SPRUHJ1I January 2013 – October 2021 TMS320F2802-Q1 , TMS320F28026-Q1 , TMS320F28026F , TMS320F28027-Q1 , TMS320F28027F , TMS320F28027F-Q1 , TMS320F28052-Q1 , TMS320F28052F , TMS320F28052F-Q1 , TMS320F28052M , TMS320F28052M-Q1 , TMS320F28054-Q1 , TMS320F28054F , TMS320F28054F-Q1 , TMS320F28054M , TMS320F28054M-Q1 , TMS320F2806-Q1 , TMS320F28062-Q1 , TMS320F28062F , TMS320F28062F-Q1 , TMS320F28068F , TMS320F28068M , TMS320F28069-Q1 , TMS320F28069F , TMS320F28069F-Q1 , TMS320F28069M , TMS320F28069M-Q1
Max Current defines the maximum output of the speed controller, different from the IQ Full-Scale Current which defines a normalization factor of currents measured with the ADC converter. Max Current must always be lower than IQ Full-Scale Current since Max Current is a software limit only, while IQ Full-Scale Current represents a maximum software representation of a maximum hardware input.
Max current must always be lower than IQ Full-Scale Current.
The definition of the maximum current sets a maximum software limit. It indicates that the maximum current commanded by the speed controller will be clamped to the maximum current definition. For example, if the maximum current definition is set to 4.2 A, and the speed controller requires an increase on the torque demand through the current controllers, the maximum commanded current will be 4.2 A, or whatever is set in this definition. It is recommended to have a maximum current less than or equal to the maximum recommended current by the motor manufacturer to avoid damage to the motor.
Max current less than or equal to motor manufacturer's recommended max current.
For example, the Anaheim motor provided with the DRV8312 Revision D board has a rated torque of 21 oz-in and a torque constant of 5 oz-in/A, which leads us to a rated current of 4.2 A to produce rated torque. 4.2 A is set to the motor maximum current (peak current amplitude) is shown in the following code example:
#define USER_MOTOR_MAX_CURRENT (4.2)
Note that the Max Current defined in user.h does not provide a hardware limitation or protection against over currents. In other words, this is not a hardware current limit, instead, this is a software limit that only limits the maximum input of the current controllers, and not their output.
Figure 6-1 shows a representation of where this USER_MOTOR_MAX_CURRENT is used in InstaSPIN. As can be seen in the diagram, the maximum current does not limit a current cycle by cycle, but it provides a saturation of the speed controller integral portion output as well as a saturation of the overall speed controller output before providing the reference to the current controller.