Wind energy has emerged as the fastest growing source of energy, with over 48,000 MW installed throughout the world today.� With the recent extension of the Production Tax Credit under the Energy Policy Act of 2005, wind power is expected to see continued strong growth in the immediate future. It is projected to provide a total cumulative world-wide capacity of 117,000 MW (roughly 1.25% of the world?s electricity generation) by 2009 according to BTM Consult ApS. As the total base of installed wind capacity continues to grow with the installation of additional wind turbines and new wind farms, compliance with interconnection criteria becomes increasingly important. In many cases, dynamic voltage regulation and continuous power factor correction are required to keep wind turbine generators online, assuring that the business interests and reliability expectations of both wind developers and utilities are met.
Technical challenges
Developers, operators, and utilities face many challenges when interconnecting large, distributed sources of generation with fluctuating output, such as wind energy. These challenges come in many forms.
Many of today?s wind turbines are induction type generators that absorb large amounts of VARs (Volt-Amperes Reactive) from the grid. For such machines, VAR flow fluctuates with the power output of the turbines. Uncompensated, these variations in VAR flow can cause severe voltage fluctuations, affecting overall power quality and the reliability of the local transmission grid. Traditionally, switched capacitors have been used to compensate for fluctuating VAR requirements. However, a typical wind farm can experience 50-100 capacitor switching events on a given day.� Such frequent switching can cause stresses, effectively reducing life-cycle times of the capacitor switches. In addition, some wind generator gearboxes are sensitive to large step changes in voltage associated with normal capacitor switching, which can overstress the gearbox - one of the costliest and most maintenance intensive components of a wind turbine.
Keeping wind turbines online under low voltage conditions is also a potential trouble spot that developers and operators need to consider. Transient voltage events that drop voltage below turbine tolerance levels can cause generators to trip offline.� Most interconnection standards today require wind farms to have the ability to ride through faults (Low Voltage Ride Through). This can be accomplished either by the wind turbine manufacturer or with a centralized solution in the wind farm substation.
AMSC solutions for wind farms
D-VAR systems
American Superconductor?s D-VAR system is ideally suited to help meet wind farm interconnection standards.� The D-VAR system is a fully integrated, inverter-based reactive compensation system (STATCOM). It can be seamlessly integrated with low cost capacitor banks in an extremely cost-effective solution that provides steady-state voltage regulation, power factor correction, and low voltage ride through capability for the entire wind farm. The D-VAR system can also ?soft-switch? capacitors, thereby eliminating the voltage step changes seen by the wind farm and the utility.
PowerModule Power Electronic Converters
The AMSC PowerModule PM1000 is a power converter designed with a building block approach that can be placed right in the wind turbine. The PM1000 inverter can provide power flow control and low voltage ride through (LVRT) capability, similar to the external D-VAR solution, and is cost effective for smaller wind farms. It is a highly power dense (130 W/ in3), fully programmable, flexible and modular system and can be applied to various wind turbine makes and models.
SuperVAR Dynamic Synchronous Condenser
AMSC?s SuperVAR Dynamic Synchronous Condenser is a new breakthrough product. Similar to D-VAR systems, SuperVAR machines can be applied at strategic locations to stabilize grid voltage, increase reliability, and maximize transmission capacity.
SuperVAR machines use standard synchronous condenser frames and stator coils paired with advanced power-dense rotor coils made from AMSC's superconductor wire. The result is a synchronous condenser that is more efficient than conventional rotating machines - without the high rotor maintenance costs typical of older, conventional synchronous condensers. SuperVAR machines are specifically designed for continuous, steady-state dynamic VAR support, with lower standby losses, higher output, and greater reliability than conventional synchronous condensers.
Both D-VAR systems and SuperVAR machines are cost effective solutions that can provide tight voltage regulation and power factor correction to alleviate fluctuating voltage and VAR demands at wind farms.
