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 a first AC voltage and applying the 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 a second AC voltage and applying the second AC voltage to the second three-phase coil;
• 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;
• a first current detector which detects a first three-phase current flowing in the first three-phase coil;
• and
• a second current detector which detects a second three-phase current flowing in the second three-phase coil, 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 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 from 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 from 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 a phase difference of 180° with respect to the first carrier wave signal;
• and
• when voltage commands in the first three-phase voltage command input from the voltage command calculator are taken to be a first maximum phase voltage command, a first medium phase voltage command, and a first minimum phase voltage command, in order of decreasing magnitude, and voltage commands in the second three-phase voltage command input from the voltage command calculator are taken to be a second maximum phase voltage command, a second medium phase voltage command and a second minimum phase voltage command, in order of decreasing magnitude, then
• the offset calculator,
• in accordance with a first differential value which is a difference between the first medium phase voltage command and the first minimum phase voltage command, wherein the first differential value is a first differential voltage value,
• executes a first calculation process for calculating the first three-phase application voltage by changing all of the voltage commands in the first three-phase voltage command by the same amount mutually in such a manner that the voltage applied to a phase corresponding to the minimum phase voltage command becomes equal to a minimum value of the first carrier wave signal, wherein the minimum value is a minimum voltage value, when the first differential value is equal to or greater than a previously established reference voltage threshold value;
• executes a second calculation process for calculating the first three-phase application voltage from the first three-phase voltage command in such a manner that the voltage applied to a phase corresponding to the first minimum phase voltage command is equal to or greater than a reference voltage lower limit value, which is a sum of the reference voltage threshold value and the minimum value of the first carrier wave signal, when the first differential value is less than the reference voltage threshold value, wherein the first switching signal is based on the first calculation process or the second calculation process;
• and
• in accordance with a second differential value which is a difference between the second medium phase voltage command and the second minimum phase voltage command, wherein the second differential value is a second differential voltage value;
• executes a third calculation process for calculating the second three-phase application voltage by changing all of the voltage commands of the second three-phase voltage command by the same amount mutually in such a manner that the voltage applied to a phase corresponding to the second minimum phase voltage command is equal to the minimum value of the second carrier wave signal, when the second differential value is equal to or greater than the reference voltage threshold value;
• and
• executes a fourth calculation process for calculating the second three-phase application voltage from the second three-phase voltage command in such a manner that the voltage applied to a phase corresponding to the second minimum phase voltage command is equal to or greater than the reference voltage lower limit value, when the second differential value is less than the reference voltage threshold value, wherein the second switching signal is based on the third calculation process or the fourth calculation process.