A practical 50 kVA active harmonic filter with near instant correction and useful transient response

A commercial active harmonic filter has been developed for parallel connection to a 3 phase, 415 V, 4 wire system. This paper presents an overview of the control methodology and three-level power stage together with operational results. An hysteretic or sliding mode type control is used to force the average line current to be sinusoidal. This results in robust, highspeed correction and a favourable transient response to load switching. The three-level power stage provides greater power bandwidth, smaller main inductors and lower capacitor currents.