Ripple voltage minimization in single phase floating bridge converter modules using a Transformer Coupled Asymmetrical bridge converter

Abstract

A method for reducing the capacitor size used in single phase floating capacitor voltage source converter modules is presented. A Transformer Coupled Asymmetrical half-Bridge (TCAB) is used to exchange energy between the capacitor regulated dc sources of the main power converter modules, without using separate power sources. This energy exchange (bidirectional) compensates for naturally occurring low frequency voltage ripple in the floating capacitor main power converters. This enables smaller film dc capacitors to be used. The latter can be used to reduce the overall system size/cost with a longer system working lifetime. The ripple voltage reduction and voltage balancing features provided is not intended to be specific to a particular modular power converter system, MMC systems are an example, but are illustrated here using utility connected single phase floating converters. The switching control methods described avoid the use of extra filter components and to maximize the average current used to transfer energy between the modules. Simulations and experimental results are presented to validate the operation and performance of the proposed system with the emphasis placed on the voltage ripple reduction feature.