Motor driving device and method for measuring phase current in motor driving device
The present invention relates to a motor driving device and a method for measuring a phase current in a motor driving device, and specifically relates to a technique of measuring three phase currents of a three-phase brushless motor using a current sensor for measuring the DC bus current in the inverter. The control unit according to the present invention shifts a pulse phase of a PWM pulse such that pulse phases of the three phase PWM pulses in a first PWM cycle of the PWM control differ from those in a second PWM cycle of the PWM control, and measures the three phase currents from the output of the current sensor in these two first and second PWM cycles. The control unit calculates an offset error of the current sensor from these three phase current measurements and learns a correction value used for performing offset correction on the electric-current measurement.
1. A motor driving device comprising:
an inverter configured to supply AC power to a three-phase brushless motor;
a current sensor configured to measure DC bus current in the inverter; and
a control unit configured to
receive at least one output of the current sensor and perform PWM control on the inverter;
determine each of three phase currents from a respective measured output of the current sensor when a combination of on and off of three phase PWM pulses is a predetermined combination;
perform pulse shifting to shift a pulse phase of a PWM pulse such that pulse phases of the three phase PWM pulses in a first PWM cycle of the PWM control differ from those in a second PWM cycle of the PWM control; and
determine the three phase currents from respective outputs of the current sensor in the two first and second PWM cycles,
wherein the control unit is configured to determine one or two phase currents in a last half of the first PWM cycle, and to determine a remaining two or one phase currents in a first half of the second PWM cycle immediately after the first PWM cycle.
2. A motor driving device according to claim 1 , comprising:
an inverter configured to supply AC power to a three-phase brushless motor;
a current sensor configured to measure DC bus current in the inverter; and
a control unit configured to
receive at least one output of the current sensor and perform PWM control on the inverter;
determine each of three phase currents from a respective measured output of the current sensor when a combination of on and off of three phase PWM pulses is a predetermined combination;
perform pulse shifting to shift a pulse phase of a PWM pulse such that pulse phases of the three phase PWM pulses in a first PWM cycle of the PWM control differ from those in a second PWM cycle of the PWM control; and
determine the three phase currents from respective outputs of the current sensor in the two first and second PWM cycles,
wherein the control unit is further configured to
perform pulse shifting to shift a pulse phase of a PWM pulse and determine the three phase currents from the respective measured outputs of the current sensor in one PWM cycle of the PWM control; and
activate sensing in accordance with whether a condition for activating the sensing is satisfied.
3. The motor driving device according to claim 1 , wherein the control unit is configured to perform pulse shifting to delay a pulse phase of a PWM pulse in the first PWM cycle, and perform pulse shifting to advance a pulse phase of a PWM pulse in the second PWM cycle.
4. The motor driving device according to claim 1 , wherein the control unit is configured to perform offset correction on an electric-current measurement of the current sensor based on the three phase currents.
5. The motor driving device according to claim 2 , wherein the control unit is configured to perform offset correction on an electric-current measurement of the current sensor based on the three phase currents.
6. A method for measuring a phase current in a motor driving device including an inverter for supplying AC power to a three-phase brushless motor, and a current sensor for measuring DC bus current in the inverter, the inverter being controlled by PWM control, the method comprising:
a first step of performing pulse shifting to shift a pulse phase of a PWM pulse in a first PWM cycle of the PWM control to generate one or two phase current measurement periods for determining one or two phase currents in the first PWM cycle;
a second step of determining the one or two phase currents from at least one measured output of the current sensor in the one or two phase current measurement periods generated in the first PWM cycle;
a third step of performing pulse shifting to shift a pulse phase of a PWM pulse in a second PWM cycle of the PWM control to generate two or one phase current measurement periods for determining a remaining two or one phase currents in the second PWM cycle; and
a fourth step of determining the remaining two or one phase currents from the at least one measured output of the current sensor in the two or one phase current measurement periods generated in the second PWM cycle,
wherein
in the first step, pulse shifting to delay a pulse phase of a PWM pulse is performed in the first PWM cycle to generate one or two phase current measurement periods for determining one or two phase currents in a last half of the first PWM cycle, and
in the third step, pulse shifting to advance a pulse phase of a PWM pulse is performed in the second PWM cycle immediately after the first PWM cycle to generate two or one phase current measurement periods for determining a remaining two or one phase currents in a first half of the second PWM cycle.
7. The method for measuring a phase current in the motor driving device according to claim 6 , further comprising a fifth step of performing offset correction on an electric-current measurement of the current sensor based on the determined three phase currents.