Low-voltage distribution network closing loop zero power-off control method and system based on energy storage pre-regulation

Abstract

The application discloses a low-voltage distribution network loop closing zero power failure control method and system based on energy storage pre-regulation, and relates to the technical field of low-voltage distribution networks; the method comprises the following steps: acquiring real-time electrical quantity information on both sides of a loop closing point, and calculating voltage amplitude difference, phase angle difference and frequency difference; if the loop closing safety threshold is not met, issuing a regulation instruction to an existing network type energy storage device in a transformer area, actively pre-regulating by regulating the active power and / or reactive power of the energy storage device until the threshold is met and the synchronous closing is executed after a preset stable time; after the closing is successful, detecting the loop current amplitude, and if the threshold is exceeded, calling the energy storage device to inject a reverse compensation current to suppress the loop current; after the loop current is stabilized, executing load transfer and opening and breaking the loop. The application reuses the existing energy storage in the transformer area for pre-regulation, does not need to add a special converter, can realize zero power failure of users in the whole process of load transfer in the low-voltage transformer area, and has a remarkable inrush current suppression effect.

Description

Technical Field

[0001] This invention relates to the field of low-voltage distribution network technology, and in particular to a method and system for zero-outage control of low-voltage distribution networks based on energy storage pre-regulation. It is used in low-voltage distribution networks (400V) to achieve loop-loop operation and load transfer between adjacent distribution areas with the assistance of existing grid-type energy storage devices in the distribution areas. Background Technology

[0002] This invention relates to the field of low-voltage distribution network technology, specifically to a loop control method and system for low-voltage distribution networks, and more particularly to a technology that utilizes energy storage devices to assist in achieving zero-power-outage load transfer in low-voltage distribution areas.

[0003] Currently, urban low-voltage distribution networks (400V and below) generally adopt a radial open-loop operation mode, meaning that the low-voltage interconnection switches between adjacent transformer substations remain open, and each substation operates independently. This operation mode can meet the operational requirements in traditional distribution networks that are mainly characterized by unidirectional power flow. However, with the large-scale integration of new power sources such as distributed photovoltaic (PV) systems, energy storage systems, and electric vehicle charging piles, the operating characteristics of low-voltage distribution networks have undergone fundamental changes: the randomness and anti-peak-shaving characteristics of distributed PV power output lead to frequent voltage exceedances in transformer substations, and the disorderly charging behavior of electric vehicles exacerbates the problem of short-term overload of distribution transformers. Traditional radial networks lack inter-substation power flow mutual assistance mechanisms and are unable to cope with increasingly complex operating conditions.

[0004] In power distribution network maintenance or fault handling scenarios, traditional operating procedures follow a "power outage-switching-power restoration" process: first disconnecting the load switch on the side to be maintained, completing the switching operation, and then restoring power. This method inevitably causes short-term power outages on the user side, ranging from a few minutes to tens of minutes. For users with high requirements for power supply continuity, such as hospitals, data centers, and industrial parks, even a power outage of a few seconds can cause significant economic losses or safety accidents. Therefore, achieving uninterrupted transfer of low-voltage loads between distribution stations (i.e., "loop closing" operation) has become a key technological direction for improving power supply reliability.

[0005] Low-voltage side loop closing operations face more stringent technical constraints than those on medium- and high-voltage sides. On one hand, 400V systems have low line impedance and an extremely low X / R ratio (resistance to reactance), typically less than 0.5. Even a small difference in voltage amplitude or phase angle between the two sides of the loop closing point can trigger inrush currents of hundreds of amperes, or even exceeding the rated breaking capacity of the circuit breaker. On the other hand, low-voltage distribution networks lack system-level synchronous phasor measurement and coordinated control mechanisms. Existing loop closing operations largely rely on the experience-based judgment of maintenance personnel, resulting in low standardization, low success rates, and significant safety risks.

[0006] To address the aforementioned issues, some publicly available technologies have proposed solutions. Chinese patent document CN114123248A (publication date March 1, 2022) discloses a distribution network loop-closing control method based on a flexible multi-state switch. This method achieves voltage and frequency tracking at the loop-closing point by adding a SOP converter, thus suppressing inrush current. However, this solution requires additional dedicated power electronic converters, with a single unit costing hundreds of thousands to millions of yuan. Given the large number of low-voltage distribution areas, large-scale implementation faces significant economic bottlenecks. Furthermore, the SOP converter in this solution performs multiple functions, including loop closure, power flow regulation, and power quality management. The control algorithm is complex, making engineering implementation difficult, and the losses of the SOP device itself reduce the overall system operating efficiency. Another example is Chinese patent document CN115051368A (publication date September 13, 2022), which discloses a loop-closing operation decision-making method based on a distribution automation master station. This method centrally calculates loop-closing conditions and issues operation commands through the master station. However, this scheme heavily relies on the communication link between the master station and the terminal, with a decision latency typically exceeding 500 milliseconds. It cannot perform loop-closing operations in scenarios of communication anomalies or interruptions. Furthermore, the master station's centralized computing mode places extremely high demands on the accuracy of the entire network topology model; any parameter deviation can lead to misjudgment of loop closure. For example, Chinese patent document CN114256842A (publication date March 29, 2022) discloses a method for suppressing inrush current in low-voltage distribution networks by inserting a current-limiting reactor in series in the loop to limit the inrush current. However, the current-limiting reactor is bulky, increases line impedance, and continuously introduces additional voltage drop and power loss under non-loop-closing conditions. Moreover, the fixed impedance value of the current-limiting reactor cannot adapt to changes in inrush current levels under different operating conditions, resulting in poor flexibility.

