基于新型换流变压器的直流输电系统改善换相的机理

基于新型换流变压器的直流输电系统在换流变压器阀侧滤除主要特征谐波，势必会对系统换相特性产生一定的影响。探讨了逆变器换相失败的根本原因，分别建立直流输电系统采用传统换流变压器与新型换流变压器时阀侧线电压的数学模型。在此基础上，分析未接入滤波器和接入滤波器时变压器漏抗及耦合电抗对逆变器换相的影响。结果表明，通过滤波，基于新型换流变压器与基于传统换流变压器的直流输电系统均能消除耦合电抗的不良影响，但前者可大大削弱变压器漏抗的消极作用，后者没有任何削弱，说明基于新型换流变压器的直流输电系统在改善换相方面具有独特的优越性。实验证实了数学模型及理论分析的正确性。

Commutation-improving Mechanism of DC Transmission System Based on a Novel Converter Transformer

DC transmission system based on a novel converter transformer can suppress the main characteristic harmonics at valve-side of the converter transformer, which certainly influences the commutation characteristic of the system. The basic reasons which caused the inverter commutation failure were analyzed, and mathematical models to calculate the valve-side line-voltage of the DC transmission system were established based on the traditional and the novel converter transformer respectively. The influences of the transformer leakage reactance and the coupling reactance on inverter commutation were analyzed in case of DC transmission system with filters and without filters. Results show that although the DC transmission system based on the novel converter transformer and that based on the traditional converter transformer can eliminate the bad effects of coupling reactance, the former can greatly weaken the negative effects of transformer leakage reactance while the later cannot at all, which indicates that the system based on the novel converter transformer has its unique advantage of improving the commutation characteristic. The experiment proves that the theory is right and the mathematical model is ideal.