Trapezoidal Control of BLDC Motors

Trapezoidal control, also called six−step or 120° block commutation, is one of the simplest brushless DC (BLDC) motor control methods available. The basic concept of trapezoidal control is to apply square−wave currents to the motor phases that align with the BLDC motor’s trapezoidal back−EMF profile for optimum torque generation. The six−step name comes from the fact that the inverter MOSFETs assume only six on/off state combinations, resulting in six possible stator field orientations within the rotor magnetic field’s plane of rotation. The six possible inverter states must follow a specific sequence depending on the desired rotation direction of the motor so that the stator and rotor field orientations arrangement produces maximal torque. Rotor position feedback, generally achieved with hall sensors mounted on the motor (sensored) or by sensing the back−EMF of the motor phases while rotating (sensorless), determines proper commutation timing. Download the asset now!