多桥换流器高压直流输电送端谐波不稳定分析与抑制

摘要

针对多桥换流器高压直流输电系统送端换流站不同工况直流偏磁下谐波不稳定问题,基于单桥6脉波换流器的开关函数和调制理论,考虑换流变压器的叠加特性,得到不同工况下多桥换流器数学模型.在此数学模型基础上,分析了谐波在交直流侧的相互调制,推导出了不同工况下多桥换流器的谐波放大倍数及谐波不稳定的定量判据,并且综合分析影响判据的多种因素,提出了通过合理设计交直流系统阻抗以及合理安排系统的运行工况从而提高系统谐波稳定性的有效措施.最后,在PSCAD中构建了多桥换流器高压直流输电系统电磁暂态仿真模型进行验证,仿真结果验证了所述措施的正确性与有效性.%For the harmonic instability problem with the multi bridge converter caused by direct current (DC) magnetic bias in a high voltage direct current (HVDC) transmission system under different operating conditions,based on the switching function and modulating theory of the single-bridge 6-pulse converter,given the superposition characteristics of the converter transformer,the mathematical model of multi-bridge converter under different operating conditions is developed.Then,the modulation of harmonic between the AC/DC system sides through the obtained model is analysed,the magnification of harmonic and reliable criteria for determining harmonic instability of the multi bridge converter are quantitatively deduced.By comprehensively going over various factors affecting the criterion,some effective measures to improve system harmonic stability by reasonably designing the AC/DC system impedance and arrangement of operating conditions of the system are proposed.A simulation model for the multi-bridge converter based on PSCAD/EMTDC is built,the results verifying the correctness and effectiveness of the proposed criteria and measures.