Session: 29-01 Active Controls of Rotordynamic Systems

Paper Number: 82897

82897 - Effect of Constant Time Delay in Active Magnetic Bearings on the Stability of Rotor Shaft Systems 

Active Magnetic Bearings (AMBs) provide energy efficient, contact less suspension of high-speed gas turbine rotor shafts systems employed in wide ranging application domains and also lead to lower noise levels during operation. In essence AMBs are a mechatronic product which work on the principle of feedback control systems, wherein the rotor shaft displacement is sensed, transferred to the controller, which processes the received information as per the control law and the appropriate amount of control current is then built up in the electromagnets. In practical applications, all these processes cannot happen instantaneously and they require definite amount of time. This leads to some amount of delay between the sensing of the rotor shaft motion and the application of control force by the electromagnet. Such delay in AMBs may lead to inefficient suspension and instability in the rotor shaft system depending upon the rotor shaft spin speed and vibration frequency. This forms the motivation behind the analysis presented in this paper.

This paper considers a single disk rigid rotor shaft system with a non-central rotor disk levitated at its end through AMBs. Constant time delay has been assumed to exist in the rotor AMB system. The equations of motion for the system are formulated in the time domain but are transformed to the frequency domain so as to exploit the second order Pade's approximation of the time delay terms. Two different control laws have been considered for analysis, namely the conventional PID control law and a control law based on the constitutive relationship of viscoelastic material models called the Four Element control law. Before comparing the performance of the two control laws, the controller gains have been optimized using Genetic Algorithm. The stability of the system is analysed using the roots of the characteristic equation of the rotor shaft system. Effect of different system parameters and the controller gains are analysed using the stability charts. In order to validate the results found using the stability analysis introduced above, numerical simulation of the time delayed differential equations is carried out. 

This study will find its application in the design and development of AMB controllers and instrumentation for the high speed rotor shaft systems.

Presenting Author: Tukesh Soni UIET

Presenting Author Biography: Dr. Tukesh Soni received his B.Tech. degree in Mechanical Engineering from the National Institute of Technology Raipur, India in 2007, his M.Tech. degree in Mechanical Engineering from the Indian Institute of Technology, Kanpur, India in 2009 and PhD. in Mechanical Engineering from the Indian Institute of Technology Delhi, New Delhi in 2020. He is currently working as Assistant Professor in the department of UIET, Panjab University, Chandigarh, India. Prior to that he worked as a Scientist in the Vikram Sarabhai Space Centre, Thiruvananthapuram, India. His research interests include active vibration control of rotors, active magnetic bearings and intelligent control.

Authors:

Tukesh Soni UIET
Jayanta K Dutt Indian Institute of Technology Delhi
Ranjana Sodhi Indian Institute of Technology Ropar