Wensong Yu

Design and operation of A 3.6kV high performance solid state transformer based on 13kV SiC MOSFET and JBS diode

This paper presents the development of a distribution network solid state transformer (SST) based on high voltage (13kV) SiC MOSFET and JBS diode. This distribution SST is composed with a medium voltage ac/dc rectifier, medium voltage medium frequency dc/dc converter and a low voltage inverter. Its able to be interfaced to 3.6kV distribution grid and output both a 400V dc and 240/120V ac. This paper presents the characterization of the high voltage SiC MOSFET devices, and the design of rectifier and dc/dc converter. The test results of its grid-connected operation including pre-charge, start up, regeneration, etc. are included to show the functionalities of the designed SST prototype.

A medium voltage bidirectional DC-DC converter combining resonant and dual active bridge converters

In this paper, an isolated bidirectional dc-dc converter for medium voltage application is proposed. It combines the resonant converter and dual active bridge converter (DAB). Under normal load condition, this isolated converter operates at resonant point to achieve zero voltage (ZVS) turn on at primary side and zero current (ZCS) turn off at secondary side. When over current happens, the voltage across the resonant capacitor will be clamped by paralleled diode and the converter will automatically switch to resonant and DAB mixed operation mode, therefore cycle-by-cycle over current protection is achieved with constant switching frequency. Different operation modes are analyzed for the proposed circuits using time domain waveform and state trajectory. Detailed theoretical analysis and design procedure for transformer, resonant tank and semiconductor devices are discussed. Performance of the proposed circuit is verified by a 3 kV to 200 V, 2.5 kW experimental prototype with high voltage SiC devices.

Design and application of a 1200V ultra-fast integrated Silicon Carbide MOSFET module

With the commercial introduction of wide bandgap power devices such as Silicon Carbide (SiC) and Gallium Nitride (GaN) in the last few years, the high power and high frequency power electronics applications have gained more attention. The fast switching speed and high temperature features of SiC MOSFET break the limit of the traditional silicon MOSFET. However, the EMI problem under high dI/dt and dV/dt is an unneglectable problem. The overshoot and oscillation on drain-source voltage and gating signal could cause breakdown of the switches. This paper proposes a 1200V integrated SiC MOSFET module. With the ultra-fast gate driver integrated with the SiC MOSFET, the parasitic inductance and capacitance could be reduced dramatically, which accordingly suppress the EMI problem caused by the parasitic parameters. Thus zero gate resistance could be adopted in the module to further increase the switching speed. The switching performance of the integrated SiC module is shown better than the discrete package device. The switching loss of the SiC MOSFET module is measured by the inverter level measurement and composition method. Zero switching loss could be achieved when the drain current is lower than a critical value. The module has been tested at 1.5MHz and 3.38MHz switching frequency to prove its high speed capability. For isolated topology applications, the impact of high frequency on the power density and efficiency is discussed in this paper.

A novel bi-directional DC-DC converter for distributed energy storage device

This paper presents a high efficiency, low-cost bidirectional isolated dc-dc converter for distributed energy storage device (DESD). Derived from dual active bridge (DAB), the proposed converter consists of a half-bridge circuit at high voltage side and a push-pull circuit with active clamp at low voltage side. The proposed topology is attractive in low voltage and high current applications and it also reduces the number of switching transistors such that the cost and complexity are considerably reduced. With single phase-shift control strategy, all the switches operate in zero-voltage switching (ZVS) condition without increasing circuit complexity. Besides, planar transformer is implemented where the low voltage windings consist of PCB trace and external copper foils. A 380V to 12V DC, 500W DESD hardware prototype has been designed, fabricated, and tested. Experimental results verify the validity of the proposed bi-directional converter, which has 97.3% peak efficiency and maintains greater than 92% efficiency over a load range between 100W and 600W.

