Practical Dynamic Security Regions Of AC/DC Parallel Systems To Guarantee Short-term Voltage Stability Of Large Disturbance

With the increased use of HVDC transmission systems in power systems, the framework of interprovincial AC/DC parallel system has come into practice. It has been found that the interaction between the parallel AC transmission system and the HVDC transmission lines in such configurations is very important to voltage stability of power systems under this framework.The traditional"point wise"approach is one of the most basic approach in the study of power systems analysis. But it also has a lot of deficiencies. Compared with traditional"point wise"approach, the dynamic security regions (DSR) concept is gradually being accepted by electrical power engineers for its advantages on dynamic security monitoring, assessment and optimal control of power systems.The paper mainly studys practical dynamic security regions (PDSR) of AC/DC parallel systems corresponding to short-term voltage stability after a large disturbance.The study on PDSR of the typical AC/DC parallel systems shows the short-term voltage stability PDSR can be surrounded by the vertical hyper-planes which are the upper and lower limits of every bus injection, one or several critical hyper-planes that describe approximately critical points of short-term voltage stability in injection space, and restriction planes of balance node, when the fault, the DC power and the convertor's control mode are given. It is validated that short-term voltage stability PDSR will expand, when CC/CV control mode and high VL of VDCOL (voltage dependent current order limiter) are adopted. In addition, the critical hyper-planes corresponding to different HVDC power, different power measuring sites with same value and different induction-motor proportion in load are approximately parallel for the same fault, the same unstable mode and the same convertor's control mode. The discovery improves the results of PDSR study.