Testing wind-turbine software with HIL simulation

Testing wind-turbine software with HIL simulation

A new system using hardware-in-the-loop (HIL) testing of embedded-control software releases keeps turbines up on the farm

BY SAMIR BICO
Siemens Wind Power A/S
Brande, Denmark
http://www.siemens.com

For its wind turbine control systems, Siemens’ engineers faced the challenge of improving the automated testing of frequent software releases, as well as the testing and verifying during the development phase of the software’s ability to control the wind turbine’s mechatronic-system components.

Wind turbines like that used in the Lillgrund offshore wind farm in the sound between Malmö and Copenhagen are complex systems needing tight control by real-time software.

Software developers regularly release new version of the controller software. Each time they do, the software needs to be tested to verify that the release will execute reliably under the actual conditions experienced in a wind park. So with every software release, our group must perform factory acceptance testing before the software can be used in the field.

Wind turbine complexity

A wind turbine system is a complex electromechanical system consisting of several components, including a rotor, gears, a converter, and a transformer that together convert kinetic wind energy to electricity (see Fig. 1 ). The turbine’s control system must interface with these components through hundreds of I/O signals and multiple communication protocols. The most complex part of the control system is the embedded control software executing the control loops.

Fig. 1. Wind turbines consist of a complex system of multiple electromechanical components.

Given the need to frequently test the control software, the new test system had to provide the ability to automate this process. The previous test system was developed 10 years ago and based on another software environment and PCI data acquisition boards.

The old test system’s architecture and performance did not meet the new requirements for fast test time and scalability. It was difficult to maintain and did not have sufficient automation capabilities for efficient testing.

It also lacked automatic test result documentation and test-case traceability and did not provide the required remote control capabilities. In addition, the old test environment did not support multicore processing, which prevented us from taking advantage of the computing power of the latest processors.

Looking ahead for test

After evaluating the technologies available, the development team chose LabVIEW software and PXI-based real-time and field-programmable gate array (FPGA) hardware to develop a new real-time test system that would employ hardware-in-the-loop (HIL) testing of the embedded control software releases. The team saw this technology as giving the flexibility and expandability needed to meet future technical requirements. Also, the products high level of support and quality provided high confidence that the solution would fulfill the requirements for availability and reliability.

Since in-depth development expertise for test systems was not available in-house, the team contracted the development to CIM Industrial Systems A/S in Denmark. CIM Industrial Systems A/S has the test engineering capability available and the largest number of certified LabVIEW architects in Europe. Ultimately, this project’s success was due in no small part to CIM.

A flexible RT test system

The new test system (see Fig. 2 ) simulates the behavior of the real wind-turbine components by running simulation models for these components in the LabVIEW Real-Time system. By using HIL, the simulator is able to supply the electromechanical simulation signals to the system under test without the need for actual hardware, and can do so in a much more flexible manner than the actual turbine hardware could.

Fig. 2. The architecture of the Siemens Wind Power Test System permits flexible adaptation to changing demands.

Running LabVIEW, the host computer provides an intuitive graphical user interface that users can easily adapt the system by moving the components in the panel (see Fig. 3 ). The Windows OS application also communicates with two external instruments that were not real-time compatible.

Fig. 3. The system’s intuitive GUI lets users easily adapt the system by moving components.

The software on the host computer communicates over Ethernet with the LabVIEW Real-Time module in a PXI-1042Q chassis. The module runs simulation software that typically consists of 20 to 25 simulation DLLs executing in parallel. This solution can call user models built with almost any modeling environment, including the LabVIEW Control Design and Simulation Module, Simulink software from The MathWorks, or ANSI C code. The execution rate of a typical simulation loop is 24 ms, leaving plenty of processing capacity to meet future expansion needs.

Customizing with FPGA

Because of the lack of standards for wind turbines, a lot of custom communication protocols are used. Using an NI PXI-7833R FPGA-based multifunction RIO module with the LabVIEW FPGA Module make it possible to interface with and simulate these custom protocols.

In addition to protocol interfacing, the FPGA subsystem is used to simulate magnetic sensors as well as for accurate three-phase voltage and current simulations. A second FPGA board is connected to an NI 9151 R Series expansion chassis to further increase the system channel count.

The new system’s benefits

The new Siemens Wind Power test system has several benefits over the previous generation solution. Because of the modularity of the system, it is easy to improve, adapt, and further develop. The system under test can be quickly replaced without any changes in the test system architecture. Remote-control capability and simple replication of the system gives the flexibility to copy the system to other sites as operations expand.

The simulator not only provides an environment to effectively verify the new software releases and test special situations in our laboratory, it also gives us a tool to test new technologies and concepts we are working on.

The modular architecture allows us to scale-up the system to meet the growing requirements of rapidly evolving wind energy technology. We envision dividing the simulation to multiple LabVIEW Real-Time targets to meet our future testing needs. NI TestStand will also be used to further automate test execution. ■