Development of 6kV SiC hybrid power switch based on 1200V SiC JFET and MOSFET

Series-connected power switch provides a viable solution to implement high voltage and high frequency converters. By using the commercially available 1200V Silicon Carbide (SiC) Junction Field Effect Transistor (JFET) and Metal Oxide semiconductor Filed-effect Transistor (MOSFET), a 6 kV SiC hybrid power switch concept and its application are demonstrated. To solve the parameter deviation issue in the series device structure, an optimized voltage control method is introduced, which can guarantee the equal voltage sharing under both static and dynamic state. Without Zener diode arrays, this strategy can significantly reduce the turn-off switching loss. Moreover, this hybrid MOSFET-JFETs concept is also presented to suppress the silicon MOSFET parasitic capacitance effect. In addition, the positive gate drive voltage greatly accelerates turn-on speed and decreases the switching loss. Compared with the conventional super-JFETs, the proposed scheme is suitable for series-connected device, and can achieve better performance. The effectiveness of this method is validated by simulations and experiments, and promising results are obtained.

A Medium-Voltage Medium-Frequency Isolated DC–DC Converter Based on 15-kV SiC MOSFETs

In this paper, a novel isolated dc–dc converter topology for medium-voltage (MV) applications is proposed by combining the advantages of resonant converters and dual active bridge (DAB) converters. In normal load scenario, this converter operates in an open loop resonant mode with a fixed switching frequency equals to the resonant frequency of the series resonant tank. Thus, zero voltage turn on at primary side and zero current turn off at secondary side are secured from zero to full load. When overload happens, the resonant capacitors will be clamped to the output voltage by the additional paralleled diodes. The proposed converter automatically switches to resonant and DAB mixed operation mode; therefore, the resonant current is naturedly limited. With zero to full load range soft switching and fast overload protection, the proposed topology is especially suitable for MV medium frequency applications utilizing high-voltage SiC MOSFETs. The converter operation modes are analyzed using time-domain waveforms and graphical state trajectory to derive the quantitative relationship between duty cycle, output voltage, and the overload current. Based on these relationships, a predictive duty cycle control is proposed to further limit the overload current of the resonant tank by sensing the output voltage. Combing the proposed topology and the predictive control, cycle-by-cycle overload and short-circuit protections are achieved. To fully utilize the capability of the 15-kV SiC MOSFET, magnetizing inductance, dead time, MV transformer, and resonant components are optimized with the operating range of 6–12 kV and 20–100 kHz. An experimental prototype running at 6 kV and 40 kHz is successfully tested with peak efficiency exceeding 98%. Test waveforms at no load and 10-kW full load validate the zero to full load range soft switching capability. Short circuit protection test demonstrates a 25-

Distributed and autonomous control of the FREEDM system: A power electronics based distribution system

\mu \text{s}

Medium voltage solid state transformers based on 15 kV SiC MOSFET and JBS diode

overload protection speed.

Decomposition and electro-physical model creation of the CREE 1200V, 50A 3-Ph SiC module

A truly distributed and autonomous control strategy is proposed for the FREEDM System-a power electronics based distribution grid. The proposed control strategy requires no communication between and among all grid assets. By utilizing available local quantities (V, f) as a way to communicate among all connected devices, the strategy contains a novel dual droop control loops between the medium voltage feeder and dispatchable resources such as energy sources, storages. The proposed control is put forward to achieve intelligent power management of the FREEDM system under all modes of operation. This is a pre-requisite to use FREEDM system as a transformative platform for plug-and-play of energy (aka Energy Internet). Simulation results verify the autonomous nature of the proposed control.

Distributed energy storage device based on a novel bidirectional Dc-Dc converter with 650V GaN transistors

This paper discusses the advancements in the development of the medium voltage solid state transformer (SST) based on 15 kV SiC MOSFET and JBS diode. Designed for 7.2 kV single phase distribution grid applications, the medium voltage SST converts high voltage AC to low voltage 240/120V ac. The use of ultra-high voltage SiC devices allows the simplification of the power conversion circuit topology. This paper presents the characteristics of the high voltage SiC MOSFET devices as well as the topology innovations to achieve ultra-efficient SST design. Specifically, three different designs are discussed which utilize three-stage, two-stage and single stage power conversion topologies to achieve the AC to AC conversion.