Recently, multilevel converters with gallium nitride (GaN) devices have shown marvelous advantages for power factor correction(PFC) conversion to meet the increasingly higher efficiency and power density requirements. In the traditional design process for the multilevel PFC converter, it is necessary to separately optimize the devices of the corresponding breakdown voltage under different level number, which causes difficulty to the overall optimization of the entire system. In this paper, a unified minimum loss model for GaN switches regardless of voltage levels is proposed to optimize the efficiency based on device’s new figure-of-merit(NFoM)(NFoM= COSS(ER) RDS(on)). With the help of this unified minimum loss model, it simplifies the efficiency optimizing methodology according to the NFoMs of GaN devices for multilevel PFC converter. According to the methodology, a 2 kW cascaded H-bridge(CHB) PFC prototype is constructed to verify the design methodology, achieving over 99% efficiency with power density over 1000 W/in3.

Conventional line frequency transformers have the disadvantages of large volume and low efficiency. The medium or high frequency transformers based on power converters can achieve high power conversion with small footprint have drawn popularity in numerous industrial applications. Unregulated resonant converters, LLC and CLLC resonant converters, with fixed voltage conversion ratio operating at resonant frequency, which are also known as DC transformers(DCXs), are attractive owning to their high efficiency characteristic. Nevertheless, there are issues associated with DCXs in real applications. Regulation capability and automatic resonant frequency tracking capability are the two most important issues for DCXs. The main work of this paper is to characterize the resonant converters based DCXs, and overview the issues and solutions associated with DCXs. Guidelines can be provided for researchers and engineers when designing the resonant converters based DCXs.

Field-programmable gate array(FPGA) is a powerful platform that can play an essential role in high-performance digital control of power electronics systems. However, the FPGA system’s design is quite different from that of a traditional micro-processor or a digital signal processor(DSP). Instead of sequential programming using high-level languages, such as C/C++, FPGA controller implementation requires a hardware description language(HDL) such as Verilog and VHDL, which requires extensive verification and optimization during the design process. This paper proposes a systematic FPGA design methodology with optimum resource utilization for rapid prototyping of high-performance power electronics applications to facilitate the widespread adoption of FPGA technology in power electronics. The FPGA controller design is concurrent with the power stage and utilizes high-level synthesis(HLS) tools and Simulink code generation toolbox. This paper covers the detailed design, implementation, and experimental validation of two specific applications, i.e., an active power filter(APF) and a motor emulator(ME), demonstrating the generalized features of the methodology. Employing fundamentally different control structures, both application examples achieve ultra-high current control bandwidth leveraging SiC MOSFETs switching at no less than 100 kHz.

In this manuscript, an advanced battery equalizer with open-loop control is proposed. This equalizer is based on a two-layer hierarchical modular architecture. The top string-to-module(S2M) layer consists of a half-bridge inverter and a voltage multiplier(VM) rectifier, and the bottom cell-to-cell(C2C) layer is implemented by bidirectional buck-boost units. Without state-of-charge(SOC) estimation, the battery charge can be automatically transferred from high-voltage cell-modules/cells to low-voltage ones. Only a pair of symmetrical pulse width modulation(PWM) driving signals with fixed switching frequency and duty cycle are required.This reduces the control complexity remarkably. Meanwhile, the balancing current of each balancing path naturally attenuates with the convergence of cell-module/ cell voltages. This ensures a fast balancing of cell-module/cell with large voltage mismatch. The battery-recovery-effect induced balancing error is also effectively mitigated. Moreover, simple control facilitates a simultaneous module and cell voltage balancing in static, charging, and discharging conditions. The operation principles are analyzed in detail. An experimental platform with eight series-connected batteries is built and tested. The measured results well validate the theoretical analysis. Both cell and module voltages automatically converge with clearly mitigated recovery effect.

This paper investigates the influences of system layout on common mode(CM) EMI noise of an electric vehicle(EV) powertrain with a traction inverter using silicon carbide(SiC) MOSFETs. First, a system level conducted EMI model for the whole SiC EV powertrain is presented, which includes a battery pack, DC cables, a SiC inverter, AC cables, and a PMSM. Then, the impacts of system layout, such as the AC cable length, the AC cable type, and the DC cable type(shielded cable and unshielded cable) on CM EMI noise are analyzed through time domain simulations of the system level conducted EMI model. Next, a conducted EMI emission test-bed for a SiC EV powertrain is built. Finally, experiments on the test-bed are carried out to verify the influences of system layout on CM EMI noise in the SiC EV powertrain.

Recent years have witnessed the booming development of wireless power transfer(WPT) via magnetic induction, which has the advantages of convenience, safety, and feasibility to special occasions. WPT can be applied to electric vehicles and ships, where high-power WPT technology is required to shorten the charging time with the increasing battery capacity. This paper reviews the state-of-the-art development of high-power static WPT systems via magnetic induction. Selected prototypes and demos of high-power WPT systems are demonstrated with key transfer characteristics and solutions. Theoretical foundation of magnetically coupled WPT systems is analyzed and the maximum power capability of coils is derived. Compensation topologies suitable for high-power applications are discussed. Four basic planar coils, namely the bipolar coil, the square coil, the circular coil, and the rectangular coil, are simulated and compared. The state-of-the-art silicon carbide MOSFET development is introduced. The power electronics converters with power elevation techniques, including cascading, paralleling and inductive elevation, are investigated. Future development of high-power WPT systems is discussed.

The International Thermonuclear Experimental Reactor(ITER) poloidal field(PF) AC/DC converters are composed by thyristor-based phase controlled converter modules. As the core component of ITER PF AC/DC converter, the thyristor is very sensitive to over-voltage and damaged in microseconds, therefore, the transient over-voltage protection strategy is desperately essential to ensure the converter safety operation. In this paper, a nanosecond respond and high reliability protection strategy which combined by Metal Oxide Varistor(MOV) and external bypass is proposed to protect the ITER PF AC/DC converter from transient DC over-voltage. The MOV is designed to certify the fast respond in nanosecond. Moreover, a bidirectional BreakOver Diode(BOD) circuit board is designed to activate external bypass to ensure the reliability of the transient DC over-voltage protection strategy. The performance-testing platform is built to study its performance. The experiments on ITER PF AC/DC converter test facility are carried out. According to the experiment results, the external bypass is triggered by BOD board effectively and the load current is transferred to the external bypass in 2 us when BOD suffers from an over-voltage. The effectiveness of the proposed transient DC over-voltage protection strategy is verified.

To achieve the constant current(CC) and constant voltage(CV) charge of the lithium battery, the traditional LLC resonant converter requires the switching frequency varies in a wide range, which brings difficulty to the magnetic components design, and the system efficiency would also be degraded. In this article, a novel topology based on LLC and LCL-T resonant tanks is proposed to reduce the range of operating switching frequency. During the CC charge state, the proposed converter is operating with the LCL-T resonant tank, and it can be regarded as a current source, which provides constant charging current to the battery. During the CV charge state, the LCL-T resonant tank is bypassed and the structure of the proposed converter is modified to a traditional LLC resonant converter, and it is functioning as a CV source. Owing to the high accuracy of the CC and voltage sources, the required operating switching frequency range can be significantly reduced when compared with traditional LLC approaches. Operational principles and design guidelines for the proposed converter are described. Experiment and simulation results from a 180 W prototype are provided to validate the theoretical analysis.