Motor drive device

A motor drive device comprising:

• a three-phase synchronous motor;
• a power conversion device configured to convert a DC voltage into a three-phase AC power of a given voltage and a given frequency through a switching operation of a plurality of semiconductor elements, and supply the three-phase AC power after conversion to the three-phase synchronous motor;
• a current detection circuit configured to detect a motor current of at least one phase of the three-phase synchronous motor;
• a voltage detection circuit configured to detect a voltage at a DC input side of the power conversion device;
• a rotational position detection circuit configured to detect a signal synchronized with a rotational position of the three-phase synchronous motor;
• a rotational speed detection circuit configured to detect a rotational speed of the three-phase synchronous motor;
• a voltage control circuit configured to provide an on/off command to the plurality of semiconductor elements in order for the power conversion device to apply a drive voltage of a given voltage and a given frequency to the three-phase synchronous motor;
• a plurality of phase adjustment circuits each configured to adjust a phase of the drive voltage;
• and
• a phase adjustment selection circuit configured to select one of calculation results of the plurality of phase adjustment circuits and output the selected calculation result to the voltage control circuit,
• wherein the plurality of phase adjustment circuits include:
• a first phase adjustment circuit configured to exert the advancing phase on a phase of the drive voltage in a case where a voltage detection value obtained by the voltage detection circuit exceeds a preset first threshold value;
• a second phase adjustment circuit configured to set, as an index, a ratio of a magnitude of the motor current obtained by the current detection circuit to a magnitude of the rotational speed obtained by the rotational speed detection circuit, and determine, on a basis of a magnitude of the index, the advancing phase or the delaying phase of the phase of the drive voltage;
• and
• a third phase adjustment circuit configured to evaluate a slope of the motor current obtained by the current detection circuit in accordance with the rotational position of the three-phase synchronous motor obtained by the rotational position detection circuit, and determine, on a basis of a result of evaluating the slope, the advancing phase or the delaying phase of the phase of the drive voltage, and
• the phase adjustment selection circuit selects control of the phase of the drive voltage based on a calculation result of the first phase adjustment circuit in a case where the voltage detection value obtained from the voltage detection circuit exceeds the first threshold value, and selects control of the phase of the drive voltage based on one of calculation results of the second and third phase adjustment circuits in a case where the voltage detection value is equal to or smaller than the first threshold value.