A method for accommodating a microgrid based on an ac-dc flexible direct current device

Abstract

This invention relates to a method for absorbing power in a feeder-type microgrid based on AC / DC flexible DC equipment. The method includes: first, selecting microgrid feeder groups based on the total installed capacity of distributed photovoltaic systems connected to the 10kV feeders and the feeder power supply topology, and constructing a microgrid flexible DC system topology diagram; second, using the distribution automation master station system, ensuring the total output power and voltage of the "renewable energy + energy storage system" reach target values; and finally, utilizing advanced application functions within the distribution automation master station system. This method constructs a microgrid system based on 10kV feeder groups. While achieving diversification of feeder power supply structure, it can improve feeder power supply reliability, enhance flexible distribution network control capabilities, increase renewable energy absorption capacity, improve grid operation stability, improve grid operation economy, and enhance the grid's comprehensive ability to resolve spatiotemporal mismatches between distribution network sources and loads, demonstrating significant demonstrative value.

Description

Technical Field

[0001] This invention relates to the field of new power system technology in distribution networks, and in particular to a method for absorbing power into a feeder-type microgrid based on AC / DC flexible DC equipment. Background Technology

[0002] In recent years, distributed photovoltaic (PV) power has shown a rapid development trend of "numerous points and wide coverage". The high proportion of distributed power generation capacity and the connection of power electronic equipment have transformed the distribution network from "passive" to "active", and the harmonic sources have increased dramatically. The pressure and challenges brought to the power grid are mainly in the following four aspects:

[0003] (1) In terms of economic operation, due to the high proportion of distributed power sources connected, the load curve of regional substations has shown a peak-valley “reversal”, and the power flow at each level is disorderly crossing, which brings new pressure to the local consumption of new energy and loss reduction. As distributed photovoltaics are connected in succession, the above-mentioned power backflow problem will be aggravated.

[0004] (2) In terms of power quality, distributed photovoltaic power generation has low anti-disturbance capability and insufficient rotational inertia, which makes it easy to disconnect from the grid, putting pressure on the safety and stability of the power grid. After large-scale distributed photovoltaic power generation is connected, it will bring problems such as over / under voltage, voltage sag, and three-phase imbalance (when low-voltage single-phase is connected) in the distribution network. When the photovoltaic output is greater than the power load, the unabsorbed photovoltaic power generation will be fed back to the bus or the upper-level power grid, increasing the loss. At the same time, it will cause the voltage of the grid connection node to rise too much, resulting in high voltage for users near the grid connection point. In severe cases, it may even cause damage to the distribution network equipment near the grid connection point. Since the distribution transformer does not have on-load voltage regulation capability, when the photovoltaic output is lower than the power load or the output will be 0, some users will have low voltage problems.

[0005] (3) In terms of power supply, photovoltaic power generation is affected by day and night changes, weather changes, and moving clouds, resulting in randomness and fluctuations. After a high proportion is connected to the grid, the peak capacity is insufficient, which puts great pressure on the grid's power supply capacity.

[0006] (4) In terms of power grid safety, the massive access of low-voltage photovoltaics has not been synchronized to the distribution automation system in real time, which may lead to the problem of incomplete implementation of power outage safety measures; the bidirectional power flow distribution not only affects the detection of power load, the coordination and setting of distribution network line protection, but also affects the accuracy of active judgment of distribution network faults; the traditional dispatch mode is difficult to achieve comprehensive dispatch and management of new energy sources with many points and wide coverage. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a feeder-type microgrid absorption method based on AC / DC flexible DC equipment, which can improve feeder power supply reliability, improve flexible distribution network control capability, improve renewable energy absorption capability, improve grid operation stability, improve grid operation economy, and improve the grid's comprehensive ability to solve the spatiotemporal mismatch between power source and load in the distribution network while realizing the diversification of feeder power supply structure.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a method for absorbing feeder-type microgrids based on AC / DC flexible DC equipment, comprising the following steps:

[0009] Step S1: Based on the distribution automation master station system, select the microgrid feeder group according to the total installed capacity of distributed photovoltaic power connected to the 10kV feeder and the feeder power supply topology connection, and construct the microgrid flexible DC system topology diagram.

