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Kevin Bai

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Personal Photograph
Office: Min Kao 515
E-mail:
ude.ktu@2iabh
Phone: 865-974-4799
Fax: 865-974-5483
Address: Min H. Kao Building, Room 515
1520 Middle Drive
Knoxville, TN 37996-2250

Biography

Dr. Hua (Kevin) Bai received B S and PHD degree from Department of Electrical Engineering of Tsinghua University, Beijing, China in 2002 and 2007, respectively. Bai was a postdoctoral fellow in University of Michigan-Dearborn from 2007 to 2010. In 2010 he joined the Department of Electrical and Computer Engineering, Kettering University (former General Motor Institute) as an assistant professor and earned his early Tenure as associate professor in 2015. He became the associate professor in CECS, UM-Dearborn from January, 2017 to 2018. In all his Michigan life since 2007, he has been devoting himself and research team to the electric vehicle related power electronics, particularly on the high-power-density and high-efficiency EV battery chargers and motor drive inverters. His industrial partners include major vehicle companies (GM, Ford, Chrysler, Daimler, etc) and suppliers (Magna, Bosch, Hella, etc). Since August, 2018 he became the Associate Professor in EECS, UT-Knoxville. He is the associate editor of SAE International Journal of Alternative Powertrains, Guest Associate Editor of Journal of Emerging and Selected Topics of Power Electronics and IEEE Access.

Publications


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Journal Papers
Title
Year
  • Yongsheng Fu; Yu Li; Yang Huang; Xi Lu; Ke Zou; Chingchi Chen; Hua Bai
    IEEE Transactions on Transportation Electrification
    2019

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    As a new application area of electric vehicles, vehicle to home (V2H) recently becomes one of the most attractive research areas. In this paper, a three-phase four-wire inverter using four half-bridge legs is adopted to realize the V2H functionality. Such three-phase inverter acts as the grid-side ac/dc part of the battery charger. In order to deal with the imbalanced load, an independently controlled neutral module has been adopted to form the neutral line and provide the path for the zero-sequence current, together with split dc-bus capacitors. Each phase employs the independent sinusoidal pulse width modulation control with the virtual resistor paralleled with the load, namely, notch-filter-incorporated capacitor voltage feedback control, which damps harmonics around the resonant frequency at various load conditions. In addition, this paper quantifies the load imbalance versus the dc-link voltage oscillation and provides the guidance for the selection of the dc-link capacitance. Finally, a 10-kW three-phase four-wire inverter working at the V2H mode is built and tested, with the three-phase imbalanced load imposed to validate the proposed design and control strategy.

  • Juncheng Lu; Liyan Zhu; Guanliang Liu; Hua Bai
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2019

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    Though wide bandgap devices are believed to be promising candidates for next-generation high-efficiency and high-power-density power electronic converters, two major challenges remain, high cost (more than twice of Si) and less options (the maximum power rating for GaN is only 650 V/60 A). From the device level, paralleling GaN with Si can inherit merits of both GaN devices (superior switching performance) and Si devices (affordable with high-current capability). In this paper, first, GaN HEMTs are paralleled to a TO-247 Si MOSFET to form a high-current switching cell for a 6.6-kW electric vehicle (EV) charging module. A time delay is added between the switch gate signals to make GaN endure the switching loss and Si conduct majority of the static current. Critical dynamic behaviors, such as the current overshoot to the GaN, current distribution during the dead time, and voltage spike during the turn off caused by parasitics, are comprehensively discussed. From the system level, series connecting the input and paralleling output of multiple such modules yield a sub-MW EV charging station. Once one phase drops, the related phase can act as the active filter, while other two phases still work to charge the battery.

  • Wei Qian; Juncheng Lu; Hua Bai; Scott Averitt
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2019

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    For any voltage above 600-V dc, it is usually recommended to use 900-1200-V SiC MOSFETs instead of GaN high-electron-mobility transistors (HEMTs), given presently commercial GaN HEMTs have the maximum voltage rating up to 650 V. This paper is an attempt of employing 650-V E-mode GaN HEMTs to build a three-level bidirectional dc/dc converter, with the input as an 800-V battery, the output as the ~400-V dc grid, and half of the switches working at the hard-switching mode. The active-balancing control instead of using clamping diodes in the conventional neutral-point clamping topology is adopted, aiming at higher efficiency. Simulation based on the double-pulse test results shows that such a design strategy with GaN has a better efficiency over the conventional 1200-V SiC MOSFETbased buck/boost converter. Two bottom-cooled GaN HEMTs are in parallel to enhance the power capability and efficiency, which require the special focus on the parasitic parameters. The effects of parasitics, especially the stray inductance in the current commutating loop and the gate drive loop during switching transitions, have been comprehensively analyzed in this paper. Experimental results under 800-V bus voltage are presented to verify the proposed solution.

  • Allan Taylor; Juncheng Lu; Liyan Zhu; Kevin Bai; Matt McAmmond; Alan Brown
    IET Power Electronics
    2018

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    As two exemplary candidates of wide-bandgap devices, SiC MOSFETs and GaN HEMTs are regarded as successors of Si devices in medium-to-high-voltage (>1200 V) and low-voltage (<;650 V) domains, respectively, thanks to their excellent switching performance and thermal capability. With the introduction of 650 V SiC MOSFETs and GaN HEMTs, the two technologies are in direct competition in <;650 V domains, such as Level 2 battery chargers for electric vehicles (EVs). This study applies 650 V SiC and GaN to two 240 VAC/7.2 kW EV battery chargers, respectively, aiming to provide a head-to-head comparison of these two devices in terms of overall efficiency, power density, thermal performance, and cost. The charger essentially is an indirect matrix converter with a dual-active-bridge stage handling the power factor correction and power delivery simultaneously. These two chargers utilise the same control strategy, varying the phase-shift and switching frequency to cover the wide input range (80-260 VAC) and wide output range (200 V-450 VDC). Experimental results indicated that at the same efficiency level, the GaN charger is smaller, more efficient and cheaper, while the SiC charger has a better thermal performance.

  • Liyan Zhu; Allan Ray Taylor; Guanliang Liu; Kevin Bai
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2018

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    An ac/dc + dual-active-bridge (DAB) circuit was found as one solution for the high-efficiency and high-power-density electric vehicle charger. One control option is to let ac/dc part only convert the grid voltage to a double-line-frequency folded sine wave, yielding near-zero switching loss of the ac/dc part and leaving the DAB stage to control both power factor and power delivery. Such a zero-to-peak input voltage and wide-range output voltage can obstruct the zero-voltage switching (ZVS) for the DAB stage, which is a must for high-efficiency applications even with SiC devices. While the conventional single-phase shift loses ZVS at light load, and the variable-switching-frequency dual phase shift (DPS) creates the grid-current distortion at the light load, this paper employs multiple-phase-shifts (MPS) control, which essentially is a fixed-switching-frequency triple-phase-shift (TPS) control at light-load conditions and jumping to DPS at medium- and heavy-load conditions. While the TPS control will sacrifice the system efficiency by introducing the circulating current, a multiobjective optimization is employed to optimize the current stress and efficiency simultaneously, using the database of the double-pulse-test result. Experimental results on a SiC-based charger validated the effectiveness of the proposed control algorithm, that is: 1) high efficiency(>97%) at heavy load (7.2 kW); 2) smooth sinusoidal current without bumps at zero-crossing points from the whole-load range; and 3) the smooth transition between the heavy load and light load.

