Master-slave phase-splitting flexible interconnection control method and system for low-voltage distribution network

Abstract

The embodiment of the application discloses a kind of low-voltage distribution network master-slave split-phase flexible interconnection control method and system, comprising: the three-phase current of two table areas is carried out sequence component decomposition, obtains to be compensated negative sequence current and to be compensated zero sequence current;According to the target power to be transmitted of two table areas, to be compensated load current, voltage stabilizing load current are solved;According to to be compensated negative sequence current and to be compensated zero sequence current, to be compensated load current, voltage stabilizing load current, compensation current reference value is calculated;If compensation current reference value changes, then the maximum one-phase compensation current reference value is obtained;According to the rated current of main back-to-back voltage source converter, maximum one-phase compensation current reference value, to the compensation current control of main and slave back-to-back voltage source converter is carried out.This application solves the flexible expansion and three-phase imbalance treatment of distribution network at low overall configuration capacity with low cost synchronously, solves the problem of table area light load and three-phase imbalance, and the flexibility and scalability of system are improved by master-slave combination control.

Description

Technical Field

[0001] The present application relates to the technical field of distribution network management, and in particular to a method and system for controlling master-slave phase-split flexible interconnection of a low-voltage distribution network. Background Art

[0002] With the massive investment of distributed power sources (DG) and random loads, especially in low-voltage distribution networks with complex network structures and user types, the interweaving and disorderly investment of single-phase / three-phase loads have caused the problems of light and heavy loads and three-phase imbalance of transformers in low-voltage distribution networks to become increasingly prominent, threatening the safe and reliable operation of low-voltage distribution networks. However, existing governance measures often only target the problems of light and heavy loads and three-phase imbalance of transformers and cannot be handled simultaneously. Moreover, in the existing technology, low-voltage flexible interconnection technology can adjust the power of two low-voltage distribution networks and has been piloted in distribution networks to solve the above problems. However, the existing flexible interconnection devices are not flexible and scalable enough, and there are situations where the capacity of the interconnection devices is excessive or the capacity does not meet the power supply demand, making it difficult to expand the capacity. Summary of the Invention

[0003] The main purpose of this application is to provide a low-voltage distribution network master-slave phase-split flexible interconnection control method and system, which can solve the technical problems in the existing technology of three-phase imbalance control and the inability to simultaneously control light and heavy loads of transformers and the lack of flexibility and scalability of existing flexible interconnection devices.

[0004] To achieve the above objectives, the present application provides, in a first aspect, a low-voltage distribution network master-slave split-phase flexible interconnection control method, which is applied to a control module in a low-voltage distribution network master-slave split-phase flexible interconnection control system. The low-voltage distribution network master-slave split-phase flexible interconnection control system further includes a master back-to-back voltage source converter, a slave back-to-back voltage source converter, and a three-to-one multi-way switch. The method includes:

[0005] Obtain the three-phase current of the first substation and the three-phase current of the second substation, perform sequence component decomposition calculation on the three-phase current of the first substation and the three-phase current of the second substation, and obtain the negative sequence current to be compensated and the zero sequence current to be compensated of the first substation and the second substation respectively;

[0006] Obtaining a target power that needs to be transmitted from the power transmitting area to the power receiving area in order to achieve equal load rates between the first area and the second area;

[0007] According to the target power, the load current to be compensated in the power receiving area and the regulated load current required for voltage regulation in the power transmission area are solved, wherein the power receiving area and the power transmission area are different areas in the first area and the second area;

[0008] Calculate a first compensation current reference value of the power receiving area and a second compensation current reference value of the power transmitting area according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first and second areas, the load current to be compensated of the power receiving area, and the regulated load current of the power transmitting area;

[0009] If the compensation current reference value changes, obtaining a maximum compensation current reference value of one phase among the three-phase compensation current reference values ​​a, b, and c of the compensation current reference value by comparison, wherein the compensation current reference value is the first compensation current reference value or the second compensation current reference value, and the compensation current reference value includes the a-phase compensation current reference value, the b-phase compensation current reference value, and the c-phase compensation current reference value;

[0010] According to the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, corresponding strategies are adopted to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter.

