An Algorithm for Switching Time Calculation in a Unipolar SPWM Grid-Connected Full-Bridge Inverter

This article presents a hybrid (offline–online) algorithm for controlling a single-phase full-bridge inverter connected to the grid using unipolar SPWM modulation and an LCL filter. The methodology could reduce the real-time computational load by shifting the solution of transcendental equations to a preliminary stage. Using Bolzano’s Theorem, the approximate switching instants are precalculated and stored in a lookup table (LUT) with high temporal resolution. During online execution, the algorithm synchronizes power injection by indexing the switching times in a lookup table (LUT) based on the phase extracted by a discrete phase-locked loop (PLL). The main contribution lies in the integration of an analytical feedforward angular compensation, which cancels the intrinsic phase shift of the LCL filter and allows operation at unity power factor in open-loop, eliminating the need for complex current controllers such as Proportional-Resonant (PR) schemes.