Álvaro Hernández

A DSP- and FPGA-Based Industrial Control With High-Speed Communication Interfaces for Grid Converters Applied to Distributed Power Generation Systems

New energy concepts such as distributed power generation systems (DPGSs) are changing the face of electric distribution and transmission. Power electronics researchers try to apply new electronic controller solutions with the capacity of implementing new and more complex control algorithms combined with internal high-speed communication interfaces. Thus, it is possible to monitor, store, and transfer a large number of internal variables that can be sent online to local or remote hosts in order to take new set points of different generation units. With this objective, this paper presents the design, implementation, and test of an industrial multiprocessor controller based on a floating-point digital signal processor (DSP) and a field-programmable gate array, which operate cooperatively. The communication architecture, which has been added to the proposed electronic solution, consists of a universal serial bus (USB), implemented with a minimum use of the DSP core, and a controller area network (CAN) bus that permits distributed control. Although the proposed system can be readily applied to any DPGS, in this paper, it is focused on a 150-kVA back-to-back three-level neutral-point-clamped voltage source converter for wind turbine applications.

Design of a Back-to-Back NPC Converter Interface for Wind Turbines With Squirrel-Cage Induction Generator

As the number of wind power applications with power electronic interfaces in the grid increases, it is becoming unacceptable to disconnect the generating units every time disturbances occur, especially under voltage dips, as was a common practice in the past. Keeping the converter online during unbalanced voltage, and guaranteeing the actual standards of the converter connected to the grid, is becoming a very critical issue. From these goals, the design of a robust back-to-back neutral point clamped (three levels) voltage source converter of 150 kVA is developed in this paper. The converter is divided into two main parts: the power electronic system and the control electronic system. Concerning the first part, on the one hand, the paper presents the designs of active and passive components as insulated gate bipolar transistor, free-wheeling diodes, clamping diodes, grid filter, DC-bus capacitors, etc.; and on the other hand, the converter requirements are analyzed to ride through real grid conditions, i.e., unbalanced voltage dips. Concerning the control electronic system, the chosen electronic structure and the task distribution between the two processors used are shown.

Ultrasonic ranging sensor using simultaneous emissions from different transducers

In recent applications based on ultrasound, several ultrasonic transducers have been geometrically and electronically associated to constitute a global sensor. There are several different methods used to process the ultrasonic signals obtained from these transducers. In this work, multimode techniques using Golay complementary sequences are proposed for processing the ultrasonic signal. The system increases scan rate, precision, and reliability. It is also capable of echo discrimination, allowing simultaneous measurements to be made and detection of the same obstacle by different transducers without cross-talk problems. The real-time implementation of the algorithm is presented on a field-programmable gate array (FPGA) device.

Modular Architecture for Efficient Generation and Correlation of Complementary Set of Sequences

Golay sequences and complementary sets of sequences have been long studied for their application in multisensor and communication systems. The feasibility of these systems strongly depends on the design of an efficient generator and correlator with the aim of reducing the computational load and hardware complexity. Recursive algorithms, which allow efficient architectures, are available in the case of complementary pairs of sequences and complementary sets of four sequences. This work presents a generalization of these algorithms with the purpose of obtaining complementary sets of M sequences with length L, the number of sequences M being a power of two (M=2m), and the length L a power of M (L=2mN) with m,Nisin N-{0}. This fact allows an ideal Kroumlnecker delta function of weight MmiddotL in the addition of the autocorrelation functions of the M sequences of the set. Furthermore, the generation of M different mutually orthogonal sets can be obtained. This fact makes their application suitable in simultaneous multiemission systems. With the proposed algorithm, an effective reduction in the number of operations necessary to implement the correlator can be obtained, if it is compared with the straightforward implementation. Also, a regular structure is provided that allows implementation of the generator and/or the correlator for complementary sets of M sequences, based on the structure for complementary sets of M/2 sequences The sequence length can also be easily extended to any multiple of M. Finally, the generation and correlation of M different mutually orthogonal complementary sets of M sequences can be immediately derived

