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The cost-effectiveness of interconnected microgrid systems with combined heat and power is examined for 36 cases involving six microgrid applications in six different U.S. locations. In the baseline analysis, microgrids are found to be good investments in areas with relatively high 'spark spreads' (electricity/natural gas price differentials). Customers with a higher value for electric reliability realize greater benefits. Results become more favorable over time if the rate of increase of electricity prices is at least 60% of the rate of increase of natural gas prices--a plausible scenario in states with substantial natural-gas fired capacity. Sensitivity analyses reveal that the choice of microgrid customer mix has a much greater impact on system economics than climate. Economies of scale are shown to be fairly modest for the systems considered here, but microgrids do show clear benefits over traditional single customer distributed generation. If performance goals of current U.S. Department of Energy research programs for 1C engines and microturbines are met, rates of return for microgrid investments increase 10-20%. DOI: 10.1061/(ASCE)0733-9402(2007)133:3(150) CE Database subject headings: Grid systems; Powerplants; Electric power supply; Sensitivity analysis.

This paper deals with a hydraulic servo system with compliance control for the operation in an environment with frequent machine-human interaction. The compliance is mechanically adjusted in the present hydraulic system by changing the neutral position of the bridge valves between the full opening and the full closing states. The mathematical model of the system is first derived, and the static and the dynamic behavior of the system are investigated through numerical simulation. Since the present system exhibits a strong nonlinear characteristic in the operating condition of large compliance, a nonlinear controller is designed with the feedback linearization technique. In the operating condition of small compliance, on the other hand, a conventional linear control is applicable as usual hydraulic control systems. The performance of the present control system is investigated through both numerical simulation and experiment, justifying that the present hydraulic servo system continuously adapts its performance between a rigid positioning against disturbances and a compliant positioning to prevent damage to obstacles on the path. [DOI: 10.1115/1.1433803]

This paper proposes a simplified theory to predict and compare the seismic performance of viscoelastical (VE)- and elastoplastical (EP)- damped passive control systems, and to demonstrate their ability to protect structures during a major seismic event. Closed-form expressions for 'equivalent period' and 'equivalent damping' of these systems are proposed by idealizing them as linear single-degree-of-freedom (SDOF) systems. The expressions are used to clarify and compare the structural parameters, seismic drift, and force for the systems, based on a common high-damping linear spectrum. By extending the SDOF theory, a seismically deficient 14-story steel moment resisting frame (MRF) is upgraded by inserting VE or EP dampers. Extensive three-dimensional multi-degree-of-freedom nonlinear dynamic analyses are performed for the MRF, VE system, and EP system using earthquakes of various intensities. The 14-story VE and EP systems responded as predicted by the SDOF theory. They show much smaller drifts than the original MRF, keep frame members elastic, and protect nonstructural components, even against major earthquakes.

Frequently, due to the irregularities in fuel properties of the wastes and variations in feed rates, the operation of a batch-fed incinerator may encounter pressure surges and transient flue gas leakages. A lumped model to simulate the flow, pressure, and temperature behavior of an incineration system was developed, according to the fundamental conservation laws governing the overall balances of flow and thermal-mechanical energies of the system components. The system dynamic responses to flow control and waste burning variations were analyzed numerically. Qualitatively, the results correctly reflected the observed operational characteristics of batch-fed incinerators. The lumped system model can serve as a tool to design control algorithms. The concepts and approaches adopted in this work can be used as the basis for further expansion in details toward the development of an incinerator system simulator for operator training purposes.

The structured singular value method is applied to continuous-time SISO repetitive control systems in order to determine their stability and performance robustness in the presence of structured parametric modeling error in the plant. Performance measures for repetitive control systems are introduced and the robust performance analysis using structured singular values is modified, taking the alternating magnitude behaviour of the sensitivity function of a repetitive control system into account. The analysis procedure is simplified considerably in the case of large time delay by noting that the upper and lower envelopes of the structured singular value plots are obtained from corresponding finite dimensional systems without any time delay. The analysis procedures developed are applied to an example on repetitive control of an electrohydraulic material testing machine, available in the literature, to demonstrate their usefulness.

