电气化铁路低频等幅振荡机理分析

Mechanism Analysis of the Sustained Low-frequency Oscillation in the Electric Railway System

近年来,牵引供电网一电力机车系统(以下简称车网系统)低频振荡现象频繁发生,造成牵引网电压、电流出现长时间的低频等幅振荡,导致牵引闭锁,严重危及行车安全。目前,已有的研究工作忽略了脉宽调制(pulse width modulation,PWM)中饱和限幅器对低频振荡的影响,难以解释持续等幅振荡的发生机理且无法有效预测振荡的幅值信。针对该问题,首先建立静止坐标系(αβ)下含二阶广义积分器(second-order generalized integrator,SOGI)、锁相环(phase-locked loop,PLL)、直流电压环(DC-link voltage controller,DVC)、电流环(current controller,CC)在内的电力机车单输入单输出(single input single output,SISO)阻抗模型,并给出饱和限幅器双正弦描述函数模型;进一步推导车网系统线性与非线性部分分离的等效闭环传递函数,并基于描述函数法,研究个饱和限幅器对低频振荡幅值和频率的影响,揭示等幅振荡的发生机理,给出振荡频率、幅值的近似计算方法;最后,通过仿真系统验证理论分析的有效性和正确性。

In recent years,low-frequency oscillation(LFO)has frequently occurred in the electric train and traction network interaction system(hereinafter train-network system),which causes the low-frequency and sustained oscillation of the traction voltage and current.This phenomenon leads to the traction locked of the train and endangers the safe operation of the train.At present,the impact of the saturation limiter of pulse width modulation(PWM)on the LFO is not fully considered,so the mechanism of the sustained LFO is not revealed.Additionally,the magnitude of the sustained LFO cannot be predicted.To solve this problem,firstly,the detailed single input and single output(SISO)impedance model of the train including second-order generalized integrator(SOGI),phase locked loop(PLL),DC-link voltage controller(DVC)and current controller(CC)were built in the stationary frame(-αβ),and a two-sinusoid-input describing function model of the saturation limiter was built.Furthermore,an equivalent closed loop transfer function that separates the linear part and nonlinear part of the train-network system was derived.Based on the describing function,impacts of saturation limiter on the frequency and magnitude of the LFO were studied,which reveals the mechanism of the sustained LFO and calculated the oscillatory frequency and oscillatory magnitude.The simulation results validate the effectiveness and correctness of the theoretical analysis.