High power voltage source converter control response at large AC voltage phase shifts

In high power applications, i.e. HVDC and SVC, the coupling between rating, performance and utilisation is of high interest. Therefore, the performance of the inner current loop control of large voltage source power converters is studied with respect to the ability to limit converter current during disturbances in the supplying AC network. The disturbance here studied is the impact of a phase shift in the AC bus voltage which can occur at line disconnection(s). A comparison is made between inner current loop implementation in either the αβ-plane or the rotating dq-plane. The influences of an extra time delay introduced using digital control and the sample period (pulse number) are also evaluated. Results are presented from dynamical studies, using both digital simulations and real time analog simulations with a digital control system. The simulations verify that the ability of the implemented inner current loop to limit the power converter current during a phase shift in the line voltage is highly dependent on the chosen sample period (i.e. switching frequency)