Auxiliary redundant power supply for energy storage system and energy storage system

Abstract

In order to provide an improved apparatus for a high voltage direct current (HVDC) system, the invention proposes an auxiliary power supply (30), an energy storage rack (22) for a high voltage direct current (HVDC) system, the power supply comprising: at least one alternating current power branch (54) comprising an input terminal (38), a delivery terminal (40) and a low voltage transformer (42), where the low voltage transformer (42) has an input branch (44) configured to receive alternating current from the input terminal (38), the low voltage transformer (42) has a delivery branch (46) configured to deliver alternating current to the terminal (40), and the low voltage transformer (42) has a power supply branch (48) configured to convert the received alternating current to a lower voltage in an extra-low voltage (ELV) range to supply power to the control unit (26); at least one DC power supply branch (60) comprising a low voltage DC power supply (62) configured to provide DC power to the control unit (26).

Description

Technical Field

[0001] This invention relates to an auxiliary power supply. It also relates to an energy storage rack and an energy storage system. Background Technology

[0002] In this disclosure, the terms "high voltage" (HV), "low voltage" (LV), and "extra low voltage" (ELV) follow the accepted definitions in IEC 61140:2016, "Protection against electric shock - Common aspects for installation and equipment". Therefore, "high voltage" refers to an alternating current (AC) exceeding 1000V and a direct current (DC) exceeding 1500V, "low voltage" refers to an alternating current less than or equal to 1000V and a direct current less than or equal to 1500V, and "extra low voltage" refers to an alternating current less than or equal to 50V and a direct current less than or equal to 120V.

[0003] US10992219B2 discloses a power conversion device having multiple cascaded converter units. In each converter unit, multiple semiconductor switching elements are connected in parallel in each of the multiple arms forming a bridge circuit. A drive controller for each converter unit is configured to control the bridge circuit according to externally provided instructions when no abnormality is detected in any of a plurality of predetermined abnormal modes. When at least one of the plurality of abnormal modes is detected, the drive controller is configured to turn on all semiconductor switching elements in at least one of the multiple arms forming the bridge circuit, thereby establishing a short circuit between the first and second input / output nodes.

[0004] Such power converters can be used in high-voltage direct current (HVDC) systems to stabilize system voltage during periods of high power demand. The power converter includes critical control, monitoring, and drive circuitry. These circuits typically require a low-voltage DC power supply to operate and ensure smooth operation of the power converter. Because HVDC involves high DC voltages, it is difficult to supply low-voltage DC power to this circuitry. Therefore, a power supply is needed that provides adequate isolation between circuits operating at different DC voltages, is easy to maintain, and reliably supplies power to critical controllers. Summary of the Invention

[0005] The object of this invention is to provide an improved device for HVDC systems. This object is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

[0006] This invention provides an auxiliary power supply for an energy storage rack (sometimes called an ESS rack) in a high-voltage direct current (HVDC) system. The HVDC system is used for static synchronous compensation (STATCOM), for example, in transmission or distribution substations. The auxiliary power supply may be included in the energy storage rack, which is part of the HVDC system, to power the local controller of the energy storage rack.

[0007] The power supply includes at least one AC power branch and at least one DC power branch. The AC portion is typically supplied from the low-voltage grid via an isolation transformer. This isolation transformer is preferably designed for high-voltage isolation. A power cable, referred to as an auxiliary feeder, supplies power to this power supply. This auxiliary feeder is also isolated from high voltage.

[0008] The DC component offers greater flexibility and can be connected to energy storage devices such as batteries or supercapacitors. Other DC power sources, such as photovoltaic modules, can also be configured.

[0009] At least one AC power supply branch includes an input terminal, a delivery terminal, and a low-voltage (LV) transformer, wherein the LV transformer has an input branch configured to receive AC power from the input terminal. The LV transformer also has a delivery branch configured to deliver AC power to the delivery terminal. The input terminal can be directly connected to an auxiliary feeder or an isolation transformer, or connected to the delivery terminal of another power source in the system. Therefore, power can be delivered from one auxiliary power source through a line to the next power source until all power sources are connected to the low-voltage grid.

[0010] The LV transformer has a power supply branch configured to convert received AC power into a lower voltage within the extra-low voltage (ELV) range to supply power to the control unit. This power supply branch can draw power from the input / transmission branch. The power supply branch employs inductive coupling and preferably has an equivalent impedance higher than that of the input and transmission branches. Therefore, a fault in this power supply branch will not interrupt the power exchange between the input and transmission branches.

[0011] At least one DC power supply branch includes a low-voltage DC power supply configured to provide DC power to the control unit. A low-voltage DC power supply is preferred in case the AC power supply branch is unable to provide the required power.

