Michele Degano

Sensitivity Analysis of Torque Ripple Reduction of Synchronous Reluctance and Interior PM Motors

The main drawback of reluctance machines is a high torque ripple, due to the interaction between the stator magneto-motive force and the rotor structure. Adopting a rotor configuration characterized by several flux barriers per pole, there is a high influence of the rotor geometry on the machine performance, in terms of both average torque and ripple. An optimization is often required to determine the optimal rotor geometry so as to achieve a high and smooth torque. Then, the geometry determined above should guarantee good performance for various operating points (i.e., changing the current amplitude and phase), as well as for small variations of the geometry. This paper investigates this aspect, showing the results of optimizations carried out on various machines. The impact of the geometry parameters is taken into account and the sensitivity of the optimal solution to the geometry variation is pointed out. The paper highlights the difficulty to get a robust geometry as far as the torque ripple reduction is concerned. Finally, a few experimental results on a Synchronous Reluctance motor prototype will be presented, compared with Finite Element Analysis simulations for validation.

Sensitivity analysis of torque ripple reduction of synchronous reluctance and interior PM motors

The main drawback of reluctance machines is a high torque ripple, due to the interaction between the stator magneto-motive force and the rotor structure. Adopting a rotor configuration characterized by several flux barriers per pole, there is a high influence of the rotor geometry on the machine performance, in terms of both average torque and ripple. An optimization is often required to determine the optimal rotor geometry so as to achieve a high and smooth torque. Then, the geometry determined above should guarantee good performance for various operating points (i.e., changing the current amplitude and phase), as well as for small variations of the geometry. This paper investigates this aspect, showing the results of optimizations carried out on various machines. The impact of the geometry parameters is taken into account and the sensitivity of the optimal solution to the geometry variation is pointed out. The paper highlights the difficulty to get a robust geometry as far as the torque ripple reduction is concerned. Finally, a few experimental results on a Synchronous Reluctance motor prototype will be presented, compared with Finite Element Analysis simulations for validation.

Selection Criteria and Robust Optimization of a Traction PM-Assisted Synchronous Reluctance Motor

In the coming years, the electrification and the deployment of the electric motors in the urban transports will become a more and more widespread reality. The optimization stage of the electric motors usually does not consider in detail the real driving conditions of the car in which the motor is installed. It follows that the actual motor performance in operating points, particularly as regards the torque ripple and the efficiency, might be worse than expected. A robust solution is a required target. This paper deals with the design and optimization of a high-speed permanent-magnet-assisted synchronous reluctance motor for traction applications, taking into account both city and highway driving cycles. A procedure is employed in order to evaluate the most representative operating points, which have to be considered when a global optimization is required. An analysis of the solution robustness has been performed. Both results and advantages of the adopted methodology are highlighted.

Improved Damper Cage Design for Salient-Pole Synchronous Generators

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions.

Permanent magnet volume minimization in permanent magnet assisted synchronous reluctance motors

In the recent years the study on new motor topologies for automotive applications has found an increasing interest. The environmental impact of conventional internal combustion engine, together with the increasing demand and the cost of the oil, are two of the main reasons that makes electric motors an attractive alternative. Machines that employ interior permanent magnet configurations are widely recognized as good performance motors for traction applications. On the other hands, the exponential increase of the price of rare earths magnets in the last years, is making rare earth motors a very expensive solution. This encourage the research of low cost, rare earth free alternatives, represented by the permanent magnet assisted synchronous reluctance machines. Three different magnet dimension configurations have been considered. This research highlights the influence and benefits of the insertion of ferrite on the machine performance, emphasizing the importance of a careful evaluation of the magnet quantity in order to optimize the performance and reduce the total cost.

