Chapter 1 - Introduction to Controls

This study presents a linear matrix inequality (LMI) approach to the sampled-data control of Takagi-Sugeno fuzzy systems, based on the intelligent digital redesign (IDR) technique. The objective of the IDR is to design a digital control system whose trajectory closely matches that of a given well-constructed analogue control system by minimising the state-matching error. In this study, state-matching performance is enhanced by using a continuous-time state-matching criterion, which guarantees that the state-matching error is minimised through the entire time interval. Unlike previous studies, mismatched information of membership functions for both analogue and digital control systems is directly manipulated. Moreover, the authors introduce an improved fuzzy Lyapunov functional that consists of both membership functions for analogue and digital control systems, which relaxes the conservativeness of LMI conditions. Finally, two examples demonstrating the effectiveness of the authors' method are provided.

The insertion of communication networks in closed-loop of digital control systems makes the system synthesis and analysis complex. In this paper, we consider the combination of classical reliability, risk and safety evaluation with typical control system through digital networked control systems. The main purpose is to study the influence of transmission delays and packet dropouts on the reliability of digital networked control systems by using a modified statistical method-Monte Carlo simulation. The behaviors of two types of fault are modelled by different statistical distribution. The control strategies we apply for digital control systems are Proportion Integration Differentiation control strategies, generated by Genetic Algorithm. In terms of a realistic system model, we evaluate and compare the influences on the reliability of digital networked control systems with different control strategies from quantitative aspect. Numerical examples are presented to illustrate the effectiveness and correctness of the approach.

A novel approach for software reliability analysis of digital instrumentation and control systems in nuclear power plants

A digital closed-loop control system with all digital phase locked loop (ADPLL) is designed and optimized, in order to improve the bias stability and transient response of the gyroscope. The nonlinear mathematical models for the closed-loop amplitude and phase control system are established. The linearization method is applied to analyze the nonlinear models. The control parameters of the drive loop are optimized. The experimental results show that the phase deviation between the demodulation reference signal of the drive loop and the sense signal is less than 0.25° in the temperature range from-40°C to 60°C, within 0.15° of the variation. At room temperature, the overshoot amount of the gyroscope control system is 4.5% with setting time of 0.12s. The bias stability is 1.45°h. Compared to the analog control scheme, the digital control system has advantages of short setting time, small overshoot, short phase locked time, large locked range, high phase precision, etc.

We proposed a parameter-tunable robust proportional-integral-differential (PID) controller for active queue management (AQM) based on modern H∞ optimal control theory in [12]. Our robust PID controller can be tuned only by one parameter unlike traditional PID controllers, which are tuned by three or more. Additionally, this new parameter assignment method can be extended to other controller designed for AQM scheme based on classical control theory or optimal control theory. In this paper, we present an analysis and implementation study on it. Taken both robustness and closed loop performance into considerations, most desirable parameters value can be identified by the analytical formulas derived by us. Theoretical analysis shows that the proposed controller can converge to the reference value in steady state. Simulation results confirm our expectation that our PID controller for AQM outperforms the existing well-known congestion controllers, such as RED and PI controller, on keeping the router queue size at the target value without queue vibration. Further, the most important feature is that the controller is robust to the network dynamics and traffic load changes.

This paper develops a comparison between two control strategies, one well-known analog control system and one digital control system, applied to a battery ZVT bi-directional charger for UPS's. The analog control system is implemented with various dedicated IC's whereas the digital control system, based on digital redesign approach, is implemented with a low cost single chip DSP controller. A prediction algorithm is used to minimize the computation time delay, and an algorithm to determine the sampling instants is developed to obtain the average values of the variables of interest, without noise caused by switching transitions. Experimental results based on a 580 W prototype have been obtained to verify the performance of these control systems.

