There are generally two types of brushless DC motor, including Hall effect sensor driven structure and sensorless structure. Although more complex, a sensor less architecture is a more preferred option. For sensorless operation, there are two control schemes.
Sequence diagram of ladder control scheme.
The working principle of ladder control is that there are two phases at any given time. Therefore, as shown above, no torque is generated during zero crossing of any phase.
This scheme will cause ripple at every 60 ° zero phase intersection, resulting in harmonics. In 120 ° mode, the BLDC drive will use the high Z state for the remaining 60 ° of each cycle.
The complexity of TFOC in the conversion of feedback control is higher.
The output of the ladder three-phase inverter generates a sinusoidal signal, which is sampled and fed through Clark transform and Park transform.
Basic block diagram of field directional control FOC.
Both of these transformations realize direct torque control by converting stator current vector from three-phase time-varying system to two coordinate time invariant system.
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