Real DC capacitor-less active capacitors

Abstract

Single-phase pulse width modulation H-bridge active capacitors have second-order harmonic ripple voltages 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 active capacitors, 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, an infinite active capacitor and three types of real DC capacitor-less active capacitors are proposed, in which the dc-bus capacitors are completely removed. The analysis and design are validated by simulations.