JP5494304B2 - Power conditioner - Google Patents

Description

  The present invention relates to an improvement in a power adjustment device that controls the output of an AC power supply and supplies the load to a load.

  As this type of power conditioner, a switch circuit in which thyristors are connected in antiparallel is connected in series to a primary winding of a transformer, and a load is connected between the secondary windings of the transformer. Yes. In this power adjustment device, the power supplied to the load is adjusted by controlling the phase of the thyristor of the switch circuit. However, in this power adjustment device, the input virtual power increases because the harmonics of the input current increase, and it is necessary to insert an active filter in parallel in the factory equipment in order to suppress the harmonics.

  Therefore, a power adjustment device according to Patent Document 1 has been proposed. The power adjustment apparatus includes a first diode series circuit in which an anode terminal of a first diode and a cathode terminal of a second diode are connected, and a second diode in which an anode terminal of a third diode and a cathode terminal of a fourth diode are connected. A three-phase bridge circuit in which a series circuit and a third diode series circuit in which an anode terminal of a fifth diode and a cathode terminal of a sixth diode are connected are connected in parallel, and switching elements are connected in reverse parallel to the respective diodes. It has.

The series connection point of the first diode series circuit is connected to one terminal of the AC power source via the first reactor, and the series connection point of the third diode series circuit is one of the loads via the second reactor. The series connection point of the second diode series circuit is directly connected to the other terminal of the AC power supply and the load, and the first capacitor that constitutes the first filter together with the first reactor is connected to the terminal. A second capacitor that constitutes a second filter together with a second reactor is connected in parallel to the power source and in parallel to the load.
In this power adjustment device, in order to adjust the power supplied to the load, switching elements connected in reverse parallel to the respective diodes of the third diode series circuit are switched by the PWM signal.

JP-A-10-150770

In the power adjustment device according to Patent Document 1, it is necessary to set the switching frequency (carrier frequency) by PWM to be several kH or more in order to suppress the increase in size of the first filter, which increases the switching loss. Cause inconvenience.
Accordingly, an object of the present invention is to provide a power adjustment device that can reduce switching loss without increasing the size of a filter.

In the first invention, one input terminal is connected to the first output terminal of the three-phase AC power supply via the first reactor, and the other input terminal is connected to the second output terminal of the three-phase AC power supply. The first bridge circuit, a plurality of first drive circuits connected in parallel between the output terminals of the first bridge circuit, and the three-phase AC power supply through one input terminal via a second reactor Connected in parallel between the second output circuit of the second bridge circuit and the second bridge circuit connected to the second output terminal of the three-phase AC power supply. A plurality of second drive circuits, a first capacitor connected between the first and second output terminals of the three-phase AC power source and constituting a filter together with the first reactor, and the three-phase AC power source Connected between the second and third output terminals of the second, Comprises a second capacitor constituting the filter with a reactor, a switching signal generating means for generating a switching signal.
The first and second bridge circuits have bridge-connected diodes and switching elements connected in antiparallel to these diodes, respectively, and the first and second drive circuits have a pair of switching circuits connected in series. Elements and diodes connected in reverse parallel to these switching elements.
The switching signal generating means includes a first switching signal for turning on / off each switching element of the first bridge circuit based on the polarity of the AC voltage between the first and second output terminals of the three-phase AC power supply; A second switching signal for turning on / off each switching element of the second bridge circuit based on the polarity of the AC voltage between the second and third output terminals of the three-phase AC power supply; and the plurality of first drives Generating a pulse width modulated third switching signal for turning on / off each switching element of the circuit and a pulse width modulated fourth switching signal for turning on / off each switching element of the plurality of second drive circuits; And the supply timing of the third switching signal to the plurality of first drive circuits is related to the third switching signal. The period of the carrier signal of the pulse width modulation is sequentially shifted by the time divided by the number of the first drive circuits, and the supply timing of the fourth switching signal to the plurality of second drive circuits is changed to the fourth The pulse width modulation carrier signal period related to the switching signal is sequentially shifted by the time divided by the number of the second drive circuits.
The number of the first and second drive circuits is different from each other. Individual loads are connected to the plurality of first drive circuits and the plurality of second drive circuits, respectively.

