V/f PWM inverter with motor parameter identification and voltage auto-boost capabilities

A V/f control algorithm is presented that is based on constant air-gap flux control with inverter output voltage autoboost. This algorithm permits the realization of variable-voltage-variable-frequency (VVVF) control with a simple system configuration. In addition, as a result of the sine wave modulation of the inverter output voltage, there is a decrease of the torque ripple, an improvement of the efficiency, and a reduction of vibrations and noise. The algorithm permits an automatic boost of the voltage which maintains the same air-gap density. The voltage autoboost method is based on knowledge of the load characteristics and equivalent circuit parameters of the induction motor. An offline automeasurement technique for these parameters is described. The complete control system has been constructed and tested. The test results have been found satisfactory with the use of simple 8 bit microprocessors