Multi-body Dynamic Modeling of Electric Vehicle with In-wheel Motors for Motion Control Study

Abstract

The world is undergoing alarming environmental hazards including air pollution, water pollution, noise pollution and energy crisis. Fossil fuel resources are depleting, and fuel prices are surging uncontrollably. Across the world, air quality index (AQI) in some cities has increased to more than thrice of the normal range. The world is concerned about the future of planet earth and the mankind. For the sake of environmental health and safety, United Nations has launched many programs and several conferences have been held to discuss the environmental hazards and their solutions. As transportation sector is one of the biggest contributors of Green House Gases GHGs in the air, a sustainable solution is required to replace the currently used vehicles. Green Energy is the ultimate solution as electric vehicles are run through battery and motors therefore, they have zero emissions and therefore several countries have planned to completely replace fossil fuel cars with electric vehicles in near future. Electric vehicle technology has a promising future in the world of transportation sector. Pakistan Electric Vehicle Policy was passed in 2019 and has set short- and long-term targets for penetration of different types of electric vehicles in the market. In Pakistan, the replacement of Fossil Fuel Vehicles FFVs offers more benefits than just the environmental safety. It will ensure decreased fuel import bills and EVs will use the idle capacity available in the national electricity grid due to intra-day and seasonal variations, for which government is already paying hefty amount, thus reducing the idle capacity payments. Furthermore, a whole new industry will be developed, and Pakistan may get able to improve its export sector as well. This new industry will also ensure many employment opportunities. In addition to environmental, economic, and industrial benefits, electric vehicles ensure better performance in terms of vehicle controls. As electric vehicle mechanism is simple and involves fewer parts, torque generation is fast and more accurate and thus ensure a safer driving experience for the driver and passengers. In our study, we have developed models for an electric vehicle with two in-wheel motors in the rear wheels. This way the torque on both the wheels can be controlled separately and differential braking and driving can be ensured. Then we developed control mechanism for preventing the most fatal road accident, i.e., vehicle rollover. We used the concept of artificial potential field to develop an algorithm which helps mitigate the propensity of vehicle rollover. Instead of changing the values of yaw rate in order to decrease the lateral acceleration of the vehicle, we have adopted an approach where vehicle is decelerated if it reaches a predefined limit of lateral acceleration. As lateral acceleration is a product of vehicle speed and yaw rate, by decelerating the vehicle lateral acceleration can be controlled, hence preventing the rollover. Vehicle’s longitudinal and lateral accelerations are coupled through a g-g diagram and limiting value of lateral acceleration beyond which the vehicle may roll over is represented by a vertical line on the diagram. As soon as the lateral acceleration reaches this value, a force will be applied which will tend to decelerate the vehicle and keep it under the limiting value of lateral acceleration by decreasing the longitudinal acceleration of the vehicle. This algorithm for control mechanism is developed in MATLAB Simulink while the vehicle modelling is done in TruckSim Software. The control concept is evaluated on the TruckSim model and found to be efficient for rollover stability.