Modeling And Simulation Of A Permanent Magnet Synchronous Motor For Brake-By-Wire Technology In Automotive Applications

Abstract

The present paper approaches a three-phase Permanent Magnet Synchronous Motor (PMSM) analytical design, modeling and simulation for an electromechanical brake system in automotive applications. Analytical design of the electrical machine is validated by static simulation using JMAG-Studio, (a Finite element method based software). The Magnetic Equivalent Circuit (MEC) method is an accurate yet simple method for predicting the flux density distribution for iterative design procedures. The MEC technique gives fast (minutes) and acceptably accurate results. It provides a trade off between conventional, empirical methods, having fast simulation times, limited accuracy and flexibility, and the Finite Element Method (FEM), which requires long simulation times (hours), but offers high accuracy and flexibility. INTRODUCTION Electromechanical Brake (EMB) Electric actuation is one of the actual trends in the automotive industry, due to its high reliability, energy efficiency and controllability. The need for faster brake responding, better fuel economy, simplified system assembly, easy maintenance, more environmentally friendly and improved safety design has resulted in new Electro-Mechanical Braking System (EMB). EMB system has already begun replacing the hydraulic one. This not only reduces the weight of vehicles, but also has the potential for a large number of new features. In the EMB case (Fig.1), the idea presented is to replace completely the hydraulic system in order to transmit the commands through the wire. For that, the braking force is generated directly at each wheel by high-performance electric motors controlled by an Electronic Control Unit (ECU), and executed by signals from an electronic pedal module, which includes 4 intelligent braking actuators [10]. Electrical motor proposed for EMB actuation As a major issue in automotives is represented by the need for improved fuel efficiency and much more flexibility concerning latest technologies used in X-ByWire’s, the current 14 V bus has become insufficient. Therefore, car manufactures has come to the conclusion that the solution is to increase the voltage and implement a new 42 V bus in the system. Some aspects have to be considered during the design of the brake by wire drive systems: reliability, performance, thermal and acoustic behavior, energy efficiency and cost. Figure 1: System layout of an electromechanical brake These applications require high performance motors with high torque/volume ratio, low inertia, high dynamic, low torque pulsations and low radial forces. In this paper a surface-mounted PMSM has been considered as a driving motor for brake-by-wire application because it offers the advantage of low rotor inertia (provide high torque at lower rotational speed), high efficiency, convenient heat dissipation structure and reduction of the motor size [2], [4], [9]. DESIGN OF THE PROPOSED PMSM Analytical Design The analytical design of a PMSM is a complex process, which includes literature studying for adopting optimal design methods for different targets as obtaining a lighter prototype, a minimum cogging torque variation, a higher torque and low losses. Proceedings 25th European Conference on Modelling and Simulation ©ECMS Tadeusz Burczynski, Joanna Kolodziej Aleksander Byrski, Marco Carvalho (Editors) ISBN: 978-0-9564944-2-9 / ISBN: 978-0-9564944-3-6 (CD) A basic configuration of an EMB system was analyzed in order to establish the specification data and the demanded torque-speed curve for the PMSM. These requirements are given in Table 1 and Fig.2 presents the torque-speed characteristic of an electrical motor for EMB [6]. Table 1: General requirements for a PMSM used in EMB application in Automotives Parameter Units Value Peak stall torque Nm 3.0 Base speed 1/min 1000 Maximal speed 1/min 3000 DC-bus voltage V 42 Duty cycle S3-5% Environment temperature C degree 40...125 Figure 2: Torque vs. speed curve of an electrical machine for EMB In addition to these requirements, several constraints must be met. These constraints address limited size, lower weight, low torque ripple content, fault tolerance. A three-phase, four-pole surface mounted PMSM was chosen with the topology presented in Figure 3. The design starts with the set of initial data that includes the input parameters presented in Table 2, the material data of the magnet, iron and conductors. The main dimensions of the stator lamination and rotor core were computed via an analytical design procedure, following the input data [1], [5], [8]. First step in sizing the motor implies the estimation of the stator inner diameter using: