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In peptide amphiphile, The positively charged amino acid arginine can inspire the ordered self-assembly of gold nanocomposites (AuNPs), transfer positive charge to AuNPs, and weaken the aggregation of AuNPs by electrostatic repulsion, whereas hydrophobic fatty acid chains regulate the self-assembly of AuNPs through hydrophobic interaction, which may be a novel strategy to overcome disordered arrangement and aggregation of AuNPs to obtain an ultra-sensitive electrochemical immunosensor for determining the total aflatoxin amount. In this study, a peptide amphiphile (C14R5), composed of five arginine residues as the hydrophilic chain and myristic acid as the hydrophobic chain, inspired AuNPs to form monodispersed hollow raspberry-like AuNPs (rasAuNPs). rasAuNPs could captured and immobilized large amounts of aflatoxin antigens via the Au-S bonds, resulting in binding to more anti-aflatoxin antibodies. In the absence of aflatoxins, the enriched antigens bound to abundant antibodies, resulting in a low blank signal current. By contrast, in the presence of aflatoxins, enough antibodies could bind to the targets and less antibodies could recognize the antigens, increasing the detection signal intensity. Under the optimal conditions, the developed sensor demonstrated a wide linear range (0.13-29.06 pg mL

A pointing and vibration isolation integrated control method for optical payload in the satellite system with a Pointing and Vibration Control Platform (PVCP) is developed and verified. Firstly, the dynamic model of the satellite system is formulated. This satellite system contains a payload, a PVCP and a satellite body. Three pointing control methods are proposed depending on different measurement information. By comparing the three methods, one reasonable control method is chosen for the pointing controller. This method could reduce the disturbance from the satellite body motion to the pointing control accuracy as well as the control error caused by the measurement accuracy of sensors. Then, the whole satellite attitude control loop is developed considering a rapid maneuver and rapid orientation mission. Finally, a series of verification experiments of the dynamic model of PVCP are carried out, and then the rotation accuracy, the stroke of PVCP, and the whole satellite attitude control loop are verified by numerical simulations. The results show that the pointing accuracy and attitude angular velocity of payload are improved using the integrated control method.

This paper presents the development of a dynamic model for a newly proposed Absorption-based Liquid Desiccant Regeneration (ALDR) system operating in vacuum condition which can reduce the regeneration temperature to around 20–35 °C. The dynamic model is developed based on the internal and external enthalpy balances and mass balances in the components and it accounts for the dynamic behavior due to the heat and mass transfer process in the components. This approach is simpler as detailed enthalpy at each state point can be avoided. The developed dynamic model is verified using the data obtained from the experimental platform constructed in the laboratory. The dynamic response of the simulation results is in good agreement with the experimental data. This model can predict the relevant parameters such as the temperature, concentration and mass flow of the desiccant solution and temperature of the heating and cooling sources when a step change of inlet water temperature is applied to system. The developed model will be useful for the elaboration of control system in the future. NRF (Natl Research Foundation, S’pore)

Liquid Desiccant Dehumidification Systems (LDDS) have been gaining attention due to its great energy saving potential in buildings. The desiccant regeneration system in LDDS plays a vital role in the system as the major energy consumed is due to the heat energy supplied to regain the concentration of the desiccant solution. The high regeneration temperature prohibits the potential use of low-grade or renewable energy as the heat source in the desiccant regeneration system. Therefore, a desiccant regeneration system operating in vacuum condition was proposed in this work. A novel Absorption-based Liquid Desiccant Regeneration (ALDR) system was developed and studied to validate this approach. A performance prediction model was also developed to predict the regeneration performance of the ALDR system. The model predicted values and the experimental values agreed well with each other with average deviation less than 5.90%. The operating parameters in the proposed ALDR system were also compared with the conventional packed-bed desiccant regeneration system available in literature. The regeneration temperature in LDDS was found to be significantly reduced to around 20–35 °C with the operating vacuum pressure between 1000 Pa and 2000 Pa when regenerating Lithium Bromide solution of 36% mass fraction. This study validated the feasibility of the ALDR system in reducing the regeneration temperature of the desiccant regeneration system. The results also showed that the proposed ALDR system was able to reduce the power consumption by 40.66% compared to the conventional packed-type regenerator from literature. NRF (Natl Research Foundation, S’pore)

