Parallel topology system and method for transformation of direct current system for stock station

Abstract

The invention discloses a parallel topology system and method for transformation of a direct current system for a stock station, and belongs to the technical field of direct current power supply systems for stations. According to the topology, reliability modeling analysis calculation is carried out on station direct current schemes such as a conventional series power supply, a typical design scheme parallel power supply, a guard power supply and grouped parallel power supplies with different topologies, and the requirements that the transformation period is shortened as much as possible and original equipment is utilized as much as possible in a stock station transformation scene are comprehensively considered. Functionally, on one hand, a storage battery pack virtual connection self-identification and bridging protection circuit under the locking working condition is designed in the DC / DC management module, so that the output capacity of a direct-current power supply system is still maintained under the extreme working conditions that all parallel parts are locked and virtual connection defects exist in a follow current loop and the follow current loop is fused, important primary equipment protection is effectively tripped off, and the service life of the storage battery pack is prolonged; and fault expansion is prevented. And on the other hand, a large-current connectivity test function is designed, so that virtual connection hidden dangers which are difficult to perceive by conventional inspection can be found in time in operation and maintenance.

Description

Technical Field

[0001] This invention belongs to the technical field of DC power supply systems for power stations, and specifically relates to a parallel topology system and method for upgrading existing DC power supply systems for power stations. Background Technology

[0002] Traditionally, 110kV substations typically use a single-cell series connection for their DC auxiliary power systems. This requires extremely high battery consistency; a single battery failure can cause the entire battery pack to fail, posing a serious safety hazard. Furthermore, the high consistency requirement for individual battery configurations means that inconsistencies in individual battery performance can lead to reduced energy output.

[0003] In recent years, technologies such as parallel power supply have emerged to improve the reliability of traditional substation DC power supply systems. However, parallel solutions are designed for newly built substations, and there is currently a lack of retrofitting solutions suitable for improving the reliability of existing substation DC power supply systems. On the one hand, many existing substations have been in operation for a long time and bear important loads, making it difficult to schedule sufficient outage time for overall parallel conversion of their DC power supply systems. On the other hand, retrofitting existing substations using existing new substation DC power supply solutions requires dismantling abandoned original charging devices, feeder panels, batteries, and other main equipment. This abandoned equipment may still be functional, resulting in significant waste and increasing retrofitting costs.

[0004] Regarding upgrade needs, the existing substations urgently requiring upgrades are those with a 110kV "single-battery, single-charger" DC station service system. Higher voltage level substations generally use "two-battery, two-charger" or "two-battery, three-charger" DC station service power supply schemes, which inherently possess redundant backup power configurations. Even in the event of a single battery failure, another battery can still provide power output. However, for 110kV substations with a "single-battery, single-charger" configuration, current regulations stipulate that only critical 110kV substations can adopt a "two-battery, two-charger" configuration. Most other 110kV substations can only use a single-battery configuration. For these substations, if a single battery fails, the DC station service system loses its power supply capability, resulting in weak operational resilience and an urgent need for reliability improvements.

[0005] In parallel power supply systems, a "freewheeling circuit" is commonly used as an emergency backup power source to handle emergencies such as lightning strikes on the DC bus that cause all parallel management modules to be locked out. The principle of the freewheeling circuit is to change the original parallel output of the batteries to series output after all parallel management modules are locked out. However, in substations with long operating times, the battery connections are prone to loose connections, which are difficult to detect through routine inspections. If a loose connection exists between the batteries, in extreme fault conditions requiring the freewheeling circuit to be activated, the series circuit in the circuit may melt due to the large current, preventing the freewheeling circuit from outputting power. Since the freewheeling circuit is the last line of defense after a power outage in the parallel system, if it fails to output power due to a loose connection, all primary equipment protection systems in the substation will fail to operate, causing the fault range to expand and resulting in significant economic losses. Therefore, the strategy of relying solely on the freewheeling circuit for power supply after all management modules are locked out poses a serious safety hazard.

