Testing times

7 December 2018



As the rate of growth in the wind energy market continues to accelerate, there is increasing pressure for wind turbines to perform more efficiently and reliably. Testing components under realistic conditions is the area of expertise of Fraunhofer Institute for Wind Energy Systems. Jim Banks speaks to the head of its wind turbine and system technology division, Martin Pilas, about how its testing facility has kept pace with demanding change.


In an increasingly competitive market, wind turbine manufacturers want their new designs to be as reliable as possible, as quickly as possible. Under pressure from investors, they also want their technology to be certified and on the market in the shortest possible time. As the wind energy industry matures, the pressure is on to develop new and more efficient technology that will prove to be robust from the first day it is deployed in the field.

As the technology itself becomes more sophisticated, the need to mitigate the risk of faults in a new design is greater than ever. At the Dynamic Nacelle Testing Laboratory (DyNaLab) operated by Fraunhofer Institute for Wind Energy Systems (IWES), the goal is to help manufacturers keep pace with the latest technological advances – and the demands of investors – by providing an environment in which refinement and, ultimately, certification of new technology can be expedited. Speed to market is essential for equipment manufacturers, so there is a need for testing processes that are in-depth, customisable, repeatable and comparable with on-site validation processes.

Martin Pilas, head of the wind turbine and system technology division at IWES, speaks about the capabilities of DyNaLab and how it features in the institute’s future strategy.

The role of wind energy in the global energy matrix is rapidly increasing, with a large volume of installed capacity already in place and much more set for construction in key markets around the world. How has the maturation of the industry put more pressure on turbine manufacturers to make sure that new designs run with maximum reliability from the start?

Martin Pilas: Of course, every manufacturer has always wanted its turbines to be as reliable as possible from the beginning, but the demand is increasing now. Turbine design is no longer a huge selling point – the designs are now quite standard – so manufacturers need to find ways to add value, such as reducing the cost of energy and improving reliability. They are mainly refining their existing designs. They still design innovations, but the innovation leaps are not as big as they once were. The market is more commoditised now, so there is a need to improve reliability. For us, that is good for business, though business has always been good.

You see many new turbines come in for testing, which gives you a good insight into what equipment manufacturers are doing. Overall, how different are the new turbine designs that come across the test bench at DyNaLab, and how reliable would you say they are in the initial testing phase?

That depends on the level of evolution of a new design. If it is a known, proven design with a higher workload but similar electrical components, cooling and so on, and a similar but bigger gearbox design, then reliability is higher at the beginning than it is for a completely new design with a new drive train in a higher power range. You need to take that into account when testing. Completely new designs suffer from more teething problems. Here, it is all about design assurance, and there can be many small steps in developing a new design to increase reliability.

As more electricity in the transmission grid is derived from regenerative sources, the demands on grid integration of wind turbines as powergenerating units have become greater, and the certification of new turbines developed to meet this demand is mandatory. Is compliance the main force behind the need for the kind of large test benches that DyNaLab provides, or are there other factors that are driving the growing need for the services you offer?

Investors are definitely the main driver of testing processes and the examination of new turbines by OEMs on large test benches. That is the main reason to test on them. Wind farm operators invest billions and the OEM may have no track record, so there is a need to build trust with the investor and show that the technology is more reliable. Certifying faster means you can sell your turbines faster. Speed is needed to stay ahead of the game. Turbines need to be more reliable, and the testing and certification process needs to be much quicker now.

Fraunhofer IWES began operations almost ten years ago in Bremerhaven, as a testing site for blade pitch bearings, but it has developed its testing capabilities significantly over that time. This evolution led to DyNaLab, which began operations in 2015 and has been busy ever since. So, what it is about your facility that gives it an advantage in the market?

The most obvious perspective for the answer to that question is the infrastructure that we have here in Bremerhaven. Our test rig has been designed with a focus on high dynamics and torsional loading. The requests that we get from our customers show that the path we took at the start is what the industry wanted.

