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H∞ based sliding mode control has several advantage viz. fast response, robustness to parameter variation and disturbance rejection ability. Inverted pendulum qualifies as a benchmark system to test the suitability of controller design for under-actuated, nonlinear unstable system. In this context, H∞ based integral sliding mode controller is designed for inverted pendulum for stabilizing the system. The H∞ state feedback gains are obtained by formulating the Riccati equation. These gains stabilize not only the closed loop transfer function, which maps the performance output to the disturbance input but also the system around its unstable equilibrium point. However this will not account for parameter variation and disturbance effect. Hence, a robust integral sliding surface is constructed such that during sliding motion the closed loop system will lead to disturbance rejection. Next, the switching control law is synthesized to maintain the states on the sliding surface from the initial time. The effectiveness of the controller design is verified by considering various uncertainties.

This paper proposes a method to implement the modified square loop digitally on the FPGA to solve the problem, that the divide circuit in the traditional square loop is difficult to achieve. The modified square loop has a similar structure to the traditional square loop. The method of modified square loop is to multiply quadrature output together to replace the divide circuit. In this paper, a specific method is given to digitize the square loop. The output carrier signal and the frequency difference will be analyzed in the condition of different initial frequency offset, parameters of the loop filter and input SNR.

Robust feedback control with large parameter uncertainties in a high precision stage with large sample mass variation is presented. Instead of expressing the nominal plant and its uncertainty by parametric models, they are expressed using the identified frequency response data. The open loop transfer function is mapped onto a Nyquist plot, to assess robust stability. Next, the complementary sensitivity function is derived from this data to describe tracking performance, which is verified by experiments. The advantage is that the parameter estimation step is omitted, without compromising robust stability and performance.

Buck-derived topologies are a popular alternative for the inverter stage of distributed generation systems. The lack of a grid connection places high reliability demands on the inverter controller. Dual-loop linear schemes are traditionally employed for the control of single-phase full-bridge inverters because of their simple implementation. However, the voltage loop dynamics are usually sluggish due to the requirement of making the outer loop's bandwidth much lower than the inner loop one. On the other hand, state-plane-based controllers offer fast and stable response against large signal disturbances, but constant switching frequency can only be achieved at the expense of a high computational cost. This work introduces a hybrid dual-loop control technique for inverters that combines the advantages of linear and state-plane-based controllers. The proposed dual loop scheme features a geometric-based voltage outer loop that provides fast and robust performance. The outer loop controller is complemented with a linear inner loop that ensures constant switching frequency and simple implementation. The derivation of the geometric controller is performed in the normalized state plane. Simulation and experimental results are provided in order to validate the proposed control scheme.

A new method for PI-PD controller tuning based on direct synthesis for integrating and unstable processes with time delay. Guidelines are provided for selection of the desired closed loop transfer function in the direct synthesis method and adjustable parameter ω. Design for some typical unstable processes with time delay shows that the PI-PD controller can reduce the overshoot effectively and achieve good tradeoff between dynamic performance and robustness.

The ball and beam is a basic reference point system with high nonlinearity and unstable system in its dynamics. Many simple and present day control methods have been used to balance the ball and beam system. The goal of this project is to model and control the ball and beam system. Here considering the beam angle of servo motor and designing controllers to control the ball position. Lagrange approach is used to find the ball position of the system. It is based on energy balance of the system. Based on the transfer function and state space model, open loop system and closed loop system are designed. The system is designed by using two Degrees-of-Freedom. The nonlinear characteristic of the second order system is regulated by using PID controller. The controller controls the ball position in moving the beam using the motor and beaten the disturbances. The parameters of the PID are tuned using PID tuning Algorithm. In order to analyse the accomplishment of PID to learn the effect of simplifying expectation, two control methods are designed and implemented using Proportional Derivative Integral (PID) as non-model based control method, Proportional Derivative and Proportional integral combination of model based and non-model based control methods.

