Coordinated hvdc system with distributed energy storage and method for coordinated protection during faults

Abstract

The application belongs to the technical field of high-voltage direct-current power supply, and discloses a collaborative HVDC system containing distributed energy storage and a fault collaborative protection method. The system comprises a power unit, a controllable switch, a load, an energy storage unit and an anti-reverse diode; each energy storage unit is connected in parallel with the corresponding load to the output end of the controllable switch, forming a distributed energy storage architecture. The power unit is in communication connection with the controllable switch. When a branch fault occurs, the controllable switch sends a cut-off request to the power unit; the power unit cuts off the direct-current output, creating a current-free time period; the energy storage unit starts to supply power to the corresponding load; the controllable switch is tripped to isolate the fault branch in the current-free state; after the power unit resumes the output, the energy storage unit automatically exits. Through system-level collaborative control, the application realizes rapid isolation of direct-current faults and uninterrupted power supply of non-fault branches, reduces the system cost, and improves the power supply reliability.

Description

Technical Field

[0001] This invention relates to the field of high-voltage direct current (HVDC) power supply technology, specifically to a collaborative HVDC system with distributed energy storage and a collaborative fault protection method. Background Technology

[0002] With the rapid growth of AI computing power loads, the power of a single data center rack has jumped from the traditional 10–20kW to 100kW or even megawatts. The current carrying capacity, losses, and copper costs of traditional 48V DC buses at this power level are no longer sustainable. The mainstream industry approach is shifting to 800V high-voltage direct current (HVDC) power distribution architectures, where medium-voltage AC is directly converted to 800V DC bus via solid-state transformers (SST). This significantly reduces AC / DC conversion steps, improving system efficiency to 97%–98.5% and reducing copper usage by 45%.

[0003] However, while the 800V HVDC architecture improves system efficiency and computing density, it also presents significant challenges to fault protection. The output side of an HVDC system is a DC bus, and the fault protection characteristics of DC systems differ fundamentally from those of AC systems. This is the core challenge facing HVDC protection technology. In AC systems, voltage and current exhibit sinusoidal waveforms with two natural zero-crossing points per cycle. When the switch or circuit breaker contacts open, the arc extinguishes naturally at the current zero-crossing point. In contrast, the voltage and current in a DC system are constant. When a short-circuit fault occurs at the end, the lack of a zero-crossing point causes the fault current to persist, resulting in a continuous elongation and temperature rise at the circuit breaker contacts, making it difficult to extinguish. In severe cases, this can lead to contact burning, welding, or even fire.

[0004] The aforementioned difficulty in arc extinguishing due to the lack of a zero-crossing point on DC circuits is exacerbated in solid-state transformers (SSTs). This is because the DC bus on the SST output side is directly fed by a capacitor supported by a low equivalent series inductance (ESL), and the fault circuit impedance is dominated by parasitic inductance at the microhenry level. The DC fault current rise rate is extremely high, reaching tens of A / µs or more. Simultaneously, the short-circuit withstand time of the SiC MOSFET power devices inside the SST is only on the order of microseconds, far less than the 30–40 ms breaking time required by traditional mechanical DC circuit breakers. Therefore, there is a time scale mismatch of more than two orders of magnitude. This means that before a traditional circuit breaker can complete its breaking process, the SST power devices will already be damaged by overcurrent, necessitating a fault isolation method that is much faster than traditional protection schemes.

[0005] To address the aforementioned challenges, the industry currently employs the following main solutions: (1) Use DC circuit breakers to cut off faults. Since the energy at DC contacts is greater than that at AC contacts, the size of components such as switch contacts and arc-extinguishing grids is larger, and the contact breaking time is usually 30–40 ms. This requires the upstream power supply section to have a stronger short-circuit current withstand capability, which leads to a sharp increase in the cost of the power supply section.

[0006] (2) Use fast-acting fuses to cut off faults. Fast-acting fuses can shorten the fault current cut-off time to less than 10ms, but fuses are disposable consumables and need to be replaced when the power is off after a fault. They cannot achieve remote control and self-reset.

[0007] (3) Use SSCB solid-state circuit breakers. Solid-state circuit breakers replace mechanical contacts with fully controllable power semiconductor devices such as SiC MOSFETs, which can complete fault shutdown within microseconds. However, they have the problem of high conduction losses, and a good heat dissipation environment must be ensured under high current conditions; silicon carbide devices are expensive and have not yet entered the stage of full commercial use. At the same time, the microsecond-level shutdown of solid-state circuit breakers will cause a sharp voltage change, and the resulting electromagnetic interference may affect the surrounding weak current control, sampling and communication lines, requiring additional buffering and shielding design.

[0008] (4) Centralized energy storage connected in parallel to the DC bus, such as the Panama Power solution. Connecting the battery directly in parallel to the DC bus can improve the power supply's withstand capability. However, centralized energy storage has the problem that battery failures will directly impact the bus, without isolation or buffering, making system protection more difficult.

[0009] (5) Networked protection scheme based on GOOSE communication. Existing schemes propose to transmit information between adjacent protections through the GOOSE (Substation Events for General Objects) network to achieve selectivity of DC protection. The core of this type of scheme is to replace traditional control cables with network communication to improve the transmission efficiency of protection signals. However, its protection logic still relies on the circuit breaker to interrupt the fault current under current conditions, without changing the physical nature of fault clearing.