[0011] To achieve the above-mentioned object, the second aspect of the present application provides a low-voltage distribution network master-slave phase-split flexible interconnection control system, the system comprising: a master back-to-back voltage source converter, a slave back-to-back voltage source converter, a first three-to-one multi-way switch, a second three-to-one multi-way switch, and a control module;

[0012] The main back-to-back voltage source converter includes a back-to-back three-phase full-bridge converter;

[0013] Both sides of the back-to-back three-phase full-bridge converter are connected to the three phases of the feeder of the first substation and the three phases of the feeder of the second substation respectively;

[0014] The back-to-back voltage source converter includes a back-to-back single-phase full-bridge converter;

[0015] The back-to-back single-phase full-bridge converters are connected to the neutral line of the first transformer zone and the neutral line of the second transformer zone respectively;

[0016] The back-to-back single-phase full-bridge converter is further connected to one phase line of the feeder of the first transformer substation via a first three-to-one multi-way switch, and is connected to one phase line of the feeder of the second transformer substation via a second three-to-one multi-way switch.

[0017] A control module is used to control three-phase imbalance according to any of the above-mentioned low-voltage distribution network master-slave phase-split flexible interconnection control methods.

[0018] The embodiments of the present application have the following beneficial effects:

[0019] The present application realizes a low-voltage distribution network master-slave phase-split flexible interconnection control scheme, that is, a low-cost solution for flexible expansion of distribution network and three-phase imbalance control based on master-slave back-to-back voltage source converters (master-slave BTB-VSCs). The master back-to-back voltage source converter (master BTB-VSC) transmits all expansion power and a small amount of three-phase imbalance compensation power; through the cooperation of the slave back-to-back voltage source converter (slave BTB-VSC) and the multi-way switch, the master BTB-VSC is given a flexible phase expansion capability, and flexible expansion between substations and high-quality control of three-phase imbalance are achieved on the basis of a lower overall configuration capacity, effectively and at low cost. The problem of light and heavy load and three-phase imbalance in the substation area is solved. In addition, the multiple combination controls of the master-slave BTB-VSC improve the flexibility of the device or system, and when the capacity of the master BTB-VSC converter is insufficient, it can be supplemented by the slave BTB-VSC, and the device is more scalable. This application can effectively improve the interconnection and mutual assistance capabilities of the distribution network, reduce the operating losses of the substation, reduce the cost of management equipment, and promote the interconnection and interoperability of new distribution networks and the absorption of distributed power sources, which has great engineering significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] in:

[0022] Figure 1 This is a flow chart of a method for controlling a master-slave phase-split flexible interconnection of a low-voltage distribution network according to an embodiment of the present application;

[0023] Figure 2 This is a structural block diagram of a low-voltage distribution network master-slave phase-split flexible interconnection control system in an embodiment of the present application;

[0024] Figure 3 This is a circuit diagram of a master-slave phase-split flexible interconnection control system for a low-voltage distribution network in an embodiment of the present application;

[0025] Figure 4 Schematic diagram of compensation current of a master-slave phase-split flexible interconnection control system for a low-voltage distribution network in an embodiment of the present application;

[0026] Figure 5 This is a diagram showing the compensation current amplification effect of the master-slave phase-split flexible interconnection control system of the low-voltage distribution network in an embodiment of the present application;

[0027] Figure 6 is the three-phase current under various working conditions in the first transformer area;

[0028] Figure 7 is the three-phase current under various working conditions in the second substation;

[0029] Figure 8 To transmit current tracking signals from BTB-VSC (from back-to-back voltage source converter);

[0030] Figure 9 The current under the condition of the first transformer area load disturbance;

[0031] Figure 10 The tracking signal from the BTB-VSC when the load in the first substation is disturbed. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0033] When it comes to managing three-phase imbalance in substations, the main current methods are switching capacitors, static VAR compensators, and phase converters. Switching capacitors is the most common way to compensate for three-phase unbalanced loads in substations, but it takes a long time to operate, cannot achieve continuous regulation of reactive power, and there are transient shocks when switching capacitors. Although static VAR compensators can continuously adjust reactive power, they still cannot compensate for active power. Phase converters can control active and reactive power simultaneously, but they require a large investment to achieve the desired three-phase imbalance management effect, resulting in high costs and low equipment utilization. Overall, existing three-phase imbalance management methods have problems such as single function, high investment costs, and low efficiency. They also fail to take into account the interoperability between different substations and the management of light and heavy load issues in substations.

