@article{pratik_pantic_2024, title={Comprehensive Modeling of a Back-to-Back Diodes-Based Linear Variable Capacitor}, volume={39}, ISSN={["1941-0107"]}, url={https://doi.org/10.1109/TPEL.2023.3335344}, DOI={10.1109/TPEL.2023.3335344}, abstractNote={The parasitic nonlinear capacitance of diodes is well-known in power electronics literature. This manuscript analytically describes how the nonlinear parasitic capacitance of two back-to-back reverse-biased diodes can act as a linear variable capacitor (LVC) when driven from an ac current or voltage source. An LVC is a bipolar symmetric structure whose conduction principle is based on the displacement current flowing through the junction capacitance of diodes, and no biasing circuit is needed. The manuscript analytically describes the LVC capacitance dependence on the circuit (current, voltage, and frequency) and diode parameters. An in-depth current- and voltage-based LVC capacitance modeling is presented, including the harmonic analysis, safe operation boundary, and the impact of parasitics. SPICE simulations were used to verify the proposed modeling methodology, followed by experiments on three LVCs made of Schottky diodes. The nonlinear capacitance of the diodes is first characterized for differential capacitance, and then, derived parameters are used to verify the proposed LVC capacitance model with current sources at 1 and 2 MHz. The proposed framework can be used to design resonant power circuits with the LVC as a passive component. An integrated LVC can be applied in high-frequency power circuits for load impedance transformation and power control.}, number={2}, journal={IEEE TRANSACTIONS ON POWER ELECTRONICS}, author={Pratik, Ujjwal and Pantic, Zeljko}, year={2024}, month={Feb}, pages={2489–2504} }
 @inproceedings{abdelraziq_pratik_akhmetov_paul_chenevert_pantic_2023, title={A Practical Implementation of a Two-Stage 350-W Universal Charger for Power Mobility Device Charging Applications}, url={http://dx.doi.org/10.1109/ecce53617.2023.10362824}, DOI={10.1109/ecce53617.2023.10362824}, abstractNote={A universal, two-stage (PFC+LLC) charger is developed for Power Mobility Device (PMD) charging applications (i.e., electric wheelchairs and scooters). A rectifier-boost PFC topology is used to interface with the AC grid, establishing a ≈386-VDC bus and maintaining around 96% efficiency for all loading conditions. A dual-loop controller for the LLC resonant converter with a wide operation region is designed to achieve CC-CV for different capacities of 24-V batteries. The LLC converter achieves a peak efficiency of 95.5%, making the two-stage charger 91.6% efficient. This paper presents a comprehensive design, implementation, and testing validation for major aspects of the charger. The charger is rigorously tested, passing all power factor (PF), total harmonic distortion (THD), and conducted EMI safety requirements set by IEC 61000-3-2 and CISPR 22 regulatory standards. The paper not only offers theoretical insights but also presents a comprehensive guide to the practical design and testing procedures of every facet of the charger.}, booktitle={2023 IEEE Energy Conversion Congress and Exposition (ECCE)}, author={Abdelraziq, Muhammad and Pratik, Ujjwal and Akhmetov, Zhansen and Paul, Stephen and Chenevert, Gabriel and Pantic, Zeljko}, year={2023}, month={Oct} }
 @article{akhmetov_pratik_pantic_2023, title={Accuracy Analysis of the LCR Meter-Based Method for C-V Characterization of a Capacitor}, ISSN={["1048-2334"]}, DOI={10.1109/APEC43580.2023.10131396}, abstractNote={The capacitance-voltage (C-V) characterization of capacitors and power semiconductor devices (MOSFETs and diodes) is crucial for circuit analysis and loss modeling. This paper discusses an LCR meter-based capacitive coupling method for C-V characterization. It requires an LCR meter and a few inexpensive passive components. However, the unaccounted effects of the parameters, such as blocking capacitance, filtering inductance, parasitic inductance, or power supply impedance can significantly affect the accuracy of the measuring circuit. In this paper, these effects are analyzed, and the expected error is described analytically. Thus, the measuring circuit can be designed using the derived formulas to achieve the targeted accuracy and frequency range. The measuring circuit with the measuring range of 10 kHz-1 MHz with less than 1% error was designed using the derived analytical equations and validated experimentally.}, journal={2023 IEEE APPLIED POWER ELECTRONICS CONFERENCE AND EXPOSITION, APEC}, author={Akhmetov, Zhansen and Pratik, Ujjwal and Pantic, Zeljko}, year={2023}, pages={2481–2488} }