[0010] Furthermore, invention patent CN104009452A proposes a protection scheme for short-circuit faults in DC power distribution systems. The core idea of ​​this scheme is: when the sudden change in DC voltage exceeds the set value, bus and line protection are activated; after the bus protection is activated, if the differential current is greater than the set value, the bus protection operates, tripping all DC circuit breakers on the power supply side. Although this scheme involves the operation of power supply-side circuit breakers during fault handling, once the power supply-side circuit breakers trip, they are permanently disconnected and cannot be restored, thus constituting a power outage protection method; moreover, this scheme does not involve distributed energy storage and cannot provide uninterrupted power supply to the load during power supply side disconnection. Summary of the Invention

[0011] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention provides a collaborative HVDC system with distributed energy storage, which aims to solve the technical problems in the existing HVDC DC system, such as the lack of zero-crossing point of fault current leading to difficulties in arc extinguishing of circuit breakers, slow breaking speed, high performance requirements of protection devices, and power interruption of non-faulty circuits during fault handling. The invention also provides a fault collaborative protection method for a collaborative HVDC system with distributed energy storage.

[0012] Technical solution: According to a first aspect of the present invention, a collaborative HVDC system incorporating distributed energy storage is provided, the system comprising: At least one intelligent power supply unit, wherein the input terminals of each intelligent power supply unit are respectively connected in parallel to an AC bus, and the intelligent power supply unit includes: A power unit, whose input terminal is connected to the AC bus, is used to convert AC power into DC power output. Multiple controllable switches are provided, with the input terminals of each controllable switch connected in parallel to the output terminal of the power unit. The power unit is communicatively connected to each controllable switch. Each controllable switch is configured to send a cut-off request signal to the power unit when a fault is detected in its branch. The power unit is configured to cut off the DC output after receiving the cut-off request signal and restore the DC output after a preset time. Multiple loads, each of which is connected to the output terminal of a corresponding controllable switch; Multiple energy storage units, each of which is connected in parallel with a corresponding load at a connection point, and the connection point is electrically connected to the output terminal of a corresponding controllable switch; Multiple first anti-reverse diodes are connected in series between the output terminal of the controllable switch and the connection point. The anode of the first anti-reverse diode is connected to the controllable switch side, and the cathode is connected to the parallel connection point side. The first anti-reverse diode is configured to allow current to flow from the power unit side to the load side and block current from flowing from the load side to the power unit side.

[0013] Furthermore, including: The controllable switch is an intelligent circuit breaker.

[0014] Furthermore, including: The controllable switch includes a load switch, a current detection element, and a communication module, which are connected in series. The current detection element is used to detect the current of its branch in real time, and outputs a trigger signal when a fault current is detected, and outputs a current disappearance signal when the current disappears. The communication module is communicatively connected to the power unit, and is used to send a disconnection request signal to the power unit when the trigger signal is received, and to control the controllable switch of the corresponding branch to perform tripping when the current disappearance signal is received.

[0015] Furthermore, including: Each energy storage unit is configured in a one-to-one correspondence with a corresponding load, and each energy storage unit supplies power only to the load of the corresponding branch.

[0016] Furthermore, including: It also includes green energy devices, which are configured one-to-one with the smart power supply units and are used to charge each of the energy storage units in the corresponding smart power supply units.

[0017] Furthermore, including: It also includes multiple second anti-reverse diodes, with the anode of each second anti-reverse diode connected to the green energy device side and the cathode connected to the corresponding energy storage unit side.

[0018] Secondly, the present invention also provides a collaborative fault protection method for HVDC systems, which is applied to the collaborative HVDC system with distributed energy storage described in the first aspect. The method includes the following steps: S1 When any branch in the system fails, the intelligent circuit breaker of that branch will detect in real time whether a fault current has occurred in the branch, and generate a disconnection request signal after detecting the fault current. The intelligent circuit breaker in S2 sends the disconnection request signal to the power unit, and the power unit receives the disconnection request signal. After receiving the cut-off request signal, the power unit described in S3 immediately cuts off the DC output, causing the current in the entire DC circuit to drop rapidly to near zero, entering a period of no current. The energy storage unit described in S4 starts to supply power after detecting the disappearance of the current in its branch, and supplies power unidirectionally to the corresponding load through the connection point, so as to maintain the normal operation of the load in the non-faulty branch during the period when the power unit cuts off the DC output. After detecting the disappearance of the current in the branch, the intelligent circuit breaker described in S5 performs a tripping operation during the period of no current, cutting off the electrical connection between the faulty branch and the power unit. After the intelligent circuit breaker described in S6 completes the tripping operation, the power unit automatically restores DC output after a preset time, and other non-faulty branches regain power supply, while the faulty branches remain de-energized because the intelligent circuit breaker has been tripped. After detecting that the power unit has resumed DC output, each of the energy storage units in S7 automatically stops supplying power, exits the operating state, and the system returns to normal power supply mode.

[0019] Furthermore, including: Step S2 of the method also includes: When the power unit is supplying power normally, the energy storage unit is in hot standby mode and is charged by the power unit or green energy device. The first anti-reverse diode is in reverse cutoff mode, and the energy storage unit does not supply power to the load of the corresponding branch.

[0020] Furthermore, including: Step S2 of the method also includes: The intelligent circuit breaker sends the disconnection request signal to the power unit through a communication connection, which is an optical fiber communication connection. The disconnection request signal is also broadcast synchronously to the power unit corresponding to the faulty branch and other non-faulty branches through the optical fiber communication connection.

[0021] Furthermore, including: Step S4 further includes: When the energy storage unit supplies power to the corresponding load in one direction, the second anti-reverse diode is in a reverse cutoff state, blocking the energy storage unit from feeding back electrical energy to the green energy device.

