Design and Analysis of the Droop-Controlled Parallel Four-leg Inverters to Share Unbalanced and Nonlinear Loads

In this paper, the performance of wireless operation of four-leg parallel inverters, at the presence of unbalanced nonlinear loads, is investigated. In order to control the parallel inverters, an inner current and external voltage control loops should be designed. In this paper, a proportional controller for the current internal loop as well as a proportional-resonant one for the voltage external loop are investigated and designed to ensure the proper performance of the system at the presence of unbalanced and nonlinear loads. In this paper, droop control and virtual output impedance loops have formed the power sharing control system for the parallel inverters. The proposed system is able to feed balanced, unbalanced, and nonlinear loads and provides an appropriate sinusoidal voltage waveform for loads by accurately sharing power between the parallel inverters. Simulation results verify the accurate and proper performance of the proposed system. Streszczenie. Zaprezentowano właściwości bezprzewodowej pracy przekształtnika w obecności niezrównoważonego, nieliniowego obciążenia. Sterowaniu podlegają wewnętrzna pętla prądowa jak i zewnętrzna pętla napięciowa. System sterowania kontroluje spadki napięcia oraz zewnętrzną impedancję. Projekt i analiza poczwórnego przekształtnika ze sterowanymi spadkami stosowanego do pracy w warunkach niezrównoważonych i nieliniowych obciążeń.