Output Saturations Research Articles

Data-driven adaptive control of wide-area non-linear systems with input and output saturation: A power system application

In this paper, a Data-Driven Adaptive Controller is proposed for wide-area Multi-Input and Multi-Output (MIMO) non-linear systems featuring input–output saturations. Complexity has always been a major concern in the modeling and control of real-world industrial processes. Traditionally, researchers look for simplified and enough precise models of these systems. However, with the significant advancement in sensor and communication technologies, a considerable amount of data is available from the process which may compensate for the lack of precise models. The emerging data-driven control systems perform both identification and control actions based on data collected from the process, making the system less dependent on a pre-identified model. In this context, an efficient MIMO Data-Driven Adaptive Control (MIMO-DDAC) is designed in this paper for stabilizing a class of unknown non-linear systems. A recursive modeling/control process is proposed for the MIMO systems in the presence of saturation in sensors and actuators, and its stability and performance are mathematically proved. This approach is applied to the load frequency control problem in an interconnected multi-area power grid in the presence of governor saturation, load and parametric uncertainties. Simulation results reveal the effectiveness of the proposed method.

Observer-Based Consensus Control for Heterogeneous Multi-Agent Systems with Output Saturations

This paper studies the consensus problem for heterogeneous multi-agent systems with output saturations. We consider the agents to have different dynamics and assume that the agents are neutrally stable and that the communication graph is undirected. The goal of this paper is to achieve the consensus for leaderless and leader-following cases. To solve this problem, we propose the observer-based distributed consensus algorithms, which consists of three parts: the nonlinear observer, the reference generator, and the regulator. Then, we analyze the consensus based on the Lasalle’s Invariance Principle and the input-to-state stability. Finally, we provide numerical examples to demonstrate the validity of the proposed algorithms.

Observer-based Distributed Consensus Algorithm for Multi-agent Systems with Output Saturations

Observer-based Distributed Consensus Algorithm for Multi-agent Systems with Output Saturations

Distributed hybrid-triggered H∞ filter design for sensor networked systems with output saturations

Abstract This paper is concerned with the distributed hybrid-triggered H∞ filter design problem for sensor networked systems (SNSs) with the output saturations. A distributed hybrid-triggered transmission scheme (DHTTS) is proposed to work in term of time-trigger and event-trigger switching, which can get a balance of saving network resources and improving system performance. Firstly, combining hybrid-triggered scheme and output saturation, the distributed H∞ filtering error system with communication delays is modeled. Then, by using Lyapunov–Krasovskii functional method and linear matrix inequality technique, some sufficient conditions for guaranteeing the asymptotic stability and average H∞ performance of the filtering error system are established, and the distributed filter parameters and hybrid-trigger matrix parameters can be obtained simultaneously. Finally, a simulation example is provided to illustrate the effectiveness of the developed method.

Fast inrush voltage and current restraining method for droop controlled inverter during grid fault clearance in distribution network

Control mode switching strategy of droop controlled inverter can effectively avoid overcurrent during grid fault, but it is easy to cause inrush voltage and current during grid fault clearance, which leads to the failure of fault ride through process of the distribution network. In this study, a new control mode re-switching method is proposed on the basis of restricting the outputs of the off-line controllers, which can make sure that the inrush voltage and current are suppressed and return to the normal condition quickly. First, the dynamic characteristics of fault current of droop controlled inverter are analysed. Then, the instantaneous inrush voltage and current caused by the output saturations of voltage controller and power controller before the re-switching process are mainly discussed. This method takes full advantage of integration of the existing off-line controllers to limit the output saturations, which can make the inrush problems well solved, and reduce the influence on grid connected inverters and the distribution network. Simulation results verify the validity of the theoretical analysis.

