Search

The transportation sector produces a large portion of greenhouse gas emissions in the United States. Meeting ambitious reductions in greenhouse gasses requires large-scale adoption of battery electric vehicles and has led to several policies and laws aimed at incentivizing their sales. While electric vehicles comprise a small percentage of the overall fleets of vehicles, the expected production of electric vehicles is soon expected to be in the millions. This will create challenges in providing an adequate charging infrastructure, as well as the ensuing management of the overall electricity demand at the grid level. In this work, a novel smart-charging protocol for battery electric vehicle charging at workplace parking structures is proposed. The Octopus Charger-based Mixed Integer Linear Programming protocol allows octopus chargers (i.e., charging stations with multiple cables) to independently schedule charging periods for their assigned vehicles. The proposed protocols can manage a parking structure demand load while reducing the number of installed charging stations. Driving patterns from the National Household Travel Survey were used to perform simulations, to verify and quantify the effectiveness of the proposed protocol. The proposed protocol resulted in improved peak load reductions for all simulated smart-charging scenarios when compared with uncontrolled charging. Critically, the assignment algorithm resulted in a number of required chargers close to the theoretical minimum. [ABSTRACT FROM AUTHOR]

• Zero net energy is feasible when clean fuel is combined with electrification. • Building energy consumption valuation method impacts the component sizing. • Time dependent valuation of energy in California reflects its cost and emissions. • Solid oxide fuel cell provides efficient electricity and heat at the building. • Building can go off-grid with optimized operation of battery and fuel cell. California is seeking to mandate Zero Net Energy (ZNE) buildings by 2030 as part of its efforts to combat climate change. A ZNE building is required to compensate its annual energy consumption from the grid (electricity or gas) by injecting clean electricity back to the grid. So far, the most common approach for a ZNE building is utilizing solar photovoltaic (PV) or a PV and battery energy storage system. One key problem is the feasibility of installing PV if the surface area requirement is too large to achieve ZNE; another issue is grid congestion during the off-peak hours of midday when a large number of houses export their excess solar power to the grid. Hence, other ZNE home scenarios need to be evaluated to tackle these restrictions in achieving California's climate goals. In this work, we proposed and evaluated different system arrangements to reduce the required PV installation that is commonly installed as power generation source for ZNE residential units in California. The aim of this technical analysis is to provide a societal level policy guidance to accelerate fulfilling the ZNE home mandate. Due to the availability of the gas grid and potential for having more renewable gas in the grid, we investigated using gas-based heat generation versus only electric-based heat appliances. In addition, we incorporated a residential solid oxide fuel cell (SOFC) on the building site as a micro combined heat and power (mCHP) to facilitate achieving ZNE. The impact and contributions of different components, including energy storage, on grid-dependence, and the overall energy demand are also studied. With analysis of different mix of technologies that could be used for a ZNE home, we propose the potential solutions and discuss their strengths and weakness. In this paper, energy performance and optimal PV capacity are assessed for a ZNE home in all 16 climate zones of California established by California Energy Commission (CEC). The ZNE measurements for all four scenarios are based on three metrics of energy evaluation: (1) site energy (energy measured by the meter used at the building site); (2) source energy (raw fuel consumption at the source of energy generation to account for energy loss in production and distribution); and (3) time dependent valuation (TDV) of energy, which has been developed by the CEC to comply with its building energy efficiency standards. The TDV of each energy type depends on the time of use, climate, grid constraints, and other factors that reflect its societal value at any given hour of the year. The PV size required by each ZNE metric is calculated and compared. The results proved that relying on some gas in addition to electricity improves the practicality of required PV for ZNE homes particularly in regions with high heating demands. It was found that depending on the energy metric (site, source, and TDV), a different arrangement is required for the most efficient ZNE performance. Unlike the site metric, using source and TDV metrics where electricity is more valuable than gas shows that having both gas and electricity significantly reduces the PV size. This encourages investment in introduction of more renewable gas in the grid as one possible solution to achieving ZNE in individual homes. The great impact of an mCHP SOFC on a ZNE home in terms of reliability and feasibility points to the need for research, development, and commercialization to reduce the cost of mCHP SOFCs in residential application. Also, the addition of a battery does not reduce the PV size with site and source metrics; it only reduces the electric grid reliance. However, with TDV, where the time of energy consumption affects its value, not only does it reduce grid reliance during peak hours, but also less PV is required to achieve ZNE. [ABSTRACT FROM AUTHOR]

