5.2. Signal Scaling in the Software of the Drive-on-Chip Design Example
- Normalize sigma-delta and ADC samples for use in the FOC algorithm
- Apply zero offsets
- Position feedback scaling
Scaling of Motor Phase Current Samples
The design treats motor phase current samples as dimensionless numbers in the FOC algorithm, rather than real current measurements.
To compensate for the differences in signal conditioning between the different ADCs, the design scales Intel® MAX® 10 ADC samples as it reads them from the ADC to normalize them to represent the same physical quantity as the sigma-delta ADC samples.
To compensate for the differences in signal conditioning between the different ADCs, the design scales any other ADC samples as it reads them from the ADC to normalize them to represent the same physical quantity as the sigma-delta ADC samples.
|Intel® MAX® 10
|Motor Phase Currents
|1024/81.9 or 12803/1024
Calculation of Zero Offsets
Offset errors arise in the ADC conversion process from a number of factors, including
- Component tolerance in sense circuits
- Offsets in sense amplifiers
- Errors in Vdd supply to sense amplifiers and ADCs
- Offsets in the ADC converters
Motor Phase Current Zero Offset
The design calculates the zero offset for the motor phase current during startup. the design samples several conversions while no motor current is flowing. The design averages the samples to calculate the offset. It applies them as a correction to the offset register in the sigma delta ADC module
Inductor Current Zero Offset on Tandem Motion Power Board
You cannot shut off the current flow through the DC-DC inductors. The design calculates approximate offsets from the average of the offsets previously calculated for the motor phase currents. The design applies power to all the converters from the same Vdd supply and in the same ambient surroundings.