Temperature limiting controller for electric machines

Electricity: motive power systems – Automatic and/or with time-delay means – Responsive to thermal conditions

Reexamination Certificate

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Details

C318S434000, C318S634000, C361S025000

Reexamination Certificate

active

06291958

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to a controller for regulating the temperature of an electric machine, and in particular to a controller which regulates the temperature of an electric machine by adjusting the motor's output based on feedback of a measured motor temperature.
When an electric motor is operated at peak power for an extended period of time, power dissipation is high and the temperature of the motor rises rapidly. It is important to protect an electric motor from overheating to prevent the motor from failure.
It is known in the prior art to control the motor output, such as the commanded torque, based on a measured motor temperature. However, prior art methods, such as the one disclosed in U.S. Pat. No. 5,227,703, reduce the commanded torque by a fixed amount resulting in an open loop control scheme that may not adequately prevent the temperature from rising too high. What is needed is an effective method for regulating temperature of a motor as a protection system for electric motors used in industrial and automotive applications.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for regulating the temperature of an electric machine.
It is another object of the present invention to provide a method that regulates the temperature of the electric machine by adjusting some aspect of the motor output based on feedback of the measured motor temperature. It is yet another object of the present invention to regulate the temperature by adjusting the torque command, the motor voltage, the motor current, or the motor power.
It is a further object of the present invention to apply the method of the present invention to an electric machine having torque control. It is yet a further object of the present invention to apply the method of the present invention to an electric machine having speed control. It is still a further object of the present invention to apply the controller and the method of the present invention to an electric machine having position control.
The present invention is advantageous in that it provides active control of the electric machine to prevent the temperature from rising above a predetermined limit. The present invention is a closed loop control that forces the machine to maintain an operating temperature below a predetermined limit.
In carrying out the above objects and other objects and features of the present invention, a method is provided that allows normal operation of the motor until its temperature exceeds a predetermined limit. Once the predetermined limit is exceeded, the method of the present invention regulates the temperature of the electric machine by adjusting the motor output based on feedback of the measured motor temperature.
The method of the present invention is used with an electric machine having torque control, speed control and/or position control. The method to regulate the temperature is accomplished by adjusting an output of the electric machine. For example, the adjustment can be to the torque control, the motor's voltage, the motor's current, or the motor's power and is adjusted so that the desired temperature limiting result is obtained.
In one embodiment of the method of the present invention, the controller performs proportional-integral (PI) control and reduces the commanded torque, voltage, current, or power to the motor to prevent the steady-state motor temperature from increasing beyond a predetermined limit set by a reference temperature. The PI branch includes a negative pass filter that prevents the controller from operating until the motor temperature exceeds the reference temperature.
In another embodiment of the present invention, the negative pass filter is eliminated from the PI controller. In this embodiment, the proportional branch of the PI controller now influences the dynamics that affect the rate at which the motor adjustment approaches the original commanded adjustment after the motor temperature falls below the reference temperature.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.


REFERENCES:
patent: 3868554 (1975-02-01), Konrad
patent: 4151587 (1979-04-01), Benejean
patent: 4672288 (1987-06-01), Abbondanti
patent: 4673031 (1987-06-01), Wiemer et al.
patent: 5160878 (1992-11-01), Nagano
patent: 5227703 (1993-07-01), Boothe et al.
patent: 5231339 (1993-07-01), Kishimoto et al.
patent: 5298845 (1994-03-01), DeBoer et al.
patent: 5659235 (1997-08-01), Yamada et al.

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