Application of Unified Power Flow Controller to Improve the Performance of Wind Energy Conversion System

This research introduces the unified power flow controller (UPFC) as a means to improve the overall performance of wind energy conversion system (WECS) through the development of an appropriate control algorithm. Also, application of the proposed UPFC control algorithm has been extended in this research to overcome some problems associated with the internal faults associated with WECS- voltage source converter (VSC), such as miss-fire, fire-through and dc-link faults

A New Converter Station Topology to Improve the Overall Performance of a Doubly Fed Induction Generator-Based Wind Energy Conversion System

This thesis presents a reliable and cost effective technique that calls for reconfiguration of the existing converters of a typical Doubly Fed Induction Generator to include a coil of low internal resistance. A coil within the DC link is the only hardware component required to implement this technique. With a proper control scheme, activated during fault conditions, this coil can provide the same degree of performance as a superconducting magnetic energy storage unit during fault conditions

Fault Ride-Through Capacity Enhancement of Fixed Speed Wind Generator by A Modified Bridge-type Fault Current Limiter

Fault Ride-Through (FRT) is a common requirement to abide by grid code all over the world. In this work, to enhance the fault ride-through capability of a fixed speed wind generator system, a modified configuration of Bridge-Type Fault Current Limiter (BFCL) is proposed. To check the effectiveness of the proposed BFCL, its performance is compared with that of the Series Dynamic Braking Resistor (SDBR). A harmonic performance improvement by the proposed method is also analyzed. Three-line-to-ground (3LG), line-to-line (LL) and single-line-to-ground (1LG) faults were applied to one of the double circuit transmission lines connected to the wind generator system. Simulations were carried out using Matlab/Simulink software. Simulation results show that the proposed BFCL is very effective device to achieve the FRT and suppress fault current that eliminates the need for circuit breaker replacement. Also, the BFCL improves the harmonic performance and helps follow harmonic grid code. Moreover, it was found that the BFCL works better than the SDBR, and has some distinct advantages over the SDBR

Loss allocation in a distribution system with distributed generation units

In Denmark, a large part of the electricity is produced by wind turbines and combined heat and power plants (CHPs). Most of them are connected to the network through distribution systems. This paper presents a new algorithm for allocation of the losses in a distribution system with distributed generation. The algorithm is based on a reduced impedance matrix of the network and current injections from loads and production units. With the algorithm, the effect of the covariance between production and consumption can be evaluated. To verify the theoretical results, a model of the distribution system in Brønderslev in Northern Jutland, including measurement data, has been studied

Active power control response from large offshore wind farms

This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel University LondonThe GB power system will see huge growth in transmission connected wind farms over the next decade, driven by European clean energy targets. The majority of the UK’s wind development is likely to be offshore and many of these wind farms will be interfaced to the grid through power converters. This will lead to a loss of intrinsic inertia and an increasing challenge for the system operator to keep grid frequency stable. Given this challenge, there is increasing interest in understanding the capabilities of converter control systems to provide a synthesised response to grid transients. It is interesting to consider whether this response should be demanded of wind turbines, with a consequential reduction in their output, or if advanced energy storage can provide a viable solution. In order to investigate how large offshore wind farms could contribute to securing the power system, wind turbine and wind farm models have been developed. These have been used to design a patented method of protecting permanent magnet generator’s converters under grid faults. Furthermore, these models have enabled investigation of methods by which a wind turbine can provide inertial and frequency response. Conventionally inertial response relies on the derivative of a filtered measurement of system frequency; this introduces either noise, delay or both. This research proposes alternative methods, without these shortcomings, which are shown to have fast response. Overall, wind farms are shown to be technically capable of providing both high and low frequency response; however, holding reserves for low frequency response inevitably requires spilling wind. Wind’s intermittency and full output operation are in tension with the need of the power system for reliable frequency response reserves. This means that whilst wind farms can meet the technical requirements to hold reserves, they bid uncompetitive prices in the market. This research shows that frequency response market prices are likely to rise in future suggesting that the Vanadium Redox Flow Battery is one technology which could enter this market and also complement wind power. Novel control incorporating fuzzy logic to manage the battery is developed to allow a hybrid wind and storage system to aggregate the benefits of frequency response and daily price arbitrage. However, the research finds that the costs of smoothing wind power output are a burden on the store’s revenue, leading to a method of optimising the combined response from an energy store and generator that is the subject of a patent application. Furthermore, whilst positive present value may be derived from this application, the long payback periods do not represent attractive investments without a small storage subsidy.The Engineering and Physical Sciences Research Council (EPSRC) and GE Energ