[0022] Furthermore, including: Step S5 of the method further includes: When the intelligent circuit breaker fails to trip successfully during the period without current, the fuse connected in series between the intelligent circuit breaker and the corresponding load will blow due to the continuous fault current, thereby cutting off the faulty branch.

[0023] Furthermore, including: In step S7, the energy storage unit exits the operating state in the following way: When the power unit resumes DC output and the bus voltage rises to a level higher than the output voltage of the energy storage unit, the first anti-reverse diode naturally cuts off, and the energy storage unit automatically stops supplying power.

[0024] Thirdly, the present invention also provides an electronic device, characterized in that it includes: a processor, a storage medium and a bus, wherein the storage medium stores machine-readable instructions executable by the processor, and when the electronic device is running, the processor communicates with the storage medium via the bus, and the processor executes the machine-readable instructions to perform the steps of the HVDC system fault collaborative protection method as described in the second aspect.

[0025] Thirdly, the present invention also provides a computer-readable storage medium, characterized in that a computer program is stored on the computer-readable storage medium, and the computer program is executed by a processor to perform the steps of the HVDC system fault collaborative protection method as described in the second aspect.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following advantages: 1. Significantly Reduced System Costs: This invention actively disconnects the DC output on the power supply side, creating a current-free period in the DC circuit, allowing the branch protection components to trip under this current-free condition. This technical solution eliminates the need for branch protection components to have DC fault current breaking capacity, allowing conventional low-cost circuit breakers or load switches to replace expensive hybrid DC circuit breakers or solid-state circuit breakers (SSCBs). Compared to existing solutions relying on solid-state circuit breakers, this invention significantly reduces the procurement and maintenance costs of system protection equipment.

[0027] 2. Ensuring uninterrupted power supply to non-faulty circuits: This invention independently configures energy storage units in each load branch, forming a branch-level distributed energy storage architecture. When the power unit cuts off the DC output, each energy storage unit automatically starts to supply power to the corresponding branch load. The self-sustaining power supply time of the energy storage unit is no less than 1 second, which is sufficient to cover the complete fault handling window from power cut-off to restoration. This invention ensures continuous power supply to non-faulty branches while disconnecting faulty branches, significantly improving the system's power supply reliability. 3. Extend equipment lifespan: In this invention, the controllable switch performs the opening operation in the absence of current, avoiding arc erosion caused by breaking the circuit under load, which can significantly extend the electrical life of the switchgear and reduce maintenance frequency and replacement costs.

[0028] 4. Achieving Precise Energy Management of Energy Storage Units: This invention, through the deployment of branch-level distributed energy storage and the physical blocking effect of the first anti-reverse diode, ensures that each energy storage unit only supplies power to the corresponding branch load and does not feed back energy to other branches or the grid side. Simultaneously, in green energy scenarios, the second anti-reverse diode further prevents the energy storage unit from flowing back to the green energy device, achieving precise management of the stored energy.

[0029] 5. Provides a reliable backup protection mechanism: This invention includes a fuse in each branch as backup protection. When any step of the main protection logic—controllable switch detection → reporting → power cut-off → no-current tripping—fails, the fuse melts under continuous fault current, physically disconnecting the faulty branch and ensuring system safety.

[0030] 6. Adaptable to multiple application scenarios: This invention is applicable to both conventional power grid supply scenarios, where the power unit charges the energy storage unit, and green energy scenarios, where wind power, photovoltaics, etc., independently charge the energy storage unit. It has strong scenario adaptability. At the same time, the controllable switch can be implemented as a smart circuit breaker or as a combination of load switch, current detection element and communication module, providing flexible choices for different cost budgets and application requirements. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating the structural principle of the existing 10kV medium-voltage solid-state transformer SST. Figure 2 This is a schematic diagram of the topology of a single power unit of the collaborative HVDC system with distributed energy storage described in this invention. Figure 3 This is a timing logic diagram of the fault collaborative protection method described in this invention; Figure 4 This is a schematic diagram of the complete topology of the multi-power unit of the collaborative HVDC system with distributed energy storage described in this invention. Figure 5 This is a schematic diagram illustrating an implementation method for connecting a collaborative HVDC system with distributed energy storage to a green energy device, as described in this invention. Figure 6 This is a comparison chart of the fault handling time curves of the present invention and conventional solutions. Figure 7 This is a flowchart of the HVDC system fault collaborative protection method described in this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1: Figure 1This is a schematic diagram illustrating the structural principle of a 10kV medium-voltage solid-state transformer (SST) in existing technology. A solid-state transformer (SST) is a new type of transformer based on power electronic conversion technology. Its core idea is to use high-frequency transformers and power electronic devices, such as SiC MOSFETs, to achieve voltage conversion and power control, replacing traditional power frequency transformers. Internally, an SST consists of multiple cascaded power units, each independently performing AC / DC conversion, collectively forming the overall conversion function of the SST.

[0034] like Figure 1 As shown, in the existing SST architecture, multiple power units (U1, U2, U3...U10) are connected in parallel on the 10kV AC bus side. Each power unit integrates an AC / DC converter, i.e., a cascaded H-bridge rectifier, to rectify the 10kV AC power into DC 800V DC power. The power units operate independently and in parallel; a failure in any one power unit does not affect the normal operation of the others. The output terminals of each power unit are connected to the corresponding DC distribution branch via isolating switches Q1, Q2, Q3...Q10, respectively, achieving multiple DC outputs. Again, the power units operate independently, and a failure in any one power unit does not affect the normal operation of the others.

