3
Systems Analysis

The PNGV Technical Roadmap, which is guiding the technical teams, states the following in Section III-A (PNGV, 1997):

The role of systems analysis in the PNGV is to support component, systems, and vehicle development by providing the analytical capability to efficiently and accurately assess competing technologies, and vehicle concepts against Goal 3 objectives and vehicle performance requirements. This will enable an objective evaluation of cost, benefit, and risk, in order to focus on the best options, with the least expenditure of resources.

A vehicle system model has been created by the systems analysis team with the assistance of TASC/Southwest Research Institute (SWRI) consultants. The model makes it possible to compare the relative performances of selected vehicle configurations. A good example of its utility is in comparing the performance of the HEV configurations. The HEV has two significant advantages that contribute to fuel economy: the potential to recover some braking energy; and the ability to run the selected power plant in a restricted, more efficient load and speed range. Disadvantages of the HEV include complexity, weight, and cost. The system models provide a means for assessing objectively the relative performance of each HEV configuration.

Systems analysis, based on effective computer modeling tools, is the most efficient way to ensure the optimization of vehicle performance for selected vehicle configurations. It also provides the opportunity to study trade-offs between candidate subsystems during the technology selection process. The models facilitate the preparation of specifications for each candidate subsystem and support the establishment of engineering targets. The ongoing technology selection



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3 Systems Analysis The PNGV Technical Roadmap, which is guiding the technical teams, states the following in Section III-A (PNGV, 1997): The role of systems analysis in the PNGV is to support component, systems, and vehicle development by providing the analytical capability to efficiently and accurately assess competing technologies, and vehicle concepts against Goal 3 objectives and vehicle performance requirements. This will enable an objective evaluation of cost, benefit, and risk, in order to focus on the best options, with the least expenditure of resources. A vehicle system model has been created by the systems analysis team with the assistance of TASC/Southwest Research Institute (SWRI) consultants. The model makes it possible to compare the relative performances of selected vehicle configurations. A good example of its utility is in comparing the performance of the HEV configurations. The HEV has two significant advantages that contribute to fuel economy: the potential to recover some braking energy; and the ability to run the selected power plant in a restricted, more efficient load and speed range. Disadvantages of the HEV include complexity, weight, and cost. The system models provide a means for assessing objectively the relative performance of each HEV configuration. Systems analysis, based on effective computer modeling tools, is the most efficient way to ensure the optimization of vehicle performance for selected vehicle configurations. It also provides the opportunity to study trade-offs between candidate subsystems during the technology selection process. The models facilitate the preparation of specifications for each candidate subsystem and support the establishment of engineering targets. The ongoing technology selection

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process for demonstration vehicles will depend heavily on the results of systems analyses. All but one of the committee's recommendations in the third report were addressed by the PNGV systems analysis technical team. The exception was that an assessment be made of the value of the expenditures during 1996 for the TASC/SWRI contractor team. During the committee's present review, the team outlined its accomplishments and its plans for 1998. The committee concluded that considerable progress has been made in the past year and that effective systems analysis is now in place to provide design support to the technical teams. The vehicle and subsystem models being created should effectively support the technology selection process. Table 3-1 outlines the systems analysis team's responses to the recommendations and observations in the committee's third report. In general, the responses, combined with presentations to the committee, indicated that the team had responded effectively to the committee's concerns. The major exception was that cost and reliability models have not been reviewed with the committee. The committee believes that both models are necessary to the effective selection of technologies for concept vehicles that will meet the program's objectives. PROGRAM STATUS AND FUTURE PLANS Modeling During the committee's review, the systems analysis technical team made a presentation describing the computer models being developed, showing typical simulation assumptions for specific vehicle configurations, detailing data on fuel economy for parallel and series hybrid vehicles, and describing the sensitivity of fuel economy to changes in vehicle mass. Detailed charts and supporting analysis were presented summarizing the timing and status of subsystem models for all the subsystems being considered. As expected, the model results varied widely, from the internal combustion engine, for which model predictions correlate well with actual data, to the Stirling engine, for which a good model may not yet exist. The PNGV management stated that the precision of the systems analysis tools, in general, exceeds the accuracy of data available for each subsystem. The committee understood this to mean that the analytical models are very powerful and complete and that the simulation models are accurate, provided that they are based on adequate subsystem and component performance data. The PNGV must now build and test subsystems and vehicles that will provide performance data to compare to the performance predicted in the models. A summary of technical tasks and timing was also presented, and the committee was given detailed plans and schedules for each model requirement indicating the status of each subsystem relative to selected key parameters, including performance, efficiency, emissions, thermal and load transients, heat rejection, scaling, volume and aspect ratio, ride and handling, cost, and reliability. These

