Improvement of electric power quality using active power filter for systems with nonlinear loads

This paper presents a simple calculation method for reference current of three-phase shunt active power filter that uses the load current feedback, reference frame transformation, and digital low-pass filter. The determination for reference current is conducted by first sensing the currents from the non-linear load. The direct and quadrature components of the reference current are then obtained from the corresponding load current components in the rotating frame by means of a low-pass filter. Applying the derived approach. the input source current harmonics and reactive power are compensated by the proposed active power filter. Unlike the traditional approach, by using the proposed control scheme, no sensor for the source voltages and no calculation for the instantaneous real and reactive powers on the load side are required. Analysis and experiments indicate that the proposed active power filter can improve the total harmonic distortion and power factor for systems with balanced, as well as unbalanced, loads.