A fast active-balancing method for the 3-phase multilevel flying capacitor inverter derived from control allocation theory

摘要

An elegant way to exploit redundancies available in multilevel converters is through a constrained optimization formulation. An interesting connection can be made with the so-called control allocation problems defined in over-actuated constrained systems. Redundancies and constraints are taken into account to achieve the best performance. In this paper, we introduce the first result of an investigation of control allocation methods for multilevel conversion. The method is dedicated to the flying-capacitor inverter with focus on the active balancing of capacitor voltages to ensure admissible blocking voltages for the switches. A linear program is formulated and solved by using the well-established simplex algorithm. Fast variations of the DC-bus voltage were applied in simulations. Disturbances are well rejected, resulting in an increased bandwidth and a safe switching operation for the semiconductors.