End barrier shape optimizations and sensitivity analysis of synchrnous reluctance machines

This paper presents an extensive study on the electromagnetic and structural influences of the end barrier shape of a Synchronous Reluctance Machine (SynRel). One of the most challenging tasks in designing these machines is to achieve a smooth torque and a mechanically robust structure, especially when high operating speed range is required. Several papers have already addressed the electromagnetic design problem related to the choice of the flux barriers thicknesses and positions. However a comprehensive work on the influence of the end part of the flux barrier on the electromagnetic and structural performance has not been yet presented. In this work two end barrier shapes are considered and optimized using the same methodology. Then the optimized machines have been deeply analyzed in terms of torque, torque ripple and rotor von Mises stress distribution. Furthermore, with the aim to further investigate the influence of such end barrier shape, a detailed sensitivity analysis is presented. In conclusion, general guidelines for the structural and electromagnetic design of such end barrier shape are drawn.

Formula SAE electric competition: Electrical motor design

Electric mobility is becoming a growing reality due to increase of the demand and cost of oil and the environmental impact of conventional internal combustion engines. To follow this trend, national student competitions belonging to Formula SAE (Society of Automotive Engineers) series have been introduced for purely electric vehicles, in addition to those traditionally associated with internal combustion engine vehicles. On the other hand, the most promising and known electric motor candidates for traction application, represented by permanent magnet synchronous machines, are highly affected by the remarkable increase of the cost of rare earth magnet. For these reasons the research of rare-earth free alternatives, such as ferrite permanent magnet assisted synchronous reluctance motor, has potentially interesting implications especially in the perspective of industrial mass production. This paper shows the design criteria of ferrite permanent magnet assisted synchronous reluctance motors for a Formula SAE electric vehicle. The electromechanical performance have been evaluated and compared, in terms of torque and power. The most promising candidate has been finally compared with two equivalent size surface mounted permanent magnet machines: one is equipped with the same stator, while the second is characterized by a fractional slot concentrated winding. Finally, this research provides a brief description of the electric supply system in order to accurately and efficiently manage the motors for achieving the requested performance.

Robust optimization of a traction PMASR motor according to given driving cycles

In the coming years, the electrification and the deployment of the electric motors in the urban transports will become a reality more and more widespread. The optimization stage of the electric motors usually does not consider in detail the real driving conditions of the car in which the motor is installed. It follows that the actual motor performance in operating points, especially as regards the torque ripple and the efficiency, might be worsen than expected. A robust solution is a required target. This paper deals with the design and optimization of a high speed permanent magnet assisted synchronous reluctance motor for traction applications, according to both city and highway driving cycles. A procedure is employed in order to evaluate the most representative operating points, which have to be considered for the global optimization. An analysis of the robustness of the solutions has been performed. Both results and advantages of the adopted methodology are highlighted.

PM synchronous machine comparison for light electric vehicles

The research of rare-earth free alternatives, such as ferrite, hot pressed NdFeB Permanent Magnet Assisted Synchronous Reluctance (PMASR) motor or pure reluctance motor, has potentially interesting implications especially in the perspective of industrial mass production. This paper shows the comparison between a sintered NdFeB PMASR, ferrite PMASR, Synchronous Reluctance (REL) and a Surface mounted PM (SPM) machines with the same overall dimensions, winding arrangement and power supply size. The electromechanical performance have been evaluated and compared, in terms of torque and power. Finally, this research provides a description of the electric supply system in order to accurately and efficiently manage the motors for achieving the requested performance.

Distributed current control for multi-three phase synchronous machines in fault conditions

Among challenges and requirements of on-going electrification process and future transportation systems there is demand for arrangements with both increased fault tolerance and reliability. Next aerospace, power-train and automotive systems exploiting new technologies are delving for new features and functionalities. Multi-three phase arrangements are one of these novel approaches where future implementation of aforementioned applications will benefit from. This paper presents and analyses distributed current control design for asymmetrical split-phase schemes composed by symmetrical three phase sections with even number of phases. The proposed design within the dq0 reference frame in nominal, open and short circuit condition of one three-phase system is compared with the vector space decomposition technique and further validated by mean of Matlab/Simulink® simulations.