To maintain the cyber security, nuclear digital Instrumentation and Control (I&C) systems must be analyzed for security risks because a single security breach due to a cyber attack can cause system failure, which can have catastrophic consequences on the environment and staff of a Nuclear Power Plant (NPP). Attack trees have been widely used to analyze the cyber security of digital systems due to their ability to capture system specific as well as attacker specific details. Therefore, a methodology based on attack trees has been proposed to analyze the cyber security of the systems. The methodology has been applied for the Cyber Security Analysis (CSA) of a Bistable Processor (BP) of a Reactor Protection System (RPS). Threats have been described according to their source. Attack scenarios have been generated using the attack tree and possible counter measures according to the Security Risk Level (SRL) of each scenario have been suggested. Moreover, cyber Security Requirements (SRs) have been elicited, and suitability of the requirements has been checked.

Neste artigo, é proposta a utilização de um único circuito de auxílio à comutação ZVT, aplicado tanto no estágio pré-regulador como no carregador de baterias de Sistemas Ininterruptos de Energia (UPS). Também, é demonstrado que a utilização de uma única célula de comutação ZVT permite que se obtenha, além da redução do número de componentes auxiliares, um melhoria no rendimento do conversor. Adicionalmente, duas estratégias de controle, digital e analógica, são analisadas e comparadas do ponto de vista de desempenho e custo. O sistema de controle analógico é implementado com vários CI’s dedicados, já o controlador digital é implementado por meio de um único DSP de baixo custo. Um protótipo em malha fechada de 580 W, com entrada universal, operando em 100 kHz, foi implementado nã só para validar o circuito de auxílio à comutação, mas também para avaliar o desempenho do sistema proposto.

DC-DC converters are used at the Advanced Photon Source (APS) at Argonne National Laboratory to power electromagnets. The electromagnets guide the photon beams, therefore the control system of the DC-DC converters should be highly accurate to provide minimum spatial spread of the beam. Currently the converters have all been regulated by analog control systems. An upgrade to digital control system is being evaluated to resolve the aging and obsolescence issues. This paper describes the design and evaluation of a digital control system to regulate the output current and reduce noise coupled in the system. A digital controller is first designed based on the small signal model of the converter. Experimental data of the output current is analyzed. Digital filters are then designed to reduce the noise in the output current. The complete control system is then simulated and results are evaluated. Wide Band Gap (WBG) power devices enable the development of smaller and more durable power converters with higher performance and less power consumptions than traditional silicon devices. Performance of the digital controlled DC-DC converters using WBG power switching devices including silicon carbide (SiC) power MOSFETs and gallium nitride (GaN) power transistorswill be evaluated, in comparison with the converters using traditional silicon power switching devices.

This paper is concerned with the development of fully Autonomous Underwater Vehicles (AUVs) for deep ocean scientific and commercial applications. Specifically, it is regarding the design of automatic feedback control systems for AUV attitude control. The design method used in this paper formulates the AUV attitude control problem within the framework of the Optimal Control Theory. This approach determines an optimal control law that keeps the state of a dynamic system near a constant reference state while minimizing a quadratic cost functional. This study has developed four optimal control laws based on different performance criteria. First, the standard Linear Quadratic performance index was used to obtain a baseline control design. The LQR control law has been found to be undesirable because it resulted in a closed-loop system with fast and slow dynamics. In order to place the closed-loop eigenvalues close to each other, a pole placement algorithm has been used in connection with the LQR performance index. Two control laws have been designed based on this approach. Finally, a fourth design has been obtained by using a Hilbert Space Norm (also known as H/sub 2/ Norm or Root-Mean-Square) performance index. The main reason for designing a control law based on H/sub 2/ Norm performance index was to minimize the fuel consumption of the AUV for longer endurance. The stability and performance characteristics of the four optimal control laws have been analyzed via computer simulation and frequency response studies. All the closed-loop AUV systems exhibited overdamped response without any overshoot. Because the yaw and pitch channels have right hand zeros indicating the controllers have finite gain margins in these two channels. Hence, stability robustness of the AUV controllers can not be ignored and must be the subject of more detailed investigation in the future.

