Introduction to Control Systems

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Introduction to Control Systems


Control systems design is a concrete example of engineering design. The control engineering design goal is to obtain the configuration, specifications, and identification of the key parameters of the proposed system to meet actual needs. The design process consists of seven main building blocks, we organize them into three groups:

  1. Establish goals and variables to control and define specifications (metrics) used to measure performance
  2. System definition and modeling
  3. Design of control and simulation systems and analysis of integrated systems

Control System Comparison

Open loop:-output variables do not affect input variables-if no unpredictable effects occur, the system will follow the required reference command-it can compensate for the interference considered-it will not change the stability of the system

closed loop:-output variable effects Input variables to maintain the desired behavior of the system-Need to measure (controlled variable or other variables)-Need to calculate the control error as the difference between the controlled variable and the reference command-Calculate the input based on the control error to minimize the control error -Ability to suppress the influence of interference-Can make the system unstable, in which the controlled variable grows infinitely.

Control Systems Overview

A control system is a system that controls the output to produce the desired response. The simple block diagram of a control system is shown in the picture below.

Control Systems

The control system is represented by a single block in this diagram. The control system was given this name because the output is controlled by variable inputs. This input will be varied using some techniques. In the following part on open-loop and closed-loop control systems, we will look in-depth at the components of the control system and how to modify the input to get the desired response.

Examples − Traffic lights control system, washing machine

A control system is illustrated by the traffic light control system. In this case, a sequence of the input signal is applied to this control system, and the output is one of the three lights that will be turned on for a set period of time. The other two lights will be turned off during this period. The on and off periods of the lights can be calculated based on a traffic analysis at a specific intersection. As a result, the input signal governs the output. As a result, the traffic light control system works on a timely basis.

Classification of Control Systems

We may categorize control systems in the following ways based on some characteristics.

Continuous-time and Discrete-time Control Systems

Control systems are divided into two types based on the type of signal used: continuous-time control systems and discrete-time control systems.

All signals in continuous-time control systems are continuous in time. However, one or more discrete-time signals exist in discrete time control systems.

SISO and MIMO Control Systems

Based on the number of inputs and outputs, control systems are categorized as SISO control systems or MIMO control systems.

SISO (Single Input and Single Output) control systems feature a single input and a single output. MIMO (Multiple Inputs and Multiple Outputs) control systems, on the other hand, have more than one input and more than one output.

Open-loop and Closed Loop Control Systems

Control systems are divided into two types based on their feedback path: open-loop and closed-loop.

The output of an open-loop control system is not sent back into the input. As a result, the control action is unaffected by the desired outcome.

The block diagram of the open-loop is shown in the picture below.

Control Systems

Open Loop

In this case, input is applied to a controller, which generates an actuating or controlling signal. This signal is fed into a facility or process that has to be managed. As a result, the plant generates a regulated output. An example of an open-loop control system is the traffic light control system we described previously.


  1. Automatic washing machine- The operation time in this system is manually specified. Because there is no feedback signal that the machine can detect beyond the specified time, the machine stops whether the desired cleanness is attained or not.
  2. Immersion rod- In this method, the rod warms the water, but it cannot detect how much hot water is necessary.


  • Open-loop systems are simple.
  • These are economical.
  • Less maintenance is required and is not difficult.


  • Open-loop systems are inaccurate.
  • These systems are not reliable.
  • These are slow.
  • Optimization is not possible.

Closed Loop

A closed-loop control system is one in which the control action is determined by the intended outcome. In this system, the output signal is compared to the reference input signal to generate an error signal, which is then given to the controller to minimize the error and get the desired output.

The output of a closed-loop control system is fed back into the input. As a result, the control action is determined by the intended output.

The block diagram of the negative feedback closed-loop is shown in the picture below.

Control Systems

The error detector generates an error signal that is equal to the difference between the input and feedback signals. This feedback signal is derived from the block (feedback components) by using the overall system’s output as an input to this block. Instead of direct input, the error signal is sent into a controller.

As a result, the controller generates an actuation signal that regulates the plant. In this configuration, the control system’s output is automatically modified until the required reaction is obtained. As a result, closed-loop control systems are often known as automated control systems. A closed-loop control system is an example of a traffic light with a sensor at the input.


  1. Automatic electric iron.
  2. Servo voltage stabilizer.
  3. An air conditioner.


  • These systems are more reliable.
  • Closed-loop systems are faster.
  • Many variables can be handled simultaneously.
  • Optimization is possible.


  • Closed-loop systems are expensive.
  • Maintenance is difficult.
  • Installation is difficult for these systems.

The differences between the Open-loop and the closed-loop control systems are mentioned in the following table.

S.No      Open Loop system                                                     Closed Loop system

1             These are easier to build.                                          These are difficult to build.

2             These systems are not reliable.                               These systems are reliable.

3             These systems are slow.                                            These systems are faster.

4             These systems are generally more stable.             These systems are less stable.

5             Optimization is not possible.                                   Optimization is possible.

6             Examples – Hand dryer, washing machine.          Servo voltage stabilizer, air conditioner.

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