When compared to plugged-in chargers, Inductive Power Transfer (IPT) methods for Electric Vehicle (EV) battery chargers have several benefits such as greater convenience and higher safety. In an EV, the battery is an indispensable component and Lithium-Ion batteries are identified as the most competitive candidate to be used in EVs due to their high power density, long cycle life and better safety. In order to charge Lithium-Ion batteries, Constant Current/Constant Voltage (CC/CV) is often adopted for high efficiency charging and sufficient protection. However, it is not easy to design an IPT Battery Charger that can charge the batteries with a CC/CV charge due to the wide range of load variations, because it requires a wide range of variation in its operating frequency, duty or phase-shift. Furthermore, Zero Phase Angle (ZPA) condition for the primary inverter cannot be achieved over the entire charge process without the help of additional switches and related driver circuits to transform the topology. This paper proposes a design method which makes it possible to implement the CC/CV mode charge with minimum frequency variation during the entire charge process by using the load-independent characteristics of an IPT system under the ZPA condition without any additional switches. A theoretical analysis is presented to provide the appropriate procedure to design the double-sided LCC compensation tank which can achieve both CC and CV mode charge under ZPA condition at two different resonant frequencies. As a consequence, the proposed method is advantageous in that the efficiency of compensation tank is very high due to achieving the perfect resonant operation during the entire charge process. A 6.6 kW prototype charger has been implemented to demonstrate the feasibility and validity of the proposed method. A maximum efficiency of 96.1% has been achieved with a 200mm airgap at 6.6 kW during the CC mode charge.
Multiple output chargers have widely been adopted in various electronic devices due to their benefit concerning cost, power density, and space for installation. On the contrary, Inductive Power Transfer (IPT) has been applied increasingly in electric vehicles (EV) since it is safer and more convenient as compared to conductive chargers. However, researches on multiple output chargers using IPT system for EV charging applications are rarely presented. This paper proposes a new concept of a multiple output IPT charger, which can charge several output batteries independently and simultaneously by adopting only one full bridge inverter at the primary side combining with multiple transmitters. Two possible IPT-coil structures are analyzed, and the minimum distance between each channel's coils is determined to neglect the cross-coupling between them. Two options are proposed to attain Zero Phase Angle (ZPA) condition for primary inverter of the proposed system. First option is to operate the compensation tanks of every output channel at exact ZPA frequencies. The other option is to let one channel working in inductive region of its input impedance and other channel working in capacitive region. By adopting an appropriate design, the reactive powers of these tanks can be nearly cancelled each other and the phase of inverter current can be nearly in-phase with the input voltage as a result. Two proposed options are compared to give recommendation whether option 1 or 2 should be selected according to various of application's requirements. To simplify control complexity, IPT output current sources topologies are selected, compared and analyzed to construct the proposed multiple output system in both above options. Double-sided LCC and Series-Parallel (SP) topologies are adopted to demonstrate the proposed idea for Option 1 and 2, respectively. In order to verify feasibility and validity of the proposed method, experimental results of two output channels with the total output power of 1.5 kW are provided. Experimental results indicate that the ZPA is achieved for primary inverter with both of two above options even under the different load conditions. Some comparisons between the conventional and the proposed IPT charging structure in terms of cost, reliability and complexity are included in discussion session. Index Terms-Inductive power transfer; multiple output charger; IPT compensation topologies, wireless EV charging.
Wireless Dynamic Charging (WDC) of Electric Vehicles (EV) is a new initiative aimed to increase EV uptake. However, pulsating output power along the driving direction is a major problem with this technology. Moreover, in order to deliver enough driving power for EVs, WDC systems must operate at high power. This paper proposes a WDC system that has the capability of providing a low pulsating and high output power to EVs. The proposed WDC utilizes multiple primary windings that guarantees a homogeneous mutual magnetic flux for the receiver along the driving direction. This results in a constant induced voltage across the receiver and hence constant output power to charge the EV battery. High output power is realized by using multiple transmitter windings which have been arranged in a novel winding method. The structure layout of the proposed WDC, including ferrite cores, windings and resonant tanks is presented. Furthermore, a theoretical analysis is conducted to determine conditions of each winding's current phase and amplitude for achieving constant output power. The crossing mutual inductances between the different transmitter's phases are compensated by adding small capacitors in series with each transmitter winding. An optimization analysis using Maxwell 3D simulation for both, transmitter and receiver is carried out to achieve the highest coupling factor by using minimum ferrite material. The effectiveness of the proposed system is analytically demonstrated and experimentally verified using a 3-kW laboratory prototype. Finally, the performance of the proposed method is compared with similar systems presented in the literature. The comparison shows that the proposed system has the advantages of using simple control, it also eliminates communications between the primary and secondary side and delivers a normalized power of 2.25 which is 125% higher compared to conventional single-phase systems.
This paper proposes an LCL-L compensation circuit for high power capacitive power transfer (CPT) aiming at minimizing number of resonant components and improving system performance. The proposed topology adopts only four external resonant components at both sides of the capacitive coupler. The output power is proportional to the capacitive coupling coefficient, therefore, it simplifies the design procedure and abolishes protection circuit requirements under coupler's misalignment. Moreover, optimizing efficiency at full-load conditions of compensation network can be easily achieved in this system by designing resonant components at the highest value of the mutual capacitance. Theoretical analysis of the proposed system is conducted alongside comparison to lasted CPT compensation circuits. Simulation and experimental results of a 1.5-kW CPT prototype with an air gap distance of 150 mm are provided to verify the feasibility and the effectiveness of the proposed system. System performances under different coupler's misalignment conditions and output power levels are also examined and discussed as well. INDEX TERMS Capacitive power transfer, compensation circuits, LCL-L topology, electric vehicles, battery charger.
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