[0010] Step S2: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, and support the data acquisition, analysis and application of microgrid equipment such as converters and inverters in the microgrid flexible DC system;

[0011] Step S3: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, support the forwarding of the active power data of feeder switches and distributed photovoltaic collected by the master station to the microgrid, and the microgrid coordination controller automatically receives and executes the optimized control values ​​issued by the DMS, and adjusts the charging and discharging power of the energy storage system in real time to make the total output power and voltage of the "renewable energy + energy storage system" reach the target value.

[0012] Step S4: Based on the advanced application functions of the distribution automation master station system, expand the cloud-edge collaborative feeder microgrid absorption calculation function, and introduce the microgrid model for analysis and calculation in feeder automation.

[0013] In a preferred embodiment: the method for selecting microgrid feeder groups based on the total installed capacity of distributed photovoltaic power connected to the 10kV feeder and the feeder power supply topology of the distribution automation master station system, and constructing the microgrid flexible DC system topology model is as follows: 10kV line 1 and its connecting line, i.e., 10kV line 2 feeder group, are selected according to the microgrid system structure. A modular parallel compact back-to-back flexible DC loop device is constructed at the connection point of the two feeders. The two 10kV AC lines are connected through flexible AC-DC conversion, and energy storage equipment is configured on the DC system side. The relevant power model of the flexible DC equipment is constructed in the distribution automation master station. Here, the AC microgrid refers to the AC microgrid composed of a substation, distributed photovoltaic power directly connected to the 10kV feeder, and flexible DC system; the DC microgrid refers to the DC microgrid composed of the flexible DC system and the DC distribution cabinet, photovoltaic energy storage, energy storage, charging piles, etc. below; the DC microgrid connecting line refers to the intermediate connection between the distribution transformer and the AC / DC in the flexible DC system.

[0014] In a preferred embodiment: the microgrid flexible DC device supports real-time acquisition of grid-connected operation information, including grid-connected equipment status, grid connection point voltage, current, active power, and reactive power;

[0015] The microgrid converter compartment, energy storage, and inverter support real-time acquisition of equipment operating status information, including temperature, operating mode, charging and discharging power, and start / stop status.

[0016] In a preferred embodiment: the active power data of feeder switches and distributed photovoltaic power collected by the distribution automation master station are forwarded down to the microgrid controller;

[0017] It supports the distribution automation master station to perform adjustment calculations on the active and reactive power output of the microgrid and adjust the charging and discharging power of the energy storage system in real time.

[0018] In a preferred embodiment: the flexible DC interconnection grid-connected operation control function, under normal operation, in order to maximize the utilization of renewable energy, the distributed power sources in the DC and AC microgrids operate at maximum output power; the energy storage controller adjusts the charging and discharging power of the energy storage system according to the instructions issued by the DMS master station; in order to keep the power of the AC and DC microgrid tie lines within the allowable range, the DMS master station sends tie line power adjustment instructions to the microgrid coordination controller to control the switching power of the AC and DC microgrids.

[0019] Compared with existing technologies, this invention has the following advantages: First, based on the distribution automation master station system, the microgrid feeder group is selected according to the total installed capacity of distributed photovoltaic power on the 10kV feeder and the feeder power supply topology connection, and the topology of the microgrid flexible DC system is constructed. Then, based on the distribution automation master station system, the master station resources are fully utilized, the communication protocol is expanded, and the data acquisition, analysis and application of microgrid equipment such as converters and inverters in the microgrid flexible DC system are supported. Second, based on the distribution automation master station system, the master station resources are fully utilized, the communication protocol is expanded, and the feeder switch and distributed photovoltaic active power data collected by the master station are forwarded to the microgrid. The microgrid coordinating controller automatically receives and executes the optimized control values ​​issued by the DMS, and adjusts the charging and discharging power of the energy storage system in real time to make the total output power and voltage of "renewable energy + energy storage system" reach the target value. Finally, based on the advanced application functions of the distribution automation master station system, the cloud-edge collaborative feeder-type microgrid absorption calculation function is expanded. This method provides a microgrid system based on 10kV feeder groups, which interconnects two 10kV feeders using a modular, scalable, flexible DC system and combines distributed photovoltaics and energy storage. While diversifying the feeder power supply structure, it can improve feeder power supply reliability, enhance the control capability of flexible distribution networks, increase the capacity for renewable energy absorption, improve grid operation stability, improve grid operation economy, and enhance the grid's comprehensive ability to address spatiotemporal mismatches between power sources and loads. It has significant demonstrative value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a microgrid system based on a 10kV feeder group, which is a preferred embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0024] A method for absorbing AC / DC flexible DC power supply in a feeder-type microgrid, referenced Figure 1The method includes the following steps:

