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US-12627158-B2 - Systems and methods of DC power conversion and transmission for solar fields

US12627158B2US 12627158 B2US12627158 B2US 12627158B2US-12627158-B2

Abstract

Systems and methods integrate advanced solar tracker, battery, inverter, and software technologies to improve performance, plant output, and costs. The systems may incorporate an advanced vanadium flow battery (VFB) that is DC-voltage (DV)-coupled to photovoltaic (PV) arrays for high, round-trip efficiency. The systems incorporate a DC architecture that optimizes performance for commercial, industrial, agricultural, and utility applications. A distributed direct current (DC) power system includes a centralized, single-stage inverter; PV arrays; maximum power point tracking (MPPT) converters coupled between the PV arrays and the centralized, single-stage inverter; batteries; and DC-DC battery converters (DCBCs) coupled to the batteries. The MPPT converters maximize solar power production by the PV arrays and minimize mismatch between the PV arrays. The DCBCs manage charge and discharge of the batteries, enable the interconnection of the PV arrays and the batteries, and supply a constant medium voltage to the central inverter.

Inventors

  • Alexander W. Au
  • Yang Liu

Assignees

  • NEXTPOWER LLC

Dates

Publication Date
20260512
Application Date
20220920

Claims (16)

  1. 1 . A distributed direct current (DC) power system comprising: a common DC bus; an inverter configured to invert DC power to alternating current (AC) power coupled to the common DC bus; a plurality of tracking controllers coupled to a plurality of photovoltaic (PV) strings and coupled to the common DC bus, the plurality of tracking controllers configured to maximize solar power production of the plurality of PV strings and minimize mismatch between the plurality of PV strings; a plurality of DC-DC battery converters (DCBCs) coupled to a plurality of batteries and to the common DC bus, the plurality of DCBCs configured to; manage charge and discharge of the plurality of batteries; enable interconnection of the plurality of PV strings and the plurality of batteries via the common DC bus; and maintain a constant DC voltage to at the inverter via the common DC bus; wherein the common DC bus connects the plurality of tracking controllers and the plurality of DCBCs to each other and connects the plurality of tracking controllers and the plurality of DCBCs to the inverter.
  2. 2 . The distributed DC power system of claim 1 , further comprising a plurality of battery management controllers coupled between the plurality of batteries and the plurality of DCBCs, respectively, the plurality of battery management controllers configured to start up the plurality of DCBCs.
  3. 3 . The distributed DC power system of claim 1 , wherein the plurality of batteries is a plurality of flow battery stacks, further comprising a battery management controller coupled between at least one flow battery stack of the plurality of flow battery stacks and a DCBC of the plurality of DCBCs.
  4. 4 . The distributed DC power system of claim 1 , wherein the plurality of batteries are vanadium flow batteries.
  5. 5 . The distributed DC power system of claim 1 , further comprising a PV combiner coupled to the plurality of PV strings and including a plurality of disconnect switches and an arc fault detector coupled to outputs of the plurality of disconnect switches.
  6. 6 . The distributed DC power system of claim 5 , further comprising a plurality of fuses coupled between the plurality of PV strings and the plurality of disconnect switches, respectively.
  7. 7 . The distributed DC power system of claim 1 , further comprising: a plurality of disconnect switches coupled to outputs of the plurality of PV strings, respectively; and a plurality of arc fault detectors coupled to outputs of the plurality of disconnect switches, respectively, wherein the plurality of tracking controllers are coupled to outputs of a plurality of arc fault detectors, respectively.
  8. 8 . The distributed DC power system of claim 1 , wherein the inverter includes a plurality of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs).
  9. 9 . The distributed DC power system of claim 1 , wherein the inverter is a single-stage inverter.
  10. 10 . The distributed DC power system of claim 1 , wherein the plurality of tracking controllers includes a plurality of maximum power point tracking (MPPT) converters, respectively.
  11. 11 . The distributed DC power system of claim 1 , further comprising a network control unit (NCU) in communication with each of the plurality of tracking controllers and each of the plurality of DCBCs, the NCU configured to control the plurality of DCBCs to maintain the constant DC voltage at the inverter.
  12. 12 . A method of controlling a distributed direct current (DC) power system, the method comprising: maintaining a constant predetermined DC voltage on a DC bus connected to an inverter; operating a plurality of DC-DC battery converters (DCBCs) in a constant voltage mode, each of the plurality of DCBCs being coupled to one or more batteries and coupled to the DC bus; charging the one or more batteries coupled to each DCBC to an initial charge; in response to the one or more batteries being charged to the initial charge, operating the plurality of DCBCs in a constant power mode, the constant power mode being distinct from the constant voltage mode; and in response to a reduction of charge or discharge current of the one or more batteries, operating the plurality of DCBCs in the constant voltage mode.
  13. 13 . The method of claim 12 , further comprising exporting, by a plurality of maximum power point tracking (MPPT) converters, power to a DC distribution bus.
  14. 14 . The method of claim 12 , wherein the constant predetermined voltage is between 1200 V and 1600 V.
