The study of hybrid modulation based on cascade SVG and its DC control method

This paper adopts PAM+PWM hybrid modulation method in a five cascade SVG (Static Var Generator). Four PAM (Pulse Amplitude Modulation) units output a voltage which is of fixed amplitude and in phase with the system voltage; and current direct controlling method was applied in the only PWM (Pulse Width Modulation) unit to adjust the output reactive current. To balance the DC-side voltage, pulses rotated cyclic between PAM units. This paper put forward a new method that rotated the pulses in an asymmetric way, in which the DC-side voltage of the PAM units was elevated and that of the PWM unit was accordingly reduced. Further, this paper successfully balanced the DC-side voltage volatility of each H-bridge by reasonably distributing capacitor parameter. Finally, PSCAD simulation results and the SVG experimental prototype prove the validity of this method.