多馈入直流输电系统换相失败的抑制措施研究

发布时间：2018-07-14 08:02

【摘要】：与单馈入直流输电相比,多馈入直流(Multi-infeed Direct Current,MIDC)输电系统具有更大的输送容量和更灵活的运行方式。然而由于各直流逆变站电气距离较近,交流系统的一个扰动可能诱发多回直流发生换相失败,一旦一回或多回直流的换相失败得不到有效控制,出现单极或双极功率停运,则将导致直流传输功率大幅度下降,继而影响电网的频率稳定,电网的安全稳定运行受到严重影响。因此,采用适当的控制策略抑制MIDC输电系统的后续换相失败具有重要意义。基于MIDC输电系统换相失败已有的国内外研究内容,本文首先对换相失败的机理进行了深入地研究,通过在高压侧、低压侧换流阀设置不同时刻故障来研究换相失败的故障特性。然后对换相失败的影响因素进行了全面地分析,将多馈入短路比(Multi-infeed Interaction Short Circuit Ratio,MISCR)、谐波及交流系统故障对换相失败的影响进行了数学模型推导及Matlab验证。同时将换相失败的影响分为换流母线电压降落故障分量及换相失败电流分量的作用,对MIDC输电系统换相失败相互影响关系进行了详细的数学关系推导。最后提出了电压补偿式变斜率低压限流(Voltage Dependent Current Order Limiter,VDCOL)的抑制措施,通过PSCAD/EMTDC仿真验证得出增加该控制策略后MIDC输电系统的暂态特性得到改善,换相失败的概率也明显降低。在该基础上,提出了选择性电压补偿式变斜率VDCOL协调控制策略,即只在严重故障时切入补偿系数K值,在正常及轻微故障情况下K值为0。搭建上海电网4回多馈入直流输电系统的PSCAD/EMTDC仿真模型并进行仿真研究,研究表明,该控制策略在减少直流系统发生换相失败概率的同时也在一定程度上提高了系统的恢复性能,防止发生因直流系统恢复速度过慢导致的交流系统功角不平衡引发后续的换相失败。
[Abstract]:Compared with single feed DC transmission system, Multi-infeed Direct current MIDC (MIDC) transmission system has larger transmission capacity and more flexible operation mode. However, because of the close electric distance of each DC inverter station, a disturbance of AC system may induce commutation failure of multiple DC. Once the commutation failure of one or more DC can not be effectively controlled, the unipolar or bipolar power outage occurs. The DC transmission power will be greatly reduced, and the frequency stability of the power grid will be affected, and the safe and stable operation of the power grid will be seriously affected. Therefore, it is important to adopt appropriate control strategy to suppress the subsequent commutation failure of MIDC transmission system. Based on the existing research contents of commutation failure of MIDC transmission system at home and abroad, the mechanism of commutation failure is deeply studied in this paper, and the fault characteristics of commutation failure are studied by setting the commutation valve at different times on the high voltage side and the low pressure side. Then, the influencing factors of commutation failure are analyzed, and the influence of multi-infeed interaction short circuit MISCR, harmonic and AC system fault on commutation failure is deduced and verified by Matlab. At the same time, the effect of commutation failure is divided into two parts: the fault component of commutation bus voltage and the component of commutation failure current, and the mathematical relation between commutation failure and commutation failure is deduced in detail. Finally, a voltage dependent current order limiter-VDCOL (Voltage dependent current order) suppression method is proposed. The simulation results of PSCAD / EMTDC show that the transient characteristics of MIDC transmission system are improved and the probability of commutation failure is obviously reduced by increasing the control strategy. On this basis, a coordinated control strategy of variable slope VDCOL with selective voltage compensation is proposed, that is, the compensation coefficient K is only cut in serious faults, and the K value is 0 in normal and slight fault cases. The PSCAD / EMTDC simulation model of Shanghai power grid 4 times multiple feed in DC transmission system is built and simulated. The research shows that the control strategy not only reduces the probability of commutation failure in DC system, but also improves the recovery performance of the system to a certain extent. To prevent the subsequent commutation failure caused by the unbalanced power angle of AC system caused by the slow recovery speed of DC system.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM721.1

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