Plug-in electric vehicles (PEVs) shift energy consumption from petroleum to electricity for the personal transportation sector. This work proposes a decentralized charging protocol for PEVs with grid operators updating the cost signal. Each PEV calculates its own optimal charging profile only once based on the cost signal, after it is plugged in, and sends the result back to the grid operators. Grid operators only need to aggregate charging profiles and update the load and cost. The existing PEV characteristics, national household travel survey (NHTS), California Independent System Operator (CAISO) demand, and estimates for future renewable generation in California are used to simulate PEV operation, PEV charging profiles, grid demand, and grid net load (demand minus renewable). Results show the proposed protocol has good performance for overnight net load valley filling if the costs to be minimized are proportional to the net load. Annual results are shown in terms of overnight load variation and comparisons are made with grid level valley filling results. Further, a target load can be approached in the same manner by using the gap between current load and the target load as the cost. The communication effort involved is quite modest. [ABSTRACT FROM AUTHOR]

Abstract: For linear systems with bounded actuators, a continuous family of controllers is designed which avoids control saturation for a given worst case disturbance. The control law acts as a scheduling scheme which, at each time, based on the closed-loop behavior (i.e., the closed-loop state vector) out of the continuous family selects a controller that provides the best performance while avoiding saturation. Graphically, the resulting scheduling scheme relies on slab regions in the phase plane. It is shown that the most aggressive controller can be set to be a nominal controller designed without any regard to the saturation bounds, resulting in an anti-windup scheme. Among advantages of this anti-windup protection scheme are its improved performance while the nominal controller is mildly saturated and its applicability to open-loop unstable plants. The benefits of the proposed technique are demonstrated through two numerical examples. [Copyright &y& Elsevier]

We discuss a variation of dilated matrix inequalities for the conventional Bounded Real matrix inequality and other similarly structured inequalities. Here, system matrices are separated from Lyapunov matrix to allow the use of different Lyapunov matrices in multi-objective and robust problems. The search involves a bounded scalar parameter that enters the problem nonlinearly and is dealt with a line search. To demonstrate the benefits of the new dilated matrix inequalities over the conventional ones, an example of controller synthesis with ℒ2-gain performance measure (ℋ∞ control) for a system with polytopic uncertainty (robust problem) has been studied. It is shown that for the resulting robust problem the performance obtained via the dilated form is at least equal to that of the conventional one. Also, the connection between the proposed dilated form and the Full Block S-procedure is discussed. [ABSTRACT FROM AUTHOR]

SUMMARY We consider the dynamic anti-windup design problem for linear systems with saturating actuators. The basic idea proposed here is to apply anti-windup only when the performance of saturated system faces substantial degradation. We provide synthesis LMIs to obtain the gains of the dynamic anti-windup compensator in a structure that delays the activation of the anti-windup. Benefits of the proposed design method over the immediate activation of the anti-windup are demonstrated using a well-known example. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we study the breakup of a circular jet subject to a manipulated disturbance applied by an actuator (here a piezoelectric) in order to control droplets sizes and patterns over a wide range. According to previous studies, breakup of a jet is strongly affected by the characteristics of the disturbance. When the breakup is not periodic and repeatable, it is described as an irregular or random breakup. On the other hand, over a frequency range for the disturbance, the breakup can be made repeatable, though not necessarily uniform, in which the droplets pinch off the stream at a constant rate. In this case, the breakup is called regular, although satellites or secondary droplets might form among the main droplets. In most applications, a very narrow frequency range (much narrower than the regular breakup frequency range) is used for operation, since it is the only range where uniform droplets form. This work demonstrates that by eliminating secondary droplets or satellites, the entire regular breakup regime becomes available for desirable operation, i.e., uniform droplet generation. The regular breakup regime is specified experimentally and an additional disturbance is added to the driving disturbance in order to eliminate the nonuniform droplets. This method provides us with droplets of the desired size when they cannot be produced with a single frequency disturbance alone. The results also demonstrate that different frequencies for the additional disturbance produce different patterns for the droplets sizes. [ABSTRACT FROM AUTHOR]

