Keith Wipke

ADVISOR 2.1: a user-friendly advanced powertrain simulation using a combined backward/forward approach

ADVISOR 2.1 is the latest version of the National Renewable Energy Laboratorys advanced vehicle simulator. It was first developed in 1994 to support the US Department of Energy hybrid propulsion system program and is designed to be accurate, fast, flexible, easily sharable, and easy to use. This paper presents the model, focusing on its combination of forward- and backward-facing simulation approaches, and evaluates the model in terms of its design goals. ADVISOR predicts acceleration time to within 0.7% and energy use on the demanding US06 to within 0.6% for an underpowered series hybrid vehicle (0-100 km/h in 20 s). ADVISOR simulates vehicle performance on standard driving cycles between 2.6 and 8.0 times faster than a representative forward-facing vehicle model. Due in large part to ADVISORs powerful graphical user interface and Web presence, over 800 users have downloaded ADVISOR from 45 different countries. Many of these users have contributed their own component data to the ADVISOR library.

ADVISOR: a systems analysis tool for advanced vehicle modeling

This paper provides an overview of Advanced Vehicle Simulator (ADVISOR)—the US Department of Energy’s (DOE’s) ADVISOR written in the MATLAB/Simulink environment and developed by the National Renewable Energy Laboratory. ADVISOR provides the vehicle engineering community with an easy-to-use, flexible, yet robust and supported analysis package for advanced vehicle modeling. It is primarily used to quantify the fuel economy, the performance, and the emissions of vehicles that use alternative technologies including fuel cells, batteries, electric motors, and internal combustion engines in hybrid (i.e. multiple power sources) configurations. It excels at quantifying the relative change that can be expected due to the implementation of technology compared to a baseline scenario. ADVISOR’s capabilities and limitations are presented and the power source models that are included in ADVISOR are discussed. Finally, several applications of the tool are presented to highlight ADVISOR’s functionality. The content of this paper is based on a presentation made at the ‘Development of Advanced Battery Engineering Models’ workshop held in Crystal City, Virginia in August 2001. # 2002 Elsevier Science B.V. All rights reserved.

HEV Control Strategy for Real-Time Optimization of Fuel Economy and Emissions

Hybrid electric vehicles (HEV’s) offer additional flexibility to enhance the fuel economy and emissions of vehicles. The Real-Time Control Strategy (RTCS) presented here optimizes efficiency and emissions of a parallel configuration HEV. In order to determine the ideal operating point of the vehicle’s engine and motor, the control strategy considers all possible engine-motor torque pairs. For a given operating point, the strategy predicts the possible energy consumption and the emissions emitted by the vehicle. The strategy calculates the “replacement energy” that would restore the battery’s state of charge (SOC) to its initial level. This replacement energy accounts for inefficiencies in the energy storage system conversion process. Userand standards-based weightings of time-averaged fuel economy and emissions performance determine an overall impact function. The strategy continuously selects the operating point that is the minimum of this cost function. Previous control strategies employed a set of static parameters optimized for a particular drive cycle, and they showed little sensitivity to subtle emissions tradeoffs. This new control strategy adjusts its behavior based on the current driving conditions. Simulation results of the RTCS and of a static control strategy on a PNGV-type baseline parallel HEV (42 kW engine and a 32 kW motor) using ADVISOR are presented. Comparison of the simulations demonstrates the flexibility and advantages of the RTCS. Compared to an optimized static control strategy, the RTCS reduced NOx emissions by 23% and PM emissions by 13% at a sacrifice of only 1.4% in fuel economy.

Analysis of the fuel economy benefit of drivetrain hybridization

Parallel- and series-configured hybrid vehicles likely feasible in next decade arc defined and evaluated using NRELs flexible ADvanced VehIcle SimulatOR ADVISOR. Fuel economics of these two diesel-powered hybrid vehicles are compared to a comparable-technology diesel- powered internal-combustion-engine vehicle. Sensitivities of these fuel economies to various vehicle and component parameters are determined and differences among them are explained. The fuel economy of the parallel hybrid defined here is 24% better than the internal- combustion-engine vehicle and 4% better than the series hybrid.

Advisor 2.0: A Second- Generation Advanced Vehicle Simulator for Systems Analysis

The National Renewable Energy Laboratory has recently publicly released its second-generation advanced vehicle simulator called ADVISOR 2.0. This software program was initially developed four years ago, and after several years of in-house usage and evolution, the tool is now available to the public through a new vehicle systems analysis World Wide Web page. ADVISOR has been applied to many different systems analysis problems, such as helping to develop the SAE J1711 test procedure for hybrid vehicles and helping to evaluate new technologies as part of the Partnership for a New Generation of Vehicles (PNGV) technology selection process. The model has been and will continue to be benchmarked and validated with other models and with real vehicle test data. After two months of being available on the Web, more than 100 users have downloaded ADVISOR. ADVISOR 2.0 has many new features, including an easy-to-use graphical user interface, a detailed exhaust aftertreatment thermal model, and complete browser-based documentation. Future work will include adding to the library of components available in ADVISOR, including optimization functionality, and linking with a more detailed fuel cell model.

