A Direct Drive System With Fuzzy Anti Skid Controller For Electric Vehicles

Azmi Demirel R.Nejat Tunçay

Faculty of Electrical and Electronics Engineering

Istanbul Technical University

Istanbul, 80626 TURKEY

Abstract

In this study, a direct drive system with anti-skidding ability for electric cars is proposed. This system is based on switched reluctance motors and fuzzy logic control. A switched reluctance motor and its hybrid power electronic converter are designed at first. Then a fuzzy rule base is constructed and drive system's computer simulation is achieved. A PC based digital fuzzy logic controller software and necessary enviromental hardware are realized and some experimental results are obtained. The simulation and experimental results show that the developed system succesfully drives the wheels and effectively prevents the system from skidding.

1 Introduction

During the past decade, there has been extensive research activities on electric vehicles (EV). Basically there are two main drive schemes for EV's. In the first group, the motor control technology involves to rotate the main shaft of the vehicle, similar to the combustion engine driven vehicles where power is transmitted to the wheels through a mechanical differential. The second group which is called direct drive, wheels are driven directly by the motors. Among these, brushless d.c. and switched reluctance motors with some unconventional topologies are worth to mention.

Direct drive offers various advantages. Elimination of the mechanical differential gearbox reduces the weight and the mechanical power losses and improves the overall efficiency. However, there are certain disadvantages as well. Since each wheel is driven individually, their torque and speed should be regulated continuously. It is also necessary to sustain the stability of the car even it is travelling on a flat road. Anti-skid control is another parameter for uneven slippery roads. As a result, control is complex with higher cost and lower reliability.

2 Proposed system

The objective of this study is to develop a mechanical differentialless direct-drive schedule for electric vehicles. First the theoretical study is attempted. The switched reluctance motors is chosen for driving the rear wheels. In the first part of the study the mathematical simulation model of the whole system is formed by using the MATLAB-SIMULINK software. The torque of SRM is proportional with the square of current and the constant current drive is only possible for low speed cases. Since back e.m.f. of the motor becomes dominant at high speeds, current is not constant and it is necessary to employ firing advance scheme or dwell angle widening techniques. Altough our model is capable to take these techniques into account but it is not found to be necessary since wheels are driven directly thus motor speed is low.

2.1 Motors

A 12/8 pole switched reluctance motor is designed to drive the each rear wheel by using classical design procedures. The nominal torque of the each SRM is calculated from a standard internal combustion engine's maximum output torque value of an ordinary car. The results of the design are not the best values for the minimum weight, cost and maximum efficiency but they are the starting values of an optimisation process.

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