On multi-phase machines and current harmonic injection for torque capability improvement

The increased energy demand and the need for electrical machines capable to deliver high torque and power in small volumes is pushing the research community to identify suitable solutions for this target. Nowadays, electrical machines are deeply used also in applications where the weight containment is important such as automotive and aerospace. Multi-phase electrical machines are a suitable candidate to help to get this goal. They present different advantages with respect to classical three-phase machines for example an increased machine torque capability and more tolerance to sustain fault conditions. The average torque is increased thanks to an improved winding factor whereas the fault tolerance improvement is due to the higher number of machine phases. In addition, the torque ripple is lower thanks to an improved magneto-motive force distribution. Moreover, the voltage on the single converter is lower, supplying the machine with the same current of a three-phase system. Another important advantage for the multi-phase arrangement is the possibility to control more harmonics of magnetic field independently thanks to the more degrees of freedom. It means new possibilities to implement various control techniques for improving the machine performance by the injection of additional harmonics higher than the fundamental. This thesis describes the work which has been carried out in the past three years, during the Ph.D program with the results achieved by analytical model implementations, finite element analysis simulations and experimental tests. The main target is to improve the machine torque capability and/or reduce its permanent magnet content. To reach this goal, the multi-phase re-arrangement of three-phase machines and current harmonic injection techniques are proposed for different machine topologies. An analytical model is implemented to reduce the magnet content in surface permanent magnet machines without affecting Joule losses and the average torque. The analytical model is validated via FEA. A model-free technique to improve the torque capability by current harmonic injection is proposed and its concept is validated experimentally on a V-Shape interior permanent magnet machine. Sensitivity analyses are carried out to optimise the V-Shape rotor configuration to improve the torque under fifth current harmonic injection. Studying the flux density in the stator core on a classical three-phase surface permanent magnet machine with a distributed winding layout, it is possible to highlight another advantage of multi-phase machines which consists in a better flux density distribution. The proposed work gives a contribution to the research community in terms of new solutions for increasing the torque capability and/or reducing the permanent magnet content in the machine without affecting its efficiency for different rotor topologies. Moreover, the proposed stator flux density analysis can give important information about the electromagnetic behaviour in three-phase distributed winding surface permanent magnet machines

Analysis and Design Optimization of a Permanent Magnet Synchronous Motor for a Campus Patrol Electric Vehicle

© 1967-2012 IEEE. This work presents the analysis, design and optimization of a permanent magnet synchronous motor (PMSM) for an electric vehicle (EV) used for campus patrol with a specific drive cycle. Firstly, based on the collected data like the parameters and speed from a test EV on the campus road, the dynamic calculation of the EV is conducted to decide the rated power and speed range of the drive PMSM. Secondly, according to these requirements, an initial design and some basic design parameters are obtained. Thirdly, optimization process is implemented to improve the performance of the designed PMSM. The permanent magnet (PM) structure, airgap length and stator core geometry are optimized respectively in this step. Different optimization processes are proposed to meet multiple optimization objectives simultaneously. Based on the finite element analysis (FEA) method, it is found that the harmonic of the optimized PMSM is lower than that of the initial design, and the torque ripple is reduced by 24%. The effectiveness of optimization on the core loss and PM eddy loss is validated and the temperature rise is suppressed effectively. Finally, a prototype is fabricated for the optimized PMSM and an experimental platform is developed. The test results verify that the optimized PMSM meets the requirements of the specific campus patrol EV well

In-wheel motor vibration control for distributed-driven electric vehicles:A review

Efficient, safe, and comfortable electric vehicles (EVs) are essential for the creation of a sustainable transport system. Distributed-driven EVs, which often use in-wheel motors (IWMs), have many benefits with respect to size (compactness), controllability, and efficiency. However, the vibration of IWMs is a particularly important factor for both passengers and drivers, and it is therefore crucial for a successful commercialization of distributed-driven EVs. This paper provides a comprehensive literature review and state-of-the-art vibration-source-analysis and -mitigation methods in IWMs. First, selection criteria are given for IWMs, and a multidimensional comparison for several motor types is provided. The IWM vibration sources are then divided into internally-, and externally-induced vibration sources and discussed in detail. Next, vibration reduction methods, which include motor-structure optimization, motor controller, and additional control-components, are reviewed. Emerging research trends and an outlook for future improvement aims are summarized at the end of the paper. This paper can provide useful information for researchers, who are interested in the application and vibration mitigation of IWMs or similar topics

Digital Control of Power Converters and Drives for Hybrid Traction and Wireless Charging

In the last years environmental issues and constant increase of fuel and energy cost have been incentivizing the development of low emission and high efficiency systems, either in traction field or in distributed generation systems from renewable energy sources. In the automotive industry, alternative solutions to the standard internal combustion engine (ICE) adopted in the conventional vehicles have been developed, i.e. fuel cell electric vehicles (FCEVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEV) or pure electric vehicles (EVs), also referred as battery powered electric vehicles (BEV). Both academic and industry researchers all over the world are still facing several technical development areas concerning HEV components, system topologies, power converters and control strategies. Efficiency, lifetime, stability and volume issues have moved the attention on a number of bidirectional conversion solutions, both for the energy transfer to/from the storage element and to/from the electric machine side. Moreover, along with the fast growing interest in EVs and PHEVs, wireless charging, as a new way of charging batteries, has drawn the attention of researchers, car manufacturers, and customers recently. Compared to conductive power transfer (usually plug-in), wireless power transfer (WPT) is more convenient, weather proof, and electric shock protected. However, there is still more research work needs to be done to optimize efficiency, cost, increase misalignment tolerance, and reduce size of the WPT chargers. The proposed dissertation describes the work from 2012 to 2014, during the PhD course at the Electric Drives Laboratory of the University of Udine and during my six months visiting scholarship at the University of Michigan in Dearborn. The topics studied are related to power conversion and digital control of converters and drives suitable for hybrid/electric traction, generation from renewable energy sources and wireless charging applications. From the theoretical point of view, multilevel and multiphase DC/AC and DC/DC converters are discussed here, focusing on design issues, optimization (especially from the efficiency point-of-view) and advantages. Some novel modulation algorithms for the neutral-point clamped three-level inverter are presented here as well as a new multiphase proposal for a three-level buck converter. In addition, a new active torque damping technique in order to reduce torque oscillations in internal combustion engines is proposed here. Mainly, two practical implementations are considered in this dissertation, i.e. an original two-stage bi-directional converter for mild hybrid traction and a wireless charger for electric vehicles fast charge