How do you find the root locus of a transfer function?

Follow these rules for constructing a root locus.

  1. Rule 1 − Locate the open loop poles and zeros in the ‘s’ plane.
  2. Rule 2 − Find the number of root locus branches.
  3. Rule 3 − Identify and draw the real axis root locus branches.
  4. Rule 4 − Find the centroid and the angle of asymptotes.

How do you find K in a root locus plot?

You can simply make characteristic equation 1+GH =0 and find K. Having characteristic equation, obtain the intersection with jω axis by Routh-Hurwitz criteria. It will give you maximum gain. Or find intersection with real axis (put s=0) it will give you gain for no oscillatory response.

What is K in transfer function?

For example consider the transfer function: In the general case of a transfer function with an mth order numerator and an nth order denominator, the transfer function can be represented as: The pole-zero representation consists of the poles (pi), the zeros (zi) and the gain term (k).

What is the difference between root locus and Bode plot?

Each point on the Root Locus corresponds to a different Bode Plot (phase and gain as functions of ). The only difference between the Bode Plots is a shift in amplitude (in dB). Note that all Bode Plots relate to the open loop ( ) ( ) transfer functions, while the Root Locus shows the closed loop poles.

What are the applications of root locus?

The Root Locus Plot technique can be applied to determine the dynamic response of the system. This method associates itself with the transient response of the system and is particularly useful in the investigation of stability characteristics of the system.

Where does the root locus start and end?

Start/End Points Root locus starts (K=0) at poles of open loop transfer function, G(s)H(s). These are shown by an “x” on the diagram above As K→∞ the location of closed loop poles move to the zeros of the open loop transfer function, G(s)H(s).

How to draw the root locus in MATLAB?

A program (like MATLAB) can do this easily, but to make a sketch, by hand, of the location of the roots as K varies we need some information: The numerator polynomial has 1 zero (s) at s = -3 . The denominator polynomial yields n = 2 pole (s) at s = -1 and 2 .

How to calculate the angle of departure of a root locus?

Angle of Departure is equal to: θdepart= 180° + sum(angle to zeros) – sum(angle to poles). θdepart= 180° + 90 – 135. θdepart= 135° This angle is shown in gray. It may be hard to see if it is near 0°. Angle of Arrival No complex zeros in loop gain, so no angles of arrival. Cross Imag.

Is the root locus symmetric about the real axis?

(The explanation of the rule applied to this loop gain is below the graph.) As you can see the locus is symmetric about the real (horizontal) axis. You can select one of the root locus rules (above) to see how it is applied for the given loop gain.