Field-oriented sensorless brushless motor control in a power tool

A power tool comprising:

• a housing;
• a brushless motor disposed within the housing, the motor comprising a stator having a plurality of windings and a rotor;
• a power switch circuit that supplies power from a power source to the brushless motor;
• and
• a controller configured to apply a drive signal to the power switch circuit to control the supply of power to the brushless motor,
• wherein the controller is configured to determine an angular position of the rotor using a high-frequency injection (HFI) scheme at a motor speed below a speed threshold and transition from the HFI scheme to a sensorless commutation scheme different from the HFI scheme during a transition period when the motor speed exceeds the speed threshold,
• wherein the HFI scheme includes injecting a plurality of voltage pulses to the motor and detecting corresponding high-frequency current components to determine the angular position of the rotor, and
• wherein, during the transition period, the controller is configured to:
• calculate an error value between a detected rotor angle from the sensorless commutation scheme and the determined angular position of the HFI scheme;
• gradually adjust a commutation sequence associated with the sensorless commutation scheme by ramping the commutation sequence up or down to reduce the error value;
• determine that the error value has fallen below a predefined convergence threshold such that the detected rotor angle from the sensorless commutation scheme is substantially close to the determined angular position of the rotor from the HFI scheme;
• and
• in response to determining that the error value has fallen below the predefined convergence threshold, gradually ramp down injection of the plurality of voltage pulses associated with the HFI scheme.