Describing Function Analysis of Control Systems with Common Nonlinearities

#Linear #and #Nonlinear #frequency #Circulation #of #higher #Harmonics #Oscillations

The Long Island (LI) Chapter of IEEE Signal Processing Society (SPS) and Cosponsor Women in Engineering (WIE) Society in collaboration with the Educational Activities Committee of IEEE LI and Renewable Energy and Sustainability Center of Farmingdale State College Presents the following Lecture:

This is an introduction to the describing functions and its use in analyzing some common nonlinearities. Linear frequency response methods that ignore these nonlinearities fail to predict limit cycle oscillations. The describing function method discussed herein predicts them. Books, at least as far back as 1955, and various contemporary online descriptions contain discussionss of the describing function. This is an account of using the describing function to predict limit cycles. Frequency response methods work well with single input single output linear feedback systems even those that have some form of nonlinearity such as a slightly nonlinear gain. These generally yield to approximation by linear elements. There are, however, some common nonlinearities containing abrupt transitions that fail to yield to linearizing approximations. These often cause limit cycle oscillations. Three such nonlinearities are dead zone, saturation, and the infinite gain limiter. The describing function is based on these assumptions:  

  • Circulation of higher harmonics through the loop attenuates them so only a miniscule amount of higher harmonic energy returns to the nonlinearity
  • Nonlinearity produces no subharmonics or DC
  • Nonlinearity in the loop exists in one transfer function.

  Date and Time




  • Date: 26 Oct 2017
  • Time: 11:00 AM to 12:15 PM
  • All times are (GMT-05:00) US/Eastern
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  • SUNY College at Farmingdale
  • Farmingdale, New York
  • United States
  • Building: Lupton Hall
  • Room Number: 247

  • Contact Event Host
  • Dr. Radu, IEEE LI Seciton WIE Chair (

    Prof. Issapour, Chair, IEEE LI Section (

    Dr. Donaldson, Chair, SPS, IEEE LI Section (

  • Co-sponsored by WIE
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  • Starts 01 September 2017 12:00 AM
  • Ends 26 October 2017 11:59 PM
  • All times are (GMT-05:00) US/Eastern
  • No Admission Charge


Lecturer: Mr. Alan Lipsky


Describing Function Analysis of Control Systems with Common Nonlinearities


Alan Lipsky specializes in feedback controls. His recent design experience includes: a 500-watt off-line power supply for an ultrasonic generator, a 6 KW degaussing power amplifier, and a data acquisition system that extrapolates. He has: a patent for a sonar signal processing equipment. His degrees consist of a Master’s degree from MIT, and a bachelor’s from RPI where he was elected to beta-kappa-Nu and Tau-Beta-Pi.

Lecturer: Mr. Alan Lipsky


Describing Function Analysis of Control Systems with Common Nonlinearities



11:00 am - 11:10am Introduction

11:10am - 12:00pm Mr. Lipsky's Lecture 

12:00pm - 12:10pm Questions and Answers

FREE PIZZA and WATER will be served.

Free for all Registration Participants (Members/Non-Members/Students)