Highly Reliable and Efficient Voltage Optimizer Based on Direct PWM AC-AC Buck Converter

A voltage optimizer (VO) to regulate overrated electricity supply voltages to optimized values with high reliability and efficiency has been developed based on a direct PWM ac-ac buck converter. A comprehensive control strategy is proposed for the ac-ac converter to address existing commutation problems and also to offer a fault handling capability against short circuits. A number of switching states are defined depending on the input voltage, whereby continuous and reliable current paths are maintained at all times especially around voltage zero-crossing points, and safe transitions between them are achieved as well. Based on a detailed power loss analysis, a hybrid scheme with silicon carbide (SiC) MOSFETs and silicon IGBTs is proposed which significantly improves the efficiency while minimizes the cost, and simultaneously enables the use of a high switching frequency, with the potential to reduce the volume of a VO. Results from simulation and experiment confirm that the proposed strategies give reliable operation of the VO with an efficiency higher than 99%.