Distant Downstream Control Research Articles

Switched control of over-topping water channels

Automated open-water channels are used to deliver water for irrigation in an efficient manner. In the distant-downstream control architecture, water is released from upstream storage in response to downstream demand. In some situations, such as when large water off-takes stop suddenly or heavy rain starts, storage capacity in the channel can be insufficient, leading to a sharp water-level rise that might breach the top of the channel walls and flood surrounding areas. In this paper, a switching strategy is presented that, when safety thresholds are exceeded, releases excess flow into downstream pools where storage capacity is available or through escapes out of the channel.

Evaluating the Effects of Constructing a Tail Reservoir in a Canal with Automatic Distant Downstream Control

AbstractAlthough canal control automation has been generally disregarded in the irrigation modernization projects in Spain, regulation reservoirs formed part of most projects. Recent projects combi...

Decentralized string-stability analysis for heterogeneous cascades subject to load-matching requirements

A heterogeneous cascade of stable linear time-invariant subsystems is studied in terms of the spatial and temporal propagation of boundary conditions. The particular context requires constant spatial boundary conditions to be asymptotically matched by the interconnection signals along the string (e.g., to match supply to demand in steady state). Furthermore, the transient response associated with a step change in the spatial boundary condition must remain bounded across space in a string-length independent fashion. With this in mind, an infinite cascade abstraction is considered. A corresponding decentralized string-stability certificate for the desired behaviour is established in terms of the subsystem $$H_\infty $$H? norms, via Lyapunov-type analysis of a two-dimensional model in Roesser form. Verification of the certificate implies uniformly bounded interconnection signals in response to the following system inputs: (i) a square-summable (across space) sequence of initial conditions; and (ii) a uniformly-bounded (across time) finite-energy input applied as the spatial boundary condition (e.g., finite duration on-off pulse). The decentralized nature of the certificate facilitates subsystem-by-subsystem design of local controllers that achieve string-stable behaviour overall. This application of the analysis is explored within the context of a scalable approach to the design of distributed distant-downstream controllers for the sections of an automated irrigation channel.

The Effect of Design Parameters of an Irrigation Canal on Tuning of Coefficients and Performance of a PI Controller

AbstractThe performance and operation of irrigation networks can be improved using canal automation. This process requires the application of control systems. At the same time, the PI controller has been employed in different areas of the world. However, its adjustment for the different geometric and hydraulic conditions of canals is still considered a major problem for design. The design parameters of a canal such as bottom slope, roughness coefficient and side slope are among the determining factors of water flow dynamic behaviour. In this study, a distant downstream proportional integral feedback control with decouplers is designed for a base canal. By changing the value of design parameters in this canal, their effects on water flow behaviour and controller tuning were investigated. Canal characteristics were determined through a system identification process, and were also used to tune the controller. To simulate the control algorithms and evaluate their performance, a link of the SOBEK model and MATLAB software were used. To evaluate the performance of a well‐tuned controller during a given operation period, the maximum absolute error, integral of absolute magnitude of error and steady‐state error indicators were used. Generally, the result showed the bottom slope to have the most effect on water flow behaviour and tuning of the control algorithm. The effect of the roughness coefficient on the control algorithm and its performance is also more noticeable than the side slope. Copyright © 2015 John Wiley & Sons, Ltd.

Offtake Feedforward Compensation for Irrigation Channels With Distributed Control

In distant-downstream control of an irrigation network, there exists a tradeoff between the local performance requirement of regulating the water level in each pool to a given set point and the global performance requirement of attenuating the amplification of flows over gates in the upstream direction. Such a tradeoff is well managed by a distributed control that inherits the interconnection structure of the irrigation network. In addition, for each subsystem, to decrease the water-level deviation from its set point in response to large offtakes, the knowledge of the offtakes can be fed forward. This brief explores a systematic approach to the offtake feedforward compensation.

Control of a String of Identical Pools Using Non-Identical Feedback Controllers

In the distant-downstream control of irrigation channels, the interactions between pools and the internal time-delay for water to travel from upstream to downstream, impose limitations on global performance, i.e., there exists propagation of water-level errors and amplification of flows over gates in the upstream direction. This brief analyzes these coupling properties for a string of identical pools, both with identical feedback controllers and with non-identical feedback controllers. A definition of string stability in terms of bounded water-level errors and bounded flows is given. It is shown that for a string of an infinite number of pools, string stability cannot be achieved by decentralized distant-downstream feedback control mainly due to the internal time-delay for water to travel from upstream to downstream. Applying the analysis results on string stability to a string of a finite number of pools, i.e., using non-identical feedback controllers in a distant-downstream control structure such that the closed-loop bandwidths of the subsystems increase from downstream to upstream, a much better global performance can be achieved than in the case of using identical feedback controllers.

