Evaluation of the Performance of Back-to-Back HVDC Converter and Variable Frequency Transformer for Power Flow Control in a Weak Interconnection

This paper compares performance of a back-to-back HVDC system with series compensation external to the converter transformers, and a variable frequency transformer for power flow control feeding or supplying a weak AC network. The steady state and dynamic simulations show that both technologies are able to control power flow accurately. The variable frequency transformer consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery and better natural damping capability. Back-to-back HVDC converters, however, provide smoother and faster recovery to pre-disturbance level for the same system faults. A back-to-back HVDC system also provides smoother and faster response to a controlled power change.