Scalar control method is widely used in industries due to its
simple structure characterized by low steady-state error.
Proportional Integral (PI) controllers are commonly used in
scalar speed control of induction motors in addition to AI
controllers. A mathematical model of the real plant is required
for the controller design with conventional methods. The
difficulty of identifying the accurate parameters for a complex
nonlinear and time-varying nature of real plants may render, in
many cases, the fine tuning of parameters which is time
consuming. PI controllers are very much sensitive to
parameter variations inherent in real plant operations. The PI
control is given by
T = Kp e + Ki e dt
The output of the PI controller is updated by updating the PI
controller gains (Kp and Ki) based on the control law in the
presence of parameter variation and drive nonlinearity. The
use of PI controllers for speed control of induction machine
drives is characterized by an overshoot during tracking mode
and a poor load disturbance rejection. This is mainly caused
by the fact that the complexity of the system does not allow
the gains of the PI controller to exceed a certain low value. If
the gains of the controller exceed a certain value, the
variations in the command torque controller gains are very
high. Then the motor reaches the reference speed rapidly and
without overshoot. Step commands are tracked with almost
zero steady state error and no overshoot, load disturbances are
rapidly rejected and variations of some of the motor