A new topology for shunt active filter without DC-link based on direct AC/AC converter

In this paper, a new topology without dc-link based on direct ac/ac converter is proposed for shunt active filter (SHAF). SHAF is an effective solution to compensate unbalanced, harmonic and distorted currents and reactive power of the non-linear and/or asymmetric loads. Most of SHAF topologies are based on voltage source converters with a relatively large capacitor as dc-link. Dc-link capacitor is a bulky and costly element and makes the control scheme more complicated. Considering unpredictable dynamic condition of utility grid and consumers connected, capacitor voltage will experience oscillations and may leave stability region, which leads to improper operation of SHAF. Elimination of the dc-link capacitor decreases the weight, bulk and cost of the SHAF, makes the control method simpler and the active filter more reliable and effective. The proposed active filter, which is more stable and reliable, has better dynamic behavior and can operate properly under distorted grid voltages and varying load conditions. The applied control strategy in order to generate compensating reference current signals is based on instantaneous power theory. Current modulation is carried out by PI technique. Operation and performance of this new topology has been verified by simulation under various load conditions.