Study of a power line conditioner aiming at compensation for unidentified harmonics in distribution systems

提出了一种由两个小额定串联有源滤波器和一个并联型无源滤波器组成的新型电力线调节器。电力线调整器针对的是一种通用的滤波系统，该系统将安装在电力系统的公共联结点，向谐波敏感负荷和未识别的谐波产生负荷供电。两个采用电压型PWM逆变器的有源滤波器中，一个与电源串联，另一个与并联无源滤波器串联。本研究中特别设计的无源滤波器由第11和第13个调谐LC滤波器和一个高通滤波器组成，电力线调节器的目的是减少连接点的电压失真，并消除进入连接点上游系统的谐波电流。也就是说，电力线调节器能够补偿电源电流和母线电压的谐波，从而使连接在公共母线上的产生谐波的负载和谐波敏感的负载之间不会产生谐波干扰。讨论了其滤波特性，重点讨论了电压和电流失真。为了验证电力线调节器的功能和性能，构建了一个20kVA的假想配电系统，该系统为谐波敏感负荷、识别的和未识别的产生谐波的负荷供电。结果，获得了良好的滤波特性，从而使电力线调节器得到了实际应用。指出谐波检测与计算电路的精度对公共母线电压的谐波抑制有很大影响。

The authors propose a new power line conditioner consisting of two small rating series active filters and a shunt passive filter. The power line conditioner aims at a general filtering system which will be installed at the point of common coupling in a power system feeding harmonic-sensitive loads and unindentified harmonic-producing loads. One of the two active filters using voltage-source PWM inverters is connected in series with the supply, while another is in series with the shunt passive filter. The specially desgned passive filter in this research consits of 11th and 13th tuned LC filters and a high pass filter.The prupose of the power line conditioner is to reduce voltage distortion at the connection point, and is to eliminate harmonic curents escaping into the system upstream of the connection point. In other words, the power line conditioner is capable of compensating for harmonics of supply currents and bus voltages, so that no harmonic interference occurs between harmonic-producing loard and harmonic-sensiteive loads which are connected on the common bus.A control scheme of the two series active filters which play and important role is described. Its filtering characteristics are discussed with the focus on voltate and current distortion. An hypothetical distribution system of 20kVA which feeds a harmonic-sensitive load, and identified and unidentified harmonic-producing loads is constructed to verify the functionality and performance of the power line conditioner. As a result, good filtering characteristics are obtained, thus leading to practical use of the power line conditioner. It is pointed out that the accuracy of the harmonic sensing and calculating circuit greatly affects harmonic reduction of the common bus voltage.