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Featured researches published by Jiejian Dai.


IEEE Transactions on Power Electronics | 2015

A Survey of Wireless Power Transfer and a Critical Comparison of Inductive and Capacitive Coupling for Small Gap Applications

Jiejian Dai; Daniel C. Ludois

Inductive power transfer (IPT) and capacitive power transfer (CPT) are the two most pervasive methods of wireless power transfer (WPT). IPT is the most common and is applicable to many power levels and gap distances. Conversely, CPT is only applicable for power transfer applications with inherently small gap distances due to constraints on the developed voltage. Despite limitations on gap distance, CPT has been shown to be viable in kilowatt power level applications. This paper provides a critical comparison of IPT and CPT for small gap applications, wherein the theoretical and empirical limitations of each approach are established. A survey of empirical WPT data across diverse applications in the last decade using IPT and CPT technology graphically compares the two approaches in power level, gap distance, operational frequency, and efficiency, among other aspects. The coupler volumetric power density constrained to small gap sizes is analytically established through theoretical physical limitations of IPT and CPT. Finally, guidelines for selecting IPT or CPT in small gap systems are presented.


IEEE Journal of Emerging and Selected Topics in Power Electronics | 2015

Single Active Switch Power Electronics for Kilowatt Scale Capacitive Power Transfer

Jiejian Dai; Daniel C. Ludois

The development of capacitive power transfer (CPT) as a competitive wireless/contactless power transfer solution over short distances is proving viable in both consumer and industrial electronic products/systems. The CPT is usually applied in low-power applications, due to small coupling capacitance. Recent research has increased the coupling capacitance from the pF to the nF scale, enabling extension of CPT to kilowatt power level applications. This paper addresses the need of efficient power electronics suitable for CPT at higher power levels, while remaining cost effective. Therefore, to reduce the cost and losses single-switch-single-diode topologies are investigated. Four single active switch CPT topologies based on the canonical Ćuk, SEPIC, Zeta, and Buck-boost converters are proposed and investigated. Performance tradeoffs within the context of a CPT system are presented and corroborated with experimental results. A prototype single active switch converter demonstrates 1-kW power transfer at a frequency of 200 kHz with >90% efficiency.


applied power electronics conference | 2015

Wireless electric vehicle charging via capacitive power transfer through a conformal bumper

Jiejian Dai; Daniel C. Ludois

Wireless power transfer (WPT) is emerging as a practical means for electric vehicle (EV) charging. Of the three main approaches to WPT, resonant inductive, inductive, and capacitive coupling, capacitive power transfer (CPT) is proposed herein to charge an EV at a kilowatt scale power level. CPT implementation replaces copper coils and ferrous core focusing/shield materials of inductive approaches with foil surfaces making CPT cost effective and structurally simple to implement, while maintaining efficient power transfer capability. This paper addresses each facet of kilowatt scale CPT system development, namely achieving high coupling capacitance between the vehicle and charging station and the associated drive power electronics. High capacitive coupling is achieved through a conformal (flexible and compressive) foam transmitter bumper that molds and contours itself to the vehicle to minimize air gap during charging. An experimental docking station to charge a Corbin Sparrow EV 156V battery pack was built and measured throughput power is demonstrated at >1kW with a coupling capacitance of 10nF operating at 540kHz.


IEEE Journal of Emerging and Selected Topics in Power Electronics | 2016

Capacitive Power Transfer Through a Conformal Bumper for Electric Vehicle Charging

