基于时域分段法-相量法混合建模的直流输电交流系统的谐波电流计算

Harmonic current calculation of DC transmission AC system based on hybrid modeling of time-domain segmentation method and phasor method

换流器作为高压交直流输电系统中的重要元件,因其存在复杂的电力电子器件而产生大量频次的谐波严重影响到输电系统的安全稳定,获取交直流输电系统交流侧谐波电流是谐波治理的基础,因此交流侧谐波电流的精确计算具有重要意义。本文基于时域分段法的思想,充分考虑到直流纹波电流的影响,提出了内外双环迭代的计算方法:内环采用时域分段法计算直流侧端口电压瞬时量、采用相量法计算直流侧纹波电流、利用直流纹波电流和直流侧端口电压耦合迭代计算的方法计算直流侧纹波电流;外环利用换相过程中退出换相的相电流在换相结束时刻电流过零的特点,结合纹波电流迭代计算换相角的方法精确获取换相角和交流侧谐波电流。与PSCAD/EMTDC模型计算结果对比表明:此方法既保证了谐波电流计算结果的精确度和计算效率,也充分计及了工频负序电压、背景谐波电压、触发角不等距、换相电感不平衡、变比误差、测量误差、纹波电流等各种非理想因素的影响,同时易于程序实现。

As an important component in the high-voltage AC/DC transmission system,the converter has a large number of frequency harmonics due to the existence of complex power electronic devices,which seriously affects the security and stability of the transmission system.The acquisition of harmonic current on the AC side of the AC/DC transmission system is the basis for harmonic control,so accurate calculation of harmonic current on the AC side is of great significance.Based on this,based on the idea of time-domain segmentation method,and fully considering the influence of DC ripple current,this paper proposes an iterative calculation method of inner and outer double loops:the inner loop uses time-domain segmentation method to calculate the instantaneous DC side port voltage,the phasor method to calculate the DC side ripple current,and the DC side ripple current is calculated using the iterative calculation method of coupling DC ripple current and DC side port voltage.The outer loop makes use of the characteristic that the phase current exiting the commutation in the commutation process crosses zero at the end of commutation,and combines the ripple current iteration method to calculate the commutation angle to accurately obtain the commutation angle and AC side harmonic current.The comparison with the calculation results of PSCAD/EMTDC model shows that this method not only guarantees the accuracy and efficiency of the calculation results of harmonic current,but also fully takes into account the influence of various non ideal factors such as power frequency negative sequence voltage,background harmonic voltage,unequal distance of trigger angle,unbalanced commutation inductance,transformation ratio error,measurement error,etc.,and is easy to program.