 @article{azad_pratik_tavakoli_pantic_2023, title={Design of Grid-side Power Management for Bidirectional DWPT Chargers on EV Roadways}, ISSN={["2473-7631"]}, DOI={10.1109/ITEC55900.2023.10186936}, abstractNote={Dynamic Wireless Power Transfer (DWPT) entails an inherently transient power profiles from the electric grid. These power profiles, ranging from tens to hundreds of kilowatts, could expose the grid to significant stress, potentially affecting grid stability. This operating scenario occurs irrespective of the grid-to-vehicle (G2V) or vehicle-to-grid (V2G) charging infrastructure on EV roadways. In this paper, bidirectional DWPT system is designed which manages the grid-side transients, significantly reducing the grid peak-power transients for both G2V and V2G charging scenarios. Supercapacitor units are employed on the grid side as power-buffering units. This design does not require additional grid-side converters, and facilitates downsizing grid side power electronics and cable ratings.}, journal={2023 IEEE TRANSPORTATION ELECTRIFICATION CONFERENCE & EXPO, ITEC}, author={Azad, Ahmed and Pratik, Ujjwal and Tavakoli, Reza and Pantic, Zeljko}, year={2023} }
 @article{pratik_pantic_2023, title={Design of a Capacitive Wireless Power Transfer System With a Vertical Four-Plate Coupler for Minimum Stray Electric Field}, url={https://doi.org/10.1109/JESTPE.2023.3303852}, DOI={10.1109/JESTPE.2023.3303852}, abstractNote={Capacitive wireless power transfer (CPT) is the emerging technology of contactless power delivery outperforming the inductive method in some applications, such as small gap designs, when a metal object is present between the plates or when an inexpensive and lightweight solution is imperative. However, stray electric field confinement is one of the primary challenges regarding CPT practical implementation. Unlike in inductive wireless systems, where various passive and active forms of field cancellation or shaping exist, this is still an active research question in a CPT system, particularly for the more recent vertical four-plate coupler (V4PC). This research studies how the prohibited zone of the excessive field around a practical V4PC coupler can be minimized using an optimum design of compensation networks at the transmitter and receiver. After the stray field evaluation metrics are defined, the optimum design of LC and LCL compensation networks is derived and tested through simulations. Experiments on an 85-W CPT system with V4PC and LC – LC compensation were conducted, confirming the existence of the optimum design and reducing the prohibitive zone of the excessive field around the LC-compensated coupler by 25%.}, journal={IEEE Journal of Emerging and Selected Topics in Power Electronics}, author={Pratik, Ujjwal and Pantic, Zeljko}, year={2023}, month={Oct} }
 @inproceedings{paul_abdelraziq_pratik_pantic_2023, title={Development of an Autonomous Wireless Charging System for Unmanned Aerial Vehicles}, url={http://dx.doi.org/10.1109/ecce53617.2023.10362525}, DOI={10.1109/ecce53617.2023.10362525}, abstractNote={Autonomous Unmanned Aerial Vehicles (UAVs) are capable of revolutionizing the delivery industry but suffer from insufficient flight range due to battery limitations and charging requirements. Wireless power transfer offers a solution by creating autonomous recharging stations that can extend the range of UAVs. This paper presents a 700 W fully autonomous wireless charging system with a motorized coil alignment mechanism. Surveying the literature, the level of integration of the system presented is rare; hence, the paper provides a comprehensive design methodology. The system achieves greater than 86% DC-to-DC efficiency for the full constant-current constant-voltage charging profile of two paralleled 7000 mAh UAV LiPo batteries. The alignment mechanism ensures lateral displacement of less than 1 cm, within a search area of 40 cm by 40 cm on the landing platform, allowing maximum power transfer.}, booktitle={2023 IEEE Energy Conversion Congress and Exposition (ECCE)}, author={Paul, Stephen and Abdelraziq, Muhammad and Pratik, Ujjwal and Pantic, Zeljko}, year={2023}, month={Oct} }
