Device for controlling sensorless brushless-DC-motor

• US 6,424,798 B1
• Filed: 05/24/2000
• Issued: 07/23/2002
• Est. Priority Date: 05/31/1999
• Status: Expired due to Fees

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Kitamine, Yasukazu
• Primary Examiner(s): Nappi, Robert E.
• Assistant Examiner(s): SMITH, TYRONE W
• Application Number:
  US09/576,631
• Time in Patent Office: 790 Days
• Field of Search: 318/138, 318/139, 318/254, 318/245, 318/439, 318/369, 318/370, 318/371, 318/268, 701/41, 701/50, 363/55, 363/41
• US Class Current: 388/800
• CPC Class Codes: B60L 50/60 using power supplied by batteries in combination with fuel cells B60L50/75
• CPC Class Codes: H02P 6/17 and for generating speed information
• CPC Class Codes: H02P 6/18 without separate position detecting elements
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A sensorless brushless-DC-motor mounted on an electric or hybrid vehicle is powered by an on-board battery through an inverter supplying a three-phase pulse width modulated voltage (PWM voltage). The inverter is controlled to generate the PWM voltage having an average voltage level corresponding to a target motor speed. The PWM voltage level is controlled by changing its duty ratio, so that a difference between the target motor speed and an actual motor speed is minimized. The actual motor speed is determined based on a signal indicating a rotor position detected from the PWM voltage imposed on the motor. When the battery voltage drops and the duty ratio becomes 100%, the target motor speed is temporarily reduced to the level of the actual motor speed. When the battery voltage is recovered and the duty ratio becomes lower than 100%, the target motor speed is gradually increased again to the original level. In this manner, even if the battery voltage abruptly increases, the PWM voltage is properly controlled, and thereby the motor is stably driven without causing loss of synchronism.

Claims

1. A device for controlling a sensorless brushless-DC-motor driven by a DC power source, the device comprising:

an inverter for supplying a three-phase pulse width modulated motor voltage to the sensorless brushless-DC-motor, the motor voltage being formed from the DC power source; and

a controller for controlling operation of the inverter, the controller including a rotational speed detector detecting a motor speed based on a rotor position determined from the motor voltage, the controller controlling a duty ratio of the three-phase pulse width modulated motor voltage to reduce a difference between a target motor speed and the detected motor speed, wherein,

the controller modifies the duty ratio to eliminate influence of the voltage variation of the DC power source to an average level of the motor voltage, and wherein,

the rotor position is determined based on the motor voltage controlled to eliminate variation of a voltage of the DC power source.

2. A device for controlling a sensorless brushless-DC-motor driven by a DC power source, the device comprising:

an inverter for supplying a three-phase pulse width modulated motor voltage to the sensorless brushless-DC-motor, the motor voltage being formed from the DC power source; and

a controller for controlling operation of the inverter, the controller including a rotational speed detector detecting a motor speed based on a rotor position determined from the motor voltage, the controller controlling a duty ratio of the three-phase pulse width modulated motor voltage to reduce a difference between a target motor speed and the detected motor speed, wherein,

the controller temporarily sets the target motor speed to a level of the detected motor speed when the duty ratio reaches 100% and the temporarily set level is kept during a period in which the duty ratio is 100%; and

the controller gradually shifts the temporarily set target motor speed to a level of the original target motor speed after the duty ratio becomes below 100%, and wherein,

the rotor position is determined based on the motor voltage controlled to eliminate variation of a voltage of the DC power source.

3. A method of controlling a sensorless brushless-DC-motor driven by a battery through a motor controller connected between the motor and the battery, the method comprising steps of:

inverting a DC voltage of the battery into a three-phase pulse voltage having a controllable duty ratio;

supplying the pulse voltage to the motor;

setting a target motor speed at a predetermined level;

detecting a motor speed based on the pulse voltage supplied to the motor;

calculating a speed difference between the detected motor speed and the target motor speed;

modulating the duty ratio of the pulse voltage to minimize the speed difference;

changing the target motor speed to a level of the detected motor speed, when the battery voltage decreases and thereby the duty ratio of the pulse voltage reaches 100%;

maintaining the target motor speed at the detected motor speed level during a period in which the duty ratio is 100%; and

gradually shifting the target motor speed maintained at the detected motor speed level to the predetermined level after the duty ratio becomes lower than 100%.