Control Strategy For Input-series Output-series Connected Inverter System

Power electronics system integration has drawn more and more attention recently. The series-parallel connection of standardized power modular becomes one hot point of the vigorous research field. The input-series output-series (ISOS) inverter system, which consists of multiple DC-AC modules connected in series at input and output sides, is very suitable for high input voltage and high output voltage applications. Input voltage sharing and output voltage sharing between the modules of the ISOS inverter system should be implemented for the normal operation of the system.The relationship between the input voltage sharing and the output voltage sharing of ISOS inverter system is analyzed firstly, and then input voltage sharing control strategy and output voltage sharing control strategy are proposed. The stability of the two control strategy is discussed. The input voltage sharing control strategy can ensure the input voltage sharing and output voltage sharing, but the output voltage sharing control strategy can not ensure the system work steadily. Based on the above analysis, a three-loop control scheme consisting of a common output voltage loop, individual inner current loops and individual input voltage sharing loops is proposed to achieve input voltage sharing as well as output voltage sharing of the ISOS inverter system. The output voltage loop provides the basic reference of the inner current loops of all modulars. The input voltage sharing loops adjust the current of output filter capacitors to realize input voltage sharing of all modulars.A 2kW ISOS inverter system consisting of two DC-AC modules is built in lab. Both simulation and experimental results verify the effectiveness of the propose control strategy.