[0034] In terms of managing light and heavy loads in substations, domestic and foreign scholars have successively proposed a variety of flexible interconnection concepts such as ring network power controllers, ring network power balancers, intelligent power routers, and soft interconnection switches, and integrated the management of light and heavy loads in substations with three-phase imbalance problems, effectively improving the utilization rate of the device and the overall management effect. However, the substation light and heavy load / three-phase imbalance management devices in the existing solutions mainly adopt fixed capacity configurations, and the fixed capacity needs to be reasonably configured in combination with the maximum power required for three-phase imbalance management at rated input / output power. When the three-phase imbalance is large, the device will have a large amount of idle capacity, resulting in its relatively high hardware cost. In addition, the large-scale access of random loads has led to an increasingly serious problem of single-phase heavy overload in substations.

[0035] Therefore, there is an urgent need to invent a low-cost distribution network flexible expansion and three-phase imbalance management device to effectively manage the problems of light and heavy loads and three-phase imbalance in the substation area and the lack of flexibility and scalability of existing flexible interconnection devices, and promote the interconnection of new distribution networks and the process of distributed power supply consumption.

[0036] like Figure 1 As shown, in one embodiment, a method for controlling a master-slave phase-split flexible interconnection of a low-voltage distribution network is provided. The method for controlling a master-slave phase-split flexible interconnection of a low-voltage distribution network specifically comprises the following steps:

[0037] S100: Acquire the three-phase current of the first substation and the three-phase current of the second substation, perform sequence component decomposition calculation on the three-phase current of the first substation and the three-phase current of the second substation, and obtain the negative sequence current to be compensated and the zero sequence current to be compensated of the first substation and the second substation, respectively.

[0038] Specifically, the low-voltage distribution network master-slave phase-split flexible interconnection control method of the present application, that is, the distribution network three-phase imbalance control method based on master-slave back-to-back voltage source converters (master-slave BTB-VSC), can be applied to the control module in the low-voltage distribution network master-slave phase-split flexible interconnection control system.

[0039] The two sides of the three-phase imbalance control system (or device) of the distribution network based on the master-slave BTB-VSC are connected to the first substation and the second substation respectively.

[0040] The three-phase current of the first substation and the three-phase current of the second substation (ie, the a-phase current, the b-phase current, and the c-phase current) can be obtained from the metering automation system through the data acquisition device.

[0041] The sequence components of the three-phase current in the first transformer substation are decomposed and calculated to obtain the negative sequence current to be compensated and the zero sequence current to be compensated in the first transformer substation.

[0042] The sequence components of the three-phase current in the second transformer substation are decomposed and calculated to obtain the negative sequence current to be compensated and the zero sequence current to be compensated in the second transformer substation.

[0043] Among them, the negative-sequence current to be compensated includes the negative-sequence current component to be compensated of phase a, the negative-sequence current component to be compensated of phase b, and the negative-sequence current component to be compensated of phase c, and the zero-sequence current to be compensated includes the zero-sequence current component to be compensated of phase a, the zero-sequence current component to be compensated of phase b, and the zero-sequence current component to be compensated of phase c.

[0044] Therefore, the negative sequence current to be compensated in the first substation includes the three-phase negative sequence current component to be compensated The zero-sequence current to be compensated in the first substation includes the three-phase zero-sequence current components to be compensated

[0045] The negative sequence current to be compensated in the second transformer area includes the three-phase negative sequence current components to be compensated The zero-sequence current to be compensated in the second transformer area includes the three-phase zero-sequence current components to be compensated

[0046] S200: Obtaining a target power that the power transmitting station needs to transmit to the power receiving station in order to achieve equal load rates between the first station and the second station.

[0047] Specifically, the target power that the power transmitting area needs to transmit to the power receiving area in order to achieve equal load rates between the first area and the second area can be obtained from the metering automation system through the data acquisition device.

[0048] The power transmission area is the first area, and the power receiving area is the second area.

[0049] The power transmission area is the second area, and the power receiving area is the first area.

[0050] Taking the power transmission from the second substation to the first substation as an example, the data acquisition device obtains the target power that substation 2 needs to transmit to substation 1 when the load rates of the first substation (substation 1) and the second substation (substation 2) are equal from the metering automation system.

[0051] Of course, the first substation may also transmit power to the second substation, which will not be described in detail here.

[0052] S300: Calculating a load current to be compensated in a power receiving area and a regulated load current required for voltage regulation in a power transmission area according to the target power, wherein the power receiving area and the power transmission area are different areas in the first area and the second area.

