In a 6-step or scalar control, normally only the frequency and magnitude of the voltage fed to the motor are controlled (current feedback is not mandatory). For permanent magnet 3-phase motors (BLDC, PMSM) rotor speed and/or position information is required in order to keep stator and rotor flux positions synchronous.
In cases where the rotor speed/position is obtained without using physical sensors (Hall, encoders, etc.) the drive is referred to as sensorless. A six-step drive (also known as block commutation) is one of the most common scalar drives available for both permanent magnet synchronous motors (PMSM) and brushless DC (BLDC) motors, due to the ease with which sensorless control can be achieved. Additionally, when a 6-step drive is in current mode the amplitude of the motor current can be controlled, allowing the motor torque to be regulated. As scalar drives do not require complex mathematical computations, they can be implemented on cost-effective microcontrollers (starting from 8-bit).