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A modular structured 12-kW resonant converter with effective zero voltage switching (ZVS) is proposed to integrate renewable energy lower voltage source to the microgrid. In this study, duty cycle control is adopted until ZVS fails and thereafter, sequential and parallel adjustment of duty cycle and the switching frequency is proposed for effective output voltage regulation. The proposed control logic ensures ZVS and output voltage regulation over wide load range even at very light loads compared to conventional control methods. Further, it maintains very high system efficiency with narrow range of frequency operation. Hence, it is easy to implement using a conventional digital controller. To minimise ripple current, each of the four converters is provided with 90° phase delayed gate pulses under the proposed control scheme. This study presents an optimal design of the tank circuit elements assimilating high permeable powder cores to reduce magnetic loss and operation with IGBT switches at an optimum point to reduce conduction loss for enhanced system efficiency. A 12-kW, 400-1600 V developed prototype is tested and experimental results are discussed. [ABSTRACT FROM AUTHOR]

Summary: In this work, an isolated modular resonant circuit with effective voltage regulation is presented as front‐end for multilevel inverter system to interface renewable sources of energy with micro grid. Inputs of each module of the converter are connected to low‐voltage DC sources. Modular‐structured module outputs may be linked in sequence or parallel to attain the desired DC link capacitor voltage for multilevel inverter. The proposed converter overcomes imbalance in the capacitor voltage of diode‐clamped inverter structure. Interleaved phase shift of 90° is supplied among the gate pulses of all four modules that minimizes the input‐side current ripples. An effective zero voltage switching (ZVS) is achieved over wide load range using duty cycle and frequency‐duty cycle double control method to improve system performance at light load condition. Adopting powder core magnetics and low forward voltage insulated‐gate bipolar transistors (IGBTs) reduces magnetic and conduction loss. A 12‐kW prototype of the designed modular resonant converter was verified by experimentation with a different‐level diode‐clamped inverter structures. [ABSTRACT FROM AUTHOR]