System and method for detection and control of circulating currents in a motor

A motor system comprising:

• a stationary assembly including windings;
• a rotatable assembly in magnetic coupling relation to the stationary assembly;
• a power supply link for providing power to the windings, said power supply link comprising an inverter bridge having upper and lower rails supplied by a power supply and having power switches responsive to a motor control signal for selectively connecting the rails to the windings to produce an electromagnetic field for rotating the rotatable assembly, said power switches each having a conducting state and a nonconducting state;
• a first resistive shunt in the upper rail of the power supply link between the power supply and the power switches for sensing current in the upper rail;
• a second resistive shunt in the lower rail of the power supply link between the power supply and the power switches for sensing current in the upper rail, said inverter bridge connecting the windings to the upper and lower rails such that current circulating in the power supply link and windings during the off intervals of the power provided to the windings is routed through either the first resistive shunt or the second resistive shunt;
• a current regulation circuit for generating an overcurrent signal as a function of the current sensed in either the first or second resistive shunt exceeding a maximum current level;
• and
• a control circuit responsive to the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor system.

A system for driving a rotatable component comprising:

• a motor having a stationary assembly and a rotatable assembly in magnetic coupling relation to the stationary assembly, said stationary assembly including windings, said rotatable assembly being in driving relation to the rotatable component;
• a power supply link for providing power to the windings, said power supply link comprising an inverter bridge having upper and lower rails supplied by a power supply and having power switches responsive to a motor control signal for selectively connecting the rails to the windings in alternating on and off intervals to produce an electromagnetic field for rotating the rotatable assembly, said power switches each having a conducting state and a nonconducting state;
• a current sensing circuit for sensing current in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings, said inverter bridge connecting the windings to the upper and lower rails such that current circulating in the power supply link and windings during the off intervals of the power provided to the windings is routed through the current sensing circuit;
• a current regulation circuit for generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level;
• and
• a control circuit responsive to the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor.

A protective circuit for a motor, said motor having a stationary assembly including windings and having a rotatable assembly in magnetic coupling relation to the stationary assembly, said motor also having a control circuit for generating a motor control signal and a power supply link for providing power to the windings, said power supply link comprising an inverter bridge having upper and lower rails supplied by a power supply and having power switches responsive to the motor control signal for selectively connecting the rails to the windings in alternating on and off intervals to produce an electromagnetic field for rotating the rotatable assembly, said protective circuit comprising:

• a current sensing circuit for sensing current in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings;
• a circuit for routing current circulating in the power supply link and windings during the off intervals of the power provided to the windings through the current sensing circuit;
• a current regulation circuit for generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level;
• and
• wherein the control circuit is responsive to the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor.

A method of controlling circulating currents in a motor, said motor having a stationary assembly including windings and having a rotatable assembly in magnetic coupling relation to the stationary assembly, said motor also having a power supply link for providing power to the windings, said power supply link including upper and lower rails supplied by a power supply and power switches each having a conducting state and a nonconducting state, said method comprising the steps of:

• selectively connecting the rails to the windings in alternating on and off intervals with the power switches to produce an electromagnetic field for rotating the rotatable assembly, said power switches being responsive to a motor control signal;
• routing current circulating in the power supply link and windings during the off intervals of the power provided to the windings through a current sensing circuit;
• sensing current with the current sensing circuit in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings;
• generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level;
• and
• generating the motor control signal as a function of the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor.

A motor system comprising:

• a stationary assembly including windings;
• a rotatable assembly in magnetic coupling relation to the stationary assembly;
• a power supply link for providing power to the windings, said power supply link comprising an inverter bridge having upper and lower rails supplied by a power supply and having power switches responsive to a motor control signal for selectively connecting the rails to the windings in alternating on and off intervals to produce an electromagnetic field for rotating the rotatable assembly, said power switches each having a conducting state and a nonconducting state;
• a current sensing circuit for sensing current in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings, said inverter bridge connecting the windings to the upper and lower rails such that current circulating in the power supply link and windings is routed through the current sensing circuit;
• a current regulation circuit for generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level, said current regulation circuit comprising a comparator circuit for comparing the current sensed in one of the rails to a peak regulated current level representative of a desired torque and/or speed of the motor, said current regulation circuit generating a current regulation signal representative of the comparison;
• and
• a control circuit responsive to the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor system, said control circuit being responsive to the current regulation circuit for generating the motor control signal as a function of the current regulation signal to regulate current in the windings and control the torque and/or speed of the motor.

A motor system comprising:

• a stationary assembly including windings;
• a rotatable assembly in magnetic coupling relation to the stationary assembly;
• a power supply link for providing power to the windings, said power supply link comprising an inverter bridge having upper and lower rails supplied by a power supply and having power switches responsive to a motor control signal for selectively connecting the rails to the windings in alternating on and off intervals to produce an electromagnetic field for rotating the rotatable assembly, said power switches each having a conducting state and a nonconducting state;
• a current sensing circuit for sensing current in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings, said inverter bridge connecting the windings to the upper and lower rails such that current circulating in the power supply link and windings is routed through the current sensing circuit;
• a current regulation circuit for generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level, said maximum current level being variable as a function of a peak regulated current level;
• and
• a control circuit responsive to the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor system.

A method of controlling circulating currents in a motor, said motor having a stationary assembly including windings and having a rotatable assembly in magnetic coupling relation to the stationary assembly, said motor also having a power supply link for providing power to the windings, said power supply link including upper and lower rails supplied by a power supply and power switches each having a conducting state and a nonconducting state, said method comprising the steps of:

• selectively connecting the rails to the windings in alternating on and off intervals with the power switches to produce an electromagnetic field for rotating the rotatable assembly, said power switches being responsive to a motor control signal;
• routing current circulating in the power supply link and windings through a current sensing circuit;
• sensing current with the current sensing circuit in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings;
• generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level;
• comparing the current sensed in one of the rails to a peak regulated current level representative of a desired torque and/or speed of the motor;
• generating a current regulation signal representative of the comparison;
• and
• generating the motor control signal as a function of the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor and generating the motor control signal as a function of the current regulation signal to regulate current in the windings and control the torque and/or speed of the motor.

A method of controlling circulating currents in a motor, said motor having a stationary assembly including windings and having a rotatable assembly in magnetic coupling relation to the stationary assembly, said motor also having a power supply link for providing power to the windings, said power supply link including upper and lower rails supplied by a power supply and power switches each having a conducting state and a nonconducting state, said method comprising the steps of:

• selectively connecting the rails to the windings in alternating on and off intervals with the power switches to produce an electromagnetic field for rotating the rotatable assembly, said power switches being responsive to a motor control signal;
• routing current circulating in the power supply link and windings through a current sensing circuit;
• sensing current with the current sensing circuit in each of the rails of the power supply link during both the on and off intervals of the power provided to the windings;
• generating an overcurrent signal as a function of the current sensed in either one of the rails exceeding a maximum current level;
• varying the maximum current level as a function of a peak regulated current level;
• and
• generating the motor control signal as a function of the overcurrent signal for causing each of the power switches to become nonconducting thereby to prevent excessive current from circulating in the motor.