Series-connected, all-hybrid converters for utility interactive applications

Power electronics systems can provide solutions to power quality problems in the form of active filters and advanced SVCs (STATCOM). A conventional approach involves a pulse-width-modulated converter which is interfaced to the utility voltage (for example at the 13.8 kV level) through a line-frequency transformer. This increases the size and the cost of the system and introduces additional losses. This paper describes a per-phase, all-active approach where the need for a line-frequency transformer is eliminated by series connected converters. This all-active solution is a hybrid combination of two (or more) converters switching at line frequency (or its low multiple) and one converter pulse width modulated at a higher switching frequency. This paper includes the following: criteria for optimization, experimental results from a proof-of-concept laboratory prototype for an active filter application, and a comparative evaluation with the six-switch PWM converter for an SVC application.