[0025] Step S1: Based on the distribution automation master station system, select the microgrid feeder group according to the total installed capacity of distributed photovoltaic power connected to the 10kV feeder and the feeder power supply topology connection, and construct the microgrid flexible DC system topology diagram.

[0026] Step S2: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, and support the data acquisition, analysis and application of microgrid equipment such as converters and inverters in the microgrid flexible DC system;

[0027] Step S3: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, support the forwarding of the active power data of feeder switches and distributed photovoltaic collected by the master station to the microgrid, and the microgrid coordination controller automatically receives and executes the optimized control values ​​issued by the DMS, and adjusts the charging and discharging power of the energy storage system in real time to make the total output power and voltage of the "renewable energy + energy storage system" reach the target value.

[0028] Step S4: Based on the advanced application functions of the distribution automation master station system, expand the cloud-edge collaborative feeder microgrid absorption calculation function, and introduce the microgrid model for analysis and calculation in feeder automation.

[0029] A method for selecting microgrid feeder groups and constructing a microgrid flexible DC system topology based on the total installed capacity of distributed photovoltaic systems connected to 10kV feeders and the feeder power supply topology of the distribution automation master station system is characterized by:

[0030] Based on the microgrid system structure, a 10kV line 1 and its connecting line (10kV line 2) feeder group were selected. A modular, parallel, compact, back-to-back flexible DC loop-connecting device was constructed at the connection point of the two feeders. The two 10kV AC lines were connected via flexible AC / DC conversion, and energy storage equipment was configured on the DC system side. The relevant power model of the flexible DC equipment was then constructed in the distribution automation master station. The AC microgrid refers to an AC microgrid composed of a substation, distributed photovoltaic systems directly connected to the 10kV feeders, and a flexible DC system; the DC microgrid refers to a DC microgrid composed of the flexible DC system and the downstream DC distribution cabinet, photovoltaic energy storage, energy storage, charging piles, etc.; the DC microgrid connecting line refers to the intermediate connection between the distribution transformer and the AC / DC converter in the flexible DC system.

[0031] Based on a distribution automation master station system, this method fully utilizes master station resources, expands communication protocols, and supports data acquisition, analysis, and application for microgrid equipment such as converters and inverters in microgrid flexible DC systems. Its features include:

[0032] The microgrid flexible DC device supports real-time acquisition of grid-connected operation information, including grid-connected equipment status, grid connection point voltage, current, active power, reactive power, etc.

[0033] The microgrid converter compartment, energy storage, and inverter support real-time acquisition of equipment operating status information, including temperature, operating mode, charging and discharging power, and start / stop status.

[0034] Based on a distribution automation master station system, this method fully utilizes master station resources, expands communication protocols, and supports forwarding active power data from feeder switches and distributed photovoltaic systems collected by the master station to the microgrid. The microgrid coordinating controller automatically receives and executes optimized control values ​​issued by the DMS, and adjusts the charging and discharging power of the energy storage system in real time to ensure that the total output power and voltage of the "renewable energy + energy storage system" reach the target values. Its key features are:

[0035] It supports forwarding the active power data of feeder switches and distributed photovoltaic power collected by the distribution automation master station to the microgrid controller;

[0036] It supports the distribution automation master station to perform adjustment calculations on the active and reactive power output of the microgrid and adjust the charging and discharging power of the energy storage system in real time.

