4.2. ADC Calibration and Compensation

Certain aspects of the MCAF are sensitive to gain and offset variation. At this time of writing, only the motor phase current readings are compensated:

Compensation topic	Calibration type	Comments
Phase current offset	Runtime, at startup	Phase currents are measured and filtered at startup, when PWM outputs are in a safe state, and currents are known to be zero.
Phase current gain	Not calibrated at present, reserved for future use by Self-Commissioning in motorBench® Development Suite, or other runtime methods	Includes compensation for cross-phase coupling.

4.2.1. Implementation Notes

Since MCAF R3, all ADC calibration and compensation functionality is located in the adc_compensation module. (In MCAF R1 and R2, some portions were located in the meas_curr module and others in the foc module.)

The currentCalibration field of MCAF_MOTOR_DATA contains four gain terms:

• Kaa
• Kab
• Kba
• Kbb

These represent a 2x2 gain matrix:

(4.1)\[\begin{bmatrix} I_a \cr I_b \end{bmatrix} = \begin{bmatrix} K_{aa} & K_{ab} \cr K_{ba} & K_{bb} \end{bmatrix} \begin{bmatrix} I_{a0} - I_{a,\text{ofs}} \cr I_{b0} - I_{b,\text{ofs}} \end{bmatrix}\]

or (more concisely)

(4.2)\[\mathbf{I}_{ab} \,=\, \mathbf{K}_\text{comp}(\mathbf{I}_{ab0} \,-\, \mathbf{I}_{ab,\text{ofs}})\]

This gain matrix is used to compensate for part-to-part variation and to correct for any board layout issues, such as those described in MCLV-2 Sense Resistors.

4.2.1.1. Modules

Module	Files	Description	Comments
parameters/adc_params	parameters/adc_params.h	ADC compensation parameters
adc_compensation	adc_compensation.c adc_compensation.h adc_compensation_types.h	ADC compensation including current offset calibration