The aim of the paper is to present the simple method of determining a fractional order controller to control the pump in Festo MPS® PA Compact Workstation. Transfer function of the controller follows directly from using of Bode's ideal transfer function as a reference one for the open loop system. Such systems generally are unsensitive to gain changes in the open loop. In Festo MPS® PA Compact Workstation by using a corresponding controllers a level and a flow rate can be set up as a cascade control system. The design process allows to use conventional continuous P, I, PI, PID controllers and discontinuous controllers (two-point controllers). In the presented study the fractional order controller is tested to obtain parameters controller of this system.

In this article, a method of designing high-order DLLs is presented and verified through both simulations and physical experiments. The general approach is based on selecting the transfer function of the closed-loop DLL and deriving the loop filter behavior based on the gain of the phase-detector and voltage-controlled delay line. The proposed approach does not rely on the principle of design based on achieving a desired phase margin specifications but rather is based on selecting a closed-loop DLL behavior based on a desired Gaussian transfer function. Experimental results are provided to support the claims.

Sigma-delta modulator structure is presented in the form of matrix equations. The equations allow to easily obtain analytical expressions for the noise and signal transfer functions for arbitrary modulator structures. As a result the modulator structures analysis and comparison become straightforward.

The purpose of this research is the modeling and Linear Control of Quad copter through pitch, roll, yaw and thrust command Interface. This research starts with derivation of nonlinear mathematical model of quad copter dynamics that consists of 6 degree of freedom(DOF) motions. The non-linear model is then linearized around equilibrium point and then 3DOF kinematics is extracted in order to design stabilizing and tracking control of three angular motions (Pitch, Yaw and roll). The Open loop transfer function of each DOF rotation motion shows that quad copter is highly unstable without any damping factor in linear mode. A Proportional integrator and differentiator(PID) controller is designed to control and stabilization of 3DOF rotations, controlling the four actuators independently in simulation. The real time 1DOF operation is done on designed Test rig in which the relation between thrust, Average RPM is evaluated and desired pitch pitch response is achieved by closed loop PID controller on Test rig. To support the above arguments, the simulated results as well as experimental results are presenented and compared.

Objective: Interferometric Fiber optic gyroscope (IFOG) is an angular rate sensor which plays a crucial role in inertial navigation system. Measuring the angular rotation rate can be done in two approaches namely open loop&closed loop. Designing and implementation of these methods using a simulation tool provides faster&accurate results. This paper presents a novel Simulink model implementation of Open loop&Closed loop Fiber optic gyroscope for the measurement of rotation rate. Method/Analysis: The gyroscope with each optical component is treated as a black box having M input and N output ports that are represented mathematically with its transfer function by connecting output to its input. This methodology is very efficient for finding the calibration&phase difference between the co-rotating&counter rotating beams. Findings: There are two major contributions in this paper. Firstly, the physical model of open loop FOG is built in Simulink model&angular rate is measured. The signal processing scheme of modulation and demodulation techniques for finding the rotation rate can also be analyzed mathematically. In second, to improve the accuracy and stability the feedback loop is very important to improve the gyro performance which can also be analyzed with different rotation rates. Experimental setup shows that an improved result is obtained in determining the direction of rotation and accuracy of the proposed model.

Luo Converters which use voltage lift technique to provide high gain is a topic of research interest. They are used in motor drives, telecom, automotive applications and as radar and electronic warfare in military. In this work, mixed signal behaviour of constant frequency controlled PWM Ultra Lift Luo Converter is analyzed. The closed loop transfer function is derived using Perturbation theory, Sample-Hold theory and Modified Pade Approximation method. To get the margin of stability accurately, Slope Compensation is used. The expressions of the control current of the inner current loop of Converter with and without slope compensation are derived. Finally the controller is designed using PSIM 9.0 and SMARTCTRL 1.0 software and stability is analysed.

Asymmetric control scheme is an approach to achieve Zero Voltage Switching (ZVS) for half bridge isolated DC–DC converters. Due to the switching property included in their structure, DC–DC converters have a nonlinear behavior and their controller design is accompanied with complexities. But by employing the average method it is possible to approximate the system into a linear system and then linear control methods can be used. Dynamic performance of half bridge converters output voltage can be controlled by Pole placement and PID controllers. In this paper, Genetic Algorithm is used to optimize the system to achieve the optimum dynamic response. Matrix coefficients and dominant poles of closed loop transfer function is selected based on Genetic Algorithm. The results show an improvement in voltage control response in a short time.

