Keywords: power factor, inverter, shunt active filters, harmonics, hysteresis controller, unbalanced supply, nonlinear loads, robust control, simulation
Power factor improvement using active filter for unbalanced three-phase non-linear loads
In this paper, a modified shunt active filter is used under unbalanced three-wire supply voltages with non-linear loads. The main objective of the proposed shunt active filter is to control the three-phase supply currents both in its waveform, magnitude and phase to follow three-phase reference signals. The reference signals are derived from one of the phase voltages. When this is achieved, ideally the supply current will then be always sinusoidal, with robust control over its magnitude and phase, irrespective of the harmonics and unbalance of the load demand or the supply voltage system. This confirms nearly unity power factor on supply side and reactive compensation by the active filter in static-compensator mode. The proposed shunt active filter control strategy is based on hysteresis control, which is very simple to implement and does not even require any measurement of the load demand. The controller performance is improved by incorporating an additional loop that can respond to the variation in the DC bus voltage due to changes in the real and reactive power demand. This paper presents the detailed design analysis of the proposed active filter with simulation and test results obtained from the laboratory implementation.