Analysis of Vehicle Power Supply Systems Using System Simulation

Abstract

Due to the introduction of new safety and comfort systems in modern automobiles, stability of the vehicle electrical system is increasingly important. The increasing number of electrical components demands that additional electrical energy be provided from robust, reliable supply sources in vehicles. When designing such systems, simulation is the development tool that is used to quickly obtain information regarding electrical system stability, battery charge level, and the distribution of power to the consumer systems. This paper describes how the Saber simulation environment from Synopsys Corporation helps develop increasingly demanding and complex vehicle power systems. A Volkswagen vehicle power net serves as an illustration. INTRODUCTION AND OBJECTIVES Automobiles do not have a constant energy supply nevertheless energy is required for starting the engine as well as for consumer systems that remain active when the engine is off. To supply this need, the battery serves as a storage device as well as a buffer. The battery has to deliver energy when there are peaks in the demand of consumption. These consumption peaks have increased by kilowatts in recent years, and this trend appears likely to continue into the foreseeable future. To increase battery life and optimally use existing resources, intelligent energy management (EM) algorithms are being introduced to ensure reliable, efficient energy and battery management. In addition, systems simulation is being turned to accelerate the development process since it provides a convenient way to quickly obtain information regarding electrical system stability, battery charge level, and the distribution of power to the consumer systems. Most importantly, simulation allows the performance of an automobile under different environmental conditions to be quickly and easily determined. Variations of ambient temperature, driving cycles or power consumption, and other dynamic factors can be easily simulated. However, the essential advantage of simulation is that it allows automobiles to be optimized at an early stage of development, before a prototype is produced. This advantage reduces time to market while delivering superior vehicles. Simulation also allows quick and easy development of energy management algorithms, as development is possible at a higher level of abstraction for the electronic control unit (ECU). Of course simulation models must be validated with conventional assessment methods, to help ensure that simulation results remain reliable. One application of simulation is energy balance simulation for quickly obtaining information about power net stability, battery charge level, and the distribution of power to conveniences for operator and passenger comfort without requiring a large amount of time for technical measurements. The following sections describe the necessary elements for designing a simulation model for automotive applications focussing on the analysis of overall electrical power consumption in the vehicle. Vehicle Equipment • Voltages • Currents • State of charge • Alternator utilization • EM validation Drive Cycle