[0012] Preferably, the auxiliary power supply further includes a power controller configured to switch between AC power branches and DC power branches in response to a received control signal. This control signal may originate from different sources or at different levels. For example, in the event of certain fault conditions, the control signal may be automatically generated by monitoring equipment. During maintenance, the control signal may be generated manually. The control signal may also originate from a system-level controller. Preferably, there is a switching state in which either the AC power branch or the DC power branch is powered. There may also be a switching state in which both branches are powered simultaneously. Another switching state may be a state in which neither the AC power branch nor the DC power branch is powered.

[0013] Preferably, the AC power branch includes a blocking element to prevent current from flowing from any AC or DC power branch into the corresponding AC power branch. This design is particularly effective when all branches are powered simultaneously. The blocking element (e.g., a diode or equivalent circuit) prevents current from flowing in the "wrong direction," i.e., from the power source to the grid instead of back to the power source. Preferably, the blocking element includes a diode.

[0014] Preferably, the DC power supply branch includes a blocking element to prevent current from flowing from either the AC or DC power supply branch into the corresponding DC power supply branch. For the DC power supply, the blocking element is also preferably a diode. This blocking element also prevents current from flowing in the "wrong direction," i.e., from the power source to the corresponding DC power source (e.g., a battery, supercapacitor, DC generator, or photovoltaic module). Preferably, the blocking element includes a diode.

[0015] Preferably, the low-voltage transformer includes a primary winding and a secondary winding inductively coupled, such that one of the primary winding and the secondary winding constitutes the input branch and the other constitutes the transmission branch. These windings allow for electrical isolation between the input and output branches of the auxiliary power supply. If multiple power supplies are connected in series, each power supply maintains electrical isolation from its input and transmission terminals. The auxiliary power supply can be electrically isolated from the low-voltage power grid.

[0016] Preferably, the low-voltage transformer includes a power supply winding that forms part of a power supply branch and is inductively coupled to the primary and / or secondary windings. This power supply winding is configured to convert alternating current received from the primary and / or secondary windings into a low voltage suitable for supplying direct current within the ELV range to the control unit. This power supply winding is used to power the local controller of the ESS rack. The power supply winding diverts the power delivered through the low-voltage transformer.

[0017] These windings can be wound around the core of the transformer. These windings are preferably electrically isolated from each other.

[0018] Preferably, the power supply branch is referenced to the same potential as either the input branch or the transmission branch. By referencing all branches to the same potential, low-voltage isolation can be achieved within the auxiliary power supply (and its applicable ESS rack).

[0019] Preferably, the input branch is electrically isolated from the transmission branch and the power supply branch, or the transmission branch is electrically isolated from the input branch and the power supply branch. This configuration ensures that each auxiliary power supply in the series connection has an independent reference potential, thereby better mitigating the risk of low-voltage isolation.

[0020] Preferably, the AC power supply branch includes an AC-DC converter electrically connected to a low-voltage transformer to generate DC power to supply power to the control unit. Preferably, the AC-DC converter is electrically connected to the power supply branch. The AC-DC converter rectifies the AC power supplied to the control unit to provide energy. The AC-DC converter can be an active rectifier or a passive rectifier.

[0021] Preferably, the AC-DC converter is electrically connected to the power supply winding. The AC-DC converter is powered by a low-voltage transformer via the power supply winding. Therefore, if a fault occurs somewhere in the circuit, the main line supplying power between adjacent auxiliary power sources can be prevented from being affected.

[0022] Preferably, the DC power supply branch includes a DC-DC converter electrically coupled to a low-voltage DC power supply to generate DC power to power the control unit. This DC-DC converter can adapt the DC power supply to the operating voltage typically required by the control unit. This allows for the use of more types of low-voltage DC power supplies.

[0023] Preferably, the low-voltage DC power supply includes an energy storage device. In this preferred configuration, an independent energy storage device is used as the low-voltage DC power supply. The energy storage device can be a battery, a supercapacitor, or other type of energy storage device.

[0024] Preferably, the low-voltage DC power supply includes at least one photovoltaic module. Using a photovoltaic module to generate low-voltage DC power isolated from high voltage offers significant advantages. In practice, in typical scenarios, the room's lighting system is sufficient to drive the photovoltaic module.

[0025] Preferably, the low-voltage DC power supply includes a DC generator. For example, the DC generator may be a field-configured emergency generator that can be started in emergency situations such as low-voltage grid failures.

[0026] Preferably, the input branch and the transmission branch are configured in concert to generate an increase in AC voltage, thereby compensating for the voltage drop caused by power losses. Power transmission between auxiliary power sources will result in a voltage drop due to resistance and shunting of power to the control unit. Therefore, the turns ratio of the low-voltage transformer should not be 1:1, but rather a slightly higher ratio (up to 1:1.2 or 1:1.5) to compensate for this voltage drop.