In the second aspect of the invention, one input terminal is connected to the first output terminal of the three-phase AC power supply through the first reactor, and the other input terminal is connected to the second output terminal of the three-phase AC power supply. The first bridge circuit, a plurality of first drive circuits connected in parallel between the output terminals of the first bridge circuit, and the three-phase AC power supply via one input terminal via a second reactor Connected in parallel between the second output circuit of the second bridge circuit and the second bridge circuit connected to the second output terminal of the three-phase AC power supply. A plurality of second drive circuits, a first capacitor connected between the first and second output terminals of the three-phase AC power source and constituting a filter together with the first reactor, and the three-phase AC power source Connected between the second and third output terminals of the second, Comprising a second capacitor constituting the filter with a reactor, a switching signal generating means for generating a switching signal.
The first and second bridge circuits have bridge-connected diodes and switching elements connected in antiparallel to these diodes, respectively, and the first and second drive circuits have a pair of switching circuits connected in series. Elements and diodes connected in reverse parallel to these switching elements.
The switching signal generating means includes a first switching signal for turning on / off each switching element of the first bridge circuit based on the polarity of the AC voltage between the first and second output terminals of the three-phase AC power supply; A second switching signal for turning on / off each switching element of the second bridge circuit based on the polarity of the AC voltage between the second and third output terminals of the three-phase AC power supply; and the plurality of first drives Generating a pulse width modulated third switching signal for turning on / off each switching element of the circuit and a pulse width modulated fourth switching signal for turning on / off each switching element of the plurality of second drive circuits; And said
The supply timing of the third switching signal to a plurality of first drive circuits is equal to the time obtained by dividing the period of the carrier signal of the pulse width modulation related to the third switching signal by the number of the first drive circuits. The supply timing of the fourth switching signal to the plurality of second drive circuits is sequentially shifted, and the period of the carrier signal of the pulse width modulation related to the fourth switching signal is the number of the second drive circuits. It is configured to shift sequentially by the time divided by.
The frequency of the pulse width modulation carrier signal related to the third switching signal is different from the frequency of the pulse width modulation carrier signal related to the fourth switching signal. Individual loads are connected to the plurality of first drive circuits and the plurality of second drive circuits, respectively.
In the first and second inventions , for example, IGBTs are used as the switching elements of the first and second bridge circuits and the switching elements of the first and second drive circuits. The load includes, for example, a heat treatment heater in a semiconductor manufacturing apparatus .

  According to the present invention, since the carrier frequency can be lowered without increasing the size of the reactor constituting the filter of the input unit, highly efficient power supply with low switching loss can be achieved.

It is a circuit diagram showing one embodiment of a power adjustment device concerning the present invention. It is a block diagram which shows the circuit element for generating a switching signal. It is a wave form chart for explaining operation of the power regulator concerning an embodiment. It is the graph which illustrated the loss characteristic of the power regulator which concerns on a prior art example, and the power regulator which concerns on this invention. It is a circuit diagram which shows the structural example of the power regulator applied to the single phase alternating current power supply.

FIG. 1 is a circuit diagram showing an embodiment of a power adjustment device according to the present invention. The power adjustment apparatus includes a bridge circuit 10, drive circuits 10-1 to 10 -N (N is an integer of 2 or more) combined with the bridge circuit 10, a bridge circuit 20, and a drive circuit combined with the bridge circuit 20. 20-1 to 20-N.
The bridge circuit 10 includes bridge-connected diodes D11 to D14 and switching elements S11 to S14 connected in reverse parallel to the diodes D11 to D14, respectively, and one input terminal (a common connection point of the diodes D11 and D12). While being connected to the R output terminal of the three-phase AC power supply 14 via the reactor L10, the other input terminal (common connection point of the diodes D13 and D14) is connected to the S output terminal of the three-phase AC power supply 14.

The drive circuit 10-1 includes a pair of switching elements S15 and S16 connected in series, and diodes D15 and D16 connected in reverse parallel to the switching elements S15 and S16, respectively. The same applies to the drive circuits 10-2 to 10-N. The drive circuits 10-2 to 10-N are connected in parallel between the line 12 connected to the positive output terminal of the bridge circuit 10 and the line 13 connected to the negative output terminal.
The bridge circuit 20 and the load drive circuits 20-1 to 20-N have the same configuration as the bridge circuit 10 and the load drive circuits 10-1 to 10-N, respectively, so A description of the configuration is omitted. The bridge circuit 20 has one input terminal (common connection point of the diodes D21 and D22) connected to the T output terminal of the three-phase AC power supply 14 via the reactor L20, and the other input terminal (diodes D23, D24 common connection point) is connected to the S output terminal of the three-phase AC power supply 14.

