Power conversion device

A power conversion device to which a DC power source which outputs DC voltage and an AC rotary machine having a first three-phase coil and a second three-phase coil are connected,

• the power conversion device comprising:
• a first power converter having a first high potential-side switching element and a first low potential-side switching element, and converting the DC voltage supplied from the DC power source into an AC voltage and applying the converted first AC voltage to the first three-phase coil;
• a second power converter having a second high potential-side switching element and a second low potential-side switching element, and converting the DC voltage supplied from the DC power source into an AC voltage and applying the converted second AC voltage to the second three-phase coil;
• and
• a control unit which respectively controls the first high potential-side switching element and the first low potential-side switching element, and the second high potential-side switching element and the second low potential-side switching element, wherein
• the control unit includes:
• a voltage command calculator which calculates a first three-phase voltage command for the first three-phase coil and a second three-phase voltage command for the second three-phase coil on the basis of a control command to the AC rotary machine, and outputs the calculated first three-phase voltage command and the second three-phase voltage command;
• an offset calculator which calculates a first three-phase application voltage to be applied to the first three-phase coil by adding a first offset voltage having a value equal to or lower than the DC voltage to each voltage command in the first three-phase voltage command input from the voltage command calculator, and outputs the calculated first three-phase application voltage, and also calculates a second three-phase application voltage to be applied to the second three-phase coil by adding a second offset voltage having a value equal to or lower than the DC voltage to each voltage command in the second three-phase voltage command input from the voltage command calculator, and outputs the calculated second three-phase application voltage;
• and
• a switching signal generator which outputs a first switching signal to the first high potential-side switching element and the first low potential-side switching element by comparing the first three-phase application voltage input from the offset calculator with a first carrier wave signal, and outputs a second switching signal to the second high potential-side switching element and the second low potential-side switching element by comparing the second three-phase application voltage input from the offset calculator with a second carrier wave signal having the same carrier period as that of the first carrier wave signal and having a phase difference of 180° with respect to the first carrier wave signal;
• and
• the first power converter
• applies the converted first AC voltage to the first three-phase coil by controlling the first high potential-side switching element and the first low potential-side switching element in accordance with the first switching signal input from the switching signal generator;
• and
• the second power converter
• applies the converted second AC voltage to the second three-phase coil by controlling the second high potential-side switching element and the second low potential-side switching element in accordance with the second switching signal input from the switching signal generator;
• and
• when a vector comprising the output voltages of each phase in a case where the converted first AC voltage is output by the first power converter is taken to be a first voltage vector, and when the first voltage vector in a case where a first bus line current flowing into the first power converter is 0 is taken to be a zero vector, and when the first voltage vector in a case where the first bus line current flowing into the first power converter is not 0 is taken to be an effective vector, and when a vector comprising output voltages of each phase in a case where the converted second AC voltage is output by the second power converter is taken to be a second voltage vector, and when the second voltage vector in a case where the second bus line current flowing into the second power converter is 0 is taken to be a zero vector, and moreover when the second voltage vector in a case where the second bus line current flowing into the second power converter is not 0 is taken to be an effective vector,
• the first offset voltage and the second offset voltage are set in such a manner that a period during which one of the first power converter and the second power converter outputs the effective vector and the other thereof outputs the zero vector occurs in the carrier period of the first carrier wave signal and the second carrier wave signal.