[0027] Preferably, either the input branch or the transmission branch is configured to regulate the voltage rise. The compensation ratio is preferably adjustable to allow the entire system to accommodate varying voltage drops. Depending on the type of low-voltage transformer, this ratio can be adjusted continuously or incrementally. This adjustment is preferably performed by a higher-level control unit, such as a system-level control unit.

[0028] This invention provides an energy storage rack for an HVDC system, comprising: a preferred auxiliary power supply; an energy storage device configured for storing electrical energy; and a control unit configured for controlling the operation of the energy storage device, wherein both an AC power branch and a DC power branch are electrically connected to the control unit to provide power. The auxiliary power supply supplies power to the control unit through a low-voltage power grid and a DC power supply. Therefore, when any power supply fails, the control unit can still maintain power supply through the remaining power sources. It should be noted that system redundancy can be enhanced by setting up multiple independent AC and DC branches.

[0029] Preferably, the power controller is part of the control unit. The power control unit can be set up independently, but is preferably part of the ESS rack control unit.

[0030] Preferably, the low-voltage DC power supply includes the energy storage device. The ESS rack includes an energy storage device within a suitable low-voltage range, enabling it to be used as a low-voltage DC power supply. Therefore, the energy storage device serves the dual function of providing redundant power to the control unit and powering the STATCOM.

[0031] Preferably, each blocking element is arranged between the low-voltage transformer and the control unit. Preferably, each blocking element is arranged between the AC-DC converter and the control unit. Preferably, each blocking element is arranged between the DC power supply and the control unit. Preferably, each blocking element is arranged between the DC-DC converter and the control unit. The blocking elements prevent "incorrect direction" cross currents between different power supplies.

[0032] Preferably, the power supply branch is electrically connected to the control unit. Preferably, the power supply branch is electrically connected to the control unit via an AC-DC converter. The control unit is powered by a low-voltage transformer, thus providing electrical isolation from the low-voltage power grid and other ESS racks.

[0033] Preferably, the energy storage rack further includes a frame and / or housing made of conductive material, and the power supply branch references the same potential as the input branch or transmission branch through this frame and / or housing. With this configuration, the ESS rack has its own reference potential, thereby avoiding the need for stringent high-voltage isolation within the rack. However, the ESS rack can remain isolated relative to ground.

[0034] This invention provides an energy storage system (ESS) for high-voltage direct current (HVDC) circuits, including a power supply transformer and multiple preferred energy storage racks, whose energy storage devices are connected in series to form a HVDC energy storage device, wherein the auxiliary power supply is connected in series. This ESS is used in STATCOM. For example, this is commonly applied in HVDC circuits in scenarios such as substations. HVDC systems can also be used to deliver large amounts of energy from power sources (such as offshore wind farms) to suitable power users (such as factories). Such ESSs are crucial for compensating for load peaks caused by power users and / or power sources.

[0035] Load peaks may occur during the inference period, and typical grids often cannot respond in time. This ESS provides series groups of low-voltage energy storage devices (preferably supercapacitors). Multiple series groups are connected in series until the typical voltage of the HVDC system is reached. Therefore, each ESS rack in the ESS is designed for low voltage, with lower requirements for electrical isolation.

[0036] Preferably, at least one of the energy storage racks is directly electrically connected to the power supply transformer via its input terminal and directly electrically connected to another energy storage rack via its output terminal. The ESS racks are connected in series with their energy storage devices to increase the voltage. Furthermore, the auxiliary power supply for the ESS racks is also connected in series. However, the auxiliary power supply is connected to the low-voltage grid, while the energy storage devices are connected to the high-voltage DC section. This allows for the connection of a large number of ESS racks. A typical application might include 20 to 50 ESS racks connected in series. With this configuration, all ESS racks can be easily powered by the auxiliary power supply.

[0037] Preferably, at least one energy storage rack is electrically connected to the input terminal of another energy storage rack via its delivery terminal. Preferably, one or two ESS racks are connected to the low-voltage grid to obtain power supply. Preferably, the remaining ESS racks are arranged symmetrically around the midpoint between the two ESS racks to maximize redundancy and safety.

[0038] In some embodiments, the power source is a multi-source auxiliary power source, providing highly reliable auxiliary power. The auxiliary power can be delivered to each rack of a large-scale energy storage system (ESS) via multiple series transformers.

[0039] In some embodiments, the multiple sources of auxiliary power include a low-voltage grid, a photovoltaic system, and a self-powered circuit. In other words, each ESS rack can be equipped with a dedicated auxiliary self-powered circuit, which draws power from rack energy storage devices (such as supercapacitor units). This circuit converts the energy taken from the energy storage device into a stable low voltage via a DC / DC converter, and then feeds this auxiliary power to a local controller within the ESS rack.