One ends of the loads R10-1 to R10-N are respectively connected to output terminals of the drive circuits 10-1 to 10-N (common connection points of the switching elements S15 and S16), and the other ends thereof are three-phase AC. It is connected to the S output terminal of the power supply 14. In addition, one end of each of the loads R20-1 to R20-N is connected to each output terminal of the drive circuits 20-1 to 20-N (common connection point of the switching elements S25 and S26), and the other end thereof is connected. It is connected to the S output terminal of the three-phase AC power supply 14.
The loads R10-1 to R10-N and the loads R20-1 to R20-N are heaters for heating a material such as a wafer in a semiconductor manufacturing apparatus, for example.
A capacitor C10 that constitutes a filter together with the reactor L10 is connected between the R and S output terminals of the three-phase AC power supply 14, and a filter together with the reactor L20 is connected between the S and T output terminals of the three-phase AC power supply 14. A capacitor C20 to be configured is connected.

  The phase detection circuit 15 shown in FIG. 2 detects the phase of the voltage of each phase of the three-phase AC power supply 14, and the voltage between the R and S output terminals of the three-phase AC power supply 14 and between the S and T output terminals. It is determined whether the voltage is a positive half-cycle voltage or a negative half-cycle voltage, and a signal indicating the determination result is output to the switching signal generation circuit 16. The switching signal generation circuit 16 switches the switching signals for the switching elements S11 to S14 of the bridge circuit 10 and the drive circuits 10-1 to 10-N based on the signal indicating the determination result and the pulse width designation signal given from the outside. Switching signals for the switching elements S15 and S16, switching signals for the switching elements S21 to S24 of the bridge circuit 20, and switching signals for the switching elements S25 and S26 of the drive circuits 20-1 to 20-N are generated.

Hereinafter, the operation of the power adjustment apparatus according to the present embodiment will be described with reference to FIG. FIG. 3A shows an AC voltage input via the R and S output terminals of the three-phase AC power supply 14. The phase detection circuit 15 in FIG. 2 outputs a determination signal as shown in FIG. 3C according to whether the AC voltage is a positive half-cycle voltage or a negative half-cycle voltage.
On the other hand, the switching signal generation circuit 16 generates the carrier signal shown in FIG. 3B, and based on the comparison between the carrier signal and the pulse width designation signal, the pulse width modulation (hereinafter, referred to as “d”) shown in FIG. Signal). The switching signal generation circuit 16 generates the switching signals shown in FIGS. 3E to 3H for switching the switching elements S11 to S14 based on the determination signal shown in FIG. 3 (i), (j) for switching the switching elements S16, S15 of the drive circuit 10-1 based on the determination signal shown in FIG. 3 (c) and the PWM signal shown in FIG. 3 (d). 3 and the switching signals shown in FIGS. 3 (k) and 3 (l) for switching the switching elements S16 and S15 of the drive circuit 10-2 are generated. Although not shown, the same applies to switching signals for switching the switching elements S16 and S15 of the drive circuits 10-3,..., 10-N.

  The switching signal shown in FIG. 3 (i) is obtained by performing an exclusive OR process on the determination signal shown in FIG. 3 (c) and the PWM signal shown in FIG. 3 (d), and the switching signal shown in FIG. 3 (j). The signal is obtained by inverting the switching signal shown in FIG. The switching signals shown in FIGS. 3 (k) and (l) are obtained by shifting the phase of the switching signals shown in FIGS. 3 (i) and (j) by a predetermined time Δt, respectively. Since the time Δt is obtained by multiplying the AC voltage cycle shown in FIG. 3A by 1 / N, the angle Δt is 360 ° / N. That is, the switching signals for the switching elements S15 and S16 of the drive circuits 10-2 to 10-N are respectively shifted by time Δt with respect to those for the switching elements S15 and S16 of the drive circuits 10-1 to 10-N-1. ing.

