Jaime Alvarez

Global nonlinear control of a continuous stirred tank reactor

Abstract A chemical reactor, modelled by two nonlinear ordinary differential equations with a manipulable input, is controlled by means of a nonlinear control law. A differential geometric approach enables the characterization, in a global sense, of the structural solvability of the nonlinear control problems. The structural characterization consists in establishing a well-defined region of the state space where global controllability, stability and transformability to a linear equivalent can be assured. The nonlinear controller arises after expressing a linear feedback, for an equivalent system, in original coordinates. The tuning of the controller is done by pole placement in the equivalent system. The nonlinear controller allows for process regulation of stable stationary points and stabilization of unstable ones. Proportional and proportional-integral designs for the equivalent system are considered. By numerical simulations, the performance of the controller is favorably compared and contrasted with the performance of conventional controllers.

Some critical aspects in sliding mode control design for the boost inverter

In this paper some critical aspects for the design of sliding mode control applied to the boost inverter are presented, including a theoretical analysis and the implementation of the control strategy. The SMC has been proposed in different papers as an option to improve the dynamic response of the electronics circuit. In this paper several design issues related to the theory as well as to the practical implementation of the SMC are discussed. A converter, which has excellent features like boost and inverting functions at the same time (boost inverter), is used as an example design.

Nonlinear disturbance decoupling control of a binary distillation column

Abstract An application of nonlinear feedback theory to the control of a binary distillation column is presented. The nonlinear control structure proposed allows the output of the process to be decoupled from external disturbances while it follows, asymptotically, a given trajectory. The internal stability of the resultant closed-loop system is analyzed together with the singularity problem of the decoupling matrix required to synthesize the control law; a nonlinear state estimator is also included. Some numerical results obtained when implementing the control-observer structure with the simulated process are shown.

Sliding mode control for DC/DC converters: a new sliding surface

In this paper a controller based on the variable structure theory is analyzed: the sliding mode control. The sliding mode control was proposed to control dc/dc converters, due to the good characteristics introduced to the complete system. In order to regulate the output voltage, the sliding mode control require a current loop in order to assure the stability of the system, the inclusion of this extra loop increases the cost. This paper presents an alternative method to obtain the good characteristics of the control strategy without the use of current sensors.

Robust control of the boost converter

Using the underlying idea of the current-mode control, a new dynamical, sliding-mode control for the boost dc-dc converter is proposed. Such controller is easy to design, robust under load and input voltage variations, exhibits fast response, does not depend on the load (although a knowledge of the load range is necessary to tune the controller), requires only voltage measurements, and can be easily implemented using standard electronic components

A comparison between the buck, boost and buck-boost inverters

In this paper, an analysis and experimental study of three kinds of inverters are presented. Beginning with the traditional full-bridge buck inverter; followed by two different inverter approaches, the boost and buck boost ones. These last two converters have the property of producing an output voltage higher or lower than the input voltage additionally to its inversion capability, which is a desired characteristic in some applications. The paper include a comparison between the different inverter approaches, additional to the analysis and experimental results of the converters. The control strategy used for all the converters is the sliding mode control in order to introduce a good dynamic response for the closed loop system.

Output feedback and dynamical sliding-mode control of power converters

Using the underlying idea of the most widely accepted controller for power converters, the current-mode control, a new dynamical and sliding-mode control for dc–dc power converters, is proposed. The controller requires only voltage measurements; is easy to design; is robust under load and input voltage variations, exhibits fast response and does not depend on the load (although a knowledge of the load range is necessary to tune the controller). In spite of these features, it can be easily implemented using standard electronics components. The stability analysis is carried out using the discontinuous (large signal) nonlinear model. This analysis provides a set of controller admissible parameters to keep closed-loop system stability.

Modified passive-based control law for the boost inverter

The passivity-based control has been proposed to control different non-linear systems, but practical implementation aspects have not been discussed on most of them. One of those systems is the buck inverter. In some applications it is necessary the boosting capability, additional to the inversion capability, therefore a boost inverter has been proposed in those cases, since the buck inverter does not have those capabilities. In this paper, the practical implementation of the passivity-based control for the boost inverter is discussed in some detail, and a modified controller is proposed.

Neuro Control for Multicomponent Distillation Column

Abstract The control problem of a multicomponent nonideal distillation column is proposed by using a dynamic neural network approach. The holdup, liquid and vapor flow rates are assumed to be time-vaying (nonideality). The technique proposed in this paper is based on two central notions: a dynamic neural identifier and a neuro-controller for output trajectory tracking. The first one guarantees boundness of the state estimation error with a small enough tolerance level. The tracked trajectory is generated by a nonlinear reference model, and we derive a control law to minimize the trajectory tracking error. The controller structure which we propose is composed of two parts: the neuro-identifier and the local optimal controller. Numerical simulations, concerning a 5 components distillation column with 15 trays, illustrate the effectiveness of the suggested approach.

A class of easy-to-implement sliding-mode controllers with constant switching frequency for power converters

Generally, sliding-mode controllers have to be modified to achieve a constant switching frequency or at least to have an upper limit for it. A family of sliding-mode controllers easy to implement is proposed in this paper. If a controller has the form specified in this paper then it can be implemented using a pulse-width modulator assuring a constant switching frequency, without requiring the control to be modified. The control structure proposed is shown to be feasible by presenting a controller for the boost converter as an example. Simulations and experimental results show that the controller structure proposed has the usual high performance and robustness of sliding-mode controllers. In addition, it has the very convenient features of constant switching frequency and easy implementation.