[0040] In some embodiments, the proposed circuit arrangement includes a dedicated multi-winding transformer configured for each ESS rack.

[0041] In some embodiments, the three-winding transformer ensures uninterrupted auxiliary power flow in the series connection, even in the event of a short circuit in any ESS rack. In other embodiments, only the third winding is connected to the respective ESS rack, while the other two windings are connected in series between adjacent ESS racks.

[0042] In some embodiments, multiple power sources and dedicated three-winding transformers can provide effective electrical isolation for each ESS rack, thereby achieving greater redundancy.

[0043] In some embodiments, multiple power sources can mitigate common faults and ensure uninterrupted high-voltage direct current (HVDC) operation.

[0044] In some embodiments, the auxiliary circuitry has an electrical reference point in each rack; thereby preventing potential fluctuations in the auxiliary circuitry and not posing a risk to the low-voltage insulation of each rack.

[0045] This solution aims to provide auxiliary power for HVDC systems, particularly advanced STATCOM or reactive power compensation systems. This power source can provide auxiliary power to each ESS rack from a large energy storage system. The ESS rack is preferably based on a supercapacitor. The auxiliary power source can receive low-voltage power from various sources, such as different types of auxiliary power sources, transformers, self-powered systems, or photovoltaic power.

[0046] This power supply, serving as a multi-source auxiliary power source, provides highly reliable auxiliary power to each ESS rack of a large-scale DC energy storage system, capable of traversing multiple series transformers, achieving higher redundancy while reducing the number of isolation transformers. The disclosed circuit layout allows for effective electrical isolation between the auxiliary power supply and the high-voltage DC energy storage system. The auxiliary power supply can also be configured with a self-powered source, drawing energy from the ESS rack itself, converting it to low-voltage DC via a DC / DC converter, and using it as auxiliary power.

[0047] Each unit of a high-voltage power system typically includes critical control, monitoring, and drive circuitry. Typical functions include charging, discharging, and bypassing the energy storage module in case of a fault or for maintenance purposes.

[0048] These circuits require a low-voltage DC power supply to operate and ensure the smooth operation of the high-voltage energy storage rack. Because the high-voltage energy storage system includes high DC voltages, it is difficult to directly supply low-voltage DC power to these circuits. The disclosed technical solution allows for a low-voltage DC power supply configuration that not only provides low-voltage DC power to these circuits but also provides critical isolation from the high-voltage DC energy storage system.

[0049] The disclosed configuration reduces or even eliminates the need for high-voltage isolation in auxiliary power systems. This also significantly reduces costs. Furthermore, the system can provide ample auxiliary power in the tens of watts range.

[0050] This disclosed concept is essentially based on the ideal use of only one high-voltage isolation transformer for the ESS high-voltage series group, with a low-voltage multi-winding transformer configured in each ESS rack. This configuration uses simpler components, improving the maintainability of the entire system. Simultaneously, the system can be installed in a more economical and convenient manner. In some embodiments, the transformer employs a short-circuit protected design, further enhancing reliability and safety. The multi-winding transformer may employ a voltage tapped design (non-1:1 turns ratio), allowing for sufficient step-up to compensate for system voltage drops.

[0051] Another advantage is that by combining different types of auxiliary power sources, transformers, and self-powered or photovoltaic devices, it is easier to achieve the target availability and redundancy of ESS rack auxiliary power. Using multiple power sources reduces the risk of common-cause failures. This further improves the reliability of the entire distributed system. This combination offers more economical design options: one power source can be designed at its rated power, while another power source uses a lower power level (service mode) for rack control.

[0052] ESS racks are generally low-voltage components of energy storage devices, typically used as building blocks for high-voltage ESS systems in STATCOMs with high-voltage DC bus voltages usually in the range of 30–100kV. Note that even higher voltages can be used.

[0053] Each ESS rack is equipped with an auxiliary power supply to power the local controller. The ESS rack local controller uses the rack's main DC voltage as its electrical reference; therefore, when the auxiliary power source is a low-voltage mains grid, its isolation level must not be lower than that of the high-voltage ESS system voltage. Furthermore, the auxiliary power feeders for different racks in a high-voltage series group should be isolated based on the voltage difference between racks. It is safe to assume that the ESS rack auxiliary power consumption is in the tens of watts range. Ideally, power consumption should be kept below ten watts or even lower.

[0054] The disclosed equipment provides system-level voltage isolation between the low-voltage grid and auxiliary feeders by configuring a high-voltage isolation transformer for each ESS series group. The equipment can also provide electrical isolation for the auxiliary power feeders of each rack via the low-voltage transformer. Redundant local auxiliary power supplies can also be configured, preferably using inter-rack auxiliary power delivery methods with quality regulation capabilities. This circuit design reduces the risk of auxiliary power supply failure.