In this paper, robust fuzzy model predictive control of a class of nonlinear discrete systems subjected to time delays and persistent disturbances is investigated. Based on the modeling method of delay difference inclusions, nonlinear discrete time-delay systems can be represented by T–S fuzzy systems comprised of piecewise linear delay difference equations. Moreover, Lyapunov–Razumikhin function (LRF), instead of Lyapunov–Krasovskii functional (LKF), is employed for time-delay systems due to its ability to reflect system original state space and its advantages in controller synthesis and computation. The robust positive invariance and input-to-state stability with respect to disturbance under such circumstances are investigated. A robust constraint set is adopted that the system state is converged to this set round the desired point. In addition, the controller synthesis conditions are derived by solving a set of matrix inequalities. Simulation results show that the proposed approach can be successfully applied to the well-known continuous stirred tank reactor (CSTR) systems subjected to time delay.

The dynamic characteristics and performance evaluation for the part strut failure of the vibration isolation platform are presented in this paper. The first step provides and mathematically describes two types of strut failure: fractured and stuck. Secondly, the dynamic model of the vibration isolation platform, which considers the part strut failure, is established using the Newton-Euler method and a constraint equation to evaluate its dynamic characteristics and performance. Then, with reasonable assumptions, the dynamic model of the satellite, which has a vibration isolation platform and vibration sources (such as control moment gyros) of three working situations (without and with two types of strut failure), is simplified to analyse the frequency domain characteristic and coupling characteristic with the attitude control system. Finally, a numerical simulation is used to study the effect of the vibration isolation platform with part strut failure on the attitude control and stabilization, and the attitude control performance is evaluated.

The strategy of active-passive integrated vibration control on the truss enveloping control moment gyroscopes (CMGs) is presented and its characteristics of time domain and frequency domain are analyzed. Truss enveloping CMGs contains pyramid-type CMGs, which are enveloped by multiple struts. These struts can be employed to realize the active-passive integrated vibration control. In addition, the struts of the trusses can maintain the working space of CMGs. Firstly, the disturbance characteristics of CMGs are analyzed considering static and dynamic imbalances of the CMG's rotor; then, an active-passive integrated vibration isolation truss structure is developed based on its characteristics. This structure can restrain the CMG vibration as much as possible and reduce its influence on the photographic quality of optical payloads. Next, the dynamic model of the active-passive vibration isolation truss structure is established. The frequency domain analysis of this model shows that the active-passive integrated vibration control method can restrain the high-frequency vibration and also improve the characteristics of low-frequency vibration. Finally, the dynamic model for the whole satellite is built with this type of CMGs. The time domain simulations of satellite attitude control verify the attitude control improvements resulting from the CMGs vibration control strategy.

In this paper, a model-based optimization strategy for a hybrid ejector air conditioning system is presented. By investigating the operating characteristics of the energy consuming components, the energy consumption models for generator, compressor, fans and pump are developed with experimental validation. The validation results indicate the proposed models are accurate enough for optimization issue. Then, the optimization problem is formulated with objective to achieve minimum energy consumption while meets the required cooling loads at the same time. The physical constraints and interaction between components are also illustrated. In order to solve this optimization problem, a PSOGA optimization approach is proposed. PSOGA takes the advantages of both particle swarm optimization (pso) and genetic algorithm (ga) with fast convergent speed and high accuracy. The cooling load is obtained based on corresponding temperature collected from 6 am to 20 pm on a single day. The comparison result between traditional on-off control and proposed PSOGA indicates the better performance of PSOGA with more energy saving achieved. Additional, the energy saving effect achieves its highest value at 32 °C with 17%.

In order to predict the performance of a hybrid ejector air conditioning system, neural network is chosen to model the proposed platform. First, three different types of neural networks, namely multi-layer perceptron (MLP), radial basis function (RBF) and support vector machine (SVM) are applied to model the component of a hybrid ejector air conditioning system. The MLP outperforms other two networks in this research and therefore it is selected to model the whole system. Since there is no formal criterion about input selection so far, a date-mining algorithm, boosting tree, is employed before system modeling to search the most significant parameters among the 19 input variables and the five most influential parameters of them are selected to be the final input of the system model. And the result shows a good agreement between predicted and measured value which indicates the excellent ability of MLP.

