直流系统采用电容换相换流器技术的特性研究

对直流输电采用电容换相换流器(capacitor com- mutated converter, CCC)技术时的系统特性进行了研究。导出了描述CCC结构直流系统稳态特性的数学模型，它由15个基本方程构成。采用数值计算方法对CCC结构直流系统的稳态数学模型进行详细的分析，并与电网换相换流器(line commutated converter, LCC)结构直流系统进行了比较，揭示了CCC结构直流系统的一些重要优势。推导出了CCC换流阀电压峰值的表达式，并在此基础上提出了选择换相电容值的方法，采用该方法所选择的换相电容值能充分发挥CCC结构直流系统的技术优势，但又不会过多增加阀的成本。采用仿真工具电磁暂态仿真程序PSCAD/EMTDC，以葛南直流单极输电系统为研究对象，交流系统发生单相对地短路故障为例，对CCC和LCC系统的暂态特性进行仿真比较，表明CCC结构直流系统具有较好的故障恢复特性。

Study on Capacitor Commutated Converter Applied in HVDC Projects

The system performance of a HVDC link applying CCC (capacitor commutated converter) technology is studied. The mathematical model representing the CCC-HVDC system's steady-state characteristics is derived, which is composed of 15 basic equations. Then the steady-state mathematical model is analyzed in detail by means of numerical computation method, some important advantages of CCC-HVDC systems are revealed compared with that of LCC (line commutated converter) based HVDC system. The peak-value expression of the valve voltage is deduced, based on which a method to select the capacitance of the commutation capacitor is proposed. With the capacitance determined by this way, the technological superiority of CCC-HVDC system can be realized, and at the same time the valve cost is increased not too much. The transient responses of CCC- and LCC- HVDC system are simulated and compared, taking a single-phase AC fault as an example. The result shows that the CCC-HVDC system has better recovery characteristics. The simulation tool is PSCAD/EMTDC. The research object is Ge-Nan HVDC monopolar transmission project.