Adrian-Cornel Pop

Comparative study of different torque sharing functions for losses minimization in Switched Reluctance Motors used in electric vehicles propulsion

In this paper the authors present a comparison between optimised versions of three torque sharing functions, with different number of degrees of freedom, used for improving the efficiency in Switched Reluctance Motors. Starting from the basic rectangular variation, the ascending and descending flanks of the function are modeled using a cosine, exponential and a more general approach (further referred to as piecewise cubic sharing function). The degrees of freedom varying between two and an arbitrary number (for the general approach) are determined so as to minimize losses, when operating in smooth torque conditions. Based upon an optimisation procedure with both linear and nonlinear constraints, the total (copper and iron) losses are minimized considering a limited available DC bus voltage. Moreover, a smooth model is presented so as to be able to separate the two main causes for the torque ripple and it is shown that, neglecting the chopping ripple, a ripple-free torque can be obtained. Extensive studies have been conducted for determining the optimal number of degrees of freedom (DoFs) for the piecewise cubic function. The proposed methods were successfully implemented on a 8/6, 30kW peak power, SRM both numerically and experimentally-wise.

Direct instantaneous torque control of SRMs versus current profiling — Comparison regarding torque ripple and copper losses

This paper presents the implementation of an instantaneous torque control technique named Direct Instantaneous Torque Control (DITC) on a 4-phase, 8/6, 30kW peak-power Switched Reluctance Machine (SRM) used for electric vehicle traction. On-line instantaneous torque estimation methods and the principles of the DITC are discussed. Simulation and experimental results are presented in the paper and a comparative study with current profiling techniques using three different torque-sharing functions is made.

Switched Reluctance Machine Drives for electrical vehicle propulsion - optimal control with regard to the losses in machine and converter

This paper deals with the losses of Switched Reluctance Machine Drives (SRDs) for electric vehicle propulsion, consisting of the losses in the Switched Reluctance Machine (SRM) and the converter, across some operating regions based on different control strategies, namely Firing Angle (FA) control and Torque Sharing Function (TSF) control. The SRM model which takes into account copper losses and converter losses is obtained through MATLAB/Simulink. The losses and efficiencies in the machine, the converter and the SRD as function of speed and average torque are compared for a 30 kW peak 8/6 SRD.

Direct torque control of a 4-phase Switched Reluctance Machine

Due to its doubly salient structure and highly nonlinear behavior, the Switched Reluctance Machine (SRM) operates with very high torque ripple. To overcome these inconveniences different average and instantaneous torque control techniques were developed. This paper presents an instantaneous torque control technique named Direct Torque Control (DTC) implemented on a 4-phase, 8/6, 0.75kW SRM. Simulations results with modified flux observer and with fast torque response are presented and discussed, along with experimental results. A discussion on choosing the switching vectors for machines with both odd and even phase number is made.

Considering half bridge converters for switched reluctance motor drive applications

The aim of the paper is to present an option of using regular half-bridges topology converters for independent driving of multi-phases switched reluctance motors (SRMs). The possibility of using a well-known and accepted topology could represent a cost-related, self-assured and more-efficient way of addressing at least some of the issues regarding the SRM acceptance in practical implementations. In this paper, the general approach, working principles, the first developments and analyses are introduced. Numerical simulations have been done considering the whole drive and the differences between the conventional and the studied converters are highlighted, when applying the converters output voltages to a three-phase 6/4 SRM.

Optimization of Low-Power Brushless PM-Machines for Automotive Applications With Focus on High-Volume Mass Production

This paper deals with the optimization for performance and cost of the low-power permanent magnet synchronous machines used in automotive applications with focus on particularities of high-volume mass production and the constraints that arise. The described optimization loop is used to compare different 12/8 and 12/10 designs of interior permanent magnet (IPM) type. After showing that the 12/10 IPM exhibits the best performance–cost ratio, results obtained at different stages in the process (i.e., sensitivity analysis and constrained single-/multiobjective optimizations), for both no-load and load case, are provided. Finally, different aspects for reducing the complexity of the multidomain optimization problem (e.g., 3-D effects, iron losses, and effects of tolerances on the motor characteristics) are addressed.

Design of induction motor for electric power-assisted steering systems

This paper presents a perspective regarding the design concepts of a small induction machine used for electrical steering systems. The particularity of this view is given by the fact that besides the output imposed parameters the geometrical dimensions are subject to major constraints. In these conditions there are some theoretical aspects that limit from the start the design choices that can be made. After approaching the design from the theoretical point of view, a numerical analysis which validates the choices made in that stage is done. A comparison between possible solutions gives a better view on the possible use of the induction machine for this kind of application.

Magnet-based vs. magnet-free electrical machines for low power automotive applications

In his paper he authors present a comparison between magnet-based and magnet-free motors for an oil pump used in automotive applications. From the first category, two inset permanent magnet (IPMs) synchronous motors are chosen whereas the later group of motors is represented by a double stator switched reluctance machine (DS-SRM). The three-phase 12s/8p and 12s/10p IPMs are compared with the four-phase 16/12 DS-SRM in terms of torque capability, power density, efficiency and cost of active materials. Comparisons were conduced both at room and high temperature and assuming two different values for the DC-bus voltage: 12V and 48V. Some rather general remarks are done about the noise vibration and harshness problems (NVH) ha an electrical machine for automotive applications designer has to deal with.

Wide-speed range control strategy for a 8/6 switched reluctance machine

A control scheme for obtaining low torque ripple and high efficiency for a minimal reduction in average torque as compared to its maximal value is presented for a four-phase switched reluctance motor. At low speed, the torque ripple is minimized by the means of current profiling techniques. As the speed increases the controller switches to optimal firing angle control strategy. The optimal values for the angles are obtained based on minimization routine for different objective functions. Starting from the one variable functions (average torque) step by step, penalties are added for improving the ripple content and eventually the efficiency. The effects of using local and global minimizers are outlined and comparative results are given. Experimental results obtained on a 0.75kW SRM are provided and discussed.

dq0-modeling of interior permanent-magnet synchronous machines for high-fidelity model order reduction

This paper presents a dq0 flux-linkage based electrical model for permanent-magnet synchronous machines. To obtain the relationship between dq0 flux-linkages and currents, a series of magnetostatic finite-element calculations for various dq0 currents at different rotor positions is carried out. This dataset has then to be inverted to avoid having to derive the flux-linkages in Simulink, thus improving the numerical stability of the model. The model was validated using a 12/10 delta- and star-connected fractional-slot concentrated-winding permanent magnet synchronous machine presenting 3rd-order harmonics in the back-emf. Results show that considering only a fraction of the rated current for the 0-sequence component allows to take circulating currents in a delta-connected machine into account, improving the accuracy of the model compared to a model based on the d-and q-axis alone. Torque and qd0 current waveforms resulting from the presented model are comparable to the ones obtained with finite-element both in terms of average value and harmonic content.