DV Lag, NonMinimum Phase Introduction
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.