Model Based Design of Robust Vehicle Power Networks

Abstract

Electrical power requirements for vehicles continue to increase. Future vehicle applications require the development of reliable and robust power supply strategies that operate over various ambient temperatures and driving conditions. Insufficient charge balance is one of the major concerns for conventional lead-acid battery systems when operated with limited charging times during short journeys or extreme climate conditions. For vehicle power supply analysis, a detailed understanding of the operational characteristics of the major components and how they interact as a part of the electric power system, including environmental and road conditions, is essential if the analysis is to aid system optimization. This paper presents a model based technique that enhances the process of vehicle electrical power system design. Vehicle system optimization using virtual prototypes has become critically important as more electrical features are added to future vehicles. Real vehicle data has been used to validate the models performance against specific design acceptance criteria. The validation measurements have been performed for different battery and ambient temperature conditions in order to demonstrate the accurate prediction of the simulation and modeling approach. TRENDS IN AUTOMOTIVE INDUSTRY The power consumption of vehicle electrical systems has increased dramatically over the last 10 years. Increased comfort and convenience features, electrification of existing mechanical systems and improved safety are some of the main trends that contribute to such an electrical power increase on any vehicle model design [1, 2, 3]. The increase of electrical power consumption suggests the need to evaluate its impact upon fuel consumption, emissions and driving performance. This is because increased electrical power consumption invariably leads to larger power supply components that increase vehicle Trends in automotive technology •Reduced fuel emissions •Improved fuel economy •Increased comfort and convenience •Improved safety Such trends require also more electrical power and increased battery durability •Investigation of different power supply techniques •Development of optimisation simulation techniques •Focus on managing major electrical loads, cranking requirements, quiescent currents and over -discharge situations •Increased Durability of Lead acid Calcium (Flooded) •Improvement of Existing Development of PMS or BMS Technologies e.g. Alternators • Figure 1: Trends in Automotive Technology weight and the power drawn from the engine. Automotive manufacturers such as Jaguar and Land Rover, often develop power management techniques and integrate various electronic components (battery monitoring systems etc.) to accommodate the increase of vehicle electrical power consumption whilst minimizing any adverse effect upon the electrical components and the whole vehicle. The development of dynamic simulation models that are based upon vehicle electrical systems provides a basis for analyzing complicated systems and predicting their performance and behavior when operating under a variety of different conditions. Modeling and simulation of various electrical power system configurations, combined with the development of new techniques for the optimization and control of a vehicle power network, can provide a competitive advantage to a vehicle manufacturer. Reduced manufacturing costs in terms of reduced delivery time of the product, improved engineering processes during development are some of the advantages that can be obtained from the use of new simulation models and techniques. Figure 1 illustrates the most important trends that are currently driving the automotive industry: VEHICLE ELECTRICAL CHARGING SYSTEM AND ITS RELEVANT COMPONENTS ARCHITECTURE OF VEHICLE POWER NETS Present vehicle electrical charging systems are usually divided into three major parts (storage battery, alternator, and electrical features/loads). The starter as a component and its associate wiring harness have not been taken into account in this development since the subject of this study is focused on simulations intended to investigate the battery charge balance of a vehicle under different ambient temperature and driving conditions. Figure 2 shows a schematic diagram of a vehicle charging system and how each part may be modeled as an equivalent circuit. Choosing and calibrating charging system components very early in the development phase of a vehicle program will avoid reliability issues from undersizing components and may prevent over-sizing the components which affects the overall cost of the vehicle in addition to increasing its fuel consumption and, sometimes, exhaust emissions. The ultimate design of an optimum charging system, which is appropriate for most operational conditions, is usually obtained through extensive charge balance experimental tests.