【摘要】 为评估混合直流输电直流侧电压质量,解析其谐波成分和幅值计算等效电路,该文采用平均开关状态法分析MMC,调制理论分析LCC产生的谐波,推导各次谐波的幅值计算表达式,简化等效电路。在此基础上,分析了LC滤波后的波形和谐波成分,在交流侧三相不平衡度较大时,LC滤波器平抑低频谐波效果差;为抑制因三相不平衡引起的直流侧低频脉动,设计了两种3阶低通滤波器,并对比了它们与LC滤波器在滤波效果和动态响应时间上的差别,结果表明巴特沃斯滤波器的指标最佳。利用MATLAB/Simulink软件建立了混合直流输电模型,仿真结果显示所推导的谐波幅值计算表达式和等效电路能正确反映直流侧的谐波特征,所设计的滤波器能更好地消除低频谐波。更多还原

【Abstract】 In order to evaluate the voltage quality of direct current(DC) side in hybrid high voltage direct current(HVDC) transmission, the harmonic component and amplitude calculation equivalent circuit of the DC side in HVDC are analyzed. The average switching state method is used to analyze modular multilevel converter(MMC)and the modulation theory is applied to analyze the harmonics generated by line commutated converter(LCC).Then, amplitude calculation expression and simplified equivalent circuit of each harmonic are derived. On this basis, the LC filtering waveform and harmonic components are further examined and the result shows that the LC filter has poor effect in suppressing the low-frequency harmonics under the large alternating current(AC)three-phase unbalance factor. Thus two kinds of third-order low-pass filters are designed to suppress low frequency fluctuation of DC side caused by three-phase unbalance. Comparing the difference of the filtering effect and the dynamic response time between the designed filters and LC filter, the results show that the Butterworth filter has the best index. The hybrid HVDC transmission model is established by using MATLAB/Simulink software. The simulation results show that the derived harmonic amplitude calculation expression and equivalent circuit can correctly reflect the harmonic characteristics of the DC side, and the designed filters has better effect in eliminating the low frequency harmonics.更多还原