Control strategy for input-parallel-output-parallel connected high-frequency isolated inverter modules

This paper presents a control strategy for input-parallel-output-parallel (IPOP) connected modular inverter systems. Each modular inverter is composed of a high-frequency isolated dc/dc converter followed by a dc-ac inverter. The control objective of the configuration is to achieve output current sharing among the constituent modules and also can suppress the circulating current among them successfully. The control of all the dc-dc converters in the proposed configuration is based on open-loop control by sharing a fixed and common duty cycle for them. For the control of dc-ac inverters, a three-loop control strategy, consisting of common output voltage regulation (OVR) loop, individual circulating current suppression (CCS) loops, and individual inner current tracking (ICT) loops, is proposed. The ICT loops are implemented by hysteresis current control. Based on hysteresis current control for all ICT loops, the relationship between the OVR loop and CCS loops is analyzed with revealing that both of them are decoupled. The compensator designs of the OVR loop and individual CCS loops are also presented. The effectiveness of the proposed control strategy is verified by simulation and experimental results of a 1100-W IPOP two-module inverter system with each module consisting of two-transistor forward dc-dc converter followed by a full-bridge dc-ac inverter.