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Supervisory Water Level Control for Cascaded River Power Plants


Gabriela Glanzmann, Martin von Siebenthal

vol. AUT04-11

River power plants are man-made constructions, which are built into the course of a river to generate electrical energy. The discharge through the facilities of a power plant must be adjusted such that the water level at a pre-specified point closely upstream is kept within given bounds. The control method currently used employs local PI controllers with additional feed-forward terms. The tuning of these controllers is demanding and constraints can not be handled explicitly. This often yields large unnatural discharge variations resulting in unsatisfactory control performance. In cascades of river power plants, these discharge variations are unpredictably amplified affecting nature and imposing problems on navigation. In this thesis, a supervisory controller for a cascade of river power plants is designed taking advantage of the coordination between multiple sites. Model Predictive Control (MPC) is applied using an internal linear, discrete time model of the power plant cascade derived from the Saint Venant equations. The objective of the controller, which is to keep the pre-specified water levels within given bounds and to dampen discharge variations, is expressed in a quadratic cost function subject to soft constraints. The optimal control problem leads to a standard Quadratic Program (QP) that can efficiently be solved using standard optimization tools. The model states are estimated from measurements of two distinct water levels per power plant with a Kalman filter. To improve the state estimation and to reduce computation time of the involved QP, balanced state reduction is applied. The main advantages of the proposed control scheme are: coordinated control moves for the cascade taking into account the interaction between the power plants, preemptive control moves for anticipated disturbances, explicit constraint handling and straightforward tuning. In closed-loop simulations with the commercial river hydraulics program FLORIS, the proposed control concept is compared with the currently implemented PI-type system demonstrating the achieved enhancements. In particular, the damping of disturbances is significantly improved while the water level constraints are met.


Type of Publication:

(12)Diploma/Master Thesis

M. Morari

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% Autogenerated BibTeX entry
@PhdThesis { GlaSie:2004:IFA_2248
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