Ricardo J. Mantz

Sliding mode control of wind energy systems with DOIG-power efficiency and torsional dynamics optimization

Wind turbines with double output induction generators can operate at variable speed permitting conversion efficiency maximization over a wide range of wind velocities. However, random wind fluctuations, wind shear and tower shadow, may excite the oscillation mode of the mechanical system, producing large torque ripple. Consequently, damage to drive train components and power quality problems may occur. In this paper, a sliding mode control is developed which provides a suitable compromise between conversion efficiency and torque oscillation smoothing. The resultant sliding dynamics is completely robust to uncertainties in the electrical variables and parameters. In addition, to prevent windup problems due to saturation, a combined sliding surface that incorporates such limitations is proposed.

Dynamical variable structure controller for power regulation of wind energy conversion systems

The paper addresses the problem of output power regulation of fixed-pitch variable-speed wind energy conversion systems. Operation is constrained by practical reasons to the low-speed side of the turbine power-speed curve. Unfortunately, this region is characterized by a nonminimum phase dynamics which is an obstacle to perform the regulation task. A dynamical variable structure controller is developed that accomplishes the control objective despite this limitation. The proposed control strategy presents attractive features such as robustness to parametric uncertainties of the turbine and generator as well as to electric grid disturbances.

A wind turbine emulator based on a dual DSP processor system

Abstract In this paper the principles and structure of a wind turbine emulator (WTE) are described. The WTE is a versatile system specially designed for the purpose of developing and testing new control strategies for wind energy conversion systems. The WTE is built around a processor module, which controls a separately-excited DC motor. The core of the processor module is a dual DSP system working in a tightly-coupled architecture. The WTE provides a friendly environment to readily modify wind speed conditions, change turbine parameters and supervise system variables. Experimental results from the WTE coupled to a grid-connected induction generator are analyzed.

Complementary rules to Ziegler and Nichols' rules for a regulating and tracking controller

Abstract Traditionally, PID controllers are designed either as regulating or as tracking controllers because, usually, it is not possible to fulfil both functions simultaneously. Designing rules complementary to Ziegler and Nichols ones are introduced. They allow, using a special connection of the classical PID, the tracking behaviour to be improved without modifying the regulating characteristics.

Brief paper: Multivariable PID control with set-point weighting via BMI optimisation

The paper focuses on the design of multivariable PID controllers with set-point weighting. The advantage of this PID structure is that the responses of the system to disturbances and to changes in the set-point can be adjusted separately. The proposed design methods rely on the transformation of the tuning of the controller gains into a static output feedback (SOF) problem. Hence, multivariable PID controllers can be designed by solving an optimisation problem with bilinear matrix inequalities (BMIs). The paper addresses the design of both time-invariant and gain-scheduled robust controllers. All of the tuning methods discussed through the paper are based on a PID structure with filtered derivative term, thus guaranteeing the well-posedness of the closed loop system.

An adaptive feedback linearization strategy for variable speed wind energy conversion systems

This paper presents a control strategy based on adaptive feedback linearization intended for variable speed grid-connected wind energy conversion systems (WECS). The proposed adaptive control law accomplishes energy capture maximization by tracking the wind speed fluctuations. In addition, it linearizes the system even in the presence of turbine model uncertainties, allowing the closed-loop dynamic behaviour to be determined by a simple tuning of the controller parameters. Particularly, the attention is focused on WECS with slip power recovery, which use a power conversion stage as a rotor-controlled double-output induction generator. However, the concepts behind the proposed control strategy are general and can be easily extended to other WECS configurations. Copyright

LPV Wind Turbine Control With Anti-Windup Features Covering the Complete Wind Speed Range

This paper addresses the control of a variable-speed variable-pitch wind turbine in the whole wind speed range. To this end, a linear parameter varying anti-windup (AW) controller is proposed as part of a control structure focused on improving the transition between low- and high-wind speed operations. The control structure is similar to classical PI controls used in commercial wind turbines. However, a more advanced gain-scheduled controller and AW compensation are proposed. As a consequence, the new control scheme is capable of improving the behavior of the wind turbine in the transition zone and provides better stability margins. The proposed control was evaluated in a 5-MW wind turbine benchmark and compared with a classical control scheme. To this end, very demanding and realistic testing scenarios were built using the FAST aeroelastic wind turbine simulator as well as standardized wind speed profiles.

Harmonic series compensators in power systems: their control via sliding mode

This paper deals with harmonic current compensation in power systems using shunt passive and series active filters. It is shown how constraints of the active filters can notoriously degrade the performance of the compensating system. The use of variable structure system theory is suggested for analysis and design of series active filters. Sliding mode control strategies to improve harmonic rejection are proposed, and active filters with different switching-ripple filters are considered. These control strategies provide robustness to active filter modeling errors and external disturbances.

Contribution of wind farms to the network stability

This paper presents how wind farms, adequately controlled, can improve the stability properties of a power system. Considerations of modeling of wind farms are presented. Then, the wind farm control laws under normal conditions are presented. Next, other wind farm control laws are added to the first ones looking for damping the system electromechanical oscillations after a network disturbance. These laws are based in the capability of the double fed induction generators of feeding active and reactive powers. Finally, some simulations are shown to support the theoretical considerations

Dynamical sliding mode power control of wind driven induction generators

Summary form only given as follows. This paper concerns power regulation of variable-speed wind energy conversion systems. These systems have two regions of operation, depending on the tip speed ratio of the wind turbines. They are distinguished by a minimum phase behavior in one of these regions and a nonminimum phase one in the other. A sliding mode control strategy is proposed that assures stability in both regions of operation and imposes the ideally designed feedback control solution in spite of model uncertainties. Moreover, power regulation by the proposed sliding control in the minimum phase region is completely robust to wind disturbances and parameter uncertainties.