[0035] Based on the existing SST architecture, this invention improves the DC distribution branches downstream of each power unit. While maintaining the cascaded structure of the power units, it adds branch-level distributed energy storage, controllable switches, and anti-reverse diodes. Furthermore, it connects the controllable switches of each branch with the power units through communication to form a unified collaborative protection system.

[0036] like Figure 2 As shown, this embodiment provides a collaborative HVDC system with distributed energy storage, including at least one intelligent power supply unit. The input terminals of each intelligent power supply unit are connected in parallel to a 10kV AC bus. Figure 1 The specific improved structure of this embodiment is illustrated using a single power unit U1 and its downstream branch as an example. In a real system, multiple power units may be included, such as... Figure 4 As shown, corresponding Figure 1 U1, U2, U3...U10 in the N+1 redundancy architecture constitute a complete N+1 redundancy architecture.

[0037] In this embodiment, each intelligent power supply unit includes: a power unit, multiple controllable switches, multiple loads, multiple energy storage units, and multiple first anti-reverse diodes.

[0038] In a preferred embodiment, the power unit has three interfaces: an AC input interface, a DC output interface, and a communication interface. The power unit connects to a 10kV AC bus via the AC input interface to receive AC power from the power grid and convert it to 800V DC output. The power unit connects to a disconnecting switch Q1 via the DC output interface, and then connects to multiple controllable switches in parallel via Q1 to distribute power to each DC distribution branch. The power unit connects to a fiber optic communication network via the communication interface, and each controllable switch is also connected to this fiber optic communication network, enabling signal interaction between the power unit and the controllable switches. The power unit is preferably a solid-state transformer (SST) power unit. The output terminal of the power unit is equipped with a disconnecting switch Q1 to provide a clear disconnection point during maintenance or fault conditions.

[0039] In a preferred embodiment, the input terminals of each controllable switch are connected in parallel to the output terminal of the power unit or the output terminal of the disconnecting switch. In this embodiment, the controllable switch has two preferred implementations: one is an intelligent circuit breaker with a built-in current detection element and communication module, capable of independently performing fault current detection, sending disconnection request signals, and tripping operations; The second method involves a combination of a load switch, an independent current sensing element, and a communication module. In this load switch implementation, the current sensing element is located on a branch line to detect the current in that branch line in real time. It outputs a trigger signal when a fault current is detected and a current disappearance signal when the current disappears. The communication module is electrically connected to the current sensing element and the load switch, and also communicates with the power unit. It sends a disconnection request signal to the power unit upon receiving the trigger signal and controls the load switch to trip upon receiving the current disappearance signal. The power unit transmits signals to each controllable switch via fiber optic communication.

[0040] In this embodiment, each load is connected to the output terminal of its corresponding controllable switch. Each energy storage unit is connected in parallel with its corresponding load at a connection point, which is electrically connected to the output terminal of the corresponding controllable switch. Each energy storage unit is configured in a one-to-one correspondence with its corresponding load, and each energy storage unit only supplies power to the load of its corresponding branch, without feeding back energy to other branches or the power grid. The self-sustaining power supply time of each energy storage unit is not less than 1 second.

[0041] In this embodiment, each first anti-reverse diode is connected in series between the output terminal of the controllable switch and the connection point. The anode of the first anti-reverse diode is connected to the controllable switch side, and the cathode is connected to the connection point side. The first anti-reverse diode is configured to allow current to flow from the power unit side to the load side, including the normal power supply direction and the energy storage charging direction, and to block current from flowing from the load side to the power unit side, preventing the energy storage unit from backflowing to the grid side.

[0042] Therefore, in this embodiment, the unidirectional output of the energy storage unit is achieved through a dual mechanism: (a) Physical hardware blocking. The first anti-reverse diode is connected in series in the output path of the energy storage unit, and its cathode is connected to the load side. It physically blocks any path for current to flow from the load side to the energy storage unit side at the circuit topology level, preventing the energy storage unit from backflowing to the grid side or feeding power to other branches.

[0043] (ii) PCS Software Direction Restriction. The PCS, either internal or external to the energy storage unit, controls the power direction via software, restricting the energy storage unit to only discharge outwards and preventing it from receiving reverse charging current from the grid or load side. Software restriction serves as the first line of defense, actively controlling the charging and discharging direction of the energy storage unit during normal operation. Hardware diodes serve as the second physical line of defense, forcibly blocking reverse current at the circuit topology level when the software fails to respond promptly to transient disturbances. Both provide redundant backups, together forming a dual anti-reverse current protection mechanism for the energy storage unit, ensuring it only discharges and does not receive reverse current.

[0044] In this embodiment, each branch circuit is also connected in series with a fuse FU, which is set between the controllable switch and the corresponding load as backup protection.

[0045] In a preferred embodiment, such as Figure 4 As shown, the system includes multiple intelligent power supply units, such as power units U1, U2...Up. The input terminals of each intelligent power supply unit are connected in parallel to the same 10kV AC bus, forming an N+1 redundancy or capacity expansion architecture. In this embodiment, n and p They can be the same, or they can be different.

[0046] In another preferred embodiment, such as Figure 5 As shown, the system also includes green energy devices, such as wind power generation devices and / or photovoltaic power generation devices. Each green energy device is paired with a smart power supply unit to charge the corresponding energy storage unit. A second anti-reverse diode is connected in series between the output terminal of the green energy device and the energy storage unit. Its anode is connected to the green energy device side, and its cathode is connected to the energy storage unit side. This allows current to flow from the green energy device to the energy storage unit and blocks current from flowing from the energy storage unit to the green energy device, preventing backflow of energy from the storage unit to the green energy side.