Observer Design for Delayed Markovian Jump Systems with Output State Saturation

This paper considers the observer design problem of continuous-time delayed Markovian jump systems with output state saturation. Different from the traditionally observer-based saturation control methods, a kind of system output state saturation with a partially delay-dependent property is proposed, where both nondelay and delay states exist at the same time but happen asynchronously. By exploiting the Bernoulli variable, the probability distributions of such two states are described and considered in the observer design. Based on an improved equality applied to deal with saturation terms, sufficient conditions for the designed observer with three kinds of output saturations are all provided with LMI forms. Finally, a numerical example is given to indicate the effectiveness of the obtained results.

Consensus With Output Saturations

This paper considers a standard consensus algorithm under output saturations. In this case, the global consensus cannot be realized due to the existence of stable equilibrium points that do not belong to the consensus manifold. Therefore, this paper investigates necessary and sufficient initial conditions for the achievement of consensus that characterize an exact domain of attraction. Specifically, this paper considers single-integrator agents with both fixed and time-varying undirected graphs. Then, we show that the consensus will be achieved if and only if the average of the initial states is within the minimum saturation level.

Asymptotic Stabilization of Delayed Systems with Input and Output Saturations

We consider in this paper the problem of controlling an arbitrary linear delayed system with saturating input and output. We study the stability of such a system in closed-loop with a given saturating regulator. Using input-output stability tools, we formulated sufficient conditions ensuring global asymptotic stability.

Asymptotic Stabilization of Delayed Systems with Input and Output Saturations

We consider in this paper the problem of controlling an arbitrary linear delayed system with saturating input and output. We study the stability of such a system in closed-loop with a given saturating regulator. Using inputoutput stability tools, we formulated sufficient conditions ensuring global asymptotic stability.

Output Saturation in Electric Motor Systems: Identification and Controller Design

Input saturation is a well-known nonlinearity in mechanical control systems; it constrains the maximum acceleration, which results in the limitation of the system response time. Input saturation has been considered in controller design in various ways, e.g., antiwindup control. In addition to the input, the state variables of mechanical systems are often subjected to saturation. For example, the maximum angular velocity of electric motor systems is limited by the maximum voltage provided to the motor windings. In the case of electronically commutated motors (i.e., brushless dc motors), the maximum speed is additionally constrained by limitations of the servo amplifier output. If gears are utilized, further constraints are introduced due to resonances in ball bearings and/or velocity dependent friction. Although such factors are significant in practice, they have not been fully considered in controller design. This paper investigates the input and output saturations, and presents how they may be considered in the controller design; a Kalman filter, a PID controller, and a disturbance observer are designed, taking input/output saturations into consideration. A case study is provided to verify the proposed methods.

Analyse de stabilité pour un système soumis à des saturations et avec des dynamiques négligée

This paper considers linear systems subject to input and output saturations, for which a stabilizing control law has been a priori designed. The effects of beforehand neglected dynamics appearing at the input are studied with respect to the stability of the closed-loop system. Constructive conditions based on matrix inequalities, or at leat linear matrix inequalities (LMI), are proposed in order to characterize some suitable dynamics preserving the closed-loop stability. The influence of these neglected dynamics on the estimate of the basin of attraction for closed-loop system is studied.

Comparison of Mini-Cardiopulmonary Bypass System With Air-Purge Device to Conventional Bypass System

Although mini-cardiopulmonary bypass systems reduce inflammation, hemodilution, and transfusion requirements, the problem of air entrainment and embolization into the system has limited its use. Newer systems incorporate an air purge to address this problem. We compared the benefits and possible risks in using the newer mini-cardiopulmonary bypass system with those for conventional cardiopulmonary bypass. Data of 60 patients who underwent cardiac surgery with a newer mini-cardiopulmonary bypass system incorporating an air purge from August 2005 to July 2006 (group A) were retrospectively collected and compared with that of 60 matched patients who underwent cardiac surgery with conventional cardiopulmonary bypass during the same period (group B). Matching criteria were prebypass hematocrit, body surface area, age, and surgical procedure. Demographic and background data were similar for both groups. There were no detectable episodes of air embolism. Patients in group A had higher initial and nadir hematocrits during cardiopulmonary bypass and received fewer transfusions. However, postoperative blood loss and transfusion requirements were similar in both groups. Episodes of low indexed flows during cardiopulmonary bypass commonly occurred in group A, and this was associated with a greater than 50% decrease in urine output and lower mixed venous oxygen saturations (58% +/- 6% versus 68% +/- 5%) as compared with group B. There were no differences in clinical outcomes. The newer mini-cardiopulmonary bypass system addressed the problem of air embolization. It preserved hematocrit and reduced transfusion during cardiopulmonary bypass, but did not improve outcomes postoperatively. It is unclear whether these benefits outweigh the potential risk of hypoperfusion associated with its use.

