Damping control in a three-phase motor with a single current sensor

A method for measuring current by a sensor in a three-phase motor operating in a damping mode, drive current to the three-phase motor switched by an upper bank of switches and a lower bank of switches controlled by a plurality of pulse width modulation signals, the method comprising the steps of:

• determining when mechanical feedback into the motor exceeds a predetermined threshold;
• closing all of the switches of one of the upper and lower bank of switches to provide damping of the mechanical feedback;
• after the closing step, switching selected first switches necessary to measure a first current in at least one phase winding of the motor at a positive voltage vector;
• sampling the first current by the sensor;
• further switching selected second switches necessary to measure a second current in the at least one phase winding of the motor at a negative voltage vector;
• sampling the second current by the sensor;
• repeating the switching and sampling steps such that an average vector voltage of the motor is substantially zero and until the sampled current in the sampling step indicates that the mechanical feedback into the motor has fallen below the predetermined threshold;
• and
• exiting the damping mode.

An apparatus for measuring current by a sensor in a three-phase motor operating in a damping mode, the apparatus comprising:

• an upper bank of switches and a lower bank of switches controlled by a plurality of pulse width modulation signals;
• and
• a controller coupled to the switches to provide the pulse width modulation signals for controlling the switches, the controller operable to receive a current measurement signal from the sensor,
• the sensor operable to measure current in each phase of the motor, the controller operable to input the signal from the sensor to determine when mechanical feedback into the motor exceeds a predetermined threshold, whereupon the controller closes all of the switches of one of the upper and lower bank of switches to provide damping of the mechanical feedback, and
• wherein after the controller closes all of the switches of one of the upper and lower bank of switches to provide damping of the mechanical feedback, the controller operates to periodically switch selected switches necessary for the sensor and controller to measure the current in at least one phase of the motor, whereupon the sensor and controller sample the current of the phase selected and repeat the switching and sampling until the sampled current indicates that the mechanical feedback into the motor has fallen below the predetermined threshold, whereupon the apparatus exits the damping mode.