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- Robust control of a Thermal Unstable PDE systemPublication . Igreja, José; Lemos, João M.Some distributed parameter systems with irrational transfer function can be written into an infinite factorized quotient for dynamic analysis and control design purposes. Hence, high accuracy approximate time solutions and frequency uncertainty bounds can be computed exactly, enabling early lumping in robust controller design. In this paper the focus is on finding a block factorization for a thermal unstable solid propellant rocket model, and design a near optimal robust finite dimensional controller.
- Modeling for control design of a multi-reach water canalPublication . Caiado, Daniela V.; Lemos, João M.; Igreja, JoséThis article addresses the problem of obtaining reduced complexity models of multi-reach water delivery canals that are suitable for robust and linear parameter varying (LPV) control design. In the first stage, by applying a method known from the literature, a finite dimensional rational transfer function of a priori defined order is obtained for each canal reach by linearizing the Saint-Venant equations. Then, by using block diagrams algebra, these different models are combined with linearized gate models in order to obtain the overall canal model. In what concerns the control design objectives, this approach has the advantages of providing a model with prescribed order and to quantify the high frequency uncertainty due to model approximation. A case study with a 3-reach canal is presented, and the resulting model is compared with experimental data. © 2014 IEEE.
- Energy management in buildings with intermittent and limited renewable resourcesPublication . Barata, Filipe; Igreja, JoséThis work reports a contribution, in a model predictive control multi-agent systems context, introducing a novel integrative methodology to manage energy networks from the demand-side point of view, in the strong presence of intermittent energy sources, including energy storage in households or car batteries. In particular, the article presents a control-based solution for indoor comfort, which, in addition, optimizes the usage of a limited shared energy resource. The control management is applied, in a distributed way, to a set of so-called thermal control areas (TCAs) and demand units, with the objective of minimizing the cost of energy while maintaining the indoor temperature within the comfort zone bounds, and simultaneously not exceeding a limited amount of shared renewable energy. The thermal control areas are, in general, thermodynamically connected, and are also coupled by energy interrelation constraints established in the particular optimization solution. Energy management is performed with a fixed sequential order established from a previously carried out auction, wherein the bids are made by each unit's demands, acting as demand-side management agents, based on the daily energy price. The developed solution is explained by a basic algorithm that has been applied to different scenarios, and the results have been compared so as to illustrate the benefits and flexibility of the proposed approach, showing less energy consumption and a 37% cost saving.
- Wind energy conversion system control using distinct controllers for different operating regionsPublication . Viveiros, C.; Melicio, Rui; Igreja, José; Mendes, VictorThis paper presents a control strategy based on two distinct controllers for different operating regions applied to a wind turbine benchmark. In previous works, we proposed the control of a wind turbine using two distinct controllers for all operating regions. The contribution of this work focus on the use of two distinct controllers for two different operation regions, the fuzzy proportional integral controller in the partial load region, i.e., Region II, and the use of model predictive controller in the full load region, i.e., Region III. The distinct controllers applied on the different operation regions are compared to a standard controller and the simulation results show the efficacy of the proposed control approach.
- On performance of distributed model predictive control in power system frequency regulationPublication . Monteiro, Luís M.; Igreja, JoséThis paper describes the implementation of a distributed model predictive approach for automatic generation control. Performance results are discussed by comparing classical techniques (based on integral control) with model predictive control solutions (centralized and distributed) for different operational scenarios with two interconnected networks. These scenarios include variable load levels (ranging from a small to a large unbalance generated power to power consumption ratio) and simultaneously variable distance between the interconnected networks systems. For the two networks the paper also examines the impact of load variation in an island context (a network isolated from each other).
- The hydraulic hammer effect in solar tower fluid circuit temperature controllerPublication . Igreja, José; Marakkos, Costas; Lemos, Joao MThis article addresses the possible occurrence of hydraulic hammer effects in solar power towers and the limitations they impose on the response bandwidth of the control loop that governs the valve actuating on heating fluid flow. The partial differential equations that model the traveling waves associated to the hammer effect are solved with different methods. A finite dimensional approximation of the exact solution, by a transfer function with a finite number of poles is obtained. It is concluded that, for the speed of response of the temperature controller associated to the valve, there is no danger of inducing hydraulic hammer effects that can damage the equipment.
