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Digital Prefilters Can Reduce Maintenance of Wind Turbines

Want to drastically cut the time you spend on maintenance of your wind turbines? Look inside at the technology you’re using.

Perhaps the biggest source of wasteful fatigue on a turbine is unnecessary blade wobbling (or oscillation or exciting or resonance -- whatever you call it at your company). Windurance’s digital prefilter -- part of our sophisticated pitch actuator system -- uses unique technology to stabilize your blade’s motion.

Just like with a car, fewer bumps in the path mean fewer trips to the mechanic. Keep reading for an explanation of how the digital prefilter eliminates roadblocks to revenue production on wind farms.

 

What Causes Frequent Maintenance of Wind Turbines

When you have no jerk (rate of acceleration change) limit on your turbine blades, they make an unnatural, robotic motion. Think of a glass of water splashing everywhere as you race it back and forth.

maintenance of wind turbines digital prefilterYou have to “tune” that motion profile to match the characteristics of the blades. In the water example, if the glass were less or more full, you’d have to adjust accordingly. In the same way, the blades, which are deceptively complex structures, have an intricate interaction with the main turbine control.

If you don’t tune the trajectory of motion, you risk turning your turbine into an oscillating spring. The effects on your turbine won’t be to your liking.

Oscillating motions of the blades can couple together and interact with the turbine closed loop controls. Unstable feedback and unnecessary pitch and activity in the control system ensue. All this leads to unnecessary fatigue of blades and other components.  Use of the digital prefilter avoids this problem by constraining the dynamics of motion appropriate for the aeroelastic capability of the blade structure.

 

What Is a Digital Prefilter?

The digital prefilter is the part of the computer algorithm that “innovates” the command -- which is the trajectory, or motion, your blades are going to take.

The SCADA system takes into account the conditional economic value of energy output. This changes based on the nature of the:

  • Power purchase agreement

  • Time of day

  • Demand for the electricity

Meanwhile, the pitch actuator system is also collecting data and providing it to the SCADA related to optimization, service life, and maintenance. Where does this fit into reducing required maintenance of your wind turbine?

Here’s a reminder of how the process works:

  • The main turbine controller decides what the pitch angle should be.

  • It tells the control unit what pitch demand should be.

  • The pitch control unit bends the torque via the pitch actuator, in whatever direction we want, at the blade root level.

  • We measure in response to the pitch angle.

maintenance of wind turbines blade exciting chart-1

 

You don’t want the main turbine controller to just be banging the pitch back and forth. You want the pitch motion to follow what we call the demand generator.

That command generator? It’s the digital prefilter.

 

How the Digital Prefilter Saves Your Turbine’s Life

With Windurance’s prefilter, you don’t have to wait for a closed-loop response. Consider it a head start -- we can directly demand the torque we need instantaneously on the blade without having to wait for it to lag and create error.

At the prefilter level, we can influence:

  • Rate limit

  • Acceleration limit

  • Deceleration limit

  • Jerk limit (rate of change of acceleration)

The digital prefilter directly outputs an “accelerate” or “torque” command. If you control the rate of acceleration change, your blades make a nice, smooth motion.

Your blades can move just as quickly, but the nature of the trajectory will prevent jerkiness. Without that pesky, destabilizing blade motion, you can optimize response according to turbine structures and control systems’ input.

It’s truly underappreciated how much power is in the wind. Lots of power has to be passed off. Your turbine could be rated for 5 MW of power, but the wind could suddenly increase to 20 MW. This is why controlling a wind turbine is hard, and why the pitch actuator (and digital prefilter) is crucial to curtailing oscillation -- and prolonging blade life.

 

How the Other Guys’ Systems Work

Most other pitch system products include no command generator. The control system has to account for error instantaneously, and since there’s no closed-loop response to a blade motion beyond the blade root, the actual effective angle of attack is changing without feedback other than changing rotor torque.)

So those processes prompt situations where all of a sudden, the response system tells the actuator to do something in response to the blade flexing. That creates fatigue and damage to the blades and other parts.

 

Other Opportunities With a Blade Pitch Actuator

To maximize your revenue-generating opportunities, you must control the trajectory of your blades’ motion and tune them in a way that doesn’t prompt resonance. A turbine that requires as little maintenance (and therefore downtime) as possible should always be a priority.

That’s just part of the big-picture look a thoughtfully designed pitch actuator system should give you. With a Windurance pitch actuator, you have additional opportunities in the realm of IIoT and your SCADA system:

  • Edge computing

  • Real-time condition data

  • Historical monitoring data

  • Predictive & preventative maintenance planning & detection

  • Actuator virtualization

  • More

Optimization of your local and remote operations monitoring is the key to cost reduction and improved downtime numbers. Talk to us today if you’d like help in making this a reality on your wind farm!

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Author: Windurance