Motor drive device and motor system

Patent metadata

Field	Value
Publication number	US-10581364-B2
Application number	US-201816189183-A
Country	US
Kind code	B2
Filing date	Nov 13, 2018
Priority date	Dec 26, 2017
Publication date	Mar 3, 2020
Grant date	Mar 3, 2020

Abstract

An output control unit controls a drive terminal for a BEMF detection object phase to a high-impedance state in a mask term. A BEMF detection unit detects a voltage of the drive terminal for the detection object phase when a center tap voltage is set as a reference as BEMF in a PWM on-term for remaining two phases per PWM period in the mask term and asserts a zero-crossing signal when the voltage is reduced to zero. A PWM fixing unit fixes the remaining two phases to the PWM on-terms in a first term from a predetermined timing after an amplitude level of BEMF becomes smaller than a BEMF threshold amplitude to assertion of the zero-crossing signal. The BEMF detection unit continuously detects BEMF in the first term.

First claim

What is claimed is:

1. A motor drive device comprising:
drive terminals for three phases which drive a three-phase motor;
a three-phase driver which includes high-side transistors for three phases which are respectively coupled between the drive terminals for three phases and a high-potential-side power supply voltage and low-side transistors for three phases which are respectively coupled between the drive terminals for three phases and a low-potential-side power supply voltage;
an output control unit which, in a state where both of the high-side transistor and the low-side transistor for a first phase which is one phase in the three phases are controlled to off-states, controls the high-side transistor and the low-side transistor for at least one phase in a second phase and a third phase which are remaining two phases with PWM signals in a mask term;
a back electromotive voltage detection unit which detects a drive terminal voltage of the drive terminal for the first phase when a center tap voltage of the three-phase motor is set as a reference as a back electromotive voltage in a PWM on-term that both of the high-side transistor for the second phase and the low-side transistor for the third phase are turned on and asserts a zero-crossing signal in a case where the back electromotive voltage is reduced to zero per PWM period included in the mask term; and
a PWM fixing unit which monitors the back electromotive voltage and the zero-crossing signal and fixes the high-side transistor for the second phase and the low-side transistor for the third phase to on-states regardless of the PWM period in a first term from a predetermined timing after an amplitude level of the back electromotive voltage becomes smaller than a predetermined threshold amplitude to assertion of the zero-crossing signal,
wherein the back electromotive voltage detection unit continuously detects the back electromotive voltage in the first term.

2. The motor drive device according to claim 1 ,
wherein the PWM fixing unit has
a first analog-to-digital converter which converts the back electromotive voltage to a digital value and
a first digital comparator which compares the digital value from the first analog-to-digital converter with a digital value which corresponds to the predetermined threshold amplitude.

3. The motor drive device according to claim 2 ,
wherein the PWM fixing unit further has a PWM fixing sequencer which receives a result of comparison by the first digital comparator and the zero-crossing signal and generates a PWM fixing signal which reaches an assertion level in the first term.

4. The motor drive device according to claim 2 ,
wherein the PWM fixing unit further has a second analog-to-digital converter which converts a current flowing into the three-phase motor into a digital value per the PWM period, and
wherein the first analog-to-digital converter is commonized with the second analog-to-digital converter by providing two not-overlapping conversion terms in a term of the same length as the PWM period.

5. The motor drive device according to claim 1 ,
wherein the PWM fixing unit has
a digital-to-analog converter which receives the predetermined threshold amplitude as a digital value and converts the digital value into an analog value and
an analog comparator which compares the back electromotive voltage with the analog value from the digital-to-analog converter.

6. The motor drive device according to claim 1 ,
wherein the predetermined threshold amplitude is determined to a magnitude of “3×Dbemf” or less when a change mount of the back electromotive voltage generated in one PWM period is denoted by “Dbemf”.

7. The motor drive device according to claim 6 ,
wherein the predetermine threshold amplitude is set from the outside of the device in advance.

8. The motor drive device according to claim 6 ,
wherein the PWM fixing unit has a threshold value setting part which detects the change amount of the back electromotive voltages among the plurality of PWM periods on the basis of the back electromotive voltage that the back electromotive voltage detection unit detects per the PWM period in the mask term and determines the predetermined threshold amplitude on the basis of the detected change amounts concerned.

9. The motor drive device according to claim 1 ,
wherein the back electromotive voltage detection unit has
a differential amplification circuit which amplifies the drive terminal voltage of the drive terminal for the first phase with the center tap voltage being set as the reference,
a sample and hold circuit which samples and holds an output voltage from the differential amplification circuit in accordance with a sampling signal and
a comparator which generates the zero-crossing signal by comparing the voltage held in the sample and hold circuit with a zero voltage and
wherein the sampling signal is asserted in the PWM on-term per the PWM period in the terms except the first term in the mask term and is continuously asserted in the first term.

10. The motor drive device according to claim 9 ,
wherein the back electromotive voltage detection unit further has
a low-pass filter which filters and then transmits the voltage held in the sample and hold circuit to the comparator and
a bypass switch which bypasses the low-pass filter when controlled to the on-state,
wherein the PWM fixing unit is made to be switchable between validity and invalidity, and
wherein at start-up of the three-phase motor, the PWM fixing unit is invalidated and the bypass switch is controlled to the off-state and at steady rotation of the three-phase motor, the PWM fixing unit is validated and the bypass switch is controlled to the on-state.

11. The motor drive device according to claim 1 , further comprising:
a PLL control loop which generates a conduction-use timing signal used for conduction of the three-phase motor and conducts feedback-control of a phase or a frequency of the conduction-use timing signal in such a manner that an assertion timing of the zero-crossing signal is maintained at a specified timing in the mask term which is determined on the basis of the conduction-use timing signal.

12. A motor system comprising:
a disk which stores data;
a three-phase motor which rotates the disk; and
a motor drive device which drives the three-phase motor,
wherein the motor drive device has
drive terminals for three phases which drive a three-phase motor,
a three-phase driver which includes high-side transistors for three phases which are respectively coupled between the drive terminals for three phases and a high-potential-side power supply voltage and low-side transistors for three phases which are respectively coupled between the drive terminals for three phases and a low-potential-side power supply voltage,
an output control unit which, in a state where both of the high-side transistor and the low-side transistor for a first phase which is one phase in the three phases are controlled to off-states, controls the high-side transistor and the low-side transistor for at least one phase in a second phase and a third phase which are remaining two phases with PWM signals in a mask term,
a back electromotive voltage detection unit which detects a drive terminal voltage of the drive terminal for the first phase when a center tap voltage of the three-phase motor is set as a reference as a back electromotive voltage in a PWM on-term that both of the high-side transistor for the second phase and the low-side transistor for the third phase are turned on and asserts a zero-crossing signal in a case where the back electromotive voltage is reduced to zero per PWM period included in

Assignees

• Renesas Electronics Corp

Inventors

• Kurosawa Minoru
• Itagaki Kichiya

Classifications

• G11B19/2009

  Turntables, hubs and motors for disk drives; Mounting of motors in the drive (means for clamping of disk to turntable G11B17/022 and subgroups) · CPC title

• H02P6/182

  using back-emf in windings · CPC title

• H02P27/08 Primary

  with pulse width modulation · CPC title

• H02P2209/09

  PWM with fixed limited number of pulses per period · CPC title

• H02M7/53875 Primary

  with analogue control of three-phase output · CPC title