[0055] In some embodiments, isolation between the low-voltage grid and the ESS series-group auxiliary feeder is provided by a transformer with a turns ratio of approximately 1:1, whose primary and secondary windings have an isolation level not lower than the ESS series-group voltage (typically tens to hundreds of kilovolts). In some embodiments, the transformer secondary winding provides a high-voltage isolated auxiliary feeder connected to the midpoint of the series-group auxiliary power supply. Thus, auxiliary power can be distributed in both directions to the positive and negative terminals of the ESS series group. In some embodiments, each ESS rack is configured with a dual-function transformer, providing both local isolated auxiliary power and supplying auxiliary power to the next rack in the series group.

[0056] In some embodiments, each low-voltage rack auxiliary feeder is electrically isolated by a low-voltage transformer with a turns ratio of approximately 1:1. In some embodiments, this transformer consists of three isolation windings W1, W2, and W3. Windings W1 and W2 can be used for auxiliary power delivery between racks. Windings W1 and W2 preferably have high rated power (typically several kilowatts) to deliver power to the auxiliary circuits of half of the racks in the series group. To compensate for voltage drops in the cables and conductors of the inter-rack auxiliary feeders, transformer winding W1 may be configured with regulating taps. This allows for increased auxiliary voltage. Winding W3 can power the auxiliary circuit of a single rack. Winding W3 may be specially designed with a lower rated power (tens of watts) sufficient to power the rack and with lower winding short-circuit power.

[0057] In the event of a fault (such as a short circuit in the auxiliary circuit of a single rack), the transformer core will not be fully saturated. Therefore, the auxiliary power supply between windings W1 and W2 can still function, and the remaining racks in the series group can still receive auxiliary power.

[0058] Preferably, the auxiliary circuits within each rack are electrically referenced, thus keeping the potential of the auxiliary circuits in a non-floating state and avoiding risks to the low-voltage insulation in each rack. Transformer windings W2 and W3 may reference the same rack frame. Winding W1 remains isolated and preferably references the frame of the next rack in the series group. This configuration achieves electrical isolation between the auxiliary feeders of each rack.

[0059] High-voltage ESS applications require high availability. Therefore, adding (redundant) auxiliary power sources can reduce the risk of auxiliary power supply failures.

[0060] By employing a multi-transformer configuration (based on redundancy and availability design) and combining it with the self-powering capability of the energy storage circuitry within each ESS rack, auxiliary power delivery from the low-voltage grid can be improved. The rack-based auxiliary self-powering circuitry preferably draws power from the rack energy storage components, converts the power to a stable low voltage via a DC / DC converter, and then supplies power to the local controller via a reverse-biased diode. This diode prevents current from interfering between different auxiliary power sources. The second auxiliary power source is a transformer, which supplies power to an AC / DC converter (rectifier), thereby providing the same stable low voltage to the local controller.

[0061] The advantage of this variation is that the self-powered design of the DC / DC converter can meet the full rated power requirements of the rack auxiliary circuitry, while the transformer and AC / DC converter can be designed with low rated power to power the rack auxiliary circuitry. Preferably, the AC / DC converter only powers the local controller when the energy storage device is fully discharged (e.g., due to maintenance or certain faults) to provide a service mode for the auxiliary circuitry. This improves system redundancy while reducing the cost of the auxiliary power supply.

[0062] Another approach to combined redundant auxiliary power supplies is to incorporate photovoltaic (PV) power generation circuitry within the rack. In typical applications, the ESS lobby lighting system provides continuous and stable brightness, allowing the compact PV panels on the rack to generate sufficient power for a single rack auxiliary circuit. The PV panel power is preferably converted to a stable low voltage via an MPPT converter. The advantages of this combination are that PV-based auxiliary power supplies can be constructed using inexpensive and widely available components. Furthermore, transformer-based auxiliary power supply circuitry can be designed at low cost, providing service-level auxiliary power only in the event of a PV power failure. Attached Figure Description

[0063] Embodiments of the present invention will be described in more detail with reference to the accompanying drawings listed below.

[0064] Figure 1 An embodiment of a high-voltage direct current system (e.g., in a substation) is shown; Figure 2 Showing the use of Figure 2 An example of an energy storage system for static synchronous compensation in a high-voltage direct current system; Figure 3 A detailed view of the energy storage rack is shown; Figure 4 An embodiment of an energy storage rack is shown; and Figure 5 Another embodiment of the energy storage rack is shown. Detailed Implementation

[0065] Reference Figure 1Substation 10 is shown. Substation 10 can be connected to high-voltage (HV) power grid 12 and can function as a transmission substation or distribution substation, for example, for supplying power to one or more power users 14. Examples of power users 14 include, but are not limited to, data centers, factories, homes, etc.

