| COORDINATED VOLTAGE FREQUENCY CONTROL IN INDUCTION MOTOR FED BY VARIABLE FREQUENCY SUPPLIES | ||||||
| Author(s) | J. Chen | |||||
| Abstract | For squirrel cage motors fed by variable voltage and variable frequency static converters, the Voltage V1 and frequency W1 can be independently adjusted. This makes the adjustment of the speed and the control of torque simple and flexible. As long as controlling the ratio of V1 / W1 the drive system can operate in the optimization of the performance or economic optimization. As the frequency W1 is greater than the rated frequency W1r, for which the motor has been designed, the induction motor should operate in corresponding "field weakening" range of operation with the rated value Vir. As the frequency W1 is less than the rated frequency W1r, the stator voltage V1 should decrease correspondingly, but the flux can be held with the brated value. Therefore drive system's maximum power should also decrease. The maximum torque can be held with the rated value. Then the drive system can only obtain a constant maximum torque characteristic. In the case of W1 < W1r, how to control and adjust the ratio V1 / W1, depends on the requirement of the drive performance and operation economics, and also on whether it is flexible and simple or not. This paper describes varied basic principles for controlling the ratio V1 / W1 to improve the speed-torque characteristics. These control principles for induction motors in variable frequency operation are: 1. Keep the ratio V1 / W1 constant 2. Keep the stator flux linkage constant 3. Keep the air-gap flux linkage constant 4. Keep the rotor flux linkage constant 5. Keep the maximum torque in variable-frequency operation equal to the maximum torque in the rated frequency and rated voltage operation. |
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| Type | Members Only | |||||
| Date | Last modified 2021-03-04 by System | |||||
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