Jiejian Dai; Daniel C. Ludois

Wireless power transfer (WPT) is emerging as a practical means for electric vehicle (EV) charging. Of the most common approaches to WPT, inductive coupling, and capacitive coupling, capacitive power transfer (CPT) is proposed to charge an EV at a kilowatt scale power level. CPT implementation replaces copper coils and permeable focusing/shielding materials of inductive approaches with foil surfaces, making CPT a cost effective and structurally simple system to implement while maintaining efficient power transfer capability. This paper addresses the primary technical hurdles to kilowatt scale CPT system development, namely, safe field confinement by achieving high coupling capacitance between the vehicle and the charging station. High capacitive coupling is achieved through a conformal (flexible and compressive) transmitter bumper that molds and contours itself to the vehicle. This minimizes the air gap and confines the field during charging. Here, a conformal surface demonstrates 3-5 times more coupling capacitance than its rigid counterpart of equal area. The associated power electronics are also discussed in detail, utilizing a Class E2 amplifier/rectifier. An experimental docking station was built to charge the 156 V battery pack of a Corbin Sparrow EV and measured throughput power is demonstrated at 1 kW at ~90% efficiency via a coupling capacitance of 10 nF operating at 530 kHz.


applied power electronics conference | 2015

Biologically inspired coupling pixilation for position independence in capacitive power transfer surfaces

Jiejian Dai; Daniel C. Ludois

A common problem with wireless/contactless power transfer is that the coupling factor is often position dependent, particularly in mobile applications. For both inductive and capacitive power transfer (IPT and CPT respectively) techniques, the transmitter and receiver usually require ideal positioning for maximum power transfer, which limits practicality. This paper aims to reduce this impediment for CPT applications. CPT is straightforward to implement with low material requirements, therefore it is very attractive for applications that require non-contact and galvanic isolation under the constraint of short distances and low cost. However, misalignment of the coupling surfaces severely impedes throughput power capability. This paper presents a nearly position-independent capacitive coupler design for CPT applications. A plant leaf cell inspired hexagon capacitor receiver array paired with multiple half bridge rectifiers achieves nearly uniform capacitance and coupling factor. Design considerations of cell shape, size, etc. for this “capacitive leaf” are developed and experimental results for a mobile phone charging application demonstrate <; 20% capacitance variation and ~12% load voltage variation regardless of position or orientation.


ieee wireless power transfer conference | 2015

Capacitive coupling through a hydrodynamic journal bearing to power rotating electrical loads without contact

Skyler Hagen; Ryan Knippel; Jiejian Dai; Daniel C. Ludois

A capacitive power coupler has been devised using a hydrodynamic journal bearing assembly that facilitates sufficient coupling for kilowatt-scale non-contact power transfer to a rotating load. The capacitive coupler, combined with associated driving circuitry, is an efficient low maintenance solution for powering a variety of rotating or pivoting electrical loads in machines and automation. A hydrodynamic journal bearing capacitor assembly utilizing an ultra-thin cushion of lubricant as dielectric between concentric capacitor electrodes is presented. Hydrodynamic operation ensures high coupling capacitance, ease of manufacturability and eliminates brush and slip ring maintenance. The systems small size, weight, and simplicity are competitive with contemporary inductive wireless power transfer methods in this small gap application. Experimental results for a ~5nF prototype coupler operating at 840 kHz are presented.


european conference on cognitive ergonomics | 2016

Design of a wound field synchronous machine for electric vehicle traction with brushless capacitive field excitation

Antonio Di Gioia; Ian P. Brown; Yue Nie; Ryan Knippel; Daniel C. Ludois; Jiejian Dai; Skyler Hagen; Christian Alteheld

This paper describes the modeling, optimization, mechanical design, and experimental characterization of a high power density wound field synchronous machine (WFSM) for electric vehicle traction applications. The WFSM is designed for brushless rotor field excitation using an axial flux hydrodynamic capacitive power coupler (CPC). A flexible design environment is described which was used for large scale multi-objective optimization. A prototype WFSM, spray cooled with automatic transmission fluid (ATF), with an 80 kW (peak) output at a base speed of 4,000 RPM has been tested. The prototyped WFSM achieves peak volumetric and specific torque and power densities of 17.22 Nm/l, 4.69 Nm/kg, 7.19 kW/l, and 1.95 kW/kg.


