High-frequency-link cycloconverter-based DVR for voltage sag mitigation

Power quality studies have established that voltage sags are the most prevalent of all power system disturbances, affecting industrial and commercial customers. Their effects are most felt in process industry equipment, like Adjustable Speed Drives and Contactors, resulting in equipment down times, clean up and re-calibration, costing to the tune of millions of dollars. Many load-end solutions have been proposed which include Constant Voltage Transformers (CVT's), UPS and line-frequency-transformer-based series voltage injection devices (example: DVR and SSVR). These approaches, however, have their respective limitations with regard to capabilities, size and/or cost. This paper investigates a new topology to mitigating voltage sags by employing high-frequency-transformer-link in the series voltage injection approach, resulting in substantial savings in size and weight. Suitable switching logic and control strategies have been implemented. Design issues of the proposed approach for different load types are discussed. Simulation results for the single-phase implementation are presented. Experimental results from a single-phase proof-of-concept prototype are shown.