This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

High-Power Wind Energy Conversion Systems: State-of-the-Art and Emerging Technologies

Doubly fed induction generators (DFIGs), often organized in wind parks, are the most important generators used for variable-speed wind energy generation. This paper reviews the control systems for the operation of DFIGs and brushless DFIGs in wind energy applications. Control systems for stand-alone operation, connection to balanced or unbalanced grids, sensorless control, and frequency support from DFIGs and low-voltage ride-through issues are discussed.

Overview of Control Systems for the Operation of DFIGs in Wind Energy Applications

A review of the recent advances in superhydrophobic surfaces and the emerging energy-related applications

The application of a dynamic voltage restorer (DVR) connected to a wind-turbine-driven doubly fed induction generator (DFIG) is investigated. The setup allows the wind turbine system an uninterruptible fault ride-through of voltage dips. The DVR can compensate the faulty line voltage, while the DFIG wind turbine can continue its nominal operation as demanded in actual grid codes. Simulation results for a 2 MW wind turbine and measurement results on a 22 kW laboratory setup are presented, especially for asymmetrical grid faults. They show the effectiveness of the DVR in comparison to the low-voltage ride-through of the DFIG using a crowbar that does not allow continuous reactive power production.

/pdf/fault-ride-through-of-a-dfig-wind-turbine-using-a-dynamic-1kl4tp229a.pdf

Fault Ride-Through of a DFIG Wind Turbine Using a Dynamic Voltage Restorer During Symmetrical and Asymmetrical Grid Faults

This paper presents a comprehensive study on the latest grid code regulations enforced by transmission system operators on large wind power plants (WPPs). First, the most common requirements included in the majority of international grid codes are compared; namely, low and high voltage ride-through capabilities, active and reactive power responses during and after faults, extended range of voltage–frequency variations, active power (frequency) control facility, and reactive power (voltage) regulation support. The paper also presents a discussion on the global harmonization of international grid codes as well as future trends expected in the regulations. Finally, the evolution of different wind generator technologies to fulfill various grid code requirements is investigated. The presented study will assist system operators to establish their connection requirements for the first time or to compare their existing regulations with other operators. It also enables wind turbine manufacturers and wind farm developers to obtain a more precise understanding from the latest international requirements imposed on modern wind farms.

Review of international grid codes for wind power integration: Diversity, technology and a case for global standard

A new approach for AC-DC power conversion with fast dynamic response is proposed, which is based on instantaneous DC-side current demand. The reference current with negligible transients is achieved in a single switching period under balanced and unbalanced source voltage conditions. Unlike conventional AC-DC systems, the output DC voltage can be higher or lower than the maximum value of the input voltage. In the buck operating mode, smaller voltage rating of switches can be selected and high voltage supplies can operate with low voltage switches. As the high frequency current harmonics are minimal, there is no need to use ferrite cores or high frequency inductors. This results in a simple product that is particularly suitable for high power applications. As the only measurements in the AC side are the three-phase currents, the phase-locked loop circuit is eliminated, computation time is reduced and high sampling rates are not required. The unique features of this new approach make it a viable solution for the grid-side converter in doubly-fed induction generators for wind power applications. Simulations results are compared to a direct power control rectifier to show the feasibility of this new approach as a power source converter.

A New Approach for Three-phase Rectification with Minimum Measurement and Computational Requirements for Wind Power Applications

This paper presents a powerline earthing assessment carried out based upon the latest Australian Standard on Overhead Lines, AS/NZS 7000:2010. The 33kV powerline under study supplies a mining process plant spread over a relatively large geographical area. A number of on-site soil resistivity tests have been undertaken to identify the electrical characteristics of the local soil, followed by network analysis in DIgSILENT PowerFactory to obtain the most onerous earth fault parameters. Safety step and touch voltage limits are obtained in accordance to AS/NZS 7000. Finally detailed modelling analysis in CDEGS software package investigates the most economically efficient earthing design that complies with the safety voltage criteria obtained from AS/NZS 7000.

http://ieeexplore.ieee.org/iel7/6954270/6966468/06966583.pdf

Powerline earthing design in compliance with the latest Australian Standard on Overhead Lines, AS/NZS 7000:2010

Current grid codes request the wind turbines (WTs) to have a decent level of fault ride through (FRT) capability and also participate in recovering the network stability following contingencies. Modern WTs are mostly equipped with power converters that allow them to control the output power under various operating conditions. However, there are some Fixed Speed Induction Generators (FSIGs) still operating. FSIGs have simple and economic construction. But under fault, they are very susceptible to rotor overspeed that may lead to disconnection from the grid. For variable speed WTs, application of power converters can improve the controllability of the turbines but modifications in their PQ capability are needed to meet the network requirements. This paper is aimed to investigate the impacts of connecting full converter wind generators (FCWGs) to improve FRT capability of FSIGs within a weak network. The implemented reactive power supports set in Danish and Australian Grid Codes will be assessed based on their influences on the FRT capability of FSIGs. Impacts of FCWGs locations as reactive power providers and fault durations on the FRT capability of FSIGs will also be discussed. Results confirm that FRT capability of FSIGs can be improved in accordance with enhanced capability of FCWGs.

Mansour Mohseni

Papers

A New Approach for Three-phase Rectification with Minimum Measurement and Computational Requirements for Wind Power Applications

Powerline earthing design in compliance with the latest Australian Standard on Overhead Lines, AS/NZS 7000:2010

Fault ride through capability of Fixed Speed Induction Generators connecting to full converter wind generation system within weak network