US-12620908-B2 - Modular multilevel converters for battery energy storage

Abstract

A battery energy storage system includes a plurality of battery cores. Each battery core of the battery energy storage system includes an array of battery cubes, and each battery core is configured to provide a first direct current power at a first voltage. The battery energy storage system further includes a plurality of direct-current-to-direct-current (DC-DC) converters. Each DC-DC converter of the battery energy storage system is configured to accept the first direct current power and each DC-DC converter is configured to provide a second direct current power at a second voltage. The battery energy storage system further includes a main modular multilevel converter (MMC). The MMC of the battery energy storage system is configured to accept the second direct current and to provide an alternating current at a third voltage.

Inventors

• Efosa Charles Osakue
• Stefan Henninger
• Sung Pil Oe

Assignees

• FLUENCE ENERGY, LLC

Dates

Publication Date

20260505

Application Date

20230322

Claims (20)

1. 1 . A battery energy storage system, comprising: a plurality of battery cores, wherein each battery core of the plurality of battery cores includes an array of battery cubes each comprising a plurality of racks of battery cells, and is configured to provide a first direct current power at a first voltage; multiple sets of direct-current-to-direct-current (DC-DC) converters wherein each set of the multiple sets of DC-DC converters includes a plurality of DC-DC converters connected in series, wherein each DC-DC converter of the plurality of DC-DC converters includes a dual-active bridge converter configured to provide galvanic isolation to the battery cores and wherein each first DC-DC converter of each set of the multiple sets of DC-DC converters is configured to accept the first direct current power and each last DC-DC converter of each set of the multiple sets of DC-DC converters is configured to provide a second direct current power at a second voltage; and a main modular multilevel converter (MMC) connected in series with each last DC-DC converter of each set of the multiple sets of DC-DC converters, the main MMC configured to accept multiple inputs of the second direct current power and provide a first alternating current power at a third voltage.
2. 2 . The battery energy storage system of claim 1 , wherein: at least one DC-DC converter of each set of DC-DC converters comprises an isolated MMC, each isolated MMC connected in series to the main MMC.
3. 3 . The battery energy storage system of claim 2 , wherein: each isolated MMC is configured to offer bidirectional power flow.
4. 4 . The battery energy storage system of claim 1 , wherein: the first alternating current power is three-phase electric power.
5. 5 . The battery energy storage system of claim 1 , wherein: each last DC-DC converter of each set of DC-DC converters is configured to provide the second direct current power of the second voltage at a set voltage level.
6. 6 . The battery energy storage system of claim 1 , wherein: the first voltage of each battery core of the plurality of battery cores is a low voltage; the second voltage of each set of DC-DC converters is a first high voltage of a greater value and different from the low voltage; and the third voltage is a second high voltage different from the first high voltage.
7. 7 . The battery energy storage system of claim 1 , wherein: at least one DC-DC converter of each set of DC-DC converters is an isolated MMC and includes a plurality of sets of submodules, wherein at least two sets of submodules of the plurality of submodules is for the first direct current power and at least another two sets of submodules of the plurality of submodules is for the second direct current power.
8. 8 . The battery energy storage system of claim 7 , wherein: each set of submodules of the plurality of submodules of the isolated MMC comprises a half-bridge submodule.
9. 9 . The battery energy storage system of claim 7 , wherein: each set of submodules of the plurality of submodules comprises a full-bridge submodule.
10. 10 . The battery energy storage system of claim 7 , wherein: a first set of submodules of the plurality of sets of submodules is electrically coupled to a second set of submodules of the plurality of submodules; the first set of submodules receives an incoming power at the first voltage, and provides an interstitial power at an interstitial voltage; the second set of submodules receives the interstitial power, and provides an outgoing power at the second voltage; and the interstitial voltage is greater than the first voltage and less than the second voltage.
11. 11 . The battery energy storage system of claim 1 , further comprising: a power controller, configured to adjust the second voltage provided by the plurality of DC-DC converters, at the array of battery cubes.
12. 12 . The battery energy storage system of claim 1 , comprising: a main DC-DC converter connected in series to the main MMC between the main MMC and the multiple sets of DC-DC converters.
13. 13 . The battery energy storage system of claim 1 , wherein each set of DC-DC converters is connected in parallel with the multiple sets of DC-DC converters.
14. 14 . The battery energy storage system of claim 1 , wherein the DC/DC converters and/or the main MMC is actively controlled via a storage dispatch unit.
15. 15 . An energy provisioning system, comprising: a plurality of power sources, wherein each power source of the plurality of power sources is configured to provide a first direct current power at a first voltage; multiple sets of direct-current-to-direct-current (DC-DC) converters wherein each set of the multiple sets of DC-DC converters includes a plurality of DC-DC converters connected in series, wherein each DC-DC converter of the plurality of DC-DC converters includes a dual-active bridge converter configured to provide galvanic isolation to the power sources and wherein each first DC-DC converter of each set of the multiple sets of DC-DC converters is configured to accept the first direct current power and each last DC-DC converter of each set of the multiple sets of DC-DC converters is configured to provide a second direct current power at a second voltage; and a main modular multilevel converter (MMC) connected in series with each last DC-DC converter of each set of the multiple sets of DC-DC converters, the main MMC configured to accept multiple inputs of the second direct current power and provide an alternating current power at a third voltage.
16. 16 . The energy provisioning system of claim 15 , wherein: at least one DC-DC converter of each set of DC-DC converters comprises an isolated MMC, each isolated MMC connected in series to the main MMC.
17. 17 . The energy provisioning system of claim 16 , wherein: each isolated MMC is configured to offer unidirectional power flow.
18. 18 . The energy provisioning system of claim 15 , wherein: the first alternating current power is three-phase electric power.
19. 19 . The energy provisioning system of claim 15 , wherein: Each last DC-DC converter of each set of DC-DC converters is configured to provide the second direct current power of the second voltage at a set voltage level.
20. 20 . The energy provisioning system of claim 15 , wherein: the first voltage of each power source is a low voltage; the second voltage of each set of DC-DC converters is a first high voltage of a greater value and different from the low voltage; and the third voltage is a second high voltage different from the first high voltage.

