Control methods and compensation characteristics of a series active filter for the neutral conductor

Due to the advance of information technologies, a large number of electronic products such as personal computers have been connected to power distribution systems in commercial buildings. Hence, voltage distortion on utility outlets and excessive neutral current on distribution lines have arisen, and those lead to a number of serious problems in the distribution system. Two control methods and the related compensation characteristics of a series active filter connected to the neutral conductor are presented in this paper. The distinct functions of the proposed active filter are mitigation of 3rd-harmonic voltage and neutral current in a three-phase four-wire distribution system in a building. The required power of the proposed active filter is less than 10% of that of the harmonic producing loads. A control method of the dc capacitor voltage on the active filter circuit is also described. it is clarified through experiments that one those two functions of the active filter can be realized selectively and the dc capacitor voltage of the active filter can be regulated to a desired value.