Panagiotis Lazari

A Computationally Efficient Design Technique for Electric-Vehicle Traction Machines

This paper describes a new design technique for electric-vehicle traction machines in order to achieve high efficiency against a defined driving cycle such as the New European Drive Cycle, while satisfying the required torque-speed operating range and other volumetric and thermal design constraints. This paper is undertaken as a part of the Personal Mobility Project funded by the European Union. By analyzing the energy distribution of a given driving cycle, the energy efficiency of the traction machine over the driving cycle can be characterized against a number of representative points, and the design optimization can be carried out with respect to these points. This dramatically reduces the computation time of the design optimization process, while improving the energy efficiency of the traction machines. The utility of the design technique has been illustrated through design case studies and its effectiveness validated by experimental results.

A High-Fidelity and Computationally Efficient Model for Interior Permanent-Magnet Machines Considering the Magnetic Saturation, Spatial Harmonics, and Iron Loss Effect

Interior permanent-magnet (IPM) machines exhibit relatively large spatial harmonics in phase voltages and high nonlinearity in torque production due to both the presence of reluctance torque and the magnetic saturation in stator and rotor cores. To simulate the real electromagnetic behavior of IPM machines, this paper proposes a high-fidelity and computationally efficient machine model considering the magnetic saturation, the spatial harmonics, and the iron loss effect based on the inverse solution of the flux linkages extracted via finite-element analysis (FEA). Neither FEA nor a derivative computation is involved in the time-stepping simulation; thereby, the proposed model is computationally efficient and numerically robust. The high fidelity of the proposed machine model is validated by both the FEA and the experimental results.

Optimizations of a permanent magnet machine targeting different driving cycles for electric vehicles

The paper assesses the influence of driving cycles on the design optimizations of permanent magnet machines for electric vehicle traction applications with the objective to minimize total loss over a defined driving cycle while satisfying performance specifications and design constraints. With the help of an efficient optimization methodology and tool, the optimizations against New European Drive cycle (NEDC), Artemis Urban Drive Cycle (Artemis), and the NEDC/Artemis combined cycle are carried out using Finite Element (FE) based technique. It is shown that for a surface mounted permanent magnet machine studied in the paper, the optimization results against the NEDC and Artemis exhibit distinct characteristics in terms of torque, speed, and energy loss distributions. Thus optimization trends for leading machine design parameters such as split ratio, stator tooth width, turn number per coil and magnet usage to minimize total loss for NEDC and Artemis are very different. For NEDC, the optimum design inclines to reduce high-speed copper loss and iron loss; for Artemis, it tries to minimize low-speed copper loss. Comparing the three optimized motors targeting different driving cycles, it is observed that they all have very high efficiency over a wide toque-speed range, and perform the best in their own target cycle, and with around 0.5% lower efficiency, or 10% higher loss in the other cycles with respect to the optimum values. Compared to the motor optimized for Artemis, the motors optimized against NEDC and the combined cycle result in close to 20% less magnets and less copper usage, making NEDC or the combined driving cycle a preferred optimization target.

Permanent Magnet Assisted Synchronous Reluctance Machine with fractional-slot winding configurations

This paper evaluates suitability of factional-slot winding configurations for Permanent Magnet Assisted Synchronous Reluctance Machine (PMA-SynRM) for applications in Electric Vehicle (EV) traction. Three typical factional-slot winding configurations, viz., concentrated nonoverlapping (12-slot 10-pole), conventional non-overlapping (12-slot 8-pole), and the overlapping (18-slot 8-pole) winding are employed for design of PMA-SynRM in order to improve power factor and torque density, and to reduce torque ripple and end-winding length over the conventional PMA-SynRM with distributed windings. All three machines are optimized against New European Drive Cycle (NEDC) efficiency via finite element analysis and thereafter compared quantitatively to evaluate their overall performance for EV traction applications. It is shown that PMA-SynRM with concentrated fractional-slot non-overlapping winding is more suited for in-wheel motor where the maximum speed is low, whilst the machines with the conventional fractional-slot non-overlapping winding and the fractional-slot overlapping winding exhibit high reluctance torque, high efficiency over a wide region and desirable flux weakening capability, thereby being attractive for high speed machines with reduction gear in EV traction applications.

