Motor drive device and phase current detecting method for three-phase brushless motor

1. A motor drive device comprising:

an inverter configured to supply an AC power to a three-phase brushless motor;

a current sensor configured to detect a DC bus current of the inverter; and

a control unit configured to receive an output of the current sensor and PWM-control the inverter,

the motor drive device executing sinusoidal driving of the three-phase brushless motor,

wherein the control unit calculates a phase current for one phase, an absolute phase current value of which becomes maximum at a detection timing that is set once per PWM control cycle, from an output of the current sensor, sets a phase shift of an actual phase current waveform relative to a motor angle to be variable according to a d-axis voltage, a q-axis voltage, and a motor rotational speed, and then estimates phase currents for the remaining two phases based on a peak value of a phase current detected at each detection timing, a motor angle, and the phase shift.

2. The motor drive device according to claim 1 , wherein the control unit sets one phase, an absolute phase current value of which becomes maximum, based on a control duty of each phase.

3. The motor drive device according to claim 1 , wherein the control unit calculates the phase shift based on an angle formed by a resistance term and an interference term in a d-q axis voltage model of the three-phase brushless motor or an angle formed by a vector obtained by subtracting an induced voltage term from a motor voltage vector and a q-axis vector.

4. The motor drive device according to claim 1 , wherein the control unit corrects the phase shift so as to decrease a current deviation at the time of switching a phase current for one phase between a detection value from the current sensor and an estimation value.

5. The motor drive device according to claim 1 , wherein the control unit calculates the phase shift based on a detection value from the current sensor obtained at the time of switching a phase current for one phase between the detection value from the current sensor and an estimation value, and the peak value.

6. A phase current detecting method for a three-phase brushless motor, which is to determine a phase current of each phase in the three-phase brushless motor that is sinusoidal-driven by PWM-controlling an inverter, based on an output of a current sensor for detecting a DC bus current of the inverter, the method comprising the steps of:

setting one detection timing for detecting a phase current for one phase, an absolute phase current value of which becomes maximum, per PWM control cycle;

setting a phase current detection value based on an output of the current sensor at the detection timing;

determining a peak value of the phase current detection value;

detecting a motor angle;

setting a phase shift of an actual phase current waveform relative to the motor angle to be variable according to a d-axis voltage, a q-axis voltage, and a motor rotational speed;

calculating a phase current estimation value based on the peak value, the motor angle, and the phase shift; and

assigning the phase current detection value as a phase current value for one phase, and assigning phase current estimation values to the remaining two phases.

7. The phase current detecting method for a three-phase brushless motor according to claim 6 , wherein in the step of setting the phase shift, the phase shift is determined based on an angle formed by a resistance term and an interference term in a d-q axis voltage model of the three-phase brushless motor and an angle formed by a vector obtained by subtracting an induced voltage term from a motor voltage vector and a q-axis vector.