Asymptotic stabilization of linear plants in presence of input and output saturations

We are considering the problem of controlling an arbitrary linear plant with saturating input and output. We investigate the stability of the control system resulting from such a plant in closed loop with a given saturating linear regulator. Sufficient conditions for global asymptotic stability are formulated using tools from the input–output approach.

Oxygen Fick and modified carbon dioxide Fick cardiac outputs

To compare cardiac outputs estimated from the classical oxygen Fick and modified CO2 Fick methods with thermodilution cardiac output. The modified CO2 Fick cardiac output was obtained by replacing the oxygen uptake (VO2) in the Fick equation with the CO2 production (VCO2) divided by either an assumed or measured value of the respiratory exchange ratio or with an independently determined constant (Crit Care Med 1991; 19:1270-1277). Criterion standard study. The medical and surgical intensive care unit (ICU) in a Veterans Affairs Medical Center. A total of 17 patients (26 studies) and 11 surgical patients (13 studies), predominantly mechanically ventilated using the intermittent mandatory ventilation mode, were studied over a period of 4.3 hrs. A respiratory gas exchange monitor was used to measure VO2, VCO2, and respiratory exchange ratio at 3-min intervals. Calculations were performed with arterial and venous oxygen saturations measured with both a laboratory cooximeter and bedside pulse and venous reflectance oximeters. In the oxygen Fick method, cardiac output was calculated from VO2 together with arterial and venous oxygen saturations. In the modified CO2 Fick methods, cardiac output values were calculated from arterial and venous oxygen saturations with VCO2, divided by either: a) an assumed value of the respiratory exchange ratio equal to 0.8 for all patients (method 1); b) the patient's measured value of the respiratory exchange ratio (method 2); or c) a constant, determined from an initial, simultaneous measurement of thermodilution cardiac output, VCO2, and oximetry saturations. Data were examined by linear regression analysis and bias and precision calculations. Thermodilution cardiac output was more related to cardiac outputs calculated with the 3 modified CO2 Fick methods than to the oxygen Fick cardiac output. Thermodilution cardiac output was closely related to the modified CO2 Fick cardiac output calculated via method 3. For this method, with pulse and venous reflectance oximetry saturations, linear regression yielded an r2 = .85, a standard error of the estimate of 0.88 L/min (n = 111) and a bias and precision of 0.11 and 0.97 L/min, respectively. Thermodilution cardiac output was less closely related to oxygen Fick cardiac output, which, when calculated with pulse and venous reflectance oximetry saturations, yielded an r2 = .50, a standard error of the estimate of 1.47 L/min (n = 128), and a bias and precision of 0.01 and 1.85 L/min, respectively. We conclude from this study that thermodilution cardiac output is more closely related to cardiac output calculated from modified CO2 Fick methods than to oxygen Fick cardiac output. Since cardiac output calculated with the modified CO2 Fick method 3 obviates the difficulties associated with measuring VO2 accurately and requires neither an assumption of nor measurement of the respiratory exchange ratio, method 3 may prove to be clinically useful for continuous cardiac output monitoring via oximetry in ICU patients.

Myocardial perfusion and performance after indomethacin administration in newborn lambs.