  15. 15 . The method of claim 12 , wherein operating the plurality of DCBCs in a constant power mode comprises controlling the plurality of DCBCs to charge the one or more batteries coupled to each DCBC at a constant power.
  16. 16 . A method of controlling a distributed direct current (DC) power system, the method comprising: exporting, by a plurality of maximum power point tracking (MPPT) converters, power to a DC bus, the DC bus connected as an input to an inverter; maintaining a constant predetermined DC voltage on the DC bus; operating a plurality of DC-DC battery converters (DCBCs) in a constant voltage mode, each of the DCBCs being coupled to one or more batteries and coupled to the DC bus; charging the one or more batteries coupled to each DCBC to an initial charge; in response to the one or more batteries being charged to the initial charge, operating the plurality of DCBCs in a constant power mode; and in response to a reduction of charge or discharge current of the one or more batteries, operating the plurality of DCBCs in the constant voltage mode.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. patent application Ser. No. 16/402,695 filed May 3, 2019, which claims benefit of and priority to U.S. Provisional Application No. 62/667,960 filed May 7, 2018 and 62/667,129 filed May 4, 2018, the disclosures of each of the above-identified applications are hereby incorporated by reference in their entirety. FIELD This disclosure is generally directed to solar power generating systems. More particularly, this disclosure is directed to solar power systems and methods utilizing distributed DC-DC battery converters, DC power transmission, and centralized power inversion. BACKGROUND Solar and wind energy are increasingly important renewable, non-polluting energy sources for consumers and businesses throughout the world. For solar energy, photovoltaic (PV) panels arranged in an array or string typically provide the means to convert solar energy into electrical energy. In operating photovoltaic (PV) arrays, maximum power point tracking (MPPT) is generally used to automatically determine a voltage or current at which the PV array should operate to generate a maximum power output for a particular temperature and solar irradiance. Although MPPT allows for the generation of maximum output power, the transmission and storage of the power generated by the PV arrays may be inefficient and costly. SUMMARY In one aspect, this disclosure features a distributed direct current (DC) power system. The distributed direct current (DC) power system includes a centralized inverter to invert DC to alternating current (AC); photovoltaic (PV) strings; maximum power point tracking (MPPT) converters coupled between the photovoltaic PV strings, respectively, and the centralized inverter; batteries; and DC-DC battery converters (DCBC) coupled to the batteries. The MPPT converters maximize solar power production by the PV strings and minimize mismatch between the PV strings. The DCBCs manage charge and discharge of the batteries and enable the interconnection of the PV strings and the batteries. In aspects, the distributed DC power system also includes battery management controllers coupled between the batteries and the DCBCs, respectively. The battery management controllers are configured to start-up the DCBCs. In aspects, the batteries are flow battery stacks and the distributed DC power system also includes a battery management controller coupled between at least one flow battery stack of the flow battery stacks and a DCBC of the DCBCs. In aspects, the batteries are vanadium flow batteries. In aspects, the distributed DC power system also includes a PV combiner coupled to the PV strings and including disconnect switches and an arc fault detector coupled to the outputs of the disconnect switches. In aspects, the distributed DC power system also includes fuses coupled between the PV strings and the disconnect switches, respectively. In aspects, the distributed DC power system also includes disconnect switches coupled to outputs of the PV strings, respectively, and arc fault detectors coupled to outputs of the disconnect switches, respectively. The MPPT converters are coupled to the outputs of the arc fault detectors, respectively. In aspects, the distributed DC power system also includes a network control unit in wired or wireless communication with each of the MPPT converters and each of the DCBCs. The network control unit manages the operation of the MPPT converters and the DCBCs. In aspects, the centralized inverter includes silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs). In aspects, the centralized inverter is a single-stage inverter. In another aspect, this disclosure features a method of controlling a distributed direct current (DC) power system. The method includes maintaining a constant predetermined medium voltage at an input to a centralized inverter; operating DC-DC battery converters (DCBC) coupled to batteries, respectively, in a constant voltage mode; in response to the startup of the batteries, operating the DC-DC battery converters (DCBC) in a constant power mode; and in response to a reduction of charge or discharge current, operating the DC-DC battery converters (DCBC) in the constant voltage mode. In aspects, the method also includes exporting, by maximum power point tracking (MPPT) converters, power to a DC distribution bus. In aspects, the constant predetermined medium voltage is between 1200 V and 1600 V. BRIEF DESCRIPTION OF THE DRAWINGS Various aspects of the present disclosure are described herein below with reference to the drawings, which are incorporated in and constitute a part of this specification, wherein: FIG. 1 is a schematic diagram of a central inverter and a distributed DC battery management system according to an embodiment of this disclosure; FIGS. 2 and 3 are schematic diagrams of DC-DC battery converters according to embodiments of this disclosure; FIG. 4 is a flow diagram of a p