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CN-121986429-A - Energy storage system connected to a high voltage power network via a tertiary winding of a transformer

CN121986429ACN 121986429 ACN121986429 ACN 121986429ACN-121986429-A

Abstract

Embodiments herein provide an energy storage system (100) connected to an electrical power network. The energy storage system (100) includes a transformer (110) having at least three windings, and a converter (120) configured to convert AC received from the transformer to DC or DC to AC, wherein an input side of the converter (120) is connected to a three-stage winding of the at least three windings of the transformer (110). The energy storage system (100) further comprises an energy storage device (130) connected to the output side of the converter (120), wherein the energy storage device (130) handles power imbalance in the power network, and wherein the ESD (130) has a protection mechanism for protecting the ESD (130) in case of a fault condition in the ESD (130).

Inventors

  • T. Bandaru
  • V. Kanan

Assignees

  • 日立能源有限公司

Dates

Publication Date
20260505
Application Date
20241031
Priority Date
20231031

Claims (15)

  1. 1. An energy storage system, ESS, (100) configured to be connected to an electrical power network, the ESS (100) comprising: -a transformer (110) having at least three windings, wherein a primary winding of the at least three windings of the transformer (110) is configured to be connected to an input from the power network, and wherein a secondary winding of the at least three windings of the transformer (110) is connected as an output to the power network; -a converter (120) configured to convert AC received from the transformer to DC or DC to AC, wherein an input side of the converter (120) is connected to a tertiary winding of the at least three windings of the transformer (110); an energy storage device, ESD, (130) connected to an output side of the converter (120), wherein the ESD (130) is configured to handle a power imbalance in the power network, and wherein the ESD (130) has a protection mechanism for protecting the ESD (130) in case of a fault condition in the ESD (130), Wherein the power network is a high voltage direct current, HVDC, system.
  2. 2. The energy storage system (100) of claim 1, wherein the converter (120) is a line to phase converter, LCC (220).
  3. 3. The energy storage system (100) of claim 2, further comprising a first filter circuit (225) for an AC side of the LCC (220) such that AC terminals of the LCC (220) are connected to the tertiary winding through the first filter circuit (225), and wherein the first filter circuit (225) is configured to filter harmonic interference to AC voltages and AC currents prior to feeding the AC voltages and AC currents from the power network to the LCC (220).
  4. 4. The energy storage system (100) of any of claims 2 or 3, further comprising -A second filter circuit (235) for a DC side of the LCC (220), the second filter circuit being connected between the LCC (220) and the ESD (130), wherein the second filter circuit (235) is configured to filter out harmonic interference to an output of the LCC (220), the output comprising a DC voltage and a DC current, before being fed to the ESD (130).
  5. 5. The energy storage system (100) of any of claims 2 to 4, further comprising -A high-speed switch HSS (240) located between the LCC (220) and the ESD (130), wherein the HSS (240) is configured to exchange DC terminals between the LCC (220) and the ESD (130) in order to facilitate a fast switching between a rectifying mode and an inverting mode of the ESS (100).
  6. 6. The energy storage system (100) of claim 5, wherein the HSS (240) is configured to perform the swapping when a DC current in a circuit of the ESS (100) is zero and the LCC (220) is in an idle/blocking mode.
  7. 7. The energy storage system (100) of claim 1, wherein the converter (120) is a voltage source converter, VSC, (320).
  8. 8. The energy storage system (100) of claim 7, further comprising a pre-insertion resistor arrangement (325) configured to control a surge current during charging of the converter (120) and the ESD (130), wherein the pre-insertion resistor arrangement comprises a bypass breaker.
  9. 9. The energy storage system (100) of any of claims 7 to 8, wherein the VSC (320) is a two-level, three-level, half-bridge or full-bridge modular multilevel converter, MMC.
  10. 10. The energy storage system (100) according to any of the preceding claims, wherein the power network is any other inverter-based resource (IBR) connected to a renewable source.
  11. 11. The energy storage system (100) of any of the preceding claims, wherein the fault condition comprises at least one of a commutation fault, a short circuit fault or a ground fault, or a DC circuit fault in the converter (120) during an inverter mode of operation of the converter (120).
  12. 12. The energy storage system (100) of any of the preceding claims, further comprising -A protection circuit (150) connected to the ESD (130), wherein the protection circuit (150) is connected to the ESD (130) in order to perform the protection mechanism, and wherein the protection circuit (150) is connected to the ESD (130) as one of an external circuit or a combined modular structure.
  13. 13. The energy storage system (100) of claim 12, wherein the protection circuit (150) includes a freewheeling diode and an Insulated Gate Bipolar Transistor (IGBT) in series with the ESD (130) when the protection circuit (150) is connected as the external circuit to the ESD (130).
  14. 14. The energy storage system (100) of claim 12, wherein the protection circuit (150) comprises a pair of insulated gate bipolar transistors IGBTs connected in a half-bridge configuration when the protection circuit (150) is connected to the ESD (130) as the combined modular structure.
  15. 15. The energy storage system (100) of any of the preceding claims, wherein the ESD (130) comprises at least one of a supercapacitor, a battery storage device, or a combination of the supercapacitor and the battery storage device.

