NXP Semiconductors 56F8000, Targeting User Manual

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Software Design
System Description, Rev. 1
Freescale Semiconductor 2-7
Preliminary
The output from the Speed PI controller is used as one of the inputs to a Torque PI controller. The second
input to the Torque PI controller is the
ADCAvg variable, which is derived from the DCBus current’s
moving average algorithm. The Torque PI controller’s output determines the duty cycle of the generated
PWM output signals.
The rotor commutation process performs mask and swap calculations’ control. The proper PWM output
can be generated by changing the PWM value (duty cycle) registers only. This has two disadvantages:
The first is that the speed controller, which changes the duty cycle, affects the commutation algorithm
(performed by changing the duty cycle). The second disadvantage is that a change in the duty cycle is
synchronized with PWM reload, which may cause a delay between a proper commutation moment and
the PWM reload. This is especially pronounced at high speed when the commutation period is very short.
The 56F801x device has two features dedicated to BLDC motor control: the ability to swap odd and even
PWM generator outputs and the ability to mask (disable) any PWM generator outputs. These two features
allow creation of a rotational field without changing the contents of the PWM value registers. The
commutation algorithms calculate PWM mask and swap values based on the
SensorState variable and the
ClockWiseCommTable look-up table. The mask and swap values are written into the PWM Channel
Control Register.
The DCBus voltage measurement acts as a fault detection, which disables PWM if voltage drops below
7V.