[0066] Substation 10 includes a power distribution and / or power transmission section 16, which is prior art and will not be described in detail here. For example, substation 10 also includes a static synchronous compensator (STATCOM) 18, which is electrically connected to the output grid 13 to compensate for load peaks.

[0067] Reference Figure 2 The energy storage system (ESS) 20 is shown in more detail. ESS 20 stores electrical energy that forms part of STATCOM 18. ESS 20 includes multiple ESS racks 22. Each ESS rack 22 includes an energy storage device 24, a control unit 26, and an auxiliary power supply 30. The energy storage device 24 includes multiple energy storage units 28, such as supercapacitors. The energy storage devices 24 of different ESS racks 22 are connected in series to form a series group and are electrically connected to a high-voltage DC circuit to provide power when needed or to charge when possible.

[0068] Control unit 26 controls the operation of each ESS rack 22, particularly the operation of the energy storage unit 24. Control unit 26 can be connected to a higher-level system control unit (not shown for simplicity), which operates the entire ESS 20.

[0069] The auxiliary power supply 30 of each ESS rack 22 is also connected to the auxiliary power supply 30 of the adjacent ESS rack 22.

[0070] The ESS 20 includes a power supply transformer 32 and preferably an auxiliary feeder 34 electrically connected to the midpoint 35 of the ESS rack 22. The power supply transformer 32 is high-voltage (HV) isolated from the auxiliary feeder 34. The power supply transformer 32 is electrically connected to a low-voltage power grid 36, which may or may not be part of the ESS 20.

[0071] See Figure 2 and Figure 3 The ESS rack 22 will be further described below. Each auxiliary power supply 30 includes an input terminal 38 and a feed terminal 40. The input terminal 38 can be connected to the feed terminal 40 of another ESS rack 22 or to an auxiliary feeder 34.

[0072] like Figure 3 As shown, the auxiliary power supply 30 includes a low-voltage (LV) transformer 42. The LV transformer 42, as well as other components of each ESS rack 22, are low-voltage isolated. The LV transformer 42 includes an input branch 44, a transmission branch 46, and a power supply branch 48.

[0073] Input branch 44 is connected to input terminal 38 and has a primary winding W1. The primary winding W1 is electrically insulated from the ESS rack frame. The primary winding W1 may be configured with an adjustable tap 53 for setting the transformer ratio of the low-voltage transformer 42.

[0074] The transmission branch 46 is connected to the transmission terminal 40 and has a secondary winding W2. The primary winding W1 and the secondary winding W2 are connected by inductive coupling, preferably through the transformer core 50. The secondary winding W2 is electrically connected to the ESS rack frame, which serves as a potential reference point.

[0075] Power supply branch 48 has a power supply winding W3. Power supply winding W3 is inductively coupled to at least the secondary winding W2. Power supply winding W3 is electrically connected to the ESS rack frame to maintain the same reference potential. This allows for relatively simple low-voltage isolation of the ESS rack 22. However, high-voltage isolation relative to ground potential may still be required. Power supply winding W3 draws power from other windings and is electrically connected to control unit 26 to supply power to it.

[0076] Reference Figure 4 An embodiment of the ESS rack 22 will be described in more detail below. The auxiliary power supply 30 includes an AC power branch 54. The AC power branch 54 is equipped with a low-voltage transformer 42.

[0077] In addition, AC power supply branch 54 includes an AC-DC converter 56 for rectifying the AC voltage transformed by low-voltage transformer 42. This generates a typical DC voltage used in the electronic control unit, such as extra-low voltage (ELV). AC-DC converter 56 can be an active or passive rectifier and may include voltage regulation or stabilization functions, depending on the application. AC-DC converter 56 is electrically connected to low-voltage transformer 42 via power supply branch 48.

[0078] The AC power branch 54 may include a blocking element 58, such as a diode. The blocking element 58 is arranged between the AC-DC converter 56 and the control unit 26. The arrangement of the blocking element 58 ensures that current can flow only from the AC-DC converter 56 to the control unit 26 and cannot flow in the reverse direction.

[0079] The auxiliary power supply 30 includes a DC power supply branch 60. The DC power supply branch 60 is equipped with a low-voltage DC power supply 62. For example... Figure 4 As shown, in this embodiment, the low-voltage DC power supply 62 is constituted by the energy storage device 24 of the ESS rack 22. In a variant, only a portion of the energy storage device 24 is used. The energy storage device 24 is used to provide energy to the static synchronizing compensator 18 and the control unit 26 on demand during fault conditions or maintenance.

[0080] The DC power supply branch 60 may also include a DC-DC converter 64. The DC-DC converter 64 is configured to convert the voltage of the low-voltage DC power supply 62 to the operating voltage of the control unit 26 and power it.

