Single phase to three phase converter

An apparatus for converting a single phase AC input signal to a three phase AC output signal, comprising:

• (a) first and second single phase AC input terminals connected to first and second input lines, respectively;
• (b) three output lines connectable to a three phase load, a first of the output lines connected to the first input line and a second of the output lines connected to the second input line;
• (c) an inverter circuit connected to the input lines to receive single phase AC power therefrom and having an output node connected to a third of the output lines, the inverter circuit responsive to inverter control signals to provide an AC output signal at the inverter circuit output node;
• (d) a bi-directional switch responsive to bi-directional switch control signals connected in series with the first input line between the first input terminal and both the first output line and the inverter circuit;
• and
• (e) controller means for providing the inverter control signals to the inverter circuit including means for phase shifting a single phase input voltage signal on the first and second input lines by 60 degrees to form an inverter output voltage waveform reference signal and means for modulating the inverter output voltage waveform reference signal to generate the inverter control signals to control the inverter to provide the AC output signal at the output node of the inverter to provide a three phase AC waveform signal on the three output lines and maximum DC bus voltage regulation means for adjusting the inverter control signals to shift the phase of the AC output voltage at the output node of the inverter to regulate the net power flow into the inverter to approximately zero, and means for providing the bi-directional switch control signals to phase control the bi-directional switch during start-up of a load to adjust the amplitude of the three phase AC waveform signal to ramp up the current provided on the output lines to soft start the load and to limit inrush current to the apparatus.

A method for converting a single phase AC input signal on first and second input lines to a three phase AC output signal on first, second, and third output lines, comprising the steps of:

• (a) connecting the first output line to the first input line and the second output line to the second input line;
• (b) connecting an inverter between the first and second input lines, to receive the single phase AC input power therefrom, and the third output line;
• (c) connecting a bi-directional switch in series with the first input line between a first input terminal and both the first output line and the inverter;
• (d) controlling the inverter to provide an inverter AC output signal on the third output line having an amplitude and phase to provide a balanced three phase AC waveform signal on the three output lines;
• and
• (e) phase controlling the bi-directional switch during start-up of a load connected to the three output lines to ramp up the current provided to the inverter and on the output lines to soft start the load.