As the demand for electric vehicle (EV)'s remaining operation range and power supply life, Lithium-ion (Li-ion) battery state of charge (SOC) and state of health (SOH) estimation are important in battery management system (BMS). In this paper, a proposed adaptive observer based on sliding mode method is used to estimate SOC and SOH of the Li-ion battery. An equivalent circuit model with two resistor and capacitor (RC) networks is established, and the model equations in specific structure with uncertainties are given and analyzed. The proposed adaptive sliding mode observer is applied to estimate SOC and SOH based on the established battery model with uncertainties, and it can avoid the chattering effects and improve the estimation performance. The experiment and simulation estimation results show that the proposed adaptive sliding mode observer has good performance and robustness on battery SOC and SOH estimation.

The objective of this study is to propose guidelines for the operating temperature range of High-Temperature Proton Exchange Membrane Fuel Cell (HT-PEMFC) considering the overall performance, CO tolerance and durability. To study the effect of temperature on HT-PEMFC performance, polarization curves of the cell operating on respective hydrogen and hydrogen/CO mixture were measured at 5 different temperatures. The electrochemical impedance spectroscopy (EIS) was used to characterize the internal resistances and the results provided the electrochemical analyses and explanations of the temperature effect on the HT-PEMFC. In addition, the stability tests (100 h) were also conducted, which were useful for trade-off study between performance requirement and lifespan of the cell. Results showed that the temperature effect on the cell performance and CO tolerance were less obvious in high temperature range (above 180 °C) compared to the low temperature range (below 160 °C). However, the degradation of cell performance is faster in the high temperature range. Analysis of experimental results revealed that the optimal operating temperature window is between 160 and 180 °C by compromising among the cell performance, CO tolerance and durability, and where the low temperature end of the range is preferred depending on the feeding fuel.

Further to a previous experimental study on the heat exchanger circuitry number for a two-way discharge active chilled beam terminal unit, an investigation of the tube connecting sequences is conducted in this paper. Given a typical air side operating condition, in situ air velocity profile across the heat exchanger is measured and non-uniformities of the air flow caused by the entrainment effect are detected. Taking the air maldistribution into consideration, heat transfer performance of the heat exchanger is simulated with a tube to tube distributed parameter model. This simulation model is calibrated with experimental results. With the calibrated model, influences of the air maldistribution on the heat transfer capacity are discovered. The heat exchanger tube connecting sequences are optimized through a particle swarm optimization program for the maximum heat transfer capacity. In addition, the potential pressure drop, manufacture difficulties, and material cost of the tube connecting sequences are qualitatively analyzed. A new heat exchanger circuitry arrangement is finally proposed for the terminal unit. Although the performance enhancement is modest, the findings obtained in the study are expected to facilitate better heat exchanger designs for the future active chilled beam terminal units.

An investigation into the effect of water in the anodic compartment on the performance of a high-temperature PBI-based PEM fuel cell (HT-PEMFC) has been carried out. This study shows that proper water management is as crucial to HT-PEMFCs as its low temperature (LT-PEMFC) counterpart. Excessive water content strongly affects the performance and stability of HT-PEMFCs. Here, a systemic study on the key parameters of anodic purging pressure, duration and frequency has been carried out in order to understand and propose a proper water management strategy for HT-PEMFCs. The results showed that proper programming of the anode purging process can effectively eliminate the serious water dilution effect in anode (similar to anodic flooding in LT-PEMFCs) and improve both the performance and fuel utilisation.

