Alejandro Rolan

Modeling of a variable speed wind turbine with a Permanent Magnet Synchronous Generator

The aim of this work is to analyze a typical configuration of a Wind Turbine Generator System (WTGS) equipped with a Variable Speed Generator. Nowadays, doubly-fed induction generators are being widely used on WTGS, although synchronous generators are being extensively utilized too. There are different types of synchronous generators, but the multi-pole Permanent Magnet Synchronous Generator (PMSG) is chosen in order to obtain its model. It offers better performance due to higher efficiency and less maintenance since it does not have rotor current and can be used without a gearbox, which also implies a reduction of the weight of the nacelle and a reduction of costs. Apart from the generator, the analyzed WTGS consists of another three parts: wind speed, wind turbine and drive train. These elements have been modeled and the equations that explain their behavior have been introduced. What is more, the whole WTGS has been implemented in MATLAB/Simulink interface. Moreover, the concept of the Maximum Power Point Tracking (MPPT) has been presented in terms of the adjustment of the generator rotor speed according to instantaneous wind speed.

Photovoltaic inverters with fault ride-through Capability

This paper presents a new control strategy that allow the photovoltaic system operate under grid faults without overpass the rated current and assuring sinusoidal currents. In the classic control strategies used in photovoltaic systems the power delivered to the grid remains constant when a fault occurs, hence the current can reach dangerous values. Therefore the converter has a protection system to disconnect it avoiding its damage. Thus it must be connected manually when the electrical grid is re-established. The strategy presented here overcomes these drawbacks. It is compared with the classic strategy through simulations in PSCAD and the experimental results prove its effectiveness.

Losses and CMV evaluation in transformerless grid-connected PV topologies

Controlling the thermal losses in the semiconductors as well as the Common Mode Voltage (CMV), are important issues in the design of power electronics converters for photovoltaic applications. At present time there are several topologies that offer a good performance regarding losses and CMV. In this paper an evaluation of three of these converters topologies: H5, HERIC and NPC transformerless for single phase PV systems will be carried out by means of simulations performed with PSIM 7.05. This software permits to estimate accurately the switching and conduction losses, thanks to its Thermal Module. This analysis together with the CMV study for each case will permit to establish the pros and cons of each topology.

Doubly Fed Induction Generator Subject to Symmetrical Voltage Sags

The aim of this paper is to analyze the dynamic behavior of the doubly fed induction generator (DFIG) subject to symmetrical voltage sags caused by three-phase faults. A simple control algorithm is considered and assumed ideal: the rotor current in the synchronous reference frame is kept constant. This hypothesis allows the electrical transient to be solved analytically, providing a comprehensive description of DFIG behavior under symmetrical sags. The fault-clearing physics of symmetrical sags is also analyzed. That is, the fault is cleared in the successive natural fault-current zeros, leading to a voltage recovery in one, two, or three steps. This clearing process, called discrete fault clearing in this paper, results in a more accurate sag modeling than the abrupt or instantaneous fault clearing (the usual modeling in the literature). The fault-clearing process has a strong influence on the rotor voltage required to control the rotor current after fault clearing. To compare the effects of both abrupt and discrete sags, different wind turbine (WT) operating points, which determine different generated powers, are considered. This study helps in the understanding of WT fault ride-through capability.

An approach to the Performance-Oriented Model of Variable-Speed Wind turbines

The aim of this work is to give an approach to the Performance-Oriented Model of Variable-Speed Wind turbines (VSWTs) equipped with permanent magnet synchronous generator (PMSG), and compare it to the component-oriented model. In the present work it will be analyzed how a change in the wind speed affects the power delivered from the generator by means of two approaches: firstly, the component-oriented model of the VSWT-based PMSG is given, i.e. the dynamic equations of the system are shown, and then, it is discussed how to obtain an equivalent transfer function of the whole system. A comparison between both approaches is discussed in this work.

Modeling and simulation of synchronous machine and its behaviour against voltage sags

This paper studies the effects of voltage sags (dips), both symmetrical and unsymmetrical, on the three-phase Synchronous Machine (SM). The vast majority of the electrical power generation systems in the world is consist of synchronous generators coupled to the electrical network though a transformer. Voltage sags on SM cause speed variations, current and torque peaks and hence may cause tripping and equipment damage. The consequences of voltage sags in the machine behaviour depends on different factors such as its magnitude (or depth), duration and initial point-on-wave, and also on the parameters of the machine. In this study, three machines of different nominal power have been used for simulate on MATLAB the effects of the voltage sags on the machine under specific conditions.

Simulation of Wound Rotor Synchronous Machine under voltage sags

This paper presents a study of the Wound Rotor Synchronous Machine (SM) stability under voltage sags (dips). Machine behavior has been analyzed by considering different magnitudes (or depths) and duration of the sag. Voltage sags cause speed variations on SM (with possible lost of synchronism), current and torque peaks and hence may cause tripping and equipment damage, which leads to financial losses. Three machines of different nominal power have been modeled and simulated with MATLAB in order to study its behavior under voltage sags. These SMs have been analyzed operating as generator, as motor, and in both cases, working under-excited and overexcited.

Control strategies for DFIG wind turbines under grid fault conditions

The classical control techniques for regulating the active and reactive power delivery in doubly fed induction generators (DFIG), for wind power applications, are normally based on voltage oriented control (VOC) strategies. Among these algorithms, those that work in a synchronous reference frame, attached to the magnetic flux vector, became very popular. In spite of the good behaviour of such algorithms their performance depends highly on an accurate detection of the stator flux position, something that can be critical under unbalanced or distorted grid voltage conditions. This paper presents a new VOC strategy able to control the operation of a DFIG in the ¿ß reference frame, with no need of flux position estimation, something that conducts to a more simple and robust algorithm. In order to evaluate the advantages of this new control proposal, namely VOC-RRF, their performance will be compared with the response obtained with a classical VOC algorithm by means of PSCAD/EMTDC® simulation models.

Control Strategies for DFIG Wind Turbines Under Grid Fault

The classical control techniques for regulating the active and reactive power delivery in doubly fed induction generators (DFIG), for wind power applications, are normally based on voltage oriented control (VOC) strategies. Among these algorithms, those that work in a synchronous reference frame, attached to the magnetic flux vector, became very popular. In spite of the good behaviour of such algorithms their performance depends highly on an accurate detection of the stator flux position, something that can be critical under unbalanced or distorted grid voltage conditions. This paper presents a new VOC strategy able to control the operation of a DFIG in the ¿ß reference frame, with no need of flux position estimation, something that conducts to a more simple and robust algorithm. In order to evaluate the advantages of this new control proposal, namely VOC-RRF, their performance will be compared with the response obtained with a classical VOC algorithm by means of PSCAD/EMTDC® simulation models.