Emilio Bueno

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.

Discrete-time implementation of second order generalized integrators for grid converters

Second order generalized integrators (SOGI) have been proposed to obtain zero steady-state error using stationary frames in grid-converters applied to active rectifiers, active filters, uninterruptible power supplies and distributed generation. These integrators have been also included in algorithms of grid synchronization, detection of sequences, harmonic compensation, etc. Due to all these algorithms are implemented over digital processors, it is very important to make a correct discretization to optimize their behaviour. This work is focused in this topic. An exhaustive study about different methods to implement the SOGIs in the discrete-time is achieved, proposing a common structure for the different SOGI applications, including proposals of C program and presenting a comparative analysis about the execution time using different digital structures.

A Generalized Delayed Signal Cancellation Method for Detecting Fundamental-Frequency Positive-Sequence Three-Phase Signals

A novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage vector based on a generalization of the delayed signal cancellation method is proposed in this paper. The technique is implemented by sampling and storing the instantaneous αβ voltage vector. A mathematical transformation is then proposed through which the current and delayed voltage vectors are combined. It is shown that the proposed transformation has unity gain for the fundamental-frequency positive-sequence voltage vector, while its gain is equal to zero for some chosen components. Cascaded transformations can then be used for eliminating the fundamental-frequency negative-sequence vector, as well as chosen positive- and negative-sequence harmonic vector components and, thus, for accurately obtaining the fundamental-frequency positive-sequence voltage vector. The output of the last transformation block is input to a synchronous reference frame phase-locked loop for detecting frequency and position of the positive-sequence vector. A proposal for making the scheme frequency adaptive is also presented. The good performance of the proposed method is verified with simulations and experiments by using distorted and unbalanced signals, containing fundamental-frequency as well as positive- and negative-sequence harmonic components. The proposed method frequency adaptation capability is also verified.

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.

Digital Filters for Fast Harmonic Sequence Component Separation of Unbalanced and Distorted Three-Phase Signals

In this paper, two methods for determining the fundamental frequency and harmonic positive- and negative-sequence components of three-phase signals are investigated. Many aspects of the space-vector discrete Fourier transform and generalized delayed signal cancellation (GDSC) such as response time for different possible implementations, frequency adaptation schemes, stability of recursive implementation, and rounding error effects are discussed. A new design procedure for GDSC transformations is presented. New indices for characterizing three-phase unbalanced and distorted signals are proposed. Simulations and experiments are included in order to verify the performances and illustrate the theoretical conclusions.

Grid Impedance Monitoring System for Distributed Power Generation Electronic Interfaces

This paper proposes a grid impedance monitoring system for distributed power generation electronic interfaces. The system estimates the grid equivalent impedance and voltage source from the voltage measurements performed at the point of common coupling. The estimation algorithm is based on a recursive least-squares algorithm implemented in the complex field. Simultaneously, the system evaluates the quality of the estimation, minimizing its influence on the grid and detecting islanding situations. The proposed system performance has been evaluated under experimental testing.

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.

Influence analysis of the effects of an inductive-resistive weak grid over L and LCL filter current hysteresis controllers

The objective of this paper is to analyse the influence of a non-ideal grid over hysteresis controllers of converters connected to the grid through both L and LCL filters. The paper will describe the different possible configurations in both cases, analysing the effect of a general R-L grid. Limit values for both grid inductance and resistance are given for the L structure. In the case of LCL connection, the analysis will overview important issues such as active damping, and switching behaviour giving limits to stability as a function of grid impedance value.

Current control of voltage source converters connected to the grid through an LCL-filter

The aim of this paper is to propose a current control of VSCs connected to the grid through an LCL-filter. The proposed algorithm controls the grid current using only two sensors. Other variables are obtained with a state estimator, and the possible disturbances of the system are attenuated with active damping. The control algorithm has been proved for different disturbances, such as temporal variations in the components of the model and perturbations in the grid, and also with the linear and nonlinear models.

SPLL design to flux oriented of a VSC interface for wind power applications

Accurate phase information is crucial for most of modern power electronic systems such as VSC connected to the grid. In this paper, it is proposed an algorithm software phase-locked loop (SPLL) to obtain phase and frequency information of the grid voltage. This is based in an algorithm of on-line separation of the grid voltage sequences (DSC), and a discrete traditional PLL. A criterion to tune the SPLL constants from a PLL discrete linearized model is discussed. The SPLL response is evaluated for different grid disturbances and different SPLL parameters. Besides, a VSC connected to the grid through and L filter with the SPLL obtained in this paper has been tested for different configurations of SPLL and different grid perturbations. Conclusions about where to apply the SPLL different configurations are obtained from these last tests.