S. I. Brand, N. Ertugrul and W.L. Soong University of Adelaide School of Electrical and Electronic Engineering Adelaide, Australia Abstract
Electric assisted bicycles are commercially available. However they are generally expensive or involve an inefficient drive mechanism. This paper examines andrealizes an alternative design for a front wheel hub direct drive, which utilizes a three-phase brushless PM motor. This study aims to provide reference information for minimal modification to convert a conventional bicycle and for the sizing of the power source and the motor drive. In the paper, the details of the dynamometer test setup is given. In addition, test results (riding cycles) areprovided using a mobile data acquisition system that can be used to optimize the sizing the battery and the motor as well as providing valuable information about the power management and programmed drive patterns for the motor controller.
Electric bicycles have been around for as long as automobiles . Currently, the electric bicycle is experiencing a “coming of age” , primarilybecause of low emission transportation alternative in large cities and for various reasons, such as convenient parking spots, shortcuts, point-to-point transportation. Furthermore, certain sectors of the population recognize the electric assisted bicycle as an excellent source of physical exercise with on-demand power source. The power assist allows riders to travel greater distances and overchallenging topography. Since the electrical assistance is controlled by the rider and may be used continuously or at the rider’s discretion, this feature of the bike broadens the areas of applications (such as in law enforcement in metropolitan areas). Although the conventional bicycles are efficient and well-understood machines, the electric versions have had limited commercial success over the pastcentury, which is largely due to the limited cruising features and higher cost. It is envisaged that by using efficient motor drives and applying power electronics and advance control technologies, this trend will be reversed in the near future. Therefore, the primary focus in this paper is to offer a cost effective solution for the electric bicycles. In addition, the paper demonstratescomprehensive testing procedures to understand the behaviour of the bicycles under real driving conditions. Due to the lack of data on long distance human cycling power for extended periods, the aim of the paper is to provide knowledge to develop control and power management strategies for the entire system. In the study, the overall
efficiency, driving conditions and rider’s choice will also beconsidered. The test results can be used to implement various electric assisted riding patterns and for power management and battery sizing. Furthermore, the paper examines the features of the existing technologies and realizes an alternative design for a front wheel hub direct drive, which aims to provide a benchmark for minimal modification to convert a conventional bicycle.
2. COMPONENTS OFELECTRIC BICYCLES
An electric bicycle essentially has four components: motor, power transmission system, control system and power source.
Two different motor types are commonly accommodated in electric bicycles: brush DC motor and brushless PM synchronous motor with trapezoidal back emf (also known as brushless DC motor). Three key features are considered in the selection of a motor :higher efficiency, minimum maintenance and higher power density, which are the characteristics of brushless DC motors. In most countries, if the power output rating of the motor does not exceed 200W, no license or registration is required. In addition, legislations are in place to limit the speed of the electric bicycles (to 15-20km/h), which is directly proportional to the speed of the motors....