DV Lag, NonMinimum Phase Introduction

Cuthbert Nyack
The open loop transfer functions for systems without and with DV lag are shown below. The magnitude of the transfer functions are the same but the phase lag of the system with DV lag is larger by wb which increases without limit as frequency increases. With a phase increasing without limit, this system can become unstable. The name distance velocity or transportation lag is used to describe this effect because it occurs when the parameter being controlled is measured some distance from where the control action is being applied.

The open loop transfer functions for systems with minimum and nonminimum phase are shown below. The magnitude of the transfer functions are the same but the phase lag of the system with nonminimum phase is larger by 2 tan-1(Tnw) which can reach up to -180°. This increased phase lag can make the system unstable.

When enabled some of the applets for Distance Velocity Lag and Nonminimum Phase appear as shown below:-
and those for nonminimum phase:-

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COPYRIGHT 2006 Cuthbert Nyack.