An active filter for retrofit applications

The increase in the occurrence of nonlinear loads in power systems has caused considerable concern to power utilities and manufacturers of power electronics equipment. To alleviate the problems caused by generation of current harmonics, there has been considerable interest in the use of active filters. This paper presents a new approach to the design of active filters which is developed from a unified approach described by Koozehkanani (1996). The proposed active filter configuration provides an alternative approach which has several advantages. Compared with the constant voltage and constant current types, this circuit is much simpler, and the switching frequency is lower, 4 kHz compared with frequencies of the order of 27 kHz. The flexibility afforded by this approach makes it suitable for retrofit applications because filters of this type can be connected to any part of a network. The experimental work reported here was carried out at 120 V supply voltage at power rating of 700 W.