Stanislav Vrána

Quadratic neural unit is a good compromise between linear models and neural networks for industrial applications

The paper discusses the quadratic neural unit (QNU) and highlights its attractiveness for industrial applications such as for plant modeling, control, and time series prediction. Linear systems are still often preferred in industrial control applications for their solvable and single solution nature and for the clarity to the most application engineers. Artificial neural networks are powerful cognitive nonlinear tools, but their nonlinear strength is naturally repaid with the local minima problem, overfitting, and high demands for application-correct neural architecture and optimization technique that often require skilled users. The QNU is the important midpoint between linear systems and highly nonlinear neural networks because the QNU is relatively very strong in nonlinear approximation; however, its optimization and performance have fast and convex-like nature, and its mathematical structure and the derivation of the learning rules is very comprehensible and efficient for implementation.

Control for ecological improvement of small biomass boilers

Abstract The aim of this paper is to present various types of research on reducing emissions in the flue gases produced by low-power biomass boilers, especially when the boilers operate outside their nominal operating regime. This long-term investigation program is being carried out on a pilot boiler in the university laboratories. The program involves acquiring additional instrumentation for performing and evaluating present and future experiments, creating various types of models of the boiler for designing and testing the control algorithms using available data, and implementing and evaluating the algorithms in real operation. The pilot device enables us to experiment using non-standard instrumentation, but throughout our research it is necessary to strike a balance between ecological policy requirements and economic considerations.

Continuous Control Issues Concerning Operation Improvement of Small-Scale Biomass Boilers

Abstract To meet the increasing environmental and efficiency requirements, the possibilities to improve the performance of a 25 kWth wood pellet boiler by utilizing PLC and feedback control are investigated. The process is first stabilized by improving the grate sweeping sequence, which originally disturbs the process. Prior to continuous combustion control development, the process is analyzed and identified. After sequential control improvements the combustion behaves well but tends to drift. A PID controller was designed to enable drifting compensation. It is shown that improved grate sweeping sequence and continuous feedback control provide a major improvement for system performance cost effectively.

Evaluation of open-loop frequency indicators in a closed loop for PID controller autotuning

In industrial practice, PID controllers are extensively used because they can be successfully implemented without knowing a model of the object or process which is controlled. Despite of the fact that many PID controller tuning algorithms have been developed since the Ziegler and Nichols tuning procedures were published in 1942, their experimental method continues to be used up to now. There are two main reasons why newer methods are not widely-used: the methods are based on a model of the controlled plant, and/or it is necessary to stop the control process during controller retuning. Our method presented in this paper is based on an experimentally performed evaluation of excited frequency responses with the aim of achieving recommended values of one or more control quality indicators known from the course of the Nyquist plot, e.g. Frequency response evaluation can be performed in a closed loop with no controller function degradation, and no model is necessary for frequency response evaluation. In this way, the main problems of other tuning methods are eliminated. Since there is no need for a model, the tuning method can be used in a control loop involving nonlinearities even in the controller.

Neural Network Evaluation of Combustion Process for Continuous Control of Small Scale Biomass Fired Boilers

Abstract Boilers based on combustion of biomass become widely used as a heating source nowadays. The modern ones are typically controlled automatically. The control algorithm of those boilers is crucial in reaching optimal operational conditions by means of maximal efficiency and minimal environmental impact. On the other hand, the acquisition costs of these advanced devices should be maintained at reasonable level. This paper deals with implementation of modern proper control algorithm and obtaining the necessary input values that cannot be easily measured operationally by a direct measurement.

Harmonie excitation based autotuning: Autotuning usable for controlling biomass combustion processes

