Abstract Inductive Power Transfer (IPT) technology is a promising solution for wireless charging ... more Abstract Inductive Power Transfer (IPT) technology is a promising solution for wireless charging of Electric Vehicles (EVs). Given the expected uptake of IPT technology for both stationary and in motion in-road charging, many technical challenges regarding the electromagnetic field and thermal aspects need to be overcome to generate cost-effective and reliable solutions. One particular design constraint of in-road IPT systems is the occurrence of local increases in temperature during operation due to power losses in the wireless charging pads. In this paper, safe operating conditions of an enclosed wireless power transfer pad within a pavement model were identified. This aspect has been studied less rigorously compared with the electromagnetic design. This paper presents a numerical thermal analysis of a double-D (DD) prototype IPT primary pad based on two possible configurations; flush-mounted or buried, within a model pavement. A coupled electromagnetic-thermal simulation has been developed to aid in the development of thermally robust in-road IPT systems. In order to validate the proposed two-way coupled electromagnetic-thermal Finite Element (FE) simulations, experiments were performed to capture the evolving thermal field within an IPT primary pad under continuous and periodic duty cycles. This method made possible analysis of the heating patterns and so the identification of internal hotspots within an IPT pad in a roading structure. A thermal camera was used to provide detailed surface temperature distributions, while suitable application of non-metallic Fiber Bragg Grating (FBG) sensing technology enabled a robust technique to measure temperatures within the intense magnetic fields of a high frequency wireless power transfer system to be developed. Comparisons at steady state of the pavement surface temperature distribution, as well as point measurements with the pad and sand, demonstrate good accuracy. The maximum steady state surface temperature occurs at the centre of the sand surface where the IPT pad is placed and is approximately 87 oC and 100 oC for buried and flush-mounted pads, respectively. Moreover, for a 2/3 duty cycle loading, the maximum temperature of the pad tended to an average of approximately 76°C, while at constant operation the average temperature is 105°C. Therefore, a 5minute cooling period significantly reduced operating temperatures within the studied model IPT system. In the future, the methodologies proposed in this paper can also be used to improve the design of higher power IPT pads by identifying hotspots and maximum thermal stresses and determination of optimal charging patterns for heat dissipation.
IEEE Transactions on Power Electronics, May 1, 2017
Inductive power transfer (IPT) systems for electric vehicle (EV) charging often have to operate u... more Inductive power transfer (IPT) systems for electric vehicle (EV) charging often have to operate under a wide range of coupling factors and loads, potentially mistuning the primary power supply. This is especially a problem in dynamic applications where the vehicles are moving. This paper investigates the design of a self-tuning power supply by utilizing a switchable bank of capacitors with a push–pull tuning topology. The proposed power supply is able to handle operation under a wide range of coupling factors and loading conditions while achieving ZVS operation at a fixed frequency. A mathematical model is developed to model the system and an experimental system is built to test the design. The experimental system is able to deliver a constant 1 kW over a coupling factor range of 0.1–0.33. A detection circuit to monitor the state of tuning of the power supply is presented along with a control scheme to maintain optimal tuning.
... Report to MACI, Auckland Uniservices , December 1996. 0. H. Stielau, G. A. Covic, Design of ... more ... Report to MACI, Auckland Uniservices , December 1996. 0. H. Stielau, G. A. Covic, Design of loosely coupled inductive power transfer systems,'' IEEE-PESflEE/CSEE International Conference on Power System Technology, POWERCON 2000,4-7 December 2000. ...