  • Juncheng Lu; Kevin Bai; Allan Ray Taylor; Guanliang Liu; Alan Brown; Philip Michael Johnson; Matt McAmmond
    IEEE Transactions on Power Electronics
    2018

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    In this paper, an enhancement-mode GaN highelectron mobility transistor (HEMT)-based 7.2-kW single-phase charger was built. Connecting three such single-phase modules to the three-phase grid, respectively, generates a three-phase ~22-kW charger with the> 97% efficiency and > 3.3 - kW/L power density, superior to present Si-device-based chargers. In addition to GaN HEMTs with fast-switching transitions yielding high efficiency, the proposed charger employs the dc/dc stage to control the power factor and power delivery simultaneously, yielding little dc-bus capacitance and thereby high power density. To secure the soft switching for all switches within full voltage and power ranges, a variable switching frequency control with dual phase shifts was adopted at high power, and a triple phase shift was employed to improve the power factor at low power. Both control strategies accommodated the wide input range (80-260 VAC) and output range (200-450 VDC). A closed-loop control for the three-phase charger was realized to minimize the output current ripple and balance the power among three single-phase modules. Experimental results validated this design.

  • Wide-bandgap (WBG) devices such as SiC and GaN switches are regarded as next-generation power semiconductors, due to their superior performance over conventional Si devices, for instance, a low switching loss and high thermal conductivity. Its bottleneck, however, is the high cost, which is critical for renewable energy and automotive industries. This study adopts SWISS AC/DC rectifier topology for the three-phase 380-480 VAC along with an isolated DC/DC converter, indicating such topology can maximise the advantages of Si (low conduction loss) and SiC (high switching loss), altogether thereby yielding the high performance and low cost. A novel space-vector pulse width modulation (SVPWM) was proposed to control such a current-source power factor correction, where only two SiC devices were adopted for the DC-bus voltage control. The closed-loop control of the grid current is realised for the unity power factor. Such topology further allows the DC-bus voltage to be varied with the output voltage, thereby minimising the system loss. A final prototype was built to charge a 48 V battery at 11 kW. Experimental results validated the effectiveness of such battery charger design.

  • A high-frequency injection (HFI) sensorless control for interior permanent magnet synchronous motors with enhanced precision and widened speed range is proposed in this paper. The injection frequency reaches up to 2 kHz under a 50~100 kHz silicon carbide (SiC)-based three-phase inverter. In addition to the high switching frequency, the field-programmable gate array (FPGA) is utilized to achieve high control bandwidth (>200 kHz) when implementing the field-oriented control algorithm. The benefits of high switching frequency and high control bandwidth in senseless controls are explained theoretically, i.e., leaving enough room for the injection frequency by using SiC while tuning down the noise-to-signal ratio by using the FPGA. Experimental results verified that such manners improved the position estimation and lifted the injection frequency effectively, which further allows us to widen the motor speed range under the HFI sensorless control from 0 to 500 r/min with the conventional Si+DSP design to 0~1200 r/min with the proposed SiC+FPGA.

  • Compared to conventional electrical-vehicle(EV) on-board chargers utilizing a front-end Power-Factor-Correction(PFC) + an isolated DC/DC converter, which limits the wall-to-battery efficiency to ~94%, a new control strategy using variable switching frequency(VSF) and variable phase shifts frees the PFC stage thereby getting rid of the DC link capacitor and further increasing the system efficiency and power density. The challenge is to secure zero-voltage-switching (ZVS) turn-on for all switches within the full-power range. In this paper a novel VSF single-dual-phase-shift(SDPS) control strategy is proposed, which consists of three control freedoms, i.e., two phase shifts and one variable switching frequency to secure ZVS and achieve PFC simultaneously. ZVS boundaries are pictured and compared among single-phase-shift(SPS), dual-phase-shift(DPS) and the proposed single-dual-phase-shift(SDPS) control. Simulation results and experimental validation through a level-2 EV on-board charger indicate that by using the proposed SDPS control, both ZVS and PFC are secured not only for the heavy load but also for the light load, without sacrificing the system efficiency.

  • Juncheng Lu; Guanliang Liu; Hua Bai; Alan Brown; Philip Michael Johnson; Matt McAmmond; Allan Ray Taylor
    IEEE Transactions on Transportation Electrification
    2017

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    An indirect matrix converter is employed directly converting the grid ac to the battery voltage, with the dual-active-bridge taking care of the power factor correction and power delivery simultaneously. Such circuit is regarded as one candidate of the high-efficiency and high-power-density electric vehicle onboard chargers, if the double-frequency current ripple to the battery is tolerated. Instead of optimizing the overall charger, this paper is focused on adopting variable switching frequency with multiple phase shifts to accommodate the wide input range (80-260 Vac) and output range (200 V-450 Vdc). In addition to the phase shift between the transformer primary-side and secondary-side voltage, one extra phase shift is added to the primary-side H-bridge when the instantaneous input voltage is higher than the reflected output, otherwise, to the secondary side. The goal is to secure zero-voltage-switching for all switches at all voltage range. Such control strategy is further optimized incorporating with the switch parasitic capacitance and deadband settings. To further enhance the charger performance, GaN HEMTs are equipped to the on-board charger aiming at higher efficiency and higher power density than Si devices. Experimental results indicated that such charger with proposed control strategy embraces the peak efficiency of >97% at 7.2 kW and a power density of ~4 kW/L.

  • Lucas Lu; Guanliang Liu; Kevin Bai
    CES Transactions on Electrical Machines and Systems
    2017

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    Wide-bandgap devices, such as silicon-carbide metal-oxide-semiconductor field-effect transistors (MOSFETs) and gallium-nitride high electron mobility transistors (HEMTs), exhibit an excellent figure of merits compared to conventional silicon devices. Challenges of applying such fast switches include accurate extraction and optimization of parasitics especially when 6high-efficiency operation, all of which require the comprehensive understanding of such switch especially its interaction with peripheral circuits. Particularly for the enhancement-mode GaN HEMTs without the intrinsic body diode, when reverse conducting, its high voltage drop causes a high dead-time loss, which has rarely a concern in silicon devices. This paper focuses on 650V/30~60A enhancement-mode GaN HEMTs provided by GaN Systems, analytically models its switching behaviors, summarizes the impact of parasitics and dead time, and applies it in two DC/DC converters. Systematic design rules are generated not only for soft switching but also for hard switching applications.

  • Wei Qian; Xi Zhang; Yongsheng Fu; Juncheng Lu; Hua Bai
    CES Transactions on Electrical Machines and Systems
    2017

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    Wide-bandgap (WBG) devices such as Gallium-Nitride (GaN) High Electron Mobility Transistors (HEMTs) have become popular in the power electronics industry as they offer a lower switching loss, higher thermal capability and higher power density than conventional silicon devices. As an attempt of applying WBG devices to the wireless charging technology, this paper adopts two different types of normally-off GaN HEMTs. One adopts the cascode structure provided by Transphorm Inc, operated under 800kHz to charge a battery pack on an electric scooter at 48 V/500W, with the air gap between the transceiver and receiver of ~10cm. The other is enhancement-mode GaN HEMTs provided by GaN Systems Inc, operated at ~6MHz to use one transceiver to charge multiple cell phones @~20W. Both of these chargers have no magnetic cores to reduce the cost and weight. Experimental results show both types of GaN HEMTs significantly increased the charging efficiency over conventional Si devices. Challenges of applying such fast-transition devices are discussed, e.g., common-source inductance and the gate-drive-loop parasitic.

