Energy Balancing With Wide Range of Operation in the Isolated Multi-Modular Converter

The series-connection of modules in multilevel converters are prone to energy imbalances in the dc capacitor due to the differences between the power absorbed and consumed. In renewable energy applications where the primary source is directly connected to each module, energy imbalances can be even worse if the primary sources are affected by unpredictable weather conditions. Therefore, control strategies are required to compensate such energy imbalances, while maintaining the correct converter operation. Focusing our attention on a cascaded transformer multilevel inverter called Isolated Multi-Modular Converter, this paper introduces the combination of two control strategies aimed at providing a wide range of operation under imbalanced energy states. A general analytical model, including the regulation capability and differences with an existing strategy are presented to demonstrate the performance of the control proposed. The effectiveness of the proposal is validated through experimental results based on a three-phase multilevel prototype.