[0006] Regarding reliability assessment, the current topology design of parallel battery systems still relies on experience, and there is a lack of reliability analysis methods for different topologies of parallel battery systems. Quantitative reliability analysis data cannot be referenced in system topology design. Therefore, for existing 110kV substations with a "single-battery, single-charger" configuration, a targeted reliability-enhancing topology upgrade solution is needed. This solution should prioritize superior reliability among different parallel power supply topologies while minimizing the upgrade period and maximizing the reuse of existing equipment in old substation upgrade scenarios. Furthermore, it should address extreme fault conditions faced by the substation's DC system, such as complete system parallel blockage and failure of the final power supply guarantee circuit due to a loose connection, ensuring the system's output capability is maintained. Summary of the Invention

[0007] The purpose of this invention is to provide a parallel topology system and method for upgrading existing DC systems in substations, so as to overcome the technical problems of high cost and insufficient reliability of the follow current circuit in the upgrading of existing 110kV substation DC systems.

[0008] To solve the above problems, the present invention adopts the following technical solution: A parallel topology system for upgrading the DC system of an existing power station includes multiple battery groups connected in parallel. Each battery group is connected to a DC bus through a DC / DC group management module. A feeder branch and a charging device are connected to the DC bus. A freewheeling circuit is also provided between the DC bus and the battery group. The DC / DC group management module has a built-in circuit for self-identification of loose connection defects and protection against cross-connections.

[0009] Furthermore, the freewheeling circuit includes multiple battery groups and a freewheeling diode connected in series with the multiple battery groups.

[0010] Furthermore, the self-identification and bridging protection circuit for the virtual connection defect is located on the battery side of the DC / DC group management module and is electrically isolated from the DC bus side of the DC / DC group management module.

[0011] Furthermore, a protection diode is installed in the self-identification and bridging protection circuit for virtual connection defects.

[0012] Secondly, a method for upgrading existing substation DC systems is provided, including: Based on reliability analysis, the parallel topology system structure is modeled and calculated to obtain the optimal number of batteries in a single group. Each battery group is connected to the DC bus through a DC / DC group management module. A freewheeling circuit is connected in series between the DC bus and the battery group; The DC / DC group management module has a built-in circuit for self-identification of loose connection defects and protection of cross-connection. If there is a loose connection defect in the battery group, the circuit for self-identification of loose connection defects and protection of cross-connection will be activated to form a cross-connection circuit and ensure the output of the freewheeling circuit. High-current continuity testing was performed on each battery group.

[0013] Furthermore, the existing substation is a 110kV existing substation. The battery group is set up with 9 groups, each group including 12 batteries. Each group has a voltage of 24V. The 9 battery groups are evenly distributed and arranged in 3 cabinets, of which 8 battery groups are set in the freewheeling circuit.

[0014] Furthermore, reliability modeling and analysis calculations are performed on the parallel topology system structure based on the fault tree analysis method.

[0015] Furthermore, the reliability modeling and analysis calculations include: Model the key components of the station DC system; Top-event failure paths are constructed in the model for traditional series, conventional parallel, protection power supply, and various grouped parallel topologies, respectively. Taking into account multiple failure modes, the failure probability of each top event is calculated.

[0016] Furthermore, the high-current continuity detection includes: The DC / DC group management system controls a single battery group under test to perform adaptive current discharge to the DC bus, while the remaining battery groups remain in hot standby mode. The test current is 40A-80A, and the test time is 1 minute.

[0017] Furthermore, the high-current connectivity test is conducted prior to the nuclear capacity test.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention proposes a parallel power supply topology scheme that is highly reliable, economical, and feasible, particularly suitable for the retrofitting of existing 110kV substations, by performing reliability modeling and analysis calculations on various station DC power supply schemes, including conventional series, parallel, backup power, and grouped parallel topologies. Based on the grouped parallel topology, a self-identification and bridging protection strategy for loop connection defects in the parallel part of the parallel station DC power supply under fully blocked conditions is proposed. Compared with conventional station DC power supply schemes, this invention has the following advantages: (1) Superior reliability: Through modeling analysis and calculation, the station DC system proposed in this invention, consisting of 12 2V batteries connected in series to form a 24V group and 9 groups connected in parallel, significantly improves the system failure rate compared to conventional series, parallel, and protection power supply topologies. It also offers superior reliability compared to common grouped topologies of 12V and 48V groups. (2) High economic efficiency and feasibility of implementation: The parallel battery system with topology proposed in this invention occupies a total of 3 cabinets, which is the same number of cabinets as the existing 110kV substation "single battery, single charge" system with 104 batteries, and can be retrofitted in place in the substation cabinet room. At the same time, the existing batteries, charging devices, feeder devices and other components can be fully utilized; (3) Preventing backup power supply circuits from failing to operate under extreme conditions due to loose connections: The circuit loose connection defect self-identification and bridging protection strategy provided by this invention can ensure that the freewheeling circuit with loose connections still has the ability to output power, avoiding the failure of the last power supply guarantee of the station DC system caused by the common defect of loose battery connections. At the same time, the design of a high-current continuity test can effectively detect loose battery connection defects that are difficult to be exposed in the normal operation of DC power supply or discovered through daily inspections. Attached Figure Description