[0007] In summary, existing technologies for achieving uninterrupted load transfer in low-voltage distribution networks either require the addition of expensive dedicated hardware, rely heavily on centralized communication architecture, or sacrifice operational economy by using passive current limiting methods. There is still no low-voltage loop control scheme that can fully utilize existing equipment resources in the distribution area, does not rely on centralized communication at the main station, does not require the addition of dedicated hardware, and can actively suppress inrush current. Summary of the Invention

[0008] In view of the problems mentioned above or existing solutions in low-voltage distribution network uninterrupted load transfer scenarios, such as the need to add expensive dedicated converters, reliance on centralized communication at the master station leading to poor real-time performance, and large inrush currents that easily trigger protection actions, this invention proposes a low-voltage distribution network closed-loop zero-outage control method and system based on energy storage pre-regulation.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method and system for zero-outage control of low-voltage distribution networks based on energy storage pre-regulation, comprising:

[0010] Applied to a system comprising a first distribution area, a second distribution area, and a connecting switch between the first distribution area and the second distribution area, wherein the first distribution area and the second distribution area are respectively equipped with a grid-type energy storage device;

[0011] The method includes:

[0012] S1: Obtain real-time electrical quantity information on both sides of the loop closure point, and calculate the voltage amplitude difference based on the real-time electrical quantity information. Phase angle difference and frequency difference ;

[0013] S2: Determine the voltage amplitude difference The phase angle difference and the frequency difference Whether the preset loop closure safety threshold is met; if not, an adjustment command is issued to the existing grid-type energy storage devices in the first and / or second distribution areas to actively pre-adjust the active and / or reactive power outputs of the grid-type energy storage devices to reduce the voltage amplitude difference. and the phase angle difference until the voltage amplitude difference The phase angle difference and the frequency difference All conditions are met, and the state remains stable for a preset time.

[0014] S3: After the loop closure safety threshold is met and the preset stabilization time is maintained, a closing command is sent to the interconnecting switch, and the closing operation is performed at the moment when the voltage instantaneous value difference on both sides of the loop closure point is the smallest.

[0015] S4: After successful closing, the circulating current amplitude in the closed loop is detected. If the circulating current amplitude exceeds the preset circulating current threshold, the grid-type energy storage device is invoked to inject a compensation current in the opposite direction of the circulating current into the closed loop until the circulating current amplitude is reduced to below the target value.

[0016] S5: After the circulating current amplitude stabilizes, perform a load transfer operation and issue a tripping command to the circuit breaker on the side to be disconnected to complete the loop disconnection.

[0017] Furthermore:

[0018] In the active pre-adjustment, the phase angle difference is adjusted by adjusting the active power output of the grid-type energy storage device. The voltage amplitude difference is adjusted by adjusting the reactive power output of the grid-type energy storage device. ;

[0019] The active power output regulation adopts a phase angle difference closed-loop control circuit, and the reactive power output regulation adopts a voltage difference closed-loop control circuit.

[0020] Furthermore:

[0021] The preset loop closure safety threshold includes: the voltage amplitude difference. ≤2%, the phase angle difference ≤5°, the frequency difference ≤0.05Hz; the preset stabilization time is 200ms.

[0022] Furthermore:

[0023] The voltage difference closed-loop control loop is a PI control loop, and its proportional coefficient is... and integral coefficient The setting is made according to the capacity of the distribution transformer in the first or second transformer area and the preset adjustment intensity mode;

[0024] For a distribution transformer with a capacity of 630kVA, under the balance regulation intensity mode, Take 14.5 , Take 41.4 .

[0025] Furthermore:

[0026] The closing operation is performed at the moment when the instantaneous voltage difference on both sides of the closing point is the smallest, specifically including:

[0027] Definition: Instantaneous value of differential pressure in closed loop ;

[0028] Based on real-time phasor estimation: the instantaneous value of the closed-loop differential pressure amplitude Frequency difference and phase angle difference Establish a mathematical model of differential pressure waveform ;

[0029] Predict the instantaneous value of the closed-loop differential pressure The next zero-crossing moment ;

[0030] Obtain the inherent closing time of the interconnecting switch. Calculate the timing of the closing pre-command. and in the The closing command is issued at all times.