Two methods of control of semi-active suspensions that specifically address the problem of structural vibrations of the vehicle body are considered. These control strategies are based on those developed for active suspension systems in Part I of this study and rely on either modifications of suspension control forces that account for body compliance or on the addition of a proof-mass actuator to reduce structural vibrations. A half-car model that includes body compliance is used to evaluate the effects of these control strategies on the performance of the suspensions with two-state and continuously modulated dampers. The performances of the systems are evaluated in both the time and frequency domains. The effect of time delays in the process of actuating the adjustable dampers is investigated. Significant reductions of structural vibrations are observed when the nodes of body beaming modes are a sufficient distance away from the suspension mounting points, and the time delays in the control system are negligible. The results deteriorate markedly when two-state dampers are used instead of continuously variable dampers or when a time delay in excess of 5 ms is present in the control loop. When the preference in suspension design shifts toward road holding it becomes increasingly difficult to improve the vehicle structural response without sacrificing other aspects of performance.

A novel nonlinear sliding mode controller has recently been developed for direct acting proportional solenoid valves. This paper presents a comparison between the valve performance using this controller, and that obtained using two alternative control strategies; state feedback and PID control. Each controller is described in turn, and experimental step response results are presented to demonstrate the validity of each strategy. These results are compared on the basis of response time, overshoot, and steady-state error. The time taken to design each controller, and the required level of knowledge of the valve dynamics, are also assessed. The ability of each controller to reject flow reaction forces is evaluated by observing the changes in the step response when oil is passed through the valve. The results demonstrate that the sliding mode controller results in a faster, more robust closed-loop response. In addition, only minimal knowledge of the valve dynamics is required in order to design the controller.

This paper describes the specification, development, and testing of the FT8-2 Dry Low N[O.sub.x] control system, and how the lean burn process requires an integration of the control system and combustion hardware. The FT8-2 digital fuel control system was developed to achieve the precise multizone fuel metering of both gas and liquid fuels, the calculation of combustor air flow necessary to achieve Dry Low N[O.sub.x] and the traditional governing/limiting control loops necessary for safe, stable engine operation. The system design goals were accomplished by the concurrent development of software-based fuel metering algorithms and fuel metering hardware. The fuel metering hardware utilizes an all-electronic valve positioner, employing a combination of feedback and software to achieve closed-loop control of actual fuel flow. Extensive testing under actual gas flow conditions and closed-loop bench testing using a real time engine model and fuel system model was conducted to prove system operation and develop system transient response prior to installation on the test engine. The setup and results of the flow testing and closed-loop testing are described. The paper describes the control scheme used to apportion the gas fuel between combustion zones and how external conditions such as ambient temperature and fuel gas composition affect the apportionment. The paper concludes with a description of the control system installation in the engine test cell and a review of engine test results.

An integrated time domain state space identification technique for structural systems is presented. This technique integrates the Observability Range Space Extraction identification algorithm, Balanced Realization model reduction algorithm, and Least Square model updating algorithm to generate low order and highly accurate state space models for structural systems based upon time domain data. The algorithms are integrated in such a manner that the Observability Range Space Extraction identification algorithm is used to generate an initial overparameterized state space model and then the Balanced Realization model reduction and Least Square model updating algorithms are used to iteratively reduce and update the model to achieve minimum prediction errors in time domain. We shall present the Observability Range Space Extraction identification algorithm and the Least Square model updating algorithm and discuss the integrated identification technique. The MIT Middeck Active Control Experiment (MACE) is used as an application example. MACE is an active structure control experiment to be conducted in the Space Shuttle middeck. Results of ground experiments using this technique will be discussed.

