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A solid oxide cell-based energy system is proposed for a solar-powered stand-alone building. The system is comprised of a 5 kWel solid oxide fuel cell (SOFC), a 9.5 kWel 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 H2 balance.

In this study, an islanded microgrid system is proposed that integrates identical stacks of solid oxide fuel cell and electrolyzer to achieve a thermally self-sustained energy storage system. Thermal management of the solid oxide electrolysis cell (SOEC) is achieved by the use of heat from the solid oxide fuel cell (SOFC) with a heat exchanger network and control strategies. The SOFC meets the building electricity demand and the heat generated from its electrochemical reactions is transferred to the SOEC for the endothermic heat and standby demands. Each component is physically modeled in Simulink and ultimately integrated at the system level for dynamic analyses. The current work simulates a system comprised of a wind farm in Palm Springs, CA, coupled with the SOEC (for H2 generation), and an industrial building powered by the SOFC. Results from two weeks of operation using the measured building and wind data showed that despite fluctuating power profiles, average temperature, and local temperature gradients of both the SOEC and SOFC were within desired tolerances. However, for severe conditions of wind power deficit, H2 had to be supplied from previous windy days’ storage or imported.

This work studies connectivity maintenance of mobile networks. A mobile network of interest consists of two types of nodes, pre-deployed (client) and intermediate nodes. Upon initial deployment of client nodes in a field, multiple stationary intermediate nodes are placed strategically to establish robust network connectivity. We study scenarios in which an initially connected network consisting of pre-deployed and intermediate nodes is exposed to mobility of the former. Two types of node mobility scenarios are investigated. The first scenario analyzes the bounds of mobility when pre-deployed nodes move at small scales. The bounds of node mobility preserving connectivity are derived through analysis and verified by simulations. The second scenario considers the movement of pre-deployed nodes beyond the bounds of the first scenario thereby breaking connected links and partitioning the connected network. This scenario then considers relocating the existing intermediate nodes in order to reestablish connectivity. A general formulation is proposed in the form of an optimization problem. We prove that the general formulation of the problem is NP-hard. Next, we turn our attention to a practical scenario in which the location of nodes is made available using GPS signals. We solve the problem of practical scenario in polynomial time and analyze the complexity of our solution. We also present comprehensive performance evaluation results of our proposed algorithm.

In this study, an islanded microgrid system is proposed that integrates identical stacks of solid oxide fuel cell and electrolyzer to achieve a thermally self-sustained energy storage system. Thermal management of the SOEC is achieved by use of heat from the SOFC with a heat exchanger network and control strategies. While the SOFC meets the building electricity demand and heat from its electrochemical reactions is transferred to the SOEC for endothermic heat and standby demands. Each component is physically modelled in Simulink and ultimately integrated at the system level for dynamic analyses. The current work simulates a system comprised of a wind farm in Palm Springs, CA coupled with the SOEC (for H2 generation), and an industrial building powered by the SOFC. Results from two-weeks of operation using measured building and wind data showed that despite fluctuating power profiles, average temperature and local temperature gradients of both the SOEC and SOFC were within desired tolerances. However, for severe conditions of wind power deficit, H2 had to be supplied from previous windy days’ storage or imported.

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.

Summary Semi-active variable stiffness resettable devices can reduce seismic demands and damages in structures. Despite their advantages, variable stiffness resettable devices are under-utilized mainly because of the shortage of fundamental research in quantifying the sensitivity of key seismic response parameters, and losses, in structures that use such systems for seismic hazard mitigation. Within this setting, the research summarized herein measures the effectiveness of semi-active resettable energy dissipating devices in the Single-Degree-of-Freedom domain aiming at quantifying the sensitivity of their seismic response to variation in control parameters and generating the required knowledge to utilize such semi-active devices in the Multi-Degree-of-Freedom domain. The performance (i.e. maximum relative displacement and peak absolute acceleration demands) of Single-Degree-of-Freedom systems with an array of semi-active control logics under various dynamic excitation regimes is studied. Two sets of 40 ground motions representing various seismic loading conditions (i.e. pulse-like and rock-site ground motions) are used, and an efficient control logic for mitigating these seismic demands is proposed. Numerical results show that proposed control logic enables a decrease of 40–60% for both maximum relative displacement and seismic base shear and 15–25% decrease for peak absolute acceleration. Copyright © 2016 John Wiley & Sons, Ltd.

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.

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.

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.

