Trapezoidal commutation is the most basic method of spinning a 3-phase Brushless-DC motor. This is accomplished by energizing the windings in a 6-step pattern every 60 electrical degrees so that one phase souring motor current, another phase is sinking motor current, and the last phase remains unconnected (Hi-Z). This produces a 120° trapezoidal-shaped current waveform for each phase (Figure 2-3).

Trap can be sensored or sensorless to determine the position of the motor and commutate the motor effectively. It is a low-cost, simple solution to implement that can generate high amounts of torque and speed and minimal MOSFET switching losses. However, it is low resolution and results in torque ripple and audible noise due to a non-ideal current drive.

Figure 2-3 Trapezoidal Control (120°)