Zeljko Pantic

Cutting the Cord: Static and Dynamic Inductive Wireless Charging of Electric Vehicles

In this article, we have reviewed the state of the art of IPT systems and have explored the suitability of the technology to wirelessly charge battery powered vehicles. the review shows that the IPT technology has merits for stationary charging (when the vehicle is parked), opportunity charging (when the vehicle is stopped for a short period of time, for example, at a bus stop), and dynamic charging (when the vehicle is moving along a dedicated lane equipped with an IPT system). Dynamic wireless charging holds promise to partially or completely eliminate the overnight charging through a compact network of dynamic chargers installed on the roads that would keep the vehicle batteries charged at all times, consequently reducing the range anxiety and increasing the reliability of EVs. Dynamic charging can help lower the price of EVs by reducing the size of the battery pack. Indeed, if the recharging energy is readily available, the batteries do not have to support the whole driving range but only supply power when the IPT system is not available. Depending on the power capability, the use of dynamic charging may increase driving range and reduce the size of the battery pack.

ZCS

Inductive power transfer (IPT) is commonly used to transmit power from an extended loop (track) to a number of galvanically isolated movable pick-ups. To maximize the power transfer and minimize converter requirements, various compensation circuits have been proposed for both the track (primary) and the pick-up (secondary). This paper investigates the suitability of the LCC series-parallel compensation for IPT primary design. A new compensation-circuit design procedure is proposed that considers high-order current harmonics and results in inverter zero-current switching. The proposed compensation is compared with the classical compensation designed for zero phase angle between the inverter voltage and current fundamental components. Expressions for the bifurcation boundary, voltampere rating of reactive-compensation elements, and the current at the moment of switching are derived and analyzed. Analytical results are verified both via PSpice simulations and experimentally using a 1-hp MOSFET-based prototype.

LCC

We present a new topology appropriate for “dynamic” wireless charging. Possible applications include charging of electric vehicles or robots moving in a large, predesignated area. We propose a system with a transmitter made from multiple coils commensurable with the moving receiver(s), and powered by a single inverter. The proposed system uses the reactance reflected by the receiver to automatically increase the field strength in coupled portions of the transmitter-receiver system, thus allowing efficient power transfer and adherence to electromagnetic field emission standards without complex shielding circuits, switches, electronics, and communication. The power transfer is at its peak when the transmitting and receiving coils approach their maximum coupling (as defined by the geometrical constraints of the system), resulting in improved system-level efficiency. The presented analysis is supported with simulations and experiments.

-Compensated Resonant Inverter for Inductive-Power-Transfer Application

Wireless power transfer (WPT) based on magnetic coupling is becoming widely accepted as a means of transferring power over small to medium distances. An unresolved issue is the source and receiver resonance matching in multireceiver systems where the source operating frequency adjustment is not possible. This paper presents a framework to analyze the effect of parallel-compensated receiver detuning on the power transfer in WPT systems. Building on this analytical study, we present a new receiver design for WPT systems. The proposed design combines a parallel compensated resonant tank with a tristate boost converter. By synchronizing the tristate boost switching period with the half-period of the resonant tank voltage, we position the inherently discontinuous current pulse drawn by the tristate boost to control both active and reactive power flows from the resonant circuit. Controllable reactive current can be used effectively to emulate appropriate inductance or capacitance to tune the resonant tank and achieve optimal power transfer.

Reflexive Field Containment in Dynamic Inductive Power Transfer Systems

Economic and environmental issues are main motivation for developing efficient and sustainable electrical vehicle for urban transportation. Electrical vehicles (EV) have two main advantages compared to hybrid and gasoline vehicle: eliminated tailpipe emissions and simplified drive-train. However, electric vehicles have a limited range between recharges when fitted with the current state-of-the-art energy storage. To mitigate the limitations of the energy storage technology, we propose to use inductively coupled power transfer (ICPT) to supply power to the vehicle while it is moving. ICPT is an efficient technique for transferring power with no physical connection between the source and the load. In this paper we investigate the ICPT requirements for two types of vehicles operating in combination with ICPT system. The first vehicle makes use of a battery as primary and ICPT as secondary energy source for electric vehicle supplying. The goal is to achieve 300 miles range of covering. The second uses electrochemical capacitors (Ultracapacitors) as the power source and ICPT as the energy source. The goal is to provide unlimited range for the vehicle. The result is system analysis of feasibility of battery-ICPT and ultracapacitor-ICPT combinations for different driving conditions and vehicles as well as rough evaluation of expected length and optimal positions of ICPT track for specified driving cycles.