A correlation equation is established between open-loop test data and the desired closed-loop system characteristics permitting control system synthesis to be done on the basis of a numerical approach using experimental data. The method is applicable when the system is linear-time-invariant and open-loop stable. The major merits of the algorithm are two-fold: 1) Arbitrary placement of the closed-loop system equation is possible, and 2) explicit knowledge of an open-loop system model is not needed for the controller synthesis.

Model-based monitoring systems based on state observer theory are attractive for machine monitoring because practical, inexpensive, and reliable sensors can be located remote to the signal(s) of interest. Then, a model of the machine plus an estimation algorithm are utilized to convert the output of the remote sensors to signals representing the desired local behavior. While this type of monitoring system has shown much promise in the laboratory, it has not been widely accepted by industry because, in practice, these systems often have poor performance with respect to accuracy, bandwidth, reliability (false alarms), and robustness. In this paper, the limitations of the deterministic state observer are investigated quantitatively from the machine monitoring viewpoint. The limitations in the transient and steady-state observer performance are quantified based on the estimation error bounds, and from these error bounds, performance indices are selected. Then, based on the relationships between the indices, a main index is determined in order to represent the overall observer performance. The index is the condition number of the observer eigenvectors in [L.sub.2] norm. It is shown that observers with small condition numbers are guaranteed to have small error bounds. This index can be utilized as a quality condition for any linear observer regardless of how it is designed as well as form the basis for an observer design methodology for high performance observer-based monitoring systems.

All real-world control systems have saturation nonlinearity in final control elements (including actuators). When controllers involve integral action, reset windup can cause instability as well as make system performance unsatisfactory. Based on the describing function method and the generalized Popov criterion, this paper presents analysis of the global stability of a control system having a saturating second-order plant, both with and without using a deadbeat limiting scheme to constrain its controller output. The improvement of system performance by incorporating the anti-windup feature in the controller is illustrated by computer simulations.

The fundamental concept of feedback to control dynamic systems has played a major role in many areas of engineering. Increases in complexity and more stringent requirements have introduced new challenges for control systems. This paper presents an introduction to and appreciation for intelligent control systems, their application areas, and justifies their need. Specific problem related to automated human comfort control is discussed. Some analytical derivations related to neural networks and fuzzy optimal control as elements of proposed intelligent control systems, along with experimental results, are presented. A brief glossary of common terminology used in this area is included.

In this essay, on the observance of the 50th anniversary of the founding of ASME's Dynamic Systems and Control Division, I try to connect the technology of control to the way in which control practitioners think. Despite some tension between the conclusions implied in the introductory paragraphs and conclusions drawn later in the essay, I have left them to stand in their original form to emphasize tensions in control thinking, for which the source might not be apparent. The opinions expressed here are strictly my own, but I must acknowledge the creative proddings of my colleagues in getting these thoughts recorded at all.

The effects of test machine dynamic response and control systems strategies on the outcome of rate-dependent metal flow experiments are investigated. Pure 1145 aluminum specimens are tested using a servoelectric test machine with analog electronic control circuitry. Data are collected using a data acquisition system with 16 bit resolution. Results show that the dynamic response of the machine must be characterized prior to any rate-change experiment in order to achieve a transient response.

The stability of a controller used to control the water level in the forebay or afterbay of a hydroelectric power plant is investigated by using the Routh-Hurwitz stability criterion. It is shown how the characteristics of the controller influences the required size of the forebay in a plant with a surge tank, while there are no restrictions regarding stability for a plant without a surge tank. Computer simulations of the water-level oscillations in a hydropower plant including all major nonlinearities verify these conclusions and show that the operation with small flows is critical as far as the stability is concerned. Guidelines are given to select the dimensions of the forebay for preliminary design. A practical example illustrates the application of this type of control system.

