Wireless power transfer system (WPTS)-based wireless electric vehicles, classified into roadway-powered electric vehicles (RPEVs) and stationary charging electric vehicles (SCEVs), are in the spotlight as future mainstream transportations. RPEVs are free from serious battery problems such as large, heavy, and expensive battery packs and long charging time because they get power directly from the road while moving. The power transfer capacity, efficiency, lateral tolerance, electromagnetic field, air-gap, size, weight, and cost of the WPTSs have been improved by virtues of innovative semiconductor switches, better coil designs, roadway construction techniques, and higher operating frequency. Recent advances in WPTSs for RPEVs are summarized in this review paper. The fifth- and sixth-generation online electric vehicles, which reduce infrastructure cost for commercialization, and the interoperability between RPEVs and SCEVs are addressed in detail in this paper. Major milestones of the developments of other RPEVs are also summarized. The rest of this paper deals with a few important technical issues such as coil structures, power supply schemes, and segmentation switching techniques of a lumped inductive power transfer system for RPEVs.

Wireless power transfer systems (WPTSs) with inductive coupling are advantageously used to charge the battery pack of electric vehicles. They basically consist of coil coupling, power supply circuitry connected to the transmitting side of the coil coupling, and power-conditioning circuitry connected to the receiving side of the coil coupling. This paper presents the design and implementation of a wireless power transfer (WPT) battery charger for an electric city car. A short overview on the working principles of a series-series resonant WPTS is given before describing in detail the design procedure of the power circuitry needed for its operation, i.e., an alternating-current-direct-current converter cascaded by a high-frequency inverter in the transmitting section and a diode rectifier cascaded by a chopper in the receiving section. The coil coupling with spiral coils is designed with the help of a finite-element-method code. A prototype of the WPT battery charger is built up according to the design results, and experiments that validate the design procedure are carried out.

Vehicle-to-grid (V2G) paradigm is a way of executing services in favor of the grid by electric vehicles (EVs) with bidirectional battery chargers (BBC). The V2G service that has attracted the major interest is the exchange of active power for load leveling purposes. Less attention has received the so-called ancillary V2G services, such as the reactive power compensation. This service is much attractive since it does not involve any exchange of active power and, therefore, leaves the EV batteries charged and does not expose them to additional discharging-charging cycles. The purpose of this paper is to investigate the capabilities of V2G-enabled EVs in executing the reactive power compensation, whether done alone or simultaneously with either battery charging or battery power delivery to the grid. Two topologies of BBC are examined, namely the topologies with the dc side of the charger either directly connected to the battery or through a bidirectional dc-dc converter of buck type. This paper closes by reporting experimental results that corroborate the theoretical findings.

Dynamic wireless charging (DWC) of electric vehicles (EVs) is an emerging technology that could lead to the breakthrough of EVs. The technology is based on the inductive coupling between an electrified track deployed under the road surface and a pickup coil fitted in EV. This paper refers to a lumped track made of DD coils and is concerned with the design of the track layout, namely coil dimension in the motion direction and track coil distance for a given energy requirement. This paper starts by comparing the coupling characteristics of DD coils with different dimensions by a finite-element method (FEM) analysis. Afterward, an analytical procedure is developed to establish the track coil distance able to transfer to a moving EV the propulsion energy required per unit of traveled space. The procedure utilizes the DD-coil coupling characteristics to calculate the power and, from it, the energy transferred from the track coils to the pickup coil along the track. Instrumental in the calculation is the definition of a parameter, denoted as track flux coverage, which gives the ratio between the dimension of the track coils in the motion direction and the coil distance; such a parameter corresponds to the percentage of road populated with track coils so that it is a cost index of the DWC system implementation. Effects of a lateral displacement of the EV motion from the line joining the track coil centers are also analyzed. Design findings are checked against the results obtained with a computer-assisted analysis.

The paper presents a number of advanced solutions on electric machines and machine-based systems for the powertrain of electric vehicles (EVs). Two types of systems are considered, namely the drive systems designated to the EV propulsion and the power split devices utilized in the popular series-parallel hybrid electric vehicle architecture. After reviewing the main requirements for the electric drive systems, the paper illustrates advanced electric machine topologies, including a stator permanent magnet (stator-PM) motor, a hybrid-excitation motor, a flux memory motor and a redundant motor structure. Then, it illustrates advanced electric drive systems, such as the magnetic-geared in-wheel drive and the integrated starter generator (ISG). Finally, three machine-based implementations of the power split devices are expounded, built up around the dual-rotor PM machine, the dual-stator PM brushless machine and the magnetic-geared dual-rotor machine. As a conclusion, the development trends in the field of electric machines and machine-based systems for EVs are summarized.

Further to the vector analysis in the stationary plane of the behavior of a permanent-magnet brushless dc (PM BLDC) drive, this paper proposes a method of synthesizing the current supply of the motor that ensures torque ripple-free operation of the drive. The synthesis is carried out analytically by the vector approach, and the resulting current vector is then expressed in motor phase coordinates. It comes out that the current vector has a petal-shape trajectory in the stationary plane. The operation of the drive with such a current supply is extensively examined; in particular, the torque capability for an rms value of the phase currents equal to the rated one, the requirements for the voltages to be applied across the motor terminals, and the base speed in correspondence to the supply voltage saturation are determined. At last, experimental traces obtained from an in-wheel PM BLDC drive used for the traction of light electric vehicles are included to corroborate the theoretical findings.