QZSI DC/DC converters in input-series output-parallel connection for distributed generation

This paper presents the configuration and control strategy for an input-series- and output-parallel-(ISOP) connected isolated DC/DC converter. The constituent modules are voltage-fed quasi-Z-source inverters with a single-phase isolation transformer and a voltage doubler rectifier. Experimental measurements with common duty cycle in open loop operation mode are shown in order to observe divergence of the system caused by the parasitic elements of the converters. In order to ensure the proper operation of the system, inverters input voltage sharing must be ensured. The control strategy is based on a common voltage control loop to regulate the output voltage and the input voltage balancing is ensured by means of the addition of a voltage control loop in the remaining converters.