This paper proposes a novel two-stage topology for a 6.6-kW on-board charger. The first stage, employing an interleaved bridgeless totem-pole ac/dc in critical conduction mode to realize zero-voltage switching, is operated at over 300 kHz. A bidirectional CLLC resonant converter operating at 500 kHz is chosen for the second stage. A variable dc-link voltage is adopted to track the wide battery voltage range, so that the CLLC resonant converter can always operate at its most efficient point. The 1.2-kV SiC devices are adopted for the ac/dc stage and the primary side of dc/dc stage, while 650-V GaN devices are used for the secondary side of dc/dc stage. In addition, PCB winding coupled inductors and integrated transformer are implemented in ac/dc stage and dc/dc stage, respectively, for the purpose of high density and manufacture automation. The proposed structure is demonstrated to have 37-W/in3 power density and above 96% efficiency over the entire battery voltage range, which far exceeds the current practice.

A High-Efficiency High-Density Wide-Bandgap Device-Based Bidirectional On-Board Charger

The momentum toward high power density high-efficiency power converters continues unabated. The key to reducing the size of power converters is high-frequency operation and the bottleneck is the magnetic components. With the emerging widebandgap devices, the switching frequency of power converters increases significantly, to hundreds of kilohertz, which provides us the opportunity to adopt printed circuit board (PCB) winding planar magnetics. Compared with the conventional litz-wire-based magnetics, planar magnetics can not only effectively reduce the converter size, but also offer improved reliability through automated manufacturing process with repeatable parasitics. Another way to reduce the number of magnetic components and shrink the size of power converters is through the magnetic integration. In this paper, a novel PCB winding based magnetic structure is proposed to integrate both inductor and transformer into one component. In this structure, the inductor value can be easily controlled by changing the cross-sectional area of the core or the length of the air gap. A 6.6-kW 500-kHz CLLC resonant converter prototype with 98% efficiency and 130-W/in3 (8 kW/L) power density is built to verify the feasibility of the proposed PCB winding based magnetic structure.

High-Frequency PCB Winding Transformer With Integrated Inductors for a Bi-Directional Resonant Converter

In this article, a high-efficiency high-power-density wide-bandgap-based CLLC resonant converter with a low-stray-capacitance and well-heat-dissipated planar transformer is presented, which is used as the isolated dc–dc stage for an electric vehicle on-board charger. A generalized planar transformer design methodology is proposed and validated by practical designs and experimental tests. A novel and simple transformer configuration is proposed to reduce the winding stray capacitance and enhance the winding thermal dissipation. The proposed transformer configuration is compared with different planar transformer designs, and the tradeoffs of employing the proposed design are well analyzed. Moreover, the system design and optimization of the high-efficiency high-power-density CLLC resonant converter is studied. The proposed transformer design and the system optimization approach are employed in a 6.6-kW/500-kHz CLLC resonant converter prototype. The prototype achieves a peak efficiency of 97.85% and a power density of 114 W/in $^\text {3}$ .

High-Efficiency High-Power-Density CLLC Resonant Converter With Low-Stray-Capacitance and Well-Heat-Dissipated Planar Transformer for EV On-Board Charger

Because of the global trends of energy demand increase and decarbonization, developing green energy sources and increasing energy conversion efficiency are recently two of the most urgent topics in energy fields. The requirements for power level and performance of converter systems are continuously growing for the fast development of modern technologies such as the Internet of things (IoT) and Industry 4.0. In this regard, power switching devices based on wide-bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) are fast maturing and expected to greatly benefit power converters with complex switching schemes. In low- and medium-voltage applications, GaN-based high-electron-mobility transistors (HEMTs) are superior to conventional silicon (Si)-based devices in terms of switching frequency, power rating, thermal capability, and efficiency, which are crucial factors to enhance the performance of advanced power converters. Previously published review papers on GaN HEMT technology mainly focused on fabrication, device characteristics, and general applications. To realize the future development trend and potential of applying GaN technology in various converter designs, this paper reviews a total of 162 research papers focusing on GaN HEMT applications in mid- to high-power (over 500 W) converters. Different types of converters including direct current (DC)–DC, alternating current (AC)–DC, and DC–AC conversions with various configurations, switching frequencies, power densities, and system efficiencies are reviewed.

Review of GaN HEMT Applications in Power Converters over 500 W

A two-stage electric vehicle (EV) battery charger typically consists of an ac–dc converter cascaded with a dc–dc converter In such a cascaded system, maintaining stability at the intermediate dc link is imperative for reliable operation of the battery charger under different operating modes This paper addresses the intermediate dc-link stability challenges that exist in a bidirectional two-stage grid connected single-phase battery charger It is delineated that the small-signal load-dependent resistance of the ac–dc converter plays a crucial role in determining the stability of the bidirectional battery charger A virtual-resistor-based active damping control strategy that does not require any additional sensors is explored for the ac–dc converter to stabilize the cascaded system under all operating modes irrespective of the power flow direction Experimental results on a grid-connected single-phase battery charger hardware prototype are presented to validate the proposed models and showcase the improvement in the dc-link stability due to the virtual-resistance-based active damping approach

Small-Signal Stability Assessment and Active Stabilization of a Bidirectional Battery Charger