  In the positive half cycle period of the AC voltage shown in FIG. 3A, the switching elements S11 and S14 are turned on. Therefore, when the switching element S15 of the drive circuit 10-1 is turned on, the power supply 14 (R output terminal) → Reactor L10 → Diode D11 → Switching element S15 → Load R10-1 → Power supply 14 (S output terminal) A path is formed to supply power to the load R10-1. At this time, assuming that the phase of voltage and current is different (voltage is positive and current is negative), power source 14 (S output terminal) → load R10-1 → diode D15 → switching element S11 → reactor L19 → power source 14 ( Current flows through the path of the R output terminal.

  Next, when the switching element S15 is turned off and the switching element S16 is turned on, the voltage application path between the power supply 14 and the load R10-1 is cut off, so that the applied voltage of the load R10-1 becomes zero. The current from the load R10-1 side circulates along the path of the load R10-1, the switching element S14, the diode D16, and the load R10-1. At this time, if the phase of the voltage and the current is different (the voltage is positive and the current is negative), the current from the load R10-1 side is the path of R10-1 → switch S16 → diode D14 → load R10-1. It will circulate with.

  On the other hand, in the negative half cycle period of the AC voltage shown in FIG. 3A, the switching elements S12 and S13 are turned on, so that the switching element S16 of the drive circuit 10-1 is turned on, whereby the power supply 14 (S output Terminal) → load R10-1 → switching element S16 → diode D12 → reactor L10 → power source 14 (R terminal) to supply power to the load R10-1. At this time, assuming that the phase of voltage and current is different (voltage is negative and current is positive), power source 14 (R terminal) → reactor L10 → switching element S12 → diode D16 → load R10-1 → power source 14 (S Current flows through the terminal) path.

  Next, when the switching element S16 is turned off and the switching element S15 is turned on, the voltage application path between the power supply 14 and the load R10-1 is cut off, so that the applied voltage of the load R10-1 becomes zero. The current from the load R10-1 side circulates along the path of the load R10-1, the diode D15, the switching element S13, and the load R10-1. At this time, if the phase of the voltage and the current is different (the voltage is negative and the current is negative), the current from the load R10-1 side is the load R10-1 → the diode D13 → the switching element S15 → the load R10-1. It will circulate in the route of.

During one cycle of the AC voltage, the above operation is repeated at a cycle defined by the carrier frequency, and as a result, a voltage having a waveform approximate to the AC voltage waveform is applied to the load R10-1. At this time, the filter circuit including the reactor L10 and the capacitor C10 acts to suppress the ripple of the input / output current.
The electric power supplied to the load R10-1 is set according to the value of the pulse width command shown in FIG.

  The other drive circuits 10-2 to 10-N are simultaneously operated in a form according to the operation form of the drive circuit 10-1. At this time, as described above, since the switching signals for the respective drive circuits 10-1 to 10-N are sequentially shifted by Δt, the ripple frequency of the current flowing through the reactor L10 is increased. That is, when the phases of the switching signals for the drive circuits 10-1 to 10-N match, the ripple frequency matches the carrier frequency, but the drive circuits 10-1 to 10-N By setting the phase difference, the ripple frequency rises to a frequency that is N times the carrier frequency.

As is well known, the switching loss of the switch element decreases as the switching frequency decreases. On the other hand, it is necessary to use a reactor having a large capacity, that is, a large reactor, as the ripple frequency is lowered.
According to the power adjustment device according to the above-described embodiment, for example, when the number N of loads is 6 and the conventionally applied carrier frequency is 18 kHz, the carrier frequency may be reduced to 3 kHz (18/6 kHz). The ripple frequency is maintained at 18 kHz. Therefore, it is possible to reduce the switching loss of the switching elements S15 and S16 of the drive circuit 10-1 without increasing the size of the reactor L10. That is, for example, when the carrier frequency is reduced from 18 kHz to 3 kHz as described above, the switching loss can be reduced to about 1/3.
FIG. 4 shows the switching loss when the carrier frequency is 18 kHz by a dotted line, and shows the switching loss when the carrier frequency is 3 kHz by a solid line. This loss characteristic is obtained when the number N of loads is 6 and the capacity thereof is 100 kW.

  The operation of the bridge circuit 10 and the drive circuits 10-1 to 10-N has been described above. However, the bridge circuit 20 and the drive circuits 20-1 to 20-N also operate according to the above.

FIG. 5 shows a power adjustment device applied to the single-phase AC power supply 4. The power adjustment apparatus includes a bridge circuit 1 and drive circuits 1-1 and 1-2 combined with the bridge circuit 1.
The bridge circuit 1 includes a bridge circuit composed of diodes D1 to D4 and switching elements S1 to S4 connected in reverse parallel to the diodes D1 to D4, respectively, and one input terminal (a common connection point of the diodes D1 and D2). Is connected to one output terminal of the single-phase AC power supply 4 via the reactor L1, and the other input terminal (common connection point of the diodes D13 and D14) is connected to the other output terminal of the power supply 4. .

The drive circuit 1-1 includes a pair of switching elements S5 and S6 connected in series, and diodes D5 and D6 connected in reverse parallel to the switching elements S5 and S6, respectively. The same applies to the drive circuit 1-2. The drive circuits 1-1 and 1-2 are connected in parallel between the line 2 connected to the positive output terminal of the bridge circuit 1 and the line 3 connected to the negative output terminal.
One end of each of the loads R1-1 and R1-2 is connected to the output terminals of the drive circuits 1-1 and 1-2 (common connection point of the switching elements S5 and S6), and the other end of the loads R1-1 and R1-2 It is connected to the other output terminal.
Between each output terminal of the power supply 4, the capacitor C1 which comprises a filter with the reactor L1 is connected.

  The switching elements S1 to S4 of the bridge circuit 1 are turned on and off by switching signals corresponding to the switching signals shown in (e) to (h) of FIG. The switching elements S5 and S6 of the drive circuit 1-1 are turned on and off by switching signals corresponding to the switching signals shown in (i) and (j) of FIG. 3, and the switching elements S5 and S6 of the drive circuit 1-2 are turned on. These are turned on and off by switching signals corresponding to the switching signals shown in (k) and (l) of FIG. Therefore, also in the power adjustment apparatus shown in FIG. 5, the switching loss can be reduced similarly to the power adjustment apparatus shown in FIG. 5 includes two drive circuits 1-1 and 1-2. Of course, three or more drive circuits can be provided.

The present invention is not limited to the above-described embodiment, and includes various modifications. That is, the number of the drive circuits 10-1, 10-2,... And the drive circuits 20-1, 20-2,. However, it is desirable that the loads (capacities) on the drive circuits 10-1, 10-2,... And the loads (capacities) on the drive circuits 20-1, 20-2,. . 2, the switching signal for the drive circuits 10-1, 10-2,... And the switching signal for the drive circuits 20-1, 20-2,. However, it is also possible to form the former switching signal and the latter switching signal using individual PWM carrier signals having different frequencies. However, in this case, it is desirable to select the frequency of each PWM carrier signal so as not to cause a beat phenomenon.
Are different from the number of drive circuits 10-1, 10-2,... And the number of drive circuits 20-1, 20-2,. , The switching signal mutual shift time (see Δt in FIG. 3) for the drive circuits 10-1, 10-2,... And the switching signals for the drive circuits 20-1, 20-2,. The mutual shift time is different.
Furthermore, the loads R10-1 to R10-N and the loads R20-1 to R20-N shown in FIG. 1 are not limited to the heaters described above.

DESCRIPTION OF SYMBOLS 1,10 Bridge circuit 1-1, 1-2 Drive circuit 10-1 to 10-N, 20-1 to 20-N Drive circuit D1-D4, D5, D6 Diode D11-D14, D15, D16 Diode S1-S4 , S5, S6 switching elements S11-S14, S15, S16 switching elements R1-1 to R1-2 loads R10-1 to R10-N, R20-1 to R20-N loads L1, L10, L20 reactors C1, C10, C20 Capacitors 4, 14 AC power supply 15 Phase detection circuit 16 Switching signal generation circuit

Claims (6)