Abstract: The intrinsic transient performance capability and limitation of integrated solid oxide fuel cell (SOFC) systems is evaluated based on the system balance-of-plant response and fuel cell operating requirements (i.e., allowable deviation from nominal operation). Specifically, non-dimensional relations are derived from conservation principles that quantify the maximum instantaneous current increase that a solid oxide fuel cell system can safely manage based on (1) the desired fuel cell operating point, (2) the maximum allowable fuel utilization, (3) the maximum average fuel cell temperature deviation, (4) the response delay and (5) the operating requirements of the system balance-of-plant components. New non-dimensional numbers representing the ratio of species or thermal convection to volumetric capacitance in the fuel cell during balance-of-plant delay have been developed. The analyses indicate: (1) SOFC intrinsic transient performance is largely limited by fuel processor flow delays that can cause fuel depletion in the anode compartment and (2) that with proper system actuators and control design transient operation of SOFC systems should be possible while maintaining SOFC average temperature within a degree. The SOFC system fuel processor lag appears to be the cause of SOFC load following limitation, while lag in air handling appears to be manageable. To demonstrate methods to avoid fuel depletion limitation a fuel flow lead compensator is developed. Integrated system simulations with proper control demonstrate significant SOFC transient performance within fuel cell operating requirements. [Copyright &y& Elsevier]

This paper investigates the containment control problem for multi-agent systems (MASs) with multiple leaders which have non-zero control inputs. Agents' tracking errors are described by a linear system with an external disturbance. The containment control problem is then solved by applying a distributed observer-based output feedback controller. Anti-windup (AW) compensation is designed by convex conditions, to improve the performance in the presence of actuator saturation. Finally, simulations are presented to illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: A novel SOFC system control strategy has been developed for rapid load following. The strategy was motivated from the performance of a baseline control strategy developed from control concepts in the literature. The basis for the fuel cell system control concepts are explained by a simplified order of magnitude time scale analysis. The control concepts are then investigated in a detailed quasi-two-dimensional integrated dynamic system model that resolves the physics of heat transfer, chemical kinetics, mass convection and electrochemistry within the system. The baseline control strategy is based on the standard operating method of constant utilization with no control of the combustor temperature. Simulation indicates that with this control strategy large combustor transients can take place during load transients because the fuel flow to the combustor increases faster than the air flow. To alleviate this problem, a novel control structure that maintains the combustor temperature within acceptable ranges without any supplementary hardware was introduced. The combustor temperature is controlled by manipulating the current to change the combustor inlet stoichiometry. The load following capability of SOFC systems is inherently limited by anode compartment fuel depletion during the time of fuel delivery delay. This research indicates that future SOFC systems with proper system and control configurations can exhibit excellent load following characteristics. [Copyright &y& Elsevier]

Abstract: A detailed dynamic model incorporating geometric resolution of a molten carbonate fuel cell (MCFC) with dynamic simulation of physical and electrochemical processes in the stream-wise direction is presented. The model was developed using mass and momentum conservation, electrochemical and chemical reaction mechanisms, and heat-transfer. Results from the model are compared with data from an experimental MCFC unit. Furthermore, the model was applied to predict dynamic variations of voltage, current and temperature in an MCFC as it responds to varying load demands. The voltage was evaluated using two different approaches: one applying a model developed by Yuh and Selman [C.Y. Yuh, J.R. Selman, The polarization of molten carbonate fuel cell electrodes: I. Analysis of steady-state polarization data, J. Electrochem. Soc. 138 (1991) 3642–3648; C.Y. Yuh, J.R. Selman, The polarization of molten carbonate fuel cell electrodes: II. Characterization by AC impedance and response to current interruption, J. Electrochem. Soc. 138 (1991) 3649–3655] and another applying simplified equations using average local temperatures and pressures. The results show that both models can be used to predict voltage and dynamic response characteristics of an MCFC and the model that uses the more detailed Yuh and Selman approach can predict those accurately and consistently for a variety of operating conditions. [Copyright &y& Elsevier]