[0047] In this embodiment, the energy storage unit is an independent modular device, including an energy storage body, an energy storage controller, and a DC / DC converter selected according to voltage matching requirements, all integrated in the same housing.

[0048] In a preferred embodiment, the energy storage device is an electrical energy storage medium, which can be a lithium battery pack, such as a lithium iron phosphate battery, a supercapacitor, or a hybrid configuration of both. Lithium battery packs have the characteristics of high energy density and long self-sustaining time, making them suitable for scenarios requiring long-term backup power support; supercapacitors have the characteristics of fast response speed and long cycle life, making them suitable for scenarios requiring instantaneous high-power support; the hybrid configuration can meet the dual requirements of energy density and response speed.

[0049] The energy storage controller is electrically connected to the energy storage unit and is used to monitor the voltage, current and state of charge (SOC) of the energy storage unit, and control the charging and discharging process of the energy storage unit.

[0050] In this embodiment, the energy storage unit also includes a Battery Management System (BMS). The BMS is electrically connected to the energy storage unit and is used to monitor the voltage, current, temperature, and state of charge (SOC) of the energy storage unit in real time. It controls the charging and discharging process of the energy storage unit to prevent abnormal states such as overcharging, over-discharging, and over-temperature. When an abnormality is detected, it reports fault information to the system via a communication interface. The BMS includes a voltage sampling module, a current sampling module, a temperature sampling module, an SOC estimation module, and a protection execution module. Each module is connected to the energy storage unit to achieve comprehensive monitoring and protection of the energy storage unit's state.

[0051] The DC / DC converter is positioned between the energy storage unit and the output terminal. Its input terminal is connected to the positive terminal of the energy storage unit, and its output terminal is connected to the positive output terminal of the energy storage unit. In this embodiment, the DC / DC converter is an optional component: when the DC bus voltage, such as 800V, is higher than the output voltage of the energy storage unit, a DC / DC boost converter is configured to boost the voltage of the energy storage unit to match the DC bus voltage before output; when the DC bus voltage is the same as the output voltage of the energy storage unit, such as in a 48V system, no DC / DC converter is configured, and the energy storage unit outputs directly.

[0052] In a preferred embodiment, the positive output terminal of the energy storage unit is connected to the connection point of the corresponding branch via a first anti-reverse diode, and the negative output terminal is connected to the negative terminal of the DC bus or the system ground terminal. The energy storage unit and the corresponding load are deployed in physical proximity to ensure that the power of the energy storage unit is preferentially supplied to the load of the corresponding branch.

[0053] In this embodiment, when the power unit is supplying power normally, i.e. in normal power supply mode, the 10kV AC power is converted into DC power by the power unit and then supplied to the load via the controllable switch and the first anti-reverse diode. At this time, the bus voltage is higher than the output voltage of the energy storage unit, the first anti-reverse diode is in the forward conduction state, and the current path is: power unit → controllable switch → first anti-reverse diode (anode → cathode) → connection point → load.

[0054] At the same time, the power unit charges the energy storage unit through the same path, replenishing the energy storage unit and keeping it fully charged. At this time, the energy storage unit is in hot standby mode and does not output power to the load.

[0055] In the preferred embodiment equipped with a green energy device, the green energy device and the power unit jointly provide electrical energy to the system. At this time, the second reverse-biased diode is in the forward-biased state, and the current path is: green energy device → second reverse-biased diode (anode → cathode) → energy storage unit, enabling independent charging of the energy storage unit by the green energy source. The energy storage unit is charged independently by the green energy device; the power unit does not participate in charging the energy storage unit.

[0056] Therefore, during the charging of the energy storage unit by the green energy source, the energy of the energy storage unit will not flow back to the green energy device due to the presence of the second anti-reverse diode.

[0057] Example 2: Figure 3 and Figure 7 As shown, this invention also provides a collaborative fault protection method for HVDC systems, applied to the aforementioned system. When the system is operating normally, each energy storage unit is in hot standby mode, maintaining full charge through float charging or supplementary charging via power units (i.e., conventional grid scenarios or green energy devices, i.e., green electricity scenarios). When the system detects a branch fault, the following collaborative protection process is executed: S1 When any branch in the system fails, the intelligent circuit breaker of that branch will detect in real time whether a fault current has occurred in the branch, and generate a disconnection request signal after detecting the fault current. The intelligent circuit breaker in S2 sends the disconnection request signal to the power unit, and the power unit receives the disconnection request signal. After receiving the cut-off request signal, the power unit described in S3 immediately cuts off the DC output, causing the current in the entire DC circuit to drop rapidly to near zero, entering a period of no current. The energy storage unit described in S4 starts to supply power after detecting the disappearance of the current in its branch, and supplies power unidirectionally to the corresponding load through the connection point, so as to maintain the normal operation of the load in the non-faulty branch during the period when the power unit cuts off the DC output. After detecting the disappearance of the current in the branch, the intelligent circuit breaker described in S5 performs a tripping operation during the period of no current, cutting off the electrical connection between the faulty branch and the power unit. After the intelligent circuit breaker described in S6 completes the tripping operation, the power unit automatically restores DC output after a preset time, and other non-faulty branches regain power supply, while the faulty branches remain de-energized because the intelligent circuit breaker has been tripped. After detecting that the power unit has resumed DC output, each of the energy storage units in S7 automatically stops supplying power, exits the operating state, and the system returns to normal power supply mode.

