LAUSR

This article proposes an approach to control a photovoltaic cascaded H-bridge multilevel inverter with failed cells and changing meteorological conditions for large-scale grid-connected applications. The controller development is based on an analysis of the interaction between the inverter common-mode and differential-mode quantities, which is done in the time domain, supported by a space vector representation analysis. The proposed approach is able to produce balanced three-phase line-to-line voltages and currents even if there is a failed cell or if the fluctuating meteorological conditions cause uneven power distribution among the bridges. This is achieved through the modification of the pulsewidth modulation reference phase voltage angles combined to the injection of a dynamic homopolar component. Such an approach avoids tripping the system due to the protective functions #25 and #87 for per grid applicable codes and standards. Numerical simulations and laboratory experiments performed on a seven-level converter with different abnormal conditions to confirm the effectiveness of the suggested control strategy.