Some of the control hardware is mounted inside the turbine blade.
Denmark based Vestas Wind Systems focuses only on developing wind energy. If company projections prove accurate, by 2020 as much as 10% of the world’s electricity consumption will be met by wind energy.
The company also claims many wind energy innovations. Pitch controls, for instance, continue to get close scrutiny because they govern a turbine’s power output. In a recent project, an engineering team led by Vestas’ Niels Anker Olesen set a goal to measure loads and control turbine blades in a way to better optimize turbine outputs. This is challenging because it involves multiple real-time measurements and control tasks. The packaging is challenging too, because the team had to fit the system hardware into limited space inside the root of wind turbine blades, which also means the system had to work in temperature and humidity extremes.
System requirements
The goal was a versatile control system that is easy to modify and maintain. In the current system, some measurement enclosures were installed in a way that would require a lot of work to reconfigure later if the requirements changed.
Imagine the general maintenance challenge in a wind turbine. Supervisors really don’t want to send a tech up tower just to modify control code after it is installed. Also, because the hardware is built into the space in a blade root, accessing the hardware would require taking a turbine out of service. This makes it necessary to have the capability that allows updating the control program from the ground. Olesen says the software-defined hardware platform offered by NI CompactRIO was a good choice for this.
The pitch system has to take in readings from different sensors, run advanced algorithms in real-time, and based on results, pitch the blades. To make it even more challenging, the team wanted the controls to use data from all three blades at the same time.
System architecture
Olesen’s team selected the NI CompactRIO hardware and NI LabVIEW system-design software from National Instruments (www.ni.com) to build this challenging measurement and control equipment. Because of the difficult project architecture, the team decided to work with National Instruments Gold Alliance Partner CIM Industrial Systems A/S to design and deliver the solution. The team had worked with CIM on similar projects, and was confident they could address the challenge.
The control system’s high-level architecture gives an idea of the equipment required and where it was mounted.
CIM designed the hardware architecture with multiple NI cRIO-9025 real-time embedded controllers, an NI 9144 EtherCAT expansion chassis, and NI 3110 industrial controller systems with multiple measurement channels. The design team selected one master controller to handle communication between different controllers inside the blades along with the Vestas HUB controller. Data is acquired using an NI Scan Engine so it could access the data from six EtherCAT chassis running at 100 Hz. Data is filtered, scaled, and sent to the two other blades by the master controller at the same rate using a controller area network (CAN) and NI-XNET. Upon receiving similar information from the neighboring blades, the blade controller adjusts pitch using a combination of feed forward and proportional integral derivative (PID) controls.
To cope with the prospect of evolving and changing specifications, CIM opted for modular event-based code so every software component within the target could run independently. This greatly reduced testing time and provided flexibility when modules were changed, removed, enabled, or disabled to cope with ongoing hardware modifications along with changes in CAN or TCP/IP protocol
Benefits
The team set demanding requirements and a tough schedule for this complex measurement and control system, but in the end, Olesen says the team exceeded some of those requirements. The NI CompactRIO software-defined hardware platform was a good fit. The team built a flexible and versatile system that can be reconfigured as new demands arise. The amount of data and the rate it is acquired helps show elusive phenomena such as second and third-order harmonics. The determinism and synchronicity of the system provides the fast control loop needed for the project execution.
The lessons learned from this project will help further optimize the efficiency of Vestas wind turbines. The NI CompactRIO and LabVIEW platform has proven reliable and versatile. The flexibility of the systems make the platform well suited for measurement and control projects, where the scope is not always completely defined from a project’s onset. WPE
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