Luis Alvarez-Icaza

Real-time identification of wind turbine rotor power coefficient

A scheme for real-time identification of a wind turbine power coefficient curve is presented. Knowledge of this curve is important to maximize the generated electric power. The precise shape of this curve is difficult to predict as it depends on several factors: air density, humidity, temperature, wind speed and tip speed. Once the power coefficient curve is found, it is possible to propose optimal operation points for the turbine that are fed to a controller for the electric generator. Simulation results show good performance of the identification scheme

Passivity-based control for variable speed constant frequency operation of a DFIG wind turbine

A standard passivity based control for a double fed induction generator of a wind turbine is presented. The control problem is posed as a variable speed constant frequency operation with the aim to maximise the generated electric power. The controller is designed in such a way that the dual control objective, unity power factor in the stator side and speed tracking in the mechanical port, are satisfied guaranteeing internal stability. The proposed scheme is the first attempt to approach the speed tracking operation from the energy dissipation (passivity) perspective. Simulation results show good performance of the control scheme for wind speeds in different operating regimes.

Identification of seismically excited buildings with two orthogonal horizontal components

An algorithm is presented here to identify parameters of linear models of buildings under orthogonal bi-dimensional seismic excitation, using acceleration measurements of sensors arbitrarily arranged on the stories, in real time. The model considers three degrees of freedom for each story and uses an efficient reparameterization of the least-squares algorithm that allows a very important reduction in the number of calculations, when compared with the standard formulation. Results obtained from simulations and with data obtained from instrumented buildings confirm the efficacy of the proposed method.

3D IDENTIFICATION OF BUILDINGS SEISMICALLY EXCITED

Abstract An algorithm to identify the parameters of a 3D model of a building subjected to two orthogonal components of seismic excitation is presented. A convenient reparameterization is proposed for a least-squares algorithm that allows an important reduction in the order of the covariance matrix, when compared with the standard formulation. This reduction facilitates real time implementation of the algorithm. Simulation results for a three stories building, that confirm analytical findings, are presented.

Adaptive compensation of dynamic friction in an industrial robot

A new dynamic model to describe joint friction in a industrial robot is presented. This model is an extension of the popular LuGre dynamic friction model. However, the description of the Stribeck effect is modeled with a first order nonlinear differential equation. This yields a second order dynamic friction model that still preserves the intuitive base of previous models, reproduces the pseudo-steady state behavior and offers the same input-output properties. The advantage with respect to other dynamic friction models is in the possibility of identifying all the relevant parameters. This particularly important when this parameters change with time making it difficult to continuously calibrate the model. The validity of a dynamic friction adaptive compensation scheme is verified by means of experimental results.

Passivity based control of under-actuated mechanical systems with nonlinear dynamic friction

Passivity-based control of under-actuated mechanical systems with nonlinear friction effects in the generalized coordinates of motion is analyzed in this paper. Nonlinear friction is modeled with a modified LuGre dynamic friction model. The internal states of the dynamic friction model are incorporated as generalized coordinates in a port-controlled Hamiltonian formulation for the complete mechanical system in such a way that all passivity properties of this formulation are preserved for the extended generalized coordinates system. Interconnection and damping assignment passivity-based control laws are developed for the models of two case studies: a building with a magneto-rheological damper and a double pendulum. Simulation results are also presented.

Reduced order dynamical model for supercapacitors

A novel dynamical model for a single cell electric double-layer capacitor is proposed. The model was derived from a distributed-parameter electrochemical model, first reformulated and then approximated to reduce its order. Finite dimension approximations were obtained by applying finite differences, finite element and differential quadrature semidiscretization methods. The best approach was obtained with differential quadrature and the final result is a linear time invariant dynamical model relating the input current and the output voltage in the supercapacitor. The model has physical meaning, high accuracy, low order and few parameters, is controllable, observable and well suited for control design, dynamical analysis and numerical implementation.

Modeling mechanical torque in wind turbines

The mechanical torque of a wind turbine is modeled from a friction phenomenon perspective. Two models for the torque generated are proposed based on a relative speed between the wind and turbine blades. The main advantage of these models is the possibility of using real-time standard identification techniques for recovering their parameters value. Models are compared with a heuristic reference model showing good performance.

Power flow control strategies in parallel hybrid electric vehicles

Two control strategies for power flow control in hybrid electric vehicles (HEVs) with parallel configuration and a planetary gear system as a power coupling device between the internal combustion engine and the electric machine are proposed in this paper. The aim of both strategies is to determine, for a given driving cycle, an appropriate mixture of the power provided by the two engines. Performance is measured not only in terms of fuel consumption; driving cycle tracking and preservation of energy in the bank of batteries are also considered. The first strategy, named the PGS strategy as it is designed around the planetary gear system, is heuristic, inspired by bang–bang optimal control formulations and has low computational load, while the second is an optimal one derived from Pontryagin’s minimum principle (PMP). It is shown that, under appropriate choice of the weighting parameters in the Hamiltonian of the PMP, both strategies give very similar results and, therefore, that the PGS strategy corresponds to a feasible solution to an optimization problem. Both strategies can be implemented in real time, however, the PGS strategy is easier to tune. Tuning of the strategies’ parameters is independent of the driving cycle. The power flow control laws are continuous and enforce the use of the internal combustion engine with the maximum possible efficiency. The strategies are tested with simulations of a power train of a hybrid diesel–electric bus subjected to the demands of four representative urban area driving cycles. Although optimization solutions are based on simplified dynamic models, simulation results are verified with more detailed dynamic models of the HEV main subsystems. This allows us to evaluate the accuracy of the results and to verify the hypothesis established in the optimization formulation. Simulation results indicate that both strategies attain good fuel consumption reduction levels.

Hysteretic Cell Transmission Model

A new macroscopic model for traffic in freeways, the Hysteretic Cell Transmission Model (HCTM), is presented. The model is based on the Cell Transmission Model (CTM) and incorporates a feature to reproduce the capacity drop phenomenon observed in real traffic. An auxiliary dynamic state is included that induces hysteretic behavior on the density-flow relationship. The hysteresis is dependent on the time derivative of the density in a particular cell and allows to change the congested flow traffic wave velocity in the fundamental diagram and, with this, to produce a capacity drop. A Lyapunov stability analysis for a stretch of highway is presented that is compared with a similar analysis for the CTM. Simulation results show that the capacity of a congested stretch of highway is reduced when its vehicular density is decreasing.