Basics of Control System

 An Extensive Guide to Control System:

The unsung hero of modern engineering is the control system. In this technology-oriented world, networks of components are regulated and managed to achieve a predetermined goal. Look at the consistent temperature of your room. Look at the navigation of an airplane. They’ve come true after enabling control systems based on precision.

What is a control system?

“Control is The Art of Guided Behaviour”

When the combination of some physical components works together to achieve a goal, the phenomenon is called a system. Control, on the other hand, means the command or direction in any machine or mechanism to manage the quantity of interest to attain a desired objective.

A control system is the combination of three- input, process and output. The purposeful arrangement of components to govern the behavior of other devices or systems. A ship can reach its destination with a proper guide, control system acts like the guidance here.

Objectives of Control System

• Controlled variables should follow a predefined path.
• In external disturbances, the system will be directed in the desired manner.
• To ensure constant and predictable behaviour of a specific variable.

Why Is A Control System Important?

In brief, a control system systematically offers the following:

Stability: The Control system ensures stability of the system to attain the desired output, reducing instability.

Automation: Automatic operation of machines and systems has become possible.

Precision: Enhances precise and accurate control.

Efficiency: Energy usage is optimized, cost is reduced, and waste is reduced.

Anatomy of Control: Components of A Control System

Input: It is meant for a reference signal, which is actually the desired value.

Controller: It is the “brain” or “intelligence” of the system. The output is compared with the input and corrective action is decided by it. It compares and generates a control signal and then to influence the process, it is sent.

Actuator: The Controller signal is converted to a physical action. It can be compared to a human muscle that takes action against any external influence in the body. Motors, pumps, valves etc. are some examples of actuators.

Process: The system or machine whose behavior is being controlled.

Sensor: For enabling feedback, sensors are used. Actual output is measured, and feedback is sent to the controller.

Output: The control system works to regulate the actual value or characteristic, which is known as the output.

Categories of Control System

According to different purposes, the control system is classified into different categories.

Based on hierarchy:

1. Open-loop Control System
2. Closed-loop Control System
3. Adaptive Control System
4. Learning Control System
5. Optimal Control System

According to the techniques involved:

1. Manual Control System
2. Automatic Control System

Depending on the creation of the control system:

1. Natural Control System
2. Manmade Control System
3. Combinational Control System

Based on the time-dependence of output variables:

1. Regulating Control System
2. Tracking Control System

Depending on time-type control:

1. Continuous Control System
2. Discrete Control System

Concerning linearity:

1. Linear Control System
2. Non-Linear Control System

Depending on the type of damping:

1. Undamped Control System
2. Underdamped Control System
3. Critically Damped Control System
4. Overdamped Control System

Based on the number of input-output:

1. Single-input-single-output (SISO)
2. Multi-input-multi-output (MIMO)

Depending on the main purpose:

1. Position Control System
2. Traffic Control System
3. Velocity Control System
4. Process Control System
5. Temperature Control System

Two Pillars of Control:

1 1. Open Loop Control System:

Actual output isn’t measured in it. As no feedback is present, no correction is here to achieve the desired output. Example- Electric toaster, washing machine, etc. ( No output is fed back, made only based on knowledge).

Figure 1: Open Loop System Block Diagram

Advantages:

• Simple due to a less complex design
• Cost-effective because of less number of components.
• Less instability is felt.
• These systems are economical.
• When output is difficult to measure, it is effective and convenient.

Disadvantages:

• No correction is made, and that’s why the output isn’t accurate.
• Applications are limited.
• For maintaining quality, recalibration is required. 

2 2. Closed Loop Control System:

Output is always monitored, fed back, and input is adjusted by the feedback in this system. Accuracy is the priority that is implemented in a closed loop.

Figure 2: Closed-loop control system block diagram

Advantages:

• Accuracy is achieved.
• Stability is enhanced.
• Reduced sensitivity.
• Variable conditions are handled effectively.
• The nonlinearity effect is reduced
• High Bandwidth.
• Higher facilities are present for automation.

Disadvantages:

• Design is complex.
• Not cost-effective, expensive.
• Oscillatory or unstable behavior can be experienced if feedback isn’t properly designed. 

Design Techniques of Control System:

For achieving fast response and accuracy, the following methods are employed:

• PID Control (Proportional–Integral–Derivative): P-controller renders output proportional to current state, I-controller eliminates steady-state error and D-controller helps to dampen oscillations.
• Root Locus and Bode Plot Techniques: With the variation of parameters, poles move and these are analyzed by graphical tools.
• Lead-Lag Compensators: Phase and gain margins are improved by using these in the frequency-domain method.

Working Principle:

Open-Loop Control System: The Input is directly fed to the controller and the output is produced. The initial signal is not modified and the error isn’t used to compensate the output.

Closed-Loop Control System: predefined or desired output and obtained output are compared and the error is adjusted. The process is modified from the error fed to the controller. This loop goes continuously and a precise, desired output is obtained.

Mathematical Modelling in Control Systems:

For implementing the design of control system, a mathematical model is important. Some models include:

• Transfer Functions: To relate input and output in the frequency domain, this method is employed in linear time-invariant systems.
• Differential Equations: In the time domain, it presents the systems.
• State-Space Representation: A set of first-order differential equations suitable for complex and MIMO systems. 

Application of Control System:

1. Industrial Automation:

• Automatic packaging, Conveyor
• PLC-based systems
• Robotic welding
• Motor speed control

2. Automotive Systems:

• Automatic transmission
• High-performance vehicles
• Cruise control
• Anti-lock braking systems (ABS)

3.     Aerospace and Defense

• Autopilots
• Flight control systems
• Missile guidance
• Satellite positioning

4. Home and Building Automation:

• Smart lighting
• Thermostats
• HVAC systems

5. Healthcare:

• Prosthetic limbs
• MRI, CT scan
• Infusion pumps
• Automated drug delivery systems
• Robotic surgery

6. Environmental Control:

• Water treatment plants
• Pollution control systems.

7. Energy Sector:

• Energy generation, transmission, and distribution
• Smart grid management
• Power system frequency control
• Wind and solar energy tracking

Embedded Control System

In this system, real-time autonomous decisions are made, which include a dedicated computing system that combines control engineering with embedded system design. Reliability and robustness are also the priority in embedded systems.

Future Trends:

Control system will be highly appreciated as it keeps pace with the following modern trends that will lead the future world:

• Autonomous Systems
• AI (Artificial intelligence)
• Machine Learning
• Cyber-digital systems
• IoT (Internet of Things) based control

Conclusion:

Control system is nothing but the “brain” behind machines, the “intelligence” behind processes, the “driving force” behind mechanisms. In a modern technology-dependent world, the precise operation of machines or systems is badly in need of a control system.

Then, what makes you leave behind without utilizing the control system?