SMART POWER FACTOR CONTROL STRATEGIES FOR ADVANCED INTERIOR PERMANENT MAGNET (IPM) MOTORS

Abstract

New AC motor-drive systems require high power-factor operation and strong speed control to be efficient, minimize line losses and enhance the quality of power. Traditional rectifier-inverter front-ends have low power factor and higher harmonic distortion particularly under dynamic load operation leading to increased current stress and unstable motor operation. In order to overcome these shortcomings, this paper suggests a combined power-factor enhancement and speed-control approach to an interior permanent-magnet (IPM) motor drive. This paper presents a novel method of Power factor improvement, which consists of an ac power source, a diode rectifier bridge, dc-link capacitor, PWM driven inverter and interior permanent magnet motor. The inverter plays two critical roles: (1) It enhances the quality of input supply current to be closer to the ideal sine waveform in order to have Power factor of unity and (2) varying of motor speed in compensating increase in current resulted due to sudden decrease in the voltage observed during overloading conditions. In this approach three phase current of inverter (I_a, I_b, I_c) and rotor angle(α) of IPM motor are employed to transform the three-phase model into d-q axis (I_d, I_q). The actual motor speed (Wm) is compared with the reference speed (W_r) by PID speed controller, whose output is demanded current (I_dem). The model d-q currents (I_d, Iq₎ are compared with sought current (I_dem) through PID current controller to obtain desired current (I_d, Iq). The reference d-q currents are then converted back into three phases (I_a, I_b, I_c). These are compared with a triangular carrier wave to produce PWM signals which serve as gating pulses for the inverter. The inverter commences using 120∘ PWM pattern and then the inversely generated PWM signals are applied to IGBTs. This method provides PF improvement and reduces current ripple and harmonics together.