A carrier magnitude varying modulation for distributed static series compensator to achieve a maximum reactive power generating capability

Conventional single-phase H-bridge applications have second-order harmonic ripple power on the dc bus. However, in applications like a voltage source inverter (VSI) module of a Distributed Static Series Compensator (DSSC), a larger dc bus voltage fluctuation is acceptable since the dc bus connects to no load. This paper releases the constraints on dc bus voltage ripples so that the dc-bus capacitor can be fully utilized. Based on this idea, a carrier magnitude varying modulation is proposed, in which the VSI can generate ten times the reactive power of a conventional SPWM based VSI. The system reactive power generating capability is assessed to compare with the conventional SPWM based VSI and the constant duty cycle control based VSI. A PI controller is applied to the system to regulate the ac current. The analysis and design are validated by simulation and experiments.