Indomethacin is a drug widely used to achieve pharmacologic closure of a patent ductus arteriosus in the premature infant. In several vascular beds (brain, kidney, intestine), indomethacin has been shown to cause vasoconstriction. Possible negative effects on myocardial blood flow and performance could be deleterious in premature infants with limited cardiac reserve. Before, during, and 30 and 60 min after administration of 1 mg.kg-1 of indomethacin in nine newborn lambs, we measured coronary blood flow velocity (Doppler flow probe around the left circumflex coronary artery), left ventricular (LV) pressure (by tip manometer) and volume (by conductance catheter technique), cardiac output, arterial pressure, arterial and venous saturations and calculated systemic and coronary vascular resistance, LV systolic function by the end-systolic pressure-volume relationship, and myocardial oxygen extraction. To investigate the effect of indomethacin on the flow regulation of the coronary vascular bed, we measured coronary flow and LV function under different levels of myocardial demand, achieved by stepwise occluding of the descending aorta. During indomethacin infusion, coronary and systemic vascular resistance increased significantly (by 43 and 76%, respectively), resulting in an increase in arterial pressure from 10.2 to 16.9 kPa, whereas neither coronary flow nor LV systolic function changed despite the increase in afterload. Thirty and 60 min after indomethacin, coronary and systemic vascular resistance had returned to baseline levels and LV systolic function remained unchanged. The relationship between coronary flow and cardiac demand was not different before or after indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Fever in young lambs: carotid denervation alters the febrile response to a small dose of bacterial pyrogen.

Experiments were done on 13 young lambs to determine if carotid denervation influences the cardiovascular and metabolic responses to i.v. administration of bacterial pyrogen [Salmonella abortus equi (SAE) 0.3 micrograms]. Each lamb was anesthetized with halothane and prepared for measurements of cardiac output, arterial and mixed venous oxygen saturations, and body core temperature. No sooner than 3 d after surgery, measurements were made during a control period and at 10-min intervals for 120 min after i.v. administration of SAE in seven carotid-intact lambs and six carotid-denervated lambs. Administration of SAE produced a short-lived fever of about 1 degrees C in the carotid-intact lambs, whereas no change in body core temperature was observed in the carotid-denervated lambs. In carotid-intact lambs, the rise in body core temperature began approximately 40 min after administration of SAE and continued for approximately 50 min. This rise in body core temperature was preceded by the onset of shivering and an increase in total body oxygen consumption. Carotid denervation produced changes in some of the cardiovascular variables during the control period (i.e. arterial oxygen content, cardiac index, heart rate, and pulmonary blood pressure); however, there were no additional significant changes in any of the metabolic or cardiovascular variables after administration of SAE. The mechanism of these unexpected findings remains to be determined.

Oxygen Homeostasis: Theory, Measurement, and Therapeutic Implications

The ultimate goal of therapeutic intervention in a critically ill patient is to maintain oxygen homeostasis where delivery of oxygen to the cells is greater than, or at least equal to, the oxygen demand of the cells. Oxygen demand varies from organ to organ. Total body oxygen demand is the sum of all oxygen required by all tissues and organs for aerobic cellular function. Oxygen consumption (VO2) is the quantity of oxygen actually used by the cells. VO2 may be calculated if the values of cardiac output (CO), hemoglobin concentration, and arterial and venous oxygen saturations (SaO2 and SvO2, respectively) are known. Under normal circumstances, the quantities of oxygen demanded and oxygen consumed are equal, but in situations of inadequate oxygen delivery, oxygen demand may not be satisfied and the quantity of oxygen actually consumed will be governed by the quantity delivered. This then may result in an oxygen deficit and, ultimately, cellular death. This article discusses the principles of oxygen homeostasis, techniques for measuring VO2, CO, and SvO2, and the relevance of these principles and techniques to clinical practice.

Continuous, on-line, real-time measurement of cardiac output and derived cardiorespiratory variables in the critically ill.

A previously reported monitoring system provided continuous direct measurements of oxygen consumption and intravascular pressures. These data were combined with interval measurements of cardiac output and blood oxygen saturations to derive various hemodynamic and oxygen transport variables. This system has now been modified so that cardiac output is measured continuously in real-time.