Improved low-voltage-ride-through capability of fixed-speed wind turbines using decentralised control of STATCOM with energy storage system

The design and implementation of a new control scheme for reactive power compensation, voltage regulation and transient stability enhancement for wind turbines equipped with fixed-speed induction generators (IGs) in large interconnected power systems is presented in this study. The low-voltage-ride-through (LVRT) capability is provided by extending the range of the operation of the controlled system to include typical post-fault conditions. A systematic procedure is proposed to design decentralised multi-variable controllers for large interconnected power systems using the linear quadratic (LQ) output-feedback control design method and the controller design procedure is formulated as an optimisation problem involving rank-constrained linear matrix inequality (LMI). In this study, it is shown that a static synchronous compensator (STATCOM) with energy storage system (ESS), controlled via robust control technique, is an effective device for improving the LVRT capability of fixed-speed wind turbines

The control of power electronic converters for grid code compliance in wind energy generation systems

This research report reviews some of the latest control schemes for the power electronic converters found in modern variable speed wind turbines in order to comply with various grid codes. Various control schemes, in order to comply with low voltage ride-through requirements, active and reactive power control and frequency control, are presented. The report first investigates the South African grid code requirements for wind energy generation, and then makes a comparison to grid codes of countries with significant penetration levels and vast experience in wind energy generation. This is followed by a review of the state of the art in fixed and variable speed wind turbine technologies. The research revealed that Type 3 generators offer significant advantages over others but suffer due to grid faults. Various active control schemes for fault ride-through were researched and the method of increasing the rotor speed to accommodate the power imbalance was found to be the most popular. It was found that Type 4 generators offer the best fault ride-through capabilities due to their full scale converters. The research will assist power system operators to develop appropriate and effective grid codes to enable a stable and reliable power system. The research will also provide turbine manufacturers and independent power producers with a comprehensive view on grid codes and relate them to the associated turbine technologies

Power Quality Improvement and Low Voltage Ride through Capability in Hybrid Wind-PV Farms Grid-Connected Using Dynamic Voltage Restorer

© 2018 IEEE. Translations and content mining are permitted for academic research only. Personal use is also permitted, but republication/redistribution requires IEEE permission.This paper proposes the application of a dynamic voltage restorer (DVR) to enhance the power quality and improve the low voltage ride through (LVRT) capability of a three-phase medium-voltage network connected to a hybrid distribution generation system. In this system, the photovoltaic (PV) plant and the wind turbine generator (WTG) are connected to the same point of common coupling (PCC) with a sensitive load. The WTG consists of a DFIG generator connected to the network via a step-up transformer. The PV system is connected to the PCC via a two-stage energy conversion (dc-dc converter and dc-ac inverter). This topology allows, first, the extraction of maximum power based on the incremental inductance technique. Second, it allows the connection of the PV system to the public grid through a step-up transformer. In addition, the DVR based on fuzzy logic controller is connected to the same PCC. Different fault condition scenarios are tested for improving the efficiency and the quality of the power supply and compliance with the requirements of the LVRT grid code. The results of the LVRT capability, voltage stability, active power, reactive power, injected current, and dc link voltage, speed of turbine, and power factor at the PCC are presented with and without the contribution of the DVR system.Peer reviewe

STATCOM and SVC with Wind Turbines

The large wind parks are the feasible solution in order to generate clean energy compared with conventional power plants. Therefore, the interest in the Wind Energy Conversion System (WECS) is quickly increasing to reduce the fossil fuels dependencies. While the penetration of the WECS increases into the grid, many of the technical challenges have appeared. Low voltage Ride Through (LVRT) is the new requirement which needs to be fulfill when the amount of wind power generation increases, to be able to guarantee the power system reliability and stability. The voltage dips that result from faults in the grid can lead to a loss generation unit. According to the LVRT, WTs are required to be always connect during the fault, and to support the power system by supplying reactive power to ensure grid stability. The main purpose of the thesis was to investigate that how the LVRT of Doubly Fed Induction Generator (DFIG) based Wind Turbine Generator (WTG) can be enhanced using shunt connected Flexible AC Transmission System (FACTS) devices Static Synchronous Compensator (STATCOM) and Static Var Compensator (SVC). The theoretical background related to the LVRT enhancement using STATCOM and SVC is performed, and results are verified by the simulation model. This thesis is constructed in 5 Chapters, Chapter 1 gives an overview about the problems related to wind power. Chapter 2 explains the different grid codes and different topologies of the wind turbine technologies. Chapter 3 explains the working principle, construction and applications of the STATCOM and SVC. A comprehensive comparison between the STATCOM and SVC is also explained in this chapter. The operation of DFIG wind turbine during voltage dip is analyzed by using the simulation model in the next Chapter. In the first case, the effect of a three-phase fault on the power system was analyzed without using any compensation device. The LVRT requirements were not fulfilled without any compensation device. Therefore, in the second case, SVC was added in the model. Some improvement was observed in this case, but it was not enough to fulfill very strict LVRT requirements such as German Grid Codes (GGCs).Therefore, in the third case, SVC is replaced by STATCOM to meet the LVRT requirement of GGCs. In the last case, three different ratings of STATCOM were utilized to see the effect on the grid voltage and reactive power support by STATCOMs. The key findings of this thesis work are reported by Chapter 5

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 Review on Stability Improvement of Wind Farm Using FACTS Device

This paper represents a review on Stability improvement of wind farm using the Flexible AC Transmission System (FACTS) device. FACTS devices are used to increase the transient stability on the presence of faults and the integration of renewable sources, like wind energy. Due to continuously varying wind speed and also due to fault the active and reactive power along with terminal voltage fluctuates continuously. By connecting Static Synchronous Compensator (STATCOM) into the grid, the active power, reactive power, and terminal voltage are maintained constant and also help to improve the transient stability of the system

Particle swarm optimization-based superconducting magnetic energy storage for low-voltage ride-through capability enhancement in wind energy conversion system

This article presents a novel application of the particle swarm optimization technique to optimally design all the proportional-integral controllers required to control both the real and reactive powers of the superconducting magnetic energy storage unit for enhancing the low-voltage ride-through capability of a grid-connected wind farm. The control strategy of the superconducting magnetic energy storage system is based on a sinusoidal pulse-width modulation voltage source converter and proportional-integral-controlled DC-DC converter. Control of the voltage source converter depends on the cascaded proportional-integral control scheme. All proportional-integral controllers in the superconducting magnetic energy storage system are optimally designed by the particle swarm optimization technique. The statistical response surface methodology is used to build the mathematical model of the voltage responses at the point of common coupling in terms of the proportional-integral controller parameters. The effectiveness of the proportional-integral-controlled superconducting magnetic energy storage optimized by the proposed particle swarm optimization technique is then compared to that optimized by a genetic algorithm technique, taking into consideration symmetrical and unsymmetrical fault conditions. A two-mass drive train model is used for the wind turbine generator system because of its large influence on the fault analyses. The systemic design approach is demonstrated in determining the controller parameters of the superconducting magnetic energy storage unit, and its effectiveness is validated in augmenting the low-voltage ride-through of a grid-connected wind farm