Three-phase modular permanent magnet brushless machine for torque boosting on a downsized ICE vehicle

The paper describes a relatively new topology of 3-phase permanent magnet (PM) brushless machine, which offers a number of significant advantages over conventional PM brushless machines for automotive applications, such as electrical torque boosting at low engine speeds for vehicles equipped with downsized internal combustion engine (ICEs). The relative merits of feasible slot/pole number combinations for the proposed 3-phase modular PM brushless ac machine are discussed, and an analytical method for establishing the open-circuit and armature reaction magnetic field distributions when such a machine is equipped with a surface-mounted magnet rotor is presented. The results allow the prediction of the torque, the phase emf, and the self- and mutual winding inductances in closed forms, and provide a basis for comparative studies, design optimization and machine dynamic modeling. However, a more robust machine, in terms of improved containment of the magnets, results when the magnets are buried inside the rotor, which, since it introduces a reluctance torque, also serves to reduce the back-emf, the iron loss and the inverter voltage rating. The performance of a modular PM brushless machine equipped with an interior magnet rotor is demonstrated by measurements on a 22-pole/24-slot prototype torque boosting machine

Post-Demagnetization Performance Assessment for Interior Permanent Magnet AC Machines

This paper assesses the post-demagnetization performance of interior permanent magnet (IPM) ac machines by employing the more accurate recoil line approach based on a 2-D transient finite-element analysis (FEA). The method predicts continuous demagnetization of each magnet element undergoing partial demagnetization and evaluates the machine behavior after an event of short-circuit faults across its terminals. Along with the short-circuit faults, a failure in a drive controller or a position sensor, which may lead to a reverse voltage across the machine terminals that can eventually be more fatal and can cause significant reduction in the performance due to high levels of demagnetization, is analyzed as the worst case scenario. The FE predicted post-demagnetization performance is validated by experimental measurements in which a six-phase IPM machine designed for electric vehicle traction is allowed to lose its synchronization with the inverter when forced to operate on a torque-speed envelope, which is way beyond the drive voltage setting

Advanced Electrical Machines and Machine-Based Systems for Electric and Hybrid Vehicles

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

Effective turn fault mitigation by creating zero sequence current path for a triple redundant 3x3-phase PMA SynRM

Effective mitigation of excessive stator turn fault current is crucial for fault tolerant machine drives. In this paper, a simple and effective method is proposed for a triple redundant 3x3-phase permanent magnet assisted synchronous reluctance machine (PMA SynRM) by using 3-phase 4-leg inverters. The fourth leg creates a zero sequence current path when a terminal short circuit (TSC) is applied in an event of a turn fault in a 3-phase winding set. Consequently, the zero sequence flux linkages are reduced by the resultant zero sequence current. This leads to lower residual flux linkage and decreased fault current. The machine drive can therefore have larger safety margin or can be designed for improved torque density and efficiency. The proposed approach is verified by both FE simulations and experimental tests in a wide operation range. It shows the fault current is reduced by ~40% and the output torque is not affected

Enhanced Availability of Drivetrain Through Novel Multiphase Permanent-Magnet Machine Drive

This paper deals with a novel multiphase permanent-magnet (PM) machine drive to enhance drivetrain availability in electric traction applications. It describes the development of new winding configurations for six-phase PM brushless machines with 18 slots and eight poles, which eliminate and/or reduce undesirable space harmonics in the stator magnetomotive force. In addition to improved power/torque density and efficiency with a reduction in eddy current loss in rotor PMs and copper loss in end-windings, the developed winding configuration also enhances availability of drivetrain, in a variety of applications requiring a degree of fault tolerance, by employing it as two independent three-phase windings in a six-phase interior-PM machine, which is designed and optimized for a given set of specifications for an electric vehicle, under thermal, electrical, and volumetric constraints. This paper also describes the design and development of a six-phase inverter with independent control for both sets of three-phase windings. The designs of the motor and the inverter are validated by a series of preliminary tests on the prototype machine drive

A high torque density, direct drive in-wheel motor for electric vehicles

PhD ThesisThe use of in-wheel motors, often referred to as hub motors as a source of propulsion for pure electric or hybrid electric vehicles has recently received a lot of attention. Since the motor is housed in the limited space within the wheel rim it must have a high torque density and efficiency, whilst being able to survive the rigours of being in-wheel in terms of environmental cycling, ingress, shock, vibration and driver abuse. Part of the work of this PhD involved an investigation into different slot and pole combinations in order determine a superior machine design, within given constraints based upon an existing in-wheel motor drive built by Protean Electric. Finite element analysis and optimisation have been applied in order to investigate the machine designs and achieve the optimum combination. The main work of this PhD, presents a high torque dense machine employing a new method of construction, which improves the torque capability with a smaller diameter, compared to that of the existing Protean in-wheel drive system. The machine is designed with an open slot stator and using magnetic slot wedges to close the slots. Having an open slot stator design means the coils can be pre-pressed before being inserted onto the stator teeth, this improves the electrical loading of the machine as the fill factor in the slot is increased. The electromagnetic impact of the slot wedges on the machine design has been studied, also a method of coil pressing has been studied and the impact upon coil insulation integrity verified. To ensure adequate levels of functional safety are met it is essential that failures do not lead to loss of control of the vehicle. Studies on a fault tolerant concept which can be applied to the design of in-wheel motors are presented. The study focuses on the ability to sustain an adequate level of performance following a failure, while achieving a high torque density. A series of failures have been simulated and compared with experimental tests conducted on a Protean motor. Finally a prototype is constructed and tested to determine the true level of performance. The prototype is compared to a new motor built in-house by Protean and achieves an improved level of performance.Protean Electri