A hybrid solid state phase shifter using PWM AC converters

Active power flow in transmission lines can be varied using a conventional or thyristor controlled phase shifter in series with the line, which introduces a phase shift between sending and receiving end voltages. However, the control of the phase shift can be executed only in steps depending on the taps available in the phase shifting transformer. An approach to obtain continuous control of the phase shift using a conventional tap changing transformer and a pulse width modulated buck ac-ac converter is presented in this paper. Operating principles, design considerations and other practical issues are discussed. Detailed computer simulation results are presented in the paper. The advantages and disadvantages of the proposed approach in relation to the conventional approaches are discussed.