Control System: Fundamentals and Applications

Chapter 1: Control system

A control system uses control loops to manage, command, direct, or govern the behavior of other equipment or systems. It can range from a single thermostat-controlled boiler in a single-family home to massive industrial control systems that are used to manage whole production lines. Control engineering is used to create the control systems.

A feedback controller is used to automatically control a process or operation for constantly modulated control. The control system compares the desired value or setpoint (SP) with the value or status of the process variable (PV) being controlled and uses the difference as a control signal to bring the process variable output of the plant to the setpoint.

Software logic, such as that found in a programmable logic controller, is utilized for sequential and combinational logic.

Open-loop control (feedforward) and closed-loop control are the two basic forms of control loops (feedback).

When using open-loop control, the controller's control action is unrelated to the process output (or controlled process variable). A central heating boiler that is exclusively regulated by a timer, which ensures that heat is applied for a constant period of time regardless of the building's temperature, is an excellent illustration of this. Since the boiler is being controlled open-loop, which does not provide closed-loop control of the temperature, the controlled variable should be the building's temperature, but this is not the case.

The controller's control action during closed loop control is based on the process output. In the boiler instance, this would contain a thermostat to track the building's temperature and send a signal back to the controller to make sure it keeps the building at the set temperature. Therefore, a closed loop controller has a feedback loop that makes sure the controller exerts control action to produce a process output that is identical to the reference input or set point. Closed loop controllers are also known as feedback controllers because of this.

A feedback control system, on the other hand, attempts to maintain a specified relationship between two system variables by comparing the functions of these variables and employing the difference as a control mechanism.

Contrary to an open-loop controller or non-feedback controller, a closed-loop controller or feedback controller has a control loop that includes feedback. Using feedback, a closed-loop controller regulates the states or outputs of a dynamical system. Its name is derived from the system's information flow: process inputs, such as voltage applied to an electric motor, have an impact on the process outputs, such as the motor's speed or torque, which are measured with sensors and processed by the controller; the result (the control signal), then, is fed back as input to the process, closing the loop.

A control loop made up of sensors, control algorithms, and actuators is built up in linear feedback systems in an effort to maintain a variable at a setpoint (SP). An example from daily life is the cruise control on a car, which allows the driver to vary the intended set speed in response to external factors like hills. By regulating the engine's power output, the PID algorithm in the controller optimally returns the real speed to the intended speed with little delay or overshoot. Feedback is used by control systems that can, to some extent, adapt to changing conditions and contain some sensing of the results they are seeking to attain. Open-loop control systems only operate in predetermined ways and do not use feedback.

The following benefits of closed-loop controllers over open-loop controllers:

rejection of disruption (such as hills in the cruise control example above)

assurance of effectiveness even with model errors, when the structure of the model does not exactly reflect the real process, and when the model parameters are not accurate

It is possible to stabilize unstable processes.

decreased sensitivity to parameter changes

better reference tracking results

There are certain systems that combine closed-loop and open-loop control. The open-loop control used in these systems is known as feedforward, and it helps to further increase the performance of reference tracking.

The PID controller is a typical closed-loop controller architecture.

Ladder logic was previously used to construct logic control systems for commercial and industrial machinery employing interconnected electrical relays and cam timers. Today, programmable logic controllers or microcontrollers are used to build the majority of these systems (PLCs). A common way to program PLCs is still using the ladder logic notation.

Switches and sensors may trigger logic controller responses, and actuators may be used to initiate and stop various processes on the machinery. In many applications, mechanical actions are sequenced using logic controllers. Elevators, washing machines, and other systems with connected processes are examples. To complete a task, a series of mechanical actuators may be triggered by an automatic sequential control system in the right order. For instance, several electric and pneumatic transducers may fold, glue, fill, and then seal a cardboard box with a product in an automatic packing machine.

There are numerous techniques to write PLC software, including ladder diagrams, SFCs (sequential function charts), and statement lists.

A feedback controller that abruptly changes between two states is used for on-off control. An on-off controller is the best way to define a basic bi-metallic household thermostat. The heater turns on when the ambient temperature (PV) falls below the user-set temperature (SP). A pressure switch on an air compressor is another illustration. The compressor turns on when the pressure (PV) falls below the setpoint (SP). Similar mechanics are found in vacuum pumps and refrigerators. These straightforward on-off control mechanisms are both affordable and efficient.

In order to provide a control signal to keep the regulated process variable (PV) at the intended setpoint, linear control systems and control theory rely on negative feedback (SP). There are numerous varieties of linear control systems with various features.

Fuzzy logic is an attempt to use the simple logic controller design for the control of intricate systems with constant variation. In a fuzzy logic system, a measurement can essentially be partially accurate.

The system's rules are expressed in fuzzy logic after being translated from natural language. As an illustration, the design of a furnace would begin with: Reduce the fuel going into the furnace if the temperature gets too high. Increase the fuel going into the furnace if the temperature is too low.

In order to control equipment, measurements from the real world (such as the temperature of a furnace) are fuzzified, logic is derived using arithmetic rather than Boolean logic, and the outputs are defuzzified.

A strong fuzzy design starts to resemble a typical feedback loop solution when it is simplified to a single quick computation, leading some to question whether the fuzzy design was essential. The fuzzy logic paradigm, however, might offer scalability for big control systems when conventional approaches become cumbersome or expensive to develop.

In contrast to the two-value logic more frequently utilized in digital electronics, fuzzy electronics uses fuzzy logic.

Compact controllers, which frequently have software tailored to a specific machine or device, to distributed control systems for industrial process control for a big physical plant make up the range of control system implementation.

Programmable logic controllers are typically used to create logic systems and feedback controllers.

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Chapter 2: Control engineering

Control systems or control engineering Using control theory to create machinery and systems with desired behaviors in control settings, engineering is a branch of engineering that deals with control systems.

In the process of controlling a process, sensors and detectors are utilized to monitor the output performance. These measurements are then used to provide corrective feedback, which aids in achieving the intended performance. Automatic control systems are created to operate without requiring human input (such as cruise control for regulating the speed of a car). Control systems engineering operations are multidisciplinary in nature and concentrate on the implementation of control systems primarily generated from mathematical modeling of a wide variety of systems.

The development of technology during the 20th century led to a major increase in interest in the field of modern control engineering, which is a relatively recent academic discipline. It can be broadly categorized as a real-world use of control theory. From basic washing machines for the home to high-performance fighter jets, control engineering is crucial to many different control systems. It aims to comprehend physical systems in terms of inputs, outputs, and numerous components with different behaviors through mathematical modeling; to construct controllers for those systems using control system design tools; and to apply controllers in physical systems utilizing available technology. Depending on the nature of the design challenge, control theory may be applied in one or more of the time, frequency, and complex-s domains to the mathematical modeling, analysis, and controller design of a system that can be mechanical, electrical, fluid, chemical, financial, or biological.

The field of engineering known as control engineering focuses on modeling a wide range of dynamic systems (such as mechanical systems) and designing controllers to make these systems behave as the designer intends. Control engineering is sometimes seen as a subject of electrical engineering even though such controllers don't necessarily need to be electrical.

Control systems can be implemented using electrical circuits, digital signal processors, and microcontrollers, among other devices. There are several uses for control engineering, from the propulsion and flight systems of commercial airplanes to the cruise control found in many modern cars.

Control engineers frequently use feedback when creating control systems. A PID controller system is frequently used to do this. For instance, a vehicle with cruise control continuously monitors the vehicle's speed and feeds that information back