Impedance model based stability analysis of grid-tied inverters

Abstract

This Bachelor's thesis investigates the stability of single-phase LCL grid-connected inverters through an impedance model approach, establishing impedance as a key stability factor. It introduces the DB-DB-PI controller, a tailored triple-loop control strategy for enhancing inverter performance by integrating single-phase voltage source inverters with LCL output filters. This controller combines dual dead-beat (DB-DB) internal loops with an external proportional-integral (PI) loop for precise regulation of inverter output current, filter capacitor voltage, and grid-injected current. The dead-beat internal loop's quick response facilitates a wider adjustment bandwidth for the external loop, boosting system dynamics and stability. MATLAB/Simulink simulations and the small signal injection method were used to analyze output impedance and validate the control strategy's effectiveness through Bode plot comparisons, offering insights for developing efficient and stable grid-connected inverters.