HVDC换流器交流等值谐波阻抗研究

Study on AC-side Equivalent Harmonic Impedances of HVDC Converter

高压直流(HVDC)输电换流器交流等值谐波阻抗的计算对交直流系统谐波不稳定的研究和HVDC系统交流滤波器的设计具有重要意义。基于开关函数法,计及换流器直流侧谐波电流调制到交流侧产生的两种主导谐波电流的影响,同时考虑这些谐波经换流器的反复多次调制,提出了新的换流器交流等值谐波阻抗模型。通过分析换流器谐波对其交流等值谐波阻抗的影响,提出了基于时域仿真计算换流器交流等值谐波阻抗的方法并给出了具体的计算步骤,该方法消除了换流器自身是一个谐波源对仿真结果的影响。最后,以宜华直流工程为算例,将换流器交流等值谐波阻抗数学模型计算结果与时域仿真结果进行对比,表明新的换流器交流等值谐波阻抗模型较当前主流数学模型的准确性有较大改善并且在低频范围内有较高的准确度。

The calculation of AC-side equivalent harmonic impedances of HVDC transmission converter is of great significance to the study on harmonic instability of the AC / DC systems and the design of AC filter of HVDC system. Based on switch function, this paper considers the effects of two kinds of dominant harmonic currents generated in the modulation process from the DC side harmonic current to the AC side which are modulated by converter over and over again and presents a new model of AC equivalent harmonic impedance of converter. Through the analysis of the influence of converter harmonics on the AC equivalent harmonic impedance, the time domain simulation calculation method of AC equivalent harmonic impedances of converter is presented which solves the problem of harmonic generated by converter in the simulation results, and the detailed calculation steps are also given. At last, Yi Hua HVDC project is taken as an example, the accuracy of AC equivalent harmonic impedances model of converter proposed in this paper is higher than that of the current mainstream mathematical model, and this model also has higher accuracy in the low frequency range by comparing calculation results of the mathematical model of the AC equivalent harmonic impedances of converter with time domain simulation results.