[0053] Specifically, the load current to be compensated is the load current to be compensated in the power receiving station area, and the load current to be compensated includes a phase a load current component to be compensated, a phase b load current component to be compensated, and a phase c load current component to be compensated, that is:

[0054] The regulated load current is the load current required for voltage stabilization in the power transmission area. The regulated load current includes the a-phase regulated load current component, the b-phase regulated load current component, and the c-phase regulated load current component, namely:

[0055] S400: Calculate a first compensation current reference value of the power receiving station and a second compensation current reference value of the power transmitting station according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first station and the second station, the load current to be compensated of the power receiving station, and the regulated load current of the power transmitting station.

[0056] Specifically, the first compensation current reference value and the second compensation current reference value each include an a-phase compensation current reference value, a b-phase compensation current reference value, and a c-phase compensation current reference value.

[0057] S500: If the compensation current reference value changes, obtain the maximum compensation current reference value of one phase among the three-phase compensation current reference values ​​a, b, and c of the compensation current reference value by comparison, wherein the compensation current reference value is the first compensation current reference value or the second compensation current reference value.

[0058] Specifically, if the first compensation current reference value is changed compared with the historical first compensation current reference value, the three-phase compensation current reference values ​​I ca1_ref , I cb1_ref , I cc1_ref , get the first maximum phase compensation current reference value I c1_max I c1_max That is I ca1_ref , I cb1_ref , I cc1_ref The maximum value in .

[0059] If the second compensation current reference value is changed compared with the historical second compensation current reference value, the three-phase compensation current reference values ​​I ca2_ref , I cb2_ref , I cc2_ref , get the second maximum phase compensation current reference value I c2_max I c2_max That is I ca2_ref , I cb2_ref , I cc2_ref The maximum value in .

[0060] Whether the first compensation current reference value and the second compensation current reference value are changed is determined independently. One of them may be changed while the other remains unchanged, both may be changed, or neither may be changed.

[0061] If the first compensation current reference value is not changed, the steps S100 to S400 related to the power receiving station are re-executed.

[0062] If the second compensation current reference value is not changed, the steps S100 - S400 related to the power transmission section are re-executed.

[0063] S600: Based on the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, adopt corresponding strategies to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter.

[0064] Specifically, based on the comparison result between the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, a corresponding strategy is adopted to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter.

[0065] This embodiment implements a low-cost solution for flexible capacity expansion and three-phase imbalance control in distribution networks based on master-slave back-to-back voltage source converters (BTB-VSCs). The master BTB-VSC transmits all expansion power and a small amount of three-phase imbalance compensation power. By coordinating the slave BTB-VSCs with a multi-way switch, the master BTB-VSC is endowed with flexible phase-by-phase capacity expansion capabilities. This allows for flexible capacity expansion between substations and high-quality three-phase imbalance control at a relatively low overall capacity, effectively and cost-effectively addressing light and heavy loads and three-phase imbalance issues in substations. Furthermore, the various combinations of master and slave BTB-VSC control enhance device flexibility, and when the master BTB-VSC converter capacity is insufficient, the slave BTB-VSC can supplement it, further enhancing the scalability of the device or system. This embodiment effectively enhances the interconnectivity and mutual assistance capabilities of distribution networks, reduces substation operating losses, and lowers the cost of control equipment. It achieves high equipment utilization, efficiently achieves three-phase imbalance control, and promotes the interconnectivity of new distribution networks and the integration of distributed power sources, thus possessing significant engineering significance.

[0066] In one embodiment, if the compensation current reference value changes in step S500, obtaining the maximum compensation current reference value of one phase among the three compensation current reference values ​​a, b, and c by comparison includes:

[0067] If the first compensation current reference value changes, obtaining a first maximum phase compensation current reference value by comparing and obtaining a maximum phase compensation current reference value among the three phase compensation current reference values ​​a, b, and c of the first compensation current reference value;

[0068] If the second compensation current reference value changes, obtaining the maximum phase compensation current reference value among the three-phase compensation current reference values ​​a, b, and c of the second compensation current reference value by comparison to obtain a second maximum phase compensation current reference value;

[0069] In step S600, according to the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, a corresponding strategy is adopted to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter, including:

[0070] If the first compensation current reference value changes, a first strategy is used to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between a first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, wherein the first rated current is the rated current of the side of the master back-to-back voltage source converter connected to the power receiving station, and the first side is the side connected to the power receiving station;

[0071] If the second compensation current reference value changes, a second strategy is adopted to perform second compensation current control on the second side of the main back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the main back-to-back voltage source converter and the second maximum phase compensation current reference value, wherein the second rated current is the rated current of the side of the main back-to-back voltage source converter connected to the power transmission station area, and the second side is the side connected to the power transmission station area.