[0019] Figure 1 This is a diagram of a parallel topology system structure for upgrading an existing DC system in a power station, as described in an embodiment of the present invention. Figure 2 This is a schematic diagram of a parallel topology system for upgrading existing DC systems in a substation, as described in an embodiment of the present invention. Figure 3 This is a schematic diagram of a self-identification and bridging protection strategy for loop connection defects in the parallel section of a parallel-type DC power supply under fully blocked operating conditions. Detailed Implementation

[0020] To make the technical problems solved by the present invention, the technical solutions, and the beneficial effects clearer, the following specific embodiments provide a further detailed description of the present invention. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of the invention.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0023] A parallel topology system for retrofitting existing substation DC systems, such as Figure 1 As shown, the system includes multiple battery groups connected in parallel. Each battery group is connected to the DC bus via a DC / DC group management module. A freewheeling circuit is provided between the DC bus and the battery groups. In the current topology, if all DC / DC group management modules fail and are locked out, the freewheeling circuit needs to be activated. It is evident that different battery groups are connected in series to form a freewheeling circuit, while maintaining circuit connections to the locked-out DC / DC group management modules on both sides of each group. On the battery side of the DC / DC group management module, a built-in self-identification and bridging protection circuit for loose connections is designed, such as... Figure 2 As shown, if a loose connection defect in one of the managed battery groups is blown by a high current, the voltage across the protection circuit rises, causing the protection circuit to conduct and forming a jumper circuit. This jumpers the battery group with the loose connection defect away from the freewheeling circuit. This ensures that the freewheeling circuit with the loose connection defect still maintains its power output capability, preventing the failure of the last line of defense for the station's DC system caused by the common defect of loose battery connections.

[0024] Optionally, this invention targets a 110kV substation with a "single battery, single charging" configuration. The parallel topology system includes an AC input and switching circuit, an AC-DC conversion module (charging device), a DC bus, nine independent battery groups, nine DC / DC group management modules, a freewheeling circuit, and feeder branches. By reusing existing batteries and adding a ninth group to ensure that the capacity of the upgraded batteries is not lower than that of the pre-upgrade series system, a topology is formed with nine independent battery groups and nine DC / DC group management modules constituting nine parallel power supply redundancy channels that serve as backups for each other. Groups 1-8 are connected to the DC bus via series diodes, forming a freewheeling circuit with the DC bus operating voltage. The DC / DC group management module has a built-in self-identification and bridging protection circuit for loose connections on the battery side. This protection circuit is electrically isolated from the DC bus side via an isolation transformer. If a loose connection defect in one of the managed battery groups is blown by a large current, the voltage across the passive protection circuit rises, causing the protection circuit to conduct and forming a bridging circuit. This disconnects the battery group with the loose connection defect from the freewheeling circuit, maintaining the discharge path.

[0025] This invention also provides a method for retrofitting existing DC systems used in power stations, comprising: The aforementioned parallel topology system for upgrading existing substation DC systems includes: Based on reliability analysis, the parallel topology system structure is modeled and calculated to obtain the optimal number of battery groups. Each battery group is connected to the DC bus in parallel through a DC / DC group management module. A freewheeling circuit is connected in series between the DC bus and the battery sub-modules; The DC / DC group management module has a built-in circuit for self-identification and bridging protection of loose connections. If a loose connection defect in a battery group is melted by a large current, the circuit for self-identification and bridging protection of loose connections will be activated to form a bridging circuit and ensure the output of the freewheeling circuit. High-current continuity testing was performed on each battery group.

