Wind power control systems go to (temperature) extremes
High-temperature uninterruptible power supply helps Danish control system designers handle Mongolian temperatures up to 55 ºC (131 ºF).
Renee Robbins, Control Engineering
Wind turbines have been in use for many decades, but the combination of rising fuel costs, tighter company budgets, and environmental initiatives to use renewable/greener energy sources is spurring greater-than-ever interest in them. Control systems are a key component in wind turbines, and so is design for extreme conditions.
kk-electronic a/s has been developing and producing complete turnkey wind turbine control systems for leading wind turbine manufacturers for nearly three decades. Systems from this Danish company currently can be found in more than 15,000 wind turbines operating around the world — from major U.S. wind farms like King Mountain in Texas to established offshore wind farms like ones in Middelgrunden, Copenhagen, and Nysted, Denmark.
kk-electronic’s control systems for wind turbines range from simple control elements to state-of-the-art complex control systems that have the high reliability needed for what are frequently rough-weather conditions. Six months may go by before scheduled maintenance is conducted on components, which are mounted at the top of a 450-ft. tower and are subjected to temperature extremes, lightning strikes, and other hazards. So, systems include built-in remote monitoring and reporting that acknowledge the difficulty of on-site inspection.
Let’s first take a look at the wide range of electrical and electronic components that ensure the safe and reliable generation of electricity from a wind turbine. These include:
Main computer, I/O modules, relays, and components for turbine monitoring and control;
Continuous condition monitoring of wind turbine operation;
Hub computer to control blade pitch;
Frequency converter, yaw motor protection, etc. for the soft yaw system;
Terminal box in the top of the tower, which connects the aluminum cables in the tower to the flexible copper cables from the generator;
Power converter (full or dual fed), filter, phase compensation, etc.;
High-temperature uninterruptible power supply, I/O modules, interface computer, operating panel, network components, and SCADA interface;
High voltage, medium voltage, and low voltage distribution boards;
Main circuit breaker, grid connection, power unit, etc., plus power quality analyzers;
Anemometers, wind vanes, aviation warning lights; and
Elements for supply of crane, hatch, heating, cooling, smoke detection, etc.
A challenge to wind turbine control system designers is the extreme temperatures and temperature swings that turbine facilities can be subjected to. The control systems (and the turbine itself) must be able to continue working in these conditions. Qianwei Chongqing Qianwei Instrument & Meter Factory of China was looking for a wind turbine control system that could provide the uptime numbers needed to achieve a return on investment within their turbines’ targeted timeframe. Qianwei evaluated wind turbine controls from several vendors, and selected kk-electronic.
kk-electronic has since entered into a joint venture with Qianwei. The new company, kk-Qianwei, will market and manufacture control panels. kk-electronic’s contribution to the joint venture includes its newest wind turbine control system, named “Commander,” which is a turnkey solution for wind turbine control. This system consists of a combination of pre-engineered control elements with modular add-ons that can be implemented rapidly. kk-electronic also has completed a new $2 million plant in Ikast, Denmark, for the production of electronic control circuits.
The most important task in wind turbine control is continuous control of wind turbine blade pitch and braking during short-term grid failure or utility loss. This is essential for safe operation, since failure to assure this control can result in mechanical stress of the drive train and its tower, in addition to the possibility of loss of life.
To stop the turbine blades from turning, the angle of every blade (pitch) is adjusted so the edges of the blades are in line with the wind; eliminating the force of wind against the blades decreases rotor speed. Next, brakes are applied to stop and hold the rotor. If the brakes are applied before the rotor speed is below allowed braking speed, the brakes will be damaged.
To eliminate single-point-of-failure in braking control, kk uses two separate control subsystems dedicated to the monitoring and control of the turbine blade pitch control and braking.
As these computers are only as reliable as their power source, kk-electronic realized that both systems needed to have their own sources of backup power, in addition to the utility power source. Engineers decided on a battery-operated uninterruptible power supply (UPS), but knew it was critical to find a high-temperature-rated UPS designed to operate in locations subjected to extremely wide temperature ranges. According to Claus Damgaard, electrical power engineer, research & development, “Our wind turbine control systems were slated to be operating in Mongolia and other remote regions in China, where the daytime temperature reaches 55
The cold problem was solved easily enough by adding heating elements to the control cabin, says Damgaard, but in the case of a utility loss, the temperature could drop to -40
“I contacted Falcon Electric while the Qianwei project was in its infancy,” explains Damgaard. “I had searched the Internet for high-temp industrial UPSs and found out that Falcon offered the only UL-rated UPS for 55
Falcon has supplied industrial UPSs for companies like GE, Siemens, and Johnson Controls. “Falcon engineer Mike Stout told me that GE had used Falcon’s UPS to power their WTCs [wind turbine controls], so I was even more confident,” says Damgaard. “More importantly, since the new Falcon SSG Series hi-temperature UPS was too deep for the tray we had designed for the UPS, Falcon accepted my request to integrate the UPS electronics only, and let kk-electronic source military-grade high-temperature batteries.
“The fact that Falcon was willing to customize its UPS, then spend time ensuring our battery pack worked with these batteries, was fantastic. In my experience, UPS companies will not even consider offering this level of customization and support, especially for a quantity of 50 or 100 units.”
kk-Qianwei is currently testing its initial joint-venture wind turbine in Mongolia, where it has been operating for several months. Damgaard says plans call for kk-Qianwei to install more than 100 additional turbines in 2010.
Renee Robbins is senior editor for Control Engineering. Reach her at email@example.com .
Resources for wind energy control system design
Whitepapers, Webcasts and online links to more information are available via www.controleng.com .
Whitepaper: A free whitepaper from Dataforth explains wind turbine operations in detail. “Extreme I/O applications and signal conditioning tips” addresses the extreme temperature and vibration issues associated with wind turbine control.
Video: Winergy Drive Systems builds specialized gearboxes for wind turbines, and claims world leadership in that industry segment with 50% of the market globally and 60% in the U.S. This short video, “The Heart of a Wind Turbine,” takes you on a tour of the Winergy Drive Systems assembly floor, showing these huge units in their final production stages.
Webcast: One issue often missing from the discussion of alternative energy initiatives such as wind power is what engineers across all manufacturing industries can learn from these industries in terms of business development and technology application. These green-energy industries may be new, but they’re leveraging a lot of tried-and-true control technologies to make them viable. Online at www.controleng.com/webcasts , you can access “Wind Energy: Control Engineering Lessons and Opportunities.” Speakers in this free webcast include Brian MacCleery, National Instruments senior product manager for renewable energy, and Javier Gutierrez, National Instruments senior product manager for control & simulation. MacCleery and Gutierrez discuss how wind turbines are manufactured and controlled, how wind turbine control teams are developing advanced control systems using embedded system platforms, and the wind energy industry’s use of hardware-in-the-loop simulations for controller testing.