Nidec Drive Systems has a strong passion and history of engineering solutions for customers with tough and vital applications. One such application is the pitch motor for wind turbines ranging from 1.5MW to 5.5MW. The pitch system is the critical safety system on a wind turbine, and in many cases, the only mechanism capable of braking the wind turbine to a complete stop from full operating speed.
Top-tier wind turbine OEMs have relied on Nidec Drive Systems for over a decade to provide electric motors for this safety system. Each blade of the wind turbine has a high gear reduction system, an electric motor and a variable frequency drive to control the motor. An emergency pitch is required where wind speeds are excessively high or grid power is lost, resulting in unloading of the primary generator. Both situations can result in a catastrophic failure and loss of the turbine if the pitch system does not do its job.
Nidec Drive Systems provides brushed DC series-wound, brushed DC compound-wound and brushless permanent magnet AC (PMAC) electric motors, equipped with a rugged electric brake and encoder for reliable operation in the turbine application. Our pitch motors have been highly engineered with premium performance synthetic bearing grease, Class H insulation, redundant sensors and tough connectors for the high requirements of a wind turbine.
Every mechanical detail has been architected and checked through robust FEA. These Nidec motors are engineered with a design life of 25 years to match the needs of the application, and they boast a low inertia design to minimize acceleration and deceleration torque required from the pitch system. Our PMAC motors achieve very high peak efficiency and power density. We use only Class H insulation systems.
The pitch system is used as a critical safety system in emergency pitch situations, but it is also used to constantly adjust the pitch of the turbine blades for the purpose of optimizing turbine efficiency. These motors are constantly working while spinning 300 ft in the air to allow the turbine to provide clean, reliable, safe and sustainable energy to our communities. Our pitch motors have undergone rigorous engineering analysis and test validation for application noise factors such as temperature, moisture, salt spray, vibration and fatigue loading over life.
Brushless AC vs. Brushed DC Tradeoffs for Wind Turbine Pitch Systems
In a wind turbine, the decision for brushed DC vs. brushless AC is a system level decision. A brushed DC motor is a proven and robust technology. Although designed and tested for the application, a brushed DC motor requires carbon brushes to transmit power to the rotating armature, and the brushes require a maintenance schedule. In addition to requiring no brushes, a brushless permanent magnet AC (PMAC) motor offers a significant efficiency advantage of as much as 10 percentage points over a brushed DC solution, with fewer watts lost in the form of heat to dissipate.
The machine size, and thus inertia, is smaller in a brushless solution. An important factor to consider is the total reliability of the system in an emergency pitch situation. In general, fewer components in the system means fewer parts or opportunities for failure, so the reliability for the entire system may be higher for the same general system cost and configuration.
A brushless PMAC motor requires a variable frequency drive to operate. The variable frequency drive contains many components that could be sensitive to lightning or other factors. There are few options simpler than applying battery power directly to the motor with no sensitive electronics required to drive the motor. The brushed DC motor solution offers this simplicity. It can function with direct current (DC) power applied with no inverter needed.
Pitch system designers do have methods available to mitigate the reliability challenge of depending on a variable frequency drive in an emergency pitch scenario. Each approach is viable with different tradeoffs, and both approaches are used in the wind turbine industry. Nidec Drive Systems offers reliable and energy-efficient versions of both brushed DC and brushless AC pitch motors.