The phosphoric acid doped polybenzimidazole (PBI) membrane is the most commonly used electrolyte in high-temperature PEM fuel cells (HT-PEMFCs). The aims of this study are to investigate the transport of water vapour from the cathode to the anode and the effect of water vapour on the performance of a single cell HT-PEMFC using a commercial PBI-based membrane-electrode-assembly (MEA). The amount of water vapour transportation is determined by weighing the water vapour condensed from the fuel off-gas stream located at the anodic outlet of HT-PEMFC under a flow-through mode. Experimental results show that up to 31.7% of the generated water vapour is transported from the cathode to the anode. To study the effect of water on the cell performance, the polarization curves, transient voltage curve and transient ohmic resistance (due to on/off of the outlet solenoid valve) are measured under anodic dead-end and flow-through modes. The study shows that excessive water vapour in the anode can significantly deteriorate the performance of a cell operated in an anodic dead-end mode, but negligible in an anodic flow-through mode. The performance can rapidly recover after switching the cell from a dead-end mode to a flow-through mode. The study allows fundamental understanding of the operation in anodic dead-end and flow-through modes, which offers guidelines for operating a HT-PEMFC with improved fuel utilization.

This paper proposes a hybrid dynamic model of active chilled beam (ACB) terminal unit. The model encapsulates mechanical and thermal aspects of the confined air jet and the cooling coil contained in the terminal unit and could be divided into two sub-models respectively. The models for the primary air, secondary air and mixing of them are together taken as the confined air jet sub-model. Another sub-model is the heat transfer description of the cooling coil. The model is kept simple and practical, avoiding sophisticated jet flow theories as well as heat transfer theories. Thus, in deriving the model using first principles and estimating it experimentally, a reasonable compromise is made between capturing exact underlying physics and suitability for engineering applications. Supported by experimental results from a pilot plant, unknown model parameters are identified by either a linear or nonlinear least-squares method. It is shown that static and dynamic performances of the model are satisfied, which reflect the effectiveness of this hybrid modeling technique as well. The model developed in this work is expected to have wide control and optimization applications. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

Lithium-ion (Li-ion) battery state of charge (SOC) estimation is important for electric vehicles (EVs). The model-based state estimation method using the Kalman filter (KF) variants is studied and improved in this paper. To establish an accurate discrete model for Li-ion battery, the extreme learning machine (ELM) algorithm is proposed to train the model using experimental data. The estimation of SOC is then compared using four algorithms: extended Kalman filter (EKF), unscented Kalman filter (UKF), adaptive extended Kalman filter (AEKF) and adaptive unscented Kalman filter (AUKF). The comparison of the experimental results shows that AEKF and AUKF have better convergence rate, and AUKF has the best accuracy. The comparison from the radial basis function neural network (RBF NN) model also verifies that the ELM model has lighter computation load and smaller estimation error in SOC estimation process. In general, the performance of Li-ion battery SOC estimation is improved by the AUKF algorithm applied on the ELM model.

This paper investigates the problem of H ∞ stabilization for nonuniform sampling fuzzy systems. A method to design a fuzzy controller is proposed by taking the variation ranges of membership functions within sampling intervals into consideration. To reduce the computational complexity, Jensen's integral inequality method is employed. Based on a well-known inequality, a convex combination technique is developed to deal with nonlinear time-varying coefficients derived from Jensen's integral inequality. Combining with capturing the characteristic of sampled-data systems with a novel piecewise Lyapunov–Krasovskii functional (LKF), a less complex and less conservative H ∞ stabilization criterion is formulated as linear matrix inequalities (LMIs), which can be easily checked by using standard numerical software. Some illustrative examples are given to show the effectiveness of the proposed method and the significant improvement on the existing results.

This paper proposes a precise real-time wind speed estimation method and sensorless control for variable-speed variable-pitch wind turbine power generation system (WTPGS). The wind speed estimation is realized by a nonlinear input-output mapping extreme learning machine (ELM). A specific design characteristic of the wind turbine is used for improving the mapping accuracy with considering the variable pitch angle. Moreover, since the design is independent of the environmental air density, the proposed ELM wind speed estimation method is robust to the air density variations. The estimated wind speed is then used to determine the optimal rotational speed command for maximum power point tracking. A fast and effective ELM mapping based pitch controller is proposed too when the WTPGS operates in its high wind speed region. The ELM pitch controller can act much faster and more precise than conventional pitch controllers. Furthermore, the complicated design precess for the parameters of conventional pitch controllers will be avoided in the proposed method. The effectiveness of the proposed methods are verified both by simulations and experiments on a WTPGS installed with Permanent Magnet Synchronous Generator (PMSG).

