Ramon Costa-Castelló

Digital Repetitive Control of a Three-Phase Four-Wire Shunt Active Filter

Shunt active power filters have been proved as useful elements to correct distorted currents caused by nonlinear loads in power distribution systems. This paper presents an all-digital approach based on a particular repetitive control technique for their control. Specifically, a digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances is used for the current control loops of the active filter. This approach does not introduce a high gain at those frequencies for which it is not needed and, thus, improves robustness of the controlled system. The active power balance of the whole system is assured by an outer control loop, which is designed from an energy-balancing perspective. The design is performed for a three-phase four-wire shunt active filter with a full-bridge boost topology. Several experimental results are also presented to show the good behavior of the closed-loop system

Demonstration of the internal model principle by digital repetitive control of an educational laboratory plant

A key topic in classical control theory is the Internal Model Principle (IMP). A particular case of the IMP for tracking periodic references or attenuating periodic disturbances in closed-loop control systems is a technique called repetitive control. This work proposes and describes an educational laboratory plant to show the students the advantages of repetitive controllers in systems with periodic references or disturbances. The plant has been designed to be low cost, easy to build, and subject to periodic disturbances with a clear physical explanation. More specifically, it consists of a pulsewidth modulation (PWM) electronic amplifier, a small dc motor, and a magnetic setup that generates a periodic load torque under constant mechanical speed operation. The control objective for the closed-loop control system is to regulate the mechanical speed to a constant value in spite of the periodic load torque disturbance. In order to accomplish this performance specification, a detailed design of a digital repetitive controller is presented, and some basic experimental results are provided to prove its good behavior. The paper also includes some repetitive control concepts and facts that teaching experience shows as essential to understand the design process.

High-Performance Control of a Single-Phase Shunt Active Filter

Shunt active power filters are devices, connected in parallel with nonlinear and reactive loads, which are in charge of compensating these characteristics in order to assure the quality of the distribution network. This paper analyzes the dynamics of a dc bus split-capacitor boost converter used as an active filter and proposes a control system which guarantees the desired closed-loop performance (unity power factor and load-current harmonics and reactive-power compensation). The proposed controller is hierarchically decomposed into two control loops, one in charge of shaping the network current and the other in charge of assuring the power balance. Unlike previous works that appeared in the literature, both control loops are analytically tuned. This paper describes the analytical design of the controller and presents some experimental results that show the good performance of the closed-loop system.

On preserving passivity in sampled-data linear systems

Passivity is a well known phenomenon. Due to its interesting properties, it is widely used in several areas of control engineering. In general, passivity is lost under direct discretization. In this work, a new methodology which allows to preserve continuous-time passivity is revisited. This methodology is based on choosing a proper output which preserves the passivity structure, while keeping the continuous-time energy function. As this new output needs information about the system state, an state observer is added.

High Performance Control of a Single-Phase Shunt Active Filter

Shunt active power filters are devices connected in parallel with nonlinear and reactive loads which are in charge of compensating these characteristics in order to assure the quality of the distribution network. This work analyzes the dynamics of boost-converter used as an active filter and proposes a control system which guarantees closed-loop performance (power factor close to 1 and current harmonics compensation). Proposed controller is hierarchically decomposed in two control loops, one in charge of shaping the current and the other in charge of assuring the power balance. Differently from other works both control loops are analytically tuned. The work describes both the analytical development and the experimental results showing the good performance of the closed- loop system.

Digital control of a single-phase shunt active filter

Shunt active power filters are proved a useful elements to correct the distorted currents caused by nonlinear loads in power distribution systems. This work presents an all digital approach, based on the repetitive control technique, for their control and a design is performed for the particular case of single-phase shunt active filters with a full-bridge boost topology. Several experimental results are also presented to show the behavior of the closed loop system.

High Performance Repetitive Control of an Active Filter under Varying Network Frequency

Abstract Shunt active power filters are power electronics devices that are connected in parallel with nonlinear and reactive loads to compensate these characteristics in order to assure the quality of service of the electrical distribution network. This work proposes and designs a controller, based on combined feedforward and feedback actions, the last using repetitive control, to obtain a good closed-loop performance (power factor close to 1 and, load current harmonics and reactive power compensation) in spite of the possible frequency variations that may occur in the electrical network. It is known that these variations clearly affect the performance of the usual discrete-time implementations of the repetitive based controllers. This work analyzes the effect of these variations and describes the architecture of the controller, its design, and the mechanism to compensate the network frequency variations. Some experimental results that show the good performance of the closed-loop system are also included.

A Passive Repetitive Controller for Discrete-Time Finite-Frequency Positive-Real Systems

This work proposes a new repetitive controller for discrete-time finite-frequency positive-real systems which are required to track periodic references or to attenuate periodic disturbances. The main characteristic of the proposed controller is its passivity. This fact implies closed-loop stable behavior when it is used with discrete-time passive plants, but additional conditions must be fulfilled when it is used with a discrete-time finite-frequency positive-real plant. These conditions are analyzed and a design procedure is proposed

On Preserving Passivity in Sampled-data Linear Systems

Passivity is a well known phenomenon in several engineering areas. Due to its interesting properties, it is used in several areas of control engineering. Generally, this property is lost under direct discretization. In this work a new methodology which allows preserving continuous-time passivity is presented. This methodology is based on choosing a proper output, which preserves the passivity structure, while keeping the continuous-time energy function. Analytic formulation and numerical examples, both for open and closed loop, are provided in the paper

Digital repetitive control under time-varying sampling period: An LMI stability analysis

Digital repetitive control is a technique which allows to track periodic references and/or reject periodic disturbances. Repetitive controllers are usually designed assuming a fixed frequency for the signals to be tracked/rejected, its main drawback being a dramatic performance decay when this frequency varies. A usual approach to overcome the problem consists of an adaptive change of the sampling time according to the reference/disturbance period variation. This article presents a stability analysis of a digital repetitive controller working under time-varying sampling period by means of an LMI gridding approach. Theoretical developments are illustrated with experimental results.