System-level power loss sensitivity to various control variables in vector-controlled induction motor drives

Vector-controlled induction motor drives include several design and control variables that affect power losses. Flux may be weakened to reduce machine losses; switching and conduction losses in the inverter are affected by the flux ripple and current hysteresis bands. This paper combines the machine and inverter to investigate the effects of various control variables on the total system power loss. Both indirect field-oriented control and direct torque control are evaluated. Power losses considered include semiconductor switching and conduction losses and machine core and copper losses. Magnetic saturation is taken into account. A 1.5-hp system is simulated and experimentally tested to find minimum-loss operating points for various control variable combinations. Experimental results show that the operating point for minimum system-level power loss is slightly different from that for minimum machine power loss, but both can yield significant energy savings. The results presented here suggest that, for efficient system operation, control aspects should be utilized and integrated into motor drive designs.