Departamento de Engenharia Electrotécnica (DEE)
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Browsing Departamento de Engenharia Electrotécnica (DEE) by Author "Albuquerque, Daniel"
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- Flexible Power Control of Photovoltaic Plants Connected to Distribution NetworksPublication . Ribeiro, Susana; Costa, Paulo Moisés; Gouveia, Eduardo; Sousa, Pedro; Albuquerque, DanielThis paper presents a system to control the power injected by a photovoltaic (PV) plant on the receiving network. This control is intended to mitigate some of the negative impacts that these units may produce on such networks, while increasing the installed power of the plant. The controlled parameters are the maximum allowed value of injected active power and the corresponding power factor, whose setpoints values may be fixed or dynamic. The developed system allows a local and a remote control. The injected power and the corresponding power factor may be set by following a predetermined profile or by real time adjustments to fulfill specific operation constraints on the receiving network. The system acts by adjusting the control parameters on the PV inverters. The main goal of the system is, in the end, to control the PV plant, ensuring the accomplishment of technical constraints and, at the same time, maximizing the installed power of the PV plant, which may be an important issue concerning the economic performance of such plants
- High Energy OFDM Pulse Design Algorithm for Acoustic ToF Ranging and LocalizationPublication . Albuquerque, Daniel; Vieira, José; Lopes, Sérgio; Aguilera, Teodoro; Álvarez, FernandoThis paper proposes an algorithm to design band-limited Orthogonal Frequency Division Multiplexing (OFDM) pulses for accurate time-of-flight ranging in acoustic-based localization systems. The proposed algorithm is capable to generate OFDM pulses with higher energy when compared with other common pulse design approaches with similar characteristics. The results attained have shown that it is possible to design OFDM pulses with 17% more energy than a chirp or a BPSK pulse with the same characteristics. The proposed algorithm uses an iterative approach to increase the pulse energy while keeping the same amplitude, bandwidth and duration in each iteration. Two different OFDM pulses are provided and compared with two common pulses, namely chirp and BPSK pulses, with the same characteristics.
- Indoor Location Using UltrasoundsPublication . Albuquerque, Daniel; Vieira, José; Bastos, Carlos; Ferreira, PauloThis thesis presents a location system based exclusively on ultrasonic signals, without using any other technology. This location system was designed to operate in environments where the use of other technologies is not possible or the use of them is limited, such as underwater applications or hospital environments. The proposed location system uses a network of fixed beacons allowing the mobile stations to locate. Due to the necessity of data transmission and distance measurement an ultrasonic pulse robust to echoes was developed that allows to perform both tasks with success. The location system allows that mobiles locate themselves only listening to the information in the ultrasonic pulse sent by the beacons, for that an algorithm based on time difference of arrival is used. Therefore, the user privacy is guaranteed as well as the complete independence of the system number of users. To simplify the network implementation it is only necessary to manually define the position of some of the beacons, called anchor beacons. These will allow the remaining autonomous beacons to locate themselves by an iterative location algorithm based on a local cost function minimization. For this system to work properly the beacons must synchronize their clocks and measure the distance between them. Therefore, this thesis proposes a clock synchronization protocol which also allows to measure the distance between the beacons by exchanging only three ultrasonic messages. Additionally, the location system permits that damaged beacons may be replaced without compromising the network operability reducing the maintenance complexity. Additionally, a simplified ultrasonic simulator for indoor environments was developed, which has proved to be very accurate and a valuable tool to simulate the location system behavior under controlled conditions.
- TheremUS: the Ultrasonic ThereminPublication . Gomes, André; Albuquerque, Daniel; Campos, Guilherme; Vieira, JoséIn the Theremin, the performer’s hand movements, detected by two antennas, control the pitch and volume of the generated sound. The TheremUS builds on this concept by using ultrasonic sensing for hand position detection and processing all signals digitally, a distinct advantage in terms of versatility. Not only can different sound synthesis algorithms be programmed directly on the instrument but also it can be easily connected to other digital sound synthesis or multimedia devices; a MIDI interface was included for this purpose. The TheremUS also features translucent panels lit by controllable RGB LED devices. This makes it possible to specify sound-colour mappings in the spirit of the legendary Ocular Harpsichord by Castel.