Actuator Drives

This section describes the pitch actuator mechanisms that can be simulated in Bladed.

No actuator drive

The user may select no actuator drive when defining the pitch system. The pitch actuators are modelled as hinge joints with no motor inertia.

For a parked simulation, and if no control system is defined then the pitch system is removed and instead replaced by a rigid link.

Rotary Actuator

A rotary actuator system models a pitch motor with a gearbox between the motor and blade gear ring. Please see the multibody diagram of the pitch actuator.

The Motor Rotational Inertia and Gearbox Ratio must be specified to define the components of the multibody system used to define the pitch actuator. The Gear Efficiency is used to scale the motor applied torque. When using this option the user must specify the Brake torque, that is applied when a safety limit switch is activated, and is permanently applied in parked or idling simulations. The brake acts on the motor side of the pitch gearbox.

The user must also select the Closed Loop PI(D) response type as an actuator torque must be applied to actuate the pitch bearing.

A Response to torque demand can also be selected by the user to model dynamics between the demanded and applied torque:

• instantaneous The applied torque will correspond directly to the demanded pitch actuator torque.

• 1st order passive First order passive dynamics are represented by a transfer function.

• 2nd order passive Second order passive dynamics are represented by a transfer function.

• Other passive The user may enter a custom Laplace transfer function.

Actuator torque limits are defined on the motor side of the gear ratio. These can be defined as fixed limits, as a lookup table according to pitch angle (blade side) or as a lookup table according to motor rate (motor side). The torque limits are applied to the demanded pitch actuator torque.

Backup actuator torque limits can also be defined analogous to actuator torque limits. These are defined on the motor side of the gear ratio. These can be defined as fixed limits, as a lookup table according to pitch angle (blade side) or as a lookup table according to motor rate (motor side). The torque limits are applied to the demanded pitch actuator torque.

It is also possible to select a flexibility on the high-speed shaft on the motor side of the gearbox. This flexibility is modelled as a single degree of freedom torsional spring-damper system.

Linear Actuator

In the linear actuator model a ram and crank-arm, connected via a revolute joint, are used to convert linear motion to rotary pitching motion. The user must specify the Brake force of a pitch brake, which is applied when a safety limit switch is activated, and is permanently applied in parked or idling simulations. The brake acts on the linear ram. The pitch angle at the point of maximum torque is the value of the pitch angle when the ram is perpendicular to the radius arm from the pitch axis to the connection point of the ram. The Pivot offset is the distance from the pitch axis and the pivot centre for the ram. Please see Linear actuator theory for more details on the theory and a diagram of the linear acuator system.

The user must also select a Closed Loop PI(D) response type as an actuator force must be applied to actuate the pitch bearing.

Force limits can be defined as fixed limits, as a lookup table according to pitch angle (blade side) or as a lookup table according to motor rate (motor side). The force limits are applied to the demanded force.

Backup power force limits can also be defined analogous to force limits. The backup limits are used during a grid loss event when pitch action occurs. These can be defined as fixed limits, as a lookup table according to pitch angle (blade side) or as a lookup table according to motor rate (motor side). The limits are applied to the demanded force.

Single Actuator Drive

In some turbines the blades pitch collectively as the result of a linear actuator ram driven though the hub. The ram actuates all blades simultaneously via crank-arms. In this the user can select the Single Actuator Pitch System checkbox and the following will apply:

• To represent the physical system accurately, the multibody hub component only simulates one degree of freedom and pitch motion of all blades follows this degree of freedom.

• Only a single pitch actuator response response and actuator drive are simulated.

• The external pitch bearing load is summated across all three blades to represent the actuator driving all blades collectively.

• The user should set the collective pitch demand via the external controller. Do not use set individual demand option as this could cause incorrect simulation behaviour.

• Blade pitch faults should be applied to blade 1 only and the other blades will pitch in sync.

Last updated 10-09-2024