牵引变流器直流母线电压脉动下的无拍频电流控制方法

Repetitive Prediction of Fluctuating DC Link Voltage for Traction Drives

交流供电方式下,单相整流器的工作特性导致牵引变流器的输入功率呈现脉动形式。为吸收该脉动分量,业界主流方法是在直流母线上并联LC无源滤波器,该方案大大降低了装置的功率密度。取代该滤波器的有效途径是通过实时计算对牵引逆变器的PWM脉冲宽度进行精确补偿,使得逆变器即便工作于剧烈脉动的母线电压下,也不会输出有害的拍频电压/电流。然而对于大功率低开关频率应用场合,传统的前馈补偿方案效果不佳。本文提出了一种母线电压重复预测器,使前馈补偿性能得到极大改善。该预测器利用母线电压脉动的重复性,精确预测下一个开关周期内母线电压的平均值,再应用面积等效算法计算下一拍所需的脉冲宽度。稳态实验结果表明,相比传统的前馈补偿方法,本方法将逆变器输出侧的拍频电流降低了6～7倍。负载突变时,只需通过控制手段确保整流器输出的母线电压跌落小于10%,则动态过程中的拍频电流亦不大。

AC-fed railway traction drives suffer from pulsating input power because of the single-phase rectifier at the front end.LC passive filter is often installed at DC link to absorb the pulsating power.However this greatly reduces the power density.An effective approach to get rid of this bulky filter is to compensate pulse width of the traction inverter so that it does not produce harmful beat components in the output voltage/current even with a fluctuating DC link.For low switching frequency at high power level,it is difficult for conventional feed-forward compensation methods to achieve good results.A repetitive DC link voltage predictor is proposed to improve the performance.It utilizes the repetitiveness of DC ripple and can predict the average value of DC link voltage in the next switching period.An area-equalization algorithm is then used to calculate the required pulse width.Experiments show that compared with conventional methods,the proposed one can reduce the steady-state beat current by 6-7 times.The dynamic beat current during load transients is also negligible only if dynamic drop of DC link voltage is kept below 10%.