System for controlling motor and method for the same

• US 6,735,284 B2
• Filed: 04/14/2003
• Issued: 05/11/2004
• Est. Priority Date: 10/10/2002
• Status: Expired due to Fees

• Current Assignee: LG Electronics, Inc. (LG Corporation)
• Original Assignee: LG Electronics, Inc. (LG Corporation)
• Inventors: Lee, Kyung Hoon, Won, June Hee, Oh, Jae Yoon, Cheong, Dal Ho
• Primary Examiner(s): Masih, Karen
• Application Number:
  US10/412,249
• Publication Number:
  US 20040070364A1
• Time in Patent Office: 393 Days
• Field of Search: 378/801, 378/804, 378/807, 378/798, 378/716, 378/432, 378/434, 378/609, 378/809
• US Class Current: 318/801
• CPC Class Codes: H02P 21/05 specially adapted for damping motor oscillations, e.g. for reducing hunting
• CPC Class Codes: H02P 21/18 Estimation of position or speed
• CPC Class Codes: H02P 21/26 Rotor flux based control
• CPC Class Codes: H02P 25/08 Reluctance motors

Abstract

The present invention relates to a system and a method for controlling a motor. A rotation/fixed coordinates converter converts a reference magnetic flux voltage and a reference torque voltage of a rotation coordinates system into data of a fixed coordinates system, and outputs the data to the three-phase voltage generator. A fixed/rotation coordinates converter converts a three-phase current applied from the inverter to the motor into a two-phase current. An estimation unit estimates a rotation angle and rotor speed of the motor upon receiving currents applied to the fixed/rotation coordinates converter. A control block receives the estimated rotation angle and the estimated speed from the estimation unit, and outputs the reference magnetic flux voltage and the reference torque voltage of the motor to the rotation/fixed coordinates converter to compensate an error caused by loads generated when driving the motor. Thus, the control system greatly reduces noise and vibrations of a compressor without being affected by loads generated by compression/expansion strokes of the compressor at a startup time of the motor, and prevents a performance of the compressor from being deteriorated.

Claims

1. A system for controlling a motor, comprising:

a three-phase voltage generator for outputting a three-phase voltage to an inverter driving the motor;

a rotation/fixed coordinates converter for converting a reference magnetic flux voltage and a reference torque voltage of a rotation coordinates system of the motor into data of a fixed coordinates system, and outputting the data to the three-phase voltage generator;

a fixed/rotation coordinates converter for converting a three-phase current applied from the inverter to the motor into a two-phase current so as to convert currents of the fixed coordinates system into currents of the rotation coordinates system;

an estimation unit for estimating a rotation angle and rotor speed of the motor upon receiving currents applied to the fixed/rotation coordinates converter; and

a control block for receiving the estimated rotation angle and the estimated speed from the estimation unit, outputting the reference magnetic flux voltage and the reference torque voltage, in which an error caused by loads when driving the motor is compensated, to the rotation/fixed coordinates converter.

2. The system as set forth in claim 1, wherein the control block includes:

a first subtracter for generating a difference between a reference speed of the motor and a motor'"'"'s estimated speed estimated by the estimation unit;

a speed controller for generating a reference torque current controlling a speed of the motor upon receiving the difference between the reference speed and the estimated speed from the first subtracter;

a second subtracter for generating a difference between the reference torque current and a real torque current;

a magnetic flux command generator for generating a reference magnetic flux current by controlling a magnetic flux according to the estimated speed;

a third subtracter for generating a difference between the reference magnetic flux current and a real magnetic flux current;

a current controller for generating a reference magnetic flux voltage and a reference torque voltage according to an output difference generated from the third subtracter; and

a speed compensator for outputting a compensation signal compensating ripples generated in the reference torque current generated from the speed controller to the second subtracter.

3. The system as set forth in claim 2, wherein the speed compensator generates the compensation signal according to loads recognized by the rotation angle of the motor'"'"'s rotor.

4. The system as set forth in claim 2, wherein the speed compensator generates the compensation signal on the basis of a ripple waveform generated at the estimated speed of the motor.

5. The system as set forth in claim 4, wherein the compensation signal and the ripple waveform are 180 degrees out of phase with each other.

6. The system as set forth in claim 4, wherein the speed compensator includes:

a lookup unit for inserting a fundamental wave component of the compensation signal considering both a ripple component generated in load characteristics of the motor and a ripple component generated in speed characteristics into a lookup table;

a PI (Proportional Integral) unit for determining a magnitude of the compensation signal in a direction of reducing the ripple component generated in the speed characteristics; and

a combiner for combining an output signal of the lookup unit with an output signal of the PI unit to generate the compensation signal.