[0058] Based on the above method flow, this embodiment implements fault handling in the following ways, including: Step 1: Fault Detection. When a fault occurs in any branch of the system, the controllable switch of that branch continuously detects whether a fault current has appeared in the branch. The built-in or external current detection element of the controllable switch continuously collects the branch current signal. When the current value exceeds the preset fault current threshold, it is determined that a short circuit fault has occurred in the branch, and a disconnection request signal is generated after detecting the fault current.

[0059] Step 2: Signal Transmission. The communication module of the controllable switch sends a cut-off request signal to the power unit via fiber optic communication. The transmission delay of fiber optic communication is in the microsecond range (μs), far smaller than the millisecond time window of other stages in the fault handling process. The transmission delay of the fault signal is negligible, ensuring that all relevant components can receive the signal synchronously. It should be noted that this embodiment utilizes the low-latency characteristics of fiber optic communication to achieve system-level coordinated control, rather than basing its invention on fiber optic communication technology itself.

[0060] Step 3: Power Cut-off. Upon receiving the cut-off request signal, the power unit immediately controls its internal AC / DC converter to stop working or controls the isolating switch Q1 to open, cutting off the DC output and causing the current in the entire DC circuit to rapidly drop to near zero, entering a current-free period. The cut-off duration is preferably 10ms to 20ms, which can be adjusted according to the system configuration. This time window is sufficient for the DC circuit current to drop to near zero.

[0061] like Figure 6 The time curve of this scheme is shown in the figure, with the horizontal axis representing time. t The unit is milliseconds (ms), representing the time axis from the moment the fault occurred; the vertical axis is the fault branch current I, in amperes (A), representing the current change curves of the corresponding branches in each scheme after the fault occurred. The solid line represents the fault current waveform of this scheme, while the dashed line represents the conventional scheme, i.e., the existing technology scheme represented by publication number CN104009452A in the background art, which uses a traditional DC circuit breaker to directly interrupt the fault current waveform under current conditions. The figure also marks the "low-voltage arcing interval," referring to the time period in the conventional scheme where the circuit breaker contacts continue to arc and the current cannot be effectively interrupted.

[0062] from Figure 6 The fundamental difference between the two solutions in terms of fault handling timing is clearly visible: exist tAt 0ms, a short-circuit fault occurs in the system, and the fault current in both branches begins to rise rapidly. In this scheme, the controllable switch of the faulty branch immediately sends a disconnection request signal to the power unit via fiber optic communication after detecting the fault current. Due to the microsecond-level transmission delay of fiber optic communication, the power unit completes the DC output disconnection in about 10ms, and the fault current rapidly drops to near zero, entering a current-free state. In contrast, in the conventional scheme, the circuit breaker is still in an arcing state at the same time point, and the arc between the circuit breaker contacts continues to burn, failing to effectively disconnect the fault current.

[0063] Therefore, the time from the occurrence of the fault to the completion of the power unit's disconnection in this step is approximately 10ms. Within these 10ms, this scheme has already entered a current-free state. That is, in this scheme, from the occurrence of the fault to the completion of the power unit's disconnection, it takes approximately 10ms; from the completion of the current-free tripping of the controllable switch, it takes approximately 20ms; and from the resumption of output by the power unit, it takes approximately 20ms. The entire fault handling cycle is completed within 20ms. The energy storage unit's self-sustaining power supply time is no less than 1 second, approximately 50 times the fault handling cycle, providing ample margin for various extreme situations. In contrast, conventional schemes use traditional DC circuit breakers to directly disconnect under current conditions while still in an arcing state at the same time point, with the arc between the circuit breaker contacts continuing to burn and the contacts continuously subjected to high-temperature erosion. A significant difference already exists between the two schemes within the first 10ms after the fault occurs.

[0064] During the period of no current after the power is cut off, the states of each diode change. The first reverse protection diode is in a state of no current flow because the main circuit current disappears; for the branch equipped with the green energy device and the second reverse protection diode, the voltage of the energy storage unit is higher than the voltage of the green energy side, and the second reverse protection diode is in a reverse cut-off state, physically blocking any current path from the energy storage to the green energy side.

[0065] Step 4: Energy Storage Start-up and Power Supply. Each energy storage unit automatically starts up after detecting the disappearance of the current in its branch. When the energy storage controller detects that the bus voltage has dropped below the output voltage of the energy storage unit, the energy storage unit supplies power unidirectionally to the corresponding load through the connection point. At this time, the output voltage of the energy storage unit is higher than the bus voltage, the first reverse protection diode turns forward, and the current direction is energy storage → load. The energy storage current path is: energy storage unit → connection point → load. Due to the presence of the first reverse protection diode, the energy of the energy storage unit is limited to the load side and will not be fed back to the power unit side.

[0066] At this time, the energy storage unit only supplies power to the load of the corresponding branch, without supplying power to other branches or feeding back energy to the power unit. The self-sustaining power supply time of the energy storage unit is no less than 1 second, which is much longer than the complete fault handling cycle from power disconnection to restoration, i.e., power disconnection 10-20ms + circuit breaker tripping + power restoration 10-20ms. ms The total cycle is usually less than 100 ms Sufficient engineering margins are provided for various extreme situations, such as communication retransmission, circuit breaker operation delays, and system redundancy assessments. This ensures that the loads of non-faulty branches continue to operate normally while the power unit disconnects the DC output.

[0067] For branches equipped with green energy devices and second anti-reverse diodes, when the energy storage unit supplies power to the corresponding load, the second anti-reverse diode is in a reverse cut-off state, physically blocking the energy storage unit from feeding back power to the green energy device.

