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ABSTRACT: Increasing concerns about energy security and reliability are intensifying the interest in microgrid and vehicle-to-grid (V2G) technologies. Although the role of V2G technology within the context of optimal scheduling for larger grids has received much attention in the literature, its role within the regulation of microgrids has not yet been studied extensively. In this paper, we focus on the voltage and frequency regulation problem. We develop a microgrid model that is representative of the microgrid architecture considered in the SPIDERS (Smart Power Infrastructure Demonstration for Energy Reliability and Security) project of the Department of Defense. The model is parameterized to reflect the characteristics of Camp Smith, HI, the targeted installation of the SPIDERS project, and the long term Army goals regarding renewable energy penetration and reduction in fuel consumption. The model is augmented by power, frequency, and voltage control algorithms for the inverters that connect microsources to the microgrid. It also incorporates charging/discharging control algorithms for plug-in electric vehicles (PEVs) to take advantage of their capacity as both controllable loads and sources. Using this model, we study the impact of PEVs on the microgrid at different penetration levels and for different control parameters, with the aim of identifying the conditions needed for the vehicle-to-grid technology to have a positive impact on microgrid performance.
Power and Energy Society General Meeting, 2011 IEEE; 08/2011
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ABSTRACT: The paper describes a range of educational activities that are being developed to provide opportunities for K-12 students to learn about vehicle electrification. Whilst the focus is primarily on technology, students are also encouraged to consider environmental and societal impacts. Activities include development of school-based learning materials, summer camps, and a toolkit that brings together simulation and physical models, allowing children to play with electric vehicles. This K-12 outreach is part of a larger project, funded by the Department of Energy, to develop a comprehensive educational program in vehicle electrification.
Power and Energy Society General Meeting, 2011 IEEE; 08/2011
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ABSTRACT: Vehicle active safety systems stabilize the vehicle by controlling tire forces. They work well only when the commanded tire forces are within the friction limit. Therefore, knowledge of the tire/road friction is important to improve the performance of vehicle active safety systems. This paper presents two methods to estimate the friction coefficient: one based on lateral dynamics, and one based on longitudinal dynamics. The two methods are then integrated to improve working range of the estimator and robustness. The first method is a nonlinear observer based on vehicle lateral/yaw dynamics and Brush Tire model, the second method is a recursive least squares method based on the relationship between tire longitudinal slip and traction force. The performance of the estimation algorithm is verified using test data under a wide range of friction and speed conditions.
American Control Conference (ACC), 2011; 08/2011
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ABSTRACT: Intelligent management of power generation and dispatching is important when renewable energy sources and electrified vehicles (EV/PHEV) are introduced to the grid. Intermittency of renewable power and vehicle charging loads disturbs power supply and demand and could cause instability. Fortunately, EV/PHEV can be connected as controllable load or even used as energy storage, which makes it possible to reduce their negative impact and can even be explored to improve grid resilience. By coordinating power generation and charging, it is possible to reduce power generation cost and carbon emission. To improve practicality, a decentralized charging algorithm is formulated by emulating the charging pattern identified through linear programming (LP) optimization solutions. The resulting decentralized control algorithm is a function of forecasted total power demand on the grid, estimated number of vehicles, estimated EV/PHEV plug off time, and state of charge of the vehicle battery. Simulation results are presented to demonstrate the performance of the proposed decentralized algorithm.
American Control Conference (ACC), 2011; 08/2011
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ABSTRACT: Hydraulic hybrid vehicles are more suitable for heavy-duty applications in urban driving than hybrid electric vehicles because of the high power density and low cost of hydraulic devices. However, the low rotational speeds of hydraulic pump/motor and the low energy density of the accumulator impose severe constraints on the design and control for these vehicles. The split configuration is an efficient and more flexible transmission configuration and is the focus of this study. A three-step design methodology is developed to systematically and exhaustively explore all possible split configurations using two planetary gears: Step 1 checks mechanical feasibility of configurations; Step 2 develops optimal power management inspired by Pontryagin's Minimum Principle; and Step 3 finds optimal component sizes. After the screening, we identify three new configurations that achieve best fuel economy for the hydraulic vehicle/drive cycle studied, together with their best design and control executions.
