Proper Controller Research Articles

Effect of sensor location on controller performance in a wastewater treatment plant.

Complete mixing is hard to achieve in large bioreactors in wastewater treatment plants. This often leads to a non-uniform distribution of components such as dissolved oxygen and, hence, the process rates depend on them. Furthermore, when these components are used as input for a controller, the location of the sensor can potentially affect the control action. In this contribution, the effect of sensor location and the choice of setpoint on the controller performance were examined for a non-homogeneously mixed pilot bioreactor described by a compartmental model. The impacts on effluent quality and aeration cost were evaluated. It was shown that a dissolved oxygen controller with a fixed setpoint performs differently as a function of the location of the sensor. When placed in a poorly mixed location, the controller increases the aeration intensity to its maximum capacity leading to higher aeration costs. When placed just above the aerated zone, the controller decreases the aeration rate resulting in lower dissolved oxygen concentrations in the remainder of the system, compromising effluent quality. In addition to the location of the sensor, the selection of an appropriate setpoint also impacts controller behavior. This suggests that mixing behavior of bioreactors should be better quantified for proper sensor location and controller design.

Feedforward actuator controller development using the backward-difference method for real-time hybrid simulation

Real-time hybrid simulation (RTHS) has emerged as an important tool for testing large and complex structures with a focus on rate-dependent specimen behavior. Due to the real-time constraints, accurate dynamic control of servo-hydraulic actuators is required. These actuators are necessary to realize the desired displacements of the specimen, however they introduce unwanted dynamics into the RTHS loop. Model-based actuator control strategies are based on linearized models of the servo-hydraulic system, where the controller is taken as the model inverse to effectively cancel out the servo-hydraulic dynamics (i.e., model-based feedforward control). An accurate model of a servo-hydraulic system generally contains more poles than zeros, leading to an improper inverse (i.e., more zeros than poles). Rather than introduce additional poles to create a proper inverse controller, the higher order derivatives necessary for implementing the improper inverse can be calculated from available information. The backward-difference method is proposed as an alternative to discretize an improper continuous time model for use as a feedforward controller in RTHS. This method is flexible in that derivatives of any order can be explicitly calculated such that controllers can be developed for models of any order. Using model-based feedforward control with the backward-difference method, accurate actuator control and stable RTHS are demonstrated using a nine-story steel building model implemented with an MR damper.

Controller parameter tuning of delta robot based on servo identification

High-speed pick-and-place parallel robot is a system where the inertia imposed on the motor shafts is real-time changing with the system configurations. High quality of computer control with proper controller parameters is conducive to overcoming this problem and has a significant effect on reducing the robot’s tracking error. By taking Delta robot as an example, a method for parameter tuning of the fixed gain motion controller is presented. Having identifying the parameters of the servo system in the frequency domain by the sinusoidal excitation, the PD+feedforward control strategy is proposed to adapt to the varying inertia loads, allowing the controller parameters to be tuned by minimizing the mean square tracking error along a typical trajectory. A set of optimum parameters is obtained through computer simulations and the effectiveness of the proposed approach is validated by experiments on a real prototype machine. Let the traveling plate undergoes a specific trajectory and the results show that the tracking error can be reduced by at least 50% in comparison with the conventional auto-tuning and Z-N methods. The proposed approach is a whole workspace optimization and can be applied to the parameter tuning of fixed gain motion controllers.

Design Considerations of Digitally Controlled LCL-Filtered Inverter With Capacitor- Current-Feedback Active Damping

Due to the effect of the computation and modulation delays on the capacitor-current-feedback active damping, the digitally controlled LCL-filtered inverter tends to be unstable as the LCL-filter resonance frequency approaching to one-sixth of the sampling frequency. Therefore, to guarantee sufficient stability margins, the guideline for choosing the LCL-filter resonance frequency is proposed in this paper. After the resonance frequency is selected, a systematic design method is proposed to facilitate the selection of the proper controller parameters. With this design method, a satisfactory region of the controller parameters for meeting the system specifications is obtained, from which the proper controller parameters can be easily determined. Moreover, it is convenient and explicit to optimize the system performance according to the satisfactory region. A 6-kW prototype is built and tested. The simulation and experimental results validate the theoretical analysis.

Synchronization of Identical and Nonidentical Memristor-based Chaotic Systems Via Active Backstepping Control Technique

This paper investigates the problem of synchronization of identical and nonidentical memristor-based chaotic systems via active backstepping control technique. In order to achieve synchronization for identical chaotic systems, a memristor-based Lorenz system is considered as both master and slave systems, and for nonidentical chaotic systems, memristor-based Lorenz and Chuas systems are considered as master and slave systems, respectively. Based on the Lyapunov stability theory and active backstepping control technique, proper controllers are designed to achieve synchronization. Finally, numerical simulations are provided to show the effectiveness of the proposed controller.

