PWM drives: voltage-type harmonic sources in power systems

PWM inverter induction motor drives with capacitive DC links are becoming more common. Using circuit analysis, physical measurement and numerical simulation, the paper investigates the generation of power-system harmonics by the PWM drive. It is shown that its harmonic characteristics differ from other nonlinear power-system loads and the drive can be more accurately represented as a voltage rather than a current type of harmonic source. This has implications for both analytic harmonic evaluation and practical filter design. In the paper, a modulation function model is developed which can be used to assess the impact of a PWM drive on a power system, when only limited design data are available