In each one of the mission phases, it is possible to configure a controller for each controller channel defined on Veronte Configuration. There are three different options for the control status.
|Off||Disables the PID controller.|
|On||Enables the PID controller.|
|Fixed||Sets the control parameters to a fixed value.|
PID Control Status
When creating the controller for a channel, it is possible to select up to four different loops connected in series.
For each block, it is possible to configure the controller type and its parameters by selecting it on the pull-down menu shown in the following figure.
There are six different options that can be implemented for a controller on Veronte Pipe:
- PID: classical PID controller. Its configuration is the one shown in the previous figure. The values for each one of the elements (proportional, integral, derivative and so on) can be changed directly on the screen.
- AP: adaptative-predictive control.
- Tsched: gain scheduling controller with variation of the parameters according to a table interpolation. In this option, the values of the PID controller vary according to a variable that is selected when this option is marked. For example, if the IAS is selected as the scheduling parameter, depending on the velocity of the aircraft the parameters of the PID will change.
Table Scheduler controller
- Esched: in this case, the only gain that changes according to a certain variable is the proportional one. Now there is not a table interpolation but a mathematical expression, that can be inverse (KP1/V1=cte), proportional (KP1 * V1=cte) and quadratic (KP1 *V1^2=cte). The following figure shows the quadratic case, where the proportional gain changes according to the IAS, having as nominal point (KP1 and V1) 0.2 and 20 m/s respectively. The values Min and Max are used to establish a limit of the scheduler. Below and above those limits, the system works as a conventional PID with the gain indicated in KP1.
Quadratic Scheduler controller
In addition to the controller type, there are another set of parameters that can be changed in the window of each block.
- Enable Sys ID: activates the option of system identification. The plant is modified continuously by predicting a new one according to a set of parameters. This option must be activated when working in Adaptative-.Predictive control.
- Respect: this option is used for transition between phases. When activated the output of the controller is respected (is kept) when going from one phase to another. Normally, this is used in the internal control loops (rates) to avoid great steps in one control parameters in the transitions. If Respect is active in the external loops, the control will maintain attitude angles and heading/fly path angles during phase changing, and this kind of control could be too much aggressive for the platform (depending on phases configuration).
- Noise Level & Filtering constant: parameters used for the AP controller.
- Initial A & B: these buttons are used to establish the initial plants for the system identification process.
Focusing now on the PID structure the next figure and table describe all its elements and what means each one of them
|2||· Invert: Change error sign|
· Wrap: Wrap to pi [-π, π]
It is used in some angular variables (radians) for avoiding numerical errors on the –π to π change and keep continuity of the error signal
|4||Discrete filter parameter|
|5||Derivative time parameter|
|7||Constant value added to output (Feedforward Control)|
|9||Inverse integral time parameter|
|10||The maximum value of integral admitted|
Output values for PID controller refer to virtual control channels, units must coincide with servo trim configuration settings.
PID diagram represents the following PID model:
- Kp=proportional gain
- Ti=Integrator time
- Td=Derivative time
- N=Derivative filter constant
For the derivation and integration models, Trapezoidal and Backward Euler models have been integrated:
where is the time constant on a first order FPB. When ND is set to 0, the FPB is disabled.
Sampling time has already been integrated:
Exporting PIDs to other phases
Once it is considered that the PID is tuned, the user can easily export that PID in order to use it in other phases. To do so, just select Copy by right clicking on the desired PID and click on the “Block” cell of the desired phase. That would copy only the gains of the PID (P, D and I), if the user also wants to copy the limits, that column has to be checked.
The fixed mode allows establishing a ramp input for the selected controller channel. When this option is selected the following diagram is displayed:
Fixed Value Settings
Three values must be entered, the remaining time in the starting conditions, the transition time and the variable final value.