Controls and operation of variable frequency drives

A method comprising:

• providing a system comprising a refrigerant circuit including a compressor configured to compress refrigerant, a condenser configured to receive refrigerant from the compressor and an expander configured to receive refrigerant from the condenser, an electric motor configured to drive the compressor, a motor drive configured to drive the electric motor, and a controller configured to control the motor drive to drive the electric motor;
• operating the controller to first evaluate whether the compressor is idle based upon a control state of the controller being configured not to operate the motor drive to drive the motor;
• operating the controller to second, in response to an affirmative evaluation that the compressor is idle, evaluate a risk of undesired or un-commanded compressor rotation based upon a combination of two or more system conditions, each of the two or more system conditions indicating the risk of undesired or un-commanded compressor rotation;
• and
• operating the controller to third, in response to an affirmative evaluation of the risk of undesired or un-commanded compressor rotation, control the motor drive to oppose rotation of the compressor.