Three-level converters feature with low switching loss and small filter size. In order to realize high power density design for three-level converters, SiC MOSFETs may be selected instead of using Si IGBTs. However, all SiC MOSFETs based converters suffer from extreme high total cost. In this paper, a SiC MOSFET & Si device hybrid ANPC converter is proposed. It consists of four Si active switches and only two SiC MOSFETs. Thus, it has lower total cost compared to all SiC MOSFETs based ANPC converter. Furthermore, a dedicated modulation scheme is proposed to completely move all the switching events from Si devices to SiC MOSFETs by using redundant switching states. As a result, the switching losses are significantly reduced and extremely high efficiency is achieved. The proposed converter has fully utilized the low switching loss advantage of SiC MOSFET and the low-cost advantage of Si devices, which shows significant superiority in high-end grid-connected inverter and rectifier applications.

Multilevel circuits can achieve high-voltage level, power density, and performance. This article considers a dual active bridge (DAB) based on the active neutral-point-clamped (ANPC) three-level circuit (ANPC–DAB). The soft-switching characteristics of the ANPC circuit during the switching process between switching states are analyzed, and the conditions for enabling all 12 switching devices to achieve zero-voltage switching (ZVS) on all the turn- on switching transitions are obtained. Based on this, the distribution of hard-switching turn- off and conduction losses of power devices is further analyzed, and an optimized switching strategy that can balance the loss distribution of power devices is proposed by the evaluation of all zero states and analysis of a switching-state sequence. Moreover, this article examines the effect of the proposed switching strategy by analyzing the loss distribution of power devices and efficiency of the ANPC–DAB. Finally, experiments are conducted using a 1-kW prototype. The simulation and experimental results show that the proposed switching strategy can effectively improve the loss distribution of power devices while all the power devices realize ZVS.

The utilization of wide bandgap devices such as silicon carbide (SiC) diode and MOSFET can significantly increase the power density and the efficiency of rectifier circuits. However, SiC-based circuits always suffer from the high cost of their power stage. In this paper, a high efficient low-cost hybrid three-phase three-level rectifier is proposed. Instead of using SiC diode and Si IGBT, it consists of SiC MOSFET and Si diode. It presents extremely low switching losses because the reverse recovery losses of all the Si diodes are eliminated. At the same time, the total device cost of this rectifier is much lower than the all-SiC-based rectifiers. Furthermore, half-bridge modules can be used to comprise the rectifier circuit, which makes it suitable for high power applications. In this paper, the circuit operational analysis, simulation, and experimental results are given. A comparison is given to show the advantages of the proposed rectifier.

Discontinuous conduction mode (DCM) for inverters can lower the size of filter inductors and can realize the soft switching for switches. However, the current stress under the DCM is high. Aiming to solve this problem, this article uses a T-type three-level circuit to construct an LCL -type grid-connected inverter, which introduces the trapezium conduction mode (TPCM) with the zero-voltage switching to lower the current stress when the grid current is large. Both the DCM and the TPCM can work at a fixed switching frequency, but it is difficult to design controllers using the conventional average state model. To address this challenge, this article proposes a charge quantity model (CQM) that is applicable to any inverter topology and conduction mode, where the output charge quantity of the bridge is used as a control variable. The proposed model represents a linear two-order model, which can greatly simplify controller design. Based on the CQM, a direct charge control method working at a fixed switching frequency is developed, which combines a PID regulator and a feedforward controller of the grid voltage. The excellent steady-state and dynamic control performances of the proposed model and control method are verified by simulations and experiments.

The discontinuous conduction mode (DCM) of the inductor current is an effective way to achieve high efficiency and high power density of inverters because it has the advantages of zero-current switching and small inductance of the filter inductor. Although the DCM can operate at a fixed switching frequency, there has been no linear model for realizing high-performance digital control. This paper provides a solution for this problem. Firstly, a linear first-order charge quantity model (CQM) for a DCM inverter with a fixed switching frequency is established, which uses charge quantities output by the inverter bridge as a control variable. Secondly, a direct charge control (DCC) method is proposed, and the design process is significantly simplified. Finally, the performance of the proposed control method is verified by the experiments using a 1 kW prototype, and a high-quality output voltage waveform with a peak efficiency of above 98% was achieved. The proposed method outperforms existing works because the CQM is a first-order linear model that realizes the high-performance digital control and significantly simplifies the design of controller.