Abstract: Current high temperature fuel cell (HTFC) systems used for stationary power applications (in the 200–300kW size range) have very limited dynamic load following capability or are simply base load devices. Considering the economics of existing electric utility rate structures, there is little incentive to increase HTFC ramping capability beyond 1kWs−1 (0.4%s−1). However, in order to ease concerns about grid instabilities from utility companies and increase market adoption, HTFC systems will have to increase their ramping abilities, and will likely have to incorporate electrical energy storage (EES). Because batteries have low power densities and limited lifetimes in highly cyclic applications, ultra capacitors may be the EES medium of choice. The current analyses show that, because ultra capacitors have a very low energy storage density, their integration with HTFC systems may not be feasible unless the fuel cell has a ramp rate approaching 10kWs−1 (4%s−1) when using a worst-case design analysis. This requirement for fast dynamic load response characteristics can be reduced to 1kWs−1 by utilizing high resolution demand data to properly size ultra capacitor systems and through demand management techniques that reduce load volatility. [Copyright &y& Elsevier]

State and output feedback controllers are designed for disturbance attenuation in linear systems with bounded actuators. The controller is scheduled according to the proximity to the origin of the state of the plant in the state-feedback case and the compensator state in the case of output feedback. This procedure yields a linear parameter-varying structure for the controller that allows higher-gain and hence higher-performance controllers as the states move closer to the origin. The main results give sufficient conditions for the satisfaction of a parameter-dependent performance measure, without violating the saturation bounds. Linear splines are used to obtain solutions that can be obtained by standard LMI software. Examples—including an open-loop unstable system—highlight the application of the results. [Copyright &y& Elsevier]

Novel low-power or semiactive devices are developed for vibration suppression applications. By manipulating the structural stiffness, the resisting forces generated by the devices are quite large and independent of velocity. Experimental results are presented to demonstrate the feasibility of the devices and to justify the main assumptions used. The critical design issue of device placement is addressed analytically and verified. While much of the development here applies to the case of variable stiffness devices, we focus on resettable devices in which the device behaves like a linear spring. However, at appropriate times, the effective unstretched length of the device is changed—or reset—to extract energy from the vibrating structure. [ABSTRACT FROM AUTHOR]

Discusses a class of low-power devices and their corresponding control laws. Novel low power control technique; Manipulation of the stiffness of the structure through setting the effective stiffness of the element; Motivation for the resetting approach; Behavior of the actuator in the proposed control approach; Concept of actuator resetting.

Discusses the design of controllers that provide quadratic stability and a desirable disturbance attenuation level for systems with time varying, real and structured uncertainty. Problems associated with designing dynamic output feedback; Description of design of controllers; Detailed information on controllers.

Recently developed H∞ control techniques are used to design controllers to suppress the effects of earthquake ground motion on the response of building structures. In particular, controllers are designed to reduce both the interstory drift and the absolute acceleration of selected floors on which sensitive equipment may be installed. Further, the H∞ control techniques are extended to include the capability of using acceleration sensors, since direct measurement of floor accelerations is the most reliable and least expensive measurement to make in earthquake engineering applications. Simulation results for a six-story building are used to demonstrate the effectiveness of the control method presented. [ABSTRACT FROM AUTHOR]

• Smart-charging protocol for workplace, battery electric vehicle charging. • Protocol orders vehicles based on load shifting flexibility to improve performance. • Decentralized protocol allows vehicles to individually schedule charging. • Algorithm assigns vehicles to charging stations with multiple cables. • Protocol reduces peaks in demand load and number of required charging stations. Battery electric vehicles can help reduce fossil fuel consumption and greenhouse gas emissions. Specifically, workplace charging can alleviate the curtailment of renewable resources, while providing charging opportunities to long-range commuters. In this work, a comprehensive smart-charging protocol for workplace charging is proposed. The protocol first uses an ordering strategy, based on each vehicle's load shifting flexibility, to develop a queue. Next, a decentralized smart-charging strategy is used that allows battery electric vehicles to generate their own charging profile via linear programming. By using an appropriate cost signal, the proposed smart-charging strategy can generate a parking structure demand load with desirable characteristics. Finally, an assignment algorithm is proposed to assign battery electric vehicles to octopus chargers. Driving patterns from the National Household Travel Survey are used to simulate workplace charging for parking structures under various charging scenarios. The proposed ordering strategy resulted in improved peak reductions for all simulated charging scenarios, when compared with chronological ordering. Furthermore, monthly electricity costs and the number of required chargers were both reduced in all cases where smart charging was combined with the proposed ordering strategy, compared to uncontrolled charging. Thus, the proposed protocol can reduce electricity and charging infrastructure costs associated with workplace charging. [ABSTRACT FROM AUTHOR]

