Series active power filter compensates current harmonics and voltage unbalance simultaneously

An active power filter connected in series to the power distribution system is presented and analysed. The series active power filter is implemented with a three-phase PWM voltage-source inverter and operates with a resonant LC passive filter connected in parallel to the power lines. The proposed scheme is able to simultaneously compensate current harmonics, the fundamental negative and zero sequence voltage components generated by the voltage source unbalance, and also eliminates the zero sequence current harmonic components that circulate through the neutral conductor. The active power filter is discussed in terms of the principles of operation under steady-state and transient conditions. The design and implementation of the power and control circuits are reported. Key predicted results are verified experimentally on a 5 kVA prototype model