Photovoltaic power plant with distributed DC-to-DC power converters

• US 20100195361A1
• Filed: 01/28/2010
• Published: 08/05/2010
• Est. Priority Date: 01/30/2009
• Status: Active Grant

• Current Assignee: Parker Intangibles LLC (Parker-Hannifin Corporation)
• Original Assignee: Renewable Power Conversion, Inc.
• Inventors: Stem, Michael Joseph
• Granted Patent: US 8,648,497 B2
• Time in Patent Office: Days
• US Class Current: 363/132
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 7/5387 in a bridge configuration
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A solar photovoltaic plant is disclosed where a number of distributed DC-to-DC converters are used in conjunction with a central DC-to-AC converter. Each DC-to-DC converter is dedicated to a portion of the photovoltaic array and tracks the maximum power point voltage thereof. The DC-to-DC converters also boost the photovoltaic voltage and regulate a DC output current for transmission to the central DC-to-AC converter. Five distinct advantages are had over the prior art. First, efficiencies in intra-field power collection are greatly improved by transferring power at higher DC voltages. Second, the number of independent photovoltaic maximum power point trackers in the power plant can be increased, in a cost effective manner, to optimize the overall photovoltaic array energy harvest. Third, each DC-to-DC converter output “looks” like a current source at the input of the DC-to-AC converter and therefore can be easily paralleled. Fourth, the current source nature of the DC-to-DC converter outputs enables the DC-to-AC converter to operate with a minimum, fixed DC bus voltage to provide maximum DC-to-AC power conversion efficiencies. And fifth, each distributed DC-to-DC converter can isolate a faulted portion of the photovoltaic array while the remainder of the array continues producing power.

Claims

1. A method of collecting and converting DC power from a plurality of solar photovoltaic sources to polyphase AC power using a plurality of DC-to-DC converters and one DC-to-AC converter where the photovoltaic sources are arranged to cover an area described as the array field and where said DC-to-DC converters are distributed within this array field and where each converter, DC-to-DC and DC-to-AC, has an input and an output and where each DC-to-DC converter input is connected to a distinct portion of said photovoltaic sources and where each DC-to-DC converter output is connected to the input of the DC-to-AC converter and where the output of the DC-to-AC converter is connected to an AC polyphase load.

2. A method according to claim 1 where each DC-to-DC converter output is regulated as a current source.

3. A method according to claim 1 where each DC-to-DC converter functions as a transconductance amplifier or a photovoltaic-to-DC current converter.

4. A method according to claim 1 where each DC-to-DC converter tracks and maintains the instantaneous or time-averaged maximum power point voltage of the photovoltaic source or sources connected at its input.

5. A method according to claim 1 where each DC-to-DC converter output is regulated as a current source and where the DC-to-AC converter regulates the collective output voltage of all the DC-to-DC converters connected at the DC-to-AC converter input by adjusting the amount of power delivered to the AC polyphase load.

12. A method according to claim 1 where each DC-to-DC converter provides a voltage boost function from input to output and furthermore where the overall method is expressly intended to make the power collection of said photovoltaic sources more efficient by reducing resistive conductor losses by first, providing local power collection hubs around each DC-to-DC converter and second, by providing higher voltage/lower current power transmission from the distributed DC-to-DC converters to the DC-to-AC converter.

6. An apparatus for converting DC power from solar photovoltaic sources to AC polyphase power and comprising a plurality of DC-to-DC power converter sections and a DC-to-AC power converter section each having an input and an output and where photovoltaic sources are connected to inputs of the DC-to-DC power converter sections and where the outputs of all DC-to-DC power converter sections are connected in parallel at and to the input of the DC-to-AC power converter section and where each DC-to-DC power converter section seeks and tracks the maximum power point voltage of a photovoltaic source connected at the input of each DC-to-DC converter section and where the output current of each DC-to-DC converter section is regulated as a current source over a range of voltages set by the DC-to-AC converter section and where the output of the DC-to-AC converter section is connected to and sources power into a polyphase electric utility grid.

7. An apparatus according to claim 6 where a DC-to-DC power converter section has capabilities that may include boost regulation, buck regulation, photovoltaic array ground fault detection, photovoltaic array ground fault interrupt, photovoltaic array isolation monitoring, photovoltaic array disable, data acquisition, self-diagnostics, self-isolation and the ability to communicate with, control and respond to other equipment.

8. An apparatus according to claim 6 where a DC-to-DC power converter section provides galvanic isolation between input and output and is based on a typical full bridge input power topology with a full bridge rectifier output and is further described as having plus and minus input terminals with a capacitor and a full bridge circuit across said input terminals and where said full-bridge circuit feeds a primary of a high frequency transformer and where a secondary of said high frequency transformer is connected to a rectifier bridge and where the common cathodes of said rectifier bridge are connected through an inductor to a plus output terminal and where the common anodes of said rectifier bridge are connected to a minus output terminal.

9. An apparatus according to claim 6 where the DC-to-DC converter sections and the DC-to-AC converter sections are linked by conductors and/or communication cables of any length.

10. An apparatus according to claim 6 where a DC-to-DC power converter section is used based on a typical, non-isolated boost converter topology but with an added inductor and freewheeling diode to provide more continuous output current and is further described as having plus and minus input and output terminals where the minus input and output terminals are electrically common and where there is a capacitor across said input terminals and where one end of a first inductor is connected to the plus input terminal and the other end of the first inductor is connected to the anode of a first rectifier and to a first semiconductor switch and where the remaining side of the first semiconductor switch is connected to the minus input terminal and where the cathode of the first rectifier is connected to the cathode of a second rectifier and to one end of a second inductor and where the other end of the second inductor is connected to the positive output terminal and where the anode of the second rectifier is connected to the minus output terminal.

11. An apparatus according to claim 10 where one end of a third inductor is connected to the plus input terminal and the other end of the third inductor is connected to the anode of a third rectifier and to a second semiconductor switch and where the remaining side of the second semiconductor switch is connected to the minus input terminal and where the cathode of the third rectifier is connected to the cathodes of the first and second rectifiers and where first and second semiconductor switches may, in certain modes of operation, be switched on and off at high frequencies where first semiconductor and second semiconductor switches never switch on at the same time and where this interleaved high frequency operation is intended to reduce the input and/or output voltage and/or current ripple at the switching frequency or switching frequency multiples of first and second semiconductor switches.