Realisation of an ac link unified power flow controller

Unified power flow controllers (UPFC) have been demonstrated to be a versatile approach for realising ac power flow control in transmission systems. Although the conventional approach for UPFC has been based on dc link converters, direct ac link power conversion at the power frequency is being introduced as an alternative means for unified power flow control. In this study, the realisation of an ac link UPFC based on vector switching converters is presented. The control function that can independently control real and reactive power throughput in a transmission line is accomplished by direct ac↔ac conversion without frequency change, adopting the strategy of pulse width modulation and operated in conjunction with an appropriate configuration of typical power transformers. Operating principles, equivalent circuits, computer simulation and experimental results are presented on the basis of a laboratory-scale prototype.