INTRODUCTION OF THE HARMONIC DISTORTION DETERMINING FACTOR AND ITS APPLICATION TO EVALUATING REAL-TIME PWM INVERTERS

Frequency spectra of inverter output currents are one of the important factors in order to evaluate PWM methods. These spectra are, however, influenced not only by the PWM method itself but by the operating conditions of the inverter such as the switching frequency or load parameters. The harmonic distortion determining factor (HDDF) is considered to be a common quality index that represents the intrinsic spectral property of individual PWM methods. As it has a close relation to RMS values of the harmonic current or torque ripples of driven motors and, further, it is almost independent of the operating conditions, HDDF is quite useful for evaluating PWM methods. In this paper three typical analog PWM methods and four digital PWM methods are compared and evaluated based on HDDF values.