Paralleling control technique with no intercommunication signals for resonant controller-based inverters

Abstract

Paralleling inverters remains a challenging task despite the advances that have proposed techniques based on frequency and amplitude droop methods. Problems arise when high performance inverters with very low output impedance (such as those employing resonant controllers) are to be directly connected in parallel through a near zero impedance cable. The present paper proposes a solution that retains most of the benefits of using resonant controllers while allowing good sharing when inverters are locally paralleled with very low or near zero impedance connection between them. Low THD content and good current sharing are simultaneously obtained by controlling the load angle through an LMS estimator and by synthesizing a variable inductance in series with the output impedance of the inverter, while the harmonic current sharing is achieved by controlling the gain of the resonant controllers at the selected frequencies. The method can be used with only a single voltage loop or it can be used in a high performance multi-loop approach.