A fast algorithm for voltage unbalance compensation and regulation in faulted distribution systems

Among the factors affecting power quality in distribution systems are occurrence of faults. This paper discusses an approach to ensure a high quality power supply to critical loads under the most common faults, short circuits on adjacent feeders, resulting in temporary partial or total collapse of one or more phases. The approach is based on static series voltage compensators (single phase voltage source inverters), rated at only a fraction of the load. A voltage regulation algorithm is proposed to ensure fast response of the compensator in suppressing voltage sags and swells. It is demonstrated that good voltage regulation is achieved under the more severe faults. Compensation capability and voltage boost requirements are derived. Control and power circuit design procedures are presented. Static and dynamic performance characteristics are demonstrated on a 2 kVA experimental unit