Research On Permanent Magnet BLDC for small electric vehicle

In this paper, different electric motors are studied and compared to see the benefits of each motor and the one that is more suitable to be used in the electric vehicle (EV) applications. There are five main electric motor types, DC, induction, permanent magnet synchronous, switched reluctance and brushless DC motors are studied. It is concluded that although the induction motors technology is more mature than others, for the EV applications the brushless DC and permanent magnet motors are more suitable than others. The use of these motors will result in less portion, less fuel consumption and higher power to volume ratio. The reducing prices of the permanent magnet materials and the trend of increasing efficiency in the permanent magnet and brushless DC motors make them more and more attractive for the EV applications. This paper first describes the main features of BLDC control methods, then after comparison it’s parameters will be controlled using Field Oriented Control or Vector control method. INTRODUCTION Permanent Magnet (PM) motors are nowadays regarded as an interesting solution for variablespeed drives which are faded with all ranges of inverters. The interest in these motors has been increased because of their feasibility for vehicle propulsion. Consequently, they are also of good for small electric drives applications. The most important advantages that are expected in comparison to the asynchronous motors are lower losses and a higher torque density. The thesis presents the study and the design analysis of a permanent magnet brushless dc motor for small vehicle drive. Various aspects of the design of PM motor drives are under consideration with special attention to the requirement of maximum torque and field weakening concepts among all these aspects particularly, the sensor-less control or vector control without a mechanical rotor position sensor, is considered in this paper. The term sensorless does not represent the lack of sensors entirely, but the fact that in comparison with other drives from the same category of FOC, it denotes that the speed and/or position sensor is missing. This feature decreases the cost of the drive system which is always desired, but this is not the only reason for this approach, as some applications have requirements concerning the size and lack of additional wiring for sensors or devices mounted on the shaft (due to hostile environments such as high temperature, corrosive contacts e.t.c.).So the field oriented control (FOC) technique of sensor less control is used in this paper. An advantage of FOC is that it is a less complex algorithm and as it is a vector control technique so angle of the rotor can also be identified along with the magnitude. As in case of motor the frequency, amplitude, toque and angle of rotation matters so all these purposes can be easily solved with the use of FOC. The scope of the paper is to simulate the FOC. The so called brushless DC (BLDC) motors are broadly used as actuators. PERMANENTMAGNET (PM) motors have been the choices for electrical vehicle (EV) applications due to their high efficiency, compact size, high torque at low speeds, and ease of control regenerative breaking [5]. Since the permanent magnet synchronous motor has the feature of small size, high efficiency and superior reliability, it is widely used in many important areas such as modern industrial automation, military, chemical industry, aviation and aerospace [1-4]. PM motors with higher power densities are also now increasingly choices for aircraft, marine, naval, and space applications. Permanent magnet brushless motors for electric vehicles are presently given an increasing attention. With this trend, this paper deals with an interior permanent magnet (IPM) brushless DC motor (BLDCM). In this work, the simulation of a field oriented controlled Permanent Magnet Brushless DC (PMBLDC) motor drive system is developed using Simplorer. For simplicity purpose the Simplorer software is used in this thesis. The simulation circuit will include all realistic components of the drive system. This enables the calculation of currents and voltages in different parts of the inverter and motor under transient and steady state conditions. A closed loop control system with a PI controller in the speed loop has been designed to operate in constant torque and flux weakening regions. Implementation has been done in Simplorer. A comparative study of hysteresis and PWM control schemes associated with Space Vector Modulation (SVM) has been made in terms of Harmonic spectrum and to the harmonic distortion. Simulation results are given for two speed of operation, one below rated and another above rated speed. Control Techniques A wide range of control algorithms are available: Figure A. Control Techniques 1. Trapezoidal control: Also known as six-step control, this is the simplest algorithm. For each of the six commutation steps, a current path is formed between a pair of windings, leaving the third winding disconnected. This method generates high torque ripple, leading to the vibration, noise, and poorer performance compared to other algorithms. 2. Sinusoidal control: Also known as voltage-over-frequency commutation, sinusoidal control it overcomes many of the issues involved with trapezoidal control by supplying smoothly (sinusoidal) varying current to the 3 windings, thus reducing the torque ripple and offering a smooth rotation. However, these time-varying currents are controlled using basic PI regulators, which lead to poor performance at higher speeds. 3. Field Oriented Control (FOC): Also known as vector control, FOC provides better efficiency at higher speeds than sinusoidal control. It also guarantees optimized efficiency even during transient operation by perfectly maintaining the stator and rotor fluxes. FOC also gives better performance on dynamic load changes when compared to all other techniques. 4. Scalar control: Scalar control (or V/Hz control) is a simple technique to control speed of induction motor. In this paper Vector Control or Field Oriented Control (FOC) is used because of it’s following advantages Transformation of a complex and coupled AC model into a simple linear system  Independent control of torque and flux, similar to a DC motor  Fast dynamic response and good transient and steady state performance  High torque and low current at start-up