Low loss and anti-shoot-through pulse width modulated inverter controller

Claim 2

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to inhibit an ON signal to one switching element in order to keep said one switching element in the OFF state while any other switching element can repeat an ON or OFF state on the basis of the polarity of said output current command value; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element of the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier.

Claim 3

An inverter controller according to claim 1, wherein said inhibiting circuit comprises a circuit for operating in such a manner that, when said output current command value is positive, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the positive side of said DC power supply and inhibits the supply of said ON siganl to the switching element constituting the electric valve connected to the negative side of said DC power supply, whereas, when said output current command value is negative, said inhibiting circuit supplies said ON/OFF siganl to the switching element constituting the electric valve connected to the negative side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply.

Claim 4

An inverter controller according to claim 2, wherein said ON/OFF signal calculating means comprises: first timer circuit adapted to operate in such a manner that, when said output current command value changes from positive to negative, said first timer circuit inhibits the supply of the ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the positive side of said DC power supply, whereas, when said output current command value, changes from negative to positive, said first timer circuit inhibits the supply of the ON signal to the switching element constituting the electric value connected to the positive side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 5

An inverter controller according to claim 1, wherein said inhibiting circuit comprises a circuit for operating in such a manner that, when said output current command value exceeds a negative threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the positive side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply, whereas, when said output current command value is smaller than a positive threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the negative side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply.

Claim 6

An inverter controller according to claim 1, wherein said ON/OFF signal calculating means comprises: first timer circuit for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the positive side of said DC power supply; and second timer circuit for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 7

An inverter controller according to claim 1, wherein, when an operation mode in which said inhibiting circuit supplies said ON/OFF signal to any switching element other than said specific switching element shifts to an operation mode in which said inhibiting circuit supplies said ON/OFF signal to said specific switching element and inhibits the supply of the ON signal to any switching element other than said specific switching element on the basis of said output current command value, said inhibiting circuit inhibits the supply of said ON signal to said specific switching element for a predetermined period after the OFF signal has been supplied to any switching element other than said specific switching element.

Claim 8

An inverter controller according to claim 1, wherein said inhibiting circuit comprises a circuit for operating in such a manner that, when said output current command value exceeds a positive threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the positive side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply, whereas, when said output current command value is smaller than a negative threshold value, said inhibiting circuit supplies said ON/OFF siganl to the switching element constituting the electric valve connected to the negative side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply.

Claim 9

An inverter controller according to claim 7, wherein said inhibiting circuit inhibits the supply of the ON signal to all the switching elements when said output current command value is between the positive threshold value and the negative threshold value.

Claim 10

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; detecting means for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; an inhibiting circuit adapted to output a second ON/OFF signal which becomes ON when said output current command value is positive and which becomes OFF when said output current command value is negative and to inhibit an ON signal to one switching element in order to keep said one switching element in the OFF state while any other switching element can repeat an ON or OFF state on the basis of the polarity of said output current command value; a first AND gate for supplying the logical product of said first and second ON/OFF signals to the switching element constituting the electric valve connected to the positive side of said DC power supply; and a second AND gate for supplying the logical product of a signal obtained by inverting said first ON/OFF signal and a signal obtained by inverting said second ON/OFF signal to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 11

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; detecting means for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; an inhibiting circuit adapted to output a second ON/OFF signal which becomes ON when said output current command value is positive and which becomes OFF when said output current command value is negative and to inhibit an ON signal to one switching element in order to keep said one switching element in the OFF state while any other switching element can repeat an ON or OFF state on the basis of the polarity of said output current command value; a first AND gate for supplying the logical product of said first and second ON/OFF signals to the switching element constituting the electric valve connected to the positive side of said DC power supply; and a second AND gate for supplying the logical product of a signal obtained by inverting said first ON/OFF signal and a signal obtained by inverting said second ON/OFF signal to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 12

An inverter controller according to claim 9, wherein said current control amplifier calculates and outputs a first ON/OFF signal which becomes OFF when said output current rises and exceeds the upper limit of a predetermined range centering at said output current command value and which becomes ON when said output current lowers and becomes smaller than the lower limit of said predetermined range.

Claim 13

An inverter controller according to claim 9, wherein said current control amplifier comprises: a calculating circuit adapted to calculate a deviation of said output current from said output current command value and output a deviation signal; and a comparator with hysteresis which is supplied with said deviation signal as an input.

