A high-power PWM quadrature booster phase shifter based on a multimodule AC controller

Pulse-width-modulated (PWM) phase shifters allow the smooth control of power flow in a transmission line. This paper analyzes a PWM quadrature booster phase shifter based on a multimodule AC controller structure to attain high voltage levels and improve the harmonic spectrum. The modules are based on a three-phase PWM AC controller topology that employs only four force-commutated switches and is controlled by duty-cycle variation. The PWM technique is carrier based and the individual modules are gated through phase-shifted triangular carriers. As a result, harmonic cancellation takes place in the input current and output voltage. Low-order harmonics are therefore eliminated and the amplitude of remaining components reduced. An additional operating mode with negligible harmonic generation and step-like control is identified. The feasibility and advantages of the proposed phase shifter are demonstrated by means of a power system simulator.