Wind Engineering

A model of the back-to-back converter is set up and implemented in the simulation tool PSS/E as a user-developed model. This model is applied with that of the doubly-fed induction generator (DFIG), described in previous parts of this work [parts II and I]. The latter models variable-speed wind turbines in power stability investigations. Subjected to a short circuit fault, there will be a risk of converter blocking, followed by tripping of the wind turbine [1, 3]. The main reasons of blocking are over-current in the rotor converter and over-voltage in the dc-link. The DFIG model, with representation of the back-to-back converter, results in (a) more accurate replication of the current in the rotor converter and (b) improved computation of the dc-link voltage. These improvements are compared with the model with representation of the rotor converter only. Hence, the DFIG model with representation of the back-to-back converters might be preferred, in practical investigations of power system stability, to models with representation of the rotor converter only.

A control strategy to improve the stability of a large wind farm using a Static Reactive Power Compensator (STATCOM) and Dynamic Braking Resistor (DBR) is proposed and investigated. The STATCOM supplies the reactive power demand of the wind farm dynamically in order to maintain the network voltage. The DBR is controlled by Liapunov's stability criterion to absorb the active power of the wind farm during the network fault. The performance of the STATCOM and DBR, applied to a large wind farm (60MW), is studied in PSCAD/EMTDC. The simulation results show that effective control of the STATCOM and DBR together can enhance the stability of large wind farms.

An innovative delta-star three-phase winding, developed earlier for harmonic reduction in 3-phase induction motors, is applied for constant speed grid-connected induction generators. A method has been developed for the prediction of the performance of the generator with such an unconventional winding. It has been demonstrated that with a suitable switching arrangement, the proposed delta-star generator can result in increased real power delivered to the grid and reduced reactive power drawn from the grid, as compared to a fixed stator configuration. A suitable microcontroller-based switching-scheme has also been designed for changing the stator connection according to the wind speed. The facility for using the star mode of the generator while connecting it to the grid with much reduced inrush current is also illustrated.

This study examines the integrated use of wind turbines, natural gas and high temperature fuel cells to produce methanol. The purpose is to produce transportation fuel from national local resources with the least polluting emissions. The fuel would displace petroleum imports and reduce greenhouse gas emissions by converting wind power, natural gas and fuel cell energy. The proposal includes the utilization of waste heat and exhaust gas (CO₂) into clean liquid fuel (methanol) that is compatible with future vehicle technology based on fuel cells. Potential designs are presented and assessed for methanol yield, production cost and emissions reductions. Results show that this process (a) can produce significant amounts of vehicle fuel, comparable to what is annually consumed in the U.S. (∼19 EJ/y); (b) can minimize emissions; (c) is potentially cost competitive with other technologies that produce methanol; and (d) is compatible with the requirements of a new generation of vehicles based on fuel cells.

This paper analyses the potential for wind power in Brazil replacing thermal power plant and hence contributing to greenhouse gases (GHG) mitigation through emission reductions credits. The focus of the analysis is concentrated on the Brazilian states of Ceará and Rio Grande do Norte. These states have participated strongly in the allocation of generating licenses for wind power plant granted by ANEEL in Brazil (ca. 68% of 5,637.9 MW). If 20% of the coastal areas of Ceará's and Rio Grande do Norte's have wind parks (409 km²), then the wind power delivered is expected to be nearly 17 TW h/y, giving GHG emission reduction of at least 8 times 10⁶ tonnes/y of CO₂. Consequently, the value of their credits in the GHG emission markets in these states would be about US$ 83 million/y.

This paper summarizes a feasibility study of potential wind-hybrid power systems for the islands of New England. The work included the compilation of an inventory of New England coastal islands, a categorization of the islands according to energy related criteria, and an overview of their present electricity supply. It also includes a proposal of wind-hybrid power systems for two selected islands, and an estimation of their technical performance and economic merits.