[0037] Based on the advanced application functions of the distribution automation master station system, this paper expands the cloud-edge collaborative feeder-type microgrid absorption calculation function, and introduces a method for analysis and calculation of microgrid models in feeder automation. Its key features include: flexible DC-DC interconnected grid-connected operation control function. Under normal operating conditions, to maximize the utilization of renewable energy, distributed power sources within the DC and AC microgrids operate at maximum output power. The energy storage controller adjusts the charging and discharging power of the energy storage system according to instructions issued by the DMS master station. To keep the AC and DC microgrid tie-line power within the allowable range, the DMS master station sends tie-line power adjustment instructions to the microgrid coordination controller to control the switching power of the AC and DC microgrids.

[0038] The microgrid system structure selects 10kV line 1 and its interconnecting line (10kV line 2) feeder group. At the connection point of the two feeders, a modular parallel compact back-to-back flexible DC loop device is built. The two 10kV AC lines are connected through flexible AC-DC conversion. Energy storage is then configured on the DC system side, which can basically meet the self-balancing requirements of feeder-type microgrids under most operating modes (except for specific holidays).

[0039] Ø Data Description

[0040] Network side data Remark Output Remark P1 10kV line 1 outgoing line active power Pset1 10kV line 1 transfer of flexible DC power P2 10kV line 2 outgoing line active power Heavy load 0.8Pe1 = 6.98MW PV1 10kV line 1 photovoltaic power output Heavy load 0.8Pe2 = 6.98MW Pe1 10kV line 1 rated power = 8.725MW Power balance threshold for flexible DC system 3 MW Pe2 10kV line 2 rated power = 8.725MW Unit (MW)

[0041] Ø Adjustment methods

[0042] The main station combines data from end-side equipment, substation outgoing switch data, and photovoltaic data from the lines. After analysis, it adjusts the microgrid operation using the following two strategies based on the analysis results:

[0043] 1. Power mutual assistance strategy: According to the operating conditions and the results of strategy analysis, power transfer is carried out between 10kV Line 1 and 10kV Line 2 through the flexible DC system.

[0044] 2. Power balancing strategy: According to the operating conditions and the results of strategy analysis, when the result of strategy analysis is to execute the load balancing strategy, after power transfer is carried out between 10kV Line 1 and 10kV Line 2 through the flexible DC system, the line load rates of 10kV Line 1 and 10kV Line 2 are the same. Balancing strategy: formula (p1 + Pset1) / (p2 - Pset1)=pe1 / pe2.

[0045] Ø Microgrid regulation strategy

[0046] Combined with data such as the active power of the lines on both sides of the microgrid and the photovoltaic output, microgrid strategy analysis is carried out for the following 6 operating conditions:

[0047] 1) Photovoltaic power is not output

[0048] Operating conditions:

[0049] Photovoltaic power is not output, and neither of the two lines is overloaded, that is, the photovoltaic output PV1 of 10kV Line 1 is 0, 0 < P1 < 0.8Pe1 and 0 < P2 < 0.8Pe2. When the two lines are operating normally, consider whether the flexible DC system converter transfers power.

[0050] Strategy:

[0051] 1. The flexible DC system converter does not transfer power, and the line operates normally. At this time, there is no need to adjust the power.

[0052] 2. The flexible DC system converter has transferred power, and all the power is transferred from P1 to P2, from 10kV Line 1 to 10kV Line 2. At this time, the line operates normally. It is necessary to consider whether the existing P1 on 10kV Line 1 minus (the power transferred from 10kV Line 1 to 10kV Line 2) satisfies 0 < P1 < 0.8Pe1, and whether the existing P2 on 10kV Line 2 plus (the power transferred from 10kV Line 1 to 10kV Line 2) satisfies 0 < P2 < 0.8Pe2. If it is satisfied, the converter does not need to adjust the power at this time, adjust Pset1. If it is not satisfied, the converter continues to adjust the power to ensure the power balance of the two lines and execute the power balance control strategy.

