TYPES OF COMPENSATION
This is the most commonly used system where the controller is placed in series with the controlled process.
Figure shows the series compensation
This is the system where the controller is placed in the sensor feedback path as shown in fig.
This is a system which generates the control signal by feeding back the state variables through constant real gains. The scheme is termed state feedback. It is shown in Fig.
The compensation schemes shown in Figs above have one degree of freedom, since there is only one controller in each system. The demerit with one degree of freedom controllers is that the performance criteria that can be realized are limited.
That is why there are compensation schemes which have two degree freedoms, such as:
(b) Feed forward compensation
Series-feedback compensation is the scheme for which a series controller and a feedback controller are used. Figure 9.6 shows the series-feedback compensation scheme.
The feed forward controller is placed in series with the closed-loop system which has a controller in the forward path Orig. 9.71. In Fig. 9.8, Feed forward the is placed in parallel with the controller in the forward path. The commonly used controllers in the above-mentioned compensation schemes are now described in the section below.
It has a zero and a pole with zero closer to the origin. The general form of the transfer function of the load compensator is
It has a zero and a pole with the zero situated on the left of the pole on the negative real axis. The general form of the transfer function of the lag compensator is
Therefore, the frequency response of the above transfer function will be
The lag-lead compensator is the combination of a lag compensator and a lead compensator. The lag-section is provided with one real pole and one real zero, the pole being to the right of zero, whereas the lead section has one real pole and one real came with the zero being to the right of the pole.
The transfer function of the lag-lead compensator will be