[0068] In this embodiment, the first and second reverse protection diodes can be selected from fast recovery diodes, ultra-fast recovery diodes, or silicon carbide Schottky diodes. As an example, the first reverse protection diode can be an 800V / 80A fast recovery diode of model VS-80APS08-M3, with a DC reverse withstand voltage of 800V, an average rectified current of 80A, and a forward voltage drop of 1.17V. The second reverse protection diode can be a device of the same series or specifications. The above models are merely illustrative examples; those skilled in the art can select other suitable diode models based on the branch current and system voltage level, such as a 1200V / 30A KSF30A120N or a 1700V / 32A silicon carbide Schottky diode SC6D10170H, as long as the current and withstand voltage requirements of the branch are met.

[0069] Step 5: No-current tripping. After detecting the disappearance of current in its branch, each controllable switch performs a tripping operation during the no-current period, disconnecting the electrical connection between the faulty branch and the power unit. Since there is no current in the branch during tripping, no arc is generated in the switch contacts, and no special arc-extinguishing design is required. Therefore, the controllable switches do not need to have DC fault current breaking capacity, and conventional low-cost circuit breakers or load switches can be used.

[0070] like Figure 6 As shown, in this scheme, the controllable switch has completed the tripping operation in approximately 20ms, the power unit has restored DC output, the non-faulty branch has restored normal power supply, and the system has completed fault clearing and resumed normal operation. The entire fault handling process is completed within 20ms. In contrast, the conventional scheme remains in an arcing state at the same 20ms point in time, and the circuit breaker is still attempting to interrupt the persistent fault current. The arcing interval in the conventional scheme may last for more than 100ms, during which the circuit breaker contacts are continuously subjected to high-temperature arc erosion until the contacts are completely separated and the arc is stretched to the point where it can no longer be sustained before the interruption can be completed. Therefore, the conventional scheme not only has a long fault clearing time, but the circuit breaker contacts also suffer severe thermal damage and electrical erosion during the arcing process that lasts for more than 100ms.

[0071] If the controllable switch fails to trip successfully after the current disappears for any reason, the fuse connected in series between the controllable switch and the corresponding load will blow due to the continuous fault current. The backup protection of the corresponding fuse will operate for approximately 50ms, physically isolating the faulty branch to ensure system safety. This time value is greater than the normal operating time of the main protection logic, i.e., the time for power disconnection + circuit breaker tripping is approximately 20ms, ensuring that the fuse will not malfunction when the main protection is operating normally.

[0072] Step 6: Power Restoration. After the controllable switch completes the tripping operation, the power unit automatically restores DC output after a preset time, preferably 10ms to 20ms, which is the same cutting-off duration as S3. Other non-faulty branches regain power, while the faulty branch remains de-energized because the controllable switch has been tripped.

[0073] Step 7: Energy Storage Deactivation. Each energy storage unit automatically stops supplying power and exits operation after detecting that the power unit has resumed DC output. The deactivation process is as follows: when the power unit resumes DC output and the bus voltage rises above the output voltage of the energy storage unit, the first anti-reverse diode naturally cuts off, switching from conduction to cutoff. The energy storage unit automatically stops supplying power, and the system returns to normal power supply mode.

[0074] The states of the two diodes at each stage of fault handling are shown in the table below:

[0075] Therefore, the first anti-reverse diode performs conduction / cutoff control in two directions throughout the fault handling process: after the power is cut off in step 3, it allows the energy storage to supply power to the load while blocking the energy storage from flowing back to the grid side; after the power is restored in step 7, it naturally cuts off due to the rise in bus voltage, allowing the energy storage to automatically exit. The second anti-reverse diode remains in a reverse cutoff state in steps 4 and 7, ensuring that the energy storage does not flow back to the green energy device side.

[0076] As can be seen, this embodiment shifts from a permanent power cut-off to an active control strategy of recovery after temporary disconnection, and introduces branch-level distributed energy storage to provide uninterrupted power supply to non-faulty branches during power cut-off, changing the circuit breaker tripping condition from current-carrying tripping to current-free tripping, thereby allowing the use of conventional low-cost circuit breakers to replace expensive hybrid or solid-state circuit breakers.

[0077] This embodiment also provides an electronic device, including: a processor, a storage medium, and a bus. The storage medium stores machine-readable instructions executable by the processor. When the electronic device is running, the processor communicates with the storage medium via the bus, and the processor executes the machine-readable instructions to perform the steps of the HVDC system fault collaborative protection method as described in Embodiment 2.

[0078] Finally, this embodiment also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the HVDC system fault collaborative protection method described in Embodiment 2.

[0079] The device embodiments described above are merely illustrative. The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0080] Through the detailed description of the above embodiments, those skilled in the art can clearly understand that each implementation can be achieved by means of software plus necessary general-purpose hardware platforms, and of course, it can also be achieved by hardware. Based on this understanding, the above technical solutions, in essence or the parts that contribute to the prior art, can be embodied in the form of software products. These computer software products can be stored in computer-readable storage media, including read-only memory, random access memory, programmable read-only memory, erasable programmable read-only memory, programmable read-only memory, electronically erasable rewritable read-only memory, read-only optical disc or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium capable of having or storing data.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0082] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations to the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A collaborative HVDC system incorporating distributed energy storage, characterized in that, The system includes: At least one intelligent power supply unit, wherein the input terminals of each intelligent power supply unit are respectively connected in parallel to an AC bus, and the intelligent power supply unit includes: A power unit, whose input terminal is connected to the AC bus, is used to convert AC power into DC power output. Multiple controllable switches are provided, with the input terminals of each controllable switch connected in parallel to the output terminal of the power unit. The power unit is communicatively connected to each controllable switch. Each controllable switch is configured to send a cut-off request signal to the power unit when a fault is detected in its branch. The power unit is configured to cut off the DC output after receiving the cut-off request signal and restore the DC output after a preset time. Multiple loads, each of which is connected to the output terminal of a corresponding controllable switch; Multiple energy storage units, each of which is connected in parallel with a corresponding load at a connection point, and the connection point is electrically connected to the output terminal of a corresponding controllable switch; Multiple first anti-reverse diodes are connected in series between the output terminal of the controllable switch and the connection point. The anode of the first anti-reverse diode is connected to the controllable switch side, and the cathode is connected to the parallel connection point side. The first anti-reverse diode is configured to allow current to flow from the power unit side to the load side and block current from flowing from the load side to the power unit side.

