Performance of HVDC Converters in Enhancing Transient Stability of Power Systems and in the Torsional Stressing of Generator Shafts Due to Balanced and Unbalanced Operation of the Rectifier

This paper examines performance of HVDC converters with respect to real and reactive power at the inverter or rectifier following a command for power injected into or taken from the AC system to enhance power system stability. It also considers the effect balanced and unbalanced operation of inverters in asynchronous links has on torsional stressing of large turbine-generator shafts. First a 6-pulse bridge is modeledto determine characteristics for reactive power at both the inverter and rectifier as a function of AC power at the inverter or rectifier. Responses for real and reactive power following transient commands for AC real power are determined for a range of commands for real power to enhance transient performance of the power system. The characteristics relate to a link with typical parameters rated at 200 MW ~ 1000 MW. Performance of a 12-pulse bridge configuration that was modeled is then summarized. Noncharacteristic harmonic currents injected by the inverter into the AC system due to balanced and unbalanced operation of the rectifier in an asynchronous link is then reviewed. Excitation of turbine-generator shaft torsional vibrations by noncharacteristic currents injected into the AC system on account of balanced and unbalanced operation of the rectifier is then discussed.