Electronically commutated motor and control system employing phase angle control of phase current

A method of controlling a power tool, comprising:

• providing a power tool with an electronically commutated motor for powering a working implement of the power tool, the electronically commutated motor including a rotor having multiple internally mounted permanent magnets;
• using a gear reduction unit to receive an output from the electronically commutated motor, and to drive a working implement of the power tool;
• using a pulse width modulation (PWM) control technique to control operation of the electronically commutated motor until a substantially maximum power output of the electronically commutated motor is reached;
• once the substantially maximum power output of the electronically commutated motor is reached, using a field weakening control technique to reduce a back EMF generated by the electronically commutated motor such that an output power of the electronically commutated motor is maintained at a substantially constant level over a predetermined motor speed range, and such that the speed of the electronically commutated motor is decreased;
• and
• wherein using the field weakening control technique comprises using a look-up table to obtain a phase advance angle by which the current signal applied to the electronically commutated motor is advanced.

A method of controlling a motor driven power tool, comprising:

• providing a motor of a power tool having a rotor and multiple internally mounted permanent magnets;
• using an output of the motor to drive a gear reduction unit, an output of the gear reduction unit driving a working implement of the power tool;
• controlling a voltage of an input signal applied to the motor so that variable motor power is available to the gear reduction unit, and thus to the working implement, based on a user input being provided to the power tool;
• and
• for operation of the motor after a point at which maximum power output of the motor is reached but an increasing torque demand is being placed on the motor, using a field weakening control technique including controlling a phase advance angle of a current of the input signal applied to the motor to controllably increase a reluctance torque generated by the motor, and to decrease a speed of the motor, and thus decrease a back EMF being generated by the motor, such that motor power and motor efficiency of the motor are maintained substantially constant while the speed of the motor is decreased.

A power tool comprising:

• an electronically commutated motor having a rotor, the rotor having multiple internally mounted permanent magnets;
• a gear reduction unit responsive to an output of the electronically commutated motor, an output of the gear reduction unit being in communication with a working implement of the power tool;
• a switching subsystem for generating drive signals for electrically powering the electronically commutated motor;
• a controller for controlling the switching system to implement:
• a first control technique to obtain a variable power output from the electronically commutated motor until a maximum power output for the electronically commutated motor is reached, in response to reaching a first torque output level;
• and
• a second control technique involving field weakening when a torque output of the electronically commutated motor is increased beyond the first torque output level to a second torque output level, such that a substantially constant motor output power and efficiency between the first and second torque output levels is maintained while a speed of the electronically commutated motor is decreased;
• the second control technique including controlling a phase advance angle of a current component of the drive signals to implement a degree of phase angle advance of the current component of the drive signals;
• and
• a look-up table accessible by the controller, the look-up table including a plurality of advance angles usable by the controller to control the phase angle of the current component of the drive signals applied to the electronically commutated motor.