  • Xuntuo Wang; Chenguang Jiang; Bo Lei; Hui Teng; Hua Kevin Bai; James L. Kirtley
    IEEE Journal of Emerging and Selected Topics in Power Electronics
    2016

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    It is expected that wide-bandgap devices like silicon-carbide MOSFETs and gallium-nitride HEMTs could replace Si devices in power electronics converters to reach higher system efficiency. This paper adopts the conventional half-bridge LLC topology to realize a 10-kW all-SiC bidirectional charger used in electric vehicles. Though it is a well-known topology for the unidirectional charger, it has not been comprehensively explored for the bidirectional energy flow yet. A double-pulse-test (DPT) platform is utilized to provide accurate power losses. A state-space model is built to obtain accurate switching current waveforms, which is eventually combined with the DPT results to accurately predict the system efficiency. Based on this model, to further enhance the system efficiency, the dc-bus voltage is varied with LLC dc/dc converter running at the resonant frequency through the whole power range. Experimental results validated that the proposed approach could realize the bidirectional power flow. By varying the dc-bus voltage, the V2G and G2V modes reach ~96 % wall-to-battery efficiency.

  • Fei Yang; Allan Ray Taylor; Hua Bai; Bing Cheng; Ahmad Arshan Khan
    IEEE Transactions on Transportation Electrification
    2015

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    The switching frequency is one of the most important control parameters of the dc/ac inverter. In most motor drives for transportation, it is set as a constant value at some specific torque or speed. The variable switching frequency pulse width modulation (VSFPWM), which changes the switching frequency cycle to cycle based on a current ripple prediction method, has been proposed in previous literatures and realized in resistance- inductance (RL) loads and induction motors (IMs). It proves effective to increase the overall system efficiency and improve electromagnetic interference (EMI) performance. However, the previous current ripple prediction method encounters difficulty in dealing with more complex motors, e.g., interior permanent magnet (IPM) motors, which is widely used in electric vehicles. As a result, the benefits of VSFPWM cannot be fully utilized for IPM drive systems. This paper proposed a new current ripple prediction method using the d-q transformation instead of the conventional Thevenin equivalent circuit method and successfully implemented VSFPWM to IPM drives. Simulation and experiments on a 400-V IPM test bench validated the effectiveness of the method, which will vary the switching frequency from cycle to cycle in order to 1) restrain the three-phase current ripples; 2) increase the overall system efficiency; and 3) enhance the system electromagnetic capability (EMC).

  • Chen Duan; Hua Bai; Wei Guo; Zhong Nie
    IEEE Transactions on Transportation Electrification
    2015

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    This paper proposes the design of a 2.5-kW 400/12 V high-efficiency isolated dc/dc converter for electric vehicles. The designed system accommodates the wide-range input voltage (450 V-220 VDC) and output voltage (16 V-6 VDC). An LLC halfbridge topology is adopted as the primary side of the dc/dc converter. For the secondary side, a novel synchronous rectification control (SRC) strategy is developed to switch metal oxide semiconductor field effect transistors (MOSFETs) through accurately tracking the target switching moments. Experimental results were carried out to charge the on-board 12-V battery and validate the proposed control algorithm. The maximum system efficiency is 93.2%. System power loss is also itemized.

  • Philip Mike Johnson; Kevin Bai; Xiaofeng Ding
    IEEE Transactions on Transportation Electrification
    2015

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    This paper presents an open-loop control strategy, dubbed the Hijacker algorithm, which governs startup from standstill, low-speed operation in open-loop, the transition to closed-loop, and sensorless motor control. The goal of the Hijacker is to eliminate the torque ripple encountered by a sudden switch from the open to closed loop operation, providing a smooth transition between the two control mechanisms and reliable operation over the motor's entire speed range without the use, or added cost of speed/position sensors. Implementation of the Hijacker exhibits extreme simplicity, so as not to add heavy computational loads on the processor. The algorithm, along with its development and justification, is then validated through both simulation and the test bench using a 1.4-kW/4500 rpm brushless dc motor.

  • Chen Duan; Chenguang Jiang; Allan Taylor; Kevin Bai
    IET Power Electronics
    2013

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    This study proposes a design and development of a wireless power transfer system to charge the battery in electric vehicles. A parallel-parallel topology is adopted to realise 10-15 cm-distance power transfer using the resonance theory. Finite-element method is used to extract the coil parameters. The advantages of the proposed design compared with the previous similar research are (i) low operational frequency (42 kHz) which avoids the electromagnetic interference to the on-board automotive electronics equipment and (ii) low electric stress to the semi-conductor switches through using zero-voltage-switching technique. A 2 kW prototype to charge 200 V battery was built to experimentally verify the theoretical analysis. The overall system efficiency is ~86%.

  • Presents corrections to the above titled paper (ibid., vol. 23, no. 6, pp. 2905-2914, Nov. 2008).

  • Sideng Hu; Zhengming Zhao; Hua Bai; Liqiang Yuan
    IEEE Transactions on Power Electronics
    2011

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    This paper proposed an enhanced dc preexcitation for a variable-voltage variable-frequency-controlled induction motor drive system. Voltage vectors were adjusted according to the reactive component of the motor current, which promptly established the effective value of the motor flux linkage at the preexcitation stage and restrained its trajectory strictly as a round circle all through the starting process. The enhanced dc preexcitation control led to more negligible flux-linkage distortion, less torque vibration, and significantly smaller inrush current. Experiments on a 380-VAC/315-kW adjustable speed drive system validated the effectiveness of the proposed method.

  • Xuesong Wang; Hua Bai; Zhengming Zhao; Liqiang Yuan
    IEEE Transactions on Vehicular Technology
    2011

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    With the development of plug-in hybrid electric vehicles (PHEVs), power electronics plays an increasingly important role in electric power train systems. The economic and reliable design of these power electronic systems, e.g., dc/ac inverter and battery charger, will be the inward search to popularize electric vehicles. As an extension of system-level safe operational areas (SSOAs) proposed in our previous literature, this paper details the criteria and mathematical models of SSOA for a battery charger and a three-phase two-level dc/ac inverter. Operational areas were established based on the SSOA. Thermal characteristics of the semiconductor devices, operational modes, and load characteristics were enclosed to enhance the mathematical models. Experiments on a 5-kW charger and a 55-kW/380-VAC inverter validated the effectiveness of SSOA.

  • 2010

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    Three different control algorithms, traditional single-phase-shift control, dual-phase-shift control (DPSC), and model-based phase-shift control (MPSC), are implemented in a hardware setup and compared for a full-bridge-based isolated bidirectional dc-dc converter. The differences among their dynamic performance and steady-state operations are quantitatively analyzed. Experimental results showed good agreement with theoretical analysis. MPSC showed the best dynamic performance, while DPSC can eliminate reactive power under light-load conditions.

