The motor’s initial speed from a Stop condition is zero. This makes the
application of sinusoidal current drive difficult since there is no reference speed
available. In this application, a low-speed trapezoidal drive is used as the starting
commutation until the motor stabilizes for the sinusoidal drive. The trapezoidal drive
is executed by configuring the CWG peripherals to Steering mode. Each time a Hall
transition is detected, the PWM signal is steered to the output pin based on the 6-step
drive table stored in program Flash, as shown in Figure 6-2. Each drive table array contains six
elements based on the six states of Hall sensor logic. As the motor starts to turn, the
PWM duty cycle is increased gradually until it establishes speed and completes a
mechanical revolution. Figure 6-2. Trapeziodal Look-Up
Table
By the time it completes a mechanical revolution, the CWG peripherals are
changed to Half-Bridge mode for the preparation of transition to sinusoidal drive. The
timers used on angular transition are all reloaded and the functions on IOC ISR are
changed with respect to sinusoidal function.
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