- LPV water delivery canal control based on prescribed order modelsPublication . Caiado, Daniela V.; Lemos, João M.; Igreja, JoséThis article addresses the problem of designing an LPV controller for a water delivery canal based on reduced complexity linear models with a priori chosen order. For that sake, by applying a method based on the Laplace transform and the linearization of the Saint-Venant equations, a finite dimensional rational transfer function is obtained for each canal reach. An LPV gain-scheduling controller that relies on H1 optimization is then designed for local upstream canal control. The scheduling variables are the inlet canal flow and the downstream-reach mean level. The uncertainty bound is computed on the basis of the high frequency error of the frequency response of the model used with respect to the one of the infinite-dimensional model by linearizing the Sain-Venant equations. This approach has the advantage of yielding na LPV controller that relies on a model with specified complexity and to relate model uncertainty to physical canal parameters, allowing operation over an extended envelop of water flow and level equilibria.
- Distributed MPC for Thermal Comfort and Load Allocation with Energy AuctionPublication . Barata, Filipe André de Sousa Figueira; Igreja, José; Neves-Silva, RuiThis paper presents a distributed predictive control methodology for indoor thermal comfort that optimizes the consumption of a limited shared energy resource using an integrated demand-side management approach that involves a power price auction and an appliance loads allocation scheme. The control objective for each subsystem (house or building) aims to minimize the energy cost while maintaining the indoor temperature inside comfort limits. In a distributed coordinated multi-agent ecosystem, each house or building control agent achieves its objectives while sharing, among them, the available energy through the introduction of particular coupling constraints in their underlying optimization problem. Coordination is maintained by a daily green energy auction bring in a demand-side management approach. Also the implemented distributed MPC algorithm is described and validated with simulation studies.
- Performance assessment of a wind energy conversion system using a hierarchical controller structurePublication . Viveiros, Carla; Melício, Rui; Igreja, José; Mendes, VictorThis paper deals with a hierarchical structure composed by an event-based supervisor in a higher level and two distinct proportional integral (PI) controllers in a lower level. The controllers are applied to a variable speed wind energy conversion system with doubly-fed induction generator, namely, the fuzzy PI control and the fractional-order PI control. The event-based supervisor analyses the operation state of the wind energy conversion system among four possible operational states: park, start-up, generating or brake and sends the operation state to the controllers in the lower level. In start-up state, the controllers only act on electric torque while pitch angle is equal to zero. In generating state, the controllers must act on the pitch angle of the blades in order to maintain the electric power around the nominal value, thus ensuring that the safety conditions required for integration in the electric grid are met. Comparisons between fuzzy PI and fractional-order PI pitch controllers applied to a wind turbine benchmark model are given and simulation results by Matlab/Simulink are shown. From the results regarding the closed loop point of view, fuzzy PI controller allows a smoother response at the expense of larger number of variations of the pitch angle, implying frequent switches between operational states. On the other hand fractional-order PI controller allows an oscillatory response with less control effort, reducing switches between operational states. (C) 2015 Elsevier Ltd. All rights reserved.
- Fractional order control on a wind turbine benchmarkPublication . Viveiros, Carla; Melício, Rui; Igreja, José; Mendes, VictorThis paper is about a hierarchical structure with an event-based supervisor in a higher level and a fractional-order proportional integral (FOPI) in a lower level applied to a wind turbine. The event-based supervisor analyzes the operation conditions to determine the state of the wind turbine. This controller operate in the full load region and the main objective is to capture maximum power generation while ensuring the performance and reliability required for a wind turbine to be integrated into an electric grid. The main contribution focus on the use of fractional-order proportional integral controller which benefits from the introduction of one more tuning parameter, the integral fractional-order, taking advantage over integer order proportional integral (PI) controller. Comparisons between fractional-order pitch control and a default proportional integral pitch controller applied to a wind turbine benchmark are given and simulation results by Matlab/Simulink are shown in order to prove the effectiveness of the proposed approach.
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