Motor controller, washing machine, and motor control method

1. A motor controller, comprising:

an output voltage modulator that outputs sinusoidally-modulated voltage for driving a motor;

a modulation factor specifier allowing specification of a modulation factor greater than 1.0 for the output voltage;

a current detector that detects a current flowing in the motor; and

a field-oriented controller that divides the current detected by the current detector into a d-axis current component and a q-axis current component and that conforms each of the components to a command current produced based on a command rotational speed;

a rotational position estimator that estimates motor rotational speed and rotor rotational position for use by the field-oriented controller;

wherein the rotational position estimator includes a filter that smoothes a d-axis induced voltage obtained during the estimation, and the motor rotational speed and the rotor, rotational position are estimated based on the d-axis induced voltage smoothed by the filter.

2. The motor controller of claim 1 , wherein the filter variably specifies a constant for determining a cutoff frequency based on the modulation factor specified by the modulation factor specifier.

3. The motor controller of claim 1 , wherein the filter variably specifies a constant for determining a cutoff frequency based on a change rate of the rotational speed estimated by the rotational position estimator.

4. The motor controller of claim 1 , wherein the filter is configured by an EMA (Exponential Moving Average) filter.

5. The motor controller of claim 4 , wherein the EMA filter includes a non-linear term.

6. The motor controller of claim 5 , wherein the non-linear term performs differential calculation on the rotational speed estimated by the rotational position estimator.

7. A washing machine, comprising:

an output voltage modulator that outputs sinusoidally-modulated voltage for driving a motor;

a modulation factor specifier allowing specification of a modulation factor greater than 1.0 for the output voltage;

a current detector that detects a current flowing in the motor; and

a field-oriented controller that divides the current detected by the current detector into a d-axis current component and a q-axis current component and that conforms each of the components with a command current produced based on a command rotational speed;

a rotational position estimator that estimates a motor rotational speed and a rotor rotational position for use by the field-oriented controller;

wherein the rotational position estimator includes a filter that smoothes a d-axis induced voltage obtained during the estimation, and the motor rotational speed and the rotor rotational position are estimated based on the d-axis induced voltage smoothed by the filter.

8. The washing machine of claim 7 , wherein the filter variably specifies a constant for determining a cutoff frequency based on a modulation factor specified by the modulation factor specifier.

9. The washing machine of claim 7 , wherein the filter variably specifies a constant for determining a cutoff frequency based on a change rate of the rotational speed estimated by the rotational position estimator.

10. The washing machine of claim 7 , wherein the filter is configured by an EMA (Exponential Moving Average) filter.

11. The washing machine of claim 10 , wherein the EMA filter includes a non-linear term.

12. The washing machine of claim 11 , wherein the non-linear term performs differential calculation on the rotational speed estimated by the rotational position estimator.

13. The washing machine of claim 7 , further comprising a compressor constituting a heat pump for generating warm air for laundry dry, the washing machine controlling a motor provided in the compressor.

14. A method of motor control, comprising:

executing an over-modulation control when driving a motor by outputting sinusoidally-modulated voltage, the output voltage being specified at a modulation factor greater than 1.0;

detecting a current flowing in the motor;

executing a field-oriented control that divides the detected current into a d-axis current component and a q-axis current component and that controls each component to conform with a command current produced based on a command rotational speed by utilizing an estimated motor rotational speed and an estimated rotor rotational position; wherein the motor rotational speed and the rotor rotational position are estimated based on a d-axis induced voltage produced during the estimation, the d-axis induced voltage being smoothed by filtering.

15. The method of claim 14 , wherein a constant for determining a cutoff frequency of the filter is variably specified based on the modulation factor.

16. The method of claim 14 , wherein a constant for determining a cutoff frequency of the filter is variably specified based on a change rate of the estimated rotational speed.

17. The method of claim 14 , wherein the filter is configured by an EMA (Exponential Moving Average) filter.

18. The method of claim 17 , wherein the EMA filter includes a non-linear term.

19. The method of claim 18 , wherein the non-linear term performs differential calculation of estimated rotational speed.