This paper addresses the H"~ and mixed H"2/H"~ control synthesis problems of nonlinear discrete-time systems, which are represented by a new type of T-S fuzzy models. The fuzzy systems consist of local nonlinear models and are with fewer fuzzy rules than the conventional T-S fuzzy systems with local linear models. A fuzzy control scheme with local nonlinear feedbacks is proposed and H"~ and mixed H"2/H"~ control synthesis conditions are given in terms of solutions to a set of linear matrix inequalities (LMIs). In contrast to the existing conditions for designing fuzzy controllers, the new ones can be used to design fuzzy controllers based on fewer control rules as well as are with less computational burden. In particular, the new methods can also give less conservative results. A numerical example is given to illustrate the effectiveness of the proposed methods.

A homing mechanism is required for repositioning as a system performs tasks repeatedly. By examining the effect of poor repositioning on the tracking performance of iterative learning control, this paper develops a varying-order learning approach for the performance improvement. Through varying-order learning, the resultant system output trajectory is ensured to follow a given trajectory with a lowered error bound, in comparison with the conventional fixed-order method. A discrete-time initial rectifying action is introduced in the formed varying-order learning algorithm, and a sufficient condition for convergence is derived. An implementable scheme is presented based on the proposed approach, and illustrated by numerical results of two examples of robotic manipulators.

This Letter studies the exponential stability for a class of neural networks (NNs) with both discrete and distributed time-varying delays. Under weaker assumptions on the activation functions, by defining a more general type of Lyapunov functionals and developing a new convex combination technique, new less conservative and less complex stability criteria are established to guarantee the global exponential stability of the discussed NNs. The obtained conditions are dependent on both discrete and distributed delays, are expressed in terms of linear matrix inequalities (LMIs), and contain fewer decision variables. Numerical examples are given to illustrate the effectiveness and the less conservatism of the proposed conditions.

This paper studies the problem of stability analysis for discrete-time recurrent neural networks (DRNNs) with time-varying delays. By using the discrete Jensen inequality and the sector bound conditions, a new less conservative delay-dependent stability criterion is established in terms of linear matrix inequalities (LMIs) under a weak assumption on the activation functions. By using a delay decomposition method, a further improved stability criterion is also derived. It is shown that the newly obtained results are less conservative than the existing ones. Meanwhile, the computational complexity of the newly obtained stability conditions is reduced since less variables are involved. A numerical example is given to illustrate the effectiveness and the benefits of the proposed method.

This paper investigates stability analysis and design of reset control systems where the reset time instants are pre-specified. Firstly, in order to quantify stability of reset control systems, we propose an approach which does not rely on the stability of base linear systems. Based on this, some Lie-algebraic conditions for stability of reset control systems are obtained. Then, we develop a method for reset law design which aims at improving transient responses of the base linear systems. In addition, observer-based design is also considered. We prove that under some mild conditions, reset controller and observer can be designed separately. The obtained results are applied to short-span-seeking control of a kind of single stage hard disk drive servo systems. Simulations show that the proposed design is much more capable of improving transient response than traditional control design techniques.

This paper addresses the H∞ control synthesis problem of nonlinear discrete-time systems, which are represented by a new type of T-S fuzzy systems. The fuzzy systems consist of local nonlinear models and with fewer fuzzy rules than the conventional T-S fuzzy systems with local linear models. A fuzzy control scheme with a nonlinear feedback control law in each control rule is proposed and an H∞ control synthesis condition is given in terms of solutions to a set of linear matrix inequalities (LMIs). In contrast to the existing conditions for designing fuzzy controllers, the new ones can design fuzzy controllers based on fewer control rules as well as with less computational burden. In particular, the new methods can also give less conservative results. A numerical example is given to illustrate the effectiveness of the proposed methods.

This paper considers scheduling of transmission order for a set of continuous linear systems with a shared sensor-to-controller channel. By transferring the channel allocation problem to the problem of switching law design for a switched system, different allocation schemes including state-dependent scheme, periodic allocation scheme and random allocation scheme are proposed.