IEEE journal of emerging and selected topics in industrial electronics, Jul 1, 2020
Many inductive power transfer dynamic systems have been proposed over the last decade; however, f... more Many inductive power transfer dynamic systems have been proposed over the last decade; however, few consider interoperability to various secondaries in the design. This article proposes a limited-length two-phase meandering track primary to investigate the feasibility and tradeoffs between this multicoil track topology and a typical lumped pad primary topology for dynamic applications. The purpose of the proposed track system is to deliver continuous power with a smooth coupling profile which naturally lowers the rating requirements of the secondary electronic components, and to be interoperable with many secondary topologies. The proposed track is compared with a previously published lumped system using double-D primary pads distributed one per meter by a normalized coupling metric. The results show that this meandering track primary has a smaller impact on system electronic components and has better interoperability while it requires lower primary compensation rating compared to the lumped pad primary for the same power level. A prototype of the track was built and the simulation results were verified. A 10 kW power experiment was achieved a dc–dc efficiency of around 83%, and the potential of this multicoil topology for interoperable and low-cost high-power dynamic charging was demonstrated.
This paper introduces a new ferrite-less magnetic structure for roadway charging of Electric Vehi... more This paper introduces a new ferrite-less magnetic structure for roadway charging of Electric Vehicles (EVs). Most of the existing magnetic pads for roadside EV charging rely on ferrimagnetic materials to produce single-sided flux and boost power levels while minimizing undesired field emissions and losses. But the properties that roadway pads must have are mechanical robustness coupled with the ability to throw single-sided, high arching flux while being subjected to stringent conditions under asphalt, bitumen, or concrete. Ferrite is very brittle and expensive and its performance under transient forces when buried under a roadway is questionable. This new ferrite-less magnetic coupler is proposed as a primary pad for roadway EV charging. Simulated and experimental results are shown, followed by a discussion on its capabilities, limitations, and possible updates.
2020 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
Misalignment of pads and the charging and discharging of the electric vehicle (EV) battery makes ... more Misalignment of pads and the charging and discharging of the electric vehicle (EV) battery makes delivering constant power with an inductive power transfer (IPT) system non-trivial. One solution is to add Tunable Matching Networks (TMNs), which are essentially variable reactances, in between the converters and compensation networks. However, TMNs are costly to implement. As an alternative, this paper proposes a method of tuning and controlling the system known as Active Impedance Control (AIC) that emulates the behaviour of a TMN. Mathematical modelling was used to design an AIC system that can transfer 7.7 kW of power with near unity power factor under a 2.35-fold change in induced voltage for a constant battery voltage. Additionally, rectifier input current varies by only 1.4 times across the operating range. Furthermore, simulation results show good agreement with the mathematical model.
2020 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
Inductive power transfer (IPT) is a promising method for electric vehicle (EV) charging that is s... more Inductive power transfer (IPT) is a promising method for electric vehicle (EV) charging that is safe and practical. The critical aspects of IPT systems to achieve roadway charging are robustness, reliability, low cost and high power transfer. This paper presents two variations of a primary IPT double-D (DD) coupler that reduce ferrite volume, stray-fields and cost while having increased power rating at the expense of magnetic coupling and higher primary pad currents. A two-step ferrite shaping method is used for optimisation while keeping the primary coil and secondary pad unchanged. The ferrite volume is limited to the high flux density locations in a first step to reduce ferrite volume by 70%. Following this, an additional 14% ferrite volume is added to shape and reduce the stray fields by 23%.
IEEE Journal of Emerging and Selected Topics in Industrial Electronics
Inductive power transfer is a technology that enables power to be transferred from a primary (gro... more Inductive power transfer is a technology that enables power to be transferred from a primary (ground assembly) to a secondary (vehicle assembly) without a physical connection. Recommended practice proposed by the SAE J2954 working group has put flux limitations for human exposure in stationary electric vehicle charging applications. The latest version has constrained the leakage flux to 27 μT RMS for EMF limitations. In this article, a new multicoil ground assembly (MCGA) is proposed to reduce the leakage flux. The MCGA can decrease the flux levels by over 25%. All the vehicle assemblies studied can meet the EMF requirements. The ground assembly is the main contributor to leakage flux, except when the DDP WPT3/Z3 secondary vehicle assembly becomes the main contributor. The proposed MCGA is also able to provide similar dc–dc efficiencies compared to the existing Universal Ground Assembly of $>$89% at the most misaligned point.
