Variable speed air compressing system having AC and DC power sources

A variable speed drive for an air compressing system, comprising:

• a rectifier configured to receive alternating current from a first power source and to provide rectified direct current having a first voltage;
• an inverter configured to receive the rectified direct current and to receive direct current from a second power source having a second voltage, the inverter further configured to provide alternating current to a motor, wherein the alternating current provided to the motor is based on the rectified direct current if the first voltage is greater than the second voltage and wherein the alternating current provided to the motor is based on the direct current from the second power source if the second voltage is greater than the first voltage;
• and
• a controller configured to raise the first voltage to increase the voltage at which the system will transition between the second power source and the first power source and to lower the first voltage to decrease the voltage at which the system will transition between the second power source and the first power source.

A variable speed air compressing system, comprising:

• a compressor;
• a motor configured to actuate the compressor;
• a rectifier configured to receive alternating current from a first power source and to provide rectified direct current having a first voltage;
• a second power source;
• an inverter configured to receive the rectified direct current and to receive direct current from a second power source having a second voltage, the inverter further configured to provide alternating current to the motor, wherein the alternating current provided to the motor is based on the rectified direct current if the first voltage is greater than the second voltage and wherein the alternating current provided to the motor is based on the direct current from the second power source if the second voltage is greater than the first voltage;
• and
• a controller configured to control an amount of allowable sag of the second voltage by raising or lowering the first voltage effective to change the point at which power to the motor is switched from the second power source to a combination of the first power source and the second power source.