CIFER®-MATLAB Interfaces: Development and ... - Cal Poly

Frequency responses are typically represented using a Bode plot format that graphs magnitude on
a log scale and phase of an input-to-output ratio against frequency. Nonparametric models are
useful in determining characteristics such as bandwidth, time-delay, and pilot-in-the-loop
behavior. They can also be used to validate math models and determine parametric model
structure and order. This project will be dealing primarily with frequency response analysis.
A parametric model assumes an order and structure with primary representations including
transfer functions and state-space models. Transfer functions are pole-zero representations of
individual input-output pairs. State-space models describe an entire system in terms of stability
and control derivatives. Parametric models are used primarily in control system design and for
wind tunnel or math model validation.
1.1 About CIFER ® (Comprehensive Identification from FrEquency Responses)
There are many programs that offer time domain analysis 1
of system response data but
comparatively few that offer analysis in the frequency domain. One very successful frequency
domain program, and the focus of this project, is called CIFER ® , or Comprehensive Identification
from FrEquency Responses. CIFER ® was developed by the Army/NASA Rotorcraft Division at
the Ames Research Center during from 1988-1994 and has been constantly updated, modified,
and improved since. It is used extensively by the Army/NASA Rotorcraft Division and also by
many commercial aerospace companies. Some of the applications at the Ames Research Center
have included development of control laws for the UH-60, identification of the XV-15 tilt-rotor
demonstrator, assistance in CH-47 control development, investigation of slung load dynamics,
and a wide variety of work involving unmanned aerial vehicles (UAVs). CIFER ® is considered to
be one of the best programs available for frequency domain analysis.
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