Controlling combustion processes is an important task, mainly with respect to energy efficiency and ecological impacts. This problem has become significant with the increased use of biomass-fired boilers, including low-power boilers. The combustion process is a process that we have limited information about. The equations for the chemical reactions are known, but in reality combustion of biomass is much more complicated and more variable than a mathematical model can express. It is therefore not simple to design a controller that is able to control the combustion process effectively in the whole range. Small-scale biomass-fired boilers are usually equipped with simple two-state (on/off) controllers. Many laboratories have attempted to develop a model of the combustion process suitable for controller setting and parameter adaptation, but the results are not yet satisfactory or generally valid. Thus, advanced model-based control strategies are not usable, while the use of a model-free controller is not excluded if well-designed tuning rules can be provided. An approach which tries to satisfy most of the requirements of industrial practice is presented in this paper, which is based on an experimentally performed evaluation of small amplitude excited frequency responses with the aim to achieve recommended values of one or more control quality indicator known e.g. from the course of the Nyquist plot. The indicators can be evaluated experimentally in control loops involving nonlinearities. In this sense, the method has a philosophy similar to that of the popular Ziegler and Nichols method, but no interruption of the control process is necessary and the amplitude of the excited oscillation can be set by operator. The main advantages of the method presented here are: there is no use of any mathematical model, it can be used as an addition to the existing controller purely by software, and there is no need to interrupt the control process while retuning the controller.

Frequency response based the derivative component tuning approach

The controllers of PID type remain the most wide-used controllers in industrial practice. Many PID controller tuning method have been developed since Ziegler and Nichols published their technique, but they are not so widely used as the Ziegler and Nichols methods. The majority of presented tuning methods usually skips tuning of the derivative component, or they use set the derivative component parameter to be proportional to the integrative component parameter. The new approach to the derivative component tuning is presented in the paper.

Commonly Untaught Information Concerning Practical Use of Tuning Procedures in Control

Abstract There are many types of controllers and various methods for their tuning. It is not possible to explain the principles of all of them to students. Usually, PID controller and the Ziegler-Nichols methods are taught at universities and then some other one or two other types of control, if they are practiced and not only briefly mentioned. The theoretical principles and approaches are mainly explained without details about implementation that sometimes needs special procedures. Several problems that should be more focused in control engineering education on are presented in the paper.

Saturation in Engineering Simulation

Abstract The wind-up effect is a phenomenon known mostly from implementing PI(D) controllers in real operation when saturation of the manipulated variable may occur and cause worse control results. Nowadays many publications exist on this topic where several anti wind-up mechanisms are presented and discussed. However, the wind-up phenomenon, i.e. the problem of continued integration after the output has become limited (saturated), is a problem appearing not only in connection with numerically calculated control actions of digital controllers, but also in computer models of controlled plants. In this field, existence of the wind-up effect is somehow missed. Results and conclusions obtained by such inaccurate simulation may be misleading. Surprisingly, occurrence of this situation is not so rare, because use of amplitude limiting blocks in simulation is considered to be the only necessary precaution. In education of many control engineers, information about wind-up effect in simulation is not sufficiently pointed out. In models of higher than first order, the same approach as the one used the filed of PI(D) controllers is not always correct. The publications focused on the solutions for this case seem to be rare, if any exist. This paper presents one possible approach to wind-up and anti wind-up mechanism in modeling and simulations.Individual disciplines, and even subfields within those disciplines, typically exhibit distinctive pedagogical approaches that have developed over time, influenced by the content of the discipline and technology. In control engineering, mathematical symbolic and diagrammatic forms are a key element, and have been traditionally taught using oral and handwritten approaches (so called chalk-talk). The widespread use of computer display technology and PowerPoint has influenced the way in which the development of ideas is presented, leading to mathematics presented as solutions, rather than a process, and the isolation of the mathematics from the control engineering context. This paper reviews educational trends and personal experience that suggests the use of digital pen-enabled tablet technologies can facilitate the reintroduction of elements critical to developing an effective pedagogy for control engineering.

Often overlooked pitfalls of straightforward implementation of textbook controller tuning methods

Abstract Various approaches to the PID controller tuning account for a substantial part of the undergraduate control engineering curricula. At the most general level, these approaches can be divided into two groups. Model based methods use some kind of mathematical model of the controlled plant while the experimental methods rely on a simple experiment that is performed with the plant. The students usually understand that obtaining a sufficiently accurate mathematical model of the plant is not easy and may involve many complex issues. On the other hand, the experimental methods may be regarded as an easy to follow recipe that can be directly applied according to the textbook to obtain the desired tuning. This paper shows the common pitfalls that can arise when these methods are applied in their idealized textbook form. The main focus is on how these pitfalls can be demonstrated using experiments with two laboratory plants of different complexity.