A control method that improves performance of series-resonant converters that operate with a wide input voltage and/or output voltage range by substantially reducing their switching frequency range is introduced. The switching-frequency-range reduction is achieved by controlling the output voltage with a combination of variable-frequency and delay-time control. Variable-frequency control is employed to control the primary switches, while delay-time control is used to control secondary-side rectifier switches provided in place of diode rectifiers. A series-resonant converter with the proposed control method is employed as the output stage of the on-board charger module that operates with a wide battery-voltage range. By substantially reducing the switching frequency range, the overall operating frequency is increased to reduce the sizes of the passive components, and hence, increase power density. The performance evaluation of the proposed series-resonant converter with delay-time control was done on a 3.3-kW prototype delivering energy from 400-V bus, which is the output of the power factor correction front end, to a battery operating with voltage range between 180 and 430 V. Two implementations of the prototype circuit, one employing gallium nitride (GaN) and the other employing silicon (Si) switches, were evaluated and compared. The prototype with Si switches that at full load over the entire output voltage range operates with a switching frequency variation from approximately 150 to 190 kHz exhibits the maximum full-load efficiency of 98.1%, whereas the corresponding frequency range and efficiency of the prototype with GaN devices are 145–190 kHz and 97.4%, respectively.

Implementation of a 3.3-kW DC–DC Converter for EV On-Board Charger Employing the Series-Resonant Converter With Reduced-Frequency-Range Control

A new, three-phase, single-stage, isolated ac–dc converter (rectifier) that employs only two switches and achieves less than 5% total harmonic distortion of the three-phase input currents and provides a tightly regulated, isolated, output voltage is introduced. The rectifier features zero-voltage-switching of both switches over the entire input and load range without any additional soft-switching circuitry. The rectifier is derived by combining the three-phase, power-factor-correction, discontinuous-current-mode boost rectifier that is also known as Taipei rectifier with the conventional LLC resonant half-bridge converter. The introduced rectifier requires single feedback loop with frequency control to regulate the output voltage. The evaluation was performed on a 1-kW prototype operating with a three-phase line-voltage range from 180 to 264 $V_{\text{L}-\text{L}}$ and delivering a tightly-regulated, isolated, output voltage of 54 V. The measured efficiency of the prototype at nominal line voltage V IN = 208 VL-L is above 95% from 90% of full load down to 50% of full load. The maximum voltage stress is approximately 430 V.

A Two-Switch, Isolated, Three-Phase AC–DC Converter

In this article, a new two-switch, single-phase, power-factor-correction, discontinuous-conduction-mode boost rectifier that features zero-voltage switching turn on and can achieve less than 5% input-current total harmonic distortion (THD) by injecting a simple feedforward signal obtained from input and output voltages to the output voltage feedback control is introduced. Since low THD is achieved without high- bandwidth active current shaping control, the proposed topology is suitable for modern aviation applications that require line frequency up to 800 Hz. The evaluation was performed on a 320-W prototype designed to operate from 94–134-V line input and deliver 220-V dc output. The prototype achieves 3.3% THD at full load over the line frequency range from 360 to 800 Hz and meets the required harmonic limits specified by the DO-160 standard that describes the environmental conditions and test procedures for airborne equipment.

A Low-THD Two-Switch PFC DCM Boost Rectifier for Aviation Applications

PROBLEM TO BE SOLVED: To obtain a zero-current zero-voltage switching cell that reduces a loss caused by the reverse recovery of a boost rectifier, and at the same time can eliminate the switching loss of main and auxiliary switches. SOLUTION: In this method, a switching cell with a snubber coil, a clamp diode, a clamp capacitor, and main and auxiliary switches is used, and the switching loss of a PWM converter caused by the turn-on and turn-off characteristics of the switch and the inverse recovery ones of a rectifier is nearly reduced. The loss caused by the inverse recovery is reduced by the snubber coil that is connected to the main switch and the rectifier in series, and controls the time rate of change of the current of a rectifier that is being turned off. The main switch is operated by a zero-current zero-voltage switching, and the auxiliary switch is operated by zero-voltage switching. To have the circuit operated appropriately, the gate drive of the main and auxiliary switches needs to be overlapped.

Soft switching cell for reducing switching loss in pwm(pulse width modulation) converter

A harmonic three-phase boost rectifier for a low input current comprises an input stage for receiving a three-phase input voltage with respect to a neutral node and an output stage, which is adapted for coupling with at least one load. The rectifier further includes one or more switching converter stages, each having a plurality of switches that are coupled to the neutral node, wherein the plurality of switches work with a fixed duty cycle, wherein the fixed duty cycle of a duty cycle of substantially 50%. The rectifier further includes one or more control units, which are designed for varying the switching frequency of the plurality of switches based on a state of the at least one load and / or the input voltage, and comprises one or more decoupling stages each comprise one or more inductive elements which are designed for inductive decoupling of the output stage of at least one of the one or more switching converter stages.

Yungtaek Jang

Papers

Implementation of a 3.3-kW DC–DC Converter for EV On-Board Charger Employing the Series-Resonant Converter With Reduced-Frequency-Range Control

A Two-Switch, Isolated, Three-Phase AC–DC Converter

A Low-THD Two-Switch PFC DCM Boost Rectifier for Aviation Applications

Soft switching cell for reducing switching loss in pwm(pulse width modulation) converter

Soft-switched three-phase PFC rectifier