Introduction
After having a proper identification of the system plant, you can configure the control loop.
You have to perform minimum one plant model in the previous step. Otherwise, this step will be disabled.
This page is not available if trapezoidal commutation is selected.
For further technical information about how Current control loop works, click on here.
Overview of this page
The page is divided in 3 parts:
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System configuration and verification (red).
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Bode diagrams of magnitude and phase (blue).
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Display and Control widgets (yellow).
System Configuration and Verification
There are 3 main subparts:
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Plant model choice (orange).
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Control Loop configuration (purple).
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System verification (green).
Bode diagrams of magnitude and phase
You have two tabs:
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Closed loop (recommended)
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Open loop
Both tabs show the Gain and Phase in frequency domain.
The Closed Loop Transfer Function (CLTF) is the most common way to describe the control system in the frequency domain. The data is taken while the loop is closed, so all of the closed loop dynamics are captured in this transfer function. The gain of the CLTF is very close to unity at low frequency and rolls off at high frequency, with some amplification in between. The phase of the CLTF is near 0 at low frequency and near -180 degrees at high frequency. This curve is typically used to state the system’s “Bandwidth”.
The Open Loop, or “Loop” transfer function (OLTF) is representative of all the frequency dependent blocks that make up of the servo loop, meaning the control, the drive, the plant, and the sensor. The OLTF for some systems can be taken with the servo loop open, but in many cases it must be either derived from the Closed Loop.
Plant model choice
Depending on the identification method used on previous page, Electrical tuning: identification, you should select the model you want to use to design your controller.
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If theoretical identification was used, the only option will be “Design from datasheet parameters”.
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If experimental identification was used, the only option will be “Design from estimated model”.
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If both identification methods have been performed, both options will be available for selection, allowing you to choose the one that best suits your application and provides the most satisfactory results.
Methods
Depending on the selected design method, the controller design process and the resulting control parameters will vary.
There are 3 available methods:
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Pole placement: You will be able to tune the system response quickness and overshoot with Bandwidth and Damping ration.
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Pole-zero cancelation: You will be able to choose the system response quickness for a stable system (where the zero is cancelled)
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Manual: You will be able to freely adjust the proportional gain (Kp) and integral gain (Ki).
Pole-zero cancellation and Pole-placement are automatic methods that calculate the Kp an Ki. Manual is to adjust the parameters manually and see the frequential response.
For more information about these parameters, go to the https://drives.novantamotion.com/mot3/how-to-tune page.
Pole placement
Pole-zero cancelation
Manual
Loop adjustment
The primary objective of this step is to tune the control loop parameters, namely the proportional gain (Kp) and the integral gain (Ki).
These parameters can be obtained using the selected design method and evaluated through simulation before being saved to the drive. This allows you to assess their impact on system performance without modifying the current drive configuration.
The simulation results are displayed in a set of plots, providing a visual representation of the expected system behavior for the selected Kp and Ki values.
Once you are satisfied with the selected parameters, click “Save to Drive” to apply them. Bellow you can encounter several examples about how the closed loop behaves with different Kp's and Ki's.
In order to check if they are properly saved, you can see:
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These parameters in the Control widget in green color.
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Drive Saved Closed Loop plots change their shape like Suggested Closed Loop.
Verification
To compute it, just click on the “Verification” button. The main goal in this step is to check how your actual system works with the current saved on the drive controller.
Example
In the case of Pole-zero cancellation.
When changing the bandwidth, Kp and Ki parameters will be modified automatically.
The label under the slider indicates the stability of the system
Check the frequential response of your system and adjust the slider until the expected result is obtained. Also, you can compare the response of the controller values saved on the drive against the suggested new ones.
For more information, go to the https://drives.novantamotion.com/mot3/how-to-tune page.
You can find further information related to the closed-loop poles and zeros in the Terminal tab:
In order to make a verification, you can follow the steps below:
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Modify the bandwidth value.
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Click on the “Save to the Drive” button.
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And click on the “Verification” button.
Finally, the overall verification result is displayed next to the verification enable button.
The charts are updated with the experimental measurement for direct comparison against the estimated model.
The terminal displays a goodness-of-fit metric that quantifies the quality of the verification. This metric compares the simulated response with the experimentally measured response, providing an indication of how accurately the model represents the real system.
Some specialized applications may require adjusting the excitation parameters. These settings can be modified through the Advanced Options menu.
These options should match those used during the Identification step, as the verification algorithm is based on the same procedure.
The description of the parameters is the following:
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Mode:
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Current: The amplitude and offset below define the current values expected during the identification. An additional Resistance estimation step is performed to calculate the voltage excitation needed. This is the default mode, since it allows a better control of the current flow during identification and reduces the risk of overcurrent.
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Voltage: The amplitude and offset below define the voltage excitation used for the identification.
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Amplitude: The Amplitude of the excitation signal
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In current mode, in Amperes.
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In voltage mode, in Volts.
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Offset: An offset to the excitation is recommended to have an always positive excitation and avoid changes in the magnetic field direction of the motor.
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In current mode, in Amperes.
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In voltage mode, in Volts.
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fmin: The minimum frequency used for the identification.
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fspacing: The resolution of the frequency.
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fmax: The maximum frequency.
The simulation results are represented in closed-loop and open-loop bode plots.
In these charts there are no Experimental Closed Loop plots, just the estimated ones.
There are two configurable filters per signal for your system.
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Two for the current reference
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Two for the current feedback
You can find further information at Filters and Offset section.
To enable/disable them, make use of the Control widget:
