Regenerative variable frequency drive with auxiliary power supply

A regenerative variable frequency drive for converting single phase AC power from a power grid to three phase, variable frequency AC power and said three phase, variable frequency AC power to single phase AC power, comprising:

• a single phase AC power source,
• a DC bus having a positive bus bar, a negative bus bar and a bus capacitor, said bus capacitor connecting between said positive and negative bus bars,
• a first inverter that converts DC power to variable frequency, three phase AC power, and variable frequency, three phase AC power to DC power, said first inverter connecting to said positive and negative bus bars,
• a second inverter that converts DC power to three phase AC power, said second inverter connecting to said positive and negative bus bars and including a sine wave filter, and
• an active converter that converts single phase AC power to DC power and DC power to single phase AC power, including:
• first and second input lines connected to said source,
• first, second, third and fourth switches each having a collector, a base and an emitter, said emitter of said first switch and said collector of said second switch connecting to said first input line and said emitter of said third switch and said collector of said fourth switch connecting to said second input line, said collectors of said first and third switches connecting to said positive bus bar, said emitters of said second and fourth switches connecting to said negative bus bar,
• first, second, third and fourth diode each having an anode and a cathode, said anode of said first diode connecting to said emitter of said first switch, said cathode of said first diode connecting to said collector of said first switch, said anode of said second diode connecting to said emitter of said second switch, said cathode of said second diode connecting to said collector of said second switch, said anode of said third diode connecting to said emitter of said third switch, said cathode of said third diode connecting to said collector of said third switch, said anode of said fourth diode connecting to said emitter of said fourth switch, and said cathode of said fourth diode connecting to said collector of said fourth switch, and
• a controller connected to said bases of said first, second, third and fourth switches and driving said switches with a pulse width modulation according to a hybrid voltage switching scheme wherein said first, second, third and fourth switches are switched according to a unipolar voltage switching scheme through most of each cycle while said first, second, third and fourth switches are switched according to a bipolar voltage switching scheme around each zero crossing, said controller including a current reference generator that generates a current reference command to drive said first, second, third and fourth switches to maintain a selected DC voltage on said DC bus, said current reference generator connecting to one of said positive and negative bus bars and to one of said first and second input lines, and including a voltage comparator that compares the voltage on said DC bus with a reference DC voltage.

An active converter that converts single phase AC power to DC power and DC power to single phase AC power, for a regenerative variable frequency drive that converts single phase AC power from a power grid to three phase, variable frequency AC power and said three phase, variable frequency AC power to single phase AC power, said variable frequency drive including a DC bus having a positive bus bar and a negative bus bar, said converter comprising:

• a single phase AC power source,
• first and second input lines connected to said source,
• first, second, third and fourth switches each having a collector, a base and an emitter, said emitter of said first switch and said collector of said second switch connecting to said first input line and said emitter of said third switch and said collector of said fourth switch connecting to said second input line, said collectors of said first and third switches connecting to said positive bus bar, said emitters of said second and fourth switches connecting to said negative bus bar,
• first, second, third and fourth diodes each having an anode and a cathode, said anode of said first diode connecting to said emitter of said first switch, said cathode of said first diode connecting to said collector of said first switch, said anode of said second diode connecting to said emitter of said second switch, said cathode of said second diode connecting to said collector of said second switch, said anode of said third diode connecting to said emitter of said third switch, said cathode of said third diode connecting to said collector of said third switch, said anode of said fourth diode connecting to said emitter of said fourth switch, and said cathode of said fourth diode connecting to said collector of said fourth switch, and
• a controller connected to said bases of said first, second, third and fourth switches and driving said switches with a pulse width modulation according to a hybrid voltage switching scheme wherein said first, second, third and fourth switches are switched according to a unipolar voltage switching scheme through most of each cycle while said first, second, third and fourth switches are switched according to a bipolar voltage switching scheme around each zero crossing, to maintain a selected voltage on said DC bus.