The structure and its function about a dual-axis rate turntable has been elaborated, its principle block diagram of control system is given. And its electromechanical system’s transfer function of the dual-axis rate table has been calculated and simplified reasonably based on experiments and practical situation, then a double loop control system constituted with a speed loop and a stabilization loop is got. Its’ correction link of the stabilization loop is calculated, which has a 2-order open loop transfer function. In order to achieve a suitable stability margin, the corresponding digital controller is designed, and its’ pulse transfer function response and the three-step iterative simulation results to a same sinusoidal excitation are got and compared, the same results verified the correctness of the design to the correction link.

A flight control system design technique previously introduced in the literature is applied to four challenging synthesis problems: (1) design of a hypersonic vehicle autopilot, (2) design of a stability augmentation system for a fighter aircraft, including human-in-the-loop desktop simulator evaluation, (3) design of an autopilot for a cruise missile, and (4) design of a control system for an uninhabited rotorcraft. The vehicle models used in the first and third problems have been employed by other researchers using competing design approaches. Human-in-the-loop desktop simulation of the design in the second problem provides a novel evaluation of the resulting stability and command augmentation system’s ability to accommodate system failures from the standpoint of their effect upon operator dynamics. Finally, the ability of the design procedure to accommodate velocity dependent changes in vehicle dynamics is demonstrated in the rotorcraft example The nine-step synthesis procedure to be exercised is based in the frequency domain and evolves from sliding mode control theory.

Take generator system included AVR (automatic voltage regulator) and PSS (power system stabilizer) as an example, Using the time simulation method, Study the equivalence between the transfer function model and the equivalent circuit simulation, and establish the corresponding relations between the circuit structures, internal parameters and transfer function parameters, based on the energy of equivalent circuit, the Hamiltonian function of transfer function is derived indirectly, and the Hamiltonian model is established. The study in this paper provides a new way to establish generalized Hamiltonian model for linear system based on transfer function.

Missiles may be damaged when aeroservoelastic problem occurs, which is caused by the interaction of structure flexibility and flight control system. Because of the limit of wind tunnel test condition, numerical methods are mostly used in previous aeroservoelastic studies. However, series of assumptions and simplification on structures, aerodynamics and flight control systems are unavoidably introduced, and various nonlinear factors are also ignored, therefore, they result in considerable errors. A novel method called aeroservoelasticity semi-physical simulation test is proposed in this paper, which takes the flexible missile with control system as the test object. Vibration signals at several locations of the missile are measured by accelerometers, then corresponding unsteady aerodynamics is computed based on the fact that airflow at high Mach is nearly quasi-steady, and finally unsteady aerodynamics is exerted simultaneously by shakers at certain locations of the missile. The aeroservoelasticity semi-physical simulation test system can be constructed after the control system is closed. Open loop transfer function test and closed loop stability test are carried out in sequence. The test principle and method proposed in this paper are verified by the concordance between the results of numerical simulation and experiment.

G AS turbine engines are subjected to several operational constraints, both at steady state and in the transient regime. These constraints correspond to mechanical limits such as speed and acceleration; limits in thermodynamic variables such as pressures and temperatures; and limits preventing engine components from undergoing dynamic instabilities, mainly surge, stall and flame blowout. Engine control systems incorporate measures to protect the engine from crossing these limits at all times. Achieving limit protection while ensuring fast transient response represents a design challenge, which was summarized by Spang and Brown in their 1999 paper [1]: “. . .much of the complexity of the control comes from the need to operate the engine as close as possible to its limits.” This paper presents a novel and very effective way to achieve such maximal exploitation of the available limits to enable fast responses in thrust or other relevant variables. The proposed technique is based on thewidely usedmultiregulator architecture with max–min limit protection logic [1,2], which uses linear compensators in its original form. As shown in Fig. 1, this architecture uses a single control input (fuel flow) to drive the desired output (typically fan speed or engine pressure ratio) to a setpoint through a control loop with integral action and a linear compensator. Additional compensators are set up to control limited variables to their permissible values, still using fuel flow as the control input. A max–min selection logic stage decides whether the main output regulation task or any of the limit protection tasks should be made active at anygiven time. Integral action is used to achieve type 1 loops for offset-free regulation. The regulators, thus, provide control input rates. Define two index sets as L f1; 2; . . . lg and H fl 1; l 2; . . . hg, where L contains the indices of the regulators associated with the min selector, while the elements of H are the indices of the regulators associatedwith themax selector. No index is defined for the output of the min selector. As shown in Fig. 1, the control rate applied to the integrator is selected according to the formula

