Lithium-Ion Ultracapacitor Energy Storage Integrated with a Variable Speed Wind Turbine for Improved Power Conversion Control

The energy of wind has been increasingly used for electric power generation worldwide due to its availability and ecologically sustainability. Utilization of wind energy in modern power systems creates many technical and economical challenges that need to be addressed for successful large scale wind energy integration. Variations in wind velocity result in variations of output power produced by wind turbines. Variable power output becomes a challenge as the amount of output power of the wind turbines integrated into power systems increases. Large power variations cause voltage and frequency deviations from nominal values that may lead to activation of relay protective equipment, which may result in disconnection of the wind turbines from the grid. Particularly community wind power systems, where only one or a few wind turbines supply loads through a weak grid such as distribution network, are sensitive to supply disturbances. While a majority of power produced in modern power systems comes from synchronous generators that have large inertias and whose control systems can compensate for slow power variations in the system, faster power variations at the scale of fraction of a second to the tens of seconds can seriously reduce reliability of power system operation. Energy storage integrated with wind turbines can address this challenge. In this dissertation, lithium-ion ultracapacitors are investigated as a potential solution for filtering power variations at the scale of tens of seconds. Another class of issues related to utilization of wind energy is related to economical operation of wind energy conversion systems. Wind speed variations create large mechanical loads on wind turbine components, which lead to their early failures. One of the most critical components of a wind turbine is a gearbox that mechanically couples turbine rotor and generator. Gearboxes are exposed to large mechanical load variations which lead to their early failures and increased cost of wind turbine operation and maintenance. This dissertation proposes a new critical load reduction strategy that removes mechanical load components that are the most dangerous in terms of harmful effect they have on a gearbox, resulting in more reliable operation of a wind turbine

A coordinated control of PMSG based wind turbine generator to improve fault-ride-through performance and transient stability

With the high penetration of wind power into the medium and low voltage power grid, ensuring power quality and transient stability following the utility grid codes become challenging nowadays. Wind power fluctuates with the variation of wind speed which leads to the voltage regulation and frequency control problems in the power grid. Among the issues wind power systems are facing, grid fault is a major one. According to the utility grid codes, wind turbine generators (WTGs) need to have enough fault ride through (FRT) capability. Different configurations of power converters and control techniques have been developed to address this issue. However, a coordinated controller which is capable of the grid voltage regulation, frequency control, and DC link overvoltage minimisation altogether at the time of grid faults is yet to be reported in any literature. This PhD research is focused on developing such a coordinated control method for a permanent magnet synchronous generator (PMSG) based WTG. This coordinated control combines a pitch angle control, a flux weakening control and a reactive power control to enhance the low voltage ride through (LVRT) capability of the PMSG based variable speed wind energy conversion system (WECS). The design process of the controller parameters and the stability of proposed control strategy have been analysed. Here, the pitch angle controller is modified to adjust the pitch for wind power smoothing as well as LVRT enhancement during variable wind speeds and grid fault respectively. The flux weakening controller is used to reduce the flux linkages of PMSG by supplying negative field regulating current to reduce the DC link overvoltage during grid voltage dips. Additionally, static compensator (STATCOM) or grid side converter (GSC) is used to provide reactive power support during the grid faults. Extensive simulations of the proposed method have been carried out under different cases. The proposed control method is compared with the braking chopper (BC) and the battery energy storage system (BESS) based conventional controls via simulations results and are verified to perform better in providing FRT. Frequency stability of the grid connected WECS after the fault recovery is also an important issue which needs to be solved. If the frequency fluctuation goes beyond the safe limit, the power system will collapse creating a cascaded failure that was seen in the South Australian Power System in 2016. Therefore, it is essential to provide primary frequency control support for a stable operation of the power system. Two control methods are considered in this PhD research to provide the grid frequency stability. A simultaneous controller is developed based on the inertia support from the wind turbine and the DC-link capacitor energy to provide the primary frequency control from a PMSG based variable speed WECS. Another approach is developed based on the PMSG flux linkage controller with a Superconducting Magnetic Energy Storage (SMES). The SMES is considered here due to its higher efficiency over other energy storage devices. In this approach, the PMSG flux increases or decreases according to the frequency variation. Similarly, SMES also absorbs or injects some amount of real power when the system frequency is increased or decreased. Both strategies are verified with the WTGS connected to the single and multi-machine power systems under different wind speeds, load demand variations, and grid faults. Time series simulation results illustrate that a significant enhancement of frequency regulation is achieved with both proposed controllers

Overview of storage energy systems for renewable energy system application

The integration of renewable energy system into modern power grids has significantly increased during the last decade. Solar and wind energy are the most popular renewable energy sources recently. Solar energy has reached about 17,3 GW in 2010 whilst about 340 TWh of wind energy source has been installed worldwide. In this paper, the overview of updated information regarding proposed storage energy systems for renewable energy is presented. It is useful information for practitioners in considering the possible options of storage energy technologies to be connected with renewable energy sources

DC-DC converters in wind systems for micro-generation: a systematic review

A literature review about wind systems for micro-generation is presented in this paper. The review is made analyzing four topics of the wind systems: wind system topologies, modeling, power converters design, and power converters control. The review results are presented in two matrices, which highlight research problems that should be addressed

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

Advances in Supercapacitor Technology and Applications Ⅱ

Energy storage is a key topic for research, industry, and business, which is gaining increasing interest. Any available energy-storage technology (batteries, fuel cells, flywheels, and so on) can cover a limited part of the power-energy plane and is characterized by some inherent drawback. Supercapacitors (also known as ultracapacitors, electrochemical capacitors, pseudocapacitors, or double-layer capacitors) feature exceptional capacitance values, creating new scenarios and opportunities in both research and industrial applications, partly because the related market is relatively recent. In practice, supercapacitors can offer a trade-off between the high specific energy of batteries and the high specific power of traditional capacitors. Developments in supercapacitor technology and supporting electronics, combined with reductions in costs, may revolutionize everything from large power systems to consumer electronics. The potential benefits of supercapacitors move from the progresses in the technological processes but can be effective by the availability of the proper tools for testing, modeling, diagnosis, sizing, management and technical-economic analyses. This book collects some of the latest developments in the field of supercapacitors, ranging from new materials to practical applications, such as energy storage, uninterruptible power supplies, smart grids, electrical vehicles, advanced transportation and renewable sources