Roboteq

Roboteq controllers using firmware 2.1 or later support cascaded control operation. According to that structure, one or more control loops can work cascaded to achieve optimal motor control. It is strongly suggested to use cascaded configuration because of the benefits it offers in the safety of the controller and in the performance of the motor.

The simplified operation of cascaded control modes can be seen below:

In this setup, the Speed loop works by utilizing the current (FOC) loop and the Position mode utilizes both Speed and Current loops. The user will send the initial desired command, depending on the operating mode used, and the controller will generate the internal commands required to drive the intermediate loops. At all cases, the output will be PWM voltage.

From the previous diagram we can derive the following:

• Speed mode requires the configuration of Current (FOC) mode and Speed mode
• Position mode requires the configuration  of Current (FOC) mode, Speed mode and Position mode

Below is the detailed representation of cascaded control modes:

Still there is the ability to use single mode operation, however it is not recommended, mostly because of the lack of current control during the motor operation. Next it will be explained how each control mode can be set.

The current mode is configured by setting the FOC torque and flux gains 

The gains can be set using the motor characterization tool or by using the formula in the manual. Refer to Roboteq Controllers User manual or to the relevant guides to calculate the gains.

In Open Loop operation, only the Flux (Proportional and Integral) gains are taken into consideration. The Closed Loop (Torque, Speed or Position) will supply current by using the configured FOC Torque gains.

Cascaded Operation

For the cascaded operation, the FOC and the speed PID gains must be set.

Warnng! When the FOC gains are used, the necessary Speed PID gains to drive the motor will be much smaller than the simple (no FOC) operation. The same gains will not work.

Single Operation

As seen on the previous diagram, the speed command will be directly related to the provided voltage without any intermediate loop. A big difference in the speed error will create a big change in the PWM voltage with uncontrolled impact on the motor current. 

Speed mode should be configured similar to below for the simple operation:

The FOC Torque (Proportional and Integral) gains have been removed, so Current loop went off. The flux gains are still required, because they are used for commutation of the motor in general.

Also notice that the Speed PID gains have changed. Now integral gain is dominant. 

Cascaded Operation

The cascaded operation requires all the control loops to be enabled. First Torque gains must been set, then Speed mode should be configured and finally Position mode should be tuned, by having the Torque and Speed gains enabled. 

Single Operation

For single operation, no FOC torque gains as well as Speed PID gains should be used:

Position gain will be typically be higher. Again this is not a suggested configuration, due to the lack of current control and speed control that would be used to keep the motor current at safe levels and ahcieve the desired speed profile.