A real-time nonlinear adaptive speed control scheme based on backstepping control technique is proposed for a permanent magnet synchronous motor. In the controller design, the input–output feedback linearization is firstly used to compensate the nonlinearities in the nominal system. Then, adaptive backstepping control approach is adopted to derive the control scheme, which is robust to the parameter uncertainties and load torque disturbance. Simulation and real-time experimental results clearly show that the proposed control scheme can track the speed reference signal generated by a reference model successfully under parameter uncertainties and load torque disturbance without singularity and overparameterization.

The friction and load variation are the main uncertainties in the linear piezoelectric motor system. Only the viscous friction is considered in previous work, but it is quite different with the practical condition. Highly nonlinear friction in the system is measured and compensated by a radial basis function (RBF) network. A discrete-time sliding mode controller, which is insensitive to the perturbed state matrix and input matrix and disturbances, is proposed for LPM drive system. Furthermore, three free design parameters are optimized to achieve better transient performance by genetic algorithm and one online mass estimator is adopted to extend the robustness. The simulation and experiment results show that the proposed controller has a stronger robustness than PID controller.

In single-stage hard disk drives (HDDs), it is difficult to suppress mid-frequency narrow band disturbances caused by disk flutter or windage effectively. This article presents a nonlinear compensation scheme to deal with narrow band disturbance around 1 kHz. The nonlinear compensator that provides additional phase lead without degrading the magnitude characteristic is proposed. This scheme is used to compensate for phase loss due to narrow band filter and enhance the mid-frequency disturbance suppression capability. Settling performance is verified not to be degraded significantly due to harmonics from the nonlinear element. Our results show that the peak value of power spectra of NRRO due to disk vibration are decreased by 99% and position error signal 3σ value is improved 68%.

A dynamic nonlinear control scheme to improve the seek-settling process in hard disk drive (HDD) servo systems is proposed. In order to reduce the impact of the control gains on the tracking performance, tracking differentiator (TD) is introduced as a dynamic reference of the feedback controller. The problems of the large and small gain control theory do not arise with this method, and the actuator saturation can be avoided as well. The stability analysis is given through Lyapunov functions. Simulation and experiment results show that the proposed control scheme performs well for both short and long seeking length.

Narrow-band disturbance caused by high speed disk rotation is one of the significant contributors to the track misregistration (TMR) in HDD track following. The peak filter design is an effective control method to suppress the narrow-band disturbance, but the activation of peak filter may produce some oscillations in the output response, which would prolong the settling time of HDD servo system. This paper presents a scheme of state initialization to deal with the undesirable transient response caused by control component. The proposed method is applied to an HDD dual-stage servo system with peak filter design. Testing results demonstrate that the settling performance would not be deteriorated when the high-gain filter is properly initialized. This technique would enhance the disturbance attenuation of HDD dual-stage servo system without the degradation of settling performance.

A robust nonlinear coordinated generator excitation and thyristor-controlled phase shifter (TCPS) controller is proposed to enhance the transient stability of a multimachine power system. To eliminate the nonlinearities and interconnections of the multimachine power system, a direct feedback linearization (DFL) compensator through the excitation loop is designed. Considering the effects of plant parametric uncertainties and remaining nonlinear interconnections, a robust decentralized generator excitation controller is proposed to ensure the stability of the DFL compensated system. Only the bounds of the generator parameters are necessary to be known in the design of the proposed controller, while the transmission network parameters, system operating points or the fault locations need not be known. Since the proposed controller can ensure the stability of large-scale power system within the whole operating region for all admissible parameters, the transient stability of the overall system can be enhanced significantly. Digital simulation studies were conducted on a three-machine power system to show the effectiveness of the proposed control scheme in enhancing the transient stability of the system regardless of the network parameters, operating points and fault locations.

This paper discusses coordinated excitation and UPFC control to improve power system transient stability. The power system is linearized through direct feedback linearization technique. Robust approach is employed to deal with the uncertainties caused by parameter variations and the inclusion of UPFC controller. Only local measurements are required for designing the excitation controller. The series branch of UPFC is designed to damp the power oscillation during transient period. The shunt branch aims at maintaining bus voltage. The performance of the controllers is tested on a single-machine infinite-bus (SMIB) power system. Simulation results show that both of the series and shunt branch of UPFC help improve transient stability.