[0053] 2) Photovoltaic power is not output, and 10kV Line 2 is overloaded

[0054] Operating conditions:

[0055] Photovoltaic power is not output, and 10kV Line 2 is overloaded, that is, the photovoltaic output PV1 of 10kV Line 1 is 0, 0 < P1 < 0.8Pe1, P2 > 0.8Pe2

[0056] Strategy:

[0057] Implement a power balancing strategy to balance the power of P1 and P2, considering the following two cases during the balancing process:

[0058] a) If the power transfer needs to be greater than 3, due to the power balance threshold limitation of the flexible DC system, it can only be transferred to 3. If the power transfer is less than 3, it will be transferred normally.

[0059] b) If the power transfer results in a heavy load on 10kV line P1, then the power cannot be fully transferred. The current transfer threshold is set to 6.88-P1.

[0060] 3) Photovoltaic power is not generating power, and the 10kV line is under heavy load.

[0061] Operating conditions:

[0062] The photovoltaic system is not generating power, and 10kV line 1 is under heavy load, meaning the photovoltaic output of 10kV line 1 is PV1 = 0. <P2<0.8Pe2,P1> 0.8Pe1

[0063] Strategy:

[0064] Implement a power balancing strategy to balance the power of P1 and P2, considering the following two cases during the balancing process:

[0065] a) If the power transfer needs to be greater than 3, due to the power balance threshold limitation of the flexible DC system, it can only be transferred to 3. If the power transfer is less than 3, it will be transferred normally.

[0066] b) If the power transfer results in a heavy load on 10kV line 2 P2, then the power cannot be fully transferred. The current transfer threshold is set to 6.88-P1.

[0067] 4) Photovoltaic power is not being used, and 10kV line 1 and 10kV line 2 are under heavy load.

[0068] Operating conditions:

[0069] With no photovoltaic output, 10kV line 1 and 10kV line 2 are heavily loaded, meaning the photovoltaic output of 10kV line 1 is PV1=0, P1>0.8Pe1, P2>0.8Pe2.

[0070] Strategy:

[0071] Implement a power balancing strategy to balance P1 and P2, thereby reducing the load rate of heavily loaded lines.

[0072] 5) Photovoltaic power output, no heavy-load lines.

[0073] ① Operating Condition 1

[0074] The active power output of the photovoltaic system is less than 2 MW, the line is heavily loaded, and there is no reverse power flow on the 10 kV line 1, that is, the photovoltaic output of the 10 kV line 1 satisfies 0 < |PV1| < 2, 0.05Pe1 < P1 < 0.8Pe1 and 0 < P2 < 0.8Pe2

[0075] Strategy:

[0076] Judge whether the converter of the flexible DC system transfers power, and consider the following two cases:

[0077] a) The converter of the flexible DC system does not transfer power, and the line operates normally. At this time, there is no need to adjust the power.

[0078] b) The converter of the flexible DC system has transferred power, and all the power is transferred from P1 to P2, from the 10 kV line 1 to the 10 kV line 2. At this time, the line operates normally. It is necessary to consider whether the existing P1 on the 10 kV line 1 minus (the power transferred from the 10 kV line 1 to the 10 kV line 2) satisfies 0.15Pe1 < P1. Here, considering 0.15Pe1 mainly takes into account the problem of frequent adjustment at the critical value, and 0.15Pe1 avoids frequent adjustment. Here, if it is satisfied, the converter does not need to adjust the power at this time, adjust Pset1 + 0. If it is not satisfied, the converter continues to adjust the power to ensure the power balance of the two lines and execute the power balance control strategy.

[0079] ② Operating condition 2

[0080] The active power output of the photovoltaic system is less than 2 MW, |PV1| < P2 - 0.1Pe2, the line is not heavily loaded, and there is reverse power flow on the 10 kV line 1, that is, the photovoltaic output of the 10 kV line 1 satisfies 0 < |PV1| < 2, P1 < 0.05Pe1, (P2 - |PV1|) > 0.1Pe2

[0081] Strategy:

[0082] Execute the power transfer of the 10 kV line 1, Pset1 = |PV1|, Qset1 = -0.48PV1. First, transfer the power. After the transfer, there is a power difference between the two lines, and then balance the active power of the two lines.

