Sveobuhvatan pregled LVRT mogućnosti i kliznog režima upravljanja vjetroagregata spojenog na mrežu s dvostruko napajanim asinkronim generatorom

In this paper, a comprehensive review of several strategies applied to improve the Low Voltage Ride-Through (LVRT) capability is presented for grid-connected wind-turbine-driven Doubly Fed Induction Generator (DFIG). Usually, the most proposed LVRT solutions in the literature based on: hardware solutions, which increase the system costs and software solutions, which increase the control system complexity. Therefore, the main objective of this study is to take into account grid requirements over LVRT performance under grid fault conditions using software solution based on Higher Order-Sliding Mode Control (HOSMC). Effectively, this control strategy is proposed to overcome the chattering problem and the injected stator current harmonics into the grid of the classical First Order Sliding Mode (FOSMC). Furthermore, the resultant HOSMC methodology is relatively simple; where, the online computational cost and time are considerably reduced. The LVRT capacity and effectiveness of the proposed control method, compared to the conventional FOSMC, are validated by time-domain simulation studies under Matlab on a 1.5 MW wind-turbine-driven DFIG.U ovom radu, prikazan je sveobuhvatan pregled strategija primjenjenih za poboljšanje sposobnosti rada tijekom prolaznih smetnji niskog napona mreže za vjetroagregat s dvostruko napajanim asinkronim generatorom (DFIG). Uobičajeno, većina predloženih LVRT rješenja u literaturi temelji se na: hardverskim rješenjima, što povećava troškove sustava i softverskih rješenja te složenost sustava upravljanja. Stoga je glavni cilj ovog istraživanja da se uključuje i zahtjevi mreže kroz ponašanje LVRTa u uvjetima mrežnih kvarova korištenjem softverskog rješenja zasnovanoga na kliznom režimu rada višeg reda (HOSMC). Efektivno, ova upravljačka strategija je predložena kako bi se prevladali oscilacije i ubacivanje harmonika struje statora u mrežu klasičnim metodama kliznog režima rada prvog reda (FOSMC). Nadalje, rezultantna metodologija HOSMC je relativno jednostavna; gdje su online računski zahtjevi i potrebno vrijeme značajno smanjeni. LVRT kapacitet i učinkovitost predložene metode upravljanja, u usporedbi s konvencionalnim FOSMC potvrđene su simulacijama u vremenskoj domeni u Matlabu na 1.5 MW vjetroagregatu s DFIG-om

DFIG Driven Wind Turbine Grid Fault-Tolerance Using High-Order Sliding Mode Control

International audienceThis research note deals with grid fault-tolerance of a doubly-fed induction generator-based wind turbine using high-order sliding mode control. Indeed, it is proposed to assess the main and attractive features of high-order sliding modes which are robustness against external disturbances (e.g. grid) and chattering-free behavior (no extra mechanical stress on the drive train). Simulations using the NREL FAST code on a 1.5-MW wind turbine are carried-out to evaluate ride-through performances of high-order sliding mode control

Low-voltage ride-through techniques for DFIG-based wind turbines: State-of-the-art review and future trends

This paper deals with low-voltage ride-through (LVRT) capability of wind turbines (WTs) and in particular those driven by a doubly-fed induction generator (DFIG). This is one of the biggest challenges facing massive deployment of wind farms. With increasing penetration of WTs in the grid, grid connection codes in most countries require that WTs should remain connected to the grid to maintain the reliability during and after a short-term fault. This results in LVRT with only 15% remaining voltage at the point of common coupling (PCC), possibly even less. In addition, it is required for WTs to contribute to system stability during and after fault clearance. To fulfill the LVRT requirement for DFIG-based WTs, there are two problems to be addressed, namely, rotor inrush current that may exceed the converter limit and the dc-link overvoltage. Further, it is required to limit the DFIG transient response oscillations during the voltage sag to increase the gear lifetime and generator reliability. There is a rich literature addressing countermeasures for LVRT capability enhancement in DFIGs; this paper is therefore intended as a comprehensive state-of-the-art review of solutions to the LVRT issue. Moreover, attempts are made to highlight future issues so as to index some emerging solutions