A solid oxide cell-based energy system is proposed for a solar-powered stand-alone building. The system is comprised of a 5 kW el solid oxide fuel cell (SOFC), a 9.5 kW el solid oxide electrolysis cell (SOEC), and the required balance of plant. The SOFC supplies: 1- building demand in the absence of sufficient solar power, 2- heat for SOEC in endothermic and standby modes. Thermal integration of SOFC and SOEC is implemented through a network of heat exchangers, combined with set of control algorithms. Two control strategies were implemented to actuate the SOFC in response to endothermic heat demands of SOEC by manipulating: 1- electric power, 2- fuel utilization. The results of dynamic simulation of system for two scenarios (sunny day and cloudy day) showed successful compliance of temperature constraints with both methods. Manipulation of fuel utilization, however, resulted in better system performance in terms of efficiency and H 2 balance. Schematic of proposed thermally self-sustaining energy storage system. [Display omitted] • A dynamic multi-function energy system is designed for a solar PV powered building. • Power-to-Gas technology is used to convert excess electricity to hydrogen via SOEC. • SOFC is thermally integrated to SOEC to eliminate external heat sources for SOEC. • Analyzed system dynamics for two solar power scenarios: sunny day and cloudy day. • Designed two control strategies for actuating SOFC (electric power, fuel utilization). [ABSTRACT FROM AUTHOR]

This work investigates the active defense problem wherein a target aircraft launches a defending missile (i.e. a defender) to intercept an attacking missile in three-dimensional (3D) space. The novelty of this work includes: adding a safe distance for the target, which protects the target from being influenced by defensive interception, and designing a new 3D defensive guidance strategy without linearization to meet different guidance requirements. The defensive guidance strategy combines the approach of analyzing 3D pursuit-evasion engagement and the optimal control to obtain the guidance law. The approach derives the analytical solutions of 3D pursuit-evasion engagement, and a fast algorithm to predict the trajectory of attacking missile is proposed based on these analytical solutions. The advantages of this guidance strategy include incorporation of the added safe distance requirement directly without hindering the ability of the optimal guidance law to meet other requirements, and straight-forward extension for advanced scenarios where multi-defenders intercept the attacking missile simultaneously from different directions. The performance of the 3D defensive guidance law is evaluated via simulations. [ABSTRACT FROM AUTHOR]

This paper investigates gain-scheduled control design for linear systems with time-varying state delays subject to actuator saturation and external disturbance. Assuming the disturbance is peak bounded, a sufficient delay-dependent condition is established to guarantee that a family of level sets, corresponding to a novel parameter-dependent Lyapunov–Krasovskii functional, are nested and invariant to the closed-loop system. The invariant sets are then used to obtain nested reachable sets (ellipsoids) to bound the closed-loop states. A family of continuous controllers are designed based on these nested ellipsoids. The controller with the best performance is selected, each time, based on the closed-loop state vector, while complying with the saturation bound, and the resulting closed-loop system is locally input-to-state stable. All conditions are represented in the form of linear matrix inequalities (LMIs) by the linear spline method. Finally, the benefit of the control method is illustrated by two examples. [ABSTRACT FROM AUTHOR]

