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MMC-based back-to-back (B2B) converters are promising for hybrid AC/DC transmission systems when integrating large scale PV sources. This paper proposes a novel configuration for hybrid AC transmission systems with B2B converters and multi-terminal direct current (MTDC) operation which facilitates the integration of PV energy and enhances the system stability and reliability. This is achieved by an advanced interconnection with two operation modes: 1-A bi-directional power flow via AC connections, and 2- Direct active power injection to the MTDC from PV source. Conventional outer, inner and capacitor voltage balancing control systems are utilized in this study for regulating the currents and voltages of B2B converter. Also, The Perturb and observe (P and O) technique is implemented for obtaining maximum power point tracking (MPPT) of the PV generation considering a dc-dc boost converter. The efficacy of this proposed configuration is verified through time-domain simulations carried out by MATLAB/SIMULINK. 

Abstract—Wide band gap (WBG) devices, like silicon carbide (SiC) MOSFET has gradually replaced the traditional silicon counterpart due to their advantages of high operating temperature and fast switching speed. Paralleling operations of SiC MOSFETs are unavoidable in high power applications in order to meet the system current requirement. However, parasitics mismatches among different paralleling devices would cause current unbalance issues, which would reduce the system reliability and maximum current capability. Thus, to achieve current balancing operation, this paper proposes a solution of using multi-level active gate driver, where the dynamic current sharing during turn-on and turn-off processes are achieved by adjusting the delays, intermediate turn-on and turn-off voltages. The static current sharing is maintained by regulating the static turn-on gate voltage, where the on-state resistance mismatch between different devices can be compensated. A double pulse test setup with two different SiC MOSFETs is built to emulate the scenario of worst case application with large differences of threshold voltage and on-state resistance. The experimental results demonstrate that the proposed active gate driver can achieve both dynamic and static current sharing operations for SiC MOSFETs with paralleling operation. Moreover, the system control diagram is discussed. Simulation studies are conducted to achieve closed-loop control of the paralleled SiC MOSFETs with the aid of the active gate driver approach. 

Wide band gap (WBG) devices have been widely adopted in numerous industrial applications. In medium voltage applications, multi-level converters are necessary to reduce the voltage stress on power devices, which increases the system control complexity and reduces power density and reliability. High voltage silicon carbide (SiC) MOSFET enables the medium voltage applications with less voltage level, simple control strategy and high power density. Nevertheless, great challenges have been posed on the gate driver design for high voltage SiC MOSFET. Wireless power transfer (WPT) can achieve power conversion with large airgap, which can satisfy the system isolation requirement. Thus, in this article, a WPT based gate driver is designed for the medium voltage SiC MOSFET. The coil is optimized by considering voltage isolation, coupling capacitance, size, and efficiency. Experimental prototype was built and tested to validate the effectiveness of the proposed WPT based gate driver. 

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) has been widely used in numerous industrial applications owning to their characteristics of low on-state resistance, high thermal conductivity, and high operating temperature. To fully utilize the potential of SiC MOSFET, an accurate device model is desired to evaluate the device performance before fabrication. In this article, an accurate subcircuit based model is used to describe the SiC MOSFET dynamic performance. In the model, the non-linearity of device parasitic capacitance is considered by extracting capacitance values under multiple drain-source voltage values from datasheet. All the possible circuit parasitic inductances are extracted by using ANSYS Q3D. To reduce the model complexity, the threshold voltage based model for MOSFET is adopted. Finally, the subcircuit based model is implemented in MATLAB/SIMULINK. The developed model has the advantages of high accuracy, convenient, fast execution time. The model would be a convenient tool to evaluate the device performance and help understanding the experiment phenomena. To validate the accuracy of the developed model, double pulse test (DPT) results of a 1.2 kV SiC MOSFET (ROHM) from both simulation and experiment are compared, the results shown that the developed model is an effective evaluation tool for the SiC MOSFET performance. 

Wide band gap (WBG) devices have been widely applied in industrial applications owning to their advantages of low switching loss, low on-stage voltage drop, and high operating temperature. Paralleling operation of power devices/modules is attractive due to its cost-effective and high power characteristics. In applications require very high current capability, paralleling operation of off-the-shelf power devices/modules becomes the only choice. However, current balancing operation of individual power device/module becomes difficult due to the differences of circuit parasitics. To investigate the device/module and circuit parasitics influences on the current sharing performance, in this article, a subcircuit model was built in MATLAB. Comprehensive comparisons and analysis are performed, which can provide guidance for engineers when designing the system with paralleling devices/modules. Moreover, the solutions to achieve current balancing operating are proposed with the aid of active gate driver. Experiment results are presented and analyzed to validate the effectiveness of current sharing solutions. 

Silicon carbide (SiC) MOSFET features low switching loss and it is advantageous in high switching frequency application, but the manufacture per Ampere cost is approximately five times higher than the silicon (Si) IGBT. Therefore, by paralleling Si IGBT and SiC MOSFET together, a trade-off between cost and loss is achieved. In this paper, a four control freedoms active gate driver (AGD) including turn-on delay, turn-off delay, and two independent gate voltages, is proposed to optimize the performance of the paralleled device. By adjusting these four control freedoms, optimal operation for paralleled device can be obtained. Moreover, the proposed AGD can dynamically adjust the current ratio between two paralleled devices, which can help achieve thermal balance between two devices and improve system reliability. Double pulse test (DPT) experimental results are presented and analyzed to validate the effectiveness of the proposed AGD for paralleled Si IGBT and SiC MOSFET application. 

Wide band gap (WBG) devices feature high switching frequency operation and low switching loss. They have been widely adopted in tremendous applications. Nevertheless, the manufacture cost for SiC MOSFET greater than that of the Si IGBT. To achieve a trade off between cost and efficiency, the hybrid switch, which includes the paralleling operation of Si IGBT and SiC MOSFET, is proposed. In this article, an active gate driver is used for the hybrid switch to optimize both the switching and thermal performances. The turn-on and turn-off delays between two individual switches are controlled to minimize the switching loss of traditional Si IGBT. In this way, a higher switching frequency operation can be achieved for the hybrid switch to improve the converter power density. On the other hand, the gate source voltages are adjusted to achieve an optimized thermal performance between two individual switches, which can improve the reliability of the hybrid switch. The proposed active gate driver for hybrid switch is validated with a 2 kW Boost converter.