Method and apparatus for the safe limitation of motor torque in a three-phase drive

A torque-limiting safety circuit servo drive for an AC permanent magnet motor comprising:

• a three-phase inverter bridge;
• a first current sensor detecting current in a first motor phase;
• a second current sensor detecting current in a second motor phase;
• a third current sensor detecting current in a DC bus;
• a drive control circuit providing pulse-width-modulated gate drive signals to the three-phase inverter bridge, the drive control circuit having a first safety channel safe-torque-off input and a second safety channel safe-torque-off input, the drive control circuit adapted to emit a signal set representing a switching state of the three-phase inverter bridge to modify a pulse-width-modulated switching pattern;
• a first safety processor controlling the first safety channel safe-torque-off input of the drive control circuit;
• a second safety processor controlling the second safety channel safe-torque-off input of the drive control circuit;
• a first current vector calculator and error detector configured to detect a discrepancy based on a signal from the third current sensor and the signal set representing a switching state of the three-phase inverter bridge, said signals compared against the first and second current sensor signals and provide a fault signal to the first safety processor based on the discrepancy;
• and
• a second current vector calculator and error detector configured to detect a discrepancy based on a signal from the third current sensor and the signal set representing a switching state of the three-phase inverter bridge, said signals compared against the first and second current sensor signals and provide a fault signal to the second safety processor based on said discrepancy;
• wherein the drive control circuit is adapted to shut down the three-phase inverter bridge responsive to input from either of the first safety processor or the second safety processor.

A torque-limiting safety circuit servo drive for an AC permanent magnet motor, comprising:

• a three-phase inverter bridge fed from a DC bus;
• a drive control circuit for providing pulse-width modulated gate drive signals to the three-phase inverter bridge, the drive control circuit having a first safety channel safe-torque-off input and a second safety channel safe-torque-off input;
• a first safety processor controlling the first safety channel safe-torque-off input of the drive control circuit based upon a first estimate of a motor current vector;
• a second safety processor controlling the second safety channel safe-torque-off input of the drive control circuit based upon a second estimate of the motor current vector;
• a first current sensor detecting current in a first motor phase;
• a second current sensor detecting current in a second motor phase;
• a third current sensor detecting current in a DC bus;
• a rotor position sensor sub-system configured to supply a first rotor position measurement to the first safety processor;
• and
• a second rotor position measurement to the second safety processor;
• wherein the drive control circuit is configured to emit a signal set representing a switching state of the three-phase inverter bridge;
• wherein the drive control circuit is configured to shut down the three-phase inverter bridge responsive to input from either of the first safety processor or the second safety processor, and
• wherein the first rotor position measurement is independent of the second rotor position measurement.