An H-Bridge-based single-phase VAr generator with minimum DC capacitance

Conventional single-phase H-bridge applications have second-order harmonic ripple power on the dc bus. The second-order harmonic power is usually filtered by a bulk capacitor on the dc bus to maintain a constant dc-bus voltage, which results in low power density. However, in applications like VAr generator, 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 fluctuation so that the dc-bus capacitor can be fully utilized. Based on this idea, an H-bridge-based single-phase VAr generator with minimum dc capacitance is proposed, which reduces the dc-bus capacitor to 1/10th of the size compared to that of the sinusoidal pulse width modulation (SPWM)-modulated H-bridge inverter, without increasing components' count. A general modulation method of the proposed VAr generator is derived to utilize the fluctuating dc-bus voltage. The system volume and power loss are assessed to compare with the conventional SPWM-modulated H-bridge and the circuits with power-decoupling cells. A proportional-integral controller is applied to the system to control the input ac current. The analysis and design are validated by simulations and experiments.