european conference on cognitive ergonomics | 2016

Synchronous generator field excitation via capacitive coupling through a journal bearing

Jiejian Dai; Skyler Hagen; Daniel C. Ludois; Ian P. Brown

Wound field synchronous generators (WFSG) are the standard for back-up and utility scale power generation. Rotor field current and prime mover speed are the only control parameters required to regulate power conversion in a generator application. Maintenance costs may be minimized by adopting non-contact or “brushless” technologies to replace sliding slip ring connections. This paper presents a brushless excitation approach using ceramic insulated sleeve (journal) bearings with oil lubrication to form capacitively coupled slip rings, in contrast to more traditional inductive brushless exciters and rotary transformers. This capacitive power transfer (CPT) approach exhibits advantages including low weight, low volume and has a relatively simple construction using off-the-self components. Analysis, design and prototype construction of the CPT system are presented. Experimental results demonstrate that ∼1.7nF of capacitive coupling transfers 340W to the rotor field winding of a 10kW 208V WFSG. Voltage regulation of a WFSG is demonstrated during steady state and 1 per unit load step changes yielding a NEMA-MG1 class G2 rating.


IEEE Transactions on Industry Applications | 2017

Synchronous Generator Brushless Field Excitation and Voltage Regulation via Capacitive Coupling Through Journal Bearings

Jiejian Dai; Skyler Hagen; Daniel C. Ludois; Ian P. Brown

Wound field synchronous generators (WFSG) are the standard electromechanical converter for back-up and utility scale power generation. Maintenance costs may be minimized by adopting noncontact or “brushless” technologies to replace sliding slip ring connections for rotor field excitation. This paper presents a brushless excitation approach using ceramic insulated sleeve (journal) bearings with oil lubrication to form capacitively coupled slip rings, in contrast to more traditional inductive brushless exciters and rotary transformers. This capacitive power transfer (CPT) approach exhibits advantages including low weight, low volume, and has a relatively simple construction using off-the-shelf components. Analysis, design, and prototype construction of the CPT system are presented. Experimental results demonstrate that 1.7 nF of capacitive coupling transfers 340 W to the rotor field winding of a 10 kW 208 V WFSG. Voltage regulation of a WFSG is demonstrated during steady state and 1 per unit load step changes yielding a NEMA-MG1 class G2 rating.


applied power electronics conference | 2017

Linear motion system cable elimination via multiphase capacitive power transfer through sliding journal bearings

Jiejian Dai; Skyler Hagen; Daniel C. Ludois

Electrical loads that slide on moving gantries or rails are common in industry and automation, e.g. assembly lines, spindle heads, x-y tables, etc. These systems often use insulated linear bearings to support mechanical movement during the intended process and a flexible wire-way or cable track provides an electrical connection to power moving parts. This paper proposes eliminating the cable connection by using the capacitance of the linear bearings to transfer power between stationary and moving parts, i.e. the bearings/rails form the coupling of a capacitive power transfer system. This is enabled by a 3–5 MHz, 3 phase, resonant inverter capable of driving AC current through the bearing-rail capacitance where it is ultimately rectified on a carriage for final use. The high switching frequency enables smaller bearing coupling capacitance to be used with lower developed voltages. The inverter uses 650V Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) in a 3 phase configuration to extend switching frequencies to multi-MHz, thus enabling power transfer levels towards 102-103 watt levels. The brushless and wireless excitation of a sliding electrical load, using linear plain bearings sliding on conventional 1 inch diameter anodized shafting serves as a demonstration application. Experimental tests at 3.66 MHz demonstrate 111.9W power transfer to a sliding carriage load.

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Daniel C. Ludois

University of Wisconsin-Madison

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Skyler Hagen

University of Wisconsin-Madison

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Ian P. Brown

Illinois Institute of Technology

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Ryan Knippel

University of Wisconsin-Madison

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Antonio Di Gioia

Illinois Institute of Technology

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Yue Nie

Illinois Institute of Technology

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