Method and system for controlling permanent magnet AC machines

A method for controlling a permanent magnet (PM) machine, the method comprising the steps of:

• generating a d-axis voltage command and a g-axis voltage command, the d-axis voltage command based on a d-axis current command;
• producing a modified d-axis current command based on the g-axis voltage command and the d-axis current command;
• converting the modified d-axis current command to a modified d-axis voltage command;
• and
• transmitting the modified d-axis voltage command and the g-axis voltage command to the PM machine;
• wherein the PM machine has a peak torque;
• and wherein said step of producing a modified d-axis current command comprises producing the modified d-axis current command based on the q-axis voltage command and the d-axis current command if the PM machine is operating with a load less than or equal to about 10% of the peak torque of the PM machine.

A method for controlling a permanent magnet (PM) machine, the PM machine configured to operate based on a torque command, a d-axis current command, and a q-axis current command, the method comprising the steps of:

• generating a d-axis voltage command and a q-axis voltage command, the d-axis voltage command based on the d-axis current command, the q-axis voltage command based on the q-axis current command, each of the d-axis current command and the q-axis current command based on at least the torque command;
• producing a modified q-axis voltage command based on a modified q-axis current command if the torque command is greater than or equal to a first torque value;
• and
• producing a modified d-axis voltage command based on the q-axis voltage command and the d-axis current command if the torque command is less than or equal to a second torque value, the first torque value greater than the second torque value.

A system for controlling a permanent magnet (PM) machine, wherein said PM machine is configured to operate with a modulation reference, a modulation index, and a torque command;

• the system comprising:
• a regulator having an input configured to receive a d-axis current command and a q-axis current command and having an output configured to couple to the PM machine, said regulator configured to produce a d-axis voltage command based on said d-axis current command and a q-axis voltage command based on said q-axis current command;
• a first module having an input configured to receive said q-axis voltage command and having an output coupled to said input of said regulator, said first module configured to produce a d-axis current correction based on said q-axis voltage command, said regulator further configured to produce a modified d-axis voltage command based on said d-axis current correction and said d-axis current command;
• and
• a second module coupled to said input of said regulator, said second module configured to produce a q-axis current correction when said torque command is greater than or equal to a first torque value, said q-axis current correction based on said modulation reference and said modulation index.

A system for controlling a permanent magnet (PM) machine, the system comprising:

• a regulator having an input configured to receive a d-axis current command and a q-axis current command and having an output configured to couple to the PM machine, said regulator configured to produce a d-axis voltage command based on said d-axis current command and a q-axis voltage command based on said q-axis current command;
• and
• a first module having an input configured to receive said q-axis voltage command and having an output coupled to said input of said regulator, said first module configured to produce a d-axis current correction based on said q-axis voltage command, said regulator further configured to produce a modified d-axis voltage command based on said d-axis current correction and said d-axis current command;
• wherein said first module comprises:
• a low-pass filter having an input configured to receive said q-axis voltage command and having an output;
• a summing block having an input coupled to said output of said low-pass filter and having an output, said summing block configured to produce an error between a q-axis voltage reference and said q-axis voltage command;
• a proportional-integral (PI) controller having an input coupled to said output of said summing block and having an output, said PI controller configured to produce a current based on said error;
• a limiter having an input coupled to said output of said PT controller and having an output coupled to said input of said regulator, said limiter configured to negatively limit said current to produce said d-axis current correction.

A system for controlling a permanent magnet (PM) machine, wherein said PM machine is configured to operate with a modulation reference, a modulation index, and a torque command, the system comprising:

• a regulator having an input configured to receive a d-axis current command and a q-axis current command and having an output configured to couple to the PM machine, said regulator configured to produce a d-axis voltage command based on said d-axis current command and a q-axis voltage command based on said q-axis current command;
• a first module having an input configured to receive said q-axis voltage command and having an output coupled to said input of said regulator, said first module configured to produce a d-axis current correction based on said q-axis voltage command, said regulator further configured to produce a modified d-axis voltage command based on said d-axis current correction and said d-axis current command;
• and
• a second module coupled to said input of said regulator, said second module configured to produce a q-axis current correction if said torque command is greater than or equal to a first torque value, said q-axis current correction based on said modulation reference and said modulation index;
• wherein said first module is further configured to produce said d-axis current correction if said torque command is less than or equal to a second torque value, said first torque value greater than said second torque value;
• and
• wherein said regulator is further configured to produce a modified q-axis voltage command based on said q-axis current correction and said q-axis current command.