D-Σ digital control for three-phase active power filter

This paper presents a division-summation (D-Σ) digital control applied to a three-phase active power filter (APF) with a three-leg inverter. The three-leg inverter shapes the source current sinusoidally by injecting harmonic currents to compensate the load current. The proposed D-Σ digital control approach summarizes the inductor-current variations over one switching cycle to derive control laws directly, which can overcome the limitation of abc to stationary d-q frame transformation. In the design and implementation, the inductances corresponding to various inductor currents were measured at the startup and stored in the microcontroller for scheduling loop gain cycle by cycle. Compared to conventional approaches, the proposed control can cover wide filter inductance variation and achieve wide bandwidth upto switching frequency. Measured results from a 5 kVA 3D APF have confirmed the analysis and discussion of the proposed control approach.