DyNaLab provides turbine manufacturers with a realistic testing environment in the multimegawatt range to carry out tests under reproducible conditions, and it combines mechanical tests and a grid emulator to test wind turbines up to 10MW. Using an artificial network with a 44MVA installed converter power, it can reproduce typical grid faults, such as voltage dips, with a high repetition rate, and it uses the hardware-in-theloop (HiL) method to create realtime models and corresponding control algorithms to operate the test bench. But is it all about the technology?

From my perspective, the people we have here make the difference. We have electrical and mechanical engineers, as well as experts in measurement systems and methodologies, and many more people from diverse backgrounds. The infrastructure needs the people. Our strategy was never to just provide standard tests but to play a part in creating new methodologies and testing techniques, and to keep improving our infrastructure. For that to happen, you need people who really know what is required of testing and validation processes.

You mention that you are always looking to improve the infrastructure and the testing processes you offer. What are some of the latest improvements that you have made that have been beneficial to your customers?

In the past year, we tested many turbines and have learned a lot from that. We provide not only a rotor to drive the specimen, but also a test environment in which we use our own rotor models to simulate real rotors. We can run tests in real time with high dynamics to verify that the turbines can handle extreme loads in different conditions, and we develop new technology and processes based on what we learn from one customer to another. Everything is driven by the demands of the industry.

Our test rig has been designed with a focus on high dynamics and torsional loading. The requests that we get from our customers show that the path we took at the start is what the industry wanted.

The purpose of DyNaLab is to provide a testing environment that can simulate realistic, on-site conditions, but with the advantage that the parameters of those tests can be precisely controlled. The HiL method is growing in importance as a means to validate control concepts by allowing electronic control units to be tested even though they are directly integrated into a test bench rather than a real system. The control unit is connected to the HiL platform by means of a corresponding electronic interface, so that what it experiences on the bench is no different to what it will experience later in the controlled system. How does this system pave the way for more advances in simulations in the future?

In the HiL test environment, we can run a virtual rotor model to simulate all of the hardware components that are not present on the test bench. So, the hardware can react as if it were part of an operating turbine in the field. We can simulate, for example, transient wind fields so that the test is close to a real deployment, although there are some extremely harsh weather environments that we cannot simulate. But we can simulate random weather conditions, including extremely turbulent winds.

Demand for what we do is growing, and we’ve come a long way since we started with blade-testing ten years ago. Since DyNaLab started its operation, we have done tests for five customers. We hope we can continue to have a big impact on the industry by improving reliability. We are developing a new approach that will include the virtualisation of testing procedures. Virtualisation is a big step that the industry is already working on to improve the efficiency of future tests. Everything is becoming more digital in the wind industry, so we are a good partner across the whole value chain of wind turbine development.

At the moment, the testing of grid compatibility for the certification, or recertification, of the electrical characteristics of new wind turbines is usually done using mobile test installations in the field. How does DyNaLab compare with that type of testing process, and do you think it offers advantages compared with testing processes done on-site?

The difference between testing on a stationary bench and a mobile testing unit is that we control all of the parameters, and the tests are reproducible. With us, you can adjust your technology step by step, and you can check the turbine directly. You don’t have to go inside the tower for approval. You are much closer to the prototype and don’t need to take experts out into the middle of nowhere to inspect the system. Instead, they can come to our facility for planned tests. That issue alone is a big benefit compared with mobile test installations. Also, we have our own electrical grid, so we can set its parameters – frequency, voltage level, impedance and so on – in a way that is not possible in the field.

Testing and validation processes are vitally important to OEMs and investors, and increasing competition in the industry is driving innovation on all fronts. IWES is leading the way on virtualisation and is also investing in new facilities, such as its new blade pitch bearings test site, in Hamburg, to ensure that certification of new technology is not a roadblock in the industry’s development.

A generator being tested on DyNaLab´s Stewart platform.
Fraunhofer’s test rig is geared towards high dynamics and torsional loading.
Virtualisation, as apposed to physical testing, is the next big step.


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