MPPT performance enhancement of low-cost PV microconverters

This paper presents a performance enhancement method for the high-gain isolated dc-dc converters intended for module level photovoltaic applications. DC voltage gain of a microconverter should change in a wide range, which requires use of undesirably high or low values of the switch duty cycle that result in high losses in the front-end stage. A reconfigurable rectifier at the output stage of the photovoltaic microconverter enables dc gain control and, consequently, limits variation of the duty cycle to more favourable range. This work proposes use of a reconfigurable rectifier capable of reconfiguring its topology from a voltage doubler to a voltage quadrupler. The paper explains the derivation, operation and the control principle of a reconfigurable rectifier. A single-switch quasi-Z-source front-end stage was used as an application example of the wide input voltage range photovoltaic microconverter in the experimental study. It is demonstrated that by the application of the proposed approach the lower boundary of the input voltage could be shifted from 20 V down to 8 V, which has enabled for the microconverter a unique possibility of shade-tolerant operation with the implementation of a global MPPT.