Improving the dynamic performance of a complex AC/DC system by HVDC control modifications

Enhancement of the overall system dynamic performance of an AC/DC scheme is possible by minor modifications in the HVDC (high-voltage DC) controls. The Chateauguay HVDC scheme comprises two back-to-back converter blocks, each with a rated capacity of 400 MW. It is designed to export power from Quebec to the NYPA (New York Power Authority) system. Some control modifications currently under consideration for the Chateauguay HVDC scheme (which has interconnections to the Beauharnois generators and to the 765 kV intertie to NYPA) are presented. The salient features of such control modifications are discussed using the results of an investigation by digital and analog simulations that demonstrate the achieved improvements. The modifications lead to a remarkable improvement in the damping of AC voltage and tieline power oscillations under heavy loading conditions. Voltage instability following disturbances under very weak AC-system conditions can also be avoided