Conference Papers
Title
Year
  • Yongsheng Fu; Yang Huang; Hua Bai; Xi Lu; Ke Zou; Chingchi Chen
    2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2018

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    With the development of power electronics, three-phase voltage source inverters(VSls) are widely used in industry application. In this paper a SiC device based EV battery charger consisting of dual active bridge(DAB) and three-phase four-wire VSI is built. In order to undertake the unbalanced load, an independently controlled neutral module(ICNM) has been adopted for the VSI control to form the neutral line and provide the path for the zero-sequence current. Split DC-bus capacitors with the fourth leg are equipped to the conventional VSI. Meanwhile, the control performance is improved by paralleling virtual resistors to the load, namely, notch-filter-incorporated capacitor voltage feedback control(NF-CVFC), which not only enhances the quality of the output voltage but also ensures the system stability. Finally, a 10kW prototype is built and tested. Experimental results verified the proposed control strategy and the practical feasibility.

  • Livan Zhu; Hua Kevin Bai; Alan Brown; Matt McAmmond
    2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2018

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    Wide-Bandgap devices are believed to be promising candidates for the next-generation power electronics converter. However, the prohibitive cost and limited variety are still the main constrains before being widely used. One possible solution to mitigate these issues is hybrid switches, a combination of Si MOSFETs and WBG devices. To maximize merits of both GaN HEMT and Si MOSFET, this paper proposes a hybrid switch consisting of two GaN HEMTs and two Si MOSFETs. For such a design, a robust gate-drive loop is critical to secure the safe operation of all switches. As an instructive work, this paper presents a comprehensive analysis of the switching transient process and its impact on the gate-drive loop, practical tuning tips of gate-drive loop design are also given based on the simulation and experimental results. A 400V/ 80A full bridge prototype is developed to validate our design. Experimental result shows that, with enhanced gate-drive loop, we can continuously turn off 400V/80A@100kHz and 400V/40A@300kHz with only one GaN device paralleled to two commercial Si MOSFETs.

  • Fanning Jin; Wei Qian; Hua Bai; Dingguo Lu; Bing Cheng
    2018 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2018

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    In order to reduce the resources utilization of Field Programmable Gate Array (FPGA) chip thereby using one FPGA to control multiple motors together, a novel time-division multiplexing (TDM) method is proposed in this paper. The field-oriented control (FOC) algorithm is developed using Xilinx system generator (XSG) in Matlab/Simulink environment. Due to the fast calculation speed of FPGA and the pipeline optimization technology, the execution time of FOC algorithm can reach <;2.5 μs and the switching frequency can be increased to >100 kHz. In order to verify the proposed TDM method, the dual-motor scenario is studied in this paper. Experimental results show that by adopting the proposed TDM method, the resource utilization of the FPGA chip can be further greatly reduced.

  • Fanning Jin; Hua Bai; Dingguo Lu; Bing Cheng
    2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2018

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    As the effort to maximize the potential of SiC devices, the Field Programmable Gate Array (FPGA) is utilized in this paper to achieve high control bandwidth (>200 kHz) when implementing the Field-oriented Control (FOC) algorithm. This can greatly enhance the high-frequency injection (HFI) sensorless control for Permanent Magnet Synchronous Motors (PMSMs) by widening the applicable speed range, for instance, increasing the injection frequency up to 2 kHz from the conventional 500Hz. To offset the cost, it is also validated that one FPGA can control two motors simultaneously.

  • Guanliang Liu; Kevin Hua Bai; Matt McAmmond; Allan Brown; Philip Mike Johnson; Allan Taylor; Juncheng Lu
    2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2017

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    As two exemplary candidates of wide-bandgap devices, SiC MOSFETs and GaN HEMTs are regarded as successors of Si devices in medium-to-high-voltage (>1200V) and low-voltage (<;650V) domains, respectively, thanks to their excellent switching performance and thermal capability. With 650V SiC MOSFETs coming into being the direct competition of SiC and GaN in <;650V domains is inevitable, such as Level-2 battery chargers for electric vehicles. This paper applies 650V SiC and GaN to two 240VAC/7.2kW EV battery chargers, respectively, aiming to provide a head-to-head comparison of these two devices in terms of the efficiency, power density, thermal and cost, with the same control strategy of varying the phase-shift and switching frequency to cover the wide input range (80VAC~260VAC) and wide output range (200V~450VDC).

  • Allan Taylor; Juncheng Lu; Hua Kevin Bai; Alan Brown; Matt McAmmond
    2017 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2017

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    To filter the 120Hz output current ripple in our previously designed 7.2kW single-phase EV charger, this paper proposes to equip the charger with a buck-type active filter. 650V/60A enhancement mode GaN HEMTs provided by GaN Systems Inc are adopted to work at hard-switching mode. Experimental results indicated that four such switches could be paralleled to hard switch on/off ~240A, which is the key for the buck-type active filter. A model-based proportional-resonant controller is adopted to smooth the output current. Such control will enhance the dynamic response of the active filter, compared to the conventional PI controller. The experimental output current ripple and power loss analysis are given.

  • Philip Mike Johnson; Kevin Hua Bai
    2017 IEEE Symposium Series on Computational Intelligence (SSCI)
    2017

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    Present electric vehicles usually use 3.3kW or 6.6kW chargers. With three-phase 380VAC~480VAC available, it is possible for the charger to deliver much higher power, e.g., 20kW, which will expedite the battery charging speed. Meanwhile, wide-bandgap devices (WBG) like silicon carbide MOSFETs and gallium nitride HEMTs provide higher efficiency than Si devices, which potentially will increase the power density thereby fitting such a fast charger on board. This paper uses the conventional LLC topology to realize a 20kW all-SiC EV onboard charger. Two half-bridge LLC converters are series connected on the primary side and parallel connected on the secondary side to provide 20kW together. Matrix transformers are utilized to facilitate the system assembly. Experimental results validated that such design approach could realize 20kW and reach ~96% wall-to-battery efficiency.

  • Guanliang Liu; Kevin Hua Bai; Matt McAmmond; Allan Brown; Philip Mike Johnson; Juncheng Lu
    2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2017

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    Wide-bandgap (WBG) devices are believed as the alternate of silicon switches for high-efficiency and high-power-density power electronics converters. While two major challenges of WBG devices remain as high cost (~5 times of Si) and less options (the maximum power rating for GaN is only 650V/60A), paralleling GaN with Si could be the potential solution to solve pains above. In this paper, two SMT GaN HEMTs are paralleled to a TO-247 Si MOSFET. A time delay is added between switch gate signals to make GaN endure the switching loss and Si conduct majority of the current, which maximizes advantages of both switches. The proposed design is found particularly useful for zero-voltage-switching applications. Critical dynamic behaviors such as the current overshoot to the GaN, current distribution during the dead time, and voltage spike during the turn-off caused by parasitics are comprehensively discussed. Its impact on the control performance and system loss is evaluated as well.