[0031] Furthermore:

[0032] The detection of the circulating current amplitude in the closed loop specifically includes:

[0033] The current on the first side is collected by the measurement and control terminal of the first switch on both sides of the closed loop. Second side current Calculate circulation ;

[0034] The circulating current is transformed using the dq transform. Decomposed into the active component of the fundamental circulation and reactive components ;

[0035] The injected compensation current, which is opposite to the circulating current direction, specifically includes: issuing a compensation amount to the grid-type energy storage device. as well as ,in, This is the rated voltage.

[0036] Furthermore:

[0037] The target value for the circulating current amplitude is that the peak value of the circulating current is less than 5% of the rated current;

[0038] The convergence time for the circulation amplitude to decrease from exceeding the preset circulation threshold to below the target value is no more than 40ms.

[0039] A low-voltage precision closed-loop control system, the system comprising:

[0040] The regional autonomous controller, deployed on the transformer substation side, is used to acquire real-time electrical quantity information on both sides of the loop closing point, perform loop closing condition judgment, issue adjustment commands to the grid-type energy storage device, and issue closing commands to the loop closing control box;

[0041] The loop control box is deployed at the low-voltage tie line and has a built-in intelligent circuit breaker and synchronous closing controller. The synchronous closing controller is used to receive the closing command of the regional autonomous controller and drive the intelligent circuit breaker to close when the voltage instantaneous value difference on both sides of the loop point is the smallest.

[0042] A communication interface connects the regional autonomous controller and the grid-type energy storage device, and is used to transmit active power regulation commands and reactive power regulation commands.

[0043] Furthermore:

[0044] The regional autonomous controller and the closed-loop control box, as well as the regional autonomous controller and the grid-type energy storage device, communicate peer-to-peer using the IEC61850 GOOSE protocol.

[0045] The decision latency of the regional autonomous controller is less than 100ms;

[0046] The loop control box also includes a waveform recording module, which is used to record current waveforms and voltage waveforms throughout the closing and opening process, with a sampling rate of not less than 100 kSa / s.

[0047] Furthermore:

[0048] The method is applied to load switching with zero power outage in planned maintenance scenarios, or to emergency power switching in fault scenarios.

[0049] In the emergency power transfer scenario, the loop closing operation is triggered by the local autonomous decision of the regional autonomous controller, without waiting for instructions from the master station;

[0050] The method also includes a failure handling security strategy:

[0051] If the loop closure safety threshold is not met within the preset timeout period after the start of the active pre-adjustment, the operation will be terminated.

[0052] If the circulating current amplitude exceeds the emergency tripping threshold after successful closing, the circuit will immediately trip and lock.

[0053] If the communication of the grid-type energy storage device is interrupted, it will be downgraded to a passive synchronous closing mode without pre-adjustment.

[0054] The beneficial effects of this invention are as follows:

[0055] First, the present invention directly reuses the existing grid-type energy storage devices in the distribution area as active pre-regulation execution units, without the need to add new flexible multi-state switches (SOPs) or current-limiting reactors and other special hardware equipment. This fundamentally avoids the problem of the existing technology requiring the addition of hundreds of thousands to millions of yuan worth of special equipment, greatly reducing the economic threshold for the loop-connection transformation of low-voltage distribution networks and facilitating large-scale promotion and deployment.

[0056] Secondly, this invention actively changes the line voltage drop and power flow distribution to reduce the phase angle difference by regulating the active power of energy storage, and actively changes the bus voltage amplitude to reduce the voltage difference by regulating the reactive power of energy storage. It actively adjusts the loop closing conditions from an unsatisfied state to a satisfied state, without having to passively wait for the natural loop closing window. This avoids the problem of loop closing failure caused by the failure to meet the set synchronization conditions in the existing master station centralized control scheme.

[0057] Third, the present invention uses a synchronous closing algorithm based on zero-crossing prediction, combined with the inherent operating time compensation of the circuit breaker, to control the closing timing error within 1 millisecond. With the help of energy storage pre-regulation, the peak value of the closing inrush current is reduced from 410 amperes in traditional direct closing to 70 amperes, a reduction of 83%. This effectively solves the inherent problem of low voltage systems with low X / R ratio and large inrush current during closing, and greatly improves the safety of closing operation.

[0058] Fourth, this invention adopts a control architecture that prioritizes local closed-loop decision-making by the regional autonomous controller and supplements it with master station monitoring. The judgment of loop closing conditions, the issuance of energy storage regulation commands, and the control of closing timing are all completed within the local regional autonomous controller, with a decision delay of less than 100 milliseconds. In emergency power transfer scenarios, the system can autonomously complete the loop closing and power transfer without waiting for master station commands. The time from fault detection to load transfer completion is no more than 2 seconds, far superior to the recovery time of several minutes caused by communication dependence in traditional master station centralized control schemes.

