Dear Mohan,

any real influence can be added, including friction, loose parts, liquid friction and lags.

To extend this, friction can be assumed temperature and speed dependant .

Thank you very much Dr.Martin..i ll reflect on what you have said.

The Following Articles  may give some ideas on what else are to be considered.

1.   Model of induction motor changes to power system disturbances

Parveen, Tania, Ledwich, Gerard F., & Palmer, Edward W. (2006) Model of induction motor changes to power system disturbances. In Proceedings of the 2006 Australasian Universities, Australia, Victoria, Melbourne.

The main objective of this paper to develop an induction motor with different types of shaft loads to model of real (∆P) and reactive (∆Q) power changes to power system Voltage (∆V), frequency (∆f) random changes. The new developments are to consider cases where the system affects the load as well as having the load affect the system.

Link:   http://eprints.qut.edu.au/4999/

2.   HIGH PERFORMANCE CONTROL OF INDUCTION MOTOR BASED ON AUTO-DISTURBANCE REJECTION CONTROLLER

FENG Guang, HUANG Li-pei, ZHU Dong-qi (Department of Electrical Engineering,Tsinghua University,Beijing 100084,China)  

The field oriented control technique is widely used in high performance motion control of induction motors. However, in real-time implementation, precise decoupling which requires accurate motor parameters can't be fully realized due to significant plant uncertainties such as external disturbances, parameter variations and plant nonlinear dynamics. This may deteriorate the dynamic performances of flux and torque significantly. To achieve high dynamic performance of drive system, a nonlinear auto-disturbance rejection controller which substitutes the classic PID controller to the control of induction motor is presented in this paper. The auto-disturbance rejection controller is composed of three parts: tracking-differentiator, extended state observer and nonlinear state error feedback control law. By using the extended state observer, the proposed controller can estimate the derivative signals accurately and precise decoupling of induction motor is achieved. In addition, the proposed strategy realizes the disturbance compensation without accurate knowledge of induction motor parameters, so that the accurate model of induction model is not required. That means the design of auto-disturbance rejection controller is independent of the controlled system model, and this controller can achieve good adaptability and robustness as well. The simulation and experiment results show that the controller ensures very good robustness and adaptability under modeling uncertainty and external disturbance, and it is concluded that the proposed controller produces better dynamic performance such as small overshoot and fast transient time than conventional PID controller in the overall operating conditions.

Link:   http://en.cnki.com.cn/Article_en/CJFDTOTAL-ZGDC200110012.htm

3.    A new switching surface sliding-mode speed control for induction motor drive systems

Kuo-Kai Shyu ; Dept. of Electr. Eng., Nat. Central Univ., Chung-Li, Taiwan ; Hsin-Jang Shieh

In this paper, a sliding-mode speed controller based on a new switching surface is proposed for induction motor systems. With this variable structure control switching surface, the exponential stability is guaranteed for the speed servo control and insensitivity to uncertainties and disturbances are obtained as well. Moreover, an adaptive variable structure speed control is studied to relax the need for the bound of disturbance in variable structure control. The insensitivity or robustness of the proposed method for general speed servo systems is maintained, and the dynamic performances are improved as well. Finally, the validity of proposed scheme is demonstrated by computer simulations and experimentations

Link:   http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=506132&abstractAccess=no&userType=inst

P.S.

Thank you Dr.Subramanyam for your elaborate response. I ll definitely look into your suggestion.

Dear Mohan Krishna,

You may upvote the Reply if you are Satisfied.

P.S.

Please refer to these articles:

https://www.researchgate.net/publication/313576646_From_PID_to_Nonlinear_State_Error_Feedback_Controller

https://www.researchgate.net/publication/312046377_Improved_Sliding_Mode_Nonlinear_Extended_State_Observer_based_Active_Disturbance_Rejection_Control_for_Uncertain_Systems_with_Unknown_Total_Disturbance

https://www.researchgate.net/publication/309655805_On_the_Improved_Nonlinear_Tracking_Differentiator_based_Nonlinear_PID_Controller_Design

Article From PID to Nonlinear State Error Feedback Controller

Article Improved Sliding Mode Nonlinear Extended State Observer base...

Article On the Improved Nonlinear Tracking Differentiator based Nonl...

 Thank you Dr Adheem for sparing your time and the articles. It was very useful.

Dear Mohan,

The machine parameters such as rotor resistance , stator resistance variations due to heating can also be included.

Thank you Dr. Bhavnesh for you time and response.