  • Chenguang Jiang; Bo Lei; Hui Teng; Hua Kevin Bai
    2016 IEEE Energy Conversion Congress and Exposition (ECCE)
    2016

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    It is expected that wide-bandgap devices like silicon carbide MOSFETs and gallium nitride HEMTs could replace Si devices in power electronics converters to reach higher system efficiency, e.g., a 3-phase 380VAC bidirectional battery charger for electric vehicles. This paper uses the conventional half-bridge LLC topology to build a 10kW all-SiC bidirectional charger. As a well-known topology for the unidirectional charger, it has not been comprehensively explored for the usage of the bidirectional energy flow, which falls into the scope of this paper. A double-pulse-test platform is utilized to provide the accurate power losses, which, combined with the state-space model deriving the accurate switching current waveforms eventually accurately, estimates the system efficiency. Based on this model, to further enhance the system efficiency the DC-bus voltage is varied while keeping the LLC DC/DC converter running at the resonant frequency through the whole power range. Experimental results validated our proposed approach that such topology could realize the bidirectional power flow with zero-voltage-switching turn on. With varying the DC-bus voltage, the V2G and G2V modes reach ~96% wall-to-battery efficiency.

  • Qi Tian; Alex Q. Huang; Hui Teng; Juncheng Lu; Kevin Hua Bai; Alan Brown; Matt McAmmond
    2016 IEEE Energy Conversion Congress and Exposition (ECCE)
    2016

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    At present time, the most common electrical vehicle (EV) chargers employ a two-stage design, i.e., a front-end AC/DC stage + an isolated DC/DC converter. In this paper, an isolated dual-active-bridge (DAB) based single-stage AC/DC converter was proposed, which has the power-factor-correction (PFC) and zero-voltage-switching (ZVS) functions over the full-load range. By reducing one power stage and eliminating the large DC link capacitor, a high efficiency and high power density are achieved. Such topology can be used as a modular building block to scale up to 50kW by serial connecting the input terminals and paralleling output terminals. A novel energy-balanced variable switching frequency control for such input-series-output-parallel (ISPO) modular designed is proposed. A single-phase d-q transformation is implemented to achieve zero steady-state error. Simulation analysis and experimental validation are presented.

  • Ismail Yasar; Lei Shi; Kevin Bai; Xi Rong; Yang Liu; Xuntuo Wang
    2016 IEEE Transportation Electrification Conference and Expo (ITEC)
    2016

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    In this paper, wireless power transfer for mobile phones via coupled magnetic resonance with multiple transmitters (Txs) and / or receivers (Rxs) are investigated and tested. The system is able to charge cellphones with more than 3 W in a distance between 5 and 15 cm and also in different angles. The resonant frequency is 6MHz. For lower charging powers the distance between the Tx and Rx can go up to 20 cm. Additionally, the three-dimensional movement of the Rx and its effect to the charging power is tested, as self-rotation and rotation around the Tx coil. This achievement is significant to improve user experience of wireless charging for portable electronic devices.

  • Qi Tian; Alex Q. Huang; Hua Bai; Juncheng Lu; Hui Teng; Matt Mcammond; Alan Brown
    IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society
    2016

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    Full-bridge power-factor-correction (PFC) front-end + dual-active-bridge (DAB) AC/DC topology is widely used in industry, e.g., electrical vehicle on-board charger. Such two-stage topology limits the system efficiency, and the bulky DC link bus capacitor makes the system power density relatively low. Compared to the two-stage design, the single-stage design, unfolding bridge + DAB, eliminates the bulky DC link bus capacitor and operates the front-end with only 60Hz switching frequency, thereby has the potential to increase the system power density and efficiency. A novel variable-switching-frequency and hybrid single-dual-phase-shift (VSF-SDPS) control strategy is proposed and analyzed for the DAB based single-stage topology. The proposed VSF-SDPF control consists of two phase shifts to guarantee Zero-Voltage-Switching (ZVS) over the full range of the AC line voltage, and frequency modulation to achieve boost PFC. The conventional front-end PFC is simplified to an unfolding bridge by changing DAB control strategy to achieve PFC and ZVS at the same time. Besides, a special ZVS boundary is utilized to solve the grid current distortion problem when the switching frequency saturated, which is especially severe at light load condition. Simulation results and experimental validation are presented under 50Vrms AC line voltage and 200V DC battery voltage test condition.

  • Juncheng Lu; Hua Bai; Alan Brown; Matt McAmmond; Di Chen; Julian Styles
    2016 IEEE Applied Power Electronics Conference and Exposition (APEC)
    2016

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    This paper designed the gate driver circuits and optimized the PCB layout in a 7.2kW battery charger using paralleled GaN HEMTs. 650V/60A enhancement mode GaN HEMTs provided by GaN Systems Inc are adopted. To optimize the switching performance of paralleled GaN HEMTs with low loss and high reliability, effects of parasitic inductance and capacitance are modeled and analyzed. Through cancelling the flux in the commutation loop, the power-loop parasitic inductance is reduced to only 0.7nH, which significantly decreases the electrical stress in the switch turn-off process. A diverse-parameter gate driver design has been proposed to achieve the reliable switching off. The Finite-Element-Analysis and Spice simulation show our current design could effectively suppress the voltage overshoot and gate-drive ringing on HEMTs. Experiments were carried out on both double pulse test platform and the 7.2kW charger to verify the proposed design strategy.

  • Xi Zhang; Hua Bai; Xuan Zhou
    2016 IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia)
    2016

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    In this paper, a soft switching DC-DC converter control strategy based on fixed boundary layer sliding mode control (FBLSMC) and switching frequency modulation is presented with application to an electric vehicle (EV) powered by a hybrid energy storage system (HESS). This strategy is aimed at improvement of transient performance, energy transfer efficiency and system robustness for the HESS By fully taking into account all PWM operating modes and the occurrence of system uncertainties, the state-space model of the studied DC-DC converter is newly established. The chattering-free FBLSMC scheme for current/voltage tracking is proposed to guarantee the systematic robustness. Meanwhile, in order to ensure soft switching operating effectiveness and accordingly high efficiency, an adaptive switching frequency modulation method is presented complying with the state equations and proposed principles. Finally, experimental results considering the transient response and driving cycle operation confirm the validity and application feasibility of the proposed strategy in the HESS powered electric vehicle.

  • Zhe Li; Xi Zhang; Wei Qian; Hua Bai
    2016 IEEE 7th International Symposium on Power Electronics for Distributed Generation Systems (PEDG)
    2016

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    In this paper, a novel topology of a non-isolated buck converter with zero-current-transition (ZCT) capabilities is presented. In order to realize ZCT condition, the auxiliary circuit consists of a coupled inductor, a capacitor and an auxiliary switch, which also operates with a ZCT condition. It should be noted that the coupled inductor is comprised of three inductors on the same ferrite core which plays an important role in different branches. Moreover, the coupled inductor plays an effective role in achieving soft-switching condition. The detailed operating analysis of the proposed converter is presented. Finally, a 720 W prototype is built to verify the theoretical principles. The switching waveforms are also measured to validate the proposed topology.

