This paper reviews the current status and implementation of battery chargers, charging power levels, and infrastructure for plug-in electric vehicles and hybrids. Charger systems are categorized into off-board and on-board types with unidirectional or bidirectional power flow. Unidirectional charging limits hardware requirements and simplifies interconnection issues. Bidirectional charging supports battery energy injection back to the grid. Typical on-board chargers restrict power because of weight, space, and cost constraints. They can be integrated with the electric drive to avoid these problems. The availability of charging infrastructure reduces on-board energy storage requirements and costs. On-board charger systems can be conductive or inductive. An off-board charger can be designed for high charging rates and is less constrained by size and weight. Level 1 (convenience), Level 2 (primary), and Level 3 (fast) power levels are discussed. Future aspects such as roadbed charging are presented. Various power level chargers and infrastructure configurations are presented, compared, and evaluated based on amount of power, charging time and location, cost, equipment, and other factors.

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Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and Hybrid Vehicles

The author evaluates the state of the art in pulsewidth modulation for AC drives fed from three-phase voltage source inverters. Feedforward and feedback pulsewidth modulation schemes with relevance for industrial application are described and their respective merits and shortcomings are explained. Secondary effects such as the influence of load-current dependent switching time delay and transients in synchronized pulsewidth modulation schemes are discussed, and adequate compensation methods are presented. Recorded oscillograms illustrate the performance of the respective pulsewidth modulation principles. The author provides a guideline and quick reference for the practicing engineer to decide which methods should be considered for an application of a given power level, switching frequency, and dynamic response. >

Pulsewidth modulation-a survey

The efficient and fast control of electric power forms part of the key technologies of modern automated production It is performed using electronic power converters The converters transfer energy from a source to a controlled process in a quantized fashion, using semiconductor switches which are turned on and off at fast repetition rates The algorithms which generate the switching functions-pulsewidth-modulation techniques-are manifold They range from simple averaging schemes to involved methods of real-time optimization This paper gives an overview >

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Pulsewidth modulation for electronic power conversion

Inductive power transfer (IPT) has progressed to be a power distribution system offering significant benefits in modern automation systems and particularly so in stringent environments. Here, the same technology may be used in very dirty environments and in a clean room manufacture. This paper reviews the development of simple factory automation (FA) IPT systems for both today's complex applications and onward to a much more challenging application-IPT roadway. The underpinning of all IPT technology is two strongly coupled coils operating at resonance to transfer power efficiently. Over time the air-gap, efficiency, coupling factor, and power transfer capability have significantly improved. New magnetic concepts are introduced to allow misalignment, enabling IPT systems to migrate from overhead monorails to the floor. However, the demands of IPT roadway bring about significant challenges. Here, compared with the best FA practice, air-gaps need to be 100 times larger, power levels greater than ten times, system losses ten times lower to meet efficiency requirements, and systems from different manufacturers must be interoperable over the full range of operation. This paper describes how roadway challenges are being met and outlines the problems that still exist and the solutions designers are finding to them.

Modern Trends in Inductive Power Transfer for Transportation Applications

A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive power transfer

Several sophisticated or "optimum" modulation strategies have been suggested for voltage source pulsewidth modulated (PWM) inverters for ac motor control. These modulation strategies may suppress specific low-order harmonics or minimize total harmonic content and have been successfully implemented in practical drive systems. The effectiveness of these PWM techniques in minimizing harmonic losses and reducing torque pulsations is investigated analytically, and their performance is compared with that of the usual sinusoidal or subharmonic PWM approach. The influence of skin effect on rotor 12R copper loss is taken into consideration, and harmonic core losses are compared. Peak current is also an. important factor in inverter design, and the various modulation strategies are again compared on this basis. Fourier analysis techniques are used in order to allow skin effect phenomena to be taken into consideration, and performance criteria are developed to allow comparisons of waveform quality in respect of harmonic copper and iron losses.

A Comparison of PWM Strategies for Inverter-Fed Induction Motors

The recommended practice for electric vehicle battery charging using inductive coupling (SAE J-1773), published in January 1995 by the Society of Automotive Engineers, Inc., outlines values and tolerances for critical vehicle inlet parameters which must be considered when selecting a coupler driving topology. The inductive coupling vehicle inlet contains a significant discrete capacitive component in addition to low magnetizing and high leakage inductances. Driving the vehicle interface with a variable-frequency series-resonant power converter results in a four-element topology with many desirable features: unity transformer turns ratio; buck/boost voltage gain; current-source operation; monotonic power transfer characteristic over a wide load range; throttling capability down to no load; high-frequency operation; narrow modulation frequency range; use of zero-voltage-switched MOSFETs with slow integral diodes; high efficiency; inherent short-circuit protection; soft recovery of output rectifiers; and secondary d/spl nu//dt control and current waveshaping for the cable, coupler and vehicle inlet, resulting in enhanced electromagnetic compatibility. In this paper, characteristics of the topology are derived and analyzed using two methods. Firstly, the fundamental mode AC sine-wave approximation is extended to battery loads and provides a simple, yet insightful, analysis of the topology. A second method of analysis is based on the more accurate, but complex, time-based modal approach. Finally, typical experimental results verify the analysis of the topology presented in the paper.

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

The authors present important new closed-form expressions for the harmonic components of space-vector-modulated waveforms. These expressions are considerably more compact than those previously published. The analysis is a direct extension of the well known geometric-wall-model method used to good effect in the analysis of asynchronous sinusoidal modulation schemes. The models and expressions developed in the paper are valid for the inherent regularly sampled characteristic of digital-space-vector modulation and for both symmetrical and asymmetrical sampling. The developed expressions for the harmonic amplitudes are valid only over the continuous-modulation range of the inverter. The analysis successfully predicts the complete suppression of certain harmonic sidebands and resultant superior harmonic performance that is characteristic of asymmetrically sampled modulation schemes. Similar expressions for the harmonics of a single-edge space-vector-modulation strategy are also developed. The occurrence of undesirable low-order harmonics of the modulating frequency for the different schemes is also discussed. The predicted harmonic spectra are completely verified by comparison with measured results from an experimental digital-signal-processor (DSP)-based modulator.

Theoretical spectra of space-vector-modulated waveforms

The nonlinear torque-production mechanisms in the doubly salient, switched reluctance motor drive are both current and position dependent. It is shown that the shape of the static torque-angle-current characteristics of this drive can be fully determined by a series of measurements performed with the drive in a self-learning mode, without the need for an external loading device. These measurements consist of static tests, in which the torques produced by currents in different phases are balanced, and dynamic measurements, in which the relative currents required to produce the same torque at different positions are ascertained. The controller can then achieve very smooth low-speed performance by determining the current required to obtain the optimum torque contribution from each phase, at each rotor position. >

Torque ripple minimization in switched reluctance drives using self-learning techniques

In a servo control system for a reluctance motor, the output of a reference waveform generator is applied to a power converter through a current controller. Under standstill conditions, at least two of the motor windings are energised so that both forward and reverse torques are established, the forward torque being in equilibrium with the reverse torque. The controller may be responsive to a bias signal to establish said torques. The control system may form part of a reluctance motor drive system.

J.M.D. Murphy

Papers

A Comparison of PWM Strategies for Inverter-Fed Induction Motors

Wide-load-range resonant converter supplying the SAE J-1773 electric vehicle inductive charging interface

Theoretical spectra of space-vector-modulated waveforms

Torque ripple minimization in switched reluctance drives using self-learning techniques

Servomotor control systems