Discrete PI Controller Research Articles

Real-world application of a discrete feedback control system for flexible biogas production

Using renewable energy is increasingly prevalent as part of a global effort to safeguard the environment, with a reduction in {mathrm{CO}}_{2} being one of the primary objectives. A biogas plant provides an opportunity to produce green energy, but its profitability prevents it from being utilized more frequently. A suitable response to this economic issue would be flexible biogas production to exploit fluctuating energy prices. Nevertheless, the complex nature of the anaerobic digestion process that proceeds within the biogas plant and the wide range of substrates that may be utilized as the plant’s feeds make it challenging to achieve flexible biogas production truly. Most plant operators will rely on their experience and intuition to run the plant without knowing exactly how much biogas they will produce with the feed substrate. This work combines a system model estimation and feedback controller to provide an intuitive yet precise feedback control system. The system model estimation represents the biogas plant mathematically, and a total of six distinct approaches have been compared and evaluated. A PT1 model most accurately approximated the step-down and the step-up by the time percentage method, with the Akaike Information Criterion as the primary evaluation criterion for selecting the best model. The downward model was controlled by a discrete PI controller modified with the Root Locus Method and an Anti-Windup scheme, and the upward model was controlled by a state space controller. The quality of the controller was evaluated in both simulation and at the actual biogas plant in Grub, and the controller was able to reduce the biogas production rate approaching the setpoint in the expected period. Furthermore, the developed feedback control system is effortless enough to be installed in many biogas plants.

2-DOF Decoupled Discrete Current Control for AC Drives at Low Sampling-to-Fundamental Frequency Ratios

In high performance drive systems, wide bandwidth and reference tracking accuracy of current control loop are fundamental requirements. The conventional PI controller provides robustness against the machine parameter mismatching and zero steady-state error, but its dynamic performance degrades at high-speed due to the bandwidth limitation. In this paper, a new control structure of discrete PI controller with a deadbeat response is proposed, which combines the advantage of conventional PI controller with deadbeat characteristic. The proposed controller shows a decoupled tracking performance of up to 15% of the switching frequency, while also providing an extra control freedom of the disturbance rejection, which effectively improves the system stability. Experiments show a reduction of oscillation by 30% compared to the conventional PI and the validity and applicability of the proposed control method for high-speed applications with low sampling to fundamental frequency ratios.

A novel hierarchical temperature control method of an electric oven and its experimental evaluation

PurposeOvens are semi-industrial multipurpose equipment that are used to provide a desired temperature for specific chemical processes. Temperature regulation in the presence of different type of disturbances and dealing with nonlinear dynamics with large dead time (up to a few minutes) are some undesirable factors that have to be considered in the controller design procedure of the oven systems. Due to these factors, the classical PID controller tuned using Cohen-Coon or Ziegler–Nichol’s tuning methods often fails to meet satisfactory closed-loop performance.Design/methodology/approachIn this paper, to deal with the limitations on the oven system due to the undesirable factors, a hierarchical automaton-guided form controller has been designed. The proposed controller includes several discrete PI controllers, each of which operates locally in the defined operating regions whose separation idea is specific to this paper. Based on the idea proposed in the separation of regions, the controller’s coefficients tuning rules are extracted prior to any determination. Then, a supervisor controller has assumed the task of switching between local controllers. In the next step, by considering a conceptual model for the oven system and using a candidate Lyapunov function, the stability conditions of closed-loop system are discussed and the necessary conditions for the asymptotic stability are derived. The proposed controller is practically implemented with the help of the Arduino Nano platform.FindingsUsing several experiments, the superiority of the proposed hierarchical controller in terms of performance and energy consumption has been demonstrated.Originality/valueThe proposed hierarchical controller has been implemented practically and an acceptable closed-loop performance has been achieved. To illustrate the efficiency of the proposed method, the closed-loop stability of this method is shown using the Lyapunov theory.

Design of Nonlinear Control Systems for Autorobots

Currently, various types of robots are increasingly being used to solve different tasks. Most often, these are mobile robots that move on the earth’s surface performing the assigned tasks, in particular, they are four-wheeled robots similar to a car — autorobots. As control objects, the robots are essentially nonlinear, which requires the use of nonlinear methods for the control system design. At the same time, it is difficult to apply traditional methods for designing nonlinear control systems due to a complex type of nonlinearities in the equations of mobile robots and, in particular, autorobots. In this paper, the design problem is solved using a discrete-continuous quasilinear model, which is created on the basis of the nonlinear differential equations in the Cauchy form. Due to the great complexity of the nonlinearities of the autorobot equations, the corresponding quasilinear model is created by the numerical method. The quasilinear model obtained by this method is discrete-continuous and controllable, moreover, its state variables are measurable. The discrete autorobot control system includes two practically independent control subsystems: longitudinal speed and turns. A discrete PI control law is used to control the speed, and the discrete turn control subsystem is designed by the method of desired dynamics. The resulting autorobot control system provides a stable movement along the trajectory, which can be set as a function of time or as a function of the coordinates of the moving autorobot’s position.The suggested approach can be used to design control systems for nonlinear objects of various purposes with complex differentiated nonlinearities. However, the design problem has a solution if the corresponding discrete-continuous quasilinear model of the object is controllable, and the state variables are measurable.

