Multivariable low order structured-controller design by frequency response approximation

Abstract

The method presented here offers an effective and time saving tool for multivariable controller design. The relation between controller complexity and closed loop performance can easily be evaluated. The method consists of five steps: 1. A desired behavior of the closed loop system is specified. Considering the nonminimum phase part of the process model the closed loop attainable performance is determined. 2. The process model and the attainable performance are scaled by the RPN-scaling procedure. 3. This defines an "ideal" scaled controller, which is usually too complex to be realized. 4. The frequency response of the ideal scaled compensator is approximated by a simpler one with structure and order chosen by the user. 5. Since the approximation in frequency response is performed with the scaled system, it is necessary to return to the original system’s units

Closed Loop System Identification Using Virtual Control Approach

“…Assuming the identified model T y has all the analyzed information about the system in the frequency domain, it is possible to use it to obtain the model G, using the basic idea of the frequency domain approach (Trierweiler et al, 2000), without restriction.…”

Multi Model Approach to Multivariable Low Order Structured-Controller Design

“…The desired performance is established to each output through specifications in the time domain ( rise time and maximum % of overshoot) that are mapped into a second order transfer function. The models must be factorized to insert some restrictions in the performance like RHP -zeros and -poles and time delay to maintain the internal stability of the feedback system (Trierweiller et al, 2000).…”

Quantifying Closed Loop Performance Based on on-Line Performance Indices

“…Three different PI controllers were designed for each plant, using Frequency Domain Methodology (Trierweiler et al 2000): Table 1. This simple example clearly shows the scale and resolution problems of Harris's index.…”