This paper describes an application of nonlinear decentralized robust control (Guo, Jiang & Hill, 1998) to large-scale power systems. Decentralized power controllers are designed explicitly to maintain transient stable closed-loop systems. For the first time, nonlinear bounds of generator interconnections are used which achieves less-conservative control gains. The proposed controllers are robust with regard to uncertain network parameters and attenuate the persistent disturbances in the sense that the L"2-gain from the disturbance to the power frequency is reduced to a certain level. Simulations on a two-generator infinite bus power system exhibit enhancement of system transient stability at different conditions of operation points, fault locations and network parameters.

A robust nonlinear coordinated generator excitation and static var compensator (SVC) controller is proposed to enhance the transient stability of power systems. The SVC is located at the midpoint of the transmission line in a power system. A nonlinear feedback law for the generator is found which linearizes and decouples the power system model. Robust nonlinear control theory is employed to design the coordinated controller, which consists of two controllers, a generator excitation controller and an SVC controller. The proposed coordinated controller is designed based on local measurements. The design of the resulting controllers is independent of the operating point. Simulation results show that the proposed controller can enhance the transient stability of the power system under a large sudden fault, which may occur at the generator bus terminal.

A decentralised robust load-frequency controller (DRLFC), in coordination with auxiliary frequency controllers (AFCs), is introduced. It is designed for a power system comprising areas interconnected by normal tie-lines and frequency-controllable high-voltage direct current (HVDC) transmission links where AFCs are present. The bounds of system parameter uncertainties are also considered for robustness. The DRLFC comprises local load-frequency controllers, one for each area, which operates on its local measurements. Overall system stability, for all admissible uncertainties, is ensured when the DRLFC and the AFCs are in operation. The coordination among the DRLFC and AFCs is demonstrated by a three-area example system.

In this paper, a robust decentralized excitation control scheme is proposed for multimachine power system transient stability enhancement. First, a direct feedback linearization (DFL) compensator through the excitation loop is designed to eliminate the nonlinearities and interconnections of the multimachine power system. Then, a robust decentralized controller is proposed to guarantee the asymptotic stability of the DFL compensated system considering the effects of plant parametric uncertainties and remaining nonlinear interconnections. The design procedure for an n-machine power system involves in solving n Riccati equations. In the design of the robust nonlinear decentralized controller, only the bounds of generator parameters need to be known, but not the transmission network parameters, system operating points or the fault locations. Since the proposed robust nonlinear decentralized controller can guarantee the stability of the large scale power system within the whole operating region for all admissible parameters, transient stability of the overall system can be greatly enhanced. The design procedure is tested on a three-machine example power system. Simulation results show that the proposed control scheme can greatly enhance the transient stability of the system regardless of the network parameters, operating points and fault locations.

In the event of severe disturbances, a power system can undergo structural changes, following the clearing of faults by protection gear. The response of the power system is then highly nonlinear. In this paper, a nonlinear adaptive excitation and dynamic brake controller is proposed, to enhance the transient stability of a power system. The thyristor-controller braking resistor is located near the generator terminal. Nonlinear feedback control laws are found which linearize and decouple the power system. An adaptive control law is used to design the controller. The controller design is based on local measurements, and it is independent of operating points and fault locations. Simulation results demonstrate that the proposed controller can ensure transient stability of the power system under a large sudden fault which may occur at the generator bus terminal.

A new nonlinear voltage controller is proposed in this paper. The design of this controller involves the direct feedback linearization (DFL) technique and robust control theory. The performance of the proposed nonlinear controller in a single machine-infinite bus power system is simulated. The simulation results show that both voltage regulation and system stability enhancement can be achieved with this proposed controller, regardless of the system operating condition, and compared to other kinds of controllers, the proposed nonlinear controller gives better dynamic performance and robustness.

A new robust load-frequency controller using incomplete state feedback is proposed. It is suited for an uncertain power system using reheat type turbines. Such a plant contains system parameter uncertainties and an immeasurable state. The new controller design, based on the Riccati equation approach, considers the bounds of system parameters and feedback gains. Appropriate feedback gains can be chosen from their predefined bounds. This includes the selection of zero-gains for immeasurable states. The new robust controller thus uses incomplete state feedback. No observer is needed. Good performance is reported for an example system.

