Michael Le Gallais Kissin

A Three-Phase Inductive Power Transfer System for Roadway-Powered Vehicles

The development of a new three-phase bipolar inductive power transfer system that provides power across the entire width of a roadway surface for automatic guided vehicles and people mover systems is described. A prototype system was constructed to verify the feasibility of the design for a number of moving loads (toy cars). Here, 40 A/phase is supplied at 38.4 kHz to a 13-m-long test track. Flat pickups are used on the underside of each vehicle to couple power from the track to the vehicle. Finite element modeling software was used to design the geometrical position of the track cables and to predict the power output. This design resulted in a considerably wider power delivery zone than possible using a single-phase track layout and has been experimentally verified. Mutual coupling effects between the various track phases require additional compensation to be added to ensure balanced three-phase currents.

Interphase Mutual Inductance in Polyphase Inductive Power Transfer Systems

Roadway powered electric vehicles with minimal or no onboard energy storage have been proposed for many years, but the concept has only recently become feasible via three-phase inductive power transfer (IPT) systems. A wide zone can be created over which power transfer is relatively constant. This gives good tolerance to the alignment of the pickup relative to the track allowing simple low-cost pickup structures to be used. While three-phase IPT tracks make the vehicle pickup and power transfer simpler, they are difficult for the power supply to drive due to the presence of mutual coupling between the track phases resulting from the physical layout of the track. These mutual inductances induce voltages within each track phase that, because of the inductor-capacitor-inductor network, cause large currents within the power supply inverter and imbalances within the system. This paper presents an analytical assessment of the problems caused by the interphase mutual inductance, and three possible solutions. Two of the methods involve modifications to the track layout to alter or remove the mutual inductances, while the third and preferred technique requires additional ferrite cores between the various phases to compensate this adverse mutual inductance without affecting the power transfer to the pickup loads.

A bipolar primary pad topology for EV stationary charging and highway power by inductive coupling

Electric vehicles have been rapidly gaining in popularity in recent years, and with them inductive charging solutions. The ideal stationary charging system requires no input from the user, and places as few restrictions on either parking location, or environmental conditions (i.e. rain or snow) as possible. The success of inductive charging systems is contingent largely on the design of the magnetic coupling components; i.e. the track pad and the pickup. This paper details a new topology for the track pad, consisting of two largely coplanar, partially overlapping coils positioned such that there is no mutual inductance between them. This arrangement prevents interaction of the two coils, and allows the currents within them to be independent in both phase and magnitude. By controlling the phase and magnitude of the two coil currents, the magnetic field can be shaped to assist in power transfer to a pickup underneath an EV.

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.

Steady-State Flat-Pickup Loading Effects in Polyphase Inductive Power Transfer Systems

Polyphase inductive power transfer systems have been proposed as a method of increasing the tolerance of roadway-based vehicular systems to the lateral movement of pickups. However, the design of the power supply is challenging due to the changing nature of the load presented by mobile pickups. An inverter driving a traditional single-phase system must be designed with only the peak power in mind, as the reactive load of the pickups is essentially constant due to the relatively constrained pickup movement and will normally be compensated when the system is designed. This is not possible for an inverter driving a polyphase track, as the reactive load will vary with the lateral position of the pickup, just as a portion of the real load that must be supplied by each phase will also vary. This paper presents a simple but accurate method of determining the real and reactive load on each phase of the track as the pickup moves, allowing the inverter to be correctly designed with appropriate component ratings.

A practical multiphase IPT system for AGV and roadway applications

Recent advances in Inductive Power Transfer (IPT) technology have made it possible to transfer enough power across an air gap of sufficient size that electric vehicles can receive operational power and be charged while they are in motion on a roadway. However, in order to provide the vehicle with the required tolerance to lateral movement, bulky pickups or complex track arrangements are required. The challenge is to provide the vehicle as much freedom of movement as possible so that drivers are not artificially restricted, while utilizing a simple and low cost pickup, track and power supply. This paper will show that a simple, low cost two-phase track and power supply system can provide similar benefits to a more complex three-phase system, while also lowering the system cost with a simpler installation. A quadrature pickup provides additional benefits in maintaining a constant power transfer across the width of the roadway. Used together, these provide the vehicle with high freedom of movement, and a low total system cost.

Estimating the output power of flat pickups in complex IPT systems

Inductive power transfer (IPT) has been successfully applied to single phase track systems to transfer power to moving vehicles without contact. Such systems suffer from a rapid reduction in transferred power as the track and pickup become misaligned. This has hindered their use in vehicular systems where the pickups must be allowed to move freely. Poly-phase IPT tracks have recently been proposed as a method of increasing the tolerance of the system to horizontal misalignment of mobile pick-ups. The substantial improvement in the tolerance of the system to misalignment is complicated by the number of design variables in the system, making it difficult to produce an optimal design. This paper presents a method of obtaining a first order estimate of the output power from a standard flat pick-up when used in an IPT system with an arbitrary track. This is achieved by exploiting the linear nature of non-saturating magnetic circuits to combine the system response from one track conductor into a composite that accounts for all the conductors. The estimate can be used to quickly and easily optimize the design of an entire IPT system. The final solution can then be simulated, built and experimentally verified.

A parallel topology for inductive power transfer power supplies

High-power inductive power transfer (IPT) systems operate at power levels of 100 kW or more. However, existing high-power IPT power supplies are typically designed for one power level and are expensive to make, due to the use of high-power electronic components. This paper presents a parallel IPT power supply topology that can achieve high output power levels in a cost effective manner. The parallel topology can minimize uneven power sharing due to component tolerance, and does not require any additional reactive components for parallelization. In addition, it can continue to operate when a faulty parallel unit is electronically shut down, dramatically improving the availability and reliability of the systems. Furthermore, flexible output power levels may be achieved by connecting identical modules in parallel. A 6 kW parallel power supply has been constructed by connecting three 2 kW power supplies in parallel. The maximum efficiency of the power supply and track is measured to be 94%.