Abstract Economic dispatch for micro-grids and district energy systems presents a highly constrained non-linear, mixed-integer optimization problem that scales exponentially with the number of systems. Energy storage technologies compound the mixed-integer or unit-commitment problem by necessitating simultaneous optimization over the applicable time horizon of the energy storage. The dispatch problem must be solved repeatedly and reliably to effectively minimize costs in real-world operation. This paper outlines a method that greatly reduces, and under some conditions eliminates, the mixed-integer aspect of the problem using complementary convex quadratic optimizations. The generalized method applies to grid-connected or islanded district energy systems comprised of any variety of electric or combined heat and power generators, electric chillers, heaters, and all varieties of energy storage systems. It incorporates constraints for generator operating bounds, ramping limitations, and energy storage inefficiencies. An open-source platform, EAGERS, implements and investigates this optimization method. Results demonstrate a >99% reduction in computational effort when comparing the newly minted optimization strategy against a benchmark commercial mixed-integer solver applied to the same combined cooling, heating, and power problem. Highlights • Newly developed optimization strategy for unit-commitment/economic dispatch problem. • Open-source platform simulating combined heat, cooling, power, and storage: EAGERS. • Generalized method applicable to grid-connected or islanded district energy systems. • Demonstrated 500× improvement from commercial mixed-integer solver. [ABSTRACT FROM AUTHOR]

Abstract A new structure for the anti-windup (AW) compensation for rate limited actuation is proposed which is less conservative than structures currently used. For peak bounded disturbances or reference inputs, we develop AW augmentation loops for both magnitude and rate actuator saturation. To reduce conservatism further, the proposed technique is combined with a multi-stage AW loops to obtain different gains for different levels of saturation. [ABSTRACT FROM AUTHOR]

A dynamic solid oxide fuel cell (SOFC) model is used to investigate the effects of different flow arrangements, as well as those of non-uniform air flow across channels, on temperature profile and thermal gradients under transient and steady state response. A high performance multi-input multi-output feedback controller has been developed to minimize SOFC spatial temperature variations during changes in power demands for different flow patterns. Numerical results show that the controller would result in negligible temperature variations for the modified cross-flow arrangement proposed here, even for large changes in the power drawn. The combination of a high performance controller and design modification results in a more uniform temperature profile at steady state nominal conditions, and modest variations in temperature profile, from the nominal, for ±15% change in power. Similarly, non-uniform air flow rate decreases the temperature gradient as well as maximum temperature across the cell, though its effect is less pronounced in the closed loop response. [ABSTRACT FROM AUTHOR]

The control system for fuel cell gas turbine hybrid power plants plays an important role in achieving synergistic operation of subsystems, improving reliability of operation, and reducing frequency of maintenance and downtime. In this paper, we discuss development of advanced control algorithms for a system composed of an internally reforming solid oxide fuel cell coupled with an indirectly heated Brayton cycle gas turbine. In high temperature fuel cells it is critical to closely maintain fuel cell temperatures and to provide sufficient electrochemical reacting species to ensure system durability. The control objective explored here is focused on maintaining the system power output, temperature constraints, and target fuel utilization, in the presence of ambient temperature and fuel composition perturbations. The present work details the development of a centralized linear quadratic regulator (LQR) including state estimation via Kalman filtering. The controller is augmented by local turbine speed control and integral system power control. Relative gain array analysis has indicated that independent control loops of the hybrid system are coupled at time scales greater than 1 s. The objective of the paper is to quantify the performance of a centralized LQR in rejecting fuel and ambient temperature disturbances compared with a previously developed decentralized controller. Results indicate that both the LQR and decentralized controller can well maintain the system power to the disturbances. However, the LQR ensures better maintenance of the fuel cell stack voltage and temperature that can improve high temperature fuel cell system durability. [ABSTRACT FROM AUTHOR]

The article presents information on structural vibrations which use semi-active actuators that are capable of manipulating stiffness and producing variable stiffness. It is observed that vibration suppression is done by using damping devices rather than stiffness devices because stiffness devices can produce large forces and have advantages for shock isolation purposes.

Abstract: A high performance feedback controller has been developed to minimize SOFC spatial temperature variation following significant load perturbations. For thermal management, spatial temperature variation along SOFC cannot be avoided. However, results indicate that feedback control can be used to manipulate the fuel cell air flow and inlet fuel cell air temperature to maintain a nearly constant SOFC electrode electrolyte assembly temperature profile. For example temperature variations of less than 5K are obtained for load perturbations of ±25% from nominal. These results are obtained using a centralized control strategy to regulate a distributed temperature profile and manage actuator interactions. The controller is based on H-infinity synthesis using a physical based dynamic model of a single co-flow SOFC repeat cell. The model of the fuel cell spatial temperature response needed for control synthesis was linearized and reduced from nonlinear model of the fuel cell assembly. A single 11 state feedback linear system tested in the full nonlinear model was found to be effective and stable over a wide fuel cell operating envelope (0.82–0.6V). Overall, simulation of the advanced controller resulted in small and smooth monotonic temperature response to rapid and large load perturbations. This indicates that future SOFC systems can be designed and controlled to have superb load following characteristic with less than previously expected thermal stresses. [Copyright &y& Elsevier]

