Transformer coupled asymmetrical half bridges for voltage balancing of floating capacitor converters

A non-dissipative system using Transformer Coupled Asymmetrical Half-Bridge (TCAB) power converters is presented for voltage balancing of floating capacitor converter modules. A sample system that benefits from the voltage balancing network is considered that uses single phase H-bridge converters connected to a three-phase grid: smaller dc link capacitors can be used with a reduced low frequency voltage ripple and more balanced 3 phase pwm voltage output waveforms. Two different scenarios: transformer with high leakage and transformer with low leakage are being considered. Several switching patterns are presented that maximize the average capacitor charging currents that are generated to correct the voltage unbalances between modules. Simplified equivalent circuit models and waveform analysis are presented to illustrate the charge transfer mechanisms that result from the switching patterns considered. Practical operational limitations and design considerations are described. Simulations and experimental results are presented to validate the operation and performance of the voltage balancing approach being examined.