A new 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 discretetime finite-frequency positive-real plant. These conditions are analyzed and a design procedure is proposed.Peer Reviewe

Demonstration of the Internal Model Principle by Digital

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.Peer Reviewe

Non-uniform sampling in digital repetitive control systems: 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 report 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

An educational approach to the internal model principle for periodic signals

This article presents an educational approach to resonant control and repet- itive control, which are Internal Model Principle-based control techniques speci cally de- signed for the tracking/rejection of periodic signals. The analytical formulation is com- pleted by a set of simulations and physical experiments on a mechatronic educational plant integrated in a virtual/remote laboratory. The laboratory features are oriented to realize the limited performance of classic PID control to reject non-constant disturbances and, at the same time, to show the effectiveness of the Internal Model Principle for the rejection of periodic disturbances by means of resonators and repetitive control. Assess- ment based on students' perception reveals it as a useful distance learning tool. The laboratory is integrated in Automatl@bs, a Spanish interuniversity network of web-based laboratories devoted to distance learning of control engineering.Postprint (published version

A repetitive controller for discrete-time passive systems

This work proposes and studies a new repetitive controller for discrete-time systems which are required to track or to attenuate periodic signals. The main characteristic of the proposed controller is its passivity. This fact implies closed-loop stable behaviour when it is used with discrete-time passive plants. The work also discusses the energetic structure, the frequency response and the time response of the proposed controller structure. Some examples are included to illustrate its practical use

Odd-Harmonic Digital Repetitive Control of a Single-Phase Current 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 work presents an all-digital approach, based on the repetitive control technique, for their control. In particular, a special digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances is used. This approach does not introduce high gain at those frequencies for which it is not needed, and thus it improves robustness. Additionally, the necessary data memory capacity is lower than in traditional repetitive controllers. The design is performed for the particular case of single-phase 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.Peer Reviewe

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.Peer Reviewe

Plug-In Repetitive Control Strategy for High-Order Wide-Output Range Impedance-Source Converters

High-order wide-output (HOWO) impedance-source converters (ISCs) have been presented for ac inverter applications that require voltage step-up ability. With intrinsic passive impedance networks as energy sources, these converters are able to achieve voltage boosting with either polarity, leading to improved dc-link voltage utilization compared with the conventional two-level converter. However, HOWO-ISCs suffer from transfer functions giving low bandwidth, a penalty of increased passive devices and right-half-plane zeros, which result in lower order distortion of the ac output power. In this paper, a modified plugin repetitive control scheme is presented for HOWO-ISCs with accurate reference tracking (hence low distortion), fast dynamic response, and enhanced robustness. By using zero-phase-shift finite impulse response filters in both the internal model of the repetitive controller and its compensation network, the proposed method achieves zero steady-state error and an extended closedloop bandwidth. For HOWO-ISC cases, this method outperforms conventional proportional-integral (PI) control, which has considerable steady-state error. It also eliminates the need of parallel loops for several frequencies when proportional resonant control or orthogonal transformation-based PI schemes are used to remove lower order distortion. The design process and performance analysis of the proposed repetitive control strategy are based on a novel three-phase HOWO-ISC configuration with a reduced number of switches. Simulation and experimental results confirm the feasibility and effectiveness of the proposed control approach