|The control selection
and tuning procedure works as follows. First, some essential
canal properties (delay time, surface area, critical resonance frequency,
if any, and corresponding resonance peak gain) are derived from the nonlinear hydrodynamic
model of the canal. With these canal properties, as well as some additional
data on the control hardware that needs to be used (such as the sample time),
and preferences on the control structure, an 'initial' feedback
control system is selected, consisting of Proportional Integral (PI) controllers with
or without decouplers (see below).
Then for each PI controller
its limit settings (= the settings of the control constants at which control
is close to instability) are computed and the control constants are optimised using
a multiple model optimisation technique , .
Then the control system is tested if it
will satisfy the performance requirements. If not, a control
system with better performance is selected (see below) and tuned again using multiple
Details on the control structure
An hierarchical master-slave
control structure is always applied. The master controller controls the water level by adjusting
the flow through the check-structure (such as a gate). The slave controller
controls the flow through the check-structure by adjusting the check-structure
inputs, such as gate openings. The advantages of applying this hierarchical
master-slave control structure are multiple:
nonlinearities of the check-structure
do not affect the water level control loop which improves performance;
complicated requirements on the operation
of the check-structure are easily taken into account (for instance, operating
requirements to avoid damage to the canal walls);
interactions between two adjacent reaches
are avoided which improves performance (decoupling).
Depending on the preferred choice,
completely decentralized feedback control system (distributed control) can be applied
as master controller, or a centralized one. For a completely decentralized feedback
control system, local PI controllers are selected. For a completely centralized
feedback control system, PI controllers are selected first that add their control
input signal to an adjacent PI controller (PI control with decoupler).
The slave (flow) control algorithm
that is usually applied is a bisection algorithm that numerically 'inverts' the
gate-discharge relation. The algorithms have guaranteed convergence and
solve the problem fast enough to allow real-time operation. Gate-discharge
relations do not need to be known exactly for this, (nor do they have to
In some cases, a filter is connected
in series with the PI controller to improve performance. The tuning procedure
automatically detects if such a filter is useful.
If the resulting performance of the
controlled canal is inadequate, the control problem is hard and a feedforward controller
has to be added. The feedforward controller is provided
either with a schedule of disturbances and/or real-time measured disturbances
(depending on your preferences) and computes anticipating control actions
based on that knowledge. The feedforward controller is simple to program
and very reliable, because it makes use of a very simple algorithm. The
control signal of the feedforward controller is added to that of the feedback
If the resulting performance is still
inadequate, more advanced feedback controllers,
such as LQG, and/or more advanced feedforward controllers or Model Predictive Control.
 P.J. van Overloop. 'Model Predictive Control on Open Water Systems', ISBN 1-58603-638-6, 2006, The Netherlands.
 J.Schuurmans. 'Control of Water
Levels in Open-Channels', ISBN 90-9010995-1, 1997, The Netherlands.
 J. Schuurmans, A. Hof, S. Dijkstra, O.H. Bosgra, R. Brouwer, 'Simple
Water Level Controller for Irrigation and Drainage Canals', J.
of Irr. and Drainage, 125(4), p. 189-195
More information on our method of modelling irrigation canals can be
 J. Schuurmans, A. Hof, S. Dijkstra,
O.H. Bosgra, R. Brouwer, 'Simple Water Level Controller for Irrigation
and Drainage Canals', J. of Irr. and Drainage, 1999, ASCE, 125(4),
 Overloop, P.J. van, Schuurmans, J., Brouwer, R., Burt, C.M., 'Multiple Model Optimization of PI-Controllers on Canals', Journal of Irrigation and Drainage Engineering, 2005.
 Overloop, P.J. van, Schuurmans, W., Brouwer, R., 'Model Predictive Control of water systems in the Netherlands', USCID-Proceedings International Conference, Phoenix, 2003.
¹Any of this references can be obtained by contacting firstname.lastname@example.org