[0059] Fifth, this invention continuously monitors the circulating current after the circuit is closed, and decomposes the circulating current into active and reactive components through dq transformation. Reverse compensation commands are then sent to the energy storage on both sides to achieve decoupling and suppression of the active and reactive components of the circulating current. The circulating current suppression time does not exceed 40 milliseconds, and the suppression target is to reduce the peak value of the circulating current to less than 5% of the rated current, ensuring that the system quickly returns to steady-state operation after the loop is closed.

[0060] Sixth, this invention constructs a unified closed-loop control framework covering multiple scenarios such as planned maintenance and emergency power transfer. In the planned maintenance scenario, the time from receiving the task to completing the power transfer is no more than 3 minutes with zero power outages throughout the process. In the emergency power transfer scenario, the user-perceived power outage time is reduced from the traditional 15 to 30 minutes to less than 2 seconds. At the same time, a graded safety response mechanism is established, including abnormal situations such as pre-adjustment timeout, circulating current exceeding limit, communication interruption, and measurement failure, which significantly improves the operational flexibility and power supply reliability of the low-voltage distribution network. Attached Figure Description

[0061] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 This is a schematic diagram of the topology of the low-voltage precision closed-loop control system of the present invention;

[0063] Figure 2 This is a schematic diagram of a typical topology of the low-voltage precision closed-loop control system of the present invention;

[0064] Figure 3 This is a schematic flowchart of the low-voltage precision closed-loop control method of the present invention;

[0065] Figure 4 This is a block diagram of the energy storage pre-regulation closed-loop control of the present invention;

[0066] Figure 5 This is a comparison diagram of the closed-loop current waveform of the present invention.

[0067] Figure label:

[0068] 1-First 10kV distribution transformer, 2-Second 10kV distribution transformer, 3-Tie switch (HCB)

[0069] 4-Regional autonomous controller, 51-First grid-type energy storage device, 52-Second grid-type energy storage device, 6-Loop control box, 7-First low-voltage bus, 8-Second low-voltage bus, 9-First low-voltage feeder, 10-Second low-voltage feeder, 11-Communication link. Detailed Implementation

[0070] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0071] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0072] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0073] Example 1

[0074] This embodiment is illustrated in conjunction with the accompanying drawings. Figure 1 and Figure 2 The specific embodiments of the present invention will be described in further detail;

[0075] like Figure 1 As shown, the low-voltage precision loop control system provided by the present invention is applied to a dual-transformer power supply area including a first transformer T1 and a second transformer T2. The 400V low-voltage busbars of the two transformer areas are connected by a low-voltage tie line, and a tie switch 3 is installed on the tie line.

[0076] The first transformer T1 is equipped with a first grid-type energy storage device 51 on the low-voltage bus side, and the second transformer T2 is equipped with a second grid-type energy storage device 52 on the low-voltage bus side.

[0077] The regional autonomous controller 4 is deployed on the transformer substation side, specifically in a box-type transformer or switch box. Its communication interface is connected to the loop control box 6, the first grid-type energy storage device 51, and the second grid-type energy storage device 52.

[0078] The loop closing control box 6 is deployed at the low-voltage tie line and has a built-in intelligent circuit breaker and synchronous closing controller. The regional autonomous controller 4 is used to acquire real-time electrical quantity information on both sides of the loop closing point, perform loop closing condition judgment, issue adjustment commands to the grid-type energy storage device, and issue closing commands to the loop closing control box 6.

[0079] The synchronous closing controller is used to receive the closing command from the regional autonomous controller 4 and drive the smart circuit breaker to close at the moment when the instantaneous voltage difference on both sides of the closing point is the smallest.

[0080] The first grid-type energy storage device 51 and the second grid-type energy storage device 52 are respectively connected to the low-voltage bus of the corresponding transformer area through their respective energy storage converters (PCS). The energy storage converters support decoupled independent control of active power and reactive power.

[0081] In this embodiment, the regional autonomous controller 4 and the closed-loop control box 6, and the regional autonomous controller 4 and the grid-type energy storage devices 51 and 52, use the IEC61850 GOOSE protocol for local peer-to-peer communication to ensure that the transmission delay of key control commands is less than 4ms.

[0082] The decision delay of the regional autonomous controller 4 is less than 100ms. The loop control box 6 is also equipped with a waveform recording module, which records the current waveform and voltage waveform throughout the entire closing and opening process, with a sampling rate of not less than 100kSa / s.

[0083] The closing time of the intelligent circuit breaker is no more than 80ms, and the opening time is no more than 50ms. The regional autonomous controller 4 adopts an industrial-grade ARM Cortex-A7 microcontroller with a main frequency of no less than 528MHz, runs the RT-Linux real-time operating system, has a task scheduling jitter of less than 1ms, and has communication interfaces including RS485 and Ethernet interfaces, and supports the IEC61850 protocol.