Framework and Topology for Active Tuning of Parallel Compensated Receivers in Power Transfer Systems

This paper presents a generalized analysis of an inductive power transfer system where multiple frequencies are used to transfer power through the magnetic link. Specifically, we consider a system that amplifies both the fundamental and the third harmonic generated by a full-bridge inverter in order to transfer power to a receiver at both frequencies. The system is analyzed in a generalized manner, by looking at the transconductance function at the transmitter and the receiver for each of the harmonics. Using this approach, the emitted field strength, inverter losses, combined transmitter and receiver coil conduction losses, and VA ratings are compared to a reference single-frequency system. The analysis shows that the dual-frequency system can outperform the single-frequency equivalent for all metrics considered; however, in practice, a tradeoff between the performance criteria is necessary, since the optimal operation points for each criterion cannot be attained with a single design.

Inductively coupled power transfer for continuously powered electric vehicles

In this paper, design of a primary resonant tank for resonant converters compensation in an Inductive Power Transfer (IPT) system is analyzed and some criteria for selecting its reactive components are established. The optimization goal is to maximize the transferred power, while limiting the number of compensation components to no more than two reactive components. Additionally, VA limits of the inverter are taken into consideration. Current track requirements are relaxed and instead of constant track current, small track load dependency is allowed, which is acceptable in practice. The theoretical investigations and calculations, as well as simulations for two important practical cases considered are presented in the paper. It is shown that LC compensation structure allows maximum delivered power, but not for the case when the impedances of compensation elements are the same as it would be expected. Additionally, the impact of converter ratings and allowed load dependent track current variation on the optimal design are investigated through the set of numerical simulations.

Multifrequency Inductive Power Transfer

This paper studies three fundamental switching patterns for resonant converters to achieve Zero Voltage Switching (ZVS) operation. To evaluate the performance of the three control methods, three resonant topologies are taken into consideration: series resonant, parallel resonant and seriesparallel resonant. The criteria functions for ZVS operation are derived for each control method and topology. The results show that the Asymmetrical Clamped Mode control (ACM) can guarantee lower switching frequency than other two control methods while keeping ZVS operation. Moreover, the circulating power for each control method is analyzed. The relationships between the switching frequency and the maximum power transfer of the three resonant topologies are derived and the series-parallel resonant topology shows a superior characteristic. Experiment results are given to verify some of the results.

Optimal resonant tank design considerations for primary track compensation in Inductive Power Transfer systems

Traditional in-motion (dynamic) wireless power transfer (WPT) is based on elongated power transmitting tracks. It suffers from low efficiency, having complex and not fully utilized magnetic structures, among other drawbacks. In the case of lumped transmitter coils commeasurable in size with the receiver coil, which has been recently proposed for the in-motion WPT, the power transfer is intermittent with variable power transfer efficiency. Although it is characterized by a very high efficiency when the pads are aligned (>90%), high efficiency of the overall energy transfer will be maintained only if the transmitter coil is energized in a proper, synchronized manner with respect to the position of the receiver coil. Considering the actual state of communication and sensing technology, identification of the actual position of the receiver pad in realtime would be a very challenging task and no reliable solution has been proposed so far in the WPT arena. This paper provides a thorough analysis of the power transfer characteristics of an in-motion system with lumped coils, meaning the analytic description of time-varying power transfer and efficiency profiles. Possible compensation topologies are studied and the most suitable structure is selected. A control algorithm is proposed to control the amount of energy transferred to the receiver, without the utilization of any position detection system. The energizing profiles are designed to maximize energy efficiency, while at the same time transferring the required amount of energy to the receiver. The control algorithm is analyzed by using analytical modeling of the WPT system and then verified by MATLAB-Simulink simulation tool. A scaled-down hardware prototype is developed and employed to test the operation of the control algorithm for different transferred energies.

A comparison study of control strategies for ZVS resonant converters

In this paper we explore the concept of transmitting and receiving power wirelessly at multiple frequencies. This proposed frequency multiplex is achieved by using multi-resonant tanks at the transmitter and receiver to amplify and extract power at multiple frequencies. Frequency multiplexed IPT system is a new concept that has numerous advantages over the state of the art: (1) low switching frequency converters can be used to drive high-frequency IPT systems, (2) emission standards may become easier to meet by spreading the power transfer over a spectrum of frequencies, (3) single-frequency receivers tuned to different frequencies can be charged simultaneously even though their coils are at close proximity and mutually coupled, etc. In this paper we develop the theory of source and receiver resonant tank design, and present the complete methodology for determining the system quality factor, effective resistance and power transfer at each frequency. We present a case study of a system that transfers equal amounts of power at 25 kHz and 75 kHz through simulations and experiments.