Impact of PV string shading conditions on panel voltage equalizing converters and optimization of a single converter system with overcurrent protection

Abstract

Unequal irradiance of series connected PV panels in a string strongly decreases the output power of the PV system, as either PV panels are bypassed or operated below their MPP. By connecting balancing converters around each pair of adjacent PV panels, all panels can maintain the operation close to their MPP regardless of any mismatched operating condition. In this paper a balancing converter concept with ZVS is introduced and the operation of a string of PV panels equipped with balancing converters is analytically described. Based on this analytic framework, different examples of shading scenarios of a PV string are examined regarding the average inductor current values that occur within the balancing modules, in order to derive the required specifications of a balancing converter. Moreover, a two-level overcurrent protection concept is introduced which enables to keep all balancing converters within the safe operating area at all times, even at shading conditions with high mismatch. Furthermore, the design optimization of a highly efficient PV voltage balancing converter with a wide input voltage range is explained in detail and finally the concept is verified with measurement results of a demonstrator system.