大规模交直流电力系统仿真计算的相关问题

针对大规模交直流电力系统仿真计算中涉及到的几个相关问题进行了讨论。指出用于大规模交直流电力系统仿真计算的最有效的工具是带有用户自定义功能的交直流电力系统数字仿真程序，传统的动模试验和最新出现的实时数字仿真器并不适合于对大规模交直流电力系统进行系统研究。通过考察直流输电换流器准稳态模型导出的条件，阐明了直流输电换流器的准稳态模型在交流系统不对称故障期间是不适用的。论证了影响逆变器换相失败的因素有多个，重点研究了触发越前角、换流站交流母线电压跌落，直流电流增大以及换流变压器短路阻抗等因素对换相失败的影响。通过实例论证了交流系统故障时直流输电系统的动态响应特性，必须在仿真过程中通过对直流输电系统及其控制器的行为进行精确的仿真计算才能得出，凭经验事先估计直流输电系统在交流系统故障时的响应特性是不科学和不可靠的。

SOME PROBLEMS IN THE SIMULATION OF LARGE-SCALE AC/DC POWER SYSTEMS

Some problems in the simulation of large-scale AC/DC power systems are discussed. It can be justified that the most effective tool for large-scale AC/DC systems analysis is the digital simulation software with the functions of users' definition. Both the conventional dynamic modeling device and the newly real-time digital simulator are not suitable for the analysis of large-scale AC/DC systems. By studying the presupposition of the quasi-steady state model of the HVDC converter, the quasi-steady state model of the HVDC converter is proven to be invalid when asymmetrical faults occur in the AC system. It is also demonstrated that there are several factors causing HVDC converter commutation failure, the most important factors include the advance firing angle, the voltage drop of the converter AC bus, the direct current increment and the short circuit impedance of the converter transformer. An example further proves that the dynamic response of the HVDC system under AC system faults can only be calculated in the process of the simulation and can not be determined in advance.