A Solid Oxide Fuel Cell (SOFC) integrated with a variable speed blower is studied. The idea is to maximize the usable power of the fuel cell, by artificially bounding the inlet flow rate, thus, avoiding the overshoots in the blower power. Anti-windup techniques are then incorporated in order to guarantee the stability and provide a satisfactory performance. Significant temperature drops in cathode inlet (second actuator signal) caused by AW are also avoided in order to minimize the temperature gradients along the cell.

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.

We consider systems with actuator magnitude and rate limitations, and assume there are high performance compensators with highly desirable properties as long as the actuator limitations are not violated. A multi-stage anti-windup (AW) scheme is presented that provides stability and performance measures, for commands with known bound. More critically, it uses different gains for different levels of saturation, allowing for more aggressive anti-windup gains when the command signals are moderately above the actuator limitations. The benefits are shown through an illustrative example.

We discuss adding a measure of scheduling to the popular Anti-Windup design. The main idea is to develop a scheme in which the Anti-Windup gains depend on how much the actuator command exceeds the saturation bound. The aim is to design and implement more aggressive Anti-windup gains in lower levels of saturation. Global stability and performance are addressed by adding an outer-loop Anti-windup compensation which become active when the system is in higher levels of saturation. We present results for both static and dynamic Anti-Windup gains, along with the convex synthesis LMIs. Benefits of the proposed design method are shown using well-known examples.

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.

We present an Anti-windup scheme in which once saturation is encountered the nominal controller is replaced with a continuous scheduled family of controllers. In the proposed scheme, when the command to the actuator reaches the saturation limit, based on the system behavior (e.g., the closed-loop state vector or compensator states), the control law selects a member of the family of controllers that provides the best performance while avoiding saturation. As a result, the controller has a quasi linear parameter varying structure. Numerically, the family of the controllers is based on linear splines, and can be obtained by standard LMI software.

We investigate the effects of deferring the activation of anti-windup by allowing actuators to remain in the saturated regime longer, without any assistance. The basic idea is to apply anti-windup when the performance of the saturated system faces substantial degradation. For this, we present a modified anti-windup scheme along with the appropriate LMIs to obtain the gains. For two examples, we show that the modified anti-windup scheme renders better performance than the immediate application of anti-windup.

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. © 2008 Elsevier B.V. All rights reserved.

We modify a class of scheduled controllers, originally developed to address actuator saturation in the disturbance attenuation problem, for the problem of tracking of generally unknown signals. The main assumption is that some (possibly conservative) bounds are known for peak magnitude and rate of the tracking signal. Both state feedback, for comparison, and output feedback controllers are presented. The solvability conditions and effectiveness are shown through an example.

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. © 2008 Elsevier B.V. All rights reserved.

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.

A control law is developed for an inexpensive pneumatic motion control system using four solenoid on/off valves and a position feedback sensor. A sliding-mode approach is used, which is well known for its tolerance for system uncertainties. In contrast to previous control laws, our approach does not use pulsewidth modulation. The control law has an energy-saving mode that saves electrical power, reduces chattering, and prolongs the valve's life. Our simulation and experimental results show that the proposed tracking control law performs very well with good tracking and relatively low steady-state position errors

Because of many advantages over other control systems, semi-active control devices have received considerable attention for applications to civil infrastructures. A variety of different semi-active control devices have been studied for applications to buildings and bridges subject to strong winds and earthquakes. Recently, a new semi-active control device, referred to as the resetable semi-active stiffness damper (RSASD), has been proposed and studied at the University of California, Irvine (UCI). It has been demonstrated by simulation results that such a RSASD is quite effective in protecting civil engineering structures against earthquakes, including detrimental near-field earthquakes. In this paper, full-scale hardware for RSASD is designed and manufactured using pressurized gas. Experimental tests on full-scale RSASDs have been conducted to verify the hysteretic behaviours (energy dissipation characteristics) and the relation between the damper stiffness and the gas pressure. The correlation between the experimental results of the hysteresis loops of RASADs and that of the theoretical ones has been assessed qualitatively. Experimental results further show the linear relation between the gas pressure and the stiffness of the RSASD as theoretically predicted. Finally, shake table tests have also been conducted using an almost full-scale 3-storey steel frame model equipped with full-scale RSASDs at the National Center for Research on Earthquake Engineering (NCREE), Taipei, Taiwan, and the results are presented. Experimental results demonstrate the performance of RSASDs in reducing the responses of the large-scale building model subject to several near-field earthquakes. Copyright © 2007 John Wiley & Sons, Ltd.

