Nuno E.,University of Guadalajara |
Basanez L.,University of Barcelona |
Ortega R.,Laboratoire des Signaux et Systemes
Automatica | Year: 2011
This tutorial revisits several of the most recent passivity-based controllers for nonlinear bilateral teleoperators with guaranteed stability properties. These schemes, which include scatteringbased, damping injection and adaptive controllers, ensure asymptotic stability in multiple situations that range from constant to variable time-delays, with or without scattering transformation and with or without position tracking capabilities. Although all controllers exploit the basic property of passivity of the teleoperators, they have been developed invoking various analysis and design tools, which complicates their comparison and relative performance assessment. The objective of this paper is to present a unified theoretical frameworkbased on a general Lyapunovlike functionthat, upon slight modification, allows to analyze the stability of all the schemes. © 2011 Elsevier Ltd. All rights reserved.
Chen J.,Stanford University |
Yang S.,Laboratoire des Signaux et Systemes |
Ozgur A.,Stanford University |
Goldsmith A.,Stanford University
IEEE Transactions on Information Theory | Year: 2016
We consider communication over heterogeneous parallel channels, where a transmitter is connected to two users via two parallel channels: a multiple-input multiple-output (MIMO) broadcast channel (BC) and a noiseless rate-limited multicast channel. We characterize the optimal degrees of freedom (DoF) region of this setting when the transmitter has delayed channel state information (CSIT) regarding the MIMO BC. Our results show that jointly coding over the two channels strictly outperforms simple channel aggregation and can even achieve the instantaneous CSIT performance with completely outdated CSIT on the MIMO BC in the sum DoF sense; this happens when the multicast rate of the second channel is larger than a certain threshold. The main idea is to send information over the MIMO BC at a rate above its capacity and then use the second channel to send additional side information to allow for reliable decoding at both receivers. We call this scheme a two-phase overload-multicast strategy. We show that such a strategy is also sum DoF optimal for the K-user MIMO BC with a parallel multicast channel when the rate of the multicast channel is high enough and can again achieve the instantaneous CSIT performance (optimal sum DoF) with completely outdated CSIT. For the regime where the capacity of the multicast channel is small, we propose another joint coding strategy, which is sum DoF optimal. © 2016 IEEE.
Del Puerto-Flores D.,University of Groningen |
Ortega R.,Laboratoire des Signaux et Systemes |
Scherpen J.M.A.,University of Groningen
International Journal of Circuit Theory and Applications | Year: 2012
Recently, it has been established that power factor (PF) improvement for nonlinear loads with nonsinusoidal source voltage is equivalent to imposing the property of cyclodissipativity to the source terminals. Using this framework, the classical capacitor and inductor compensators were interpreted in terms of energy equalization. The purpose of this brief note is to extend this approach in three directions. In the result reported in the literature, the supply rate is a function of the load, which is usually unknown, stymieing the applicability of the technique for compensator synthesis. Our first contribution is a new cyclodissipativity condition, which is also equivalent to PF improvement, but whose supply rate is now function of the compensator. Second, we consider general lossless linear compensators, instead of only capacitive or inductive compensators. As a result, we show that the PF is improved if and only if a certain equalization condition between the weighted powers of inductors and capacitors of the load is ensured. Finally, we exhibit the gap between the ideal compensator, namely the one that achieves unitary PF, and the aforementioned equalization condition. This result naturally leads to the formulation of a problem of optimization of the parameters of the compensator. Copyright © 2011 John Wiley & Sons, Ltd.
Benammar M.,Huawei |
Piantanida P.,Laboratoire des Signaux et Systemes |
Shamai S.,Israel Electric
IEEE International Symposium on Information Theory - Proceedings | Year: 2015
This work investigates the Multicast Cognitive Interference Channel (CIFC) where many secondary users are interested in the same cognitive message. The focus is to study the role that Multiple Description (MD) coding can play under simultaneous transmissions. Though for the very weak, very strong, and mixed very weak/strong interference regimes, resorting to a Common Description (CD) alone is capacity achieving, in the weak interference regime it becomes crucial to resort to a more evolved coding scheme relying on multiple descriptions that could each accommodate differently the interference experienced at the secondary users. A Gaussian example illustrates this claim and various capacity results are likewise reported. © 2015 IEEE.
Doria-Cerezo A.,Polytechnic University of Catalonia |
Bodson M.,University of Utah |
Batlle C.,Polytechnic University of Catalonia |
Ortega R.,Laboratoire des Signaux et Systemes
IEEE Transactions on Control Systems Technology | Year: 2013
In this brief, a new control scheme is presented for the doubly fed induction machine (DFIM). The proposed control algorithm offers the advantages of proven stability and remarkable simplicity. In contrast to the classical vector control method, where the DFIM is represented in a stator-flux-oriented frame, a model with orientation of the stator voltage is adopted. This approach allows the decomposition of the active and reactive powers on the stator side and their regulation on the rotor side. A main contribution of this brief is the use of the Hurwitz test for polynomials with complex coefficients that has had little prior application in control theory. This results in a proof that a proportional-integral (PI) control regulating the stator currents ensures global stability for a feedback-linearized DFIM. The specific condition that the PI gains must satisfy is derived as a simple inequality. The PI controller has a particular structure that directly relates the $d$-component of the rotor voltages to the $q$-component of the stator currents and vice versa. The feedback linearization stage only uses the direct measurement of the rotor and stator currents and is thus easily implementable. Furthermore, it is also shown that the PI controller (without the feedback linearization terms) is also stable for a large range of control gains and does not require the knowledge of the machine parameters. Finally, the control system is validated in simulations and in experiments. © 2013 IEEE.