A PLC-based Hybrid Fuzzy PID Controller for PWM-driven Variable Speed Drive

In adjustable-speed drive applications, the range of speed and torque achievable is
very important. A power electronic converter is needed as an interface between the
input AC power and the drive. A controller is needed to make the motor (drive),
through the power electronics converter meets the drive requirements. The widely
used conventional control that is based on mathematical model of the controlled
system is very complex and not easy to be determined since it requires explicit
knowledge of the motor and load dynamics.
This thesis proposed a design and implementation of a PLC-based hybrid
controller from a basic PLC to a PWM-driven variable-voltage variable-frequency
(VVVF) speed control of an induction motor and the analysis, evaluation and
improvement of the control strategies. A simulation model in MA TLAB/Simulink is
developed using system identification technique to perform verification of the PLCbased
intelligent controller of the PWM-driven VVVF algorithm. To provide stability
in response to sudden changes in reference speed and/or load torque, a switching type
controller consisting of two control modes are devised: a PID-type fuzzy controller
consisting of a PI-type and a PD-type fuzzy controller, and a conventional PID. The
proposed scenario is implementing a strategy when the actual value is closed to setpoint.
At the early phase of the control action, the control task is handled by the PIDtype
fuzzy controller. At a later phase when the absolute of error is less than a
threshold value, the input of integrator at the output side is no longer given by fuzzy
action but fed by the incremental PID action. In term of control action, this is an
enhanced proportional and derivative action when the actual value is closed to
reference. Detailed evaluations of the controller's performance based-on a predefined
performance indices under several conditions are presented. The findings
demonstrate the ability of the control approach to provide a viable control solution in
response to the different operating conditions and requirements.