The article presents a new approach to the analysis of the stability of automatic systems with discrete links. In almost all modern automatic control systems (ACS), there are links that break signals in time. These are power controlled switches—transistors or thyristors operating in a pulsed mode and digital links in regulators. Time discretization significantly affects the stability of processes in the automatic control system. The theoretical analysis of such systems is rather complicated and requires a significant change in engineering approaches to analysis. With the improvement of digital controllers and a significant increase in their performance, this problem has practically been forgotten. However, its mathematical “content” has not changed since the 1980s when discreteness began to play a major role in hindering the transition to digital automatic control systems. In this paper, we propose a new approach that consists of interpreting the sampling operation by a link with the proposed frequency characteristic, which determines the suppression of input high-frequency signals. This link greatly simplifies engineering calculations and demonstrates the new capabilities of sampling systems. These possibilities include the rational distribution of digitalization resources—the number of bits and the sampling interval between the regulator channels, depending on the frequency range of the efficiency of these channels. We verify and confirm our theoretical statements through simulations and show how this approach makes it possible to formulate new principles of construction of seemingly well-known controllers—PID (Proportional Integral Differential) controllers and variable structure systems (VSS).

Recently, the Plant Input Mapping (PIM) method was proposed as a digital-redesign (or an emulation) approach in digital control system design. This method guarantees stability of a redesigned digital control system for a wide range of sampling periods. In this paper the PIM method is applied to the design of a digital model-matching flight control system. In the model-matching control system design a plant must have no unstable zeros. However, unstable zeros appear for small sampling periods in a step invariance model of a continuous-time (CT) plant with the relative degree greater than two, even if the CT plant has no unstable zeros. Hence, in such a case, the direct-digital approach cannot be applied to the design of a digital model-matching control system. By contrast, the digital-redesign approach such as the Tustin's method or the PIM method is free from the problem. Simulation results for an unstable VTOL aircraft show that the proposed method gives better performance than the conventional design methods.

The DC-DC converters at the Advanced Photo Source at Argonne National Laboratory are over 15 years old. An upgrade to digital control system is being evaluated to resolve the aging and obsolescence issues. These converters supply power to electromagnets that are used to guide high energy beams. Thus a highly accurate control system is required for the DC-DC converters. This paper describes the design and evaluation of a digital control system to regulate the output current. The digital control system is proposed to replace the current analog control system thereby resolving the aging and obsolescence issues. A digital controller is first designed based on the small signal model of the converter. Experimental data of the output current is analyzed. The complete control system is then simulated and results are evaluated.

The article discusses an approach that allows you to move from a discrete model of a digital controller to its analog representation, which provides analysis and synthesis of digital systems in the continuous domain, taking into account the quantization period. In the proposed method for the control system, a transition is made from the discrete z-region to the Laplace region. This approach makes it possible to consider the quantization time as an additional parameter of the digital control system settings, evaluate the influence of the selected quantization period not only on the behavior of the set for discrete at the moments of quantization, but also in between, to evaluate the temporal characteristics of the control system at any time. The analog representation of the digital controller enables the calculation of transients using MatLAB. The article provides examples of the synthesis for a digital control system in the frequency domain based on the frequency response characteristic of an open-loop control system taking into account the quantization period. The method can be used by automation specialists to analyze and setting digital control systems

A series of structural vibration control experiments and related theory are developed to check the effectiveness of analog and digital control system with piezoelectric material sensors and actuators. Velocity feedback analog control has been tried for the cantilever beam with PZT (lead-zirconate-titanate) wafer sensors and actuators. To improve the control system, steady- state quadratic optimal control algorithm using a digital micro-computer has been used. To apply optimal control algorithms, signals sensed by partially distributed sensors were converted to point concept signals like those from conventional displacement or velocity sensors. Actuating voltage signals were then synthesized from point force output signals. This paper presents excellent results for structural vibration control using both analog and digital systems.