[0081] The DC power supply branch 60 also includes a blocking element 66 (e.g., a diode) disposed between the DC-DC converter 64 and the control unit 26. The blocking element 66 is configured to prevent current from flowing back from the control unit 26 to the DC-DC converter 64.

[0082] AC power branch 54 and DC power branch 60 jointly power control unit 26. Blocking elements 58 and 66 prevent current from flowing from AC power branch 54 to DC power branch 60 and vice versa.

[0083] Control unit 26 includes a power controller that can switch between power supply branches 54 and 60 when necessary. It should be noted that both power supply branches 54 and 60 can supply power to control unit 26 simultaneously.

[0084] Although the auxiliary power supply 30 is described only as including one AC power branch 54 and one DC power branch 60, it may actually include multiple AC power branches 54 and / or multiple DC power branches 60, and these branches can adopt any of the aforementioned configurations. Preferably, if there are multiple power supply branches 54 and 60, these power supply branches 54 and 60 should be independent of each other. In other words, a failure of any branch 54 or 60 will not affect the other power supply branches 54 and 60.

[0085] refer to Figure 5 Another embodiment of the ESS rack 22 will be described in more detail here, as it differs from the previously described embodiment. A low-voltage DC power supply 62 is configured as one or more photovoltaic (PV) modules 68. The PV modules 68 are mounted on top of the ESS rack 22, preferably on the ESS rack frame. The PV modules 68 are preferably arranged upwards. As shown, the ESS lobby lighting system 70 can provide sufficient light intensity for the PV modules 68 to generate electricity.

[0086] In a variant not shown, the photovoltaic module 68 may also be detached from the ESS rack 22 and mounted externally. Another variant uses a DC generator (e.g., driven by an internal combustion engine) as the DC power source 62. Furthermore, it should be noted that the different types of DC power supply branches 60 described herein can be combined to further enhance redundancy.

[0087] List of reference numerals: 10 substations 12 High Voltage (HV) Power Grid 14 electricity users 16. Transmission and Transformation Section 18 Static Synchronous Compensator (STATCOM) 20. Energy Storage System (ESS) 22ESS racks 24 energy storage devices 26 control units 28 energy storage units 30 Auxiliary Power Supply 32 power supply transformer 34 auxiliary feeders 35 midpoint 36 Low-voltage power grid 38 input terminals 40 delivery terminals 42 Low-voltage (LV) transformer 44 input branches 46 Conveyor Branches 48 power supply branches 50 transformer core 52ESS rack frame 53 Adjustable taps 54 AC power supply branches 56 AC-DC converter 58 blocking elements 60 DC power supply branch 62 Low-voltage DC power supply 64 DC-DC converter 66 blocking elements 68 photovoltaic (PV) modules 70 Lighting System W1 primary winding W2 secondary winding W3 power supply winding

Claims

1. An auxiliary power supply (30) for an energy storage rack (22) in a high-voltage direct current (HVDC) system, the power supply comprising: - At least one AC power branch (54), the at least one AC power branch (54) including an input terminal (38), a transmission terminal (40) and a low-voltage transformer (42), wherein the low-voltage transformer (42) has an input branch (44) configured to receive AC power from the input terminal (38), the low-voltage transformer (42) has a transmission branch (46) configured to transmit the AC power to the transmission terminal (40), and the low-voltage transformer (42) has a power supply branch (48) configured to convert the received AC power into a lower voltage in the extra-low voltage (ELV) range to power the control unit (26); - At least one DC power supply branch (60), the at least one DC power supply branch (60) including a low-voltage DC power supply (62) configured to provide DC power to the control unit (26).

2. The auxiliary power supply (30) according to claim 1 further includes a power controller configured to switch between each AC power branch (54) and each DC power branch (60) in response to receiving a control signal.

3. The auxiliary power supply (30) according to any of the preceding claims, wherein the AC power supply branch (54) includes a blocking element (58) that prevents current from flowing into the respective AC power supply branch (54) from either the AC power supply branch or the low-voltage power supply branch.

4. The auxiliary power supply (30) according to any of the preceding claims, wherein the DC power supply branch (60) includes a blocking element (66) that prevents current from flowing from either the AC power supply branch or the DC power supply branch into the corresponding low-voltage power supply branch.

5. The auxiliary power supply (30) according to any one of claims 3 or 4, wherein the blocking element (58, 66) comprises a diode.

6. The auxiliary power supply (30) according to any of the preceding claims, wherein the low-voltage transformer (42) comprises a primary winding (W1) and a secondary winding (W2) inductively coupled to each other, such that one of the primary winding (W1) and the secondary winding (W2) constitutes part of the input branch (44) and the other constitutes part of the transmission branch (46).