[0084] The closed-loop control box 6 also has a built-in 2Ah lithium iron phosphate backup power supply, ensuring continuous operation for 8 hours after AC voltage loss, and supports continuous operation of the switch opening and closing 3 times. The closed-loop control box 6 is also equipped with a local operation panel, supporting dual-mode switching between local manual operation mode and remote automatic operation mode.

[0085] Example 2

[0086] like Figure 3 As shown, the complete operation flow of the low-voltage precise loop-closing control method of the present invention is described in detail, including the following steps:

[0087] Step S1: The regional autonomous controller 4, through the voltage and current transformers in the loop control box 6, collects the voltage and current signals on both sides of the loop closure point in real time, with a sampling rate of 128 sampling points per power frequency cycle. Based on the collected real-time electrical quantity information, the regional autonomous controller 4 calculates the voltage amplitude difference on both sides of the loop closure point. Phase angle difference and frequency difference Specifically, voltage amplitude difference The difference between the effective values ​​of the voltages on both sides of the loop closure point, and the phase angle difference. The phase difference and frequency difference between the voltage phasors on both sides of the loop closure point. This represents the frequency difference between the two systems.

[0088] Step S2: Regional Autonomous Controller 4 determines the voltage amplitude difference. Phase angle difference and frequency difference Whether the preset loop closure safety threshold is met. The preset loop closure safety threshold includes: voltage amplitude difference. ≤2%, phase angle difference ≤5°, frequency difference ≤0.05Hz. If any of the above conditions are not met, the regional autonomous controller 4 issues adjustment commands to the existing grid-type energy storage devices 51 in the first substation and / or the existing grid-type energy storage devices 52 in the second substation. Active pre-adjustment is performed by adjusting the active power output and / or reactive power output of the grid-type energy storage devices to reduce the voltage amplitude difference. and phase angle difference During the active pre-adjustment process, the Regional Autonomous Controller 4 continuously monitors... , and The real-time value is used to dynamically adjust the energy storage output command, forming a closed-loop control until... , and All conditions meet the loop closure safety threshold and this state remains stable for a preset time. The preset stability time is 200ms.

[0089] Step S3: After the loop closure safety threshold is met and the system remains stable for a preset time of 200ms, the regional autonomous controller 4 sends a closing command to the loop closure control box 6. The synchronous closing controller in the loop closure control box 6 drives the smart circuit breaker to perform the closing operation at the moment when the instantaneous voltage difference on both sides of the loop closure point is the smallest.

[0090] Step S4: After the smart circuit breaker successfully closes, the regional autonomous controller 4 detects the circulating current amplitude in the closed loop. If the circulating current amplitude exceeds a preset circulating current threshold, the regional autonomous controller 4 calls the grid-type energy storage device 51 and / or 52 to inject a compensation current in the opposite direction to the circulating current into the closed loop until the circulating current amplitude is reduced to below the target value. The target value for the circulating current amplitude is that the peak value of the circulating current is less than 5% of the rated current. The convergence time for the circulating current amplitude to decrease from exceeding the preset circulating current threshold to below the target value is no more than 40ms.

[0091] Step S5: After the circulating current amplitude stabilizes, the regional autonomous controller 4 executes a load transfer operation, issuing a tripping command to the circuit breaker on the side to be disconnected, thus completing the loop disconnection. Specifically, it first confirms that the remaining current carrying capacity of the feeder on the transfer side meets the load transfer requirements and that the voltage deviation meets the preset standard. Then, it issues a tripping command to the circuit breaker on the side to be disconnected, switching the system from a closed-loop operation state to a new radial operation state. After tripping, it monitors the operating parameters of the first and second transformer areas to confirm successful load transfer. Finally, it uploads the entire process waveform data and operation timing record to the main station system.

[0092] Example 3

[0093] like Figure 4 As shown, it illustrates two parallel operating control loops: a phase angle difference control loop (active power control) and a voltage amplitude difference control loop (reactive power control).

[0094] This embodiment provides a detailed description of the specific implementation of the energy storage pre-regulation closed-loop control of the present invention;

[0095] Figure 4 In the phase angle difference adjustment circuit, the first phasor measurement unit 6 detects the phase angle of the first transformer area bus voltage in real time. The second phasor measurement unit 7 detects the phase angle of the second transformer area bus voltage in real time. The first subtractor 8 is based on and Calculate the measured phase angle difference .

[0096] The first comparator 2 will measure the phase angle difference. The target phase angle difference set by phase angle difference target value setter 1 (Usually set to 0°) Compare and calculate the phase angle difference deviation. .

[0097] First PI controller 3 pairs Perform proportional-integral calculations to output the active power regulation. This active power regulation Simultaneously, data is sent to the first energy storage unit (PCS4) and the second energy storage unit (PCS5) to adjust the active power output of the energy storage devices on both sides. Changes in active power output alter the line voltage drop and power flow distribution, thereby affecting the phase angle on both sides. and This forms a closed-loop regulation until... Approaching zero.