[0083] ③ Operating condition 3

[0084] The active power output of the photovoltaic system is less than 2 MW, |PV1| > P2 - 0.1Pe2, the line is not heavily loaded, and there is reverse power flow on the 10 kV line 1. The photovoltaic output of the 10 kV line 1 satisfies 0 < |PV1| < 2, P1 < 0.05Pe1, 0 < (P2 - |PV1|) < 0.1Pe2

[0085] Strategy:

[0086] After the transfer of power Pset1=P2-0.12Pe2 and Qset1=-0.48PV1 of the 10kV line 1 is completed, continue to balance the active power of the two lines; otherwise, directly balance the power of the two lines.

[0087] ④ Operating Condition 4

[0088] The photovoltaic output is too large for both 10kV line 1 and 10kV line 2 to absorb; that is, the photovoltaic output of 10kV line 1 is 0 < |PV1|, and pv1 - p2 - 0.5 - p1 > 0.

[0089] Strategy:

[0090] A threshold is set for 10kV line 2, leaving 0.5MW to be carried by 10kV line 2. The remaining power that 10kV line 2 can carry is transferred to 10kV line 1. P2-0.5 If it is greater than 3, transfer to line 3.

[0091] ⑤ Operating Condition 5

[0092] The photovoltaic system is outputting power, but 10kV line 1 is under heavy load, meaning the photovoltaic output PV1 of 10kV line 1 is greater than or equal to 0. <P2<0.8Pe2,P1> 0.8Pe1

[0093] Strategy:

[0094] To implement a power balancing strategy, the power of P1 and P2 needs to be balanced. The following two scenarios need to be considered during the balancing process:

[0095] a) If the required power transfer is greater than 2.5 kW, then only 2.5 kW can be transferred. Reactive power transferred = Active power transferred * 0.48. If the transferred power is less than 2.5 kW, normal transfer occurs.

[0096] b) If the power transfer results in a 2P2 overload on the 10kV line, then not all power can be transferred. Currently, the transfer threshold is set to 6.88 - P2. Reactive power transfer continues to be multiplied by 0.48.

[0097] ⑥ Operating Condition 6

[0098] The photovoltaic system is generating power, but 10kV line 2 is under heavy load, meaning the photovoltaic output of 10kV line 1 |PV1| > 0. <P1<0.8Pe1,P2> 0.8Pe2

[0099] Strategy:

[0100] To implement a power balancing strategy, the power of P1 and P2 needs to be balanced. The following two scenarios need to be considered during the balancing process:

[0101] a) If the required power transfer is greater than 2.5 kW, then only 2.5 kW can be transferred. Reactive power transferred = Active power transferred * 0.48. If the transferred power is less than 2.5 kW, normal transfer occurs.

[0102] b) If the power transfer results in a heavy load on line 1P1 of the 10kV line, then not all power can be transferred. Currently, the transfer threshold is set to 6.88 - P1. Reactive power transfer continues to be multiplied by 0.48.

[0103] ⑦ Operating Condition 7

[0104] The photovoltaic output exceeds 2MW, and a power backflow occurs on 10kV line 1. The load on 10kV line 2 exceeds 2.87MW. Therefore, the photovoltaic output of 10kV line 1, |PV1|, is greater than 2, P1 < 0.05Pe1, and (P2 - 2) > 0.1Pe2.

[0105] Strategy:

[0106] Perform a power transfer of 10kV line 1, Pset1=2, Qset1=Pset1*0.48. After the transfer is complete, continue with power balancing between the two lines.

[0107] ⑧ Operating Condition 8

[0108] If the photovoltaic output is greater than 2MW, and power backfeed occurs on 10kV line 1, while the load on 10kV line 2 is less than 2.87MW, then the photovoltaic output of 10kV line 1 |PV1| > 2, P1 < 0.05Pe1, and (P2 - 2) < 0.1Pe2.