Dual-Active-Bridge Model and Control for Supporting Fast Synthetic Inertial Action

This article proposes a dual-active-bridge control to support the fast synthetic inertial action in DC microgrids. First of all, the selection of the isolated DC/DC converter to link an energy storage system with the DC bus in a microgrid is analyzed and the advantages of the dual-active-bridge converter controlled by a single-phase shift modulation justify its selection. An active front-end can be then adapted to connect the DC bus with an AC grid. Secondly, this paper presents the design of a discrete PI controller for supporting fast synthetic inertial action. In particular, a discrete dual-active-bridge model based on the transferred power between both converter bridges, which overcomes the approximations of the output current linearization model, is proposed. Moreover, the article introduces a novel equation set to directly and dynamically tune discrete PI parameters to fulfill the design frequency specifications based on the inversion formulae method. In this way, during the voltage/power transients on the DC bus, the controller actively responds and recovers those transients within a grid fundamental cycle. Since the developed set of control equations is very simple, it can be easily implemented by a discrete control algorithm, avoiding the use of offline trial and error procedures which may lead to system instability under large load variations. Finally, the proposed control system is evaluated and validated in PLECS simulations and hardware-in-the-loop tests.

Оптимизация цифрового регулятора системы автоматического регулирования непрерывного объекта

The article gives the analysis of optimizing the digital controller of the automatic control system (ACS) of a continuous object. The procedure for replacing a continuous controller with a discrete controller has been analyzed. The original continuous optimized ACS has been illustrated. It has been stated that the continuous ACS and its elements (all or particular) can be modeled by discrete models described by the difference equations, and not the differential ones, as is done in the case of continuous models. The specification of the sampling period of the PI controller model equal to 0.001 s has been given, the coefficients of the Z-transfer function of the digital PI controller, which is equivalent to a continuous controller, are considered. Of practical importance in the control theory is the representation of a discrete model of a controller, which helps obtain a digital transformation algorithm carried out by a controller over a control error, organize a discrete-digital control of a continuous object using a digital processor. The model with a continuous and discrete controller is illustrated. A formula for calculating the values of the lattice function of the output signal of a discrete controller is obtained. It has been found that sampling and quantization of the error signal, as well as restoring the control signal, should be carried out with the proper accuracy, which should provide the required control accuracy. There are considered the models of discrete-digital control with the correct selection of the parameters of discrete PI controllers, a model with a finite time of the transient process and a structure of its contour, given a fifth-order discrete function with a five-step transition to the steady state. It has been inferred that reducing the sampling period and quantization step significantly increases the processor speed requirements.

Dominant pole region assignment with discrete time PI, PID and PIR controllers

Dominant pole region assignment with discrete time PI, PID and PIR controllers

Event-based discrete PI controllers robustness analysis through sampled describing function technique

ABSTRACT In this work, the robustness of discrete PI controllers when used with a Symmetric-Send-On-Delta (SSOD) sampling law is addressed. Hitherto, the continuous Describing Function has been employed as a suitable tool to evaluate the robustness of such systems to limit cycle oscillations induced by the SSOD. However, due to the discrete implementation of the controllers in most of the actual applications, the Sampled Describing Function technique is used in this work to provide a more realistic approach, which takes into account the effect of both the SSOD and sampling period of the discrete controller on inducing such oscillation. A simple measure has been developed to characterise the robustness of these systems and it has been tested through several examples, showing its validity in predicting the apparition or avoidance of limit cycles. This measure has been used to evaluate the robustness of some spread tuning rules applied to a wide batch of systems reflecting the dynamics of most processes in the industry.

