Control strategy for input-series-output-parallel high-frequency AC link inverters

This paper presents a control strategy for input-series-output-parallel (ISOP) modular inverters. Each module is a high-frequency (HF) ac link (HFACL) inverter composed of an HF inverter, an HF transformer, and a cycloconverter. A PWM sequence generation based on DSP control is given, with which the circulating currents among all the constituent modules can be avoided automatically. To achieve input voltage sharing (IVS) and output current sharing (OCS) among the constituent inverter modules, a stable OCS scheme, which consists of one common output voltage regulation (OVR) loop and individual inner currents loops, is proposed. The OVR loop provides a common reference for all individual inner current loops, in which the current feedback for an individual module is the sum of all the other output currents instead of its own. The compensator designs of the OVR loop and individual inner current loops are also presented. With this control strategy, excellent IVS and OCS can be obtained. The effectiveness of the proposed control strategy is verified using the simulation and experimental results of a 1100-VA ISOP two-HFACL inverter system.