Variable frequency drive bypass energy savings

An AC motor drive system comprising:

• a variable frequency drive (VFD) for receiving AC power from a power source and developing variable frequency power at output terminals;
• a bypass contactor operatively connected between the power source and an AC motor;
• an output contactor operatively connected between the VFD output terminals and the AC motor;
• and
• a bypass control operatively associated with the VFD, the bypass contactor and the output contactor, the bypass control including a drive mode in which the output contactor is controlled to connect the VFD to the motor and a bypass mode in which the bypass contactor is controlled to connect the power source to the motor, the bypass control monitoring operation of the VFD to automatically switch to the bypass mode when motor speed as powered by the VFD approximates the motor speed that would be achieved by connecting the motor directly to the power source, wherein the bypass control is operatively associated with the VFD to monitor a frequency reference, output current and output frequency.

An AC motor drive system comprising:

• a variable frequency drive (VFD) for receiving AC power from a power source and developing variable frequency power at output terminals;
• a bypass contactor operatively connected between the power source and an AC motor;
• an output contactor operatively connected between the VFD output terminals and the AC motor;
• and
• a bypass control operatively associated with the VFD, the bypass contactor and the output contactor, the bypass control including a drive mode in which the output contactor is controlled to connect the VFD to the motor and an energy savings mode in which the bypass contactor is controlled to connect the power source to the motor, the bypass control monitoring operation of the VFD to determine if operating in the energy savings mode provides a preselect energy savings and if so then automatically switching to the energy savings mode, wherein the bypass control develops a command to the VFD to increase a frequency reference prior to switching from the drive mode to the energy savings mode.

An AC motor drive system comprising:

• a variable frequency drive (VFD) for receiving AC power from a power source and developing variable frequency power at output terminals;
• a bypass contactor operatively connected between the power source and an AC motor;
• an output contactor operatively connected between the VFD output terminals and the AC motor;
• and
• a bypass control operatively associated with the VFD, the bypass contactor and the output contactor, the bypass control including a drive mode in which the output contactor is controlled to connect the VFD to the motor and an energy savings mode in which the bypass contactor is controlled to connect the power source to the motor, the bypass control monitoring operation of the VFD to determine if operating in the energy savings mode provides a preselect energy savings and if so then automatically switching to the energy savings mode, wherein the bypass control is operatively associated with the VFD to monitor a frequency reference, output current and output frequency.