This paper describes the design of a novel actuator capable of protecting a full scale structure from severe load conditions. The design includes a cylinder filled with pressurized nitrogen and uses commercially available components. We demonstrate that the actuator behaves like a spring with an adjustable unstretched length, and that the effective spring stiffness can be changed easily by changing the initial cylinder pressure. In order to test the actuator on a full scale structure, an effective spring constant of approximately 10,000 pounds/inch was required over a two inch stroke. Because of the spring-like behavior, rather than damper-like behavior, the actuator does not transmit high forces to a vibrating structure like linear viscous dampers do when velocities are high. We analyze features of critical importance to the design of the actuator such as the cylinder dimensions, operating pressure, and valve selection. We then investigate the performance using a novel experimental apparatus that mimics the dynamics of a single story building, but has 1/400 the weight. [ABSTRACT FROM AUTHOR]

Abstract: Several methods to prevent fuel starvation in solid oxide fuel cells are developed and investigated. Fuel starvation can occur during transients, if fuel is consumed in the fuel cell faster than it can be supplied by the fuel processing and delivery system. It is demonstrated through simulation that fuel depletion can occur in the fuel cell if no corrective action is employed. Fuel starvation can be prevented by the use of rate limiters, reference governors, and modifications to the fuel-flow controller. The various methods to prevent fuel depletion within the fuel cell are developed and compared. Analysis indicates that reference governors can avoid hydrogen depletion with much less of an impact on transient load following capability than rate limiters. Hence, various reference governors ranging in level of fidelity were developed and compared for performance. It was further demonstrated that with knowledge of the fuel preprocessor response, it is possible to manipulate the fuel flow to minimize reformer flow dynamics, minimizing the need to govern the fuel cell transient capability. [Copyright &y& Elsevier]

Abstract: This study is focused on a hybrid fuel cell/gas turbine (FC/GT) system with an atmospheric pressure solid oxide fuel cell (SOFC). The impact of the gas turbine rotational speed on dynamic performance and controllability of a hybrid system is investigated. The transient response of the FC/GT system to perturbations in the power demand has been investigated. Two operational strategies of gas turbines are compared: (1) fixed speed operation, and (2) variable speed operation. For both operation strategies, a wide range of power production is numerically simulated. The results show that variable speed operation is superior for the FC/GT hybrid configuration studied. Variable speed operation allows a 50% turn down in power with no additional balance of plant equipment required. The system efficiency is maintained above 66% for variable speed operation compared to 53% for fixed speed operation with auxiliary combustion. [Copyright &y& Elsevier]

Two multiobjective control strategies are presented and applied to the wind-excited benchmark problem. The first strategy, referred to as the energy-to-peak based controller, deals with a class of “energy-bounded” excitations, whereas the second strategy, referred to as the peak-to-peak based controller, addresses a class of peak-bounded excitations. Both control strategies are derived by minimizing the sum of weighted peak response quantities with the constraints (or penalties) on the peak values of another set of quantities such as the control resources. Both the state feedback and dynamic output feedback controllers are derived and presented. The design syntheses of these two control strategies are developed and formulated within the framework of linear matrix inequalities (LMIs), so that the LMI toolbox in MATLAB can be used effectively and conveniently. These two control strategies are applied to the wind-excited 76-story benchmark building to demonstrate their applicability and control performances. Simulation results illustrate that the proposed control strategies are viable for civil engineering structures, and their performances are excellent in comparison with that of the linear quadratic Gaussian sample controller. [ABSTRACT FROM AUTHOR]