A first bridge circuit in which one input terminal is connected to a first output terminal of a three-phase AC power supply via a first reactor, and the other input terminal is connected to a second output terminal of the three-phase AC power supply When,
A plurality of first drive circuits connected in parallel between the output terminals of the first bridge circuit;
A second bridge in which one input terminal is connected to a third output terminal of the three-phase AC power supply through a second reactor, and the other input terminal is connected to a second output terminal of the three-phase AC power supply Circuit,
A plurality of second drive circuits connected in parallel between the output terminals of the second bridge circuit;
A first capacitor connected between the first and second output terminals of the three-phase AC power supply and constituting a filter together with the first reactor;
A second capacitor connected to a connection between the second and third output terminals of the three-phase AC power source and constituting a filter together with the second reactor;
Switching signal generating means for generating a switching signal,
The first and second bridge circuits include diodes connected in a bridge and switching elements connected in reverse parallel to the diodes, respectively.
The first and second drive circuits each have a pair of switching elements connected in series, and diodes connected in antiparallel to these switching elements,
The switching signal generating means includes a first switching signal for turning on / off each switching element of the first bridge circuit based on the polarity of the AC voltage between the first and second output terminals of the three-phase AC power supply; A second switching signal for turning on / off each switching element of the second bridge circuit based on the polarity of the AC voltage between the second and third output terminals of the three-phase AC power supply; and the plurality of first drives Generating a pulse width modulated third switching signal for turning on / off each switching element of the circuit and a pulse width modulated fourth switching signal for turning on / off each switching element of the plurality of second drive circuits; And the supply timing of the third switching signal to the plurality of first drive circuits is related to the third switching signal. The period of the carrier signal of the pulse width modulation is sequentially shifted by the time divided by the number of the first drive circuits, and the supply timing of the fourth switching signal to the plurality of second drive circuits is changed to the fourth It is configured to sequentially shift the period of the carrier signal of the pulse width modulation related to the switching signal by the time divided by the number of the second drive circuits,
The first and second drive circuits have different numbers.
An electric power adjustment apparatus, wherein an individual load is connected to each of the plurality of first drive circuits and the plurality of second drive circuits.   2. The power adjustment device according to claim 1, wherein IGBTs are used as switching elements of the first and second bridge circuits and switching elements of the first and second drive circuits.   The power adjustment apparatus according to claim 1, wherein the load is a heater for heat treatment in a semiconductor manufacturing apparatus. A first bridge circuit in which one input terminal is connected to a first output terminal of a three-phase AC power supply via a first reactor, and the other input terminal is connected to a second output terminal of the three-phase AC power supply When,
A plurality of first drive circuits connected in parallel between the output terminals of the first bridge circuit;
A second bridge in which one input terminal is connected to a third output terminal of the three-phase AC power supply through a second reactor, and the other input terminal is connected to a second output terminal of the three-phase AC power supply Circuit,
A plurality of second drive circuits connected in parallel between the output terminals of the second bridge circuit;
A first capacitor connected between the first and second output terminals of the three-phase AC power supply and constituting a filter together with the first reactor;
A second capacitor connected to a connection between the second and third output terminals of the three-phase AC power source and constituting a filter together with the second reactor;
Switching signal generating means for generating a switching signal,
The first and second bridge circuits include diodes connected in a bridge and switching elements connected in reverse parallel to the diodes, respectively.
The first and second drive circuits each have a pair of switching elements connected in series, and diodes connected in antiparallel to these switching elements,
The switching signal generating means includes a first switching signal for turning on / off each switching element of the first bridge circuit based on the polarity of the AC voltage between the first and second output terminals of the three-phase AC power supply; A second switching signal for turning on / off each switching element of the second bridge circuit based on the polarity of the AC voltage between the second and third output terminals of the three-phase AC power supply; and the plurality of first drives Generating a pulse width modulated third switching signal for turning on / off each switching element of the circuit and a pulse width modulated fourth switching signal for turning on / off each switching element of the plurality of second drive circuits; And said
The supply timing of the third switching signal to a plurality of first drive circuits is equal to the time obtained by dividing the period of the carrier signal of the pulse width modulation related to the third switching signal by the number of the first drive circuits. The supply timing of the fourth switching signal to the plurality of second drive circuits is sequentially shifted, and the period of the carrier signal of the pulse width modulation related to the fourth switching signal is the number of the second drive circuits. It is configured to sequentially shift by the time divided by
The frequency of the carrier signal for pulse width modulation related to the third switching signal is different from the frequency of the carrier signal for pulse width modulation related to the fourth switching signal,
An electric power adjustment apparatus, wherein an individual load is connected to each of the plurality of first drive circuits and the plurality of second drive circuits. The power adjustment device according to claim 4, wherein IGBTs are used as switching elements of the first and second bridge circuits and switching elements of the first and second drive circuits. The power adjustment apparatus according to claim 4, wherein the load is a heater for heat treatment in a semiconductor manufacturing apparatus.

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