Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-01-27
2001-04-24
Masih, Karen (Department: 3661)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S808000, C318S798000, C318S800000, C318S801000, C318S727000
Reexamination Certificate
active
06222335
ABSTRACT:
The present invention relates generally to digital control of induction machines fed by a voltage source inverter, and more particularly, to a control method for use in controlling a voltage-fed induction machine that provides maximal efficiency or maximal torque per ampere control of the voltage-fed induction machine.
BACKGROUND
The assignee of the present invention designs and develops voltage-fed induction machine drives comprising motors of electric vehicles. In electric vehicle or a hybrid electric vehicle applications, it is desirable that the drive system, comprising an inverter and an electric motor, operates under maximal efficiency. The drive system should also be capable of producing maximal torque achievable for a given inverter and machine voltage and current rating. This is especially difficult to achieve at lower DC link voltage values.
Example prior slip-control methods are optimized for steady-state operation, and the transient response to torque changes is generally slow, oscillatory, and not always monotonously increasing for a monotonously increasing torque command. Real-time efficiency control algorithms typically require complex signal processing, and typically have poor transient response, since the transient condition has to be identified, and the efficiency optimization algorithm turned off first, before responding to the increasing torque command. Consequently, conventional algorithms do not provide for maximal torque per ampere production at higher torque levels.
It would therefore be desirable to have an improved control algorithm for induction machine control that achieves the highest possible motor efficiency at the operating point. It would also be desirable to have an improved control algorithm for induction machine control that provides good transient response, and tracking of the torque command. It would also be desirable to have an improved control algorithm for induction machine control that provides for maximal efficiency control at low torque levels, and maximal torque per ampere control at high torque levels.
SUMMARY OF THE INVENTION
The present invention comprises an improved control algorithm or method for use in controlling a voltage-fed induction machine that overcomes limitations of conventional approaches. The control algorithm comprises the following steps. The DC voltage supplied to an inverter driving the induction machine is monitored. When the DC link voltage is high enough, the algorithm controls the amount of current supplied to the induction machine to provide current controlled operation of the induction machine. When the DC link voltage is too low to control the motor phase currents under transient conditions, the induction machine is controlled by imposing the maximum possible phase voltage and optimal slip angle on the machine to provide maximal torque per ampere operation of the induction machine.
The current controlled operation is performed when a) the torque level required by the induction machine is at a level that allows efficiency optimization, and b) the current regulators are not near saturation. The maximal torque per ampere operation is performed when either of the following conditions is met: a) the torque level required by the induction machine is such that efficiency optimization cannot be performed, or b) current regulators approach saturation.
REFERENCES:
patent: 5668721 (1997-09-01), Chandy
patent: 5739664 (1998-04-01), Deng et al.
patent: 5959431 (1999-09-01), Xiang
Hiti Silva
Stancu Constantin C.
General Motors Corporation
Masih Karen
Simon Anthony Luke
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