Erratum: “Extended Bandwidth Zero Phase Error Tracking Control of Nonminimum Phase Systems” (Journal of Dynamic Systems, Measurement, and Control, 1992, 114, pp. 347–351)

1992 ◽  
Vol 114 (4) ◽  
pp. 555-555
Author(s):  
D. Torfs ◽  
J. De Schutter ◽  
J. Swevers
Keyword(s):  
Dynamic Systems ◽  
Tracking Control ◽  
Phase Error ◽  
Nonminimum Phase ◽  
Nonminimum Phase Systems ◽  
Phase Systems ◽  
And Control ◽  
Measurement And Control ◽  
Zero Phase

Optimal Feedforward Prefilter With Frequency Domain Specification for Nonminimum Phase Systems

1996 ◽  
Vol 118 (4) ◽  
pp. 791-795 ◽  
Author(s):  
Dirk Torfs ◽  
Joris De Schutter
Keyword(s):  
Phase Error ◽  
Time Domain Analysis ◽  
Least Square ◽  
Superior Performance ◽  
Reference Trajectory ◽  
Nonminimum Phase ◽  
Nonminimum Phase Systems ◽  
Gain Error ◽  
Phase Systems ◽  
Zero Phase

The paper shows the influence of the location of unstable zeros on the tracking performance of feedforward prefilters. Unstable zeros are divided into a number of classes. It is shown that existing feedforward prefilters (Zero Phase Error Tracking Control (ZPETC), E-filter, Extended Bandwidth ZPETC, ...) perform well for two classes, but fail for a particular class of unstable zeros. For this class, a characteristic frequency, fc, exists such that the induced gain error attenuates all frequencies of the reference trajectory f ≤ fc and amplifies frequencies f > fc. Hence, it is impossible to freely select the tracking bandwidth. Therefore, an optimal feedforward prefilter for discrete time nonminimum phase systems is presented to deal with this class of unstable zeros. As in the ZPETC method, the prefilter compensates for unstable zeros in the inverse system model, retains the zero phase property, and introduces small gain errors. But in addition, the design minimizes a cost function for which a least square solution is found. A frequency and time domain analysis shows the superior performance of the presented optimal prefilter design even for trajectory with high frequency components.

Tracking Control of Non-Minimum Phase Systems Using Filtered Basis Functions: A NURBS-Based Approach

2015 ◽  
Author(s):  
Molong Duan ◽  
Keval S. Ramani ◽  
Chinedum E. Okwudire
Keyword(s):  
Tracking Control ◽  
Phase Error ◽  
Approximate Model ◽  
Basis Functions ◽  
Minimum Phase ◽  
Tracking Errors ◽  
Model Inversion ◽  
B Spline ◽  
Phase Systems ◽  
Zero Phase

This paper proposes an approach for minimizing tracking errors in systems with non-minimum phase (NMP) zeros by using filtered basis functions. The output of the tracking controller is represented as a linear combination of basis functions having unknown coefficients. The basis functions are forward filtered using the dynamics of the NMP system and their coefficients selected to minimize the errors in tracking a given trajectory. The control designer is free to choose any suitable set of basis functions but, in this paper, a set of basis functions derived from the widely-used non uniform rational B-spline (NURBS) curve is employed. Analyses and illustrative examples are presented to demonstrate the effectiveness of the proposed approach in comparison to popular approximate model inversion methods like zero phase error tracking control.

Precision Tracking Control of Discrete Time Nonminimum-Phase Systems

1993 ◽  
Vol 115 (2A) ◽  
pp. 238-245 ◽  
Author(s):  
Chia-Hsiang Menq ◽  
Jin-jae Chen
Keyword(s):  
Discrete Time ◽  
Tracking Control ◽  
Tracking Performance ◽  
Nonminimum Phase ◽  
Nonminimum Phase Systems ◽  
Control Scheme ◽  
Feedforward Controller ◽  
Precision Tracking ◽  
Phase Systems ◽  
Precision Tracking Control

In this paper, a precision tracking control scheme for linear discrete time nonminimum-phase systems is proposed. This control scheme consists of a preview filter, a tracking-performance filter, a command feedforward controller, and a feedback controller. A command feedforward controller, whose design is based on the minimal order inverse model of the plant being controlled, will result in a completely decoupled system. The preview filter is introduced to compensate the phase and gain errors induced by the nonminimum phase zeros or lightly damped zeros of the system. Using the command feedforward controller along with the proposed preview filter, the tracking performance of the proposed control scheme can be characterized by the frequency response of the tracking-performance filter. For the design of the preview filter, a generalized Nth order preview filter and its associated penalty function that quantifies the tracking error of a design are defined. It is shown that, given the desired bandwidth and the order of the preview filter, the optimal solution for the design of the preview filter can be obtained explicitly. The proposed control scheme together with the optimal preview filter is shown to be very effective in achieving precision tracking control of discrete time MIMO nonminimum phase systems. It is also shown that the tracking performance is improved as the order N of the preview filter is increased.

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