An investigation of voltage balancing circuit for DC capacitors in diode-clamped multilevel inverters to realize high output power density converters

Output power density of power converters has been increasing. At the same time, the power converters with lower harmonics and lower electromagnetic interference are required in many applications. To satisfy these requirements, the volume of filters and heat sinks should be reduced. As a solution to realize higher output power density and lower harmonics, diode-clamped multilevel inverters are investigated. In this case, the voltage balancing circuit must be connected to the DC capacitors because the DC voltages tend to unbalance when the number of the output level exceeds three. Therefore, the total volume of the converters including the voltage balancing circuit should be investigated. In this paper, resonant switched capacitor converter is treated as a promising solution to realize the voltage balancing circuit with smaller volume. The operating characteristics and estimated volume are clarified analytically. Finally, the applicability of the voltage balancing circuit is confirmed by the experimental results.