D-Σ digital control for three-phase Bi-directional inverters

This paper presents a division-summation (D-Σ) digital control for a three-phase bi-directional photovoltaic inverter with wide inductance variation. The bi-directional inverter fulfilling grid connection and rectification with power factor correction has been implemented in the laboratory. The proposed D-Σ approach summarizes the inductor-current variations over one switching cycle to derive control laws directly, which can overcome limitations of d-q transformation. With the digital control, the inverter can deal with wide inductance variation, reducing core size significantly. In the design and implementation, the inductances corresponding to various inductor currents are measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring stable operation. Measured results from a 10 kVA 3Φ bi-directional inverter have been presented to confirm the feasibility of the discussed control approaches.