[0026] In detail, the modification method of this invention includes the following aspects: (1) A high-reliability grouped parallel topology scheme suitable for the retrofitting of existing station DC systems: This invention conducts reliability modeling and analysis calculations for grouped parallel topologies. Based on Fault Tree Analysis (FTA) and a voting gate model, the reliability calculation algorithm models key components of the station DC system, including AC links, switching circuits, DC buses and feeder branches, grouped parallel DC / DC management modules, and battery group degradation. The model constructs top-event failure paths for traditional series, conventional parallel, backup power supply, and various grouped parallel (12V / 24V / 48V) topologies, comprehensively considering failure modes such as AC loss, switching circuit failure, bus protection malfunctions combined with multiple feeder trips, inability of parallel groups to take over, and battery cell / group degradation. In the grouped parallel scheme, an "n-to-k" voting gate and dynamic programming algorithm are introduced to describe the impact of different voltage group numbers and redundancy thresholds on the system failure probability.

[0027] In the failure probability calculation of a grouped parallel system, the system has n parallel groups, and at least k groups need to be working normally to maintain the system power supply. When the failure probability of each group is p... group In this case, the system failure probability can be calculated using a voting gate. If all groups have the same failure probability, the system failure probability is calculated using a binomial distribution:

[0028] in, The total number of groups, The minimum number of normal packets required to maintain system power supply. This indicates the minimum number of failure groups required to cause a system failure. It is the combination number.

[0029] The top-event failure probability of a grouped parallel system is obtained by combining multiple failure paths using OR gates:

[0030] in For the first The probability of a failed path. This represents the total number of failure paths. The main failure paths include: simultaneous loss of both AC inputs. Switching circuit fault Busbar protection + multiple feeder trips Parallel grouping cannot be taken over .

[0031] In the above calculations, on the one hand, the 2V batteries, which are the most widely used in 110kV substations, are taken as an example. Typical DC / DC management module specifications on the market are substituted (i.e., a single group of 12 batteries in series at 24V, a single group of 6 batteries in series at 12V, and a single group of 24 batteries in series at 48V). On the other hand, the calculations are compared with current market solutions for protection power supplies (i.e., series input / output during normal operation, with parallel input in abnormal conditions), conventional parallel solutions (i.e., a topology where individual 12V batteries are connected in parallel and output through a three-in-one AC / DC / DC management module), and conventional series solutions (i.e., the topology where 104 batteries are connected in series and supplied in large quantities in 110kV substations). The calculation results are shown in Table 1. Table 1. Failure Rate Calculation by Topology Type of Station DC System

[0032] Based on modeling analysis and calculations, the reliability of the 24V DC / DC group in the above-mentioned station DC topology is higher than that of other topologies. The failure rate is reduced by 28.5 times compared to the conventional series scheme, by 10.2 times compared to the conventional parallel scheme, and by 8.4 times compared to the protection power supply scheme. The reliability is the highest among the parallel DC / DC module groups, with a failure rate reduced by 1.7 times compared to the 12V group and by 1.4 times compared to the 48V group.

[0033] Furthermore, considering the large number of parallel 12V groups in the DC / DC management module grouping, the grouping circuits would occupy more cabinet space. In the scenario of upgrading existing stations, the number of cabinets that can be upgraded is limited by the constraints of other functional cabinets in operation, and it usually does not support adding additional cabinets, making the feasibility of the solution low. Moreover, in terms of the aforementioned reliability, the 12V grouping is not optimal, so the 12V grouping topology is not adopted. As for the 48V grouping, the total number of parallel groups is relatively small. For the original 104 batteries in the existing station, on the one hand, it is necessary to add 48 batteries to form 3 parallel groups (new and old batteries cannot be mixed within the same group, and 8 of the original 104 batteries are discarded), which requires a large number of additional batteries and is not economical. On the other hand, in terms of reliability, the 48V grouping is not optimal, so this grouping topology scheme is excluded.