Description

TECHNICAL FIELD The present subject matter relates to examples of modular multilevel voltage converters in battery energy storage systems and energy provisioning systems at large. BACKGROUND A battery energy storage system, or any energy provisioning system with a number of relatively low voltage energy provisioning devices, will often utilize a step-up component or circuit with a transformer to step the low voltage provided by the system to a high voltage. The higher voltage, and consequently lower amperage electricity, is better situated to travel across long electrical-lined distances, or to conform to the amperage requirements of a large connected load or electrical grid. The step-up component will often also convert a direct current (DC) from the battery energy storage system to an alternating current (AC) using an inverter, to conform with the electrical line or electrical grid. Battery energy storage systems, as well as some energy provisioning systems, are often set up in a distributed manner to satisfy safety and economical concerns: several hundred batteries are used rather than one single massive battery. Traditionally, battery energy storage systems, and distributed energy provisioning systems in general, would utilize a number of converters and multiple step-up transformers across the system: for example, a system with one thousand batteries may include one hundred step-up transformers, each of which converts low voltage DC power from ten batteries into high-voltage power. Then, the hundred step up-converters feed into ten additional step-up transformers, each of which converts high voltage DC power from the ten step-up transformers into higher high-voltage power, and may feed into an inverter to convert the DC power into AC power. The output from these ten step-up transformers (and inverter) would then be pushed into the electrical grid. However, as the number of step-up transformers increase, the number of computer systems required to manage, control, and synchronize the step-up transformers increases proportionally. The costs to provision all of the step-up transformers also increase proportionally to the number of batteries. SUMMARY Hence, there in a need for systems directed to converting distributed direct current low voltage power into centralized alternating current high voltage power. The modular multilevel conversion technologies disclosed herein are able to receive direct current power from an array of batteries, and provide high voltage alternating current power, with an overall reduction in the number of transformers required, improved power availability, and centralized control of power. Centralizing the control of power by utilizing the modular multilevel conversion technologies can reduce the total harmonic distortion to and from an electrical grid, and also improves robustness and redundancy of the overall array of batteries, in particular the power production and reception of the array of batteries. In a first example, a battery energy storage system includes a plurality of battery cores, wherein each battery core includes an array of battery cubes and is configured to provide a first direct current power at a first voltage. The battery energy storage system further includes a plurality of direct-current-to-direct-current (DC-DC) converters, wherein each DC-DC converter is configured to accept the first direct current power and to provide a second direct current power at a second voltage. The battery energy storage system still further includes a main modular multilevel converter (MMC) configured to accept the second direct current and to provide an alternating current at a third voltage. In a second example, an energy provisioning system includes a plurality of power sources, wherein each power source is configured to provide a first direct current power at a first voltage. The energy provisioning system further includes a plurality of direct-current-to-direct-current (DC-DC) converters, wherein each DC-DC converter is configured to accept the first direct current power and to provide a second direct current power at a second voltage. The energy provisioning system still further includes a main modular multilevel converter (MMC) configured to accept the second direct current and to provide an alternating current at a third voltage. Additional objects, advantages and novel features of the examples will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the present subject matter may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS The drawing figures depict one or more implementations in accordance with the present concepts, by way of ex