Luís Fernando Alves Pereira

Robust control design of multiple resonant controllers for sinusoidal tracking and harmonic rejection in Uninterruptible Power Supplies

This paper presents a robust control strategy for tracking sinusoidal reference signals with zero steady state error and harmonic compensation in Uninterruptible Power Supplies - UPS. Multiple resonant controllers are derived for DC-AC inverters when supplying energy to (uncertain) nonlinear loads to obtain a nice tradeoff between transient response and disturbance rejection regardless possible load variations. The controller parameters are determined by means of a convex optimization problem subject to a set of linear matrix inequalities (LMIs). Real time experiments demonstrate the potentials of the proposed approach for controlling UPS systems.

Repetitive Control Design for MIMO Systems With Saturating Actuators

This paper addresses the problem of tracking and rejection of periodic signals for linear multi-input, multi-output systems subject to control saturation. To ensure the periodic tracking/rejection, a modified state-space repetitive control structure is considered. Conditions in a “quasi” linear matrix inequality form are proposed to simultaneously compute a stabilizing state feedback gain and an anti-windup gain. Provided that the references and disturbances belong to a certain admissible set, these gains guarantee that the trajectories of the closed-loop system starting in a certain ellipsoidal set contract to the linearity region of the closed-loop system, where the presence of the repetitive controller ensures the periodic tracking/rejection.

Tuning Rules for Proportional Resonant Controllers

In this brief, we propose a particular structure for resonant controllers and a tuning method of the Ziegler–Nichols type for their tuning. Performance criteria for resonant controllers are also defined. The effectiveness of the tuning rules is illustrated by their application and corresponding performance assessment in a test batch consisting of four representative classes of processes. The control performance is analyzed in detail for one particular example, shedding light on the virtues and limitations of the control structure and of the tuning method.

Robust repetitive control with saturating actuators: a LMI approach

This paper addresses the problem of tracking and rejection of periodic signals for uncertain linear systems subject to control saturation. To ensure the periodic tracking/rejection, a modified state-space repetitive control structure is considered. From this structure, conditions in a “quasi” LMI form are proposed to simultaneously compute a stabilizing state feedback gain and an anti-windup gain. Provided that the references and disturbances belong to a certain admissible set, these gains guarantee that the trajectories of the closed-loop system starting in a certain invariant ellipsoidal set contract to the linearity region of the closed-loop system, where the presence of the repetitive controller ensures the periodic tracking/rejection. Based on these conditions, an optimization problem aiming at the maximization of the invariant set of admissible states and/or the maximization of the set of admissible references/disturbances is proposed.

Robustness analysis of nonlinear systems subject to state feedback linearization

This paper presents a methodology to the robust stability analysis of a class of single-input/single-output nonlinear systems subject to state feedback linearization. The proposed approach allows the analysis of systems whose nonlinearities can be represented in the rational (and polynomial) form. Through a suitable system representation, the stability conditions are described in terms of linear matrix inequalities, which is known to have a convex (numerical) solution. The method is illustrated via a numerical example.

Síntese de controladores repetitivos chaveados : uma aplicação à fontes ininterruptas de energia (UPS)

This paper presents a methodology for the synthesis of repetitive switched controllers to ensure the reference tracking of sinusoidal signals and the disturbance rejection on Uninterruptible Power Supplies - UPS. To improve both transitory and steady-state behavior of the output signal, we consider a state-space realization of a switched repetitive controller aiming two distinct operation conditions: transitory response (to improve the recovery time when the load is changed) and steady-state (to reduce the total harmonic distortion of the output signal when subjected to nonlinear loads). Based on a state-space framework, a state feedback is introduced to ensure the stability of the closed-loop when it is subjected to an arbitrary switching function. From a Lyapunov-Krasovskii functional, LMI conditions are derived to compute the stabilizing feedback gain. The dynamic behavior of the proposed control scheme is presented through simulation of a real UPS model subjected to non-linear loads.

A New Method for PID Tuning Including Plants Without Ultimate Frequency

The classical relay feedback method for tuning proportional-integral-derivative (PID) controllers cannot be applied to plants whose Nyquist diagrams do not cross the negative real axis; these are customarily tuned based on the reaction curve experiment. In this brief, we propose a tuning method based on a modified relay feedback experiment. In this experiment, a transfer function of constant phase in an arbitrarily large range of frequencies is inserted in the loop. The proposed methodology thus unifies the Ziegler-Nichols-like tuning methods, by allowing PID tuning based on relay feedback for a class of plants without ultimate frequency.

Robust PSC control design for sinusoidal tracking in uninterruptible power supplies

This paper proposes an alternative strategy to track sinusoidal reference signals with zero steady state error for uninterruptible power supplies - UPS. A robust proportional-sinusoidal-cosinusoidal (or in short PSC) controller is derived for sinusoidal voltage regulation subject to load variations. The controller parameters are determined by means of a convex optimization problem subject to a set of linear matrix inequalities (LMIs). Simulations and practical experiments demonstrate the potential of the proposed approach for controlling UPS systems.

Robust control design of multiple resonant controllers applied to three-phase UPS inverter under unbalanced and nonlinear loads

This paper investigates the control of a four-wire three-phase Uninterruptible Power Supply (UPS) inverter using the internal model principle by applying multiple resonant controllers in the stationary abc-frame for zero-error tracking of sinusoidal reference and harmonic disturbances rejection due to nonlinear and unbalanced loads. The synthesis of such controllers is accomplished in a robust control framework where the controller parameters are determined by means of a convex optimization problem subject to a set of Linear Matrix Inequality (LMI) constraints. Simulation results from a 15.0-kVA UPS inverter are considered to illustrate and validate the performance and behavior of the controller design under nonlinear and unbalanced loads.

A Comparative Analysis of Repetitive and Resonant Controllers to a Servo-Vision Ball and Plate System

Abstract This paper presents a comparative analysis of two alternative control strategies based on the Internal Model Principle: the Repetitive Controller and the Multiple Resonant Controller. The proposed implementations are evaluated experimentally in a servo-vision ball and plate balancing system. The plant is composed by an orientable platform with a free rolling sphere on top, where the controlled variable is the ball position. The methodology considered to synthesize the associated state gains parameters is the Linear Quadratic Regulator approach. The experimental results compare characteristics such as steady-state error, transient response and input signal for each implemented control strategy.