Parallel operating of two energy storage battery systems using quasi Z-source inverter

In this paper, a power electronic interface (PEI) system is presented to parallel two energy storage battery units with difference current and voltage ratings. The PEI system is based on quasi Z-source inverter (qZSI) which is a single-stage ac/dc converter with two controllable DC ports. In non-controlled parallel operation of battery systems, the load current is shared between them according to their equivalent impedance; therefore, an effective controller is proposed to share load current between the battery systems according to their current ratings. The current sharing between battery systems is achieved by adjusting of the shoot-through duty cycle of inverter legs in a certain load demand. Moreover, the inverter modulation index is used for control of inverter current in a closed-loop configuration. In the grid-connected mode of operation that, each battery system current is independently regulated by adjustment of inverter modulation index and shoot-through duty cycle. The performance of the proposed control system in grid-connected and islanded modes is evaluated by time-domain simulation in MATLAB/Simulink environment.