Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2000-06-27
2001-10-16
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S254100, C318S132000, C318S434000, C318S705000, C318S811000
Reexamination Certificate
active
06304052
ABSTRACT:
TECHNICAL FIELD
This invention relates to control systems for permanent magnet motors and more particularly to a control system for a permanent magnet motor that includes five regulators to obtain optimum motor efficiency under various operating conditions.
BACKGROUND OF THE INVENTION
It is known in the art relating to permanent magnet motors to control the torque of the motor by controlling the current supplied to the motor. Typically, an interior permanent magnet motor includes a stator having multiphase windings and a rotor having permanent magnets located internally which are surrounded by pole pieces. The magnetic field of the stator produced by the stator windings interacts with the magnetic field of the rotor, causing the rotor to rotate. The rotor magnetic field is produced by permanent magnets.
The rotation or torque of the motor is controlled by governing the magnitude and duration of the current applied to the stator windings. To generate the magnetic field, the stator current is switched on and off in each stator phase winding in a predetermined sequence synchronized with the rotor position. Usually, the stator current signal is a pulse width modulated signal applied by an inverter to the windings. A stator current command signal may be determined based upon a maximum torque per amp trajectory. After the desired trajectory is determined, current regulators maintain the current command signal at the stator windings. The current regulators may be a hysteretic type of current regulator or a proportional-integral PI current regulator. The motor is run most efficiently at the maximum torque per amp trajectory. Therefore, it is desirable to have a control system for a permanent magnet motor that minimizes the deviation from that maximum torque per amp trajectory.
SUMMARY OF THE INVENTION
The present invention provides a control system for controlling a permanent magnet motor that includes five regulators. The first regulator receives a torque command signal indicative of the desired motor torque and an actual motor torque signal and provides a stator current command signal in response to the difference between the actual motor torque and a torque command signal. A maximum per amp trajectory is determined from the torque command signal. The trajectory is divided into a sine and cosine component having an angle &bgr; representing the angle between the stator current and the quadrature-axis.
Next, the stator current command signal is multiplied with the sine and cosine functions to obtained a direct-axis current command signal and a quadrature-axis current command signal, respectively. The quadrature and direct axis current command signals are combined with motor quadrature and direct axis current signals to provide modified direct-axis and quadrature-axis current command signals indicative of the desired motor torque. After the modified direct-axis and quadrature-axis current command signals are provided, a limiter prevents the modified direct-axis current command signal from exceeding a maximum stator current and any current in excess of the maximum stator current is added to the modified quadrature-axis current command signal.
The second and third regulators are current regulators that provide regulated quadrature-axis and direct-axis current command signals which are responsive to the difference between the respective current command signals and motor current signals.
A fourth regulator is provided to generate a first field-weakening signal that increases the direct-axis current signal when the quadrature-axis voltage approaches a desired maximum voltage. A fifth regulator is provided to generate a second field-weakening signal that increases the direct-axis current signal when the quadrature-axis voltage approaches a desired maximum voltage. The regulated direct-axis and quadrature-axis current signals are combined to form a pulse width modulated signal that is applied to the motor through an inverter. The fourth and fifth regulators act independently from each other when modifying the direct-axis and quadrature-axis current signals. Each field-weakening signal operates independently of motor parameters, resulting in a more stable control of the motor.
In one embodiment of the invention the motor torque is determined by a torque estimator. The torque estimator determines the motor torque from the motor quadrature-axis and direct-axis current signals, motor speed and dc voltage supplied to the inverter. The estimator uses equivalence between electrical power and mechanical power in the calculations so therefore, measured magnetic core losses, copper losses and other system losses are compensated through interpolation. Therefore, this method will automatically compensate for changes inductance and magnetic flux with load and temperature. However, the only exception is the stator resistance which varies with temperature, resulting in minor changes in torque that remain uncompensated. Thus, the present invention may provide a torque that is more accurate under temperature variations of the motor and under heavy motor magnetic saturation. Further, the invention may provide a control system that operates the motor near an optimum torque per amp trajectory, resulting in reduced power inverter rating and inverter cost.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
REFERENCES:
patent: 4649331 (1987-03-01), Jahns
patent: 5585709 (1996-12-01), Jansen et al.
patent: 5818192 (1998-10-01), Nozari
patent: 6008618 (1999-12-01), Bose et al.
patent: 6037741 (2000-03-01), Yamada et al.
patent: 6051946 (2000-04-01), Yamada et al.
patent: 6163128 (2000-12-01), Hiti et al.
Pending U.S. Patent Application, Ser. No. 09/444,437, entitled, “System And Method For Controlling A Position Sensorless Permanent Magnet Motor”, assigned to the assignee of the present invention.
Pending U.S. Patent Application, Ser. No. 09/409,890, entitled, “Method For Determining Rotor Position”, assigned to the assignee of the present invention.
O'Meara Thomas P.
Patel Nitinkumar Ratilal
General Motors Corporation
Leykin Rita
Nappi Robert E.
Simon Anthony Luke
LandOfFree
Control system for a permanent magnet motor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control system for a permanent magnet motor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control system for a permanent magnet motor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2581555