This paper addresses control of structural vibrations using semi-active actuators that are capable of manipulating stiffness and∕or producing variable stiffness. Usually vibration suppression is achieved using damping devices rather than stiffness ones. However, stiffness devices can produce large forces and have significant advantages for shock isolation purposes. In this work we use a passivity approach to establish the requirements for the control law for a structure equipped with semi-active stiffness devices. We also solve an optimal control problem that demonstrates that our passive, resetting feedback control law approximates the optimal control. Simulation and experimental results are presented in support of the proposed approach.

Current high temperature fuel cell (HTFC) systems used for stationary power applications (in the 200-300 kW 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 1 kWs-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 10 kWs-1 (4% s-1) when using a worst-case design analysis. This requirement for fast dynamic load response characteristics can be reduced to 1 kWs-1 by utilizing high resolution demand data to properly size ultra capacitor systems and through demand management techniques that reduce load volatility. © 2005 Elsevier B.V. All rights reserved.

SUMMARY We discuss the application of a new class of low-cost and high-reliability semi-active devices for the response mitigation of structures subject to earthquakes. These devices, which manipulate stiffness rather than damping, are evaluated by the smart base-isolated benchmark building. The basic motivation, idealization as a stiffness resetting damper or device, development of control logic that ensures the semiactive property, and initial testing and validation results from recently developed prototypes are discussed. The principle idea allows the use of reliable and inexpensive hydraulic or pneumatic technologies, and leads to a decentralized and easy to implement architecture. The results from the benchmark simulations show performance competitive with well-known semi-active techniques. Copyright # 2005 John Wiley & Sons, Ltd.

Two H2-based control strategies are proposed and their applications to civil engineering benchmark structures are presented. The first strategy deals with a class of excitations with a specified ‘energy’ bound, referred to as the H2-based controller with energy-bounded excitations (H2B-EB), whereas the second strategy addresses a class of excitations with a specified peak bound, referred to as the H2-based controller with peak-bounded excitations (H2B-PB). Both control strategies are derived by minimizing an upper bound of the H2 performance with the constraints (or penalties) on the peak values of another set of quantities, such as the control resources. State feedback and dynamic output feedback controllers are derived and presented. The design syntheses of these 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 control strategies are applied to the Phase I long-span cable-stayed benchmark bridge subject to earthquakes and a wind-excited 76-storey benchmark building to illustrate their applicability to practical problems. Simulation results indicate that the performances of these proposed controllers for structural responses are better than that of the LQG sample controller. It is shown that these new control strategies are viable and effective for applications to civil engineering structures. Copyright © 2003 John Wiley & Sons, Ltd.

A new class of scheduled controllers is presented for improving the response of seismic-excited buildings under actuators with limited capacity. The controller is scheduled based on the response of the system on-line, to take full advantage of the inevitably limited actuation. While the controller is nonlinear, the overall approach relies on a variety of techniques from linear designs, which makes it possible to generalize the approach to a variety of systems and control objectives. For example, sufficient conditions for feasibility of a feedback controller are expressed in terms of linear matrix inequalities, thus solvable with standard software. Both state feedback and observer-based controllers are discussed. Performance of the proposed technique is illustrated through simulations of a six-story building subject to earthquake ground motion.

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 \IMATLAB\N 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.

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.

Efficient design techniques are presented for improving the response of seismic-excited buildings under actuators with limited capacity. Information regarding the actuator capacity and estimated peak ground acceleration is used to fine tune the controller and reduce conservatism. Both state feedback and observer-based controllers are discussed. The observer-based controller uses the measurement of the ground acceleration, though this requirement can be removed easily. Sufficient conditions for feasibility of a feedback controller are expressed in terms of linear matrix inequalities. Performance of the proposed techniques is illustrated through simulations of a six-story building subject to earthquake ground motion.

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.

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 and a tank that can store enough energy for the cooling demand of most days, but not all. 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 that can be used for planning and updating the chillers operations.

In this paper we present control design methods that provide desirable levels of performance and simultaneously account for actuator and sensor reliability (or malfunction) for buildings under seismic excitations. Performance is defined in terms of the disturbance attenuation (i.e. L2 gain) from the disturbances to the controlled outputs of the system. The reliability of actuators and sensors refers to the deviation of actual control forces or actual sensor measurements from their ideal levels. Simulation results for a six-storey building are used to demonstrate the effectiveness of the control analysis and design method presented. Copyright © 2000 John Wiley & Sons, Ltd.