Adaptive predictive expert control of levels in large canals for irrigation water distribution

SUMMARYProportional integral (PI) control is the most frequently used method for controlling water levels in irrigation canals. For design purposes, simplified linear models are typically used to describe the series of pools that, separated by control gates, compose the whole canal. Common models are made by series connection of integrator plus time delay or integrator with time delay plus a zero, these models being obtained from the Saint‐Venant equations. However, it is known that hydraulic processes in irrigation canals are strongly nonlinear and present dynamics that are time varying depending on the operating point and the hydraulic conditions of the pool, so that the performance of PI controls may be reduced as the operating point moves far from the nominal design state. This paper presents the application of an adaptive predictive expert control (ADEX) for the distant downstream level control in irrigation canals trying to exploit their adaptive capability to efficiently achieve changes in the setpoint levels and disturbance rejection. Both PI and ADEX controllers are compared in simulation and in real field tests in the control of the end pool of the Canal Imperial de Aragón in Spain. Copyright © 2012 John Wiley & Sons, Ltd.

Simulation Study on the Influence of Roughness on the Downstream Automatic Control of an Irrigation Canal

The controllability of an irrigation canal depends on its physical characteristics, on the control algorithm used, and on the actual condition of the canal in relation to the algorithm tuning conditions. The flow conditions and controllability in an irrigation canal may change if the hydraulic friction changes. Great variations in friction were observed in an irrigation canal in Spain owing to the presence of Rhizoclonium hieroglyphicum, a type of algae that grows in clear water. Such large variations in friction may have a significant effect on the stability and performance of automatic canal controllers. Using the unsteady-state model Simulation of Irrigation Canal (SIC), the influence of roughness on the performance of the study canal under distant downstream control of its four coupled pools was investigated. A set of proportional-integral (PI) controllers was tuned for different values of Manning's n. The controller’s performance under real conditions is sensitive to the roughness conditions under which the control gains were tuned, and a method to robustly tune the gains of the PI controllers is proposed.

Stability and performance analysis of an irrigation channel with distributed control

For a string of pools with distant-downstream control, the internal time-delay for water transport from upstream to downstream does not only limit the local control performance of regulating water-levels at setpoints and rejecting offtake disturbances in each pool, but also impacts the global performance of managing the water-level error propagation and attenuating the amplification of control actions in the upstream direction. A distributed control scheme that inherits the interconnection structure of the plant is investigated. It is shown that the decoupling terms in the controller help to improve global closed-loop performance by decreasing the low-frequency gain of the closed-loop coupling. Moreover, the decoupling terms compensate for the influence of the time-delay by imposing extra phase lead-lag compensation in the mid-frequency range on the closed-loop coupling function.

Water-Level Difference Controller for Main Canals

The operation of main irrigation canals is complicated in situations in which the operator does not have full control over the canal inflow, or in which there are very long transmission distances from the point of supply, or both. Experienced operators are able to control the canal, but often supply errors are simply passed downstream, thus creating problems further down the system. In previous work, the writer showed that it is important to contain such errors and not let them pass downstream. With automatic upstream-level control, all flow errors are passed to the downstream end of the canal. Distant downstream water-level control requires full control of canal inflow. Without this, errors will occur at the upstream-most canal pool. An alternative scheme is offered here in which the canal check gates are controlled on the basis of the relative water-level error between adjacent pools. The scheme uses a simple linear model for canal pool response. The scheme is implemented as a multiple-input, multiple-output scheme and is solved as a linear quadratic regulator (LQR). Thus, all gates respond to relative deviations from water-level set point. The scheme works to keep the relative deviations in all pools the same. If inflow and outflow do not match, it effectively treats the canal as a storage reservoir. When in equilibrium, operators will be able to judge the actual flow rate mismatch by the rate of change of water levels. The scheme acts like a combination of upstream-level and distant downstream-level control. It was tested on a simulation model of the Central Main Canal at the Central Arizona Irrigation and Drainage District (CAIDD), Eloy, AZ.

Designing and evaluating control systems of the Dez main canal

AbstractIn the present study, a distant downstream proportional integral (PI) feedback control with decouplers and a local upstream PI feedback control were applied to the West main canal of the Dez irrigation system in Iran. The model of the proposed canal was formulated in the SOBEK simulation package. The control system was programmed in MATLAB. To evaluate the control system potential, simulations were done for two months of the real offtake schedule. The performance criteria of the maximum absolute error (MAE), the integral of absolute magnitude of error (IAE), and the steady state error (StE) were determined for each pool of the canal. The results indicated that the applied controllers have considerable potential to closely match the discharge at the downstream check structures with those ordered by water users while maintaining the water level throughout the length of the canal. The performance indicator values showed that the distant downstream feedback (FB) control as a centralized control with decouplers is a satisfactory controller for the Dez main canal. Hence, operational water management in the canal may be improved if a centralized controller is used rather than individual local controllers. It is strongly recommended to implement the distant downstream FB control with decouplers as a control system in the proposed canal. Copyright © 2009 John Wiley & Sons, Ltd.

