Motor drive device, compressor drive system, and refrigeration cycle system

1. A motor drive device that controls driving of an alternating-current motor connected to a mechanical device with periodic load torque pulsation by using dq rotating coordinates, the motor drive device comprising:

a power converter to convert a direct current voltage into an alternating current voltage on the basis of a voltage command, and output the alternating current voltage to the alternating-current motor;

a current detector to detect a phase current flowing to the alternating-current motor;

a sensor to specify a magnetic pole position and a rotational speed of the alternating-current motor;

control circuitry

to generate a d-axis current pulsation command on the basis of periodic q-axis current pulsation or a periodic q-axis current pulsation command, the d-axis current pulsation command being in synchronization with the q-axis current pulsation or the q-axis current pulsation command and preventing or reducing an increase or decrease in amplitude of the voltage command; and

to generate the voltage command that controls the phase current on the dq rotating coordinates, which rotate in synchronization with the magnetic pole position, by using the magnetic pole position, the rotational speed, the phase current, the q-axis current pulsation or the q-axis current pulsation command, and the d-axis current pulsation command, wherein

the control circuitry generates the d-axis current pulsation command such that a locus of a vector of the voltage command is maintained in a circumferential direction or a tangential direction of a voltage limit circle having a specified radius.

2. The motor drive device according to claim 1 , wherein

the control circuitry generates the d-axis current pulsation command on the basis of a result of multiplication of a tangent of an average value of a voltage advance angle and the q-axis current pulsation or the q-axis current pulsation command.

3. The motor drive device according to claim 1 , wherein

the control circuitry generates a q-axis current command that has a lower frequency than the q-axis current pulsation or the q-axis current pulsation command and controls an average speed of the alternating-current motor;

the control circuitry generates the q-axis current pulsation command that suppresses speed pulsation caused by the load torque pulsation; and

the control circuitry generates a d-axis current command that has a lower frequency than the d-axis current pulsation command and maintains the amplitude of the voltage command to be less than or equal to a specified value, wherein

the control circuitry generates the d-axis current pulsation command on the basis of the q-axis current pulsation command, the d-axis current pulsation command being in synchronization with the q-axis current pulsation command and preventing or reducing an increase or decrease in the amplitude of the voltage command, and

the control circuitry generates the voltage command using the magnetic pole position, the rotational speed, the phase current, the q-axis current command, the q-axis current pulsation command, the d-axis current pulsation command, and the d-axis current command.

4. The motor drive device according to claim 1 , wherein

the control circuitry selects and generates, to the control circuitry, the d-axis current pulsation command or a first value that can reduce a loss in the alternating-current motor on the basis of control of the control circuitry, wherein

the control unit control circuitry causes the d-axis current pulsation command selecting unit to output the first value when an output voltage of the power converter is under a maximum value.

5. The motor drive device according to claim 1 , wherein

the control circuitry calculates an offset correction amount with respect to the d-axis current pulsation command on the basis of the voltage command and a voltage limit value indicating a maximum voltage that can be output as the voltage command; and

adds the offset correction amount to the d-axis current pulsation command output from the control circuitry, and output a result of the addition.

6. A compressor drive system comprising the motor drive device according to claim 1 .

7. A refrigeration cycle system comprising the compressor drive system according to claim 6 .