Switched capacitor DC-DC converter based current equalization scheme for maximum power extraction from partially shaded PV modules without bypass diodes

Abstract

The use of `by pass' diodes to prevent damage to series connected photovoltaic (PV) modules of a PV array in case of partial shading leads to complete power loss from the shaded modules. This paper explains the use of Switched Capacitor (SC) dc-dc converters in place of module by pass diodes to prevent power loss from partially shaded modules. SC converters have the advantage of being compact, cost effective and highly efficient under certain operating conditions. An SC converter is connected across each PV module. The SC converter injects an equalization current across the PV module while maintaining the module at its maximum power point voltage. The injected equalization current is the difference between the maximum current generated by any of the series connected PV modules and the current of that particular PV module. This enables the PV array to conduct the current corresponding to the current of the module generating maximum current. Thus partially shaded modules are allowed to generate what ever power they can. The choice of an optimum charge transfer capacitor for the SC converter and its efficiency issues are also discussed.