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Publications

Publications by Rui Esteves Araujo

2016

Power Transformer for a Single-stage Bidirectional and Isolated AC-DC Matrix Converter for Energy Storage Systems

Authors
Varajao, D; Miranda, LM; Araujo, RE; Lopes, JP;

Publication
PROCEEDINGS OF THE IECON 2016 - 42ND ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY

Abstract
This paper presents an approach to design the transformer and the link inductor for the high-frequency link matrix converter. The proposed method aims to systematize the design process of the HF-link using analytic and software tools. The models for the characterization of the core and winding losses have been reviewed. Considerations about the practical implementation and construction of the magnetic devices are also provided. The software receives the inputs from the mathematical analysis and runs the optimization to find the best design. A 10 kW / 20 kHz transformer plus a link inductor are designed using this strategy achieving a combined efficiency of 99.32%.

2016

Sensor Fusion Algorithm Based on Extended Kalman Filter for Estimation of Ground Vehicle Dynamics

Authors
Barbosa, D; Lopes, A; Araujo, RE;

Publication
PROCEEDINGS OF THE IECON 2016 - 42ND ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY

Abstract
The current vehicle stability control techniques relies on an accurate sensor information and a complete system definition, such information is not easily obtained and requires expensive sensor technology. In this work it is presented a fusion algorithm for estimating the vehicle handling dynamic states, using inertial measurements combined with Global Positioning System (GPS) information, based on the Extended Kalman Filter algorithm (EKF). The proposed method will be able to track the state of the variable vector that includes the yaw rate, lateral velocity and longitudinal velocity of the vehicle using the information of the available sensors combined with the non-linear model of the system. In order to validate the proposed sensor fusion algorithm a simulation with a high-fidelity CarSim model is carried out and its sensors are compared with Extended Kalman Filter state variables.

2015

Spread Spectrum Audio Indoor Localization

Authors
Moutinho, J; Freitas, D; Araujo, RE;

Publication
2015 IEEE 18TH INTERNATIONAL CONFERENCE ON COMPUTATIONAL SCIENCE AND ENGINEERING (CSE)

Abstract
This paper presents the results of an indoor localization experiment that uses spread spectrum modulated audio signals. Indoor spaces do not have line-of-sight to global navigation satellite systems and do not have a truly universal localization system to allow mobile devices to localize themselves. Previous approaches focused in using custom made hardware with several types of signals that, even though with good performance, are not feasible to adopt in a wide scale utilization. The proposed approach uses pre-existent off-the-shelf hardware and easy to handle audio signals present in our everyday lives. However, the challenges when using audible and very susceptible to multipath types of signals are many and require validation of the subjacent principles. An experiment in a real indoor environment was conducted to estimate localization while using spread spectrum noise like signals barely perceptible to people. Results demonstrated a 1.3 cm average accuracy in the center area. These and other results demonstrate the possibility of the use of audio signals with all the advantages regarding wide scale dissemination of an indoor localization solution.

2016

Sliding Mode Fault-Tolerant Controller for Overactuated Electric Vehicles with Active Steering

Authors
Lopes, A; Araujo, RE; Aguiar, AP; de Pinho, MD;

Publication
PROCEEDINGS OF THE IECON 2016 - 42ND ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY

Abstract
This paper addresses the tracking problem of the state variables of a nonlinear planar dynamic model of an overactuated electric vehicle with four-wheel independent drive (4WID) topology. In order to track the state variables of the system it is proposed a new sliding mode controller based on a nonlinear planar model. The controller explores the overactuated system in order to redistribute the control effort to the remaining actuators when a fault occurs. Although the system has multiple solutions due to the access of the torque applied in each wheel independently, there could be particular fault events where the remaining healthy actuators may not be able to maintain the system stability. In those particular cases the inclusion of the steering control variable is an important advantage as it allows the controller to manipulate the control effort in any directions. The proposed controller is validated in various driving scenarios with different fault schemes. The simulations are carried out with a high-fidelity vehicular model provided by the simulation software Carsim in co-simulation with Matlab/Simulink.

2014

Towards a new technological solution for Community Energy Storage

Authors
Varajao, D; Miranda, LM; Araujo, RE;

Publication
2014 16TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'14-ECCE EUROPE)

Abstract
Energy storage in low voltage grid is receiving increased attention due to renewables integration and consumption growth, challenges faced nowadays by grid operators. In this work, a study of main implementation issues for community energy storage (CES) is presented along with a comparison between possible solutions for the bidirectional isolated power conversion system (PCS) to interface a battery pack with the electric power grid. The aim of this research is to increase the power density of the power converter and keeping simultaneously the same reliability of traditional solutions. These goals are pursued to be achieved through the reduction of the conversion stages and utilization of new optimization methodologies to reduce the volume of the passive components. The proposed topology for the PCS is based on a matrix converter (MC) that performs a direct AC to AC conversion between the grid and a high-frequency transformer (HFT). With this solution it is possible to eliminate the traditional DC-link capacitor and obtain a single-stage power conversion with bidirectional power flow capability. This proposed solution is evaluated and compared with a conventional two-stage topology through extensive simulation. Two prototypes systems were designed for a 10kW PCS to connect the three-phase 230/400Vrms, 50Hz mains to a battery pack with voltage range of 320V to 490V. Simulation results are presented to assess the power quality provided by the front-end and the battery side converters, as well as performance evaluation and efficiency analysis.

2013

Wheel Slip Control of EVs Based on Sliding Mode Technique With Conditional Integrators

Authors
de Castro, R; Araujo, RE; Freitas, D;

Publication
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS

Abstract
This paper presents a new control system, based on field programmable gate array technology, targeting the power-train control of multi-motor electric vehicles (EVs). The control chip builds around a reusable intellectual property core named propulsion control unit, which features motor control functions with field-orientation methods, and energy loss minimization of induction motors. In order to improve the EV safety, the control system was extended with a wheel slip controller based on the sliding mode framework. The robustness to parametric and modeling uncertainties is the main attraction in this design, thanks to a simple connection that was found between the driving torque request and the model uncertainty. To overcome the chattering issue, which arrives from the discontinuous nature of the sliding control, the conditional integrator approach was employed, enabling a smooth transition to a Proportional+Integral control law, with anti-windup, when the tire slip is close to the setpoint. The controller asymptotic stability and robustness was analytically investigated through the Lyapunov method. Experimental results, obtained with a multi-motor EV prototype under low grip conditions, demonstrate a good slip regulation and robustness to disturbances.

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