This paper investigates the results of distributing the delay of a single feedback system. To distribute the delayed feedback, the single delay is replaced by the sum of two distinct delays with the same effective delay. The statistical properties of the new distribution function in the feedback, namely the sum of two delta functions, are used to quantify the effectiveness of delay distribution. We show that the distribution is effective in reducing the magnitude of the open loop transfer function, thereby, decreasing the gain-crossover frequency and improving the phase margin. Using these results, we explain the stabilizing effects of a delayed controller proposed in another publication. Finally, we demonstrate a potential application.

This paper reports the active vibration control of plates using a positive position feedback(PPF) controller with moment pair actuators. The equations of motion of the plates under a force and moment pairs are derived and the equations of PPF controllers are formulated. The numerical active control system is then achieved. The effect of the parameters - gain and damping ratio - of the PPF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the PPF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies without changing the phase behavior. The increase of the damping ratio of the PPF controller leads to decrease the magnitude of the open loop transfer function and to modify its phase characteristics, ie, system stability. Based on the behavior of the gain and the damping ratio of the controller, PPF controller for reduction of the plate vibration can be achieved. Two PPF controllers are designed with their connection in parallel to control the two modes simultaneously. Each PPF controller is tuned at the and modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the tuned modes can be obtained.

This paper investigates the active vibration control of clamp beams using positive position feedback (PPF) controllers with a sensor/moment pair actuator. The sensor/moment pair actuator which is the non-collocated configuration leads to instability of the control system when using the direct velocity feedback (DVFB) control. To alleviate the instability problem, a PPF controller is considered in this paper. A parametric study of the control system with PPF controller is first conducted to characterize the effects of the design parameters (gain and damping ratio in this paper) on the stability and performance. The gain of the controller is found to affect only the relative stability. Increasing the damping ratio of the controller slightly improves the stability condition while the performance gets worse. In addition, the higher mode tuned PPF controller affects the system response at the lower modes significantly. Based on the characteristics of PPF controllers, a multi-mode controllable SISO PPF controller is then considered and tuned to different modes (in this case, three lowest modes) numerically and experimentally. The multi-mode PPF controller can be achieved to have a high gain margin. Moreover, it reduces the vibration of the beam significantly. The vibration levels at the tuned modes are reduced by about 11 dB.

In this paper, design of PID controller is analyzed for unstable second order processes with time delay based on IMC method and H2 minimization. A new desired closed loop transfer function is obtained based on which the PID controller is designed. Maclaurin series is used to approximate the controller expression as a PID controller. Improved closed loop performances are achieved with the proposed method when compared to the recently reported methods in the literature. Comparative analysis has also been carried out with modified Smith predictor schemes and showed that the proposed method is superior. Further, an analysis is carried out based on maximum sensitivity for arriving at systematic guidelines for selection of the closed loop tuning parameter which is essential for unstable systems. The bounds for this tuning parameter are analyzed using the maximum sensitivity.

In this paper analytical expressions for PID-controllers settings for electromechanical motion systems are presented. It will be shown that by an adequate frequency domain oriented parametrization, the parameters of a PID-controller are analytically dependent on one variable only, the cross-over frequency of the open loop transfer function. Analytical expressions are derived that relate the cross-over frequency clearly to the performance criteria for the closed loop system. In this paper the latter is shown in detail for servo problems. The effectiveness of the outlined approach is demonstrated by experimental results that were obtained from a two DOF tilting mirror system.