[0098] In the voltage amplitude difference regulation circuit, the first voltage transformer 14 detects the voltage amplitude of the first transformer area bus in real time. The second voltage transformer 15 monitors the voltage amplitude of the second transformer area bus in real time. The second subtractor 16 is based on... and Calculate the measured voltage difference .

[0099] The second comparator 10 will measure the voltage difference. The target voltage difference set by the voltage difference target value setter 9 (Usually set to 0V) for comparison, calculate voltage difference deviation. The second PI controller 11 pairs Perform proportional-integral calculations to output reactive power regulation. This reactive power regulation amount Simultaneously, data is sent to the first energy storage PCS12 and the second energy storage PCS13 to adjust the reactive power output of the energy storage devices on both sides. Changes in reactive power output alter the bus voltage amplitude. and This forms a closed-loop regulation until... Approaching zero.

[0100] The loop closing condition judgment module 17 continuously receives the measured phase angle difference from the first subtractor 8. Measured voltage difference from the second subtractor 16 and frequency difference The real-time value.

[0101] When all three conditions are met ≤2%, ≤5° After the frequency is ≤0.05Hz and lasts for 200ms, the loop closing condition judgment module 17 sends a closing command to the loop closing control box 6 through the closing command output terminal 18.

[0102] In one embodiment, the second PI controller 11 of the voltage difference closed-loop control loop employs a proportional-integral (PI) control law, whose transfer function is: ,in, This is the proportionality coefficient. is the integral coefficient. and The setting is based on the capacity of the distribution transformer in the first or second distribution zone and the preset regulation intensity mode. In the most typical 630kVA distribution transformer configuration of an urban distribution network, when using the balanced regulation intensity mode... Take 14.5 , Take 41.4 .

[0103] In another embodiment, for a 315kVA distribution transformer, when using the balance regulation intensity mode, Take 8.2 kvar / V, Take 23.4 .

[0104] For a 500kVA distribution transformer, when using the balanced regulation intensity mode... Take 13.0 , Take 37.1 .

[0105] For an 800kVA distribution transformer, when using the balanced regulation intensity mode... Take 13.8 , Take 39.4 .

[0106] For a 1000kVA distribution transformer, when using the balanced regulation intensity mode... Take 17.4 , Take 49.7 .

[0107] For a 1250kVA distribution transformer, when using the balanced regulation intensity mode... Take 21.6 , Take 61.7 .

[0108] In another embodiment, if a high closing speed is required on-site, a fast-adjustment intensity mode can be selected. Taking a 630kVA distribution transformer as an example again, in fast mode... Take 20.6 , Take 58.9 .

[0109] If the site has high requirements for system stability but is not sensitive to the loop closing speed, a conservative regulation intensity mode can be selected. For a 630kVA distribution transformer in conservative mode... Take 8.5 , Take 24.3 .

[0110] The first PI controller 3 also uses a proportional-integral control law, and its transfer function is: . and The setting is typically based on the impedance characteristics of the transformer area. The value range is 5-10 , The value range is 1-3 Under a typical transformer substation configuration, Take 7.5 , Take 2.0 .

[0111] Example 4

[0112] like Figure 5 This is a comparison diagram of the closed-loop current waveform of the present invention, wherein, Figure 5 (a) shows the current waveform of the traditional direct loop closing method. Figure 5 (b) is a pair of current waveforms after applying the precise loop-closing control of the present invention;

[0113] This embodiment provides a detailed description of the specific implementation methods for predicting the synchronous closing time and suppressing the circulating current after closing the loop.

[0114] The synchronous closing controller inside the loop control box 6 defines the instantaneous value of the loop differential pressure: ,in, This represents the instantaneous voltage value on the first side of the loop closure point. This is the instantaneous value of the voltage on the second side of the loop closure point.

[0115] The synchronous closing controller estimates the instantaneous value of the closing loop differential pressure based on real-time phasors. Amplitude Em, frequency difference and phase angle difference Establish a mathematical model of differential pressure waveform .

[0116] Based on this mathematical model, the synchronous closing controller predicts the instantaneous value of the closing loop differential pressure. The next zero-crossing moment .

[0117] The synchronous closing controller obtains the inherent closing time of the intelligent circuit breaker. (Typically 30-80ms, specific values ​​are determined by factory testing and pre-stored in the controller), calculate the timing of issuing the closing pre-command. and in It constantly sends closing commands to the intelligent circuit breaker.

[0118] After receiving the closing command, the intelligent circuit breaker begins to perform the closing action, and its contacts are in When the circuit is actually closed, the instantaneous voltage values ​​on both sides of the closing point are equal (the difference is minimal), and the closing inrush current is minimal. Actual measurements show that the synchronous closing timing error is less than 1ms, corresponding to an equivalent phase angle error of less than 0.018°.

