D-Σ digital control for a three-phase transformerless bi-directional inverter with wide inductance variation

This paper presents a division-summation (D-Σ) digital control for a three-phase transformerless bi-directional photovoltaic inverter with wide inductance variation, which can eliminate the leakage ground currents due to panel parasitic capacitance. 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. Simulated and Measured results from a 10 kVA 3φ bi-directional inverter are presented to confirm the feasibility of the discussed control approaches.