Can I connect three phase frequency inverter to single phase power?

Often times those using a frequency inverter may find they need to connect a higher horsepower frequency inverter to a single phase input power source. Since most high horsepower frequency inverters only accept three phase input as a power source, they are left with few options or alternatives. Don't fret, there is a solution.

If you are using a frequency inverter rated for three phase input and the only power source you have available to you is single phase input, then you can derate the frequency inverter to accept the single phase input power source. You can almost always use a frequency inverter rated for three phase input with a single phase input power source. When only a three phase input frequency inverter is available, it is acceptable and common practice to derate the frequency inverter to work with a single phase input power source.

Before you derate your frequency inverter, it is most important to ensure the frequency inverter you are using is properly suited for your application. The following are some basic guidelines to help you in determining whether or not your frequency inverter is suitable for your application: Gather motor nameplate data including horsepower (HP), current (Amps), motor voltage, input line voltage and power source phase. Determine which type of frequency inverter your application will require. The type will fall under the category of Volts per Hertz (V/Hz), closed-loop vector, or open-loop vector (Sensor-less Vector). The internal components of the three phase input frequency inverter are rated for the appropriate current expected when three phase input power is applied. When using single phase input the line side current from the single phase is always higher. To "derate" is the process of ensuring that these components are rated for the higher current that will flow from the single phase input instead of the three phase input.

You can derate a frequency inverter by:
Determining the Horsepower of the Motor the frequency inverter will be connected too, then choosing frequency inverter with a Horsepower higher than the Horsepower of the motor to compensate for the additional input current from the single phase power source. The simplest formula used for these types of applications is:

Frequency inverter Input Current > Motor Current Rating * 1.73

The frequency inverter input current must be equal to or greater than the Motor Current Rating * 1.73

When installing most three phase input frequency inverters on an application where single phase input power is used, you will almost always connect the input line leads to L1 and L2 of the frequency inverter. L3 will be left open with nothing connected. Consult with the frequency inverter manufacturer or knowledgeable integrator to be sure.

Example:
An application has a 230 VAC single phase input power source and needs to connect it to a conveyor that has a frequency inverter connected to a 10 Horsepower 230 VAC 3 phase induction motor. Let us assume it has been determined that this application will operate well with a simple Volts per Hertz (V/Hz) frequency inverter. The issue is, since there are no frequency inverter manufacturers that offer a 10 Horsepower (HP) single phase input frequency inverter (frequency inverter), we will need to derate a frequency inverter with a three phase input for single phase input. Most manufacturers of frequency inverters only offer products up to 3 Horsepower (HP) for single phase input. The 10 Horsepower (HP) AC motor nameplate reveals that the motor is rated for approximately 27 amps at 230 VAC. We must use the equation above:

Frequency inverter Input Current > Motor Current Rating * 1.73
Frequency inverter Input Current > 27 Amps * 1.73
Frequency inverter Input Current > 46.71

This application will need a 230 VAC 3 phase Volts per Hertz (V/Hz) frequency inverter with an input current rated at or above 47.0 amps.