Very High Efficiency Three Phase Power Converter

• US 20100226159A1
• Filed: 03/01/2010
• Published: 09/09/2010
• Est. Priority Date: 03/03/2009
• Status: Active Grant

• Current Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Original Assignee: Renewable Power Conversion, Inc.
• Inventors: Stern, Michael Joseph
• Granted Patent: US 8,730,702 B2
• Time in Patent Office: Days
• US Class Current: 363/132
• CPC Class Codes: H02M 1/0048 Circuits or arrangements for reducing losses using snubbers H02M1/34
• CPC Class Codes: H02M 7/5395 by pulse-width modulation
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A DC-to-AC power converter is disclosed which provides current regulated three-phase AC outputs and very high conversion efficiencies. The converter sinks power from an external DC current source and steers that current directly into two phases of a three-phase load by using complementary semiconductor switches in disparate half-bridges of a six-pole bridge. The steering switch selection rotates every 60° to direct current into the two phases with the largest voltage differential at any given time. The remaining half-bridge acts as a high-frequency, bi-directional current source to balance the three-phase load currents. This topology and control method significantly reduces power conversion losses. The converter may also include an additional power processing stage that is used to convert an external DC voltage source to a DC current source before the three-phase conversion takes place. Prior art converters first convert “soft” DC sources to voltage sources and then to AC current sources. The invention eliminates the need for large PWM filter inductors and DC bus capacitors used in prior art converters. In addition, 90% of the power being converted is directly processed by steering current into the AC three-phase load without high frequency chopping or switching. The invention is optimized for photovoltaic, utility-grid-interactive applications.

Claims

1. A DC-to-AC power converter apparatus for converting DC power to polyphase AC power and comprising a DC input, an AC polyphase output, an arrangement of semiconductor switches, sensors and controls where power from a DC current source is converted into an AC polyphase current source to deliver power to an AC polyphase load.

2. A power converter apparatus according to claim 1 where said arrangement of semiconductor switches is described as a typical six-pole bridge comprising three half-bridge sections, one for each phase of a three-phase system, where each half-bridge section comprises a top switch and a bottom switch with a common center connection to an one line of a three-phase load and where all half-bridge sections have common top switch poles referred to as the positive bus and common bottom switch poles referred to as the negative bus where the three-phase bridge input is defined as being across the positive and negative buses and where, at any given time, two of the three half-bridges are controlled to steer current directly into the three-phase load and the remaining half-bridge functions as a high frequency, bi-directional, switched current source and where the current steering is accomplished by closing each top switch in each half-bridge in rotation with a conduction-time of 120°

per switch and closing each bottom switch in each half-bridge in rotation with a conduction-time of 120°

per switch and where the top switch and bottom switch turn-on times for a given half-bridge are out of phase by 180°

so that the three-phase bridge always has a combination of one top switch and one bottom switch in full conduction on disparate half-bridges for 60° and

where the remaining half-bridge with no switches in full conduction during this 60°

conduction time of the other two half-bridges is controlled to operate as a high frequency bi-directional current source where the direction and magnitude of the current into the AC load connected to this phase can be controlled by the conduction-time ratio of the top and bottom switches and where the half-bridge section dedicated to function as the high frequency bi-directional current source changes in rotation every 60°

.

3. A power converter apparatus according to claim 2 where the power converter apparatus is controlled to operate into an AC load where the AC load is a three-phase voltage source, including but not limited to a three-phase electric utility grid, where said conduction-times of 120°

per switch are synchronized in some way with the voltage or voltages of said AC load and where current is steered, switched, directed or otherwise sourced into the AC load to facilitate power transfer to the AC load.

4. A power converter apparatus according to claim 3 where DC power is supplied by a photovoltaic source connected to the DC input and where the DC-to-AC converter apparatus has a voltage-source-to-current-source power converter stage between the DC input and the input to the three-phase bridge and were the voltage of the photovoltaic source is regulated by controlling the amount of current out of the photovoltaic source and into said voltage-source-to-current-source power converter stage and where a boost function may be used within the voltage-source-to-current-source power converter stage to allow current out of the voltage-source-to-current-source power converter stage to be sourced into the input of the three-phase bridge at a voltage higher than the photovoltaic source voltage.

5. A power converter apparatus according to claim 4 where said voltage-source-to-current-source power converter stage comprises plus and minus inputs, plus and minus outputs, an inductor, a rectifier, and a semiconductor switch where the plus input terminal is connected to one terminal of the inductor the remaining end of the inductor is connected to the anode of the rectifier and one pole of the semiconductor switch and where the cathode is connected to the plus output terminal and where the remaining end of the semiconductor switch is connected to the minus input and minus output terminals and where the semiconductor switch is controlled to boost the voltage of the DC source to a voltage higher than that of the AC load to facilitate power transfer through the 3-phase bridge and into the AC polyphase load.

6. A power converter apparatus according to claim 5 where the voltage-source-to-current-source power converter stage also includes any number of inductor-rectifier-switch circuits connected in parallel and switched out of phase with respect to other inductor-rectifier-switch circuits to cause a more continuous flow of current in and out of the voltage-source-to-current-source power converter stage.

7. A dual power converter apparatus comprising a first power converter according to claim 1 where said arrangement of semiconductor switches is described as a typical six-pole bridge comprising three half-bridge sections, one for each phase of a three-phase system, where each half-bridge section comprises a top switch and a bottom switch with a common center connection to an AC three-phase load and where all half-bridge sections have common top switch poles referred to as the positive bus and common bottom switch poles referred to as the negative bus where the three-phase bridge input is defined as being across the positive and negative buses and where, at any given time, two of the three half-bridges are controlled to steer current directly into the three-phase load and the remaining half-bridge functions as a high frequency, bi-directional, switched current source and where the current steering is accomplished by closing each top switch in each half-bridge in rotation with a conduction-time of 120°

per switch and closing each bottom switch in each half-bridge in rotation with a conduction-time of 120°

per switch and where the top switch and bottom switch turn-on times for a given half-bridge are out of phase by 180°

so that the three-phase bridge always has a combination of one top switch and one bottom switch in full conduction on disparate half-bridges for 60° and

where the power converter apparatus is controlled to operate into an AC load where the AC load is a three-phase voltage source, including but not limited to a three-phase electric utility grid, where said on-times of 120°

per switch are synchronized in some way with the voltage or voltages of said AC load and where current is steered, switched, directed or otherwise sourced into the AC load to facilitate power transfer to the AC load and where a second power converter has a common DC input and a common AC polyphase output, both with respect to said first converter, and where the second converter is any DC to three-phase power converter with current regulated outputs and where the first converter supplies the bulk of the power to the AC load and the second converter is operated to supply the make up current necessary to balance the three-phase load currents.

8. A method of converting power from a DC current source to polyphase AC power where current is fed into a polyphase load by selectively steering a portion of the DC current source current into different phases of a polyphase load by an arrangement of solid state switches to supply synchronized polyphase current into a polyphase load.

9. A method according to claim 8 where an additional power processing stage is used to allow a DC voltage source to be used instead of a DC current source where the additional power processing stage converts a DC voltage source to a DC current source.

10. A method of converting power from a DC current source to polyphase AC power where two DC to polyphase AC converters are used and where a first converter supplies current to a polyphase load by selectively steering a portion of the DC current source current into different phases of the polyphase load by an arrangement of solid state switches to supply synchronized polyphase current into a polyphase load and where a second DC to polyphase AC converter connects in parallel with the first converter, input for input and output for output, and where the first converter supplies the bulk of the power delivered to an AC polyphase load and the second converter supplies the make up power balance all currents into the AC load.