A novel low power control technique along with a new class of actuators is developed for shock isolation and control of structural vibrations. In contrast to other techniques, including conventional viscous or rate damping, the force produced by the actuator has no velocity dependence. Several experimental, analytical, and simulation results are presented in support of this new, semi-active technique for structural control. The basic approach is to manipulate the system stiffness through the use of resetable actuators. With the proposed control approach, the actuator behaves like a linear spring. However, at appropriate times, the effective unstretched length of the actuator is changed—or reset—to extract energy from the vibrating structure. Experimental validation of the actuator model, analytical results on stability and actuator-placement, and simulation results for earthquake applications are presented. [S0022-0434(00)01603-8]

Recently developed quadratic stability and performance control techniques are used to design controllers for the active mass driver (AMD) benchmark problem. Several designs are obtained and analysed to highlight the utility of the proposed technique. Solution through the use of linear matrix inequalities is presented and extensions to systems with modelling error, actuator/sensor malfunction and saturating controllers are discussed. Simulation results indicate that the performance of the control techniques is quite remarkable.

Two design techniques are proposed to improve disturbance attenuation of seismic-excited buildings with bounded actuators. The first technique is based strictly on the quadratic stabilization with a disturbance attenuation technique and the second relies on a multiobjective approach that combines the first technique with constraints on the inputs. The second technique makes use of the available information regarding actuator capacity and peak magnitude of disturbance; hence, its results are less conservative. The sufficient conditions for feasibility of a full-state feedback controller are expressed in terms of linear matrix inequalities (LMIs). For the output feedback design, it is assumed that ground acceleration is available for measurement and the controller is assumed to have an observer-based structure. The validity and applicability of the two proposed techniques are illustrated using simulations of a six-story building subjected to earthquake.

Because of the stochastic nature of earthquakes and limited capacities of actuators, it is conceivable that the actuators used for the control of civil engineering structures may be saturated during strong earthquakes. In this paper, the stability of actively controlled linear structures under a variety of popular control methods during actuator saturation is investigated. Sufficient conditions to guarantee the asymptotic stability of the structure during actuator saturation are examined and discussed. These conditions involve the solution of a system of simultaneous linear matrix inequalities (LMI). A simple and efficient computer code to solve a system of LMI, based on the MATLAB LMI toolbox, is presented for use by the readers. Based on sufficient conditions, a method for designing general controllers, that guarantee asymptotic stability during actuator saturation, is presented. It is shown analytically that Lyapunov controllers, \iH\d∞–type controllers, and sliding–mode controllers are asymptotically stable during actuator saturation. For multi–degrees-of-freedom (MDOF) systems using pole assignment and linear quadratic regulator (LQR) controllers, it has been shown through extensive simulations results that: (1) asymptotic stability of structures is more likely to be guaranteed for low-gain controllers than for high-gain controllers; (2) adding active damping to the structure is much more beneficial than adding active stiffness, in terms of asymptotic stability; and (3) asymptotic stability can be guaranteed for quite high levels of added active damping to various modes of the structure. Further extensive simulation results demonstrate that static output feedback controllers using only velocity feedback are always asymptotically stable in the range of practical applications. Likewise, for static output controllers using collocated sensors, the region of asymptotic stability is quite large.

Power tracking and temperature control of solid oxide fuel cell (SOFC) for co-flow and counter-flow configurations have been studied. Partial internal reformation has been used to address many of the difficulties associated with delays in balance of plant (BOP). High performance controllers are used to reduce thermal stresses that can result from rapid and significant power tracking. Both co-flow and counter-flow designs are considered and advantages and disadvantage of each are then reviewed.Copyright © 2013 by ASME

This paper presents robust H∞ control for civil engineering structures using static output feedback. Within the H∞ framework, controllers which lead to desirable performance are obtained, using a limited number of sensors but without observers. In addition, the closed-loop system can be designed to be robust with respect to potentially time-varying, structured uncertainties in the system. We do not use state feedback or estimates of the state in our controller, and only use the measured output from a limited number of sensors installed at strategic locations. Necessary and sufficient conditions are presented, which guarantee stability and disturbance attenuation for all admissible uncertainties via static output feedback control. The effectiveness of such controllers is illustrated through simulations of the responses of a three-story and a six-story building under seismic excitation. The results indicate that significant reductions in the building response can be achieved with a limited number of sensor ...

