Fast Voltage Stabilization Control of Split DC Bus Midpoint in 3P4W Shunt APFs

A midpoint voltage balancer (MVB) based on dual-switching-leg is proposed in this paper. The MVB provides fast voltage stabilization of the midpoint in three-phase four-wire (3P4W) shunt active power filters (APFs). Interleaved control is adopted in the MVB to prevent high-frequency current circulation in split capacitors, and to facilitate an accurate neutral current tracking. All switches of the MVB operate in zero-voltage switching (ZVS) mode when the neutral current is smaller than the nominal phase current of the APF. MATLAB simulation is carried out to verify the effectiveness of the MVB. A 20 kVA prototype has been built, and experimental results show that the voltage ripple of the midpoint is maintained within 1.5% of the total dc bus voltage even under severe neutral current transient.