Simulation And Analysis Of VSC-HVDC System Failure

VSC-HVDC system adopts IGBT,which makes the VSC can realize self turn off, so VSC-HVDC system does not require communication voltage, and the system is more suitable for weak AC network. Inverter side can be remote isolated negative charge or passive network. Compared to the conventional HVDC system, VSC-HVDC system has high degree of modularity and can achieve the active and reactive power independent control. The system due to its own advantage is bound to become a important component in the future transmission and distribution system. VSC-HVDC system can be used in wind power, solar power and other new energy generation.VSC-HVDC System is constituted by three parts: converter station, AC system and DC transmission lines, any part of the system failure may affect the reliability of the and the safety of the related equipment, and the converter valve subjected to voltage or current abnormal damage. Converter is the key and expensive components. it is the key protection object in the device and each bridge arm consists of several IGBT.How to improve the reliability and safety of the system has become a problem needed to be solved at present. This paper mainly for typical faults simulation research, it provides the basis for fault diagnosis and reasonable fault protection strategies.This paper introduces the general structure and working principle of Flexible HVDC system firstly, and then we set up the Mathematical model of VSC-HVDC system in two phase rotating coordinate system. According to the control theory of Flexible HVDC system, the author designs the control strategy of VSC-HVDC system and also builds the simulation model to Flexible HVDC system. From the starting-stop and Step response, we can see that the direct current control in converter station can control the active power and reactive power well.1. This paper simulates the internal converter AC single phase short circuit, phase short-circuit fault. During the internal AC bus fault, the dc side capacitor discharge from the discharge path through the fault phase flow valve and the fault point, resulting in the DC voltage drop.2. Simulating the internal converter dc side short circuit fault. During the fault the dc side voltage is zero and the dc power transmission is interrupted.3. Simulating the internal converter short circuit fault. The short-circuit fault of the rectifier side will alternate with the two-phase short-circuit, three-phase short circuit and the short DC side phenomenon.4. Simulating open circuit fault of converter valve. Changes in the topology structure of the circuit, the fault phase current positive half cycle or negative half cycle was stripped, three-phase current appear DC component.5. Simulating the VSC-HVDC system DC line break, unipolar grounding, bipolar short-circuits fault conditions.At last, the response of the system is analyzed, and the characteristics of the system are described, the variation of the voltage and current during the fault is studied.