[0034] For the 24V battery grouping topology, reliability analysis shows that its failure probability is the lowest among the topologies mentioned, resulting in the best reliability. Furthermore, under this grouping topology, for the existing 104 batteries in the power station, only 12 additional batteries are needed to form a topology of 9 parallel groups totaling 108 batteries (new and old batteries cannot be mixed within the same group; 8 of the original 104 batteries are discarded). Each group has a voltage of 24V, offering good economic efficiency. Additionally, considering the conventional practice of 3 parallel groups occupying one cabinet, the 9 parallel battery groups system occupies 3 cabinets, the same number as the existing "single battery, single charging" system. Figure 1 As shown, in-situ renovation of the substation cabinet room is feasible. Simultaneously, existing components such as batteries, charging devices, and feeder systems can be fully utilized. Therefore, a scheme with 9 parallel groups of 12 batteries each (24V) is a reliable, feasible, and economical topology that can be widely adopted for the reliability improvement and parallel upgrading of existing 110kV "single battery, single charger" station DC systems.

[0035] In the topology: a) Parallel topology: Nine independent battery groups and nine DC / DC group management modules constitute nine parallel power supply redundancy channels that serve as backups for each other. A single failure will not affect the others. The reason for adding the ninth parallel module is to ensure that the battery capacity after the upgrade is not less than the total capacity of the original 104 batteries (if the ninth group is not added, the total number of batteries is 96, and the system battery capacity is lower than the original series system before the upgrade).

[0036] b) Regarding the freewheeling circuit: The freewheeling circuit is composed of groups 1-8. The reason is that if groups 1-9 were to form the freewheeling circuit, based on the nominal 2V battery's voltage of 2.25V under float charging, the total series voltage of the batteries in groups 1-9 would be 2.25 × 10⁸ = 243V when the freewheeling circuit is engaged, significantly higher than the DC bus operating voltage, posing a risk of damage to the bus feeder branch equipment. Therefore, with groups 1-8 forming the freewheeling circuit, the total series voltage of the batteries in groups 1-8 is 2.25 × 9⁶ = 216V when the freewheeling circuit is engaged, which is comparable to the DC bus operating voltage, ensuring safety.

[0037] (2) Self-identification and bridging protection strategy for loop connection defects under fully locked conditions: Currently, parallel power supplies are often equipped with a freewheeling circuit. This circuit consists of batteries connected in series in each group, connected to the DC bus via fuses, diodes, and disconnect switches. During normal operation, the freewheeling circuit is in the off state. When the bus voltage drops to the freewheeling circuit voltage, the diodes conduct, and the freewheeling circuit outputs power to the DC bus. When the bus voltage returns to normal, the diodes turn off, and the freewheeling circuit stops outputting power. Therefore, if at least one group of parallel modules can maintain output capability, the freewheeling circuit is in the off state. The freewheeling circuit only becomes active when all parallel modules are blocked by protection (e.g., due to a lightning surge current to the DC bus). Figure 3 As shown, the freewheeling circuit is switched to the on state.

[0038] However, in long-term operating substations, the battery connection links are prone to loose connections. While the system can maintain a small current output during normal operation, this defect can cause the loose connection to melt and fail during system faults requiring a large current output, leading to DC power supply failure. Therefore, this defect is difficult to detect during normal DC power supply operation or routine inspections.

[0039] To address the aforementioned issues, this invention proposes two main approaches. First, it addresses the parallel topology by proposing a self-identification and bridging protection strategy for loop connection defects under fully locked-out conditions. This strategy maintains the system's DC output capability even when the parallel section is fully locked out and the freewheeling circuit with connection defects is engaged. Second, it addresses routine maintenance by proposing a conventional testing strategy for high-current continuity detection, enabling the detection of battery connection defects during routine testing and maintenance.

[0040] 1) Self-identification and bridging protection strategy for loop connection defects: In the current topology, if all DC / DC group management modules fail and are locked out, the freewheeling circuit needs to be activated. This means that different battery groups are connected in series to form a freewheeling circuit, while both sides of each group maintain circuit connections to the locked-out DC / DC management modules.