Switching adaptive controllers to control fractional‐order complex systems with unknown structure and input nonlinearities

This article investigates the chaos control problem for the fractional‐order chaotic systems containing unknown structure and input nonlinearities. Two types of nonlinearity in the control input are considered. In the first case, a general continuous nonlinearity input is supposed in the controller, and in the second case, the unknown dead‐zone input is included. In each case, a proper switching adaptive controller is introduced to stabilize the fractional‐order chaotic system in the presence of unknown parameters and uncertainties. The control methods are designed based on the boundedness property of the chaotic system's states, where, in the proposed methods the nonlinear/linear dynamic terms of the fractional‐order chaotic systems are assumed to be fully unknown. The analytical results of the mentioned techniques are proved by the stability analysis theorem of fractional‐order systems and the adaptive control method. In addition, as an application of the proposed methods, single input adaptive controllers are adopted for control of a class of three‐dimensional nonlinear fractional‐order chaotic systems. And finally, some numerical examples illustrate the correctness of the analytical results. © 2014 Wiley Periodicals, Inc. Complexity 21: 211–223, 2015

English

The biggest weakness of wind power energy is the lack of exact predictability on its generation. Perhaps even if other energy sources can be saved by using wind energy, the short term power variation must be secured by a conventional plant. The variations in the output of a large wind farm results in many integration issues. The uncertainty in the output of a large wind plant can be overcome by using fast acting dispatchable sources. The goal is to reach the smallest possible difference between actual wind power and forecasted wind power. In this paper a model, which optimizes the wind power energy by battery based energy storage system with the help of conventional and intelligent controllers, has been developed. This paper presents controlling methodologies for a battery based energy storage system in conjunction with PID and Fuzzy logic controller. The results may show that choosing of proper controller along with battery based energy storage system will give effective control over wind power. In order to overcome the drawbacks of the wind power, the use of energy storage as power buffer has investigated.

Designing robust controller to improve current-sharing for parallel-connected inverter-based DGs considering line impedance impact in microgrid networks

Microgrids are designed to supply electrical and heat loads for small communities. An important research area related to microgrids is proper controller strategy for ensuring the current and power sharing of each generating unit under different load and system conditions. In this paper, considering effect of line impedance, a new approach based on robust control design method, H∞ loop-shaping design (HLSD) procedure, was presented for parallel-connected inverters of DGs in an islanded microgrid. Changes in the parameters of lines were considered uncertainties, based on which the system model was built. The designed controller adjusted the output voltage of each inverter by controlling duty cycles in order to change the output current delivered by each inverter. So, the controller controlled the duty cycles as control inputs to the system so that the system robustness to uncertainties was maximized and the voltage error was minimized, which in turn would cause reduction of the circulating current. For resistive, inductive, and non-linear loads, time responses of the system were achieved. Results of simulations indicated that the designed robust controller, in comparison with gain scheduling controller, was capable of guaranteeing robust stability and performance under parameter uncertainty and different loads. Also, effectiveness of the proposed controller in minimizing the circulating current among parallel-connected inverters was demonstrated.

Electric Machine Analysis, Control and Verification for Mechatronics Motion Control Applications, Using New MATLAB Built-in Function and Simulink Model

This paper proposes a new, simple and user-friendly MATLAB built-in function, mathematical and Simulink models, to be used to early identify system level problems, to ensure that all design requirements are met, and, generally, to simplify Mechatronics motion control design process including; performance analysis and verification of a given electric DC machine, proper controller selection and verification for desired output speed or angle.

Joints flexibility effect on the dynamic performance of robots

SUMMARYThis paper studies the effect of joint flexibility on the dynamic performance of a serial spatial robot arm of rigid links. Three models are developed in this paper. The first and the third models are developed using the multibody dynamics approach, while the second using the classical robotics approach. A numerical algorithm and an experimental test-rig are developed to test the final model. The links' inertial parameters are estimated numerically. Empirical formulae with assumption models are used to estimate the flexibility coefficients. The simulation results show that the joint damping is a major source of inaccuracies, causing trajectory error without a proper feedback controller.

