Abstract
This paper presents a division-summation (D-Σ) digital control for a three-phase bi-directional grid-tied inverter with either two-phase modulation (TPM) or space vector pulse-width modulation (SVPWM). The bi-directional inverter can fulfill grid connection and rectification with power factor correction and PF leading and PF lagging, and it can cover wide inductance variation, reducing core size significantly. The proposed D-Σ digital approach summarizes all of the individual inductor-current variations over one switching cycle to derive control laws directly, which can overcome limitations of abc to dq frame transformation. A universal form of the duty-ratio control laws for TPM and SVPWM is introduced and a D-Σ transformation matrix is identified for simplifying the control-law derivation. 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. The control laws based on TPM and SVPWM have been derived in detail and their feature comparison has been also presented. Measured results from a 10 kVA 3f bi-directional inverter have been presented to confirm the control-law derivation and discussion.