[0072] Specifically, the first compensation current reference value and the second compensation current reference value both include an a-phase compensation current reference value, a b-phase compensation current reference value, and a c-phase compensation current reference value.

[0073] If the first compensation current reference value is changed compared with the historical first compensation current reference value, the first compensation current reference value a, b, c three-phase compensation current reference value I ca1_ref , I cb1_ref , I cc1_ref , get the first maximum phase compensation current reference value I c1_max I c1_max That is I ca1_ref , I cb1_ref , I cc1_ref The maximum value in .

[0074] If the second compensation current reference value is changed compared with the historical second compensation current reference value, the three-phase compensation current reference values ​​I a, b, c of the second compensation current reference value are compared. ca2_ref , I cb2_ref , I cc2_ref , get the second maximum phase compensation current reference value I c2_max I c2_max That is I ca2_ref , I cb2_ref , I cc2_ref The maximum value in .

[0075] When the first compensation current reference value changes, corresponding steps are executed to implement the first compensation current control.

[0076] If the second compensation current reference value changes, corresponding steps are executed to implement the second compensation current control.

[0077] The two operate independently.

[0078] In one embodiment, if the first compensation current reference value changes, a first strategy is employed to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, including:

[0079] If the first maximum phase compensation current reference value is greater than the first rated current of the master back-to-back voltage source converter, switching the first side of the slave back-to-back single-phase full-bridge converter to be connected to a first target phase line of the power receiving station through a three-to-one multi-way switch corresponding to the power receiving station, wherein the first target phase line is a phase line corresponding to the first maximum phase compensation current reference value in the feeder of the power receiving station;

[0080] The compensation current on the first side of the master back-to-back voltage source converter is controlled to be the first rated current of the master back-to-back voltage source converter, and the compensation current on the first side of the slave back-to-back voltage source converter is controlled to be the difference between the first maximum phase compensation current reference value and the first rated current of the master back-to-back voltage source converter.

[0081] Specifically, the master back-to-back voltage source converter is the master BTB-VSC, and the slave back-to-back voltage source converter is the slave BTB-VSC. It should be noted that the rated currents of this embodiment are all single-phase rated currents.

[0082] Compare the first maximum phase compensation current reference value I of the power receiving station area c1_max Is it greater than the first rated current I of the main back-to-back voltage source converter (ie, main BTB-VSC)? N1 , if the first maximum phase compensation current reference value I c1_max Greater than the first rated current I of the main BTB-VSC N1 , then the three-to-one multi-way switch corresponding to the power receiving station area will switch from the grid connection point of the back-to-back voltage source converter (slave BTB-VSC) to the phase line corresponding to the first maximum phase compensation current reference value of the power receiving station area (i.e., the first target phase line), and the compensation current of the first side connected between the master BTB-VSC and the power receiving station area will be controlled by the PI closed loop to be the first rated current I of the master BTB-VSC. N1 , through PI closed-loop control, the compensation current of the first side connected to the BTB-VSC and the power receiving station area is the difference between the first maximum phase compensation current reference value and the first rated current of the main BTB-VSC.

[0083] The three-choice multi-way switch corresponding to the power receiving station area will switch from the grid connection point of the BTB-VSC to the phase line corresponding to the first maximum phase compensation current reference value in the power receiving station area, and control the compensation current I of the main BTB-VSC through the PI closed loop. cx1 (x=a, b, c) is the first rated current I of the main BTB-VSC N1 , through PI closed loop control from the BTB-VSC compensation current I c3 The difference between the first maximum phase compensation current reference value and the first rated current of the main BTB-VSC (I c1_max -I N1 ).

[0084] In one embodiment, if the first compensation current reference value changes, a first strategy is employed to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, including:

[0085] If the first maximum phase compensation current reference value is less than the first rated current of the main back-to-back voltage source converter, the three-to-one multi-way switch state corresponding to the power receiving station is controlled to remain unchanged, the compensation current on the first side of the main back-to-back voltage source converter is controlled to be the first maximum phase compensation current reference value, and the compensation current on the first side of the slave back-to-back voltage source converter is controlled to be 0.