A vibration avoidance and contouring error compensation algorithm for feed drives is presented. The residual vibrations are avoided by applying input shaping filters on the reference axis commands. The input shaping filter avoids the excitation of the structural modes but at the expense of increasing tracking and contouring errors. The tracking errors are estimated from the closed loop transfer function of drives, and used to predict the contouring errors which are mapped to the each axis for pre-compensation. The integrated vibration avoidance and contouring error compensation is experimentally demonstrated to improve the damping and contouring accuracy on a two-axis table.

An extension of the Symmetrical Optimum criterion for the design of PID type- p closed- loop control systems is proposed. Type- p control loops are characterized by the presence of p integrators in the open-loop transfer function. For designing a PID type- p control loop there should exist an PI p D , or PI ( p −1) D, or PID and so on, if the controlled process is of type-0 or type-1 or type-( p − 1) respectively. A type-II control loop achieves zero steady state position and velocity error, a type-III control loop achieves zero steady state position, velocity and acceleration error and therefore a type- p control loop is expected to track both faster reference signals and eliminate higher order errors at steady state. For deriving the proposed control law, a transfer function containing dominant time constants and the plant's unmodelled dynamics has been considered in the frequency domain. The final control law consists of analytical expressions that involve both dominant dynamics and model uncertainty of the controlled process. For justifying the potential of the proposed theory, simulation results for representative processes met in many industry applications are presented.

This paper investigates the filtered velocity feedback(FVF) controller for the reduction of the acoustic power radiated from a clamped beam. The instability problem due to the non-collocated sensor/actuator configuration when using PZT actuator should be sorted out. The roll-off property of the FVF controller at high frequency helps to alleviate the instability. The dynamics of clamped beams under forces and moments pair and the FVF controller are first formulated. The formulation of the sound radiated power is followed. The open loop transfer function(OLTF) synthesized with 100 modes is used to determine the stability of the control system. The control performance is finally estimated. The levels of the vibration and the sound radiated power are reduced in the wide bandbelow the tuning mode of the FVF controller.

Sea-skimmingmissiles are required to fly at a very low height over themean sea level in order to avoid detection on the one hand and to inflict substantial damage to the enemy ship on the other. The height control system of a seaskimming missile experiences a disturbance because of sea waves, which increases the probability of the missile ditching into the sea. The unmodeled dynamics and varying aerodynamic coefficients further compound the task of the height control system. In this paper, a novel method for height control based on the extended state observer, which enables an estimation of the sea-wave disturbances in real time, is proposed. The estimate can be used for realtime planning of the skimming altitude. Simulation results show that the height control system functions effectively in the presence of significant sea-wave disturbances. Finally, the proposed design is compared with some existing designs reported in the literature.

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems at high frequencies due to non-collo-cated sensor/actuator configuration with the DVFB can be alleviated by the proposed FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The dynamics of a clamped plate under forces and moments and the FVF controllers are formulated. The stability of the control system and performance are investigated with the open loop transfer function(OLTF). It is found that the FVF controller has a higher gain margin than the corresponding DVFB controller ow-ing to the rapid roll-off behavior at high frequencies. Although the gain margin cannot be fully uti-lized because of the enhancement at the high frequencies, the vibration at the modes lower than the tuning frequency is well controlled. This performance of the FVF controller is shown to be improved from that of the DVFB controller. It is, however, noted that the stability around the tuning fre-quency is very sensitive so that the enhancement in vibration level should be followed. The reduc-tion performance at low frequencies using the FVF controller should be compromised with the en-hancement in the vibration at high frequencies while designing the controller.

Fractional complex order integrator has been used since 1991 for the design of robust control-systems. In the CRONE control methodology, it permits the parametrization of open loop transfer function which is optimized in a robustness context. A CRONE Control-System-Design Toolbox for MATLAB has been developed for several years. It is composed of 4 main units. The “CRONE CSD Guided Start” unit is the starting one as it helps to choose which 1st, 2nd or 3rd Generation CRONE CSD unit needs to be used. Controllers are often implemented using Hardware in the Loop development kits or Digital Signal Processors. In this paper, we propose to design a robust controller for an hydraulic system and then to implement it into a Programmable Logic Controller (PLC).