2. The collaborative HVDC system with distributed energy storage according to claim 1, characterized in that, The controllable switch is an intelligent circuit breaker.

3. The collaborative HVDC system with distributed energy storage according to claim 1, characterized in that, The controllable switch includes a load switch, a current detection element, and a communication module, which are connected in series. The current detection element is used to detect the current of its branch in real time, and outputs a trigger signal when a fault current is detected, and outputs a current disappearance signal when the current disappears. The communication module is communicatively connected to the power unit, and is used to send a disconnection request signal to the power unit when the trigger signal is received, and to control the load switch of the corresponding branch to perform tripping when the current disappearance signal is received.

4. The cooperative HVDC system with distributed energy storage according to any one of claims 1-3, characterized in that, Each energy storage unit is configured in a one-to-one correspondence with a corresponding load, and each energy storage unit supplies power only to the load of the corresponding branch.

5. The collaborative HVDC system with distributed energy storage according to any one of claims 1-3, characterized in that, It also includes green energy devices, which are configured one-to-one with the smart power supply units and are used to charge each of the energy storage units in the corresponding smart power supply units.

6. The collaborative HVDC system with distributed energy storage according to claim 5, characterized in that, It also includes multiple second anti-reverse diodes, with the anode of each second anti-reverse diode connected to the green energy device side and the cathode connected to the corresponding energy storage unit side.

7. A method for collaborative fault protection in an HVDC system, characterized in that, It is applied to the collaborative HVDC system with distributed energy storage as described in claim 2, and the method includes the following steps: S1 When any branch in the system fails, the intelligent circuit breaker of that branch will detect in real time whether a fault current has occurred in the branch, and generate a disconnection request signal after detecting the fault current. The intelligent circuit breaker in S2 sends the disconnection request signal to the power unit, and the power unit receives the disconnection request signal. After receiving the cut-off request signal, the power unit described in S3 immediately cuts off the DC output, causing the current in the entire DC circuit to drop rapidly to near zero, entering a period of no current. The energy storage unit described in S4 starts to supply power after detecting the disappearance of the current in its branch, and supplies power unidirectionally to the corresponding load through the connection point, so as to maintain the normal operation of the load in the non-faulty branch during the period when the power unit cuts off the DC output. After detecting the disappearance of the current in the branch, the intelligent circuit breaker described in S5 performs a tripping operation during the period of no current, cutting off the electrical connection between the faulty branch and the power unit. After the intelligent circuit breaker described in S6 completes the tripping operation, the power unit automatically restores DC output after a preset time, and other non-faulty branches regain power supply, while the faulty branches remain de-energized because the intelligent circuit breaker has been tripped. After detecting that the power unit has resumed DC output, each of the energy storage units in S7 automatically stops supplying power, exits the operating state, and the system returns to normal power supply mode.

8. The HVDC system fault collaborative protection method according to claim 7, characterized in that, Step S2 of the method also includes: When the power unit is in normal power supply mode, the energy storage unit is in hot standby mode and is charged by the power unit or green energy device. The first anti-reverse diode is in reverse cutoff mode, and the energy storage unit does not supply power to the load of the corresponding branch.

9. The HVDC system fault collaborative protection method according to claim 7, characterized in that, Step S2 of the method also includes: The intelligent circuit breaker sends the disconnection request signal to the power unit through a communication connection, which is an optical fiber communication connection. The disconnection request signal is also broadcast synchronously to the power unit corresponding to the faulty branch and other non-faulty branches through the optical fiber communication connection.

10. The HVDC system fault collaborative protection method according to claim 7, characterized in that, Step S4 further includes: When the energy storage unit supplies power to the corresponding load in one direction, the second anti-reverse diode is in a reverse cutoff state, blocking the energy storage unit from feeding back electrical energy to the green energy device.

11. The HVDC system fault collaborative protection method according to claim 7, characterized in that, Step S5 of the method further includes: When the intelligent circuit breaker fails to trip successfully during the period without current, the fuse connected in series between the intelligent circuit breaker and the corresponding load will blow due to the continuous fault current, thereby cutting off the faulty branch.

12. The HVDC system fault collaborative protection method according to claim 7, characterized in that, In step S7, the energy storage unit exits the operating state in the following way: When the power unit resumes DC output and the bus voltage rises to a level higher than the output voltage of the energy storage unit, the first anti-reverse diode naturally cuts off, and the energy storage unit automatically stops supplying power.

13. An electronic device, characterized in that, include: The device includes a processor, a storage medium, and a bus, wherein the storage medium stores machine-readable instructions executable by the processor, and when the electronic device is running, the processor communicates with the storage medium via the bus, and the processor executes the machine-readable instructions to perform the steps of the HVDC system fault cooperative protection method as described in any one of claims 7 to 12.

14. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, performs the steps of the HVDC system fault collaborative protection method as described in any one of claims 7 to 12.

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