In ihis paper, we apply recently developed linear matrix inequality techniques to the design of feedback controllers for seismic-excited buildings. Unlike most applications in this area, we do not assume perfect model knowledge, but incorporate the uncertain structural parameters into the model. Both state feedback and dynamic output feedback are considered. LMIs cannot be applied easily to the dynamic output feedback case and we offer an alternative approach we believe is easier to solve.

Recently, advanced control theories have been investigated for applications to control of seismically excited structures. The H and sliding mode control methods were found to be promising for civil engineering structures, based on numerical simulation results. This paper presents the results of shaking table experiments that were conducted to confirm the validity of the H and continuous sliding mode control methods. A three-story, 1/4-scaled building model was used, equipped with an active tendon control system. Various earthquake records were used as input excitations. Both the full-state feedback controllers and the static output feedback controllers were employed. The experimental data correspond satisfactorily with numerical simulation results. Extensive test results illustrate that the H and continuous sliding mode control methods, particularly the static output feedback controllers using only the measured information from a limited number of sensors installed at strategic locations without an observer, have practical applications as active control systems on seismically excited structures.

In order to meet the demands of simplicity and reliability in active control systems for flexible structures, an inexpensive active truss element and control law has been developed in this research. A decentralized switching control law is used along with a compressible fluid in the truss element in order to dissipate energy during the motion of the structure. However, the energy is not absorbed in the same manner as a conventional viscous damper. The truss element retains its maximum stiffness, but has a reset-able nominal unstressed length. Energy is absorbed in the working fluid of the truss element through heat transfer to the environment when the nominal length is reset at the proper switching times. The control law is insensitive to changes in structural parameters such as mass, stiffness, and damping. In this paper, a mathematical model for the system is presented along with a stability analysis and experimental results.

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.

Robust control techniques are applied to civil engineering structures subjected to earthquake excitation. Full-state feedback and observer-based control laws are used to reduce the response of the building due to earthquake ground motion. Effects of actuator dynamics and a method to incorporate these dynamics into the overall design are also presented. The effectiveness of the control method is demonstrated by simulation results.

Spatial temperature feedback control has been developed for a simulated integrated non-pressurized simple cycle solid oxide fuel cell (SOFC) system. The fuel cell spatial temperature feedback controller is based on (1) feed-forward set-points that minimize temperature variation in the fuel cell electrode-electrolyte solid temperature profile for the system operating power range, and (2) decentralized proportional-integral based feedback to maintain the fuel cell spatial temperature profile during transients and disturbances. Simulation results indicate the fuel cell spatial temperature variation can be maintained within 15 degrees of nominal to significant load perturbations. Temperature gradients through the fuel cell are needed to remove the heat generated within the cell and cannot be avoided. The goal of the developed spatial temperature control is to minimize temperature variations from a nominal temperature profile in time. Minimal temperature variations in the SOFC electrode-electrolyte solid assembly will result in decreased thermal stresses and thereby decreased degradation and probability-of-failure. Simulation results demonstrating the ability to maintain the SOFC spatial temperature during large load perturbations indicates SOFC could be designed and controlled for rapid load following capability. Such performance can greatly improve SOFC system operating flexibility and thereby open new markets for SOFC systems including load following or spinning reserve services for the utility grid.Copyright © 2010 by ASME

This note considers the popular Anti-windup design problem for linear systems with saturating actuators. The main contribution of this paper is providing the synthesis LMIs to obtain the gains of the dynamic Anti-Windup compensator in a structure that delays the activation of the Anti-Windup. The basic idea is to apply Anti-Windup when the performance of saturated system faces substantial degradation. Benefits of the proposed design method over the immediate activation of the Anti-Windup are demonstrated using a well-known example.

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.

In this paper an implementation of an adaptive control law for a pneumatic actuator is presented. Pneumatic actuators are of particular interest for robotic applications because of their large force output per unit weight, and their low cost. Stabilization of a pneumatic actuator is difficult if a high bandwidth closed-loop system is desired. This is because of the compressibility of air, and of the nonlinear characteristics of air flowing through a variable area orifice. Further complications arise from the geometry of the mechanism because the equations of motion are highly nonlinear. The order of the dominant dynamics is shown to vary with the position of the mechanicsm.