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.

A systematic method is proposed to generate 2-SiC and 4-SiC hybrid three-level active neutral-point-clamped (3L-ANPC) inverter topologies from two types of switching cells based on the arrangement of freewheeling paths. The 2-SiC hybrid 3L-APNC inverter and the 4-SiC hybrid 3L-ANPC inverter are analyzed in detail with switching states and modulation strategies given. The power losses are quantitative compared between the 2-SiC hybrid 3L-ANPC inverter and the 4-SiC hybrid 3L-ANPC inverter. The junction operating temperatures of active switches in different hybrid 3L-ANPC inverters are also calculated. A universal prototype for these different Si/SiC hybrid schemes is built to evaluate these topologies at conversion efficiency. Experimental results and analysis show that the 2-SiC hybrid 3L-ANPC inverter has the highest efficiency and the lowest cost. The efficiency of the 4-SiC hybrid 3L-ANPC inverter with modulation strategy I is a litter bit lower than that of 2-SiC hybrid 3L-ANPC inverter. However, it has better thermal balance characteristic. Therefore, with the same specifications and switching device parameters, the maximum output power of 4-SiC hybrid 3L-ANPC inverter with modulation strategy I is almost 1.26 times than that of 2-SiC hybrid 3L-ANPC inverter, which shows significant superiority in high power and high power density applications.

Nowadays, due to the growing demands of data centers, the traditional line frequency transformer based data center power distribution system is becoming bulky and inefficient. Although SST based DC-PDS dramatically improves the system efficiency, the traditional multi-cell SST with input-series output-parallel (ISOP) architectures has limitations. Using high voltage devices to develop single-cell SST improves system performance, however, its application is limited by high voltage power devices. As an alternative solution, achieving high blocking voltage through the series connection of low voltage devices brings several advantages. Nevertheless, the series connection brings about voltage imbalance and switching loss increment problems. This paper proposes a medium voltage series resonant converter with series-connected SiC MOSFETs. By adding snubber capacitors to each SiC MOSFET and working at LLC resonant soft-switching mode, the voltage imbalance is reduced and switching loss is decreased. Then the analytical model of MVSRC is established. Moreover, the voltage imbalance model is established and the voltage imbalance sensitivity is defined to guide the snubber parameter selections. Afterward a design example of the 99% efficient 5kV/400V prototype is presented. Lastly, the experimental results verify the validity of proposed methods and the accuracy of analysis.

A modular multilevel resonant (MMR) DC-DC converter and its modulation and control are proposed in this paper. The MMR converter inherits the desirable features of both the modular multilevel converter and LLC resonant converter such as high voltage capability, easy fault tolerant operation and soft switching. Besides, the MMR can regulate the output voltage over a wide input voltage range with much narrower frequency range compared to conventional resonant converters. By constantly inserting certain number of submodules into the arm according to the input voltage, the resonant tank voltage can be regulated with a relatively constant amplitude regardless of the wide input variation. This modulation technique is acted as a feedforward loop to roughly regulate the output according to the input voltage, and the feedback loop in the control system precisely regulates the output by varying the switching frequency. Simulations on a 200kW MMR that converting 9~15kV to 750V are provided to verify the effectiveness of the proposed topology and control method. Experimental results on a MMR prototype are also given to demonstrate the feasibility.

Compared with full-SiC MOSFETs converters, the hybrid utilization of Si/SiC converters is an alternative approach to achieve the tradeoff between performance and cost. In this paper, a 2-SiC hybrid five-level active neutral-point-clamped (5L-ANPC) full-bridge inverter is proposed. The proposed inverter is constructed by combining a 2-SiC hybrid 3L-ANPC half-bridge inverter and a two-level half-bridge arm. The operation principle of the proposed inverter by using the conventional modulation scheme is analyzed in detail. Further, a dedicated modulation scheme is proposed to lower the conduction losses. The calculated power losses of the 2-SiC hybrid 5L-ANPC full-bridge inverter with the conventional modulation scheme and the proposed modulation scheme are addressed and compared. The proposed modulation scheme exhibits higher efficiencies under high power conditions. But the conventional modulation scheme shows efficiency superiority under low power conditions. Therefore, a hybrid modulation scheme is also proposed to achieve an overall high efficiency performance. A 4 kW prototype is built to evaluate the proposed topology and its modulation scheme at conversion efficiency. Experimental results and analysis show that comparing to the conventional modulation scheme, the hybrid modulation scheme can reduce power loss without increasing the hardware cost.

Medium-voltage high-speed drive is promising in applications, such as the centrifugal compressors and electrified transportation. However, it raises lots of design challenges for the converters, which drive the motors. A SiC and Si hybrid ANPC converter is developed to address these challenges. In this article, the essence of this hybrid structure is investigated to clearly show the derivation process of the hybrid active neutral-point-clamped (ANPC) converter and inspire future research on these hybrid topologies. A dedicated space vector modulation (SVM) scheme is proposed for the hybrid ANPC converter, which enables the three-phase hybrid ANPC converter operating with SiC mosfets in high frequency and Si IGBTs in fundamental frequency. A neutral point (NP) voltage balancing scheme is added to the SVM scheme to balance the NP voltage imbalance under low-frequency modulation index. All these efforts make the hybrid ANPC converter become a high power density and fairly low-cost solution. A 400 Hz fundamental frequency, 3.6 kHz switching frequency, medium-voltage high-speed drive system is assumed and tested by the scaled-down experimental results. The effectiveness of the proposed SVM and NP voltage balancing method have both been verified.