7. The system as set forth in claim 1, wherein the control block includes:

a first subtracter for generating a difference between a reference speed of the motor and a motor'"'"'s estimated speed estimated by the estimation unit;

a speed controller for generating a reference torque current controlling a speed of the motor upon receiving the difference between the reference speed and the estimated speed from the first subtracter;

a second subtracter for generating a difference between the reference torque current and a real torque current;

a magnetic flux command generator for generating a reference magnetic flux current by controlling a magnetic flux according to the estimated speed;

a third subtracter for generating a difference between the reference magnetic flux current and a real magnetic flux current;

a current controller for generating a reference magnetic flux voltage and a reference torque voltage according to an output difference generated from the third subtracter; and

a speed compensator for outputting a compensation signal compensating ripples, generated in speed difference signals generated from the first subtracter due to loads of the motor, to the first subtracter.

8. The system as set forth in claim 7, wherein the speed compensator generates the compensation signal according to loads recognized by the rotation angle of the motor'"'"'s rotor.

9. The system as set forth in claim 7, wherein the speed compensator generates the compensation signal on the basis of a ripple waveform generated at the estimated speed of the motor.

10. The system as set forth in claim 9, wherein the compensation signal and the ripple waveform are 180 degrees out of phase with each other.

11. The system as set forth in claim 9, wherein the speed compensator includes:

a lookup unit for inserting a fundamental wave component of the compensation signal considering both a ripple component generated in load characteristics of the motor and a ripple component generated in speed characteristics into a lookup table;

a PI (Proportional Integral) unit for determining a magnitude of the compensation signal in a direction of reducing the ripple component generated in the speed characteristics; and

a combiner for combining an output signal of the lookup unit with an output signal of the PI unit to generate the compensation signal.

12. A method for controlling a motor, comprising the steps of:

a) generating a difference between a reference speed and an estimated speed of the motor;

b) generating a reference torque current for controlling a motor speed according to the speed difference generated at the step (a) simultaneously controlling a magnetic flux according to the estimated speed of the motor, and generating a reference magnetic flux current;

c) generating a difference between the reference magnetic flux current and a real magnetic flux current simultaneously with generating a difference between the reference torque current and a real torque current of the motor, and thus compensating ripples that are generated in the reference torque current generated at the step (b) by the motor;

d) generating a reference magnetic flux voltage and a reference torque voltage according to individual differences generated at the step (c), and transmitting the reference magnetic flux and the reference torque voltage to a three-phase voltage generator adapted to output a three-phase voltage to an inverter driving the motor; and

e) allowing the inverter to control the motor upon receiving the three-phase voltage generated at step (d).

13. The method as set forth in claim 12, wherein the step (c) includes the steps of:

c1) referring to a lookup table which stores a fundamental wave component of a compensation signal considering both a ripple component generated in load characteristics of the motor and a ripple component generated in speed characteristics;

c2) determining a magnitude of the compensation signal in the direction of reducing the ripple component generated in the speed characteristics; and

c3) generating a compensation signal according to the determination results of the steps (c1) and (c2), and removing ripples caused by the motor'"'"'s loads from a difference between the reference torque current and the real torque current.

14. A method for controlling a motor, comprising the steps of:

a) generating a difference between a reference speed and an estimated speed of the motor in order to compensate a ripple component generated in the estimated speed due to loads of the motor;

b) generating a reference torque current for controlling a motor speed according to the speed difference generated at the step (a) simultaneously controlling a magnetic flux according to the estimated speed of the motor, and generating a reference magnetic flux current;

c) generating a difference between the reference magnetic flux current and a real magnetic flux current simultaneously with generating a difference between the reference torque current and a real torque current of the motor;

d) generating a reference magnetic flux voltage and a reference torque voltage according to individual differences generated at the step (c), and transmitting the reference magnetic flux and the reference torque voltage to a three-phase voltage generator adapted to output a three-phase voltage to an inverter driving the motor; and

e) allowing the inverter to control the motor upon receiving the three-phase voltage generated at step (d).

15. The method as set forth in claim 14, wherein the step (c) includes the steps of:

c1) referring to a lookup table which stores a fundamental wave component of a compensation signal considering both a ripple component generated in load characteristics of the motor and a ripple component generated in speed characteristics;

c2) determining a magnitude of the compensation signal in the direction of reducing the ripple component generated in the speed characteristics; and

c3) generating a compensation signal according to the determination results of the steps (c1) and (c2), and removing ripples caused by the motor'"'"'s loads from a difference between the reference speed and the estimated speed.