Power tool including current-based field weakening

A method of controlling a power tool including an electronic controller, the method comprising:

• receiving, via a current sensor, a first signal indicative of a current of a brushless DC motor;
• generating a current command based on a characteristic of the brushless DC motor;
• setting a conduction angle of the brushless DC motor based on the current command;
• supplying a pulse-width modulated (“PWM”) signal having a duty cycle to the brushless DC motor to control the current of the brushless DC motor;
• determining whether the duty cycle of the PWM signal is equal to a first threshold;
• maintaining, in response to the duty cycle being equal to the first threshold, the duty cycle at the first threshold;
• modifying the conduction angle to increase the current of the brushless DC motor;
• determining whether the current command is equal to a second threshold;
• and
• controlling, in response to the current command being equal to the second threshold, the conduction angle to maintain the current command at the second threshold.

A power tool comprising:

• a housing;
• a brushless direct current (DC) motor within the housing;
• a trigger;
• a power switching circuit that provides a supply of power from a battery pack to the brushless DC motor;
• a voltage sensor configured to sense a bus voltage;
• a current sensor configured to sense a current of the brushless DC motor;
• and
• an electronic controller connected to the trigger, the brushless DC motor, the voltage sensor, and the current sensor, the electronic controller configured to:
• provide, in response to actuation of the trigger, power to the brushless DC motor according to a first current limit value,
• receive, via the current sensor, a first signal indicative of the current of the brushless DC motor,
• receive, via the voltage sensor, a second signal indicative of a voltage of the power switching circuit,
• generate a current command based on a characteristic of the brushless DC motor,
• set a conduction angle of the brushless DC motor based on the current command,
• supply a pulse-width modulated (“PWM”) signal having a duty cycle to the brushless DC motor to control the current of the brushless DC motor,
• determine whether the voltage of the power switching circuit is greater than or equal to a voltage threshold,
• determine whether the duty cycle of the PWM signal is equal to a first threshold,
• adjust, in response to the voltage of the power switching circuit being less than or equal to the voltage threshold, the first current limit value to a second current limit value,
• maintain, in response to the duty cycle being equal to the first threshold, the duty cycle at the first threshold,
• modify the conduction angle to increase the current of the brushless DC motor,
• determine whether the current command is equal to a second threshold, and
• control, in response to the current command being equal to the second threshold, the conduction angle to maintain the current at the second threshold.