Pitch Actuator Dynamics

Input Demand Filtering

The Input demand must match the controller demand for the pitch system. This will either be a position or rate demand.

The user can choose to smooth input demand by the use of setpoint trajectory planning (also known as ramp control). This enables step demands coming from the controller to be smoothed according to rate Limits and acceleration limits.

Dynamic Response Options

Pitch actuator models can be defined as either passive or active. Passive models ignore the drive details using a transfer function to simulate a lag in input demand and compute an acceleration. The acceleration of the pitch freedom is then prescribed. In an active model, an actuator torque is calculated using one or two PID controllers, and this is then applied to the pitch freedom.

The possible Actuator Dynamic Response options that can be selected by the user are listed below:

• Use setpoint trajectory planning This is a feed through option and produces an acceleration output. The acceleration and rate limits of the setpoint trajectory planning smooth the input demand to prescribe the pitch freedom. This can only be used when acceleration limits have been defined, otherwise infinite acceleration would be possible and the actuator torque would be undefined. If position demand input has been selected then setpoint trajectory planning cannot be used to define the rate response. For example, a position demand system that uses a closed loop PID for position response and setpoint trajectory planning for rate response is not supported.

• The following passive open loop options can be selected. These simulate input demand and acceleration output:

  • 1st order passive Can be used to convert rate input to acceleration output. Note that for a position inputs and acceleration output, the 1st order response is converted to a second order passive system. The user must specify the time constant for the transfer function.

  • 2nd order passive Used in the case of a position input and acceleration output system. The user must specify the frequency and damping factor.

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

• Closed Loop PID PID dynamics can be selected to simulate input demand and torque/force output. Two Closed Loop PID responses can be defined in sequence to convert position input to rate and then rate to torque output. The inputs defining the closed loop PI control such as proportional and integral gains must be defined by the user. The behaviour of the closed loop response depends on the input

  • Position Response: convert the position demand into a rate demand.

  • Rate Response: convert the rate demand into a torque or force demand, depending on the whether the actuator drive type is rotary or linear respectively.

Last updated 06-09-2024