To prevent an electric power system losing synchronism under a large sudden fault and to achieve voltage regulation are major objectives in power system design. This paper applies the Riccati equation approach, together with the direct feedback linearization (DFL) technique, to design robust nonlinear controllers for transient stability enhancement and voltage regulation of power systems under a symmetrical three-phase short circuit fault. A DFL excitation controller and a DFL coordinated controller (excitation and fast valving controller) are proposed. The simulation results show that a power system can keep transiently stable, even when a large sudden fault occurs at the generator terminal. The robust nonlinear DFL controllers proposed here can greatly improve transient stability and achieve voltage regulation.

This paper investigates robust output feedback controller design for a class of uncertain dynamical systems with unknown time delays. The uncertainties considered in this paper contain parametric uncertainties, unknown nonlinear functions, unknown time delays and unknown nonlinear functions. The problems of robust stabilization and robust H ∞ performance are addressed. It is shown that the solutions to the above problems can be obtained from the solutions to algebraic Riccati inequalities. A numerical example indicates that the proposed robust controller can ensure the stability of the overall system.

Due to a variety of effects, such as lightning, severe storms and equipment failures, the configuration of an electric power system is not constant. Thus, important parameters, such as effective reactances of transmission lines, in an electric power system always contain some uncertainties. The aim of this paper is to discuss transient stability enhancement and voltage regulation of power systems using feedback linearization techniques and an adaptive control approach. A nonlinear controller design approach is employed to design an adaptive nonlinear control law to prevent the loss of synchronism in a power system under a large sudden fault. An adaptive nonlinear controller is proposed and the stability results for the overall system are established. Simulation results show that transient stability enhancement and voltage regulation of a power system under a large sudden fault can be achieved.

This paper is concerned with robust control design for a class of interconnected systems subject to real norm-bounded parameter uncertainty and unknown time delays. We address the problems of decentralized robust stabilization and robust H ∞ performance. Both decentralized linear dynamic output feedback and static state feedback control laws are investigated. It is shown that these robust control problems can be solved in terms of algebraic Riccati inequalities.

This paper is concerned with the problem of robust control of a class of discrete time systems with parameter uncertainty and unknown nonlinearities. The parameter uncertainty we consider is real time-varying norm-bounded and appears in both the state and output equations. We address the problem of designing linear dynamic output feedback controllers to achieve both robust stability and robust performance in an H∞ sense. Both the cases of finite and infinite horizon are considered. A technique is proposed for solving the above problems in terms of ‘scaled’ H∞ syntheses which do not involve parameter uncertainty and nonlinearities.

In this paper, a general design theory of nonlinear reduced-order observers for the forced nonlinear plants is proposed. Applying this method to reconstruct the power angle δ ( t ) of a synchronous generator-infinite bus power system, the nonlinear first-order δ ^ -observer with very simple structure and good performances can be found. The inherent stability region of which is | δ |= 90°. The simulation results of the DFL-LQ optimal exciter (Gao, 1992) with the δ ^ -oberver show that fast response, good trace ability, wide dynamical stability region, and ideal closed-loop response are all achieved.

This paper investigates the problem of H ∞ filtering for a class of uncertain continuous-time nonlinear systems with real time-varying parameter uncertainty and unknown initial state. We develop an infinite horizon H ∞ filtering methodology which provides both robust stability and a guaranteed H ∞ performance for the filtering error irrespective of the parameter uncertainty.

This paper is concerned with the problems of robust control and robust filtering of a class of discrete-time nonlinear systems with parameter uncertainty. The parameter uncertainty we consider is real time-varying norm-bounded and appears in both the state and output equations. Interest is focused on the design of linear dynamic output feedback controllers and linear filters for the uncertain system and three problems are addressed. The first one is the robust stability analysis and stabiIization whereas the other two problems are the design of controllers and filters to achieve both robust stability and robust performance in an H ∞ sense. A technique is proposed for the above analysis and synthesis problems by converting them into 'scaled' H ∞ analysis and control problems which do not involve parameter uncertainty and nonlinearities.