[0086] Specifically, compare the first maximum phase compensation current reference value I c1_max Is it greater than the first rated current I of the main back-to-back voltage source converter (ie, main BTB-VSC)? N1 , if the first maximum phase compensation current reference value I c1_max Less than or not more than the first rated current I of the main BTB-VSC N1 , the state of the three-to-one multiplexer corresponding to the power receiving station remains unchanged, and the compensation current on the first side of the master back-to-back voltage source converter (master BTB-VSC) connected to the power receiving station is controlled by the PI closed loop to be the first maximum phase compensation current reference value, and the compensation current on the first side of the slave back-to-back voltage source converter (slave BTB-VSC) connected to the power receiving station is controlled by the PI closed loop to be 0.

[0087] The state of the three-choice multiplexer corresponding to the power receiving station remains unchanged, and the compensation current I on the first side of the main BTB-VSC is controlled by the PI closed loop. cx1 The three-phase compensation currents (x=a, b, c) are all the first maximum phase compensation current reference value I c1_max , through PI closed loop control from the BTB-VSC compensation current Ic3 is 0.

[0088] In one embodiment, if the second compensation current reference value changes, a second strategy is employed to perform second compensation current control on the second side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the master back-to-back voltage source converter and the second maximum phase compensation current reference value, including:

[0089] If the second maximum phase compensation current reference value is greater than the second rated current of the master back-to-back voltage source converter, switching the second side of the slave back-to-back single-phase full-bridge converter to be connected to a second target phase line of the power transmission section through a three-to-one multi-way switch corresponding to the power transmission section, wherein the second target phase line is a phase line corresponding to the second maximum phase compensation current reference value in the feeder of the power transmission section;

[0090] The compensation current on the second side of the main back-to-back voltage source converter is controlled to be the second rated current of the main back-to-back voltage source converter, and the compensation current on the second side of the slave back-to-back voltage source converter is controlled to be the difference between the second maximum phase compensation current reference value and the second rated current of the main back-to-back voltage source converter.

[0091] Specifically, the master back-to-back voltage source converter is a master BTB-VSC; the slave back-to-back voltage source converter is a slave BTB-VSC.

[0092] Compare the second maximum phase compensation current reference value I c2_max Is it greater than the second rated current I of the main back-to-back voltage source converter (ie, main BTB-VSC)? N2 , if the second maximum phase compensation current reference value I c2_max Greater than the main BTB-VSC rated current I N2 , then the three-to-one multi-way switch corresponding to the power transmission section will be switched from the grid connection point of the BTB-VSC to the phase line corresponding to the second maximum phase compensation current reference value in the power transmission section (i.e., the second target phase line), and the compensation current of the second side of the connection between the main BTB-VSC and the power transmission section is controlled by the PI closed loop to be the second rated current I of the main BTB-VSC. N2 , through PI closed loop control, the compensation current on the second side connected from the BTB-VSC to the power transmission station is the second maximum phase compensation current reference value I c2_max With the second rated current I of the main BTB-VSC N2 difference.

[0093] Among them, the grid connection point of the power transmission area from the BTB-VSC and the grid connection point of the power receiving area from the BTB-VSC are two different grid connection points.

[0094] The three-choice multi-way switch corresponding to the power transmission station area will switch from the grid connection point of BTB-VSC to the corresponding phase line connection with the second maximum phase compensation current reference value, and control the compensation current I on the second side of the main BTB-VSC through the PI closed loop. cx2 (x=a, b, c) is the second rated current I of the main BTB-VSC N2 , through PI closed loop control from the compensation current I on the second side of BTB-VSC c4 The second maximum phase compensation current reference value I c2_max With the second rated current I of the main BTB-VSC N2 The difference, that is (I c2_max -I N2 ).

[0095] In one embodiment, if the second compensation current reference value changes, a second strategy is employed to perform second compensation current control on the second side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the master back-to-back voltage source converter and the second maximum phase compensation current reference value, including:

[0096] If the second maximum phase compensation current reference value is less than the second rated current of the main back-to-back voltage source converter, the three-to-one multi-way switch state corresponding to the power transmission station is controlled to remain unchanged, the compensation current on the second side of the main back-to-back voltage source converter is controlled to be the second maximum phase compensation current reference value, and the compensation current on the second side of the slave back-to-back voltage source converter is controlled to be 0.

