This paper deals with the design, modeling and control of a Tidal Stream Generator (TSG) system including a tidal turbine, a rotor shaft and a Doubly Fed Induction Generator (DFIG). Below high tidal speed the system is regulated so that for every tidal velocity reaches the maximum power. A rotational speed control based-Maximum Power Point Tracking (MPPT) for a TSG is investigated to provide the suitable rotational speed to the system in order to track the maximum power and thus keeping the pitch angle null. Two study cases were proposed to test the performance of the control strategy. The obtained results show that the proposed control provide satisfactory tracking of the MPPT reference.

This paper deals with the modelling, simulation and control of a wave power plant installed in the northern cost of Spain. This plant is an onshore Oscillating Water Column (OWC) composed of a Wells turbine coupled to a Doubly Fed Induction Generator (DFIG). The power generated by the OWC is limited by the stalling behavior, a feature of the Wells turbine; therefore an airflow control is proposed in order to avoid the stalling phenomenon. This is achieved by regulating the airflow in the turbine duct by means of the throttle valve. The proposed control is based on a Proportional Integral (PI) controller. The results shows that the proposed control strategy provides a significant improvement of the generated power.

After the 2015 United Nations Climate Change Conference (COP21) the interest for clean and renewable energy is high priority in global energy policy. In this sense, the ocean offers a great potential for energy harnessing. However, in the path to commercialization, conversion systems still lack maturity. Oscillating water column (OWC) power plants are among the most promising cost-effective and ecologically compatible technologies. The NEREIDA MOWC wave power plant, located on the Basque coast of Mutriku, is a clear example of this principle. In addition, the maximum power point tracking (MPPT) strategy, which has already been used successfully in other renewable energy systems, stands out as one of the most useful schemes. In this context, this paper focuses on the implementation of a novel MPPT control approach for the OWC systems in order to optimize the power delivered to the grid. For this purpose, a full wave-to-wire plant model is introduced, and a new MPPT-based control scheme is presented. The controller continuously adjusts the energy conversion of the doubly fed induction generator according to an established MPPT curve so as to optimize the power generated. In order to demonstrate the goodness and feasibility of the proposed control scheme, its behavior is tested and compared in two representative case studies of both uncontrolled and controlled plants. In the first case, an air valve control is employed, and in the second case, an MPPT-based control strategy has been implemented. Results show that the proposed MPPT-based control successfully matches the optimum rotational speed, allowing maximum active power generation.

The control of plasma in nuclear fusion has been revealed as a promising application of Control Engineering, with increasing interest in the control community during last years. In this paper it is developed a control-oriented linear model for the control of plasma current. For this purpose, it is provided a summary of the background necessary to deal with control problems in tokamak-based nuclear fusion reactors as it is the case of the future ITER tokamak. Besides, it is also given a review of the most used simulators and plasma models, with the aim of providing an adequate background for control engineers to derive their own control-oriented model or to choose the appropriate existing one. Finally, the proposed plasma model performance is proven in a current drive profile trajectory tracking problem using a modified anti-windup PID-based control scheme.

This paper presents a new variable structure control law that improves the performance of the control law presented in our previous work [2]. The new smoothed control law reduces the chattering phenomenon of the previous one, and therefore implies less activity control and diminish the mechanical fatigue of the system. The proposed design employs the so called vector (or field oriented) control theory for the induction motor drives and the designed control law is based on sliding-mode algorithm that overcomes the system uncertainties. The proposed sliding-mode control law incorporates an adaptive switching gain to avoid calculating an upper limit of the system uncertainties. The stability analysis of the proposed controller under parameter uncertainties and load disturbances is provided using the Lyapunov stability theory. Finally simulated results show the improvements of the new smoothed control law.

A novel sensorless adaptive robust control law is proposed to improve the trajectory tracking performance of induction motors. The proposed design employs the so called vector (or field oriented) control theory for the induction motor drives and the designed control law is based on an integral sliding-mode algorithm that overcomes the system uncertainties. The proposed sliding-mode control law incorporates an adaptive switching gain to avoid calculating an upper limit of the system uncertainties. The proposed design also includes a new method in order to estimate the rotor speed. In this method, the rotor speed estimation error is presented as a first order simple function based on the difference between the real stator currents and the estimated stator currents. The stability analysis of the proposed controller under parameter uncertainties and load disturbances is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand that the proposed controller with the proposed rotor speed 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

This paper focuses on the suboptimal regulation of multivariable discrete-time bilinear systems consisting of interconnected bilinear subsystems with respect to a linear quadratic optimal regulation criterion which involves the use of state weighting terms only. Three transformations are used in order to treat the scheme over an equivalent linear system. This leads to the appearance of quadratic weighting terms related to both transformed input and state variables. In this way, a Ricatti matrix-sequence allowing the synthesis of a standard feedback control law is obtained.

A new sensorless integral sliding mode control for induction motors which provides global asymptotic speed tracking in the presence of unknown parameters and load torque is presented. First, an improved method of speed estimation that operates on the principle of a speed adaptive flux and current observer has been proposed. An observer is basically an estimator that uses a plant model and a feedback loop with measured stator voltages and currents. Then a sliding mode controller with an integral switching surface is investigated. The stability analysis of the proposed controller under parameter uncertainties and load disturbances is provided using the Lyapunov stability theory. Finally simulated results show that the proposed controller with the proposed observer provides high-performance dynamic characteristics and that this scheme is robust with respect to plant parameter variations and external load disturbances.

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 Leverrier's 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.

The global uniform exponential stability independent of delay (g.u.e.s.i.d.) is investigated for a wide class of time-delay systems that may involve both point and distributed delays on finite intervals as well as infinitely distributed Volterra integro-differential dynamics. The stability problem is considered as a robust stability one with respect to an auxiliary system which may be defined very freely. The proposed method allows a very important generalisation related to the usual problem statement in the literature when the auxiliary system is defined by deleting the whole delayed dynamics. Conditions are established that ensure that the Laplace operator characterising the system has a bounded inverse on the closed complex right-half plane. The analysis is slightly modified for investigating uniform stability dependent of delay.