Claim 14

An inverter controller according to claim 9, further comprising: first timer circuit adapted to operate in such a manner that, when said output current command value changes from positive to negative, said first timer circuit inhibits the supply of the ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the positive side of said DC power supply, whereas, when said output current command value changes from negative to positive, said first timer circuit inhibits the supply of the ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 15

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; detecting means for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; an inhibiting circuit adapted to output a first ON/OFF signal which becomes ON when said output current command value exceeds a positive threshold value and which becomes OFF when said output current command value is smaller than the positive threshold value, and a second signal which becomes ON when said output current command value is smaller than a negative threshold value and which becomes OFF when said output current command value exceeds the negative threshold value and to inhibit an ON signal to one switching element in order to keep said one switching element in the OFF state while any other switching element can repeat an ON or OFF state on the basis of the polarity of said output current command value; a first AND gate for supplying the logical product of said first and second ON/OFF signal and said first signal to the switching element constituting the electric valve connected to the positive side of said DC power supply; and a second AND gate for supplying the logical product of a signal obtained by inverting said first ON/OFF signal and said second signal to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 16

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; detecting means for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; an inhibiting circuit adapted to output a first ON/OFF signal which becomes ON when said output current command value exceeds a positive threshold value and which becomes OFF when said output current command value is smaller than the positive threshold value, and a second signal which becomes ON when said output current command value is smaller than a negative threshold value and which becomes OFF when said output current command value exceeds the negative threshold value and to inhibit an ON signal to one switching element in order to keep said one switching element in the OFF state while any other switching element can repeat an ON or OFF state on the basis of the polarity of said output current command value; a first AND gate for supplying the logical product of said first and second ON/OFF signal and said first signal to the switching element constituting the electric valve connected to the positive side of said DC power supply; and a second AND gate for supplying the logical product of a signal obtained by inverting said first ON/OFF signal and said second signal to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 17

An inverter controller according to claim 13, wherein said current control amplifier calculates and outputs a first ON/OFF signal which becomes OFF when said output current rises and exceeds the upper limit of a predetermined range centering at said output current command value and which becomes ON when said output current lowers and becomes smaller than the lower limit of said predetermined range.

Claim 18

An inverter controller according to claim 13, wherein said current control amplifier comprises: a calculating circuit adapted to calculate a deviation of said output current from said output current command value and output a deviation signal; and a comparator with hysteresis which is supplied with said deviation signal as an input.

Claim 19

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current detector for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; a NOT circuit adapted to invert and output said first ON/OFF signal; a signal inhibiting circuit adapted to output a first signal which becomes ON when said output current command is positive and which becomes OFF when said output current command is negative, and a second signal which becomes OFF when said output current command value is positive and which becomes ON when said output current command value is negative; a first AND gate having three input terminals and connected in such a manner that said first ON/OFF signal and said first signal are respectively input to two of said input terminals; a second AND gate having three input terminals and connected in such a manner that the output signal from said NOT circuit and said second signal are respectively input to two of said input terminals; a first timer connected between the output terminal of said first AND gate and the remaining input terminal of said second AND gate and adapted to output an ON signal when a predetermined period of time has elapsed after an OFF signal has been output from said first AND gate; a second timer connected between the output terminal of said second AND gate and the remaining input terminal of said first AND gate and adapted to output an ON signal when a predetermined period of time has elapsed after an OFF signal has been output from said second AND gate; and a driver adapted to supply the output signal from said first AND gate to the switching element constituting the electric valve connected to the positive side of said DC power supply, and the output signal from said second AND gate to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 20

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current detector for detecting an output current of said inverter; a current control amplifier adapted to calculate a first ON/OFF signal for ON/OFF controlling said switching elements on the basis of said output current command value and said output current, and output said first ON/OFF signal; a NOT circuit adapted to invert and output said first ON/OFF signal; a signal inhibiting circuit adapted to output a first signal which becomes ON when said output current command is positive and which becomes OFF when said output current command is negative, and a second signal which becomes OFF when said output current command value is positive and which becomes ON when said output current command value is negative; a first AND gate having three input terminals and connected in such a manner that said first ON/OFF signal and said first signal are respectively input to two of said input terminals; a second AND gate having three input terminals and connected in such a manner that the output signal from said NOT circuit and said second signal are respectively input to two of said input terminals; a first timer connected between the output terminal of said first AND gate and the remaining input terminal of said second AND gate and adapted to output an ON signal when a predetermined period of time has elapsed after an OFF signal has been output from said first AND gate; a second timer connected between the output terminal of said second AND gate and the remaining input terminal of said first AND gate and adapted to output an ON signal when a predetermined period of time has elapsed after an OFF signal has been output from said second AND gate; and a driver adapted to supply the output signal from said first AND gate to the switching element constituting the electric valve connected to the positive side of said DC power supply, and the output signal from said second AND gate to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 21

An inverter controller according to claim 16, wherein said signal inhibiting circuit outputs a first signal which becomes ON when said output current command value exceeds a positive threshold value and which becomes OFF when said output current command value is smaller than the positive threshold value, and a second signal which becomes ON when said output current command value is smaller than a negative threshold value and which becomes OFF when said output current command value exceeds the negative threshold value.