This study develops a robust method to control the humanoid joint based on a disturbance observer (DOB). In controlling the bipedal robot, it is usually difficult to precisely compensate for the gravity torques, friction forces, model mismatch and so on. The authors regard these as disturbances and employ the DOB to design a robust controller for the humanoid joint. The requirements for joint control are firstly discussed; a single joint model, that is, inverted pendulum model, is illustrated and the open-loop transfer function of the ankle joint is also presented. The authors consider the DOB for compensation, develop the design criterions of the filter and propose the robust servocontrol structure of the joint controller. For a given simulated robot, the performance and robustness of the proposed controller are demonstrated comparing with the proportional-integral-differential controller, and the effect of model perturbations is especially considered in case of the system performance. The results show the validation and feasibility of the proposed method.

This study presents a combined control strategy for electrohydraulic shaking table (EST) systems. The position frequency bandwidth of the EST system is so low that it results in a worse tracking accuracy during seismic tests, particularly when the frequency bandwidth of the desired position signal exceeds the frequency bandwidth of the EST position closed-loop system. In order to improve the position tracking accuracy, a combined control strategy is proposed, which utilises a recursive extended least square (RELS) algorithm to offline or online estimate the position closed-loop transfer function of the EST system, then uses the estimated transfer function to offline or online yield a feedforward inverse controller for extending the position frequency bandwidth, finally, employs a minimal control synthesis (MCS) algorithm to further improve the tracking performance of the EST position system. The proposed control strategy combines the merits of offline or online feedforward inverse compensation and adaptive control. The procedure of the proposed control strategy is programmed in MATLAB/Simulink, and is then compiled to a real-time PC with Microsoft Visual Studio.NET for implementation. A better tracking performance for the proposed control strategy is achieved in experiments by using actual EST.

Experiments are conducted to investigate the ability of variable-pressure pulsed-blowing actuation to maintain a constant lift force on a low-aspect-ratio semicircular wing in a longitudinally gusting flow. Dynamic models of the lift response to actuation and the lift response to longitudinal gusting are obtained through modern system identification methods. Robust closed-loop controllers are synthesized using a mixed-sensitivity loop-shaping approach. An additional feedforward disturbance compensator is designed based on a model of the unsteady aerodynamics. The controllers show suppression of lift fluctuations at low gust frequencies, f < 0.8 Hz(reduced frequency, k < 0.09). At higher frequencies, the control performance degrades due to limitations related to the time for a disturbance, created by the actuators, to convect over the wing and establish the flowfield that leads to enhanced lift on the wing.

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated. The effects of the design parameters(cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function(OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased. The control performance is finally estimated for the clamped beam. More than 10 dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

Each subsystem of a nonlinear interconnected dynamic delayed system is approximated by a weighted combination of L transfer function delayed systems (TFDSs). The H2-norm of the difference between the transfer function of a reference model and the closed-loop transfer function of the kth TFDS of subsystem i is then minimized to obtain a suitable frequency response without incurring oscillating and sluggish phenomena. Because of the existence of the disturbance at the output of the kth TFDS, which is not only large but also contains various frequency components, the H∞-norm of the weighted sensitivity function between the output disturbance and its corresponding output of the kth TFDS is simultaneously minimized to reduce its effect. Furthermore, with proper selection of weighted sensitivity functions, certain specific modes of the output disturbance can be eliminated. Finally, two simulations are performed; one is the simulation of our designed TFDSs with different delays or nonminimum phases, and the other is the simulation of an internet-based intelligent space for the trajectory tracking of a car-like wheeled robot system. We demonstrate the effectiveness and efficiency of the proposed control. The main contributions of this paper are twofold. First, the control can simultaneously attain robust performance through the mixed H2/H∞ optimization with a Smith predictor and achieve the robust stability via L2N stable with finite gain. Second, fuzzy observer is not needed.

In this article, an existing exact algorithm for identifying a continuous transfer function from frequency data, giving major importance to phase data, is further developed. The new version allows identifying a digital transfer function, or a continuous fractional order transfer function with a fixed order of commensurability (i.e. a ratio of two polynomials in s α, α ∉ ℤ). This is straightforward if the desired transfer function is to have only zeros or only poles; if a transfer function with both zeros and poles is sought, however, a numerical method must be resorted to.