  • Qi Tian; Alex Q. Huang; Hua Bai
    IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society
    2016

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    Full-bridge power-factor-correction (PFC) front-end + dual-active-bridge (DAB) AC/DC topology is widely used and its small-signal model has been studied in depth. Compared to the two-stage design, the single-stage design, unfolding bridge + DAB, is attracting more attention nowadays. By eliminating the bulky DC link bus capacitor and operating the front-end with only 60Hz switching frequency, the DAB based single-stage AC/DC converter has the potential to increase the system power density and efficiency. Different from the conventional constant-switching-frequency (CSF) DAB control, a novel variable-switching-frequency (VSF) DAB control is more suitable for the single-stage design due to the 0 to peak input voltage. A full-order state-space model is proposed in this paper to describing the VSF control. The influence of DC blocking capacitor is stressed because there is always a low frequency excitation of VSF control which is not existed with CSF control. The resonance of DC blocking capacitor and transformer leakage inductor is well described by the full-order state-space model. Simulation and experimental results verified the correctness of proposed DAB full-order state-space model.

  • Juncheng Lu; Qi Tian; Kevin Bai; Alan Brown; Matt McAmmond
    2015 IEEE 3rd Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2015

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    Most of the present EV on-board chargers utilize a three-stage design, e.g., AC/DC rectifier, DC to high-frequency AC inverter, and AC to DC rectifier, which limits the wall-to-battery efficiency to ~94%. Instead of using the regular three-stage design, a matrix converter could directly convert grid AC to high-frequency AC thereby saves one stage and potentially increases the system efficiency, however, the control will be more complex and the high cost of building the back-to-back switches is inevitable. This paper adopts the 650V E-mode GaN HEMTs to build a level-2 on-board charger. The input voltage is 80~260VAC, the battery voltage is 200~500VDC and the rated power is 7.2kW with the bidirectional power-flow capability. Such design saves the bulky DC-bus capacitor. Variable switching frequency is combined with phase-shift control to realize the zero-voltage switching. An active filter is employed to choke the 120Hz output current ripple if needed. To further increase the system efficiency, four GaN HEMTs are paralleled to form one switching module. The overall system efficiency is >97% and the power density is 2.5kW/L with the active filter and 3.3kW/L without the active filter.

  • Juncheng Lu; Hua Kevin Bai; Scott Averitt; Di Chen; Julian Styles
    2015 IEEE 3rd Workshop on Wide Bandgap Power Devices and Applications (WiPDA)
    2015

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    Instead of using 1200V SiC MOSFETs for the >600V applications, this paper utilized 650V E-mode GaN HEMTs to build a three-level DC/DC converter. The DC-bus voltage is 800V, the output voltage of 380V and the power is 2.5kW with the bidirectional power-flow capability. Simulation and experimental results show that such design strategy is superior to a single 1200V SiC MOSFET based DC/DC converter in terms of the switching and conduction performance. On the other hand, in order to better understand the performance of GaN HEMTs, hard-switching technology is used to fully test the switching behaviors. Two GaN HEMTs are in parallel to enhance the power capability, which requires the special focus on the parasitic parameters. The effects of parasitics especially the stray inductance in the commutation loop and the gate-drive loop during switching transitions have been comprehensively analyzed and discussed in this paper.

  • Xiao Feng Ding; Guan Liang Liu; Hong Guo; Hua Bai
    2015 IEEE International Conference on Applied Superconductivity and Electromagnetic Devices (ASEMD)
    2015

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    This paper presents a novel axial-flux microelectromechanical systems (MEMS) based micromotor with dual-rotor and 10mm diameter. The characteristics of MEMS micromotor are analyzed and modeled using a 3-D magnetic equivalent circuit (MEC) taking the leakage fluxes and fringing effect into account. Such methodology yields more accurate prediction of the flux distribution inside the machine, back electromotive force (EMF) waveform and the torque. The key point of the analytical model is to compute the magnetic flux density in the air gap generated by the permanent magnet. An accurate prediction method of the leakage fluxes based on an improved pigeon-inspired optimization (PIO) algorithm is proposed in this paper. The feasibility of the proposed method is validated by the 3-D finite element analysis (FEA). Finally, the method is applied to design and manufacture the micromotor.

  • Zhong Nie; W. David Williams; Chen Duan; Wei Guo; Kevin Hua Bai
    2014 IEEE Applied Power Electronics Conference and Exposition - APEC 2014
    2014

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    In previous work, a novel design of a 2.5kW 400V-12V 93.2%-efficiency DC/DC converter with a triggering angle tracking synchronous rectifier was proposed for use in an electric vehicle to replace the electric alternator. This paper is focused on the further enhancement of the DC/DC converter to improve the system efficiency and wide-range input/output performance.

  • Yongsheng Fu; Lei Shi; Kevin Hua Bai
    2014 IEEE Workshop on Wide Bandgap Power Devices and Applications
    2014

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    The Gallium nitride high electron mobility transistor (GaN HEMT) has become popular in the power electronics industry as it offers the possibility to reach lower switching loss and higher switching frequency compared to Si devices. This paper adopts a normally-off GaN HEMT in the wireless power transfer (WPT) system to charge a 48V battery pack on the E scooter. 178W power was delivered to the battery pack with 813 kHz switching. A simulation model of GaN HEMT is also built in LTspice to itemize the system loss. At the end some thoughts of improving the system efficiency were proposed.

  • Yu Li; Allan Taylor; Kevin Bai
    2014 IEEE Transportation Electrification Conference and Expo (ITEC)
    2014

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    This paper presents a method for the sensorless control in full speed range for an interior permanent-magnet synchronous motor (IPM). At standstill and very low speed region, high frequency (HF) injection technique is used to detect the rotor initial position. A hybrid observer is applied to realize a smooth transition from low to high speed. When the rotor speed goes up to a certain value where back EMF can provide adequate information, a back EMF observer will dominate. The hybrid observer is verified through simulation and experimental results using a three-phase 1-kW IPM motor drive.

  • Fei Yang; Allan Taylor; Hua Bai; Bing Cheng; Arshan Khan; Young Joo Lee; Zhong Nie
    2014 IEEE Energy Conversion Congress and Exposition (ECCE)
    2014

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    Variable switching frequency PWM (VSFPWM) control has been adopted in the induction motor drive in recent work. Due to the position-related phase inductance, interior permanent magnet synchronous motors (IPMSM) have the difficulty to adopt VSFPWM. In contrast to using thevenin theory from previous work, this paper applies d-q transformation to IPMSM drives to predict the phase-current ripple and applies VSFPWM to control the current ripple of IPMSM. Simulation results validated the effectiveness of the theoretical analysis.

  • Fei Yang; Allan Taylor; Hua Bai; Bing Cheng; Arshan Khan; Young Joo Lee; Zhong Nie
    2014 IEEE Conference and Expo Transportation Electrification Asia-Pacific (ITEC Asia-Pacific)
    2014

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    This paper adopted the variable switching frequency PWM (VSFPWM) control to the SPMSM and combined the VSFPWM with SVPWM and DPWM. A power loss model was built to quantitatively compare the system efficiency at CSF/VSF SVPWM and CSF/VSF DPWM. Simulation and experimental validations were pursued on a 5kW surfaced-mounted permanent synchronous motor (SPMSM) drive system.

  • Yongsheng Fu; Hua Bai
    2014 IEEE Transportation Electrification Conference and Expo (ITEC)
    2014

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    This study proposes a design and development of Series-Series Compensated topology based (SSC) wireless power transfer system to charge the battery in light-duty electrified automobiles, e.g., electric scooters. An asymmetric resonant methodology is adopted by adjusting the secondary-side resonant capacitance to make the system resonate only at the secondary side, which is different from the prevalent symmetric resonant topology. The experimental data at 250W test matches the simulation result well, which improves the system efficiency.

