对称双极柔性直流输电系统功率转带控制策略

Control Strategy of Power Transfer in Bipolar HVDC Flexible Transmission System

对称双极柔性直流输电系统若发生单极故障可将故障极全部或部分功率快速转带至非故障极,降低甩负荷对交流电网稳定性的影响。为了确保功率转带过程顺利完成,首先提出功率转带的可行性条件和流程;然后建立功率转带过程实时数字仿真模型,分析直流场电气特性并提出功率转带速率参数优化方法;最后依托厦门柔性直流输电工程给出设计实例并进行试验验证。结果表明：功率转带时,平波电抗器、直流电缆等设备使直流电流不能快速达到设定值,功率不能及时输送而累积在换流阀电容上,易使直流电压过压保护动作;采用500 MW/10ms功率转带速率试验时将引起直流过压Ⅰ段保护动作,而采用优化后速率500 MW/60 ms时可确保功率转带顺利完成。厦门柔直工程在分析转带过程直流场电气特性基础上,通过优化功率转带速率的方式使功率转带过程顺利完成,证明对称双极柔性直流输电系统功率转带控制策略的有效性。

If single-pole faults occur in bipolar HVDC flexible transmission system, the power can be transferred to the normal pole quickly, and the influence of load shedding on the stability of the power grid is reduced. In order to ensure that the power transfer can be successfully completed, firstly, we put forward the feasibility conditions and the process of power transfer; secondly, we established a real-time digital simulation model during the power transfer process, analyzed the electrical characteristics of DC field, and proposed an optimization method of power transfer rate, finally, a designed example was given and the verification tests were conducted at Xiamen HVDC flexible transmission project. The test results show that the direct current rising speed is limited by reactor and cable, so the power can not be transmitted in time and accumulated in the modular multilevel converter, which can lead to DC overvoltage protection action. When the power transfer rate is 500 MW/10 ms, the DC overvoltage Ⅰ segment protection action is caused. When the power transfer rate is optimized by using the numerical valued of 500 MW/60 ms, the power transfer process is successfully completed. Based on the analysis of the electrical characteristics of DC field, the power transfer is successful implemented in a Xiamen HVDC flexible transmission project by optimizing the power transfer rate, which proves the feasibility of control strategy of power transfer process in bipolar HVDC flexible transmission system..