Catastrophic bifurcation in three-phase boost rectifiers

Active PWM voltage rectifiers are commonly used to convert ac power from a three-phase grid to a regulated dc voltage with unity input power factor. The output voltage regulation is normally achieved by an outer voltage feedback loop and a sinusoidal-pulse-width-modulation (SPWM) inner current loop. Due to output voltage disturbances, such as those produced by a capacitive load, the inner current loop can be easily driven into over-modulation and possible six-step operating regions. Current research efforts have focused on extending the linearity of the modulated voltage in the over-modulation range to reduce the input current harmonics and on studying the closed-loop stability via conventional small-signal linearization around a fixed operating point. Such linear techniques obviously fall short of predicting large-signal transient stability. In this paper, catastrophic bifurcation is reported in terms of the input current and output voltage. The physical origin of the phenomenon is identified. Boundaries of catastrophic bifurcation in the parameter space are found. The phenomenon is verified experimentally.