A Dissipation Energy Based Method for the Optimization of Fault Transient Characteristics of AC/DC Hybrid System

When the LCC-HVDC transmission system restarts at fault, the high restart DC pulsed current will deliver a second impact on the system, causing the transient power angles of rectifier-side generators to swing. In order to solve this problem, a method for the optimization of fault transient operation characteristics of the AC/DC system based on the dissipation energy is proposed. By considering different stages in the whole fault recovery process, the detailed expressions of the dissipation energy injected from the generator to the system in the stages of 'phase-shifted trigger', 'deionization' and 'restart' are derived. On this basis, the effects of the rectifier control parameters on the dissipation energy are analyzed. With the accumulated dissipation energy of the system reaching the minimum value as the object, the optimal rectifier control parameters are calculated. Finally, hardware-in-loop tests are conducted in RT-LAB to verify the proposed optimization method. Results show that the proposed method can greatly reduce the amplitude of the DC pulsed current and the peak-valley difference of the power angle swing curve during the 'restart at fault' stage, thus it can effectively improve the fault transient characteristics of AC/DC hybrid system.