Chang-Yu Huang

Development of a Single-Sided Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems

Inductive power transfer is a practical method for recharging electric vehicles because it is safe, convenient, and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Circular couplers are the most common topology in the literature; however, they have fundamentally limited coupling. Their flux patterns necessarily limit the operational air gap as well as tolerance to horizontal misalignment. A new polarized coupler topology [referred to as a double D (DD)] is presented, which overcomes these difficulties. DDs provide a charge zone five times larger than that possible with circular pads for a similar material cost and are smaller. A 0.31-m2 DD enables 2 kW of power transfer over an oval area measuring 540 mm × 800 mm with a 200-mm air gap. Leakage magnetic fields have been investigated and show that circular and DD couplers operating under similar power transfer conditions produce similar levels. Both topologies can be designed and operated to ensure compliance with international guidelines.

Development and evaluation of single sided flux couplers for contactless electric vehicle charging

Inductive Power Transfer (IPT) is a practical and preferable method for recharging stationary and moving Electric Vehicles (EV) because it is safe, convenient and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Single sided flux couplers have a unidirectional flux pattern and can be used under an EV with minimal loss to the (steel) chassis. Circular pads are single sided and the most common topology and these are investigated with consideration of magnetic field leakage guidelines. Following this, a new polarized coupler topology (referred to as a “Double-D-Quadrature” (DDQ)) is presented. An interoperability study with conventional circular couplers shows this DDQ pad is completely compatible and offers a significantly larger charge zone.

Detection of the Tuned Point of a Fixed-Frequency LCL Resonant Power Supply

Inductor-capacitor-inductor (LCL ) series-parallel resonant networks are commonly employed in inductive power transfer systems as they allow a voltage source inverter to generate a constant AC track current independent of the loading, while also allowing operation at unity power factor. To function correctly, the LCL network must be tuned properly, since any deviation in the track inductor will cause an unwanted reactive load to be placed on the inverter. This letter demonstrates how a simple frequency sweep at power-on (at reduced output voltage) can be employed to identify and protect the power supply from track tuning errors that can easily arise at installation.

Practical considerations for designing IPT system for EV battery charging

The paper proposes a hands-free Inductive Power Transfer system for charging the batteries of an Electrical Vehicle. A typical system comprises a power supply, a transfer pad on the ground, a receiving pad on the vehicle together and a power regulator. This paper describes the design of the power regulator which must ensure continuous power flow at high efficiency despite wide separation between the charging pads as a result of variation in the vehicle to ground heights. The paper also discusses the need to meet new and stringent electromagnetic field exposure regulations. Measurements show good efficiency across various separations and emissions compliance providing the pad is placed underneath the vehicle.

LCL Pickup Circulating Current Controller for Inductive Power Transfer Systems

This paper proposes a fast switching control topology for a series–parallel-tuned LCL pickup for inductive power transfer systems. This topology employs a similar idea to traditional controlled rectifiers that regulate the average output current through the rectifier. The proposed topology is able to provide continuous power regulation and smooth power transitions between the fully ON and fully OFF state. Due to the way in which the circuit operates, the proposed controller necessarily introduces additional reflected reactive power back onto the primary power supply. A steady-state analysis is presented enabling this reflected real and reactive power to be investigated and compared against SPICE simulations. These results are further verified by practical measurements on a 1.5-kW 300-V dc output pickup controller prototype which achieves an efficiency of 95% at full load and is still above 85% when operating at one third of its rated power.

Single-phase unity power-factor inductive power transfer system

An inductive power transfer (IPT) system driven from a single phase utility is shown to be suitable for low power situations applicable to home and office and other small scale applications. The complete system is low cost yet highly efficient and in a novel development achieves essentially unity power factor at the input by modulation of the power controller in the pick-ups, while still achieving constant output voltage. The complete system is straightforward to use, has simple but effective protection strategies, and is easily adapted to other applications.

LCL pick-up circulating current controller for inductive power transfer systems

This paper proposes a fast switching control topology for a series-parallel tuned LCL pick-up. This topology employs a similar idea to the traditional controlled rectifier to regulate the average output current through the rectifier. The proposed topology is able to provide the LCL pick-up with a smooth power transition between fully on and fully off. Also, it is able to achieve power regulation while allowing some variance in mutual coupling with the track without overloading the power supply. The normalized reflected impedance of the proposed controller back onto the primary track is first discussed in relation to simulation results. Then a 2.5 kW 50V output prototype is constructed and tested that achieves an efficiency of 88% at full load and 85% at half load. The reflected impedance of the prototype is also calculated using a normalized graph. It demonstrates that mistuning of the primary track with the associated reflected reactance has little input on system operations.

Implementation and evaluation of an IPT battery charging system in assisting grid frequency stabilisation through Dynamic Demand Control

The paper presents a hands free Inductive Power Transfer (IPT) system for charging Electric Vehicle (EV) batteries using a technique called dynamic demand control (DDC). A typical IPT system comprises a power supply, a pair of magnetic pads for wireless power coupling and a power regulator to drive the load as required. DDC enables suitable domestic appliances to assist grid stabilisation by adjusting their power demand according to the utility frequency variation. This paper explains the conceptual design of a wireless power charging system that includes DDC and details the experimental set up for an emulated erratic isolated power network which combines a variable speed drive, an induction motor and an AC generator. The measured performance of the emulated power network generator frequency without DDC varies between 47 Hz to 53Hz, but this same network frequency is maintained within a preset window of 49.5 Hz to 50.5 Hz when DDC is activated in the IPT battery charging system. Consequently EV charging systems employing DDC control could potentially act as a grid stabilising load, enabling increased penetration of fluctuating sources of energy (such as wind) in the generation mix.

Resonant network design considerations for variable coupling lumped coil systems

This paper investigates the impact of coupling variations in an IPT lumped coil system on the overall system behaviour. An analysis of the reactive power flow between the pick-up and the primary power supply in a variable coupling system is presented. A 1.2kW battery charging system design example was conducted on how to design the resonant networks to minimize the burden on the primary power supply due to the additional reactive power demands as a result of mistuning under variable coupling condition.