Introduction of the harmonic distortion determining factor and its application to evaluating real time PWM inverters

The harmonic distortion determining factor (HDDF), which represents the intrinsic spectral properties of pulse-width modulation (PWM) methods, is introduced. The HDDF is almost independent of the inverter operating conditions such as the switching frequencies or load parameters if the switching frequency is 40 times greater than the output frequency. Furthermore, it is closely related to the root mean square (RMS) values of the harmonic current and motor torque ripples for induction motor drives, or the RMS values of the harmonic current and DC voltage ripples for rectifier operation. Therefore, it is useful as a common quality index for the evaluation of PWM methods. Four typical analog PWM methods and four digital PWM methods are compared and evaluated based on HDDF values. It is shown that the harmonic injected PWM for analog PWM, or the digital PWM of type C has the best characteristics