The need to reduce greenhouse gas emissions and fossil fuel consumption has increased the popularity of plug-in electric vehicles. However, a large penetration of plug-in electric vehicles can pose challenges at the grid and local distribution levels. Various charging strategies have been proposed to address such challenges, often separately. In this paper, it is shown that, with uncoordinated charging, distribution transformers and the grid can operate under highly undesirable conditions. Next, several strategies that require modest communication efforts are proposed to mitigate the burden created by high concentrations of plug-in electric vehicles, at the grid and local levels. Existing transformer and battery electric vehicle characteristics are used along with the National Household Travel Survey to simulate various charging strategies. It is shown through the analysis of hot spot temperature and equivalent aging factor that the coordinated strategies proposed here reduce the chances of transformer failure with the addition of plug-in electric vehicle loads, even for an under-designed transformer while uncontrolled and uncoordinated plug-in electric vehicle charging results in increased risk of transformer failure. [ABSTRACT FROM AUTHOR]

We consider the problem of electricity demand shifting for the cooling needs of a large institution, using a thermal energy storage (TES) tank. The system is comprised of a number electric chillers with varying capacity and performance, as well as a tank that can store significant amount of chilled water but not enough for the whole day. The approach outlined here selects the number of chillers, and their time of operation, to minimize the costs, primarily by shifting the demand to the overnight period for which the electricity costs are lower and, due to lower ambient temperatures, the chillers are more efficient. The main goal is to develop a reliable and fast algorithm, through solving a linear or convex optimization problem, that operates the chillers at their peak efficiency and avoids excessive start-up and shut-down of chillers. [ABSTRACT FROM AUTHOR]

Distributed power and energy resources are now being used to meet the combined electric power, heating, and cooling demands of many buildings. The addition of on-site renewables and their accompanying intermittency and non-coincidence requires even greater dynamic performance from the distributed power and energy system. Load following generators, energy storage devices, and predictive energy management are increasingly important to achieve the simultaneous goals of increased efficiency, reduced emissions, and sustainable economics. This paper presents two optimization strategies for the dispatch of a multi-chiller cooling plant with cold-water thermal storage. The optimizations aim to reduce both costs and emissions while considering real operational constraints of a plant. The UC Irvine campus micro-grid operation between January 2009 and December 2013 serves as a case study for how improved utilization of energy storage can buffer demand transients, reduce costs and improve plant efficiency. A predictive control strategy which forecasts campus demands from weather predictions, optimizes the plant dispatch, and applies feedback control to modify the plant dispatch in real-time is compared to best-practices manual operation. The dispatch optimization and predictive control algorithms are shown to reduce annual utility bill costs by 12.0%, net energy costs by 3.61%, and improve energy efficiency by 1.56%. [ABSTRACT FROM AUTHOR]

We study a counter-flow solid oxide fuel cell system and consider the challenges faced in minimizing thermal variations from the nominal operating conditions for a reasonable range of power tracking. Blower dynamics, reformer transport delays, spatial distribution of the heat generated and the resulting thermal response are among the issues considered. A novel approach, relying on partial internal reformation of the feedstock is proposed as a remedy to maintain a strong level of power tracking with minimal thermal stress to the fuel cell. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical solid oxide fuel cell–gas turbine hybrid system has been designed using a Capstone 60kW micro-gas turbine. Through simulation it is demonstrated that the hybrid system can be controlled to achieve transient capability greater than the Capstone 60kW recuperated gas turbine alone. The Capstone 60kW gas turbine transient capability is limited because in order to maintain combustor, turbine and heat exchangers temperatures within operating requirements, the Capstone combustor fuel-to-air ratio must be maintained. Potentially fast fuel flow rate changes, must be limited to the slower, inertia limited, turbo machinery air response. This limits a 60kW recuperated gas turbine to transient response rates of approximately 1kWs−1. However, in the SOFC/GT hybrid system, the combustor temperature can be controlled, by manipulating the fuel cell current, to regulate the amount of fuel sent to the combustor. By using such control pairing, the fuel flow rate does not have to be constrained by the air flow in SOFC/GT hybrid systems. This makes it possible to use the rotational inertia of the gas turbine, to buffer the fuel cell power response, during fuel cell fuel flow transients that otherwise limit fuel cell system transient capability. Such synergistic integration improves the transient response capability of the integrated SOFC gas turbine hybrid system. Through simulation it has been demonstrated that SOFC/GT hybrid system can be developed to have excellent transient capability. [Copyright &y& Elsevier]