Modern Control System EKT 308

1. Modern Control SystemEKT 308 Design of Feedback Control Systems

2. Control System Design: Concerned with the arrangement , or the plan , of the system structure and the selection of suitable components and parameters. Compensator: Additional component or circuit that is inserted into a control system to compensate for deficient performance. Types of Compensation: Cascade Compensation ( figure 1.a) Feedback Compensation (figure 1.b) Output Compensation (figure 1.c) Input Compensation (figure 1.d)

3. Types of Compensation Figure 1: Types of compensation

4. Cascade Compensation Networks

5. Consider the following first order compensation transfer function • The compensation network is called phase-lead network if • |z| < |p|

6. Because zero occurs first on the frequency axis, we obtain a phase-lead characteristic, as shown in the following figure 3. Figure 3: Bode diagram of phase lead network.

7. Example of phase lead compensation network

8. Phase – Lag network Consider the following first order compensation transfer function • The compensation network is called phase-lag network if • |z| > |p|

9. Example of phase lag network

10. Frequency response of the transfer is given by,

11. Figure 5 : Bode diagram of the phase – lag network.

12. Phase Lag Design using Bode Diagram Steps to design an appropriate phase lag network. Obtain Bode diagram for the uncompensated system. (Gain adjusted for desired error constant). Determine the phase margin. If insufficient, follow the remaining steps. Determine the frequency where the phase margin would be satisfied, if the magnitude curve crosses 0-db at this freq. (allow 5 degree safety) Place the zero one decade below the new cross over frequency. Measure the necessary additional attenuation at the new crossover freq

14. Phase lag design example Steps: Uncompensated Bode diagram is shown in figure 6.

15. Figure 6: