三相四线制下中线谐波电流治理的新方法

提出了一种中线谐波电流治理的新结构，该结构由新型无源滤波器和有源滤波器串联构成。其中无源滤波器包括3次、9次单调谐滤波器和高通滤波器，每个滤波支路都由三相电容器连接成星形后与一个电感（高通滤波器中还有一个并联电阻）串联构成。电网中的非零序电压全部由电容器承担，同时，流经无源滤波器电感和有源滤波器中的电流仅为谐波电流，大大降低了有源滤波器的容量和成本。文中分析了其基本原理：当有源滤波器输出一定的电压时，不仅可以使零序谐波电流完全流入滤波器中，而且可以抑制系统零序谐波电压产生谐波电流，从而使电网侧中线中仅含基波电流。文中提出了一种简单的控制方法，它仅利用电网侧零序谐波电流作为控制信号来产生有源滤波器所需的驱动信号。最后，利用PSCAD／EMTDC进行了仿真验证，仿真结果表明该结构中的有源滤波器的容量较小而且滤波效果较好。

A NOVEL METHOD TO CANCEL THE NEUTRAL HARMONIC CURRENT IN THREE-PHASE FOUR-WIRE SYSTEM

A novel power filter topology for canceling the neutral harmonic current is proposed.It is composed of a novel passive filter and an active filter,which are connected in series.And the passive filter consists of a high- pass filter branch and tow tuned filter branches for the third and ninth harmonics. Each branch has three star- connected capacitors and an inductor an additional resistor connected in parallel with the inductor for the high- pass branch connected in series.The capacitors sustain the non- zero sequence part of the system voltage. Furthermore,there is only harm onic current flowing through the inductors and the active filter.These all reduce the ratings and cost of the filter.Theoretical analysis of the principle is presented. If the active filter outputs a certain voltage,the neutral harm onic currents from the load will be forced to the filter and the harmonic currents,generated by neutral system voltage,will be suppressed.Thus,the neutral system currentwill be distortion- free.Furthermore,a simple control m ethod is introduced.Merely using the neutral harm onic current as control signal,it can generate the driving signals to the active filter. To verify their validity,the PSCAD/ EMTP simulation is done. It is approved by the simulation results that the ratings of the active filter are small and the filtering perform ance is perfect.