A novel nine-level switched-capacitor multilevel inverter (SCMLI) with reduced capacitance and balanced capacitor voltage is proposed in this paper. Utilizing only two capacitors, the proposed SCMLI can boost the input voltage and realize nine output voltage levels under different kinds of load conditions. The controllable capacitor charging speed in the proposed SCMLI depends on the charging resonant inductor rather than the equivalent resistance of the devices in conventional topologies. The two capacitors can be charged or discharged independently by a DC source when their voltages deviate from the rated voltage. This makes the proposed SCMLI free of the capacitor voltage imbalance. The longest discharging time (LDT) of capacitors is reduced to twice the switching period, which contributes to reduced capacitance in the proposed SCMLI. With the required capacitor voltage ripple, the quality of output waveforms is also very high. A comprehensive comparison with previous SCMLIs in terms of capacitance, the voltage imbalance problem, the output voltage level and so on is conducted to validate the merits mentioned above. The theoretical analysis, the simulation and experiment results are accordant, confirming the feasibility of the proposed SCMLI.

In view of the large neutral-point (NP) voltage fluctuation and the high low-frequency harmonics in the input current of conventional discontinuous pulse width modulation (DPWM) for the Vienna rectifier, a hybrid DPWM (HDPWM) is proposed on the basis of three-level to two-level conversion. The proposed HDPWM combines the modulation degree of freedom, namely the vector synthesis direction and the equivalent zero vector distribution coefficient. Under the two-level modulation unit, the shift angles that satisfy the predefined NP balance requirement for HDPWM are accurately calculated. Compared with the continuous PWM and conventional DPWM, the proposed HDPWM could effectively suppress the zero-crossing distortion, reduce the NP fluctuation and the switching losses. Simulation and experiment results demonstrate that the proposed HDPWM could reduce the NP voltage fluctuation to 1/2 of the conventional DPWM with reduced input current low-frequency harmonics and no zero-crossing distortion.

Voltage and current balance are essential in an interleaved three-level dc–dc converter. In this article, a simultaneous voltage and current self-balance mechanism based on near-critical conduction mode (CRM) for an interleaved three-level dc–dc converter is discovered, which can realize current and voltage balancing automatically without sensors. First, the zero-voltage switching (ZVS) and resonance transition generated by near-CRM are analyzed in detail. Second, the actual equivalent duty cycle is formulated to disclose its relationship to the unbalanced capacitor voltages and unbalanced inductor currents. It is found that the additional equivalent duty cycles in near-CRM are created and affected by the resonance around the valley and peak currents, so that some feedback loops are naturally formed to adjust the unbalanced voltages and currents. Then, by constructing the 3D relationship and natural feedback loops, the simultaneous voltage and current self-balance mechanism is proposed, where the additional equivalent duty cycles are simultaneously compensated by the unbalanced voltages and currents to counteract the unbalanced components. Finally, a three-phase interleaved three-level dc–dc converter is tested to experimentally verify the voltage and current self-balance mechanism based on near-CRM .

The inherent neutral-point (NP) voltage fluctuation of Vienna rectifier could have side effects on the input current quality. However, such effects have not been thoroughly analyzed in the literature yet. In this paper, based on the three-level to two-level space vector modulation (SVM) transformation, a novel method to evaluate the influence of the NP voltage fluctuation on the input current quality is introduced, which could optimize the NP control parameters. The proposed method superimposes the NP voltage fluctuation on the basis vectors, thereby establishing the correlation between the NP voltage fluctuation and the square root mean square (S-RMS) of the input current ripple. The detailed model of the NP oscillation under two-level coordinates is presented. By combining the two-level modulation, NP voltage hysteresis control is adopted to simplify neutral point voltage control and suppress NP low-frequency oscillation. Comprehensive influence of the NP compensation coefficient on the input current quality under NP hysteresis control is obtained, and the hysteresis control parameters are optimized by using the proposed evaluation method. Simulation and experimental results verify the correctness and effectiveness of the proposed evaluation method.

Three-level boost (TLB) converters are a promising interface of bipolar DC microgrids. With different power of the positive and negative DC buses, the conventional modulation method used in TLB converters fails to have zero voltage switching (ZVS) for all switches, and the peak current is also high, leading to the risk of inductor saturation. In this article, an optimized modulation (OM) method is proposed to achieve ZVS for all switches even under unbalanced loads. The OM method features the same valley current at both the high and low output power sides, contributing to wider ZVS range as well as smaller peak-to-peak current. The modulation degree of freedom in TLB converters under unbalanced-load conditions is analyzed in detail for the first time, and the advantages of the proposed OM method are compared with its counterparts in terms of the ZVS range, the peak and valley current, and the efficiency. The effectiveness and advantages of the proposed OM method are finally validated by experiment.

Due to the intricate array of control parameters, achieving efficiency optimization for a typical dual active bridge (DAB) prototype becomes a laborious and time-intensive task. Traditional methodologies have revolved around an idealized lossless model of DAB, inevitably leading to a disparity between theoretical ideals and experimental realities. To surmount this challenge, we employ a hybrid data-driven model that seamlessly integrates insights derived from both simulation and experimentation. The disparity between the experimental and simulated models is represented as a residual branch, akin a nonlinear, dissipative impedance. This residual branch contributes to a fraction of power losses and subsequent output voltage/power reduction. The strategic minimization of residual branch emerges as a pivotal step in identifying the optimal control parameters. These optimal control parameters are then subjected to practical testing on the DAB prototype, allowing for the evaluation of their effectiveness. By analyzing the results obtained from experiments conducted on a 3-kW DAB prototype, we leverage a perturbation-based optimal examination technique to validate the efficacy of the proposed efficiency optimization methodology.