[0097] Specifically, compare the second maximum phase compensation current reference value I c2_max Is it greater than the second rated current I of the main back-to-back voltage source converter (ie, main BTB-VSC)? N2 , if the second maximum phase compensation current reference value I c2_max Less than or not more than the second rated current I of the main BTB-VSC N2 , the state of the three-to-one multi-way switch corresponding to the power transmission section remains unchanged, and the compensation current on the second side of the master back-to-back voltage source converter (master BTB-VSC) is controlled to be the second maximum phase compensation current reference value through the PI closed loop, and the compensation current on the second side of the slave back-to-back voltage source converter (slave BTB-VSC) is controlled to be 0 through the PI closed loop.

[0098] The state of the three-choice multi-way switch corresponding to the power transmission station remains unchanged, and the compensation current I on the second side of the main BTB-VSC is controlled by the PI closed loop. cx2 The three-phase compensation currents (x=a, b, c) are all the second maximum phase compensation current reference value I c2_max, through PI closed loop control from the compensation current I on the second side of BTB-VSC c4 is 0.

[0099] In one embodiment, step S400 calculates a first compensation current reference value of the power receiving station and a second compensation current reference value of the power transmitting station based on the negative sequence current to be compensated and the zero sequence current to be compensated of the first station and the second station, the load current to be compensated of the power receiving station, and the regulated load current of the power transmitting station, including:

[0100] Calculating a first compensation current reference value of the power receiving station area according to the negative sequence current to be compensated, the zero sequence current to be compensated, and the load current to be compensated of the power receiving station area;

[0101] A second compensation current reference value of the power transmission station area is calculated according to the negative sequence current to be compensated, the zero sequence current to be compensated and the regulated load current of the power transmission station area.

[0102] Specifically, taking the transmission of power from the second station to the first station as an example, according to the negative sequence current to be compensated in the first station Zero-sequence current to be compensated Load current to be compensated Calculate the first compensation current reference value of the first station area, that is, the power receiving station area, which includes the three-phase compensation current reference values ​​I ca1_ref , I cb1_ref , I cc1_ref .

[0103] According to the negative sequence current to be compensated in the second substation Zero-sequence current to be compensated Load current required for voltage regulation The second compensation current reference value of the second section, i.e., the power transmission section, is calculated, and the three-phase compensation current reference values ​​thereof are I ca2_ref , I cb2_ref , I cc2_ref .

[0104] The same applies to the power transmission from the first area to the second area, which will not be repeated here.

[0105] In one embodiment, if the first station is a power receiving station and the second station is a power transmitting station, the first compensation current reference value and the second compensation current reference value are calculated using the following formula:

[0106]

[0107] in, They are the negative sequence current component to be compensated for phase a, phase b and phase c of the first transformer substation, respectively. They are the zero-sequence current component of phase a to be compensated, the zero-sequence current component of phase b to be compensated, and the zero-sequence current component of phase c to be compensated in the first transformer substation, respectively. are the load current component of phase a to be compensated, the load current component of phase b to be compensated, and the load current component of phase c to be compensated in the first station area serving as the power receiving station area respectively; I ca1_ref , I cb1_ref , I cc1_ref The first compensation current reference value of phase a, the first compensation current reference value of phase b and the first compensation current reference value of phase c are respectively the first compensation current reference values ​​of the first station area;

[0108] They are the negative sequence current component to be compensated for phase a, phase b and phase c of the second transformer substation, respectively. They are the zero-sequence current component of phase a to be compensated, the zero-sequence current component of phase b to be compensated, and the zero-sequence current component of phase c to be compensated in the second substation, respectively. are the a-phase regulated load current component, the b-phase regulated load current component, and the c-phase regulated load current component of the second power transmission station area respectively; I ca2_ref , I cb2_ref , I cc2_ref The second compensation current reference value of the second stage area are respectively the a-phase second compensation current reference value, the b-phase second compensation current reference value and the c-phase second compensation current reference value.

[0109] Specifically, the formula for transmitting power from the first substation to the second substation is similar and will not be repeated here.

[0110] The first compensation current reference value is a compensation current reference value of the master-slave back-to-back voltage source converter in the power receiving section.