A Real-Time Sliding Mode Control for a Wind Energy System Based on a Doubly Fed Induction Generator

In this paper, a real time sliding mode control scheme for a variable speed wind turbine that incorporates a doubly feed induction generator is described. In this design, the so-called vector control theory is applied, in order to simplify the system electrical equations. The proposed control scheme involves a low computational cost and therefore can be implemented in real-time applications using a low cost Digital Signal Processor (DSP). The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. A new experimental platform has been designed and constructed in order to analyze the real-time performance of the proposed controller in a real system. Finally, the experimental validation carried out in the experimental platform shows; on the one hand that the proposed controller provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to the uncertainties that usually appear in the real systems.The authors are very grateful to the Basque Government by the support of this work through the project S-PE12UN015 and S-PE13UN039 and to the UPV/EHU by its support through the projects GIU13/41 and UFI11/07

Techniques for Ensuring Fault Ride-Through Capability of Grid Connected DFIG-Based Wind Turbine Systems: A Review

Renewable energy sources (RES) are being integrated to electrical grid to complement the conventional sources to meet up with global electrical energy demand. Among other RES, Wind Energy Conversion Systems (WECS) with Doubly Fed Induction Generator (DFIG) have gained global electricity market competitiveness because of the flexible regulation of active and reactive power, higher power quality, variable speed operation, four quadrant converter operation and better dynamic performance. Grid connected DFIG-based WECS are prone to disturbances in the network because of direct connection of stator windings to grid. The ability of the Wind Turbine (WT) to remain connected during grid faults is termed the Fault Ride-Through (FRT) capability. The grid code requirement for integrating the DFIG-based WTs to power networks specified that they must remain connected and support the grid stability during grid disturbances of up to 1500 ms. The use of compensation devices offers the best FRT compliance thereby protecting the DFIG and the converters from voltage fluctuations and over currents during the grid fault. The paper presents a review of techniques employed in ensuring FRT compliance. The article also proposes the state-of-the-art techniques for compensating voltage sag/swell and limiting the fault short-circuit current. Keywords: Renewable energy sources, DFIG, wind turbine system, fault ride-through, grid codes, dual-functional DV

A Review of Control Techniques for Wind Energy Conversion System

Wind energy is the most efficient and advanced form of renewable energy (RE) in recent decades, and an effective controller is required to regulate the power generated by wind energy. This study provides an overview of state-of-the-art control strategies for wind energy conversion systems (WECS). Studies on the pitch angle controller, the maximum power point tracking (MPPT) controller, the machine side controller (MSC), and the grid side controller (GSC) are reviewed and discussed. Related works are analyzed, including evolution, software used, input and output parameters, specifications, merits, and limitations of different control techniques. The analysis shows that better performance can be obtained by the adaptive and soft-computing based pitch angle controller and MPPT controller, the field-oriented control for MSC, and the voltage-oriented control for GSC. This study provides an appropriate benchmark for further wind energy research

Stator-Flux-Oriented Sliding Mode Control for Doubly Fed Induction Generator

Doubly-fed induction generator (DFIG) is the most implemented electric machine in wind energy conversion systems (WECSs) due to reduced size converter, active and reactive power control, and economic factors. However, the power electronic stage needs an accurate controller that allows to follow the stator power regulation despite the presence of disturbances. On the other hand, sliding-mode control (SMC) offers a fast-dynamic response and provides insensitivity to matched and bounded disturbance/uncertainties, and its natural discontinuous control signals can be used for direct switching of power electronic devices. Switching frequency must be maintained inside acceptable values to avoid exceeding the maximum admissible switching frequency of semiconductors. The contribution of this chapter is a stator-flux–oriented SMC with a hysteresis band that limits the switching frequency of power electronic devices to a set value. Furthermore, the proposed SMCs ensure robustness against bounded low-voltage grid faults. Unlike other nonmodulated techniques like direct torque control (DTC), there is no necessity of modifying the controller structure for withstanding low-depth voltage dips. The controller injects negative sequence voltage/currents to compensate the unbalanced conditions. The advantages of the proposed SMC control are validated via simulations