Sensorless motor control for a power tool

A power tool comprising;

• a sensorless motor, the sensorless motor including a phase coil and an injection coil;
• a direct current (DC) bus providing DC power from a power source of the power tool to an inverter bridge;
• a coupling circuit electrically connected to the injection coil;
• a de-coupling circuit electrically connected to the phase coil;
• a signal generator;
• and
• a controller coupled to the inverter bridge, the coupling circuit, the de-coupling circuit, and the signal generator, the motor controller configured to:
• generator, using the signal generator, a high-frequency injection signal;
• couple, using the coupling circuit, the high-frequency injection signal to the injection coil;
• decoupling, using the de-coupling circuit, a response to the high-frequency injection signal from the phase coil;
• determine a sensorless motor condition based upon the response of the injection coil to the high-frequency injection signal;
• and
• drive, using the power provided from the power source to the inverter bridge, the sensorless motor based upon the motor condition.

A method for automatic control switching for driving a sensorless motor of a power tool, the method comprising:

• generating, using an oscillator, a high-frequency injection signal;
• coupling, using a coupling circuit, the high-frequency injection signal to an injection coil of the sensorless motor;
• decoupling, using a de-coupling circuit, a response to the high-frequency injection signal from a phase coil of the sensorless motor;
• determining, via the coupling circuit, a sensorless motor position based upon the response of the injection coil to the high-frequency injection signal;
• and
• driving, using a controller, the sensorless motor based on the position of the sensorless motor using pulse width modulated signals having a lower frequency than the high-frequency injection signal.