Capacitor Voltage Balance Boundary Analysis of a Modified Five‐Level Boost Converter Under Unbalanced Load

ABSTRACT The unbalanced neutral‐point voltage in five‐level neutral‐point clamped (NPC) converters limits their application in industry. A modified five‐level boost rectifier as the front‐end of the converter used for power factor correction and neutral‐point voltage balance was recently proposed to solve this issue by coordinating the control strategy of the rectifier and inverter. However, the maximum allowable unbalanced degree of the converter under the unbalanced load is not clearly analyzed. Clarifying the voltage balance boundary is beneficial to simplifying the voltage balance method based on coordination. Therefore, the working principle of the modified five‐level converter is comprehensively analyzed in this paper. On this basis, the maximum allowable unbalanced load restriction is revealed, which provides a theoretical basis for the optimal coordinated control between rectifier stage and inverter stage. Simulation and experimental results verify the correctness of the voltage balance boundary analysis.