Claim 22

An inverter controller according to claim 16, wherein said current control amplifier calculates and outputs a first ON/OFF signal which becomes OFF when said output current rises and exceeds the upper limit of a predetermined range centering at said output current command value and which becomes ON when said output current lowers and becomes smaller than the lower limit of said predetermined range.

Claim 23

An inverter controller according to claim 16, wherein said current control amplifier comprises: a calculating circuit adapted to calculate a deviation of said output current from said output current command value and output a deviation signal; and a comparator with hysteresis which is supplied with said deviation signal as an input.

Claim 24

An inverter controller according to claim 16, wherein said first timer comprises: a monostable multivibrator connected at the input terminal thereof to the output terminal of said first AND gate; and a NOR gate connected at one input terminal thereof to the output terminal of said monostable multivibrator and at the other input terminal thereof to the output terminal of said first AND gate, the output terminal of said NOR gate being connected to the remaining input terminal of said second AND gate.

Claim 25

An inverter controller according to claim 16, wherein said second timer comprises: a monostable multivibrator connected at the input terminal thereof to the output terminal of said second AND gate; and a NOR gate connected at one input terminal thereof to the output terminal of said monostable multivibrator and at the other input terminal thereof to the output terminal of said second AND gate, the output terminal of said NOR gate being connected to the remaining input terminal of said first AND gate.

Claim 26

An inverter controller according to claim 16, wherein said signal inhibiting circuit is constituted by a comparator adapted to make comparison between said output current command value and a predetermined value and output a signal representing the result of the comparison.

Claim 27

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of the polarity of said output current command value; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element on the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier, said ON/OFF signal calculating means comprising: first inhibiting means for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the positive side of said DC power supply; and second inhibiting means for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 28

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of the polarity of said output current command value; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element on the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier, said ON/OFF signal calculating means comprising: first inhibiting means for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the positive side of said DC power supply; and second inhibiting means for inhibiting the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply for a predetermined period after the OFF signal has been supplied to the switching element constituting the electric valve connected to the negative side of said DC power supply.

Claim 29

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of said output current command value, said inhibiting circuit comprising a circuit for operating in such a manner that, when said output current command value exceeds a positive threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the positive side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply, whereas, when said output current command value is smaller than a negative threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connnected to the negative side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply, and in such a manner that said inhibiting circuit inhibits the supply of the ON signal to all the switching elements when said output current command value is between the positive threshold value and the negative threshold value; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element on the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier.

Claim 30

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of said output current command value, said inhibiting circuit comprising a circuit for operating in such a manner that, when said output current command value exceeds a positive threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connected to the positive side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the negative side of said DC power supply, whereas, when said output current command value is smaller than a negative threshold value, said inhibiting circuit supplies said ON/OFF signal to the switching element constituting the electric valve connnected to the negative side of said DC power supply and inhibits the supply of said ON signal to the switching element constituting the electric valve connected to the positive side of said DC power supply, and in such a manner that said inhibiting circuit inhibits the supply of the ON signal to all the switching elements when said output current command value is between the positive threshold value and the negative threshold value; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element on the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier.

Claim 31

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of the polarity of said output current command value such that, when an operation mode in which said inhibiting circuit supplies said ON/OFF signal to any switching element other than said specific switching element shifts to an operation mode in which said inhibiting circuit supplies said ON/OFF signal to said specific switching element and inhibits the supply of the ON signal to any switching element other than said specific switching element on the basis of said output current command value, said inhibiting circuit inhibits the supply of said ON signal to said specific switching element for a predetermined period after the OFF signal has been supplied to any switching element other than said specific switching element; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element of the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier.

Claim 32

An inverter controller for controlling an inverter having a series circuit formed by series-connecting electric valves each formed by connecting a switching element and a diode in anti-parallel with each other, the node between said electric valves being connected to a load, one end of said series circuit being connected to the positive side of a DC power supply, and the other end of said series circuit being connected to the negative side of said DC power supply, comprising: command value calculating means for calculating an output current command value to obtain a desired current value through said load; a current control amplifier for calculating an ON/OFF signal on the basis of said output current command value; an inhibiting circuit for calculating an inhibiting signal to turn one switching element to OFF and any other switching element to ON/OFF on the basis of the polarity of said output current command value such that, when an operation mode in which said inhibiting circuit supplies said ON/OFF signal to any switching element other than said specific switching element shifts to an operation mode in which said inhibiting circuit supplies said ON/OFF signal to said specific switching element and inhibits the supply of the ON signal to any switching element other than said specific switching element on the basis of said output current command value, said inhibiting circuit inhibits the supply of said ON signal to said specific switching element for a predetermined period after the OFF signal has been supplied to any switching element other than said specific switching element; and ON/OFF signal calculating means for supplying an OFF signal to one switching element and an ON/OFF signal to any other switching element of the basis of said inhibiting signal output from said inhibiting circuit and said ON/OFF signal output from said current control amplifier.