This paper presents a new design procedure for control of thickness and plate type of cold rolling temper mill. A novel concept for control system design - U-model based design methodology with expanded multi-input and multi-output (MIMO) formulation for this application separates specifying closed loop performance-controller from process models. In contrast to classical and methodologies, this takes two parallel formations; 1) designs an invariant virtual controller with specified closed loop transfer function in a feedback control loop; 2) determines real controller output by resolving the inverse of the plant U-model. Further, this study analyses some of the associated properties for assurance and guidance for ongoing theoretical development and applications. To validate the design procedure, it takes several computational experiments to generate simulation results, which show efficiency and effectiveness of the proposed MIMO U-model based control system design.

This paper reports active control of clamped beams using acceleration feedback controllers (AF). The equations of motion of clamped beam under force and moment pairs were derived and the equations of AF controllers were formulated. The effect of the parameters - gain and damping ratio - of the AF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the AF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies. The increase of the damping ratio of the AF controller leads to decrease the magnitude of the open loop transfer function and modifies its phase characteristics to be more stable. Three AF controllers connected in parallel were then proposed. Each AF controller is tuned at the 2nd, 3rd and 4th modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the 3 modes can be obtained.

This note proposes vibration-free motor control through modified LQG/LTR methodology. A conventional LQG/LTR method is a design tool in the frequency domain. However, unlike the conventional one, the proposed one is a time response based design method. This feature is firstly designed by parameterized settling time control gain through the target loop design procedure and the feature is secondly realized by loop transfer recovery. In order to show convergence to the target loop transfer functions, asymptotic behaviors of the open and the closed loop transfer functions are shown. At the conclusion, it is verified that the proposed method is robustly stable to parametric uncertainties through -plot.

The limits of parameter γ in FAST TCP are studied in this paper. A continuous time fluid flow model of the link buffer is considered to create a linear control system related to FAST TCP. Linearing the fluid flow model and window control model, the Laplace transform version of congestion control system are presented. It results in a negative feedback system with open loop transfer function. With the analysis of Nyquist curve of the system, a sufficient condition on asymptotical stability of FAST TCP congestion window related to the parameter γ is obtained. Packet level ns-2 simulations are used to verify the theoretical claims.

This paper first reveals that the tracking and disturbance rejection problems can be decoupled into two independent optimization problems under the 2-DOF control framework. This result is then used for the design of a 2-DOF controller for a dual-stage actuator (DSA) system to provide desired performance of disturbance rejection and step tracking. The 2-DOF controller is designed based on the doubly coprime factorization approach, with which the closed-loop transfer function is expressed explicitly in terms of design parameters. This greatly simplifies the optimization of design parameters in meeting desired specifications. We further study how to use the design parameters to deal with specific problems in the DSA, i.e., control allocation and trajectory planning. For step tracking beyond the secondary actuator range, a nonlinear controller is also used for the primary actuator to complete the task. Experimental results demonstrate the practical implementation of the DSA control system and verify its effectiveness for step tracking and disturbance rejection and its robust performance under load changes.

This paper presents an internal model control (IMC) design for lightly-damped systems subject to periodic exogenous signals. For such systems, the conventional design of the so-called IMC filter in the IMC structure can result in oscillatory behavior even when the closed-loop transfer function is designed to be well damped. To circumvent this problem, several band-pass filters are incorporated into the IMC filter based on knowledge of the frequencies of the plant's resonance modes and exogenous signals. The track-following system of an optical disk drive is employed to illustrate the design of the proposed IMC filter. Experimental results confirm the effectiveness of the proposed design.

This paper introduces an improved procedure for the identification of a transfer function from phase angle data with prescribed frequency variation. It is shown how a transfer function can be identified from phase response data samples, by fitting a normalized function with constant magnitude using the vector fitting algorithm. The presented approach is numerically robust and leads to more accurate results than conventional approaches.

