Showing papers by "Ramon Costa-Castelló published in 2013"

Stability Analysis Methods

Abstract: Repetitive control is a widely used strategy applied in the tracking/rejection of periodic signals, however, the performance of this controller can be seriously affected when the frequency of the reference/disturbance signal varies or is uncertain. One approach that overcomes this problem is the adaptation of the controller sampling period, nevertheless, the system framework changes from a Linear Time Invariant to Linear Time-Varying and the closed-loop stability can be compromised. Indeed, the proposals applying this scheme in repetitive control do not provide formal stability proofs. This work presents two different methodologies aimed at analyse the system stability under these conditions. The first one uses a Linear Matrix Inequality gridding approach which provides necessary conditions for the closed-loop Bounded Input Bounded Output stability of the system. The second one applies robust control techniques in order to analyse the stability and yields sufficient stability conditions. Both methodologies, entails a frequency variation interval for which the system stability can be assured.

Odd-Harmonic High Order Repetitive Control

Abstract: HORC is mainly used to improve the repetitive control performance robustness under disturbance/reference signals with varying or uncertain frequency. Unlike standard repetitive control, the HORC involves a weighted sum of several signal periods. With a proper selection of the associated weights, this high order function offers a characteristic frequency response in which the high gain peaks located at harmonic frequencies are extended to a wider region around the harmonics. Furthermore, the use of an odd-harmonic internal model will make the system more appropriate for applications where signals have only odd-harmonic components, as in power electronics systems. This Chapter presents an Odd-harmonic High Order Repetitive Controller suitable for applications involving odd-harmonic type signals with varying/uncertain frequency. The open loop stability of internal models used in HORC and the one presented here is analysed. Additionally, as a consequence of this analysis, an anti-windup scheme for repetitive control is proposed.

Repetitive control to counteract the effect of people on thermal comfort control

Abstract: People usually spend most of the time inside buildings. Therefore, it is necessary to reach an optimal thermal comfort situation since thermal comfort has a direct effect on people's productivity. The use of appropriate control strategies can highly contribute to this purpose. Usually the own people's influence is not taken into account at the time to maintain an optimal thermal comfort. People enter and leave the building following certain pattern which is repeated from one day to another. This paper presents a Repetitive Control (RC) approach which can counteract this periodic behaviour. This controller anticipates the effects produced by the entries and outputs of the people. Moreover, this controller is complemented by a feedback controller in order to cancel the non periodic disturbances. Simulation results obtained from the application of this control strategy to a characteristic room of a building are included and commented.

Shunt Active Power Filter

Abstract: Shunt active power filters have been introduced as a way to overcome the power quality problems caused by nonlinear and reactive loads [9, 14, 23]. These power electronics devices are designed with the goal of obtaining a power factor close to 1 and achieving current harmonics and reactive power compensation [5, 6, 15]. The usual approaches [5, 15] for the control of shunt active filters are based on two hierarchical control loops: an inner one that assures the desired current and an outer one in charge of determining its required shape and the appropriate power balance as well. The control structure followed in this Chapter is the one in [7], in which the current controller is composed of a feedforward action that provides very fast transient response, and also of a feedback loop which includes an odd-harmonic repetitive control that yields closed-loop stability and a very good harmonic correction performance. In turn, the outer control law is based on the appropriated computation of the amplitude of the sinusoidal current network and, aiming at a robustness improvement, this is combined with a feedback control law including an analytically tuned PI controller.