A technique to balance a half-bridge single-phase active filter

The half-bridge converter can be successfully employed as an active filter in single-phase systems. The impact of this configuration becomes particularly relevant if the power level is limited and the cost reduction becomes a key point. In fact the half-bridge is made by only two bi-directional switches and two capacitors, being anyway able to ensure proper compensation even of the low order harmonics generated by a diode bridge. In this paper, the problem of the balancing of the voltages of the two capacitors is investigated, aiming to do not use a separate controller but only a simple combination logic that exploits the redundancies of the configuration. The simulation and the experimental results show that the voltages can not be controlled in all the conditions but this lack of performance does not affect very much the behavior of the active filter; the compensation of the selected harmonic currents is still good.