高压直流系统改进型最小换相裕度控制策略

当直流侧发生单极故障(如线路故障、极区故障、单阀组故障等),故障极可通过线路互感引起非故障极的直流电流增大,导致阀的换相裕度减少,严重时会发生换相失败。当无交流电压畸变,最小换相裕度控制(AMIN)灵敏度不够高,无法及时启动紧急触发避免换相失败。针对最小换相裕度控制,文章首先给出现有策略的理论推导；第二,分析其未达到预期效果的影响因素；第三,针对影响因素,对应地提出了考虑换相过程中直流电流变化、采样延时及预测控制的改进型最小换相裕度控制策略；最后,基于PSCAD/EMTDC模型,对提出的改进型最小换相裕度控制策略进行测试和分析。测试结果表明,改进的策略能有效的避免因直流侧单极故障引起的非故障极换相失败的发生；验证了所提改进策略的有效性。#$NL关键词：直流输电; 单极故障; 换相失败; 紧急触发; 最小换相裕度控制; 预测型#$NL中图分类号：TM722

Improved AMIN control strategy of HVDC system

When a unipolar fault occurs on the DC side (such as line fault, pole fault, single valve fault, etc.), the DC current of the non-fault pole increases due to the mutual inductance of the line. Increasing of current results in insufficient commutation margin of the valve and commutation failure occurs in severe cases. When there is no AC voltage distortion, the sensitivity of the minimum commutation margin control (AMIN) is not enough and the emergency trigger cannot be started in time to avoid the commutation failure. For the minimum commutation margin control, firstly, the article gives the theoretical derivation of the existing strategy; secondly, analyzes the influencing factors that do not meet the expected effect of the design; thirdly, the improved minimum commutation margin control strategy which correspondingly proposes to consider DC current variation during the commutation, sampling delay and predictive control for the possible influencing factors are proposed; Finally, based on the PSCAD/EMTDC model, the proposed improved minimum commutation margin control strategy is tested and analyzed. The test results show that the improved strategy can effectively avoid the occurrence of non-faulty pole commutation failure caused by DC side unipolar failure; these verify the effectiveness of the proposed improvement strategy.#$NLKeywords: HVDC; Unipolar fault; commutation failure; emergency trigger; minimum commutation margin control; predictive type.