A.J. Garrido

An adaptive sliding mode control law for induction motors using field oriented control theory

In this paper, an indirect field-oriented induction motor drive with a sliding-mode controller is presented. The proposed sliding-mode control law incorporates an adaptive switching gain that avoid calculating an upper limit of the system uncertainties. The design also includes rotor speed computation from measured stator terminal voltages and currents. The calculated speed is used as feedback in an indirect vector control system achieving the speed control without the use of shaft mounted transducers. Stability analysis based on Lyapunov theory is also presented, to guarantee the closed loop stability. Finally simulated results show on the one hand that the proposed controller with the proposed estimator provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to plant parameter variations and external load disturbances

Control strategies for OWC wave power plants

The present work deals with the improvement of OWC-Wells turbine-generator systems by adequately choosing the applied control scheme. For this purpose, two different control strategies are presented and compared. In the first one, the control system does appropriately adapt the slip of the induction generator according to the pressure drop entry. The second control strategy consists of a traditional control of the OWC air valve. It is demonstrated that the proposed rotational speed control design adequately matches the desired relationship between the slip of the induction generator and the pressure drop input, whilst the valve control using a traditional PID controller successfully governs the flow that modulates the pressure drop across the turbine.

Ride through of OWC-based wave power generation plant with air flow control under symmetrical voltage dips

The suitability of distributed power generation systems working at medium and high capacity as it is the case of wave power generation plants, requires a reliable Fault-Ride-Through capability. When a grid fault occurs on the transmission system, the speed of the turbo-generator group increases uncontrolled, the induction generator injects large peak currents that can potentially damage the rotor converters and the plant tends to increase the reactive power consumption, so that it might intensify the voltage dip and contribute to the collapse of the power network. A simple solution would be the automatic disconnection of the plant from the grid in response to the power fault, but this policy could lead to a series of chain disconnections that would produce a massive power network failure. This is why new Grid Codes oblige the distributed power generation systems to remain connected to the power network, even in case of balanced voltage dips. In this paper, an Oscillating Water Column (OWC)-based wave power generation plant equipped with a Doubly Fed Induction Generator is modeled and controlled to overcome these balanced grid faults. The improvement relays on the implementation of a control scheme that suitably coordinates the air flow control, the crowbar, the rotor and the grid side converters to allow the plant to remain in service during the grid fault, and to contribute to its attenuation by supplying reactive power to the network. The simulated results show how it is obtained a great reduction in the rotor currents, improving the transient power stability and avoiding the rotor acceleration, complying with new Grid Codes requirements.

Control for voltage dips Ride-Through of Oscillating Water Column-based wave power generation plant equipped with Doubly-Fed Induction Generator

One of the main problems arising when dealing with Oscillating Water Column-based wave power generation plants equipped with Doubly-Fed Induction Generator, is the need of an adequate Fault-Ride-Through during voltage drops. In this paper it is proposed an innovative Fault-Ride-Through solution consisting of a control scheme that suitably coordinates the air flow control, the active crowbar and the variable frequency converter, fulfilling the Grid Code. Besides, the variety of cases presented due to different sea states (amplitude and frequency) and characteristics of the grid fault (voltage drop and fault period), makes necessary to adequately modify the references used by the controllers in order to achieve the desired Fault-Ride-Through capability. That is, the application of the same controller references for different sea scenarios, provoke different responses of the plant for the same type of grid fault. In the same way, the application of the same controller references to the plant working under the same sea scenario when a grid fault of different voltage drops occurs on the transmission system, causes different reactions in the wave power plant. In this sense, it has been also implemented a control that adapts the controller references according to the pressure drop and voltage reduction, improving the controllability of the active and reactive power and the Fault-Ride- Through capability during voltage drops.

Space-State Modeling and Control of Tokamak Reactors

Abstract Nuclear fusion has the potential to produce unlimited, clean energy, which presents itself as a reliable energy supply but it also helps to stop the threat of climate change that faces the world nowadays. However, to sustain the pulse duration long enough to produce the necessary energy, new controls have to be developed, composing a new application area of Control Engineering, with new and interesting challenges for the control community. In this sense, this paper deals with the modeling of tokamak nuclear fusion reactors. In order to control the creation of unstable modes in fusion processes, it is necessary to derive numerical models suitable for control strategies. The model presented in this paper addresses flux and energy conservation issues, discussing the mechanisms behind the creation of uncontrollable modes. The dynamics of the system is given by means of the energy functions which are solved for the currents in the structure, plasma current and plasma position. Thus, the equations for the state variables are derived based on the Hamiltonian equation of motion. In order to solve this system numerically, this model is linearized around an operation point by taking a Newton-Raphson step. Besides, the system output is completed by considering the equations for the flux and the poloidal field. Finally, the resulting low-order linear model is modified so as to obtain the corresponding state-space model which is verified by means of numerical experiments.

Design of fractional hold circuits for output reconstruction in discretized systems

The design of fractional order-holds (FROH) of correcting gains ß ∈[−1, 1] (potentially and possibly including zero-order-holds, ZOH with ß=0, and first-order-holds, FROH with ß=1) is discussed related to achieving output deviations being close with respect to its sampled values. A squared error time- integral between the current output and its sampled values is minimized to yield the appropriate correcting gain of the FROH in an analytic way.

An expert network for obtaining approximate discrete-time models for LTI systems under real sampling using parameter identification

In this paper, we present an expert scheme designed to obtain discrete transfer functions for LTI systems under real sampling of finite duration rather than an instantaneous ideal one. For this purpose, the expert network handles two different identification methods to derive parametric discrete models techniques of reduced mathematical complexity from measured input-output data series. One of the methods is based on a typically used least-squares minimization, while the other one is based on Leverriers algorithm; that is, using a data series of the impulse response of the system to identify a parametric discrete model. These techniques are of particular practical interest when the continuous-time system is unknown or when dealing with discrete-time systems whose analytical expression become very complex due, for instance, to the use of finite duration real sampling. The expert network improves the discretization process implementing a biestimation mechanism that switches to the model that provides a better performance at each considered estimation instant for different values of the hold order.

Semi-heuristically obtained discrete models for LTI systems under real sampling with choice of the hold device

In this paper, we present two different filter-based identification methods to obtain discrete transfer functions for LTI systems under real sampling of finite duration rather than an instantaneous ideal one. The first method is based on a typically used least-squares minimization, while the second one is based on the Leverrier algorithm; that is, using a data series of the impulse response of the system to identify a parametric discrete model. This second method, being also an approximated technique, provides an algebraic result at least for the first computed data of the series. The main idea is to use semi-heuristic techniques of reduced mathematical complexity to derive parametric discrete models from measured input-output data series. These methods are of particular practical interest when the continuous-time system is unknown or when dealing with discrete-time systems whose analytical expression become very complex due, for instance, to the use of finite duration real sampling. This is the case of the problem treated in the application, where the proposed discretization technique allows a simple and accurate description of the discrete system. The identification techniques are also used to improve the discretization process in the context of a bi-estimation scheme that switches to the model that provides a better performance at each considered estimation instant, which is also used to compare the two techniques.

Impulsive Vaccination for an Epidemiology Model

This research is supported by the Spanish Government through Grants DPI2012-30651 and DPI2015-64766-R

Some Preliminary Results on an SEIARD Epidemic Model with Vaccination and Antiviral Treatment Controls and Dead-Infective Culling Action

This paper studies the non-negativity and stability properties of the solutions of a newly proposed SEIADR model which incorporates asymptomatic and dead-infective subpopulations to those defining the standard SEIR model and, in parallel, it incorporates feedback vaccination and antiviral treatment controls.