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This paper proposes a dual active bridge (DAB) converter constructed with two nine-switch five-level active neutral-point-clamped (9S-5L-ANPC) bridges. The dead time effect in DAB converter with five-level active-neutral-point clamped circuit is analyzed, then an elimination method using the zero state with dual current paths is proposed in 9S-5L-ANPC circuit. On this basis, a modulation method that can effectively balance the loss distribution of power devices and balance the voltage of flying capacitor is proposed. Meanwhile, the soft switching conditions of all nine switches are derived. The performance of the proposed 9S-5L-ANPC DAB converter is verified by a 1.3 kW experimental prototype.

The five-level active neutral-point clamped (5L-ANPC) converter is getting more and more attention in recent years. The zero-sequence voltage injection can be used to control the neutral-point (NP) potential and the voltages of flying capacitor (FC) are balanced by using redundant switching states properly. However, the NP potential control needs to be decoupled with the voltage balancing of the FC to achieve superior dynamic performance. To solve this problem, the relationship between NP current and zero-sequence voltage is presented, considering the difference of the duty cycles of redundant switching states. Therefore, a phase-shift PWM based zero-sequence voltage injection method for NP potential control is proposed in this paper. The results of simulation and experiment are shown to demonstrate the superiority of the proposed method.

This paper proposes a novel voltage balancing method for Modular Multilevel Converter (MMC) under Phase- Shifted Carrier Pulsewidth Modulation (CPS-PWM). For the existing individual voltage balancing methods, an unsolved problem is that the active power transmission will greatly affect the balancing speed of MMC system. By utilizing the output current amplitude information, the effect of working condition on voltage balancing is canceled out in the proposed method. Compared with conventional voltage balancing methods, the proposed method possesses good dynamic performance under different working conditions even when the active power is extremely low. Simulation results are provided to validate the effectiveness of the proposed voltage balancing method.