The problem Dead Time in control systems is an everlasting problem which is of primary importance in process control as well. The estimation and compensation of processes with time- delays have been of interest to academics and practitioners for several decades.The first proposed solutions for this problem was the Smith predictor in 1957. It was based on the idea of removing the time-delay from the characteristic equation of the control closed loop, which seemed to be very attractive at the first.Later investigations revealed that the method is very sensitive to model mismatches, which results in destabilizing effects on the loop performance. In this paper, using work it was propose a new method for controller tuning using an optimization method. The optimization method is based on dominating the gain of the minimum phase term in the open loop transfer function of the loop, such that the non-minimum phase effects of the model and process become dominated by the minimum phase characteristic of the desired term. This idea was investigated by simulation on some selected examples among the proposed modified versions of the Smith predictor.

Modern implementations of discrete-time phase-locked loops (DT-PLLs) often contain delayed feedback. The delays are usually a side effect to pipelining, filtering, or other inner-loop mechanisms. Each delay increases the order of the system by introducing an additional pole to the closed-loop transfer function and, in many cases, makes the traditional type-2 loop equations obsolete. This brief describes how the second-order notions of damping and natural frequency can be applied to type-2 DT-PLLs in the presence of any number of delays. It provides equations for loop parameters that will provide a desired transient behavior based on damping and natural frequency, along with a test to ensure the accuracy of the results. The novelty of this brief is that loop parameters can be found in closed form and ensured to be accurate, without the need for human interaction, simulations, or numerical root-finding algorithms.

This paper proposes a design and tuning method for a complex gain controller, based on the three-phase induction motor mathematical model complex transfer function to be used in the direct torque control at low speed which is a problem so far. The design and tuning of the complex gain is done by using the closed loop system frequency-response function. Experimental results are presented to validate the controller and operation at low speed is also explored. Este trabalho propõe um método de projeto para um controlador de ganho complexo baseado na função de transferência complexa do motor de indução trifásico para uso no controle direto de torque em que a operação do motor em baixas velocidades é um problema. O projeto e a sintonia do ganho complexo é realizado com o emprego da resposta em frequência do sistema em malha fechada. Resultados experimentais são apresentados para a validação da proposta do controlador.

This paper presents an extension of the L 1 adaptive output-feedback controller to systems of unknown relative degree in the presence of time-varying uncertainties without restricting the rate of their variation. As compared with earlier results in this direction, a new piecewise continuous adaptive law is introduced, along with the low-pass-filtered control signal that allows for achieving arbitrarily close tracking of the input and the output signals of the reference system, the transfer function of which is not required to be strictly positive real. Stability of this reference system is proved using a small-gain-type argument. The performance bounds between the closed-loop reference system and the closed-loop L 1 adaptive system can be rendered arbitrarily small by reducing the step size of integration. Missile longitudinal autopilot design is used as an example to illustrate the theoretical results.

This paper presents a frequency response analysis of current controllers based on selective harmonic compensation schemes for three-phase voltage–source shunt Active Power Filters (APFs). To perform this analysis, the time delay introduced by the inverter and the sampling is taken into account in the current controller closed loop transfer function. Doing this, the differences among the schemes are pointed out, demonstrating the importance and effectiveness of the delay compensation to maintain the whole system stability. In addition, the performance of each current controller is evaluated by means of the total harmonic distortion of the mains line current and time response for fast load variations. The main goal is to identify the most suitable solution in terms of current controllers based on selective harmonic compensation for an industrial implementation. All the considered current control schemes have been tested on the same digital platform. Experimental results are presented for a 25-kVA shunt APF prototype compensating a nonlinear inductive load. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

We present a frequency domain solution to the sampled-data passivity problem. Our analysis is exact in the sense that we take into account the intersample behavior of the system. We use frequency response (FR) operators to first obtain necessary conditions on the sampling rate T and the relative degree of the open-loop transfer function G 11 for achieving a passive continuous-time closed-loop system. Then, assuming passivity of G 11 and closed-loop stability, we derive a necessary and sufficient condition for discrete-time controllers that render a passive closed-loop system. We apply the obtained results to the problem of stability of haptic systems.