[0041] Therefore, a built-in self-identification and bridging protection circuit for loose connections can be designed on the battery side of the DC / DC group management module. If a loose connection defect in one of the managed battery groups is blown by a large current, the voltage across the loose connection defect self-identification and bridging protection circuit will rise, causing the circuit to conduct and form a bridging circuit, thus disconnecting the battery group with the loose connection defect from the freewheeling circuit. This ensures that the freewheeling circuit with the loose connection defect still maintains its power output capability, avoiding the failure of the last line of power supply protection for the station DC system caused by the common defect of loose battery connections.

[0042] Specifically, the aforementioned self-identification and bridging protection circuit for loose connections should have the following characteristics: a) Electrical isolation is provided with the DC bus side circuit of the DC / DC group management module to prevent the fault current on the DC bus side from damaging the self-identification and bridging protection circuit for loose connection defects. This isolation function can be achieved through a protective isolation transformer. On the one hand, it maintains normal signal transmission between the battery side and the DC bus side of the management module during normal operation, and on the other hand, it can effectively isolate the impact of fault current on the other side. b) Self-generating identification of loose connections in the managed battery groups: Since the management module is locked when the jumper protection circuit needs to be activated, the built-in protection circuit needs to achieve self-generating identification of loose connections. This function can be achieved through a protection diode. If the connection status of the managed battery groups is normal, the voltage across the diode cannot reach the conduction voltage and remains in the off state. The discharge path is still the freewheeling circuit formed by all batteries connected in series. If a loose connection defect exists in the managed battery group and is melted by a large current, the voltage across the diode rises, causing the jumper circuit to conduct. The defective battery group is then jumpered out from the freewheeling circuit, and the discharge path is the jumper circuit and the freewheeling circuits on both sides of it.

[0043] 2) Conventional test strategies for high-current continuity testing: In substations operating for extended periods, inter-battery connections are prone to intermittent connections. While the system can maintain a small current output during normal operation, this defect can lead to current-induced failure and meltdown of the intermittent connection during system faults requiring high current output. Therefore, this defect is difficult to detect during routine operation or inspections. This invention addresses this problem by proposing a routine testing strategy for high-current continuity testing, enabling the detection of intermittent battery connections during routine maintenance.

[0044] a) Test Current: Since the purpose of this test is to verify the output capability of the station's DC power supply under fault conditions, requiring a large current output to activate all station protection systems (if there is a loose connection, the system will have a fuse defect under high current, preventing the output of a large current), considering the current requirements of the station's secondary protection systems (approximately 30A for a typical 110kV station) and the output current capability of commercially available DC / DC management modules, the preset value for the high-current continuity test current is 40A (0.2C) or higher. This can verify the station's protection system's current output capability, expose loose connection defects, and demonstrate the effectiveness of the test. Furthermore, the test current is within the output capability of existing commercially available DC / DC management modules, making it feasible.

[0045] b) Discharge Time: Since prolonged high-current discharge can cause irreversible damage to battery performance, the test time must be carefully controlled. Considering that the operation time of primary equipment protection in substations is typically on the order of seconds, plus the cascading coordination time and the interlocking time between different protection systems, a discharge time of 1 minute is sufficient to meet the substation protection operation requirements. At the same time, a discharge of 0.2C or higher for 1 minute has minimal impact on the battery's own performance. Therefore, the discharge time for the high-current continuity test can be preset to 1 minute.

[0046] c) Implementation Strategy: Considering that discharge tests of conventional series-topology substation DC systems generally require external temporary power supplies and electronic loads, the test wiring is complex, the cycle is long, and there is a risk of power loss. However, since the groups in a grouped parallel-topology substation DC system are mutually redundant, the control management module can maintain only a single group discharging to the DC bus, while the remaining groups are in hot standby (a single group outputs the current of the original 9 groups), achieving a high-current output with the DC bus of the substation DC system itself as the load. Simultaneously, the other 8 groups are in hot standby status. If a group undergoing a high-current test fails and the DC bus voltage drops, the hot standby group immediately engages to maintain the DC bus voltage. Therefore, in actual implementation, the high-current discharge current is an adaptive output current based on the DC bus load. Calculated for the DC bus load of a classic 110kV substation, this adaptive current is typically 40A-80A (0.2C-0.4C), which meets the high-current detection test current requirements. In practice, the high-current continuity test can be arranged before the battery verification charge-discharge test in the routine test. On the one hand, both are discharge tests and the battery verification charge-discharge is a routine test item with a fixed cycle. On the other hand, the activation effect of short-time high-current impulse discharge on the battery can be utilized to improve the accuracy of the battery capacity test.

