Dynamically Optimal Switching Patterns for PWM Inverter Drives (for Minimization of the Torque and Speed Ripples)

Several optimization criteria exist for pulsewidth modulation (PWM) inverter control as applied to ac motor drives. Drive dynamics, i.e., torque and speed ripples, are analyzed and optimized. As a representative example, the PWM inverter control is assumed to have three and five degrees of freedom. These degrees of freedom are realized by so-called switching angles which determine the inverter output voltage waveshape. This voltage is applied to an induction motor. Analysis is executed for a steady-state approximation (using Fourier analysis) as well as for the rigorous fifth-order dynamic equations. The results are compared. The optimal solution for the switching angles as a function of the voltage fundamental is shown. The location of the optima is compared with the efficiency optimal control presented in an earlier paper. A means is provided to compare results for different optimization criteria in order to reach an overall optimum as the best compromise between the results gained from the different optimization methods.