Evaluation of a switched reluctance motor for solar vehicle application

Abstract

The impact of global warming forces the world to develop environmentally sustainable solutions. Common practices for sustainable machines include renewable energy sources and biofuels. The automotive industry is determined to combat environmental problems by investing significantly in the research and development of electric vehicles. The development of electric vehicles using renewable energy sources are promoted by various universities competing in solar races. Solar racing uses vehicles powered from the sun to propel the vehicle. Solar energy is used as an alternative fuel source to charge a battery that provides energy for the electric motor. The first solar race was the Tour the Sol in Switzerland held in 1985 which led to several similar races. Today, solar racing is a highly competitive sport entered by universities to develop the engineering and technological skills of their students. The North-West University frequently competes in the Sasol Solar Challenge; therefore, this study aims to evaluate a switched reluctance motor for solar vehicle application. The switched reluctance motor is believed to be a possible candidate for the next-generation traction motor in electric vehicles. Although the switch reluctance motor originated in the 1850s, the 20th century brought revival to the switched reluctance motor with the improvements made in power electronics, power switches, magnetic materials, and various electric motor design simulation tools and methods. In this study, an un-optimised exploratory development model of a modular switched reluctance motor was designed instead of evaluating an off the shelf switched reluctance motor. The idea of using a modular structure instead of a conventional structure was chosen on the basis of performance and efficiency. The exploratory development model of the modular switched reluctance motor was simulated using numerical simulation software. Using the numerical simulation software, an efficiency map was constructed to evaluate the motor model using a drive cycle. The drive cycle was constructed to typically represent a solar race. The drive cycle consisted of a closed-loop route, in which the traction motor propelled the solar vehicle for eight hours using only the energy from the sun. Solar energy was extracted from the sun using a photovoltaic array. By driving the solar vehicle through the drive cycle, the total driving distance was evaluated for the eight-hour operating period.

To justify the switched reluctance motor as a possible candidate for solar vehicle application, a brushless direct current motor, currently used as the traction motor in the solar vehicle of the North-West University was evaluated as the expected reference point for motor performance. When comparing the switched reluctance motor with the brushless direct current motor, the switched reluctance motor managed a total driving distance of 375.98 km, 23 km less than the total driving distance achieved by the brushless direct current motor. Therefore, the switched reluctance motor operated at lower efficiency. Thus, more energy was used by the switched reluctance motor to maintain the same torque and speed operations as the brushless direct current motor. Although the modular switched reluctance motor did not improve the travelling distance set by the brushless direct current motor, the proposed switched reluctance motor has future potential. The modular switched reluctance motor can be designed for optimised efficiency when modifying the construction, geometric parameters or magnetic materials. Another method is to use a motor controller, designed to work with the modular switched reluctance motor that can improve efficiency over its operating range. In the conclusion of this study it was shown that an un-optimised exploratory development model of a switched reluctance motor used as a traction motor for solar vehicle application is justified for future development studies. Optimising and improving the exploratory development model of the switched reluctance motor will improve its torque, speed and efficiency, such that the achievable total driving distance could be equivalent or extended when compared to the brushless direct current motor. Only after a design is obtained that shows improved efficiency compared to the brushless direct current motor shall the manufacturing of a prototype be justified.