  • Chenguang Jiang; Allan Taylor; Chen Duan; Kevin Bai
    2013 IEEE Transportation Electrification Conference and Expo (ITEC)
    2013

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    This paper proposed a battery state of charge (SOC) estimation methodology utilizing the Extended Kalman Filter. First, Extended Kalman Filter for Li-ion battery SOC was mathematically designed. Next, simulation models were developed in MATLAB/Simulink, which indicated that the battery SOC estimation with Extended Kalman filter is much more accurate than that from Coulomb Counting method. This is coincident with the mathematical analysis. At the end, a test bench with Lithium-Ion batteries was set up to experimentally verify the theoretical analysis and simulation. Experimental results showed that the average SOC estimation error using Extended Kalman Filter is <;1%.

  • Chen Duan; Chenguang Jiang; Allan Taylor; Kevin Bai
    2013 IEEE Transportation Electrification Conference and Expo (ITEC)
    2013

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    This paper proposes a design and development of a wireless power transfer system to charge the battery in the Plugin Hybrid Electric Vehicles. A Parallel-Parallel topology is adopted to realize 15 cm-distance power transfer using resonance theory. Finite Element Method is used to extract the coil parameters. The advantages of the proposed design compared to the previous similar research are 1) low operational frequency (42 kHz) to avoid the electromagnetic interference to on-board automotive electronics equipment, and 2) low electrical stress to the semiconductor switches through using zero-voltage-switching technique. A 2 kW prototype to charge 200 V battery was built to experimentally verify the theoretical analysis. The overall system efficiency is ~86%.

  • Chen Duan; Wei Guo; Kevin Hua Bai; Zhong Nie; Mengyang Zhang; Fred Householder; Dennis Krozek
    2013 IEEE Energy Conversion Congress and Exposition
    2013

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    This paper proposes the design and development of a 2.5kW 400V→12V high-efficiency DC/DC converter with a wide input voltage range (450V~220VDC) and output voltage range (16V~6VDC). The designed DC/DC converter will be used in the electric vehicle as an electric alternator. An LLC half bridge topology is adopted as the primary side of the isolated DC/DC converter. For the secondary side, a novel rectification control strategy is developed to turn on/off the rectifier MOSFETs by actively tracking the exact triggering moments. A 2.5kW prototype to charge the on-board 12V battery was built to experimentally verify the theoretical analysis. The overall system efficiency was ~92% and the maximum is 93.2%.

  • Allan Taylor; Chenguang Jiang; Kevin Hua Bai; Adam Kotrba; Argun Yetkin; Arda Gundogan
    2013 IEEE Energy Conversion Congress and Exposition
    2013

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    For the conventional vehicle, an efficient and effective heat source that provides autonomous exhaust temperature control is of interest, and one solution is a diesel burner which needs to adjust its air delivery based on transient operating conditions through a three-phase motor drive system powered by a 12V lead-acid battery. The system proposed in this paper consists of a series-resonant LLC MOSFET full-bridge converter, which provides high-efficiency energy transfer through implementing Zero Voltage Switching, and an IGBT inverter which provides the high-side phase currents to a 1kW brushless DC motor. Experimental results on this prototype system demonstrate the LLC DC/DC part efficiency is 97.6% and the inverter efficiency is 92%.

  • Wei Guo; Kevin Bai; Allan Taylor; Jeff Patterson; James Kane
    2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference and Exposition (APEC)
    2013

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    Usually a high-efficiency Level 1~2 battery charger consists of an AC/DC (PFC) part and a DC/DC part, which in this paper is a CoolMOS based 97%-efficiency full-bridge LLC resonant DC/DC converter. Due to the existence of the output capacitance and high input voltage (usually 400VDC), the inrush current of the DC/DC converter in the starting process is inevitable, which requires an effective soft starting strategy. This paper proposed an effective soft starting strategy to gradually charge the output capacitor, decrease the inrush current and, more importantly, avoid the hard switching in the starting process, which is a must to the CoolMOS. The proposed starting strategy has been experimentally validated on a 10kW LLC resonant DC/DC converter.

  • Mori Yatsui; Hua Bai; Nicholas Cramer; Xi Zheng; Mohammadhossein Azhinehfar; David Mead
    2012 IEEE Transportation Electrification Conference and Expo (ITEC)
    2012

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    Various charging algorithms are employed in commercialized battery chargers. This study was to undergo charging tests of four various chargers dedicated to 12-V lead-acid batteries. Our previous work on the Extended Kalman Filter based State-of-charge estimation in this comparison to make sure all batteries were charged/discharged to the same level. State-of-Health (SOH) is employed to determine the battery performance. The impact of the charging algorithms on the battery life time was evaluated. Experimental results show that the medium-speed charging when SOC is low with pulse charging at the high SOC keeps the longest life time of the battery.

  • Wei Guo; Hua Bai; Gyula Szatmari-Voicu; Allan Taylor; Jeff Patterson; James Kane
    2012 IEEE Transportation Electrification Conference and Expo (ITEC)
    2012

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    Battery chargers of Plug-in Hybrid Electric Vehicles require high efficiency operation. An LLC resonant DC/DC converter is an excellent choice to reach the high efficiency with reduced current stress. In this paper, a CoolMOS based 10kW full-bridge LLC resonant DC/DC converter with >;97% efficiency is designed. CoolMOS model is utilized to analyze the system loss. Experimental results validate that this charger could charge the load at ~97% efficiency @10kW with output voltage varying from 250V to 400V. When output voltage is between 400V and 450V, the experimental efficiency remains above 95%.

  • Allan Taylor; Xuntuo Wang; Hua Bai; Gyula Szatmari-Voicu; Jeff Patterson; James Kane
    2012 IEEE Transportation Electrification Conference and Expo (ITEC)
    2012

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    Power factor correction controllers are widely used in the battery chargers of Plug-in Hybrid Electric Vehicle, connecting the grid with charging system to reach power factor equal to 1. Increasing the operational efficiency of the PFC is the inward search. This paper presents a three-phase full-bridge PFC circuit with >;97% efficiency at 10kW. Comparison of different control algorithms with corresponding power loss calculations is pursued to optimize the system design. Experiments on two 208VAC/10kW PFC prototypes equipped with either fast reverse recovery diode or Silicon Carbide Schottky Diode respectively validated the effectiveness of the design.

  • 2011

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    The battery is one of the most important energy storage components in EV/HEV. Failing to estimate the state of the charge accurately will bring the risk of overcharge or over discharge. The traditional Coulomb counting method will bring accumulated error over time, therefore high deviation occurs between the estimated and real state of charge. Different estimation strategies are compared in this paper, i.e., Coulomb counting method, open-circuit-voltage method and Kalman filter based state of charge estimation. Experimental results validate the effectiveness of Kalman filter during the on-line application.