[0047] This invention is based on reliability modeling and analysis of various station DC power supply schemes, including conventional series, parallel, backup power, and grouped parallel topologies. Considering the need to minimize the renovation period and maximize the reuse of existing equipment in existing station upgrades, this invention proposes a highly reliable grouped parallel topology scheme suitable for upgrading existing station DC power supply systems. Firstly, a battery pack misconnection self-identification and bridging protection circuit is designed in the DC / DC management module under locked-out conditions. This ensures that even under extreme conditions where all parallel connections are locked out and the freewheeling circuit has a misconnection defect causing a fuse blown, the DC power supply system's output capability is maintained, allowing the protection of critical primary equipment to trip effectively and preventing the fault from escalating. Secondly, a high-current continuity test function is designed to promptly detect potential misconnection hazards that are difficult to detect during routine inspections.

[0048] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A parallel topology system for upgrading existing DC power supply systems in substations, characterized in that, It includes multiple battery groups connected in parallel, each battery group is connected to a DC bus through a DC / DC group management module, the DC bus is connected to a feeder branch and a charging device, and a freewheeling circuit is also provided between the DC bus and the battery group; The DC / DC group management module has a built-in circuit for self-identification of loose connection defects and protection against cross-connections.

2. The parallel topology system for upgrading existing DC systems in power stations according to claim 1, characterized in that, The freewheeling circuit includes multiple battery groups and a freewheeling diode connected in series with the multiple battery groups.

3. The parallel topology system for upgrading existing substation DC systems according to claim 1, characterized in that, The self-identification and bridging protection circuit for the virtual connection defect is located on the battery side of the DC / DC group management module and is electrically isolated from the DC bus side of the DC / DC group management module.

4. The parallel topology system for upgrading existing substation DC systems according to claim 1 or 3, characterized in that, The circuit for self-identification and bridging of virtual connection defects is equipped with a protection diode.

5. A method for retrofitting an existing DC power station system, characterized in that, A parallel topology system for upgrading existing substation DC systems according to any one of claims 1-4 includes: Based on reliability analysis, the parallel topology system structure is modeled and calculated to obtain the optimal number of batteries in a single group. Each battery group is connected to the DC bus through a DC / DC group management module. A freewheeling circuit is connected in series between the DC bus and the battery group; The DC / DC group management module has a built-in circuit for self-identification of loose connection defects and protection of cross-connection. If there is a loose connection defect in the battery group, the circuit for self-identification of loose connection defects and protection of cross-connection will be activated to form a cross-connection circuit and ensure the output of the freewheeling circuit. High-current continuity testing was performed on each battery group.

6. The method for upgrading an existing DC system for a power station according to claim 5, characterized in that, The existing substation is a 110kV existing substation. The battery group is set up with 9 groups, each group includes 12 batteries, and each group has a voltage of 24V. The 9 battery groups are evenly distributed in 3 cabinets, and 8 of the battery groups are set in the freewheeling circuit.

7. A method for upgrading an existing DC power station system according to claim 5, characterized in that, The reliability modeling and analysis calculation of the parallel topology system structure is performed based on the fault tree analysis method.

8. A method for upgrading an existing DC power station system according to claim 7, characterized in that, The reliability modeling and analysis calculations include: Model the key components of the station DC system; Top-event failure paths are constructed in the model for traditional series, conventional parallel, protection power supply, and various grouped parallel topologies, respectively. Taking into account multiple failure modes, the failure probability of each top event is calculated.

9. A method for upgrading an existing DC power station system according to claim 5, characterized in that, The high-current continuity detection includes: The DC / DC group management system controls a single battery group under test to perform adaptive current discharge to the DC bus, while the remaining battery groups remain in hot standby mode. The test current is 40A-80A, and the test time is 1 minute.

10. A method for upgrading an existing DC system for a power station according to claim 5 or 9, characterized in that, The high-current continuity test was conducted prior to the nuclear capacity test.

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