2018
Authors
Mehrasa, M; Pouresmaeil, E; Taheri, S; Vechiu, I; Catalao, JPS;
Publication
IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS
Abstract
This paper aims to present a novel control strategy for modular multilevel converters (MMC) based on differential flatness theory, in which instantaneous active and reactive power values are considered as the flat outputs. To this purpose, a mathematical model of the MMC taking into account dynamics of the ac-side current and the dc-side voltage of the converter is derived in a d-q reference frame. Using this model, the flat outputs-based dynamic model of MMC is obtained to reach the initial value of the proposed controller inputs. In order to mitigate the negative effects of the input disturbance, model errors, and system uncertainties on the operating performance of the MMC, the integral-proportional terms of the flat output errors are added to the initial inputs. This can be achieved through defining a control Lyapunov function which can ensure the stability of the MMC under various operating points. Moreover, the small-signal linearization method is applied to the proposed flat output-based model to separately evaluate the variation effects of controller inputs on flat outputs. The proficiency of the proposed method is researched via MATLAB simulation. Simulation results highlight the capability of the proposed controller in both steady-state and transient conditions in maintaining MMC currents and voltages, through managing active and reactive power.
2018
Authors
Almeida, F; Cunha, E;
Publication
Journal of Information Systems Engineering and Business Intelligence
Abstract
2018
Authors
Mansouri, B; Zahedi, MS; Campos, R; Farhoodi, M;
Publication
ACM/SIGIR PROCEEDINGS 2018
Abstract
Over the last few years, an increasing number of user's and enterprises on the internet has generated a global marketplace for both employers and job seekers. Despite the fact that online job search is now more preferable than traditional methods - leading to better matches between the job seekers and the employer's intents - there is still little insight into how online job searches are different from general web searches. In this paper, we explore the different characteristics of online job search and their differences with general searches, by leveraging search engine query logs. Our experimental results show that job searches have specific attributes which can be used by search engines to increase the quality of the search results.
2018
Authors
Ferreira, C; Cunha, T; Santos, CP; Reis, LP;
Publication
2018 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS)
Abstract
Biped robots have not achieved the efficient and harmonious locomotion of the human beings, capable of walking and running on unstructured terrains, with obstacles, holes and slopes. With this in mind, researchers started the development of biomimetic solutions to control the locomotion of biped models. This work presents a new solution of motion control of bipedal robots with adaptable stiffness, by exploring effects of joint stiffness in modulating walking behavior. Further, torque adjustment is achieved through a biomimetic controller that mimics and adjusts the natural dynamics of the robot to the environment. Specifically, the torque adjustment is made using AFOs (adaptive frequency oscillator) to generate the correct equilibrium positions that will be applied to the impedance control that computes the torque of each joint. Results show that the biped model is capable of walking in several types of terrain, including flat terrain, ramps, stairs and flat terrain with obstacles.
2018
Authors
Pinto, PT; Saraiva, JT;
Publication
2018 15TH INTERNATIONAL CONFERENCE ON THE EUROPEAN ENERGY MARKET (EEM)
Abstract
This paper reports the main results obtained by the first author in the preparation of his MSc Thesis. The motivation for this work resulted from the intention announced by the Portuguese Regulatory Agency for the Energy Services to introduce dynamic tariffs as a way to induce a change of the behavior of some consumers in terms of moving some demand from peak periods to the adjacent hours. This is reported to lead to loss reductions, postponement of grid investments and generation cost reductions. In the case of Portugal, given the participation in the common market with Spain, generation costs are not publicly available so that it was investigated how the Social Welfare Function, SWF, that is maximized by the market operator would change given these demand transfers. The simulations were done using real market data for 2016 and the results suggest that the advantages are unclear since the SWF would be almost unchanged or slightly reduced.
2018
Authors
Gomes, AD; Silveira, B; Warren Smith, SC; Becker, M; Rothhardt, M; Frazao, O;
Publication
OPTICS AND LASER TECHNOLOGY
Abstract
A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg's law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 +/- 1 nm/RlU was obtained in a low refractive index regime (1.3475-1.3720) with low influence of temperature (-0.32 0.06 pm/degrees C). The cross sensitivity for this structure is 2.0 x 10(-5) RlU/degrees C.. The potential for simultaneous measurement of refractive index and temperature is also studied.
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