Control System – Subject Overview

So before we get started, I want to give you some glimpse of the main modules that we will be dealing in this Control system’ subject. Control Systems is one of the most important subject for both the engineering streams i.e Electrical and the Communication engineers . The weightage of the Control Systems has been around 7-8 marks over the years (which is much more than some of the core subjects).

The problems that generally appear in GATE from this topic are based on the application of concepts instead of directly asking a theory concept. While learning this subject , the focus must be on to solve a lot of problems (application based). For beginners, I want to suggest you to go for standard books on control system engineering like Nagrath & gopal (in this course modules I will be referring most of the concepts from this book).

If you want descriptive book then you can refer BS manke. For numericals specifically I want you to go for schaum series. So let’s have look in the important topics in Control System subject:

Transfer Functions

Transfer function gives the relationship between the input and output of a control system. Here we will start our learning by understanding the concept of positive and negative feedback systems, then we will proceed further towards Block Diagram Reduction Technique. Furthermore, Signal Flow Graphs and Mason’s Gain Formula are some of the most crucial topics to be covered here.

Time Domain Analysis

In this module we will be dealing with Laplace transform(this is a prerequisite), two most important stability analysis methods i.e. Root locus and Routh Hurtwitz criteria . This topic is very easy and majorly formula based as we have to learn the formulas for various different time domain parameters like the Rise Time, Maximum Overshoot, Settling Time, Peak Time , Damping factor, Natural and Damped frequency and also various error coefficients like Position Error Coefficient, Velocity Error Coefficient and the Acceleration Error Coefficient.

Frequency Domain Analysis

In this module we will be employing three most pronounced methods i.e. Bode plot, Nyquist plot and pole placement methods for the stability analysis. In this topic many small sub topics will be covered like resonant peak overshoot, resonant frequency, Gain Margin, Phase Margin, Gain and Phase cross over frequency, etc. Apart from that the concept of the Nyquist Criterion is important and here we need to learn the small Nyquist Plots for simple function and further how do they change once you add zeroes and poles. Moreover we will also discuss about Lag, Lead, Lead-Lag compensation.

State-Space Analysis

In this module, we have to learn about State Transition Matrix and its relation with the Transfer Function and also the solution of State Space Equation by the use of the State Transition Matrix. The concept of Controllability and Observability will also be discussed . 

Stability

Stability analysis is one of the important step for any Control System, any system is stable if the output of that system is bounded for any given bounded input(BIBO is the most common way to judge stability) Means in the event that you give some finite or bounded input to a operational system , the machine output normally finite/bounded, or otherwise not constantly growing. Stability analysis for both frequency and time domain analysis will be discussed in detail.