Low-speed sensorless brushless motor control in a power tool

A power tool comprising:

• a brushless motor having a stator defining a plurality of phases, a rotor rotatable relative to the stator, and a plurality of power terminals electrically connected to the plurality of phases;
• a power unit having a plurality of power switches connected electrically between a power source and the plurality of motor terminals and operable to deliver power to the motor;
• and
• a control unit interfaced with the power unit to output a drive signal to one or more of the plurality of motor switches to drive the plurality of phases of the motor over a plurality of sectors of the rotor rotation,
• wherein, the control unit is configured detect an incorrect direction of rotation of the rotor by applying a first plurality of voltage pulses to a present sector of the plurality of sectors and a second plurality of voltage pulses to a previous sector of the plurality of sectors, measuring motor currents associated with the first and second pluralities of voltage pulses, and comparing corresponding motor current measurements to detect a transition from the present sector to the previous sector.