With wind turbines (WTs) emerging as the fastest growing energy source in the world, there has been a continuous rise in the size of wind farms and capacity of WTs. This has required an increase in the operating voltage of wind farms to keep power transmission losses as low as possible. Electric drives in WT generators (WTGs) are a popular choice among industry entrants looking for cost-effective ways to produce power efficiently and achieve the return on investment desired, while meeting grid code requirements.
A new report from Frost & Sullivan, 'Global Outlook for Electric Drives in the Wind Power Industry,' states that the industry earned revenues of $1.6billion in 2009 and estimates this to reach $4.10billion in 2015.
Electric drives in WTGs are popular among wind farm owners because these drives do not contain any part that requires maintenance. Frost & Sullivan program manager Abhishek Gokhale explains: "The goal of electric drives is to avoid the complexity of a multistage gearbox by employing variable-speed generators and solid-state electronic converters that produce utility-quality alternating current (AC). This will help achieve compactness and, thereby, less maintenance."
There has been a marked preference for direct-drive systems in the last couple of years. Variability and intermittency of wind are encouraging suppliers to deploy direct-drive technologies with full power converter systems. This will give them higher energy efficiencies, less maintenance than conventional gearbox machines and more power output.
Gokhale adds: "Market entrants from European countries and China are adopting direct-drive technologies, which simplifies the nacelle systems, augments reliability and efficiency as well as avoids gearbox issues. WT suppliers are designing technologies that are lighter and more cost-effective than the conventional geared drive trains, and these are expected to drive the new installations."
Scientists are also developing new systems for guidance, control and connecting the WT with power grids. Wind farms are located in remote areas, while the greatest power demand is from cities. This means that the power supply depends on a robust transmission grid. However, with the proliferation of wind farms, transmission lines could be hard to procure. Indeed, a lack of transmission line infrastructure particularly affects the North American and Asian regions. Therefore future wind power plants will not only support the grid by delivering fault ride capability as well as frequency, voltage and volt-ampere-reactive (VAR) control, but also carry a share of power control capability for the grid. Modern designs of generators and electric drives are likely to be customised to suit WT operation.
Taking into account their energy yield and reliability, direct-drive generator systems with electric drives are expected to be more suited to WTs than geared drive systems, especially for offshore applications, in which maintenance is a major concern. Electric drive manufacturers can position themselves to control a share of the growing electric drives used in double-fed induction and permanent magnet generators.
Gokhale notes: "Some of the established WT suppliers already have in-house capabilities to manufacture 20 to 40 per cent of their drive requirements in-house. However, there is a huge opportunity from the end-user markets of new entrants and WTG suppliers that outsource their electric drives requirements."
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