[0109] Strategy:

[0110] Perform the power transfer for line 1 of the 10kV line: Pset1 = P2 - 0.12Pe2, Qset1 = Pset1 * 0.48. After the transfer is complete, continue with the power balancing of the two lines.

[0111] 6) Photovoltaic output, both lines are under heavy load.

[0112] Operating conditions:

[0113] Given that the photovoltaic output of 10kV line 1 is PV1>0, determine that P1>0.8Pe1 and P2>0.8Pe2.

[0114] Strategy:

[0115] Implement a power balancing strategy to balance the power of the two lines and reduce the load rate of the heavily loaded line.

[0116] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for absorbing AC / DC flexible DC power in a feeder-type microgrid, characterized in that: Includes the following steps: Step S1: Based on the distribution automation master station system, select the microgrid feeder group according to the total installed capacity of distributed photovoltaic power connected to the 10kV feeder and the feeder power supply topology connection, and construct the microgrid flexible DC system topology diagram. Step S2: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, and support the data acquisition, analysis and application of microgrid flexible DC system converters, inverters and microgrid equipment; Step S3: Based on the distribution automation master station system, make full use of the master station resources, expand the communication protocol, and support the forwarding of the active power data of the feeder switches and distributed photovoltaic collected by the master station to the microgrid. The microgrid coordination controller automatically receives and executes the optimized control values ​​issued by the DMS, and adjusts the charging and discharging power of the energy storage system in real time to make the total output power and voltage of the "renewable energy + energy storage system" reach the target values. Step S4: Based on the advanced application functions of the distribution automation master station system, expand the cloud-edge collaborative feeder microgrid absorption calculation function, and at the same time introduce the microgrid model for analysis and calculation in feeder automation. The method for selecting microgrid feeder groups and constructing the microgrid flexible DC system topology based on the total installed capacity of distributed photovoltaic power connected to the 10kV feeder and the feeder power supply topology of the distribution automation master station system is as follows: Based on the microgrid system structure, select 10kV line 1 and its connecting line, i.e., 10kV line 2 feeder group. Construct a modular, parallel, compact, back-to-back flexible DC loop device at the connection point of the two feeders. Connect the two 10kV AC lines through a flexible AC / DC converter. Then, configure energy storage equipment on the DC system side. The relevant power model of the flexible DC equipment is then constructed in the distribution automation master station. Here, the AC microgrid refers to an AC microgrid composed of a substation, distributed photovoltaic power directly connected to the 10kV feeder, and a flexible DC system; the DC microgrid refers to a DC microgrid composed of the flexible DC system and the downstream DC distribution cabinet, photovoltaic energy storage, energy storage, and charging piles; and the DC microgrid connecting line refers to the intermediate connection between the distribution transformer and the AC / DC converter in the flexible DC system. The microgrid flexible DC device supports real-time acquisition of grid-connected operation information, including grid-connected equipment status, grid-connected point voltage, grid-connected point current, grid-connected point active power, and grid-connected point reactive power; The microgrid converter compartment, energy storage and inverter all collect equipment operating status information in real time, including temperature, working mode, charging and discharging power and start / stop status; It supports forwarding the active power data of feeder switches and distributed photovoltaic power collected by the distribution automation master station to the microgrid controller; It supports the distribution automation master station to calculate and adjust the active and reactive power output of the microgrid, and adjusts the charging and discharging power of the energy storage system in real time; The flexible DC-DC interconnection grid-connected operation control function ensures that, under normal operating conditions, distributed power sources within the DC and AC microgrids operate at maximum output power to maximize the utilization of renewable energy. The energy storage controller adjusts the charging and discharging power of the energy storage system according to the instructions issued by the DMS master station. To keep the power of the AC and DC microgrid tie lines within the allowable range, the DMS master station sends tie line power adjustment instructions to the microgrid coordination controller to control the switching power of the AC and DC microgrids.

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