Modeling grid-connected hybrid electric vehicles using ADVISOR

The overall system efficiency of a hybrid electric vehicle is highly dependent on the energy management strategy employed. In this paper, an electric utility grid-connected energy management strategy for a parallel hybrid electric vehicle is presented. ADVISOR was used as a modeling tool to determine the appropriate size of the hybrid components and the energy management strategy parameter settings. Simulation results demonstrated that with this strategy it is possible to achieve double the fuel economy of a comparable conventional vehicle while satisfying all performance constraints. In addition, the final vehicle design provides an all-electric range capability in excess of 20 miles.

Modeling and Validation of a Fuel Cell Hybrid Vehicle

This paper describes the design and construction of a fuel cell hybrid electric vehicle based on the conversion of a five passenger production sedan. The vehicle uses a relatively small fuel cell stack to provide average power demands, and a battery pack to provide peak power demands for varied driving conditions. A model of this vehicle was developed using ADVISOR, an Advanced Vehicle Simulator that tracks energy flow and fuel usage within the vehicle drivetrain and energy conversion components. The Virginia Tech Fuel Cell Hybrid Electric Vehicle was tested on the EPA City and Highway driving cycles to provide data for validation of the model. Vehicle data and model results show good correlation at all levels and show that ADVISOR has the capability to model fuel cell hybrid electric vehicles.

Use of unglazed transpired solar collectors for desiccant cooling

The use of unglazed transpired solar collectors for desiccant regeneration in a solid desiccant cooling cycle was investigated because these collectors are less expensive than conventional glazed flat-plate collectors. Using computer models, we studied the performance of a desiccant cooling ventilation cycle integrated with either unglazed transpired collectors or conventional glazed flat-plate collectors. We found that the thermal coefficient of performance of the cooling system with unglazed collectors was lower than that of the cooling system with glazed collectors because the former system did not use the heat of adsorption released during the dehumidification process. Although the area required for the unglazed collector array was 70% more than that required for the glazed collector array in a 10.56 kW (3 ton) solar cooling system, the cost of the unglazed array was 45% less than the cost of the glazed array. The simple payback period of the unglazed collector was half of the payback period of the glazed collector when replacing an equivalent gas-fired air heater. Although the use of unglazed transpired collectors seems to make economic sense relative to use of glazed conventional collectors, some practical considerations may limit their use for desiccant regeneration.

Vehicle System Impacts of Fuel Cell System Power Response Capability

The impacts of fuel cell system power response capability on optimal hybrid and neat fuel cell vehicle configurations have been explored. Vehicle system optimization was performed with the goal of maximizing fuel economy over a drive cycle. Optimal hybrid vehicle design scenarios were derived for fuel cell systems with 10 to 90% power transient response times of 0, 2, 5, 10, 20, and 40 seconds. Optimal neat fuel cell vehicles where generated for responses times of 0, 2, 5, and 7 seconds. DIRECT, a derivative-free optimization algorithm, was used in conjunction with ADVISOR, a vehicle systems analysis tool, to systematically change both powertrain component sizes and the vehicle energy management strategy parameters to provide optimal vehicle system configurations for the range of response capabilities.

FCV Learning Demonstration: Project Midpoint Status and First-Generation Vehicle Results

The “Controlled Hydrogen Fleet and Infrastructure Demonstration and Validation Project,” also known as the Fuel Cell Vehicle and Infrastructure Learning Demonstration, is a 5-year U.S. Department of Energy (DOE) project started in 2004. The purpose of this project is to conduct an integrated field validation that simultaneously examines the performance of fuel cell vehicles and the supporting hydrogen infrastructure. Four industry teams are currently operating more than 77 vehicles and 14 refueling stations, with plans to add over 50 additional vehicles and several additional refueling stations during the remainder of the project duration. This paper covers the progress accomplished by the demonstration and validation project since inception, including results from analysis of six months of new data. With three sets of public results having been presented previously, this paper comes at roughly the mid-point of the project, just as second-generation fuel cell stacks and vehicles are being introduced and some early vehicles are being retired. With many fuel cell stacks having accumulated well over 500 hours of real-world operation, there is now a higher level of confidence in the trends and projections relating to the durability and voltage degradation of these first-generation fuel cell stacks.Public results for this project are in the form of composite data products, which aggregate individual performance into a range that protects the intellectual property and the identity of each company, while still publishing overall status and progress. In addition to generating composite data products, NREL is performing additional analyses to provide detailed recommendations back to the R&D program. This includes analysis to identify sensitivities of fuel cell durability to factors such as vehicle duty cycle, number of on/off cycles, time at idle, and ambient temperature. An overview of this multivariate analysis and preliminary findings will be shared, with future project activities discussed.