class for root locus and bode plote diagram
- 1. 1 IC 8451&CONTROL SYSTEMS Department of Electrical and Electronics Engineering Approved by AICTE | Affiliated to Anna University | Accredited by NAAC | Accredited NBA | Recognized by UGC under 2(f) and 12(B) Chennai Main Road, Kumbakonam- 612 501. ARASU ENGINEERING COLLEGE
- 2. 2 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS LAG COMPENSATOR A compensator having the characteristics of a lag network is called a lag compensator. If a sinusoidal signal is applied to a lag network, then in steady state the output will have a phase lag with respect to input. Lag compensation results in a large improvement in steady state performance but results in slower response due to reduced bandwidth. The attenuation due to the lag compensator will shift the gain crossover frequency to a lower frequency point where the phase margin is acceptable. Thus, the lag compensator will reduce the bandwidth of the system and will result in slower transient response. Lag compensator is essentially a low pass filter and so high frequency noise signals are attenuated. If the pole introduced by the compensator is not cancelled by a zero in the system , then lag compensator increases the order of the system by one.
- 4. 4 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS • REALISATION OF LAG COMPENSATOR USING ELECTRICAL NETWORK
- 5. 5 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS Bode plot of lag compensator
- 7. 7 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS • PROCEDURE FOR THE DESIGN OF LAG COMPENSATOR USING BODE PLOT The following steps may be followed to design a lag compensator using bode plot and to be connected in series with transfer function of uncompensated system, G(s). • Step-1: Choose the value of K in uncompensated system to meet the steady state error requirement. • Step-2 : Sketch the bode plot of uncompensated system. • Step -3 : Determine the phase margin of the uncompensated system from the bode plot. If the phase margin does not satisfy the requirement then lag compensation is required. • Step-4: Choose a suitable value for the phase margin of the compensated system.
- 10. 10 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS • Step-8: Determine the open loop transfer function of compensated system.
- 12. 12 ARASU ENGINEERING COLLEGE IC 8451&CONTROL SYSTEMS • EXAMPLE A unity feedback system has an open loop transfer function, G(s) = K/s(1+2s). Design a suitable lag compensator so that phase margin is 40◦ and the steady state error for ramp input is less than or equal to 0.2.