[0119] The specific implementation method for circulating current detection and suppression is as follows: After the smart circuit breaker is successfully closed, a continuous circulating current may be generated in the closed loop due to the slight difference in voltage amplitude or phase angle between the two systems.

[0120] The regional autonomous controller 4 collects the first-side current I through the measurement and control terminals of the first switches on both sides of the closed loop. side1 Second side current I side2 ,

[0121] Calculate the circulation I loop =(I side1 -I side2 ) / 2. The regional autonomous controller 4 uses dq transformation to convert the circulating current I loop Decomposed into the active component of the fundamental circulation and reactive components Among them, the active component The corresponding active power imbalance on both sides of the closed loop, and the reactive power component This corresponds to an imbalance in reactive power.

[0122] The regional autonomous controller sends compensation amounts to the grid-type energy storage device. as well as ,in, The rated voltage is 400V. The converter of the grid-type energy storage device outputs reverse active power compensation current and reverse reactive power compensation current according to the above compensation amounts, injecting them into the closed-loop circuit to achieve synchronous suppression of the circulating active and reactive components. The convergence time of circulating current suppression is no more than 40ms (i.e., 2 power frequency cycles), and the target of circulating current suppression is to reduce the peak circulating current to below 5% of the rated current.

[0123] In one embodiment, if the peak circulating current detected after loop closure exceeds 30% of the rated current, the regional autonomous controller 4 immediately initiates an emergency suppression procedure, amplifies the energy storage compensation by 1.5 times, and sends an alarm signal to the master station system.

[0124] Example 5

[0125] The method and system of the present invention can be applied to a variety of scenarios, including load transfer with zero power outage in planned maintenance scenarios, and emergency transfer of power during faults.

[0126] In a planned maintenance scenario, the distribution automation master station issues a loop-closing and power transfer task to the regional autonomous controller 4, specifying the transfer direction and target transformer area. The regional autonomous controller 4 autonomously completes the loop-closing and power transfer process in the order of steps S1 to S5, without any manual intervention. The time from receiving the task to completing the load transfer does not exceed 3 minutes.

[0127] In emergency power transfer scenarios, the loop-closing operation is triggered autonomously by the Regional Autonomous Controller 4 (GAC4) without waiting for instructions from the master station. When GAC4 detects a fault in its local transformer or feeder, it automatically initiates the loop-closing power transfer process after confirming that the faulty area has been isolated, transferring the load from the non-faulty area to an adjacent transformer. The time from fault detection to completion of power transfer is no more than 2 seconds.

[0128] Regarding the safety strategy for handling failures, this invention establishes a tiered response mechanism. In one embodiment, if the loop-closing safety threshold is not met within a preset timeout period of 180 seconds after the start of active pre-adjustment, the regional autonomous controller 4 suspends the current loop-closing operation, reports to the master station system, and initiates manual processing. In another embodiment, if the circulating current amplitude exceeds the emergency tripping threshold (30% of the rated current) after successful closing, the regional autonomous controller 4 immediately issues a tripping command to the circuit breaker on the side to be deactivated, initiates full-speed energy storage suppression, and locks the operation. The system will retry a maximum of three times after the environment stabilizes. In yet another embodiment, if the communication of the grid-type energy storage device is interrupted, the system degrades to a passive synchronous closing mode without pre-adjustment. The loop-closing control box 6 independently completes the synchronous closing operation, and simultaneously uploads the operation risk assessment results to the dispatching terminal for dispatchers to decide whether to continue execution. If measurement fails or any step triggers a protection action, the loop-closing operation is immediately suspended, the system is locked, fault information is recorded, and the system awaits on-site handling by maintenance engineers.

[0129] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0130] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0131] In the several embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the coupling or direct coupling or communication connection shown or discussed may be through some communication interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0132] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0133] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0134] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0135] Furthermore, although the operations of the method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

Claims

1. A precise loop-closing control method for low-voltage distribution networks. Its features are, Applied to a system comprising a first distribution area, a second distribution area, and a connecting switch between the first distribution area and the second distribution area, wherein the first distribution area and the second distribution area are respectively equipped with a grid-type energy storage device; The method includes: S1: Obtain real-time electrical quantity information on both sides of the loop closure point, and calculate the voltage amplitude difference based on the real-time electrical quantity information. Phase angle difference and frequency difference ; S2: Determine the voltage amplitude difference The phase angle difference and the frequency difference Whether the preset loop closure safety threshold is met; if not, an adjustment command is issued to the existing grid-type energy storage devices in the first and / or second distribution areas to actively pre-adjust the active and / or reactive power outputs of the grid-type energy storage devices to reduce the voltage amplitude difference. and the phase angle difference until the voltage amplitude difference The phase angle difference and the frequency difference All conditions are met, and the state remains stable for a preset time. S3: After the loop closure safety threshold is met and the preset stabilization time is maintained, a closing command is sent to the interconnecting switch, and the closing operation is performed at the moment when the voltage instantaneous value difference on both sides of the loop closure point is the smallest. S4: After successful closing, the circulating current amplitude in the closed loop is detected. If the circulating current amplitude exceeds the preset circulating current threshold, the grid-type energy storage device is invoked to inject a compensation current in the opposite direction of the circulating current into the closed loop until the circulating current amplitude is reduced to below the target value. S5: After the circulating current amplitude stabilizes, perform a load transfer operation and issue a tripping command to the circuit breaker on the side to be disconnected to complete the loop disconnection.

