A PWM quadrature booster phase-shifter for FACTS

This paper presents a static phase-shifter based on a parallel connection of modules of a non-conventional PWM ac-ac converter. Conduction losses are kept low by using only one active power conversion stage where the average number of switches through which the current flows is small. Filtering losses are also expected to be low because of the high order and small magnitude of the harmonics generated by switching. This is obtained by operating the modules with symmetrically phase shifted carriers to provide harmonic cancellation. Thus, even with the switches operating at low frequencies to keep the switching losses low, a high equivalent switching frequency is achieved. The performance of the phase-shifter for damping power oscillations in open loop is also evaluated.