Abstract Inductive Power Transfer (IPT) technology is a promising solution for wireless charging ... more Abstract Inductive Power Transfer (IPT) technology is a promising solution for wireless charging of Electric Vehicles (EVs). Given the expected uptake of IPT technology for both stationary and in motion in-road charging, many technical challenges regarding the electromagnetic field and thermal aspects need to be overcome to generate cost-effective and reliable solutions. One particular design constraint of in-road IPT systems is the occurrence of local increases in temperature during operation due to power losses in the wireless charging pads. In this paper, safe operating conditions of an enclosed wireless power transfer pad within a pavement model were identified. This aspect has been studied less rigorously compared with the electromagnetic design. This paper presents a numerical thermal analysis of a double-D (DD) prototype IPT primary pad based on two possible configurations; flush-mounted or buried, within a model pavement. A coupled electromagnetic-thermal simulation has been developed to aid in the development of thermally robust in-road IPT systems. In order to validate the proposed two-way coupled electromagnetic-thermal Finite Element (FE) simulations, experiments were performed to capture the evolving thermal field within an IPT primary pad under continuous and periodic duty cycles. This method made possible analysis of the heating patterns and so the identification of internal hotspots within an IPT pad in a roading structure. A thermal camera was used to provide detailed surface temperature distributions, while suitable application of non-metallic Fiber Bragg Grating (FBG) sensing technology enabled a robust technique to measure temperatures within the intense magnetic fields of a high frequency wireless power transfer system to be developed. Comparisons at steady state of the pavement surface temperature distribution, as well as point measurements with the pad and sand, demonstrate good accuracy. The maximum steady state surface temperature occurs at the centre of the sand surface where the IPT pad is placed and is approximately 87 oC and 100 oC for buried and flush-mounted pads, respectively. Moreover, for a 2/3 duty cycle loading, the maximum temperature of the pad tended to an average of approximately 76°C, while at constant operation the average temperature is 105°C. Therefore, a 5minute cooling period significantly reduced operating temperatures within the studied model IPT system. In the future, the methodologies proposed in this paper can also be used to improve the design of higher power IPT pads by identifying hotspots and maximum thermal stresses and determination of optimal charging patterns for heat dissipation.
IEEE Transactions on Power Electronics, May 1, 2017
Inductive power transfer (IPT) systems for electric vehicle (EV) charging often have to operate u... more Inductive power transfer (IPT) systems for electric vehicle (EV) charging often have to operate under a wide range of coupling factors and loads, potentially mistuning the primary power supply. This is especially a problem in dynamic applications where the vehicles are moving. This paper investigates the design of a self-tuning power supply by utilizing a switchable bank of capacitors with a push–pull tuning topology. The proposed power supply is able to handle operation under a wide range of coupling factors and loading conditions while achieving ZVS operation at a fixed frequency. A mathematical model is developed to model the system and an experimental system is built to test the design. The experimental system is able to deliver a constant 1 kW over a coupling factor range of 0.1–0.33. A detection circuit to monitor the state of tuning of the power supply is presented along with a control scheme to maintain optimal tuning.
... Report to MACI, Auckland Uniservices , December 1996. 0. H. Stielau, G. A. Covic, Design of ... more ... Report to MACI, Auckland Uniservices , December 1996. 0. H. Stielau, G. A. Covic, Design of loosely coupled inductive power transfer systems,'' IEEE-PESflEE/CSEE International Conference on Power System Technology, POWERCON 2000,4-7 December 2000. ...
IEEE journal of emerging and selected topics in industrial electronics, Jul 1, 2020
Many inductive power transfer dynamic systems have been proposed over the last decade; however, f... more Many inductive power transfer dynamic systems have been proposed over the last decade; however, few consider interoperability to various secondaries in the design. This article proposes a limited-length two-phase meandering track primary to investigate the feasibility and tradeoffs between this multicoil track topology and a typical lumped pad primary topology for dynamic applications. The purpose of the proposed track system is to deliver continuous power with a smooth coupling profile which naturally lowers the rating requirements of the secondary electronic components, and to be interoperable with many secondary topologies. The proposed track is compared with a previously published lumped system using double-D primary pads distributed one per meter by a normalized coupling metric. The results show that this meandering track primary has a smaller impact on system electronic components and has better interoperability while it requires lower primary compensation rating compared to the lumped pad primary for the same power level. A prototype of the track was built and the simulation results were verified. A 10 kW power experiment was achieved a dc–dc efficiency of around 83%, and the potential of this multicoil topology for interoperable and low-cost high-power dynamic charging was demonstrated.
