of the current cycle.

  The past cycle may be the cycle of the power supply voltage Vs one before the current cycle, or may be a plurality of past cycles one cycle before the current cycle. When using a plurality of past cycles, the prediction unit 80 may use an average waveform of the power supply voltage Vs of the past cycles.

  Hereinafter, a process for calculating the predicted power supply voltage Vs ′ using the waveform of the power supply voltage Vs in the cycle immediately before the current cycle will be described. FIG. 5 is a waveform diagram for explaining the processing of the prediction unit 80.

  The prediction unit 80 detects the start point P1 and the end point P2 of the waveform of the power supply voltage Vs in the previous cycle by detecting the zero cross point from the measured value of the power supply voltage Vs detected by the voltage sensor 50. Next, the prediction unit 80 detects the plus-side peak voltage Vpeak from the measured values from the start point P1 to the end point P2, and detects the time from the start point P1 to the peak voltage Vpeak as the peak phase Ppeak. . Note that the prediction unit 80 may detect the negative peak voltage Vpeak ′ and the time from the start point P1 to the peak voltage Vpeak ′ as the peak phase Ppeak ′.

  Next, the prediction unit 80 calculates a sine wave having the peak voltage Vpeak as the amplitude Vd and the peak phase Ppeak × 4 as the period Ts as the predicted power supply voltage Vs ′, and outputs the sine wave to the PWM generation unit 773. As a result, the power supply voltage Vs obtained by removing the ripple from the power supply voltage Vs is obtained as the predicted power supply voltage Vs ′.

  Since the power supply voltage Vs is composed of three-phase power supply voltages Vs (Vsu, Vsv, Vsw) of u, v, and w, the prediction unit 80 uses each of Vsu, Vsv, and Vsw individually. The predicted power supply voltage Vs ′ (Vs′u, Vs′v, Vs′w) of the three phases u, v, and w may be calculated.

  The PWM generation unit 773 calculates the voltage command value Vo using the predicted power supply voltage Vs ′ instead of the power supply voltage Vs. Specifically, the PWM generation unit 773 calculates the voltage command value Vo by the predicted power supply voltage Vs ′ + compensation voltage Vc. The PWM generation unit 773 generates a PWM signal to be supplied to the switches SW1 to SW6 using the generated voltage command value Vo.

  Thus, since the voltage command value Vo is calculated based on the predicted power supply voltage Vs from which the ripple is removed, the active filter 1 according to the second embodiment can generate a more appropriate compensation current Ic.

(Modification 1)
In the second embodiment, the change amount calculation unit 72 may calculate the power value push using the predicted power supply voltage Vs ′ instead of the power supply voltage Vs when calculating the power value push. Thereby, the power value push can be calculated using the power supply voltage Vs from which the ripple has been removed, and an accurate power value push can be calculated.

(Modification 2)
In the first embodiment, the capacitor control unit 71 calculates the energy difference between the target electric energy E1 and the electric energy E2 as the deviation e1, but the present invention is not limited to this. The capacitor control unit 71 may calculate a voltage difference between the target capacitor voltage Vdc_ref and the capacitor voltage Vdc as the deviation e1.

(Modification 3)
In the first embodiment, the controller 70 uses the low-pass filter to extract the DC component of the instantaneous reactive power q and subtracts the instantaneous reactive power q from the extracted DC component in the same manner as the instantaneous active power p. An instantaneous target power q ′ that cancels the alternating current component of q may be generated.

IL load current Ic compensation current Vc compensation voltage Iref target current SW1, SW2, SW3, SW4, SW5, SW6 switch Vdc capacitor voltage Vdc_ref target capacitor voltage Vo voltage command value Vs power supply voltage Vs 'predicted power supply voltage p instantaneous effective power p' target Instantaneous active power pa Power value q Instantaneous reactive power q 'Target instantaneous reactive power 1 Active filter 10 Capacitor 20 Inverter 30 Reactor 40 Current sensor 50 Voltage sensor 60 Current sensor 65 Voltage sensor 70, 701 Controller 71 Capacitor control unit 72 Change amount calculation unit 73 pq conversion unit 74 extraction unit 75 target power calculation unit 76 pq inverse conversion unit 77 inverter control unit 80 prediction unit 110 AC power supply 120 load

Claims (4)

An active filter that is connected in parallel with an AC power supply and a load and generates a compensation current that cancels a harmonic component of a power supply current output from the AC power supply,
A capacitor,
An inverter that converts a capacitor voltage stored in the capacitor into an AC voltage and generates a compensation voltage;
A reactor for converting the generated compensation voltage into the compensation current and superimposing the power supply current;
A first voltage sensor for detecting a power supply voltage output from the AC power supply;
A first current sensor for detecting a load current input to the load;
A second voltage sensor for detecting the capacitor voltage;
A second current sensor for detecting the compensation current;
A first power calculation unit for calculating a first power value for maintaining the detected capacitor voltage at a predetermined target capacitor voltage;
A second power calculation unit that calculates a second power value indicating the amount of change in the required power of the load by feedforward control using the detected power supply voltage and the detected compensation current;
A first converter that converts the detected power supply voltage and the detected load current into instantaneous active power and instantaneous reactive power;
A third power calculation unit that calculates a third power value that cancels the alternating current component of the converted instantaneous active power;
A target power calculating unit that calculates a target instantaneous reactive power by adding the first to third power values to calculate a target instantaneous reactive power and cancels the instantaneous reactive power converted by the conversion unit;
A second converter for converting the calculated target instantaneous active power and the calculated target instantaneous reactive power into a target current of the inverter;
An active filter comprising: an inverter control unit that calculates a voltage command value that causes the inverter to generate the compensation voltage based on the converted target current, the detected compensation current, and the detected power supply voltage. Based on the power supply voltage detected in a past cycle than the current cycle, calculate the amplitude of the power supply voltage in the current cycle and the phase corresponding to the amplitude, and based on the calculated amplitude and phase, A prediction unit that generates a predicted power supply voltage in which a pulsation component is removed from the power supply voltage of the current period;
The active filter according to claim 1, wherein the inverter control unit calculates the voltage command value based on the predicted power supply voltage instead of the detected power supply voltage.   2. The first power calculation unit calculates the first power value by feedback control in which a deviation between the energy of the capacitor in the detected capacitor voltage and the energy of the capacitor in the target capacitor voltage is zero. Or the active filter of 2. The AC power source is a three-phase AC power source,
The feedforward control is a control for calculating a value obtained by adding a multiplication value of each phase of the detected power supply voltage and the detected compensation current as the second power value. Active filter as described in.

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