±800 kV特高压直流系统换流器控制

Converter Control in 800 kV DC Transmission System

±800 kV特高压直流系统采用双12脉动换流器串联的接线方式,为研究对其实施有效控制的方法,采用EMTDC仿真分析了双串联换流器的基本控制原理、投切单一换流器和其它各种故障后换流器的控制特性。结果表明,双换流器串联的直流系统仍可采用整流侧换流器控制直流电流,逆变侧换流器控制直流电压的基本运行控制策略。当对换流器独立控制时,加入误差消除环节能有效控制发散现象,保证特高压直流系统的稳定运行和各种故障下的运行性能。

Two 12-pulse converters in series will be applied in the recent ±800kV DC transmission projects in China The basic control strategy for the double converters in series has been illustrated and analyzed in this paper. As many other HVDC systems, the basic operation control strategy of ±800kV DC transmission system is that DC current is controlled by two rectifiers simultaneously during normal operation while DC voltage is controlled by two inverters themselves or OLTC of inverters. The simulation results by EMTDC program demonstrate that independent control for each converter without inter-communication between them on this strategy can insure the performance of the system to operate symmetrically during steady operation and to response properly under fault conditions as various AC and DC faults. It is discovered that the inherent unbalance between two controllers of converters in series will lead to control shift at steady statement. For example, one of controllers is working at min. control angle as 5° and the other one at some larger angle. The error elimination part should be included into control chain to avoid such control shift. As an essential method to improve the availability of HVDC system with two converters in series the by-pass switch is usually applied to the converter. The sequence control of fault converter isolating by by-pass switch and the de-blocking of isolated converter is also simulated in this paper without any reduction and interruption of DC power.