A Multirate Control Strategy to the Slow Sensors Problem: An Interactive Simulation Tool for Controller Assisted Design

In many control applications, the sensor technology used for the measurement of the variable to be controlled is not able to maintain a restricted sampling period. In this context, the assumption of regular and uniform sampling pattern is questionable. Moreover, if the control action updating can be faster than the output measurement frequency in order to fulfill the proposed closed loop behavior, the solution is usually a multirate controller. There are some known aspects to be careful of when a multirate system (MR) is going to be designed. The proper multiplicity between input-output sampling periods, the proper controller structure, the existence of ripples and others issues need to be considered. A useful way to save time and achieve good results is to have an assisted computer design tool. An interactive simulation tool to deal with MR seems to be the right solution. In this paper this kind of simulation application is presented. It allows an easy understanding of the performance degrading or improvement when changing the multirate sampling pattern parameters. The tool was developed using Sysquake, a Matlab-like language with fast execution and powerful graphic facilities. It can be delivered as an executable. In the paper a detailed explanation of MR treatment is also included and the design of four different MR controllers with flexible structure to be adapted to different schemes will also be presented. The Smith's predictor in these MR schemes is also explained, justified and used when time delays appear. Finally some interesting observations achieved using this interactive tool are included.

AN ANALOG-DIGITAL HYDRAULIC CYLINDER VELOCITY CONTROL SYSTEM FOR MOBILE MACHINES

Hydrostatic drive systems with linear actuators are commonly used in variety of mobile machines and vehicles. One of important aspect of its operation is cylinder velocity control in variable operating conditions, such as different load, pump pressure and engine rotational velocity. The aim of this article is to create an algorithm, which would control velocity of a hydraulic cylinder used in such systems. One way to create cylinder velocity control system is to perform an identification, which would characterize this system. To do this work it was appropriate to use test stand with excavator equipment. The first part of the article includes the description of the stand and enumerates parts that compose it. Correct work of the control system is possible through use of a proper controller. For achieving a desired purpose, a PID controller was used with some modifications improving system's operation. The controller parameters were tuned based on the model of the system, obtained on the basis of estimation, for different operational conditions. To do this, a tool of MATLAB Simulink called Parameter Estimation was used. The control algorithm, in automatic mode, makes system tuning based on coefficients array. The final stage of the research work was to conduct verification tests, which let to assess a correctness of the created and proposed control system.

Design of a Non Fragile Optimal Controller Realization for Vehicle Suspension System for Different Road Profiles

This paper explains a suspension system of a vehicle which comprises of spring mass and damper. The main objective is to design a proper controller that can damp oscillations in order to provide safety, ease and comfort to passengers of vehicle during uneven road surface, bumps and small patches. To perform the desired task state space model of a quarter wheel vehicle suspension system is derived. The response of the system is simulated in MATLAB/SIMULINK. The open loop response showed that the derived model is stable. Different types of controllers are designed i.e. Linear Quadratic Regulator (LQR) and Observer based controller to analyze the system in closed loop. Both the controllers showed improved performance for different road profiles. It is observed and shown that observer based controller has better response than Linear Quadratic Regulator (LQR) controller. Simulink models for Linear Quadratic Regulator (LQR) and observer based controller are designed. Besides, different types of realization techniques (minimal realization, balanced realization, modal realization, observer canonical realization) are compared for minimum fragility in controller implementation. The difference among the different realization controllers has been analyzed in detail for rounding off error or truncation error and an optimal non fragile controller design has been presented. Different disturbances were imposed upon the simulated model. All the results are analyzed in open and closed loops. The closed loop response showed that the oscillations were damped quickly and the desire results were achieved successfully.

2A15 Decentralized Robust Optimal Control of Large Flexible Space Structures by Local Proper Controllers Using Displacement Output(The 12th International Conference on Motion and Vibration Control)

2A15 Decentralized Robust Optimal Control of Large Flexible Space Structures by Local Proper Controllers Using Displacement Output(The 12th International Conference on Motion and Vibration Control)

Analysis on the Propagation of the Fiber-Optic Signals in the Perturbed Nonlinear Schrodinger Equation

Chaos appears in the whole process of fiber-optic signal propagation with one external perturbation due to the absence of damping. Via adding a proper controller, chaos cannot be suppressed when the controller’s strength is weak. With the increase of the controller strength, the fiber-optic signal can stay in a stable state. However, unstable phenomenon occurs in the propagation of the fiber-optic signal when the strength exceeds a certain degree. Moreover, we discuss the parameters’ sensitivity to be controlled. Numerical results show that vibration, oscillation and escape can occur during the transmission of optic signals with different parametric regions.

Fine attitude maneuvering by reaction wheel via sliding mode speed driver

The objective of this paper was to design a set of proper speed controllers for reaction wheels in the presence of unknown coulomb friction and parametric uncertainties. The controller goal was to change the rotational speed of reaction wheels to adjust the satellite to a desired attitude. The mathematical model of a satellite that utilizes three reaction wheels as actuators was developed by angular kinematics and kinetic equations. Variable-structure control theory was then applied on the reaction wheel via a real-time microcontroller-based Hardware in the Loop. The simulated satellite response to wheel speed shows that the sliding mode speed controller is effective, and a small attitude angle could be tracked more effectively than with a Proportional–Integral–Derivative speed controller.

