INVERTER WITH ELECTRONICALLY CONTROLLED NEUTRAL TERMINAL

• US 3,775,663 A
• Filed: 08/24/1972
• Issued: 11/27/1973
• Est. Priority Date: 08/24/1972
• Status: Expired due to Term

• Current Assignee: Fred G. Turnbull
• Original Assignee: Fred G. Turnbull
• Inventors: Turnbull, Fred G.
• Primary Examiner(s): Pellinen, A. D.
• Application Number:
  US05/283,530
• Time in Patent Office: 460 Days
• Field of Search: 321/5,9A,27R,45R
• US Class Current: 363/41
• CPC Class Codes: H02M 7/515 using semiconductor devices only
• CPC Class Codes: H02M 7/527 by pulse width modulation

Abstract

A solid state inverter, or other single phase or polyphase power converter, has an electronic neutral to enable direct connection to unbalanced loads without requiring a fundamental frequency output transformer. The electronic neutral terminal circuit is typically an additional single phase inverter operated as a current source or sink to maintain the potential at the neutral terminal at a controlled voltage independent of neutral current flow into and out of the neutral terminal. The preferred embodiment is a three-phase pulse width modulated inverter supplying single phase and polyphase unbalanced loads.

Claims

1. A power converter with an electronic neutral comprising a solid state inverter comprising a plurality of single phase inverters for independently supplying alternating voltage to a like number of output terminals that are directly connectable to a load, said inverter further having a neutral terminal that is directly connectable to the load, and an electronic neutral terminal circuit comprising an additional single phase inverter for supplying voltage to said neutral terminal, said electronic neutral terminal circuit being operative to control the potential at said neutral terminal independent of any neutral current flow into and out of said neutral terminal.

2. A power converter according to claim 1 for use with a balanced load producing negligible neutral current flow wherein said electronic neutral terminal circuit is operative to modulate the potential at said neutral terminal, whereby the alternating voltage supplied to said output terminals and the modulated potential at said neutral terminal are summed to apply a desired waveform to the balanced load.

3. A power converter with an electronic neutral comprising a solid state inverter comprising a plurality of single phase inverters for independently supplying alternating voltage to a like number of output terminals that are selectively directly connectable to an unbalanced load, said inverter further having a neutral terminal that is directly connectable to the unbalanced load, an electronic neutral terminal circuit comprising an additional single phase inverter for supplying said neutral terminal, said electronic neutral terminal circuit being operative selectively as a current source and current sink to control the potential of said neutral terminal independent of any neutral current flow into and out of said neutral terminal.

4. A power converter according to claim 3 wherein all of said single phase inverters are connected between a pair of direct voltage input terminals, and said electronic neutral terminal circuit is operative to maintain the potential at said neutral terminal at an approximately constant average value.

5. A power converter according to claim 3 further including filter means for filtering the voltage at each of said output and neutral terminals.

6. A power converter according to claim 3 wherein said single phase inverters supplying said output terminals are selectively controlled at a high chopping frequency to generate pulse width modulated alternating voltage, and said additional single phase inverter in said electronic neutral terminal circuit is controlled at a high chopping frequency.

7. A power converter according to claim 3 wherein said single inverters supplying said output terminals are half-bridge inverters connected between a pair of direct voltage input terminals, and filter means comprising a series filter inductor and shunt filter capacitor for filtering the voltage supplied to each output terminal, and said additional single phase inverter in said electronic neutral terminal circuit is a half-bridge inverter connected between said input terminals, and filter means for filtering the voltage supplied to said neutral terminal comprising a series filter inductor connected to the junction of a pair of capacitors which in turn are connected in series between said input terminals.

8. A power converter with an electronic neutral comprising a solid state inverter comprising at least three half-bridge inverTers each connected between a pair of direct voltage input terminals and supplying alternating voltage to at least three output terminals that are selectively directly connectable to an unbalanced load, said inverter further having a neutral terminal that is directly connectable to the unbalanced load, and an electronic neutral terminal circuit comprising an additional half-bridge inverter connected between said input terminals and supplying said neutral terminal, said electronic neutral terminal circuit being operated as a current source and current sink to maintain said neutral terminal at an approximately constant potential independent of neutral current flow.

9. A power converter according to claim 8 wherein all of said half-bridge inverters are controlled at a high chopping frequency to generate pulse width modulated alternating voltage.

10. A power converter according to claim 9 further including filter means for filtering the pulse width modulated alternating voltage supplied to each output and neutral output terminal.