# Control Techniques for Electric Drives

## 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.

## Stability Control Drives

Stability Control Drives: The concept of stability is very well known. By the term stability one implies the ability of a system to return to its original position or attain a new steady-state condition when there is some disturbance or change in the input condition of the system. Following changes in input, or any disturbance,

## Correlation Between Frequency and Transient Response

Correlation Between Frequency and Transient Response: As has been stated, the use of frequency response for the design of control systems requires a Correlation Between Frequency and Transient Response. Time response specifications are available for the performance of a system. These must be translated to frequency response. There must be frequency domain specifications also, corresponding

## Polar Plot for Frequency Response

Polar Plot for Frequency Response: One of them is the Polar Plot for Frequency Response representation. The transfer function in the frequency domain is obtained by substituting jω for s as complex function of ω. It is separated into real and imaginary parts which are plotted on the real and imaginary axes to get the

## Frequency Response Transfer Function

Frequency Response Transfer Function: The previous sections- show that with the time response of a system, even though it is a direct method of analysis, the adjustment of the parameters to give a satisfactory time domain performance is rather tedious particularly with higher order systems. On the other hand methods utilising Frequency Response Transfer Function

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