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TABLE 3-1 Response of the PNGV Systems Analysis Team to the Committee's Third Report Observations and/or Recommendations Response 1. The pace of systems analysis must be accelerated and funding resources identified. USCAR and the U.S. Department of Energy have increased resources and established a long-term funding plan. 2. A lack of good model validation data is hindering systems analysis. Resources to obtain both vehicle and component data from subsystem and vehicle development sources have been committed. 3. Cost and reliability models are weak. The next version of the computer model includes a refined cost model. The reliability model is adequate, and model validation now depends on good experimental data. 4. More effort should be focused on the effective use of models by the technical teams. The systems analysis team is concentrating on designing and developing an effective graphical user interface to meet the needs of all the technical teams. 5. Greater participation and interaction with the engineering teams are necessary. The systems analysis steering group participates in the meetings of the PNGV engineering team and addresses technical concerns. 6. Systems analysis should focus on technologies that have a high probability of success in the year 2004. Model refinements in the next phase of the program will focus on the most promising technologies, as defined by the technology selection process. 7. Detailed systems studies of component technologies are needed to define system and subsystem requirements from a vehicle perspective. Analytical studies respond to the requirements established during the meetings with the technical teams. Models are based on these analyses. 8. Systems studies are needed to confirm the accuracy of the component objectives detailed in the PNGV Technical Roadmap. The PNGV Technical Roadmap is continually updated in response to systems analysis and modeling. A major update will be made after the technology selection process is completed in 1997. 9. Competitive technology assessments, especially of foreign technology, should be routinely conducted. All of the automotive companies involved routinely monitor competitive activity to ensure their competitiveness.

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plans described the interactions of the system analysis team with the other technical teams in modeling and supporting design analyses. The committee had been very critical in the third review about the lack of interaction and was gratified to see that the situation is much improved (NRC, 1997). This was confirmed by remarks made during review presentations by other technical teams. The committee is still very concerned about the status of subsystems like the fuel cell, the battery, and the power electronics module, for which reliable models are still evolving. The committee urges the systems analysis team to increase its efforts to create models for these subsystems. The technology selection process will depend largely on the computer models, and the committee's review of the preparation for technology selection revealed that models are being used effectively. The most promising models have been identified and vehicle level control strategies are being developed. Future Plans The following PNGV development needs beyond November 1997 were provided to the committee during its review (Kenny et al., 1997). (1) Nonperformance model enhancements refine cost model validate reliability model integrate optimization capability (2) Power bus formulation update component models (e.g., switch reluctance motor) validate data for component models improve parallel control algorithms (e.g., user definable) improve series control algorithms (3) Model architecture limit client server (1 PC/1 workstation) (4) Voltage bus formulation create motor and generator equivalent circuit models develop power electronics model develop new control algorithms update component models (focus on transient response) (5) Additional capabilities not being collaboratively pursued manufacturability recyclability packaging/crashworthiness noise, vibration, harshness (NVH) (6) Integration of modeling of subsystems (fuel cells, batteries, power electronics modules) with modeling of the entire vehicle system

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AREAS OF CONCERN During the committee's review, it was obvious that very little cost modeling had been done by the PNGV systems analysis team. The committee was informed that provisions for cost modeling had been made, but little has been done so far. The committee believes that probabilistic models of vehicle and subsystem costs, with confidence levels, will be very important for the technology selection process. The computer model should provide analysis and presentation of a complete cost picture for every vehicle configuration selected. Cost is still a major barrier to satisfying the original PNGV affordability objective. The PNGV is fully aware of the challenge it faces in achieving the Goal 3 cost objectives, particularly for hybrid vehicles. The committee raised this question with the PNGV, and two of the USCAR partners volunteered to share proprietary cost data with a subgroup of the committee. The data reviewed satisfied the committee that good cost estimates are available for subsystems like the CIDI hybrid vehicle, for which design and manufacturing technology has been developed. Cost estimates for mass producing more advanced subsystems, like fuel cells, are not adequately developed for accurate cost forecasting. Nevertheless, the committee believes it is imperative that the PNGV create complete cost models for all of the subsystems under consideration so that effective cost trade-offs can be considered. Even if the models are not as accurate as desired, they will at least provide baselines for comparing all of the systems under consideration and will highlight the specific developments necessary to realizing acceptable costs. Without compromising the proprietary interests of the USCAR partners, the results of their analyses should be communicated to the systems analysis team for use in their cost models. Furthermore, the USCAR partners should agree on representative subsystem target costs, which are important to guide the development efforts of the many participants in the PNGV program. Another area that deserves more attention is reliability models. Vehicle design life and safety are major considerations in meeting vehicle requirements. Each subsystem being considered introduces new failure modes that could affect design life and safety. The systems analysis team should be deliberately structuring component and subsystem reliability models that can be used to predict vehicle reliability during the technology selection process and then as a basis for hardware test verification. The PNGV's reliability model(s) should be of individual components, subsystems, and the total vehicle operation in a defined environment. The models should be statistical and should define failure modes and effects. Each component should have a design reliability model based on specific assumptions and test data.

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RECOMMENDATIONS Recommendation. Systems analysis and computer modeling are essential tools for making system trade-offs and optimizing performance. The PNGV should create detailed, rigorous cost and design reliability models as soon as possible to support ongoing technology selection. These models should be continually upgraded as new information becomes available. Recommendation. Because cost is a significant challenge to the PNGV, the USCAR partners should continue to conduct in-depth cost analyses and to use the results to guide new development initiatives on components and subsystems.