Correlation detector based on a FPGA for ultrasonic sensors

In the field of mobile robots ever more frequent use is being made of ultrasonic sensors composed of several transducers carrying out readings simultaneously and in a coordinated way. These sensors can read not only the distances but also listening angles, and they can also determine the reflector type (i.e. edge, plane or corner). To this end it is especially important that, after each emission of a pulse of ultrasound, each transducer can accurately detect the arrival of the echoes (providing accurate time-of-flight (TOF) readings). Another desirable feature is that the transducers be capable of discriminating between the echoes of simultaneous emissions (avoiding problems of crosstalk). This article describes the design and development of a correlation detector (implemented on a low-cost electronic system) allowing for both functions. q 1999 Elsevier Science B.V. All rights reserved.

Using Golay complementary sequences for multi-mode ultrasonic operation

In many of the recent array ultrasonic applications, acquisition rate is a crucial issue. Many of those applications are even impractical due to the sequential nature of ultrasound systems scanning. Obviously, one way of increasing this rate is the use of multi-mode operation. This paper introduces the basic aspects of multi-mode ultrasonic operation based on pulse compression techniques by means of binary sequences in a BPSK modulation scheme, and the advantages of Golay sequences, in multi-mode operation with respect to m-sequences, mostly used in recent works. Finally, some results of simulations using four modes simultaneously and a hardware architecture for testing these results are shown.

Using PCA in time-of-flight vectors for reflector recognition and 3-D localization

This paper presents a reflector recognition and localization technique in three-dimensional (3-D) environments, using only times-of-flight (TOFs) data obtained from ultrasonic transducers. The recognition and localization technique is based on the principal component analysis applied to the TOF vectors originating from a sensor that contains two emitting transducers and several receivers. The two emitters simultaneously transmit two coded pulses that are detected later on and discriminated by the receivers, after being reflected in the environment. The proposed technique allows for the possibility of not only recognizing the reflectors, but also estimating approximately its localization referred to the sensor. This technique has been tested with three types of reflectors in 3-D environments: planes, edges, and corners. The achieved results are very satisfactory for reflectors located in the range 50-350 cm.

Real-time implementation of an efficient Golay correlator (EGC) applied to ultrasonic sensorial systems

Abstract Multi-mode techniques reduce scanning times in ultrasonic systems, as they allow transducers in a sensor to simultaneously emit and receive without interference. In order to implement these techniques, it is necessary to encode each transducers emission. The use of orthogonal pairs of Golay sequences associated with different emitters avoids crosstalk among them. However, these sequences imply an increase in the computational complexity required in the receiver. This paper presents the practical implementation of a system, with two emitters and four receivers, using a low-cost hardware architecture based on a FPGA. The ultrasonic signal processing is performed in real time.

Classification of reflectors with an ultrasonic sensor for mobile robot applications

Abstract This paper describes a sensor model made up of four ultrasonic transducers able to classify reflectors (wall, edge or corner) in specular environments. The main goal has been to effect the classification from a single reading cycle: emission of ultrasounds and reception of echoes (measuring only times of flight—TOFs). Working from the four TOFs obtained after a single emission of ultrasounds (thereby facilitating its practical implementation in a mobile robot, when readings are taken while the robot is moving), an algorithm has been proposed for discriminating between edge and plane type reflectors. The configuration of the four transducers enabled dependent discriminating functions to be determined directly from the quadratic terms of the TOFs, without the need for previous geometric transformations. Special attention was given to the effect of the separation between the sensor transducers and the reading-associated noise. Finally, some considerations have been pointed out about the possibility of two transducers emitting, so allowing discrimination between walls and corners.

Performance comparison of different codes in an ultrasonic positioning system using DS-CDMA

In this work, several Code Division Multiple Access encoding schemes are evaluated for their application in ultrasonic sensory systems based on the determination of times-of-flight. Proper encoding improves the performance of such systems in terms of noise immunity, capability of simultaneous measurements and precision in the distance measurements. Important applications that include encoded ultrasonic signals are obstacle detection, local positioning in ubiquitous computing or non-destructive testing. Here, Kasami, Golay and Loosey Synchronous codes are experimentally tested in a privacy-oriented ultrasonic Local Positioning System based on hyperbolic trilateration.