Byline: Zhibin Xue, Jianchao Zeng The swarm foraging behaviour control scheme of stochastic swarm systems is investigated in this paper, whose agents are moving in n-dimensions Euclidean space with a family of attractant/repellent profile based on artificial potential functions under the m-dimensional standard Gauss white noise jamming. The corresponding M-member 'individual-based' Lagrangian isotropic/anisotropic continuous time social foraging swarms model is proposed. Furthermore, formation control is considered as a special form of swarm aggregation, where the final aggregated form of the swarm is desired to constitute a particular predefined arbitrary polygonal geometrical configuration that is defined by a set of desired inter-agent distance values. Through numerical simulations, the stability and validity of the proposed foraging swarm's behaviour control scheme is illustrated.

Byline: Zeng-Qiang Chen, Jia-Xiang Zhao, Zhu-Zhi Yuan An Active Disturbances Rejection Controller (ADRC) is presented for a class of single-input-single-output non-linear systems with a hysteresis non-linearity represented by the Preisach model. The designed ADRC controller is composed of the non-linearity tracking differentiator, the extended state observer and the non-linearity PID controller. It can estimate disturbances and compensate according to the information between the input and the output of the controlled object. Thus it automatically realises the suppression of disturbance. The simulation result indicates that the ADRC controller with a set of invariable parameters can maintain that the non-linear systems with a hysteresis non-linearity have ideal tracking effect.

Byline: Jianliang Sun, Yan Peng, Hongmin Liu In this paper, the integral dynamic model of four-high mill is built which includes the rolling process model, the dynamic model of mill stand-rolls and the dynamic model of hydraulic servo system. The three models are coupled and linearised, the MIMO transfer function of four-high mill system is obtained. Considering the quality of the product, the MIMO model is simplified and the thickness control system based on thickness gauge is derived. The H∞ robust controller is designed for the thickness control system based on the mixed sensitivity robust control theory. The weighting functions are selected based on genetic algorithm. Simulation results and comparison with the effect of PI controller show that the robust controller designed has better disturbance attenuation performance for parameter uncertainty and external disturbance. The dynamics performances and stability of the thickness control system based on thickness gauge are improved significantly.

Byline: Xiang-Hua Ma, Jian-Ying Xie A challenging issue in Networked Control Systems (NCSs) is how to compensate the effect made by network-induced delays. In this paper, a control scheme is proposed for compensating the effects of delays between sensor and controller and between controller and actuator within a control loop. The key idea is that the knowledge of the plant dynamics is used to reduce the usage of network. Experimental results show that the method well guarantees the stability of the system.

In this paper, a generalized design procedure for sliding mode control of nonlinear mechanical systems is proposed. The design approach combines the essential idea of the block control principle, utilizing some of the components of the state vector as a virtual control, with the basic concept of zero dynamics. For mechanical systems governed by a set of interconnected second-order equations, the block control principle cannot be directly applied. To facilitate the controller design, we assume that control systems can be transformed into a regular form consisting of second-order equations. The proposed design approach consists of reducing the original plant into the regular form, constructing a switching manifold, and enforcing sliding mode in the manifold such that the reduced order system in sliding mode has desired dynamics. Stabilization of the mechanical system with unstable zero dynamics is taken into consideration. It is shown that the approach has the advantage of decomposing the original problem into subproblems of lower dimensions, and each of them can be handled independently. As an example, control of a rotational inverted pendulum system is examined. The performance of the proposed approach is validated by both numerical and experimental results. [S0022-0434(00)01601-4] Keywords: Block Control Principle, Regular Form, Mechanical Systems, Sliding Mode Control, Rotational Inverted Pendulum, Unstable Zero Dynamics

Efficient design of high performance automatic control systems is extremely important for high technology systems. To get the best hardware cost-to-performance ratio, it is desirable to design a controller that takes full advantage of actuator capabilities, but this can lead to nonlinear behavior due to actuator saturation. The saturation nonlinearities in the system may have severe effects on system performance due to, for example, integrator windup. In this paper, a new design method is presented based on Lyapunov stability theory. By incorporating the actuator constraints directly in the design method, better utilization of the available control effort can be ensured in achieving desired system behavior. [S0022-0434(00)01801-3]