  • Hua Bai; Chris Mi
    8th International Conference on Power Electronics - ECCE Asia
    2011

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    The bidirectional DC-DC converter in a HEV is also some times called a power management converter, or an energy management converter, or boost DC-DC converter. This DC-DC converter is a high-power converter that links the high voltage battery (HV) at a lower voltage with the high voltage DC bus. The typical voltage of a battery pack is designed at 300 to 400V. The best operating voltage for a motor and inverter is around 600V. Therefore, this converter can be used to match the voltages of the battery system and the motor system. Other functions of this DC-DC converter include optimizing the operation of the powertrain system, reducing ripple current in the battery, and maintaining DC link voltage, hence, high power operation of the powertrain.

  • Hua Bai
    2011 IEEE Vehicle Power and Propulsion Conference
    2011

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    This paper extended the research on the system-level safe operation area (SSOA) of power electronic converters in our previous literatures, which proposed a comprehensive procedure of constructing SSOA, investigated the impact of the microscopic transient processes and macroscopic control algorithms, and pictured the SSOA of a battery charger for plug-in hybrid electric vehicles. The genetic algorithm is used to optimize the system parameters at the macroscopic level. More importantly, thermal characteristics of the MOSFETs and battery impedance are enclosed to enhance the system reliability and maximize the power capability. In the end, the SSOA for a SiC JFET based electric charger is also discussed.

  • Hua Bai; Chunting Mi; Chongwu Wang; Sonya Gargies
    2008 34th Annual Conference of IEEE Industrial Electronics
    2008

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    This paper presents an averaged model and a small-signal model of a bidirectional dual active bridge (DAB) DC-DC converter. Based on the proposed model, the stability and transient power flow in the system can be analyzed. A novel hybrid controller is proposed for the phase-shift based feed-back and feed-forward control of a 600V/10kW prototype. The hybrid controller can ease the difficulties of the parameter selection of a traditional PI. The effectiveness of the models and proposed hybrid controller are validated by simulations and experiments in both transient and steady state operations.

  • Hua Bai; Zhengming Zhao
    APEC 07 - Twenty-Second Annual IEEE Applied Power Electronics Conference and Exposition
    2007

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    The integrated gate commutated thyristors (IGCTs) are commonly used for construction of high voltage three-level PWM controlled voltage source converter/inverters. When the output voltage is greater than the maximum rated voltage, IGCTs are connected in series. To ensure the safe and reliable operation of the converter/inverters, special measures are required to equalize the voltages across the IGCTs connected in series. An effective method for balancing voltages is to use resistors for static voltage balancing and RC snubber circuits for dynamic voltage balancing. However, most of the previous research work reported in the literature focused on the dynamic circuit design for converters of the BUCK topology. Trade off is made only between the performance of dynamic voltage balancing and the turn-on loss without any consideration of di/dt endurance and any procedural steps, which makes the design procedure not suitable for converters of the three-level topology. Based on a functional model of IGCTs, this paper presents a procedure for optimum design of the dynamic voltage balancing circuit for a 6 kV/1250 kW inverter. The specific transient processes in the three-level topology with dynamic snubber circuit are simulated and the mechanisms are analyzed, which is absent in the previous work.

  • Liu Shu; Liu Jianzheng; Zhao Zhengming; Yuan Liqiang; Bai Hua; Zhang Haitao
    2005 International Conference on Electrical Machines and Systems
    2005

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    This paper presents an accurate flux observer used in distributed multi-processor (DMP) adjustable speed drive systems. The stator flux linkage is estimated with a full-order observer, while the rotor speed is identified by using Lyapunov theorem. In order to improve the system performance in a wide speed range, the stator resistance is estimated simultaneously. In this paper, the structure of the DMP system, the principle of the full-order observer and the method for identifying the rotor speed and state resistance are all described in details. Relevant simulation results based on MATLAB/SIMULINK are given to prove the performance of the method. Experiments of a real system also verify the feasibility of this scheme

  • Jue Qian; Zhengming Zhao; Haitao Zhang; Hua Bai; Liqiang Yuan
    2005 International Conference on Electrical Machines and Systems
    2005

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    The voltage increment in MV-ASD systems deteriorates the electromagnetic environment, therefore the communication system is facing a formidable challenge in the attempt to achieve the numerous real-time interactivities among those subsystems under such electromagnetic circumstance. This paper focuses on the real-time communication system for the MV-ASD systems, in which electromagnetic compatibility (EMC), real-time performance and system reliability are considered simultaneously. A novel fiber-CAN network is designed and implemented, which remarkably increases EMC compared to the conventional ones. The CAN system that serves in the multiprocessor control system for the MV-ASD system with the rated power of 1 MW is implemented. From the experiment results in the MV-ASD system with a 690 kW motor, it can be verified that the requests of timing performance and the reliability for the communication system are well accomplished

  • Zhang Haitao; Zhao Zhengming; Yuan Liqiang; Bai Hua
    2005 International Conference on Electrical Machines and Systems
    2005

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    In the medium voltage adjustable speed drive (MV-ASD) systems, low switching frequency results in high harmonics in the output voltage waveform, which is harmful to the isolation of the induction motor. Therefore, the power filter is usually set between inverter and motor. However, self-excitation oscillation easily occurs under this structure due to the filter capacitor, which could continuously bring up the DC-link voltage of the inverter, and even destroy the devices in inverters. One of the effective ways to eliminate the self-excitation oscillation is to set the inverter to three-phase short-circuit braking state, which is described and analyzed in detail in this paper. Three-phase short-circuit braking could be easily realized in the inverter-motor system. It can be verified by both simulation based on PSIM and test results that this is an efficient way in real applications. Finally, the characteristics of the short-circuit braking is summarized and beneficial suggestions on using this braking method are presented

  • Zhengming Zhao; Hua Bai; Shuo Meng; Jianzheng Liu; Xiaoying Sun
    Sixth International Conference on Electrical Machines and Systems, 2003. ICEMS 2003.
    2003

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    In a variable frequency and adjusting speed system with high power, the balance of neutral point is very important. This paper brings out a set of complete neutral point control strategies based on the improved space vector pulse width modulation (SVPWM) control strategy, and has obtained comparative perfect effects in practice.

  • Bai Hua; Zhao Zhengming; Meng Shuo; Liu Jianzheng; Sun Xiaoying
    The Fifth International Conference on Power Electronics and Drive Systems, 2003. PEDS 2003.
    2003

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    Sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) are the most popular modulation strategies applied to variable frequency and adjusting speed systems, and there are diverges in comparing the merits and demerits of their own. Also there is another modulation strategy called one-cycle control. This paper gathers the three strategies and does some comparisons through simulation based on a simulation tool-PSIM, and has drawn some profitable conclusions.

  • Yuan Liqiang; Zhao Zhengming; Bai Hua; Li Chongjian; Li Yaohua
    The Fifth International Conference on Power Electronics and Drive Systems, 2003. PEDS 2003.
    2003

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    This paper presents the design, simulation and implementation of circuit for IGCT (integrated gate commutated thyristor) test platform, which is an equivalent circuit for the common commutation types occurring in the 2-or 3-level VSI (voltage source inverter) circuits. Based on the equivalence, the design of the test circuit for 5SHX08F4502 without switching-off snubber, including the topology and the element parameters, especially the ones of stray inductors, is described in detail. The test circuit is simulated with the package PSIM, and the IGCT model is functional level. The simulation and experiment results are both given in the paper.