 @article{azad_tavakoli_pratik_pantic_2023, title={Rapid Prototyping of G2V/V2G DWPT Charge-Control and Grid-side Power Management for EV Applications}, ISSN={["2473-7631"]}, DOI={10.1109/ITEC55900.2023.10186929}, abstractNote={Development and testing of the impact of different wireless charging systems on Electric Vehicle(EV) infrastructures involves considerable effort as it requires different types of coil structures embedded in roadways, different types of EVs, and also requires a test-track setup. Moreover, it requires high speed real-time data measurement and communication to/from an in-motion EV which makes it involving coordinating and testing new control algorithms for such applications. To address this issue, a bidirectional wireless charging system model is proposed in a hardware-in-loop environment, which enables rapid control prototyping of such systems from a benchtop setup. The proposed system can emulate Grid-to-Vehicle(G2V) and Vehicle-to-Grid(V2G) charging profiles for stationary and dynamic charging scenarios. As an additional feature, a versatile grid-side power management algorithm is also developed which significantly reduces grid-side power transients resulted from different types of wireless charging profiles.}, journal={2023 IEEE TRANSPORTATION ELECTRIFICATION CONFERENCE & EXPO, ITEC}, author={Azad, Ahmed and Tavakoli, Reza and Pratik, Ujjwal and Pantic, Zeljko}, year={2023} }
 @article{pratik_pantic_2022, title={Design of Variable Air-Core Coupled Co-axial Solenoidal Inductors}, ISSN={["2329-3721"]}, DOI={10.1109/ECCE50734.2022.9948050}, abstractNote={Variable inductors find their application in many power electronics circuits. This paper discusses the design and prototype of an air-core coupled co-axial solenoidal inductor as a variable inductor. Analytical modeling and FEA simulations are used to design and optimize a coupled solenoidal variable inductor with a maximum inductance of 18.4 µH at 2 MHz. It is observed that the quality factor of a coupled variable inductor is a function of coupling between the inner and outer windings. It is shown that the quality factor of the variable inductor can be increased by 20% by following the proposed optimization. An experimental inductor prototype is built using 3-D printed support and Litz wire. It is observed that the experimental results closely match the simulation ones.}, journal={2022 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE)}, author={Pratik, Ujjwal and Pantic, Zeljko}, year={2022} }
 @article{ahluwalia_chenevert_pratik_pantic_2022, title={System for Wireless Charging of Battery-Powered Underwater Sensor Networks}, ISBN={["978-1-6654-6809-1"]}, ISSN={["0197-7385"]}, DOI={10.1109/OCEANS47191.2022.9977272}, abstractNote={Battery-powered Underwater Sensor Networks (USNs) can have limited durability owing to their battery life. This paper proposes an energy delivery system for wireless recharging of USNs using a Remotely Operated Vehicle (ROV), which allows us to extend their lifespans and reduce waste. The wireless charging system’s efficiency is maximized using 3-D Finite Element Analysis (FEA) and an analytical loss model to design and optimize the magnetic coupler. We evaluate the proposed method using a prototype and provide experimental results for coils submerged in water at different salinity levels. These results are also compared with coils placed in the air. A detailed analysis of system operation with changes in the surrounding medium is presented. When operated at an output power of 50 W and an output voltage of 15.6 V, the developed prototype works at a best-case efficiency of 90% with coils submerged in a seawater medium.}, journal={2022 OCEANS HAMPTON ROADS}, author={Ahluwalia, Urvi and Chenevert, Gabriel and Pratik, Ujjwal and Pantic, Zeljko}, year={2022} }
 @article{pratik_abdelraziq_ahluwalia_akhmetov_chenevert_pantic_2021, title={Design of a Dual-Loop Controller with Two Voltage- Dependent Current Compensators for an LLC-Based Charger}, ISSN={["1093-5142"]}, DOI={10.1109/COMPEL52922.2021.9645959}, abstractNote={A two-stage charger (PFC+LLC) is developed for Power Mobility Device (PMD) charging applications (i.e., power wheelchairs). The LLC topology is selected due to its ability to maintain ZVS operation over a wide range of load variations. This paper discusses the challenges of designing a dual-loop controller for an LLC-based charger with a wide operation region. It proposes modifying the inner current loop to maintain stable operation over a wide input and output range—the proposed internal loop control switches intelligently between two current controllers based on the output voltage level. A 300-W prototype is designed and tested with a resistive load. Moreover, simulation and experimental results are compared to validate the robustness and stability of the proposed controller.}, journal={2021 IEEE 22ND WORKSHOP ON CONTROL AND MODELLING OF POWER ELECTRONICS (COMPEL)}, author={Pratik, Ujjwal and Abdelraziq, Muhammad and Ahluwalia, Urvi and Akhmetov, Zhansen and Chenevert, Gabriel and Pantic, Zeljko}, year={2021} }
