Harmonic evaluation of an NPC PWM inverter employing the harmonic distortion determining factor

This paper describes a new harmonic evaluation scheme of neutral-point-clamped (NPC) PWM inverters. The scheme uses the harmonic distortion determining factor (HDDF). As the HDDF represents the intrinsic spectral property of PWM schemes and is almost independent of the operating conditions, it is quite useful for evaluating PWM schemes. In addition, the HDDF is also useful for predicting the harmonic properties in AC drives. If HDDF values for individual PWM schemes are known, the approximate harmonic characteristics, such as the current harmonics or the torque ripples, can be easily calculated using HDDF values. In this paper, HDDF values of five types of carrier-based NPC-PWM schemes are given, and the approximate harmonic characteristics calculated by the HDDF approach are discussed