Modelling and analysis of parallel operated inverters

Renewable energy sources are quickly becoming incorporated into increasingly distributed electrical utility grids. An ever present issue when interfacing these sources is that of harmonic distortion reduction at the inter-tie point. Presented in this paper is the modeling and analysis of a rarely employed technique for harmonic reduction using synchronized phase shifted parallel PWM inverters with current-sharing reactors [1-4]. A main contribution of this paper is the introduction of a parallel inverters equivalent circuit model that permits any number of inverters operated in parallel to be analyzed with accuracy, simplicity and ease. The validity of the results obtained using this equivalent is investigated analytically and simulated using MATLAB/Simulink and PSpice for one, two and three parallel phase-shifted inverters using double-edge asymmetrical RSPWM modulation with various modulation indices and carrier to reference frequency ratios.