 @article{wang_pratik_jovicic_hasan_pantic_2021, title={Dynamic Wireless Charging of Medium Power and Speed Electric Vehicles}, volume={70}, ISSN={["1939-9359"]}, url={https://doi.org/10.1109/TVT.2021.3122366}, DOI={10.1109/TVT.2021.3122366}, abstractNote={For a broad range of industrial, service, and household electric vehicles, dynamic charging is a viable option for energy replenishing that could reduce the size of the onboard energy storage, remove range limitations, and increase operating time. For these systems, timely detection of an approaching vehicle and the detection of strong coupling conditions between transmitter and receiver coils are of prime interest. A novel method is proposed in this article, which utilizes the existing embedded transmitter coil and power electronics modules to establish a precise detection system based on the power footprint of a traveling receiver. Next, a control algorithm is proposed to control charger activation and deactivation time accurately and deliver the required energy during the maximum coupling of the coils. The proposed sigmoid-curve-based control algorithm achieves a robust, speed-independent, smooth transition between two states while providing fast dynamics for aligned and misaligned conditions. Finally, a novel approach to test high-speed dynamic charging in laboratory conditions based on the receiver emulator is developed and used for experimental validation. The vehicle detection and control techniques have been validated through simulations and experimentally on a speed-controlled dynamic charging test station for a wide speed range. The proposed method does not require any additional hardware, sensing devices, or high-speed communication between the vehicle and the charging infrastructure.}, number={12}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wang, Hongjie and Pratik, Ujjwal and Jovicic, Aleksandar and Hasan, Nazmul and Pantic, Zeljko}, year={2021}, month={Dec}, pages={12552–12566} }
 @article{teeneti_pratik_philips_azad_greig_zane_bodine_coopmans_pantic_2021, title={System-Level Approach to Designing a Smart Wireless Charging System for Power Wheelchairs}, volume={57}, ISSN={["1939-9367"]}, url={https://doi.org/10.1109/TIA.2021.3093843}, DOI={10.1109/TIA.2021.3093843}, abstractNote={New technology design and its integration into a social environment in a noninvasive way are recognized as one of the main challenges of the rapidly growing technology world. The design complexity is amplified if the system is intended for a sensitive user category, e.g., persons with disabilities and aging adults. A high percentage of power wheelchairs (PWCs) users rely on caregivers or family members to charge their PWC units. In this article, a design methodology is presented that describes a system-level approach for designing a 1-kW smart wireless charger for PWCs. This article describes how power electronics, communication, automation, software, and internet technologies are integrated to deliver a functional hands-free, free-position PWC charging solution. The proposed solution utilizes a multicoil transmitter pad to achieve a free-positioning feature and dual-side control to regulate the power. The researchers adopted a human-in-the-loop approach to seek feedback from end-users and tailor the final design through multiple generations of prototypes. Moreover, some existing technical solutions regarding pad design and stray field shielding are adapted or advanced to meet the application requirements, and their effectiveness is validated on a 1-kW prototype.}, number={5}, journal={IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Teeneti, Chakridhar and Pratik, Ujjwal and Philips, Gavin and Azad, Ahmed and Greig, Mark and Zane, Regan and Bodine, Cathy and Coopmans, Calvin and Pantic, Zeljko}, year={2021}, month={Sep}, pages={5128–5144} }
 @article{azad_tavakoli_pratik_varghese_coopmans_pantic_2020, title={A Smart Autonomous WPT System for Electric Wheelchair Applications With Free-Positioning Charging Feature}, url={https://doi.org/10.1109/JESTPE.2018.2884887}, DOI={10.1109/JESTPE.2018.2884887}, abstractNote={Electric wheelchairs (EWs) are gradually replacing conventional wheelchairs as an assistive tool for people with disabilities who are unable to use the physical force to drive manual wheelchairs on their own. EW charging requires manipulating, plugging in, and unplugging an off-board charger, which can be challenging or impossible for people with severe disabilities. In this paper, a comprehensive solution to the problem of EW recharging is provided in the form of a smart, autonomous charging system, based