This paper introduces a new ferrite-less magnetic structure for roadway charging of Electric Vehi... more This paper introduces a new ferrite-less magnetic structure for roadway charging of Electric Vehicles (EVs). Most of the existing magnetic pads for roadside EV charging rely on ferrimagnetic materials to produce single-sided flux and boost power levels while minimizing undesired field emissions and losses. But the properties that roadway pads must have are mechanical robustness coupled with the ability to throw single-sided, high arching flux while being subjected to stringent conditions under asphalt, bitumen, or concrete. Ferrite is very brittle and expensive and its performance under transient forces when buried under a roadway is questionable. This new ferrite-less magnetic coupler is proposed as a primary pad for roadway EV charging. Simulated and experimental results are shown, followed by a discussion on its capabilities, limitations, and possible updates.
2020 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
Misalignment of pads and the charging and discharging of the electric vehicle (EV) battery makes ... more Misalignment of pads and the charging and discharging of the electric vehicle (EV) battery makes delivering constant power with an inductive power transfer (IPT) system non-trivial. One solution is to add Tunable Matching Networks (TMNs), which are essentially variable reactances, in between the converters and compensation networks. However, TMNs are costly to implement. As an alternative, this paper proposes a method of tuning and controlling the system known as Active Impedance Control (AIC) that emulates the behaviour of a TMN. Mathematical modelling was used to design an AIC system that can transfer 7.7 kW of power with near unity power factor under a 2.35-fold change in induced voltage for a constant battery voltage. Additionally, rectifier input current varies by only 1.4 times across the operating range. Furthermore, simulation results show good agreement with the mathematical model.
2020 IEEE PELS Workshop on Emerging Technologies: Wireless Power Transfer (WoW)
Inductive power transfer (IPT) is a promising method for electric vehicle (EV) charging that is s... more Inductive power transfer (IPT) is a promising method for electric vehicle (EV) charging that is safe and practical. The critical aspects of IPT systems to achieve roadway charging are robustness, reliability, low cost and high power transfer. This paper presents two variations of a primary IPT double-D (DD) coupler that reduce ferrite volume, stray-fields and cost while having increased power rating at the expense of magnetic coupling and higher primary pad currents. A two-step ferrite shaping method is used for optimisation while keeping the primary coil and secondary pad unchanged. The ferrite volume is limited to the high flux density locations in a first step to reduce ferrite volume by 70%. Following this, an additional 14% ferrite volume is added to shape and reduce the stray fields by 23%.
IEEE Journal of Emerging and Selected Topics in Industrial Electronics
Inductive power transfer is a technology that enables power to be transferred from a primary (gro... more Inductive power transfer is a technology that enables power to be transferred from a primary (ground assembly) to a secondary (vehicle assembly) without a physical connection. Recommended practice proposed by the SAE J2954 working group has put flux limitations for human exposure in stationary electric vehicle charging applications. The latest version has constrained the leakage flux to 27 μT RMS for EMF limitations. In this article, a new multicoil ground assembly (MCGA) is proposed to reduce the leakage flux. The MCGA can decrease the flux levels by over 25%. All the vehicle assemblies studied can meet the EMF requirements. The ground assembly is the main contributor to leakage flux, except when the DDP WPT3/Z3 secondary vehicle assembly becomes the main contributor. The proposed MCGA is also able to provide similar dc–dc efficiencies compared to the existing Universal Ground Assembly of $>$89% at the most misaligned point.
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Papers by Grant Covic