(This study is for special section ‘Design, modelling and control of electric drives for transportation applications’) The conduction and switching losses of silicon carbide (SIC) and gallium nitride (GaN) power transistors are compared in this study. Voltage rating of commercial GaN power transistors is <650 V, whereas that of SiC power transistors is <1200 V. This study begins with a theoretical analysis that examines how the characteristics of a 1200 V SiC metal–oxide–semiconductor field-effect transistor (MOSFET) change if device design is re-optimised for 600 V blocking voltage. Afterwards, a range of commercial devices [1200 V SIC junction gate FET, 1200 V SiC­MOSFET, 650 V SiC-MOSFET and 650 V GaN high-electron-mobility transistor (HEMT)] with the same current rating are characterised and their conduction losses, inter-electrode capacitances and switching energy E _sw are compared, where it is shown that GaN-HEMT has smaller conduction and switching losses than SiC devices. Finally, a zero-voltage switching circuit is used to evaluate all the devices, where device only produces turn-OFF switching losses and it is shown that GaN-HEMT has less switching losses than SiC device in this soft switching mode. It is also shown in this study that 1200 V SiC-MOSFET has smaller conduction and switching losses than 650 V SiC-MOSFET.

For electric vehicles (EVs) with severe acceleration requirement, the selected motor would be inevitably overdesigned to meet the acceleration requirement. To address this, the motor constant power speed ratio (CPSR) should be increased to remove part of the overdesign. There are different flux weakening techniques that are used to increase motor maximum speed (and increase the CPSR). Among them, hybrid excitation synchronous motor (HESM) advantages have been benefited in this study. CPSR depends on hybridisation ratio (HR) of the excitation system, and the motor inductance. The relation is analytically derived in this study. In addition to increasing CPSR, HR can control the place of motor high-efficient area over the efficiency map, which can increase EV total efficiency. A search algorithm has been developed, here, to find the optimal HR of a non-optimal HESM. The final design gives an efficient motor performance with less overdesign in drivetrain. Compared with the original permanent magnet synchronous motor, 4.1% improvement in total efficiency for an average city-highway driving cycle has been achieved, and 16% decrease in rated values of drivetrain elements is obtained.

To meet the high requirements in transport systems, permanent magnet linear synchronous motor (PMLSM) has become an important field of research. A novel trilateral PMLSM with slotless ring windings is proposed, featuring high thrust and low ripple. The structure design of the novel trilateral PMLSM is introduced first. Then mathematical model of the primary with slotless ring windings is established and analysed, the magnetic fields excited by the permanent magnets in the secondary is studied, based on the equivalent magnetising current method. The analytical calculating results of the novel motor are validated by finite-element method, and a prototype is tested to validate the analytical results of this novel motor. The study provides the fundamental characteristic analysis of the novel trilateral PMLSM with slotless ring windings. This study is provided for the special section ‘Design, modeling and control of electric drives for transportation applications’ (VPPC 2016).

High-speed electrical actuators used in harsh environments for automotive applications have surged in recent years. Examples comprise electrically assisted turbochargers, air compressors for fuel-cells, and waste heat recovery generators. In those kinds of applications, the temperature, size and efficiency are major constraining factors. Thus, the electronic and machine designs must be properly selected and adapted to work reliably in such tough environments. Then, coupled circuit and magnetic simulations must be performed to evaluate the impact of machine control on motor and inverter losses in order to find an optimum system. However, electronic driver and electric motor optimisations based on conventional simulation tools are very time-consuming, since these are based on finite-element methods for magnetic simulations and on Kirchhoff equations resolution for electronic simulations. In this context, this study presents a fast drive system model and its application on a high-power high-speed motor. The electronic and machine performances can rapidly be analysed by changing the electronic and motors parameters and substantially reducing the time required by conventional finite-element analysis software tools.

High torque ripple is inherent in switched reluctance motors (SRMs) because of the motor's doubly salient structure and highly non-uniform torque and magnetisation characteristics. Direct torque control (DTC) for SRM is one of the torque ripple reduction strategies which gets wide attention for its simpleness and effectiveness. In this study, aiming at the torque ripple phenomenon of DTC for SRM, a novel method for torque-ripple reduction is proposed. With the new methods, sector zones were redivided into 9 and 12 sector zones based on six sector zones and new control rules were adopted. Consequently, the proposed methods make the selection of voltage vector more precise. A 12/8-pole three-phase SRM drive system was designed to verify the effectiveness of the proposed new methods. The results verified that the improved DTC algorithms with 9 and 12 sector zones could indeed minimise the torque ripple to a great extent.

It is essential for electric vehicle to equalise the voltages of battery or supercapacitor (SC) cells in series connection. Comparing with other equalisation methods based on energy transfer, Cockcroft–Walton (CW) voltage multiplier brings great benefits to the simplification of equalisation structure. Voltage equaliser formed by voltage multiplier can realise voltage balance automatically without voltage detection and control unit. However, the traditional (CW) voltage multiplier structure has two demerits. One is incapable of realising the voltage balancing for all the cells in series; the other one is the large inrush current of parallel capacitors that reduces the lifetime of the equaliser. To solve these problems, a modified voltage equalisation circuit is proposed. The new equaliser is constituted by a half-bridge frontend and a multiplier backend. The half-bridge generates the alternating voltage, and the multiplier accomplishes the voltage balancing. The operation principles, circuit analysis and parameters calculation are examined in detail. The performance is evaluated by simulation and experimental with three SCs in series. The accordance between simulation and experiment further proves that the voltage balancing is achieved for all the series cells and the inrush current of capacitors is declined at the turning on of power switches.

In this study, an electric taxiing drive system for a commercial midsize aircraft is proposed. Four electric motors are integrated in the main landing gears to enable electric drive of the aircraft during the taxiing process. To achieve the same performance, a system level analysis is conducted to investigate the drive cycle requirements. Based on the recorded aircraft taxiing data, a variety of taxiing drive cycles are used as inputs to size the powertrain components. An axial flux permanent magnet (AFPM) machine is then proposed in order to meet the compact space and high torque output requirement. Both analytical calculations and three-dimensional finite element model are applied to design and improve the machine performance. A wide range of simulations has been conducted and the results confirmed that the proposed AFPM machine fulfils the given requirements for an electric taxiing drive system.

This study presents an optimal number of electric buses in the solar-assisted smart public transit system and its failure analysis. Electric buses are used to perform the mass transportation in the Guwahati city, Assam, India. The charging points have been provided through the ring road of the city to charge the electric buses. Every charging point consists of a high-capacity energy storage device (ESD) and the solar plant for achieving the smooth functionality of the transportation system. Optimal numbers of electric buses have been determined as a function of the load, the ESD, the solar plant and the passenger total. Simulations have been carried out to show the system response for the optimal number of electric buses and for the failures that exist in the system. Every charging point consists of a fuzzy logic controller to control the power flow among the grid, ESD and the solar plant.