Symmetrical Optimum: Symmetrical Optimum – Sometimes automatic control systems contain integrating also besides first order delay elements, proportional elements and deadzones. Such a system when compensated on the basis of magnitude optimum discussed in the previous sections will become oscillatory with zero damping. As has already been explained the magnitude optimum utilizes a PI controller to […]

### CONTROL TECHNIQUES FOR ELECTRIC DRIVES

## Uncompensated Large Time Constants

Uncompensated Large Time Constants: It is possible to compensate only one Uncompensated Large Time Constants using a PI controller. A PID controller is used to compensate for two large time constants. On technical grounds, compensation of more than two constants using a PID Therefore if a transfer function has more than two dominant poles, only […]

## Exponential Variation of the Input to the Controller

Exponential Variation of the Input to the Controller: The linear Exponential Variation of the input to the Controller, discussed in the foregoing section, is too involved to achieve by means of circuits using discrete elements. On the other hand a simple RC circuit connected at the input of the controller provides an input which varies […]

## Design of Controllers for Linearly Varying Inputs

Design of Controllers for Linearly Varying Inputs: The Design of Controllers for Linearly Varying Inputs discussed in the foregoing sections are for the step input. The performance has been found to depend very much upon the value of integration time in relation to the uncompensated time constant of the plant. A control system is normally […]

## Controller Transfer Function

Controller Transfer Function: While a Controller Transfer Function is designed to improve the behavior of a given control system in practice it is very difficult to realize such a controller because of the availability of components. The actual time constant of the controller may deviate from the theoretically designed value. Also the operating conditions may […]

## Phase Margin Optimum

Phase Margin Optimum: The method can be based on the phase margin in which the controller is designed to provide a minimum phase margin. The design makes use of Bode plots. The ratio of time constants can be decided depending upon the phase margin required, which directly influences the damping. Therefore this method has an […]

## Magnitude Optimum

Magnitude Optimum: The design of a controller based on the principle Magnitude Optimum that it allows all the frequencies to pass through in a similar way for a simple system is shown in Fig. 6.31. The system has an input R(s) and output C(s). The closed loop transfer function The plant transfer function Gp(s) is assumed […]

## Controller Design Frequency Response

Controller Design Frequency Response: The Controller Design Frequency Response (or root locus) alters or reshapes the frequency response (or root locus) of the original system to the desired one. Thus the ideal goal of compensation is to achieve a control system which has a desired performance, viz. having zero steady- state error, optimised dynamic performance, […]

## Methods of Compensation in Control System

Methods of Compensation in Control System: The Different Methods of Compensation in Control System are Cascade Compensation Feedback Compensation Load Circuit Compensation Input Circuit Compensation A drive system having closed loop control may not be satisfactory with regard to its stability characteristics, speed of response and steady-state accuracy. The system may be oscillatory or even […]

## Control System Performance

Control System Performance: From the foregoing discussion on control systems it can be seen that the behaviour of the control systems can be specified, based on several time domain specifications. To provide a basis for comparison of several types of control and solution, the performance indices are defined. These help as a quantitative measure of […]

## Root Locus Plot

Root Locus Plot: In the electrical drives employing closed loop control techniques, it is often necessary to investigate the effects of changing the parameters of the system on its stability. The drive motor used itself has several parameters and time constants which affect the stability of the motor itself. The controls used also introduce some […]

## Stability from Log Magnitude Angle Diagram

Stability from Log Magnitude Angle Diagram: Yet another way of portraying the frequency response is to draw a curve showing the Log Magnitude Angle Diagram in decibels on the Y-axis and phase angle on the x-axis. The frequency ω is varied from —∞ to ∞ by combining the Log Magnitude and phase plots (Fig. 6.24). […]

## Stability from Bode Plot of Open Loop Transfer Function

Stability from Bode Plot of Open Loop Transfer Function: The Nyquist criterion details how the open loop polar plot can be used for establishing. the stability of a closed loop system. In terms of phase and gain margins it has been concluded that a minimum phase function should have positive values of phase and gain […]

## Relative Stability from the Nyquist Plot

Relative Stability from the Nyquist Plot: Relative Stability from the Nyquist Plot – The considerations discussed above provide information about the absolute stability of the system, i.e., whether the system is stable or not. An equally important system behaviour to be considered is the relative stability. The relative stability is indicative of how various poles […]

## Nyquist Criterion

Nyquist Criterion: Nyquist Criterion – This stability criterion enables one to establish the stability of a system using a graphical procedure in the frequency domain. Here also there is no necessity for the evaluation of the roots of the characteristic equation. The stability of a closed loop system is revealed by subjecting the open loop […]

## Routh Hurwitz Criterion

Routh Hurwitz Criterion: The Routh Hurwitz Criterion states that the system is stable if the Routh table has no negative elements in the first column. The roots of the characteristic polynomial are negative if they are real or contain negative real parts if the elements of the first column of the Routh Table are positive. […]