the present invention provides a motor drive system that is substantially more robust than those of the prior art . generally , the motor drive system provides a redundant communication topology with the drives , thereby greatly reducing the chance of failure by a fault in the drive - to - drive communication link . specifically , the motor drive system includes a plurality of motor drives joined by a communication media . each motor drive has a motor control circuit configured to control the speed of an electric motor and a media access control unit having two communication modules . each communications module includes a transmitter and a receiver joined to the communications media . a set of routing switches in the media access control unit joins the communication modules to connect the motor drives in an independent primary and a secondary ring communicating data for controlling the motor drives .