For evaluating and optimizing the efficiency of power converters, the loss model of the power semiconductor devices is needed. The analytical loss model is favorable for its simplicity. However, the model accuracy needs to be improved. This paper proposes an analytical loss model for the commutation pair of silicon carbide (SiC) MOSFETs and SiC Schottky barrier diodes. Compared to the conventional loss calculation method, the proposed model is derived based on the conservation of energy, which considers the impact of the displacement currents on estimating the turn-on and turn-off losses. The modeling and extraction methodology of the model parameters are given, and the impact of operational conditions on the model parameters is studied. Using the proposed model, the losses can be calculated analytically and also the switching trajectories can be predicted with good consistency. A double pulse tester is built to verify the proposed model. The results show that an average modeling error is reduced from 20% using the conventional piecewise linear model, to around 10% using the proposed model under various operational conditions, and the time cost is at least 3000 times smaller compared to the existing SiC MOSFETs models.

Due to the convenience, safety and aesthetics, the wireless charging is promising for the electric vehicles (EVs). For the charging system, the real-time wireless communication between the transmitter and receiver sides is conventionally used for the closed-loop control of the transmitter-side inverter. However, since the real-time wireless communication depends on the data transmission with the high speed and the low latency, it is sensitive to the interference. In order to improve the reliability and reduce the cost, the concept of the weak communication is introduced, and a transmitter-side control scheme is proposed to realize both the constant current (CC) and constant voltage (CV) charging modes as well as the smooth transition between the two modes. In the proposed control scheme, the mutual inductance is estimated without using the structural parameters in the receiver side. The online recursive least square filter is adopted to reduce the influence of the sensor noise for the estimation. Based on the estimated mutual inductance and the information obtained from the weak communication: 1) for the CC mode, the control command for the target charging current of the battery management system is calculated out directly; 2) for the CV mode, the reference transmitter current for the target charging voltage is calculated and a closed-loop control is used to make the transmitter current trace the reference value. The proposed control scheme is robust and can be easily implemented. Experimental results have confirmed the feasibility and the validity of the proposed scheme.

This letter proposes a deadbeat current controller for isolated bidirectional dual-active-bridge dc-dc converter (IBDC). The controller uses an enhanced single phase shift (ESPS) modulation method by exploiting pulse width as an extra control variable besides phase shift ratio the only control variable of the conventional single phase shift (CSPS) modulation. The current reference can be tracked within one switching cycle during the bidirectional power transmission and transition of the two directions. Deadtime effect is studied and the compensation method for the controller is presented. Parameter robustness is analyzed by mathematical derivation and the online auto-tuning method for the inductance is presented. The proposed deadbeat current controller is simple and easy for implementation. Moreover, it shows superior dynamic performance, which is verified by experimental results during the transient processes of the converter. The effectiveness of the auto-tuning method is also validated by the prototype experiment.

For the bidirectional wireless electric vehicle charging system, when both the primary and secondary converters are active, the phase synchronization between the two converters are necessary to control the power flow direction. This paper proposes a new phase synchronization method by tracking the maximum (or minimum, depending on the power flow direction) value of the output current, without auxiliary hardware or the real-time communication between the primary and secondary sides. Firstly, the relationship between the output current and the phase difference of the control signals is derived. It is found that the maximum output current is determined by the relative phase-shift angle (time interval between the middle points of the primary and secondary voltages) and the internal phase-shift angles of the two converters (time interval when the output voltage equals to the DC-link voltage). Secondly, a new scheme for generating the control signals is proposed to ensure that the relative phase-shift angle is not influenced by the internal phase-shift angles. Thirdly, based on the perturbation and observation method, a procedure is proposed to track the extreme value of the output current and obtain the target relative phase-shift angle for the phase synchronization state. Moreover, the relationship between the internal phase-shift angle and the transfer power is derived to regulate the magnitude of the transfer power, with the dead-time effect taken into consideration. Finally, experimental results verify the validity of the proposed method with different air gaps and power levels. The method is easy to be implemented, helpful for the optimal operation of the static and quasi-static wireless charging system and suitable for the bidirectional power flow.

With high penetration of various distributed energy resources and DC loads in modern power system, AC/DC hybrid distributed grid attracts a lot of attention due to its compatibility. Aiming for interface of the AC/DC hybrid distributed grid, a four-port megawatt-level power electronic transformer (PET) is focused on in this paper. A novel high-frequency-bus based multi-port PET topology is proposed, which is found to have superiorities such as mutual isolation, mutual independence among different ports and fewer power stages, compared with the conventional DC-bus based solution. Design and implementation of the four-port PET prototype is presented in this paper. Modular structure is adopted, and similar power cell is used for all the four ports for easy manufacture. The parameter design principle based on the port-equality is proposed to guarantee the suitable operating range of all the ports. The functions of this four-port high-frequency-bus based PET are tested and verified from the cell-level, port-level to the system level with maximum efficiency over 96%, which confirms the practicability of this industrial prototype.

Aiming for mutual isolation between ports, this article proposes a four-port high-frequency-bus-based power electronic transformer (HFB-PET), the core of which is the modular multiactive bridge (MMAB). In addition to port isolation, it also has the advantages of modularity, scalability, and reduced power conversion stages. First, the configuration of the proposed PET is introduced and compared with the existing solutions. Then, based on the mathematical model, a power coordinated control scheme is presented, including the power decoupling control for the cascaded H-bridge converter of the medium-voltage ac port to handle unbalanced grid voltages and active loads, the cell-power balance control for the medium-voltage dc port to achieve dc-link voltage equalization, and the power cross-coupling suppression control employed to improve the dynamic performance of the MMAB. On top of that, a hierarchical control framework with the global synchronous clock is constructed. Besides, a soft startup scheme considering the power balance between cells is introduced. Finally, the effectiveness of the proposed control scheme under the bidirectional power flow for the dc ports and the four-quadrant power flow for the ac ports is verified by experiments conducted on the laboratory scale-down prototype and the 10 kV/2 MVA industrial prototype.