Tuning Generalized Predictive PI controllers for process control applications

Predictive PI (PPI) controllers have demonstrated to exceed traditional PID controllers when they are applied to systems with long delays. This work proposes a new controller structure and tuning that we call Generalized Predictive PI (GPPI) controller which provides greater design flexibility than PI and PPI strategies. To realize a fair comparison, the design and tuning rules for discrete PI and PPI controllers were developed using optimal arguments based on the root-locus, for critically damped response before a step change in the reference. Experimental results, using industrial equipment, have illustrated the tuning methodology and the performance of the proposed controller under real conditions. Flow and water level process in a laboratory flume were considered. For these processes, First Order Plus Time Delay (FOPTD) models are used. The GPPI control results are encouraging, reducing the settling time plus a very small overshoot before step change in the reference regarding the PI and PPI strategies, up to 41.03% for the flow control loop and up to 54.21% for the level control loop. The discrete analysis of the strategies in the Z plane was performed, allowing for a direct translation to recursive equations that can then be programmed into a Programmable Logic Controller (PLC), other industrial controllers such as Distributed Control Systems (DSC), or microcontrollers, such as Arduino, Raspberry or FPGA. This is an important result, since it demonstrates that the increased complexity of the proposed controller does not hamper its implementation in industrial controller systems. In this work, we used a Rockwell ControlLogix \\protect \\relax \\special {t4ht=®} PLC with Structured Text programming language.

RETRACTED: Research on teaching based on tennis-assisted robot image recognition

Design and development of an autonomous robot will collect the scattered tennis balls on the tennis court. To make the camera active, the robot uses a camera placed above from these recently collected the ball to roll. And, given the machine design, because it falls to prevent the ball, catch the ball. Image processing, the use of color filters, the detected edge detection algorithm, corresponds to the Raspberry Pi 3, can be achieved by the distance to the library implementation of robot OpenCV, it is sorted. After the desired robot angle is generated, it is translated to the appropriate motor speed value is sent to the motor control unit. To realize this behavior, it has four DC motors to be used. For the movement platform, one of which is a scanning operation of the ball, which is used to control the camera angle, the last one will be used for the ball detent mechanism. The realized by the discrete PI controller with two DC motors position and speed control motor controller boards of the rotary encoder. Experimental tests of the real world validate the design of the system.

Disturbance observer based discrete PI control system with back-calculation anti-windup technique for improvement transient performance of PMSM

In this paper disturbance observer-based control (DOBC) system for PMSM has been proposed. The cascade structure of the discrete-time PI-PI control system with back-calculation anti-windup scheme for both loops has been adopted. High order disturbance observer (HODO) has been adopted to estimate the total disturbance and compensate it in the speed loop of the PMSM control system. In the HODO, the disturbance estimation is based on the motion equation which takes into account torque losses due to the drug resulting from the time-varying flux, hysteresis, and friction. Unlike the traditional observers, the HODO does not require the derivatives of the disturbance to be zero, which is considered as its main advantage. The fast-varying disturbance as cogging torque and a high-frequency electromagnetic noise in the PMSM system also affect on the performance of control system, which are analyzed in the study. In the real-time experiments, the proposed control system achieves less speed errors and faster response comparing with controller without disturbances observer. The experimental results have proved the feasibility of the proposed control scheme.

Droop Control for Parallel-Connected Three-Phase UPS Units with Different Ratings

The main objective of this paper is to achieve synchronization and power sharing between different ratings three-phase Uninterruptible power supply (UPS) units. A droop control scheme is presented in such a way that a discrete PI-controller is applied. The PI-controller produces a suitable control signal to sinusoidal pulse width modulation (SPWM) circuit. The SPWM produces suitable trigger pulses to the inverter gate. The validity of the proposed control scheme is illustrated through MATLAB simulation with two different ratings three-phase UPS units. The simulation results prove that it possible to share the total load among the different rating units in proportion with their rated values in the presence of load interruption.

Robustness of event-based discrete PI controllers. A sampled describing function approach

In this paper we present a study about the robustness of event-based discrete PI controllers. Our approach is based on Sampled Describing Function technique, which has been used to characterize the non-linear effect of the Symmetric Send on Delta (SSOD) sampling strategy on the control loop. Through several examples this technique is proven to produce accurate results in predicting limit cycle oscillations and to provide guidelines to avoid them, either by detuning the controller or increasing the sampling period.

Mitigation of Voltage Sags/Swells Using Z-Source Inverter with Discrete Pi Controller Based on Dynamic Voltage Restorer (DVR)

Mitigation of Voltage Sags/Swells Using Z-Source Inverter with Discrete Pi Controller Based on Dynamic Voltage Restorer (DVR)

Tuning discrete PI controllers for direction-dependent systems with delay

Abstract Direction-dependent models can represent a wide range of nonlinear systems. The design of a discrete time PI controller for these type of systems with time delay is addressed. The asymptotic stability of the closed loop system is established by means of Lyapunov theory. The tuning strategy is based on solving an optimization problem with LMI constraints. A simple example illustrates the effectiveness of the proposed approach. Extensions to include more complex temporal closed-loop specifications and switched PI controllers are part of our current interest.