An Overview of Impact of Nonlinear Friction in Oscillating Control Loops: from Diagnosis to Compensation

Among the prominent reasons for oscillations in control loops such as poor controller tuning, inappropriate process design, oscillating load and disturbances with a high-frequency, the presence of static friction or stiction in the control valve is the most common reason. As a consequence of the friction, the control valves may present an oscillatory behavior, affecting the regulatory control performance and therefore it increases the variability of the control loop, causing loss of product quality and increasing energy consumption. Modeling of stiction using clear mathematical definition is hard due to its nonlinearity properties such as hysteresis, deadband or deadzone. This comparative study identifies the relative strengths and weaknesses of the different approaches of diagnosing of stiction in control loops and the compensation techniques to mitigate this effect. The aim is to determine the appropriate and precise model of stiction in order to design a proper controller to prevent control loops from oscillations. Numerous algorithms and methods which are either qualitative or quantitative in the literature show that despite these attempts to modeling, diagnosing and compensation of this phenomenon, lack of a reliable methodology to predict occurrence and properties of such oscillations and therefore lack of proper model is quite sensible. Furthermore exclusive of lack of precise model, even solving the problem were limited to some and different assumptions and applications and there is not one method which can cover all cases reliably. From this study too, it is seen that Data Driven model because of providing a simpler solution with fewer parameters is the most common method in contrast to physical based models with the presence of a number of unknown physical parameters. It is our view that hybrid approaches where different methods work in conjunction to solve parts of the problem are attractive and more effective methods. Lastly, numerous methods of stiction detection are available. Hence, it is suggested that the future research emphasis should be more on compensation of stiction especially for nonlinear processes.

FINITE-TIME SYNCHRONIZATION OF DYNAMICAL NETWORKS COUPLED WITH COMPLEX-VARIABLE CHAOTIC SYSTEMS

In this paper, finite-time synchronization of dynamical networks coupled with complex-variable chaotic systems is investigated. According to Lyapunov function method and finite-time stability theory, both the dynamical networks without and with coupling delay are considered through designing proper finite-time controllers. Several sufficient conditions for finite-time synchronization are derived and verified to be effective by some numerical examples.

Synchronization controller for a 3-R planar parallel pneumatic artificial muscle (PAM) robot using modified ANFIS algorithm

Parallel manipulator is a closed-kinematic chain mechanism in which performance of its end effector – moving platform is contributed by its independent actuators. In traditional designs, each elemental actuator has its own controller as well as reference input, and it works independently without gathering information from its neighbors. Consequently, as one of the actuators cannot keep up with the others, the platform performance is easily deteriorated due to the lack of coherence between these actuators. Therefore, the aim of this paper is to design a 3-R planar parallel robot and develop a proper synchronization controller for its tracking control task. Adaptive Network Based Fuzzy Inference System (ANFIS) algorithm was modified and applied as the main strategy of this synchronization controller. The controller is then able to compensate errors between the actuators and enforce them to cooperate harmonically with each other regardless external disturbances caused by the outside environment or geometrical constraints of the closed-loop structure. Simulations and practical experiments on a scaled parallel robot were carried out to evaluate the designed controller. The results showed that by applying the proposed control technique, the working errors of the component actuators converged quickly to zero almost at the same time. As a result, the tracking performance of the common platform was significantly improved in comparison with the performance when applying a non-synchronization controller. The proposed method is effective in controlling systems which require collaborations between the sub-agents.

Simultaneous positioning and non-minimum phase vibration suppression of slewing flexible-link manipulator using only joint actuator

This paper presents a new global terminal sliding mode control (GTSMC) methodology for the simultaneous positioning and vibration suppression of slewing a flexible-link manipulator. The proposed control scheme is realized using only a joint actuator without an extra actuator (for example, the widely used piezoelectric zirconate titanate), and the non-minimum phase vibration control problem is solved. Firstly, based on the differential geometry method, the initial dynamic system is decomposed into two subsystems, namely an input-output subsystem and a zero-dynamics subsystem. Secondly, a continuous GTSMC strategy without chattering phenomenon is designed for the input-output subsystem, and the limited convergence time is deduced. Moreover, the eigenvalues of the zero-dynamics subsystem can be pointed by setting proper controller parameters for Lyapunov asymptotical stability. Finally, simulation and experimental results demonstrated the efficacy and feasibility of the proposed control methodology.