A reduced switching frequency range Unipolar Hysteresis Current Controller for single phase grid connected system

Current controlled voltage source inverters (VSI) find wide applications in transporting power from various energy sources into the grid. Current control of VSI is critical and challenging to maintain grid quality. The hysteresis current control (HCC) based control strategies are effective due to inherent advantages like short circuit protection and better total harmonic distortion (THD) performance. The HCC strategy also has disadvantages like the wide variation in switching frequency, which makes LC filter design complex. The present work proposes a ripple modifier-based control structure to reduce the switching frequency range in the double-band unipolar HCC scheme. The filter function F(s) aids in extracting ripple current information from the inductor current is discussed. With the help of the LT spice simulation tool, the performance of the proposed control scheme was evaluated. A hardware setup of a 1.25 kVA single-phase grid-tied inverter system was built to evaluate and verify the proposed control scheme.