Introduction to the Discrete Time PIDmn Control for the IPDT Plant

The aims of this paper are: (a) to extend the discrete time 2DOF PI and PID controller for the integral plus dead time (IPDT) models to the 2DOF PIDmn mn control with an mth order derivative action (m = 0,1, 2) tuned by the multiple real dominant pole method, (b) to introduce simple integrated tuning procedures of all the considered controllers augmented with the n ≥ mth order series binomial filters required for the derivative action implementation and measurement noise attenuation and (c) to compare the filtered controllers as for the performance limits expressed in terms of the integral of absolute error (IAE) and the relative total variance.

Harmonic Mitigation Using DC Self Supported Shunt Active Power Filter

The advent of semiconductor technology has resulted in increased application of power electronic devices in industrial as well as domestic loads, a combination of which acts as a non-linear load. These non-linear loads are responsible for increased harmonics by drawing a distorted current from the supply system, leading to deterioration of source currents and voltages. This work proposes a method to improve the power quality with the aid of a three-phase shunt active power filter (SAPF) implementing a controlled voltage source inverter and synchronous d-q reference current generation technique for reference current generation of hysteresis controller. A discrete PI controller has been implemented to maintain a constant DC capacitor link voltage. The proportional and integral gains of the PI controller have been computed with the help of bacterial foraging optimization technique. The proposed SAPF for a three phase three wire system employing a balanced non-linear load has been simulated on MATLAB software to validate its performance. The simulation results demonstrate satisfactory performance of the proposed SAPF by effectively compensating harmonics of the supply system and lowering THD such that they fall within IEEE 519 standards for harmonic levels.

Integrated Models of a Gas Metal ARC Welding Process and Inverter based Power Supply for Process Control Simulation Studies

The objective in this paper was to combine the simulation of a Gas Metal Arc Welding (GMAW) process model with the simulation model of an inverter-based power machine. The GMAW process was considered as an electrical circuit and the mathematical model was based on physical descriptions of several parts of the GMAW process, as were the electric circuit of the power supply, the arc dynamics, and the electrode melting process. A simple welding application was simulated and the welding parameters were derived from several experimental conditions. Next, the dynamic behaviour of a full-bridge DC-DC converter was simulated and a suitable discrete PI controller proposed for welding current feedback control. Both models, the GMAW model and the inverter power supply model, were combined into a new simulation model of the GMAW process application together with an inverter based welding machine. DOI: http://dx.doi.org/10.5755/j01.eee.20.7.8016

Power Quality Improvement in Wind Energy Generation Using Fuzzy Logic Controller

Nowadays, renewable energies have been widely applied to achieve eco friendly objectives. This paper presents the development of a single-phase grid-connected wind energy generation with the improvement in power quality and efficiency. This mainly focuses on showing the improvement in power quality by overcoming the drawbacks with the existing wind energy generation based on the PLL with the discrete PI controller. It is found that Total Harmonic Distortions (THD) present in PLL Single-phase grid-connected wind energy generation can be reduced by using modified PLL method. The modified wind energy generation is based on PLL with Fuzzy logic controller instead of PLL with discrete PI controller. The PLL gets input from the load side, and compare with any one parameters current or voltage (closed loop system). The aim of this survey is to propose a new topology in (HCM) HILL CLIMB METHOD. The tasks related to the SVPWM algorithm, the PLL, the MPPT algorithm, and the monitoring of the DC voltage were successfully implemented in the DSC. Keywords – Total Harmonic Distortions, Phase Locked Loop, Discrete PI Controller, Fuzzy logic controller, Space Vector Pulse Width Modulation, Maximum Power Point Tracking, Digital Signal Controller.

Diseño e implementación de un controlador proporcional integral en un controlador industrial de procesos

El presente trabajo presenta una metodología de diseño de un controlador con estrategia proporcional integral (PI) teniendo en cuenta que la implementación se realizará en un controlador industrial de procesos. El diseño considera la modelación de la planta mediante técnicas analógicas de identifi cación de sistemas. Se utiliza en el diseño del controlador el algoritmo digital del controlador discreto PI que ejecuta el controlador de procesos utilizado. Se consideran para el diseño especifi caciones de respuesta temporal de lazo cerrado básicamente para obtener un tiempo de estabilización acorde a los que puede cumplirse sin exceder los rangos de la señal de control que puede entregar el controlador de procesos utilizado. Se implementa el sistema de control verifi cando el comportamiento del sistema de lazo cerrado en relación al objetivo de control especifi cado.