Inverter control device and motor drive system

1. An inverter control device comprising:

an inverter main circuit;

a current detector configured to detect a current of an output line of the inverter main circuit;

a startup controller comprising a rotational phase angle estimator configured to calculate, based on a current response value detected by the current detector, a value corresponding to a rotational phase angle of a motor connected to the inverter main circuit in a stationary reference frame, and a rotational speed estimator configured to calculate a value corresponding to a rotational speed of the motor by using the value corresponding to the rotational phase angle when the inverter main circuit is started; and

a regular time controller configured to calculate, with the value corresponding to the rotational speed as an initial value, an estimated rotational phase angle of the motor in a rotating reference frame,

wherein the rotational speed estimator of the startup controller is configured to count a number of times the value corresponding to the rotational phase angle crosses zero in a first predetermined period, set the value corresponding to the rotational speed to zero when the counted value is less than a predetermined value, and calculate, when the counted value is at or above the predetermined value, the value corresponding to the rotational speed based on a value obtained by counting the number of times the value corresponding to the rotational phase angle crosses zero in a second predetermined period longer than the first predetermined period, and the second predetermined period.

2. The inverter control device according to claim 1 , further comprising a high frequency voltage command generator configured to generate a high frequency voltage command in the stationary reference frame.

3. The inverter control device according to claim 1 , further comprising:

a high frequency current command generator configured to generate a high frequency current command in the stationary reference frame to be supplied to the motor; and

a current controller configured to calculate a high frequency voltage command based on the high frequency current command and the current response value.

4. The inverter control device according to claim 3 , wherein the rotational phase angle estimator is configured to calculate the value corresponding to the rotational phase angle of the motor based on the high frequency current command and the high frequency voltage command instead of the current response value.

5. The inverter control device according to claim 1 , further comprising a PWM generator configured to generate a gate command to the inverter main circuit for causing a harmonic current to be output from the inverter main circuit and the high frequency voltage command based on the gate command.

6. The inverter control device according to claim 1 , wherein the regular time controller comprises a vector converter configured to perform, based on the estimated rotational phase angle in the rotating reference frame, vector conversion of a three-phase fixed coordinate and a rotational coordinate, and wherein the vector converter performs, with the estimated rotational phase angle in the rotating reference frame set to zero when starting the inverter main circuit, a vector conversion of the stationary reference frame.

7. The inverter control device according to claim 2 , wherein the regular time controller comprises a vector converter configured to perform, based on the estimated rotational phase angle in the rotating reference frame, vector conversion of a three-phase fixed coordinate and a rotational coordinate, and wherein the vector converter performs, with the estimated rotational phase angle in the rotating reference frame set to zero when starting the inverter main circuit, a vector conversion of the stationary reference frame.

8. The inverter control device according to claim 3 , wherein the regular time controller comprises a vector converter configured to perform, based on the estimated rotational phase angle in the rotating reference frame, vector conversion of a three-phase fixed coordinate and a rotational coordinate, and wherein the vector converter performs, with the estimated rotational phase angle in the rotating reference frame set to zero when starting the inverter main circuit, a vector conversion of the stationary reference frame.

9. The inverter control device according to claim 5 , wherein the regular time controller comprises a vector converter configured to perform, based on the estimated rotational phase angle in the rotating reference frame, vector conversion of a three-phase fixed coordinate and a rotational coordinate, and wherein the vector converter performs, with the estimated rotational phase angle in the rotating reference frame set to zero when starting the inverter main circuit, a vector conversion of the stationary reference frame.

10. A motor drive system comprising:

the inverter control device according to claim 1 , and

a synchronous reluctance motor as the motor.

11. A motor drive system comprising:

the inverter control device according to claim 2 , and

a synchronous reluctance motor as the motor.

12. A motor drive system comprising:

the inverter control device according to claim 3 , and

a synchronous reluctance motor as the motor.

13. A motor drive system comprising:

the inverter control device according to claim 5 , and

a synchronous reluctance motor as the motor.