2. The method according to claim 1, Its features are, In the active pre-adjustment, the phase angle difference is adjusted by adjusting the active power output of the grid-type energy storage device. The voltage amplitude difference is adjusted by adjusting the reactive power output of the grid-type energy storage device. ; The active power output regulation adopts a phase angle difference closed-loop control circuit, and the reactive power output regulation adopts a voltage difference closed-loop control circuit.

3. The method according to claim 1, Its features are, The preset loop closure safety threshold includes: the voltage amplitude difference. ≤2%, the phase angle difference ≤5°, the frequency difference ≤0.05Hz; the preset stabilization time is 200ms.

4. The method according to claim 2, Its features are, The voltage difference closed-loop control loop is a PI control loop, and its proportional coefficient is... and integral coefficient The setting is made according to the capacity of the distribution transformer in the first or second transformer area and the preset adjustment intensity mode; For a distribution transformer with a capacity of 630kVA, under the balance regulation intensity mode, Take 14.5 kvar / V, Take 41.4 kvar / (V·s).

5. The method according to claim 1, Its features are, The closing operation is performed at the moment when the instantaneous voltage difference on both sides of the closing point is the smallest, specifically including: Definition: Instantaneous value of differential pressure in closed loop ; Based on real-time phasor estimation: the instantaneous value of the closed-loop differential pressure amplitude Frequency difference and phase angle difference Establish a mathematical model of differential pressure waveform ; Predict the instantaneous value of the closed-loop differential pressure The next zero-crossing moment ; Obtain the inherent closing time of the interconnecting switch. Calculate the timing of the closing pre-command. and in the The closing command is issued at all times.

6. The method according to claim 1, Its features are, The detection of the circulating current amplitude in the closed loop specifically includes: The current on the first side is collected by the measurement and control terminal of the first switch on both sides of the closed loop. Second side current Calculate circulation ; The circulating current is transformed using the dq transform. Decomposed into the active component of the fundamental circulation and reactive components ; The injected compensation current, which is opposite to the circulating current direction, specifically includes: issuing a compensation amount to the grid-type energy storage device. as well as ,in, This is the rated voltage.

7. The method according to claim 1, Its features are, The target value for the circulating current amplitude is that the peak value of the circulating current is less than 5% of the rated current; The convergence time for the circulation amplitude to decrease from exceeding the preset circulation threshold to below the target value is no more than 40ms.

8. A low-voltage precision closed-loop control system, Its features are, The method for precise loop-closing control of low-voltage distribution networks as described in any one of claims 1 to 7 is adopted. The system includes: The regional autonomous controller, deployed on the transformer substation side, is used to acquire real-time electrical quantity information on both sides of the loop closing point, perform loop closing condition judgment, issue adjustment commands to the grid-type energy storage device, and issue closing commands to the loop closing control box; The loop control box is deployed at the low-voltage tie line and has a built-in intelligent circuit breaker and synchronous closing controller. The synchronous closing controller is used to receive the closing command of the regional autonomous controller and drive the intelligent circuit breaker to close when the voltage instantaneous value difference on both sides of the loop point is the smallest. A communication interface connects the regional autonomous controller and the grid-type energy storage device, and is used to transmit active power regulation commands and reactive power regulation commands.

9. The system according to claim 8, Its features are, The regional autonomous controller and the closed-loop control box, as well as the regional autonomous controller and the grid-type energy storage device, communicate peer-to-peer using the IEC61850 GOOSE protocol. The decision latency of the regional autonomous controller is less than 100ms; The loop control box also includes a waveform recording module, which is used to record current waveforms and voltage waveforms throughout the closing and opening process, with a sampling rate of not less than 100 kSa / s.

10. The method according to claim 1, Its features are, The method is applied to load switching with zero power outage in planned maintenance scenarios, or to emergency power switching in fault scenarios. In the emergency power transfer scenario, the loop closing operation is triggered by the local autonomous decision of the regional autonomous controller, without waiting for instructions from the master station; The method also includes a failure handling security strategy: If the loop closure safety threshold is not met within the preset timeout period after the start of the active pre-adjustment, the operation will be terminated. If the circulating current amplitude exceeds the emergency tripping threshold after successful closing, the circuit will immediately trip and lock. If the communication of the grid-type energy storage device is interrupted, it will be downgraded to a passive synchronous closing mode without pre-adjustment.

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