on the wireless power transfer (WPT) technology. In this paper, a sufficiently large area of 0.75 m2 for a floor-charging pad involving multiple primary coils has been implemented while offering a free-positioning charging feature. A novel design methodology for primary and secondary charging pads’ optimization has been developed, taking into account various complex real-life constraints. In addition, a novel 250-W WPT controller design has been employed to maximize misalignment tolerance up to 7 cm while maintaining high system efficiency. In this paper, a novel, comprehensive, system-level organization of a master controller design has been presented which manages continuous coordination between the WPT controllers and the autonomous docking controller, records important system data, maintains safe operation of overall system, and prevents hazardous exposure to potentially harmful magnetic field beyond $15~\mu \text{T}$ . In addition, a novel design methodology for primary and secondary charging pads’ optimization has been developed, which takes into account various real-life constraints, and provides a fair comparison between different designs in a multivariable environment. The proposed design is tested in laboratory conditions and later validated in a practical environment.}, journal={IEEE Journal of Emerging and Selected Topics in Power Electronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Azad, Ahmed and Tavakoli, Reza and Pratik, Ujjwal and Varghese, Benny and Coopmans, Calvin and Pantic, Zeljko}, year={2020}, month={Dec}, pages={1–1} }
 @phdthesis{pratik_2019, title={Design of Capacitive Wireless Power Transfer Systems with Enhanced Power Density and Stray Field Shielding}, url={https://digitalcommons.usu.edu/etd/7598}, author={Pratik, Ujjwal}, year={2019}, month={Aug} }
 @article{pratik_varghese_azad_pantic_2019, title={Optimum Design of Decoupled Concentric Coils for Operation in Double-Receiver Wireless Power Transfer Systems}, volume={7}, url={http://dx.doi.org/10.1109/jestpe.2018.2871150}, DOI={10.1109/jestpe.2018.2871150}, abstractNote={Wireless power transfer is becoming ubiquitous in consumer electronics and electrified transportation, providing a convenient method to supply power or charge various devices, such as cell phones, watches, laptops, electric vehicles, and so on. Delivering power from one transmitter unit to more than one receiver can save space and reduce the cost of the overall system. For applications where the sizes of transmitter and receiver units are commeasurable, a frequently used design is the one with carefully overlapped D-shaped coils (also named bipolar pad) to achieve decoupling between coils. In this paper, an alternative optimized design of two concentric decoupled coils is proposed. The design allows the receiver coils to operate at close proximity, collecting power from a shared magnetic field generated by a single transmitter pad. The design methodology is based on a bucking coil layout where the coils’ decoupling is achieved by means of flux cancellation caused by alternating the winding direction of turns in one of the coils. Apart from eliminating coupling between the two receivers, the proposed design maximizes the coupling between the transmitter and the second receiver coil and consequently increases the power transfer capability, offering the equivalent coupling coefficient similar to or better than a pair of bipolar DD coils. Finally, the number and space between turns are selected to improve the quality factor of the proposed receiver. The proposed solution is designable analytically and the second receiver can be added even after the first receiver is already built. Moreover, the proposed design demonstrates superior misalignment tolerance, particularly in the lateral direction, compared to other decoupled coil designs. The proposed methodology is validated through simulations and experimental tests and has proved to be accurate and easy for implementation.}, number={3}, journal={IEEE Journal of Emerging and Selected Topics in Power Electronics}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Pratik, Ujjwal and Varghese, Benny J. and Azad, Ahmed and Pantic, Zeljko}, year={2019}, month={Sep}, pages={1982–1998} }
 @inproceedings{tavakoli_echols_pratik_pantic_pozo_malakooti_maguire_2017, title={Magnetizable concrete composite materials for road-embedded wireless power transfer pads}, booktitle={Energy Conversion Congress and Exposition (ECCE), 2017 IEEE}, author={Tavakoli, Reza and Echols, A and Pratik, U and Pantic, Zeljko and Pozo, Fray and Malakooti, Amir and Maguire, Marc}, year={2017}, pages={4041–4048} }