TÜV certification of pitch servo drives:
a look behind the scenes
- Automation
- Windenergy
- Drive Technology
- 3.6.2025
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Contents
A modern, electric pitch system usually consists of three independent axes, each of which consists of the following components: Pitch servo, motor, gearbox, motor encoder, blade encoder and energy storage. There may also be a central control unit.
Pitch systems are among the most safety-relevant components of modern wind turbines. They control the angle of attack of the rotor blades and thus the angle at which the wind approaches the blade edge of the rotor blade profile. This sets the torque acting on the rotor and influences the energy extracted from the wind. The pitch system thus serves as an actuator in the control loop for the generator output or the rotor speed. This allows the speed of the rotor to be limited and the wind turbine to be protected from overspeed.
In critical operating situations, the pitch system moves the rotor blade angles of the wind turbine (if necessary according to an individual profile) in the direction of the wind vane position in order to slow the turbine rotor down to a standstill. This function is also referred to as ‘Safe Feathering Run (SFR)’.
(Learn more about this in our video series “Windenergy Explained”)
Due to this critical functionality, pitch systems must fulfil the highest standards of safety and reliability requirements. TÜV certification of a pitch drive is a complex and time-consuming process that represents a true challenge.
Safety Relevance Meets Technical Complexity
In contrast to conventional servo controllers for industrial applications, pitch systems are exposed to extreme environmental conditions such as temperature fluctuations, humidity and vibrations. At the same time, they have to work reliably under all circumstances - even in the event of mains faults or failures.
One of the biggest challenges: The safety functions that pitch systems fulfil in wind turbines, the emergency stop or safe feathering run, must be proven to be functionally safe - in accordance with the requirements of functional safety (e.g. PLe according to ISO13849 at system level).
TÜV Certification Requires Systematic Proof
These safety-relevant functions are developed according to a TÜV-certified process and must be fully verified as part of the certification process. Each development step must be accompanied by corresponding verifications at various levels of the V-model: starting with module tests (e.g. whitebox tests) through to complete system tests in a realistic test environment.
The overall system can only be validated once all requirements at each level have been clearly fulfilled. The validation checks that the developed device is suitable for the application.
This development-based way of certifying pitch systems produces extremely reliable software that includes a high level of quality testing. By using software with these safety standards, very stable systems can be designed for practical use.
Testing Without Downtime – A Balancing Act
In addition to the software tests that accompany development, it is necessary to be able to analyse faults directly on the wind turbine as quickly as possible in order to avoid long downtimes and the associated revenue losses.
As wind turbines in which the pitch servo controllers are used are installed worldwide, high travel costs/time can be incurred for on-site fault analyses. In addition, the pitch system is installed in the rotating hub of the wind turbine - a location that is difficult to access. Access to this during operation is generally not possible anyway.
If downtimes occur, in addition to the above-mentioned costs, further costs are incurred in the form of yield losses and resources tied up in service and engineering.
Acceptance tests and fault analyses are therefore usually carried out on test benches that enable a realistic simulation of plant operation.
Read more about ‘Hall vs. HIL test bench’ in our next blog article (will be published shortly).
Conclusion: software tests lead to greater security and increase efficiency
Software testing is the key to guaranteeing the safety, reliability and efficiency of a pitch system. They enable critical functions such as the safety run to be verified under all conditions, check the integration of all system components and fulfil the stringent TÜV certification requirements - all before the system goes into operation. The use of modern HIL test systems and automation solutions not only saves costs and time, but also makes a sustainable contribution to the safe and economical utilisation of wind turbines.
Find out more about our software test solutions in the white paper: Efficient testing of embedded software on system test benches with variable test environment - now available for free download.
