Excitation circuit and control method for flux switching motor

An excitation circuit for a flux switching motor having a field winding and an armature winding, comprising:

• a rectifier circuit for converting an AC input signal into a rectified AC signal;
• an H-bridge switching circuit responsive to said rectified AC output and being coupled across said armature winding;
• an armature energy recovery capacitor coupled across an output of said switching circuit;
• a controller for controlling an on and off switching of each of said switch components of said H-bridge circuit;
• and
• an on/off switch operably associated with said controller and engageable by a user between an on position and an off position, for signaling said controller when a user is powering on and off said excitation circuit;
• and
• a detection circuit responsive to said position of said on/off switch and to an application of said AC input signal to said excitation circuit for preventing immediate turn on of said excitation circuit if said AC input signal is first applied to said excitation circuit while a user is holding said on/off switch in an on position.

An excitation circuit for a flux switching motor having a field winding and an armature winding, said excitation circuit comprising:

• a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;
• an H-bridge switching circuit coupled across said DC bus lines, said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit;
• an armature recovery capacitor coupled across said DC bus lines and across said switching circuit;
• said H-bridge switching circuit including a plurality of bypass components for permitting recirculation of armature current flowing through said armature winding during a start-up phase of operation of said motor;
• and
• a controller for generating a switching signal for controlling said H-bridge switching circuit, said controller producing a pulse width modulated (PWM) switching signal for controlling selected ones of said switch components.

A method for exciting a flux switching motor having a field winding and an armature winding, said method comprising:

• providing an AC input signal from an AC power source;
• using a rectifier to receive said AC input signal and generate a rectified AC signal on a pair of DC bus lines;
• using an H-bridge switching circuit operably coupled across said armature winding to selectively direct current flow of said rectified AC signal through said armature winding;
• using a plurality of bypass components associated with said H-bridge circuit to permit recirculation of said current flow through said armature winding during a start-up phase of operation of said motor;
• using a controller to control said H-bridge to operate said motor;
• and
• using an armature energy recovery capacitor coupled across said H-bridge switching circuit to store armature energy during operation of said motor.

A method for exciting a flux switching motor having a field winding and an armature winding, said method comprising:

• providing an AC input signal from an AC power source;
• rectifying said AC input signal to generate a rectified AC signal;
• applying said rectified AC signal to a switching circuit associated with said armature winding to alternately switch a direction of armature current flowing through said armature winding;
• using a plurality of bypass components with said switching circuit to permit recirculation of said armature current flowing through said armature winding when switching the direction of said flow of said armature current through said armature winding;
• using a controller to control operation of said switching circuit;
• and
• using an energy recovery capacitor to store armature energy during operation of said switching circuit.

A method for controlling a flux switching motor, comprising:

• defining a first start-up speed range;
• defining a second start-up speed range subsequent to said first start-up speed range;
• defining a first time envelope during which a pulse width modulated (PWM) switching signal having a predetermined duty cycle is to be applied to said flux switching motor;
• applying said PWM switching signal, in accordance with said first time envelope, to said flux switching motor to commutate said flux switching motor during said first start-up speed range;
• modifying said first time envelope to produce a second time envelope;
• at a beginning of said second start-up speed range, applying said PWM switching signal in accordance with said second time envelope to continue commutating said flux switching motor.

A method for commutating a flux switching motor, said method comprising:

• defining a first speed range for said flux switching motor;
• defining a second speed range for said flux switching motor;
• applying a plurality of turn-on electrical commutation pulses to said flux switching motor during said first speed range, each of said turn on electrical commutating pulses comprising a pulse width modulated (PWM) commutating signal having a predetermined duty cycle;
• said PWM commutating signal being further applied in accordance with a first predefined time envelope such that an overall time period of each of said turn-on electrical commutation pulses is controlled;
• and
• modifying said first predefined time envelope to produce a second predefined time envelope such that said overall time period of each of said turn-on electrical commutating pulses is modified.

A method for commutating a flux switching motor, comprising:

• sensing a motor speed of said flux switching motor;
• generating a commutating signal including a plurality of turn-on commutating pulses that are applied to said flux switching motor to commutate said motor, each said turn-on commutating pulse being comprised of a pulse width modulated (PWM) signal;
• and
• modifying a time envelope during which each said turn-on pulse is applied to said flux switching motor in accordance with said sensed motor speed to further control the power applied to said motor as said motor increases in speed from a non-rotating condition to a condition wherein said motor is operating at a rated motor speed.

A power tool comprising:

• an on/off switch engageable by a user for turning on and off said power tool;
• a flux switching motor having a field winding and an armature winding;
• an excitation circuit including:
• a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;
• an H-bridge switching circuit coupled across said DC bus lines, said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit;
• an armature recovery capacitor coupled across said DC bus lines and across said switching circuit;
• said H-bridge switching circuit including a plurality of bypass components for permitting recirculation of armature current flowing through said armature winding during a start-up phase of operation of said motor;
• and
• a controller responsive to said operation of said on/off switch for generating a pulse width modulated switching signal for controlling said H-bridge switching circuit to control on and off switching of selected ones of said switch components to commutate said motor.

A power tool comprising:

• an on/off switch engageable by a user for placing said tool in an on condition and an off condition;
• a flux switching motor having a field winding and an armature winding, said excitation circuit comprising:
• a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;
• an H-bridge switching circuit coupled across said DC bus lines, said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit;
• an armature recovery capacitor coupled across said DC bus lines and across said switching circuit;
• and
• a controller for generating a switching signal for controlling said H-bridge switching circuit, said controller producing a pulse width modulated (PWM) switching signal for controlling selected ones of said switch components;
• said power tool further including a detection circuit responsive to a position of said on/off switch for preventing powering on of said power tool if said AC input signal is initially applied to said power tool while said user is holding said on/off switch in an on position.