MEASUREMENT OF SPEED AND DIRECTION OF COASTING PERMANENT MAGNET SYNCHRONOUS MOTOR

• US 20080211440A1
• Filed: 03/03/2008
• Published: 09/04/2008
• Est. Priority Date: 03/02/2007
• Status: Active Grant

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Borisavljevic, Ana
• Granted Patent: US 7,965,053 B2
• Time in Patent Office: Days
• US Class Current: 318/400.35
• CPC Class Codes: G01P 13/04 Indicating positive or negative direction of a linear movement or clockwise or anti-clockwise direction of a rotational movement
• CPC Class Codes: G01P 3/48 by measuring frequency of generated current or voltage in general G01R23/00
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 8/00 Arrangements for controlling dynamo-electric motors of the kind having motors rotating step by step vector control H02P21/00

Abstract

A method for determining the speed of rotation of an unpowered, coasting electric motor, driven, when powered, by an electronic inverter, and without activating switches of the inverter. The steps include determining an electrical frequency of a back emf signal generated at a terminal of the motor or switching node of the inverter when the motor is coasting and determining the mechanical motor frequency and thus speed of rotation by dividing the electrical frequency by the number of motor pole pairs.

Claims

1. A method for determining the speed of rotation of an unpowered, coasting electric motor, driven, when powered, by an electronic inverter, and without activating switches of the inverter, the method comprising:

determining an electrical frequency of a back emf signal generated at a terminal of the motor or switching node of the inverter when the motor is coasting; and

determining the mechanical motor frequency and thus speed of rotation by dividing the electrical frequency by the number of motor pole pairs.

2. The method of claim 1, wherein the step of determining the electrical frequency comprises:

determining a time period between two successive waveform points of the back emf signal at a terminal of the motor or switching node of the inverter with respect to a common point.

3. The method of claim 2, wherein the successive waveform points are successive upward or downward zero crossings of the back emf signal.

4. The method of claim 2, further comprising determining a direction of rotation of the motor by the steps of:

determining a back emf voltage value at one motor terminal or switching node of the inverter with respect to the common point at an instant when the voltage at another motor terminal or switching node of the inverter goes through a predefined waveform point; and

from the value at the one motor terminal or switching node of the inverter, determining the direction of rotation.

5. The method of claim 4, wherein the predefined waveform point is a zero crossing.

6. The method of claim 5, wherein the value will be zero in one direction of rotation and positive for the other direction of rotation.

7. The method of claim 5, wherein the predefined zero crossing is either an upward or downward zero crossing.