A new Loss Minimization Algorithm for Interior Permanent Magnet Synchronous Machine drives

A new Loss Minimization Algorithm (LMA) for an Interior Permanent Magnet Synchronous Machine (IPMSM) drives is presented in this paper. Usually, IPMSMs efficiency is increased by minimizing the controllable loss such as copper or/and iron loss. However, the parameters of an IPMSM vary with operation conditions due to magnetic saturation, and the iron loss is highly non-linear, both of which increase the difficulties of searching the true minimum loss solution. A method of generating optimal currents look-up tables for IPMSM loss minimization with due account of the voltage drop on the stator windings resistor is proposed. The parameter variations due to saturation effects and a high fidelity iron loss model are employed to generate the look-up tables via an optimisation process. The utility of the loss minimisation algorithm is illustrated through simulation studies.

A Nine-Phase 18-Slot 14-Pole Interior Permanent Magnet Machine With Low Space Harmonics for Electric Vehicle Applications

One of the key challenges of utilizing concentrated winding in interior permanent magnet machines (IPMs) is the high rotor eddy current losses in both magnets and rotor iron due to the presence of a large number of lower and higher order space harmonics in the stator magnetomotive force (MMF). These MMF harmonics also result in other undesirable effects, such as localized core saturation, acoustic noise, and vibrations. This paper proposes a nine-phase 18-slot 14-pole IPM machine using the multiple three-phase winding sets to reduce MMF harmonics. All the subharmonics and some of the higher order harmonics are cancelled out, while the advantages of the concentrate windings are retained. The proposed machine exhibits a high efficiency over wide torque and speed ranges. A 10-kW machine prototype is built and tested in generator mode for the experimental validation. The experimental results indicate the effectiveness of the MMF harmonics cancellation in the proposed machine.

A High-Fidelity Computationally Efficient Transient Model of Interior Permanent-Magnet Machine With Stator Turn Fault

An accurate transient model of interior permanent-magnet (IPM) machine with stator turn fault with due account of magnetic saturation is essential to develop robust and sensitive interturn fault detection algorithms and to evaluate drive controller performance and stability under fault conditions. This paper proposes a general method of modeling stator turn fault using flux linkage map of IPM machine under fault extracted from finite-element (FE) analysis. Simulation results from the proposed fault model are compared against FE and experimental results. The results show that the proposed model matches well with experimental data.

A detailed transient model of Interior Permanent Magnet motor accounting for saturation under stator turn fault

The development of an accurate transient model of Interior Permanent Magnet (IPM) motor with stator turn fault with due account of magnetic saturation is essential to evaluate drive controller performance and stability under fault conditions, and to develop robust and sensitive inter-turn fault detection algorithms. The paper proposes a new semi-analytical model of IPM motor under stator winding inter-turn fault conditions. The model uses dq flux-linkage map of the healthy IPM motor derived from Finite Element (FE) model, and combines it with analytical equations of turn fault motor in the dq frame, to derive transient model for the motor with stator turn fault. Simulation results derived from the proposed fault model are compared against FE results of the turn faulted IPM motor. It is shown that the proposed model predicts with much better accuracy the peak currents and current wave shape when compared to the current state-of-art transient models.

A computationally efficient multi-physics optimization technique for permanent magnet machines in electric vehicle traction applications

This paper describes a computationally efficient optimization technique for permanent magnet machines in electric vehicle (EV) traction applications. It addresses multi-physics machine designs against driving cycles, including inverter-machine system energy efficiency, thermal behaviors and mechanical stress in rotor lamination. To drastically reduce computation time of repeated finite element analysis (FE) of the non-linear electromagnetic field and mechanical stress in permanent magnet machines especially interior permanent magnet machines (IPM), a set of analytical machine models characterized from FE calculations are developed which lead to significant reduction in computation time without compromising accuracy during an optimization. The proposed technique is applied to a multi-physics design optimization of an IPM machine for EV traction against 6-8 leading design parameters, and is validated by a series of tests on a prototype machine.