American Control Conference (ACC), 2010; 08/2010
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ABSTRACT: Frictional coefficient between tire and road is difficult to detect but crucial for vehicle active safety systems. Several approaches for friction coefficient estimation were developed based on various vehicle dynamic phenomena. This paper suggests nonlinear state observers that use vehicle dynamics, steering system dynamics, and tire force dynamics as a viable approach. The stability of the observer highly relies on observer gains. We present two different ways to select the gains and discuss the stability of the observer. Furthermore, we introduce a hybrid estimator which uses a nonlinear observer and a nonlinear least square method which provides enhanced performances. These estimators are verified using the commercial software, Carsim, under various scenarios.
American Control Conference, 2009. ACC '09.; 07/2009
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ABSTRACT: Knowledge of tire friction force capacity, i.e. tire-load frictional coefficient, is important for the control of vehicle active safety systems. In this paper we review several methods for friction estimation and develop two robust and cost effective methods based on a nonlinear least square approach and the peak aligning torque. The methods proposed in this paper utilize simple vehicle lateral dynamics, steering system, and front tire dynamics. The first estimator uses direct calculation based on front tire self-aligning torque and the second method is based on a nonlinear least square method. These estimators are verified with Carsim under various conditions.
American Control Conference, 2009. ACC '09.; 07/2009
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ABSTRACT: The estimation of vehicle lateral speed, a critical variable for vehicle stability control, four-wheel-steering and other advanced dynamic control systems, is studied in this paper. We presented three different approaches, one each from three categories: transfer function approach, state-space approach, and kinematics approach. The first two methods rely on a vehicle dynamic (bicycle) model, and the last approach is based on the kinematics relationship of measured signals. The basic formulation of all three methods assumed that the road bank angle is negligible, and thus needs to be enhanced by a road bank angle estimation algorithm to work satisfactorily when the road bank is significant. The performance of these three (enhanced) methods are investigated using simulation and experimental data. For the experimental verification, we present four cases: nominal (high friction, flat road), banked road, low-friction, and low-friction-near-spin. Weakness of the three estimation algorithms is discussed.
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ABSTRACT: Evaluation of active safety control systems usually relies heavily on field testing and is time-consuming and expensive. Advances in computer simulations make it possible to perform exhaustive design trials and evaluations before field testing, and promise to dramatically reduce development cost and cycle time. In this paper, a comprehensive simulation-based evaluation procedure is proposed, which combines standard evaluation maneuvers, worst-case techniques, and a driver model for closed-loop path following evaluations. A vehicle dynamic controller (VDC) for a popular Sport Utility Vehicle is evaluated using the proposed procedure. Simulation results show that the proposed procedure can be used to assess the performance of the VDC under various conditions and provides valuable information for the re-design of the VDC.
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ABSTRACT: Three lateral speed estimation methods proposed in the literature are evaluated in this paper, including a transfer function (system identification) method, a state-space method, and a kinematics method. Test data from nominal as well as adverse driving conditions were used to assess the performance of these methods under realistic driving conditions. 1. INTRODUCTION Lateral speed is one of the most important vehicle dynamic variables for vehicle stability control systems and is crucial for many other chassis control functions such as four-wheel-steering. While vehicle lateral speed can be directly measured by instrumental sensors such as optical sensors or GPS sensors, there are practical issues such as cost, accuracy and reliability that inhibit production vehicles from using these sensors at present or in the near future. Therefore, the estimation of vehicle lateral speed based on other vehicle input/output signals is an important topic and has been widely discussed in the literature. Examples include Senger and Kortum [1], Cao [2], Kaminaga and Naito [3], Liu and Peng [4], Farrelly and Wellstead [5], Fukada [6], Nishio et al. [7], Sasaki and Nishimaki [8], Hac and Simpson [9]. Even though the lateral speed (or side sip angle) estimation problem had been actively studied, there were few comparison studies between representative methods, which is the main focus of this paper. We will compare three methodologies: a transfer function approach, the state-space approach by Liu and Peng [4], and the kinematics approach by Farrelly and Wellstead [5]. The basic ideas of these three methods are quite different. For example, the transfer function method uses an ARX least-square estimation method to construct a best estimation of the system input (steering) and output (yaw rate) behavior. The identified model is then used to construct an estimated vehicle lateral speed transfer function. The state space model needs to deal with both parameter (cornering stiffness) and state (lateral speed) estimation problems simultaneously. This is a challenging task and an adaptive observer was developed for this problem. The kinematics method proposed by Farrelly and Wellstead [5] was based on longitudinal and lateral kinematics, and does not rely on a dynamic model as the previous two methods. Due to the difference in underlying techniques, these methods exhibit dissimilar behavior.