Description

Energy storage system connected to a high voltage power network via a tertiary winding of a transformer Technical Field The present disclosure relates generally to energy storage requirements for managing power imbalance in an AC power grid. More specifically, the present disclosure relates to an energy storage system that manages power imbalances in an AC power grid. Background Advances in High Voltage Direct Current (HVDC) converter technology have enabled planning and establishment of high power land and marine renewable energy transmission projects. With such renewable based sources penetrating through unsynchronized and non-rotating mass media (such as HVDC), the inertia of the connected power system is reduced, thereby increasing the frequency instability risk. Generally, energy storage systems in the grid for short term (e.g., primary reserves) and long term (e.g., secondary reserves and tertiary reserves) duration support of the grid provide solutions to the frequency instability risk. The energy storage system uses a separate transformer in addition to the main transformer to connect the energy storage device to the power network, which increases the overall capital cost of the system. Disclosure of Invention Accordingly, there is a need for a new energy storage system that is cost effective, redundant that alleviates at least some of the problems described above. It is therefore an object of the present disclosure to provide an energy storage system for inertial and fast frequency response support that alleviates, mitigates or eliminates all or at least some of the above-mentioned disadvantages of currently known solutions. This and other objects are achieved by an Energy Storage System (ESS) as defined in the appended claims. The term "exemplary" is to be understood in this context as serving as an example, instance, or illustration. In accordance with one aspect of the present disclosure, an Energy Storage System (ESS) is disclosed for providing inertial support and controlling the frequency of an electrical power network to which the ESS is connected. The ESS includes a transformer having at least three windings, a primary winding of the at least three windings of the transformer being connected to an input from a power network, a secondary winding of the at least three windings being connected as an output to the power network. The ESS further includes a converter that converts AC received from the transformer to DC or DC to AC, wherein an input side of the converter is connected to a tertiary winding of the at least three windings of the transformer. The ESS further includes an Energy Storage Device (ESD) connected to an output side of the converter, wherein the ESD addresses a power imbalance in the power network, and wherein the ESD has a protection mechanism for protecting the ESD in the event of a fault condition in the ESD. The power network is a high voltage direct current HVDC system. Further, the topology of the ESS eliminates the need for a dedicated expensive transformer required for ESS operation. Advantageously, the power network may share a relatively expensive high voltage transformer for connecting the ESS in order to control inertia and/or frequency in the power network due to more and more renewable source-based penetration. Thereby, frequency imbalance in the power network can be efficiently handled. In addition, connecting the ESS to the tertiary windings of existing power network transformers achieves cost reduction as compared to implementing a different dedicated transformer for the ESS. In some embodiments, the converter is a Line Commutated Converter (LCC). In some embodiments, the ESS further includes a filter circuit for the AC side of the LCC such that the AC terminals of the LCC are connected to the tertiary winding through the filter circuit, and the filter circuit filters harmonic interference to the AC voltage and AC current before feeding the AC voltage and AC current to the power network. In some embodiments, the ESS further comprises a filter circuit for a DC side of the LCC, the filter circuit connected between the LCC and the ESD, wherein the filter circuit is configured to filter out harmonic interference to an output of the LCC, the output comprising a DC voltage and a DC current, prior to feeding the output to the ESD. In some embodiments, the ESS further comprises a high-speed switch (HSS) located between the LCC and the ESD, wherein the HSS exchanges DC terminals between the LCC and the ESD to facilitate fast switching between a rectification mode and an inversion mode of the ESS. In some embodiments, the HSS performs this exchange when the DC current in the circuitry of the ESS is zero and the LCC is in idle/blocking mode. In another embodiment, the converter is a Voltage Source Converter (VSC). In some embodiments, the ESS further comprises a pre-insertion resistor arrangement that controls the inrush current during charging of the converter and the