Simulation of automatic control of an irrigation canal

Improved water management and efficient investment in the modernization of irrigation schemes are essential measures in many countries to satisfy the increasing demand for water. Automatic control of the main canals is one method for increasing the efficiency and flexibility of irrigation systems. In 2005, one canal in the irrigation scheme ‘Sector B-XII del Bajo Guadalquivir’ was monitored. This canal is representative of irrigation schemes in Southern Spain; it is divided into four pools and supplies an area of 5154 ha. Ultrasonic sensors and pressure transducers were used to record the gate opening and water levels at the upstream and downstream ends of each canal pool. Using the recorded data and the SIC (Simulation of Irrigation Canals) hydraulic model, two canal control options (local upstream control and distant downstream control) were evaluated using a PI (Proportional-Integral) control algorithm. First, the SIC model was calibrated and validated under steady-state conditions. Then the proportional and integral gains of the PI algorithm were calibrated. The controllers were tested using theoretical demand changes (constant outflow followed by a sudden demand increase or decrease) and real demand changes generated on the basis of a spatially distributed crop water balance that included a number of sources of variability (random and not random) in the determination of field irrigation timing and depth. The results obtained show that only the distant downstream controller was able to adjust quickly and automatically the canal dynamics to the varying water demands; it achieved this efficiently and with few spills at the canal tail, even when there were sudden and significant flow variations.

Downstream-Water-Level Control Test Results on the WM Lateral Canal

On steep canals, distant downstream-water-level control can be challenging. The Software for Automated Canal Management was developed, in part, to test various distant downstream water-level controllers. It was implemented on the WM canal of the Maricopa Stanfield Irrigation and Drainage District, Stanfield, Ariz. to compare the performance of various controllers. In 2004, Clemmens and Schuurmans used optimization to determine the coefficients for a variety of controllers. These controllers vary in their complexity from a series of simple, single-input-single-output, proportional-integral controllers to a fully centralized, multiple-input-multiple-output, optimal controller. The controller design also varies regarding which pools are under downstream, or upstream, control and according to the conditions (e.g., flow rate) assumed for controller design. These controllers were tested under actual operating conditions and with unscheduled disturbances. The results of these tests are presented in this paper.

Tuning of Robust Distant Downstream PI Controllers for an Irrigation Canal Pool. II: Implementation Issues

Based on the companion paper results, this paper presents a robust tuning method to tune a proportional integral (PI) controller that fulfills the design requirements for a single pool with different hydraulic conditions. The robust PI controller parameters are obtained analytically as a function of the physical parameters of the canal pool. Important implementation issues are also considered. Rules are provided for the sampling time selection in order to recover the continuous-time performance. When the sampling time is imposed, it has to be included in the controller design, by modifying the delay of the system. A simple way is proposed to take account of the gate opening as control action variable, instead of the upstream discharge. This robust PI tuning method is evaluated by simulation on a full nonlinear model of two different canal pools for different flow conditions and different implementations: continuous-time control, discrete-time control, using the discharge or the gate opening as control action variable. Simulation results show that the method leads to efficient realistic PI controllers for a canal pool.

Tuning of Robust Distant Downstream PI Controllers for an Irrigation Canal Pool. I: Theory

The paper proposes a new method to tune robust distant downstream proportional integral (PI) controllers for an irrigation canal pool. The method emphasizes the role of gain and phase margins in the controller design, by linking the selection of these robustness indicators to the time domain specifications. This leads to link the frequency domain approach used by automatic control engineers to the time domain approach used by hydraulic engineers. The maximum error corresponding to an unpredicted perturbation is shown to be directly linked to the gain margin and the settling time to the phase margin of the controlled system. The tuning method gives analytical expressions for the controller parameters as function of physical parameters of the canal pool in order to satisfy desired performance requirements. The model is first expressed in terms of dimensionless variables, in order to get generic tuning formulas. The dimensionless PI coefficients are then expressed as functions of time-domain performance requirements. The PI tuning method is evaluated by simulation on a full nonlinear model for a canal pool taken from the ASCE test cases.

H/sub /spl infin// control of an irrigation canal pool with a mixed control politics

This paper presents a method to design efficient automatic controllers for an irrigation canal pool, that realize a compromise between the water resource management and the performance in terms of rejecting unmeasured perturbations. This mixed controller design is casted into the H/sub /spl infin// optimization framework, and experimentally tested on a real canal located in Portugal. The experimental results show the effectiveness of the method. We also interpret classical control politics for an irrigation canal (local upstream and distant downstream control) using automatic control tools, and show that our method enables to combine both classical politics, keeping the distant downstream control water management while recovering the local upstream control real-time performance with respect to the user.