7. The auxiliary power supply (30) according to claim 6, wherein the low-voltage transformer (42) includes a power supply winding (W3) that forms part of the power supply branch (48) and is inductively coupled to the primary winding (W1) and / or the secondary winding (W2), the power supply winding (W3) being configured to convert alternating current received from the primary winding (W1) and / or the secondary winding (W2) into a lower voltage of direct current in the ELV range, the lower voltage of direct current being suitable for supplying to the control unit (26).

8. The auxiliary power supply (30) according to any of the preceding claims, wherein the power supply branch (48) is referenced to the same potential as either the input branch (44) or the transmission branch (46).

9. The auxiliary power supply (30) according to any of the preceding claims, wherein the input branch (44) is electrically isolated from the transmission branch (46) and the power supply branch (48), or the transmission branch (46) is electrically isolated from the input branch (44) and the power supply branch (48).

10. The auxiliary power supply (30) according to any of the preceding claims, wherein the AC power supply branch (54) includes an AC-DC converter (56) electrically connected to the low-voltage transformer (42) for generating DC power to supply power to the control unit (26).

11. The auxiliary power supply according to claim 10, wherein the AC-DC converter (56) is electrically connected to the power supply winding (W3).

12. The auxiliary power supply (30) according to any of the preceding claims, wherein the DC power supply branch (60) includes a DC-DC converter (64) electrically coupled to the low-voltage DC power supply (62) for generating DC power to supply power to the control unit (26).

13. The auxiliary power supply (30) according to claim 12, wherein the low-voltage DC power supply (62) includes an energy storage device (24).

14. The auxiliary power supply (30) according to claim 12 or 13, wherein the low-voltage DC power supply (62) comprises at least one photovoltaic module (68).

15. The auxiliary power supply (30) according to any one of claims 12 to 14, wherein the low-voltage DC power supply (62) comprises a DC generator.

16. The auxiliary power supply (30) according to any of the preceding claims, wherein the input branch (44) and the transmission branch (46) are configured to generate an alternating current voltage rise, thereby compensating for voltage drop due to power loss.

17. The auxiliary power supply (30) according to claim 16, wherein either the input branch (44) or the transmission branch (46) is configured to regulate the voltage rise.

18. An energy storage rack (22) for an HVDC system, comprising: - An auxiliary power supply (30) according to any of the preceding claims; - An energy storage device configured to store electrical energy (24); as well as - A control unit (26) configured to control the operation of the energy storage device (24); The AC power supply branch (54) and the DC power supply branch (60) are electrically connected to the control unit (26) to provide power.

19. The energy storage rack (22) according to claim 18, wherein the power controller is part of the control unit (26).

20. The energy storage rack (22) according to claim 18 or 19, wherein the low-voltage DC power supply includes the energy storage device (24).

21. The energy storage rack (22) according to any one of claims 18 to 20, wherein each blocking element (58, 66) is arranged between the low-voltage transformer (42) and the control unit (26).

22. The energy storage rack (22) according to claim 21, wherein each blocking element (58) is arranged between the AC-DC converter (56) and the control unit (26).

23. The energy storage rack (22) according to any one of claims 18 to 22, wherein each blocking element (66) is arranged between the DC power supply and the control unit (26).

24. The energy storage rack (22) according to claim 23, wherein each blocking element (66) is arranged between the DC-DC converter (64) and the control unit (26).

25. The energy storage rack (22) according to any one of claims 18 to 24, wherein the power supply branch (48) is electrically connected to the control unit (26).

26. The energy storage rack (22) according to claim 25, wherein the power supply branch (48) is electrically connected to the control unit (26) via the AC-DC converter (56).

27. The energy storage rack (22) according to any one of claims 18 to 26 further includes a frame and / or housing made of conductive material, wherein the power supply branch (48) is referenced to the same potential as the input branch (44) or the transmission branch (46) through the frame and / or the housing.

28. An energy storage system (20) for a high-voltage direct current (HVDC) circuit, comprising: - Power supply transformer (32); as well as - A plurality of energy storage racks (22) according to any one of claims 18 to 27, wherein the energy storage devices (24) of the energy storage racks (22) are connected in series to form a high voltage DC energy storage device, wherein the auxiliary power supply (30) is electrically connected in series.

29. The energy storage system (20) according to claim 28, wherein at least one energy storage rack (22) is directly electrically connected to the power supply transformer (32) via an input terminal (38) of the at least one energy storage rack (22), and is directly electrically connected to another energy storage rack (22) via a transmission terminal (40) of the at least one energy storage rack (22).

30. The energy storage system (20) according to claim 28 or 29, wherein at least one energy storage rack (22) is electrically connected to the input terminal (38) of another energy storage rack (22) via a transmission terminal (40) of the at least one energy storage rack (22).

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