One-inductor-based auxiliary circuit for dc-link capacitor voltage equalisation of diode-clamped multilevel converter

The one-inductor-based auxiliary balancing circuit is proposed to equalise dc-link capacitor voltages of diode-clamped multilevel converters (DCMC) in this study. After theoretical analysis of balancing unit in traditional one-level-based balancing schemes, one-inductance-based schemes are designed according to the same operating principle. Via some conducted diodes and switches by simple control, this circuit provides energy exchange paths of all the dc-link capacitors by only one inductor. Firstly, the inductor absorbs energy from the capacitor with the highest voltage. Then, this capacitor is discharged and its voltage will decrease. Secondly, the inductor releases energy to the capacitor with the lowest voltage. Then, this capacitor is charged and its voltage will increase. After performing this operation a number of times, all the voltages of the dc-link capacitors will finally reach the same value. The circuit configurations, conducting paths and control strategies of one-inductor-based scheme for five-level DCMC are analysed, respectively. Owing to small equivalent resistances of capacitor and inductor, the small power loss could be achieved. Simulations and experiments have been carried out. The steady-state and dynamic results verify the effective balancing performance of this circuit.