[0111] The second compensation current reference value is a compensation current reference value of the master-slave back-to-back voltage source converter in the power transmission section.

[0112] refer to Figure 2 The present application also provides a low-voltage distribution network master-slave split-phase flexible interconnection control system 1, that is, a distribution network three-phase imbalance control device or system based on master-slave back-to-back voltage source converters. The low-voltage distribution network master-slave split-phase flexible interconnection control system 1 includes: a master back-to-back voltage source converter 10, a slave back-to-back voltage source converter 20, a first three-to-one multi-way switch 30, a second three-to-one multi-way switch 40, and a control module (not shown in the figure);

[0113] The main back-to-back voltage source converter 10 comprises a back-to-back three-phase full-bridge converter;

[0114] Both sides of the back-to-back three-phase full-bridge converter are connected to the three phases of the feeder of the first substation and the three phases of the feeder of the second substation respectively;

[0115] The back-to-back voltage source converter 20 includes a back-to-back single-phase full-bridge converter;

[0116] The back-to-back single-phase full-bridge converters are connected to the neutral line of the first transformer zone and the neutral line of the second transformer zone respectively;

[0117] One side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the first substation through the first three-to-one multi-way switch 30, wherein the target phase line of the first substation is the phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the first substation;

[0118] The other side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the second substation through the second three-to-one multi-way switch 40, wherein the target phase line of the second substation is the single-phase phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the second substation;

[0119] A control module is used to control three-phase imbalance according to any of the above-mentioned low-voltage distribution network master-slave phase-split flexible interconnection control methods.

[0120] Specifically, the back-to-back voltage source converter is Back-to-back voltage source converter, BTB-VSC.

[0121] The master back-to-back voltage source converter 10 has a larger capacity, and the slave back-to-back voltage source converter 20 has a smaller capacity.

[0122] The back-to-back three-phase full-bridge converter includes two back-to-back three-phase full-bridge converters.

[0123] Among them, one three-phase full-bridge converter is connected to the three phases of the feeder of the first substation (i.e., phase a, phase b, and phase c) through different terminals. Another three-phase full-bridge converter is connected to the three phases of the feeder of the second substation (i.e., phase a, phase b, and phase c) through different terminals.

[0124] The three first connection terminals of the first three-to-one multi-way switch 30 are respectively connected to the three phases of the feeder of the first substation.

[0125] The three first connection terminals of the second three-to-one multi-way switch 40 are respectively connected to the three phases of the feeder of the second substation.

[0126] The slave back-to-back voltage source converter 20 includes two back-to-back single-phase full-bridge converters.

[0127] A single-phase full-bridge converter is connected to the neutral line of the first transformer substation, and is also connected to a target phase line in the feeder of the first transformer substation via the second connection end of the first three-to-one multiplexer 30 .

[0128] Another single-phase full-bridge converter is connected to the neutral line of the second transformer substation, and is also connected to a target phase line in the feeder of the second transformer substation via a second connection end of a second three-to-one multiplexer 40 .

[0129] In one embodiment, the back-to-back three-phase full-bridge converter includes two first three-phase full-bridge inverters and a second three-phase full-bridge inverter connected back-to-back and in parallel, and a first DC-side energy storage capacitor connected in parallel and located between the two three-phase full-bridge inverters;

[0130] The first three-phase full-bridge inverter comprises three first sub-circuits respectively connected to the three phases of the feeder of the first substation, and each first sub-circuit comprises two IGBTs connected in series;

[0131] The second three-phase full-bridge inverter includes three second sub-circuits respectively connected to the three phases of the feeder of the second substation, and each second sub-circuit includes two IGBTs connected in series;

[0132] Specifically, the first three-phase full-bridge inverter and the second three-phase full-bridge inverter are both three-phase full-bridge converters.

[0133] The first three-phase full-bridge inverter includes three phases or three first sub-circuits, each first sub-circuit is connected to a phase line of the first stage through a filter inductor, and different first sub-circuits are connected to different phase lines of the first stage.

[0134] The second three-phase full-bridge inverter includes three phases or three second sub-circuits, each second sub-circuit is connected to a phase line of the second stage through a filter inductor, and different second sub-circuits are connected to different phase lines of the second stage.

[0135] Each of the first sub-circuit and the second sub-circuit includes two IGBTs connected in series.

[0136] Each of the first sub-circuit and the second sub-circuit is connected to the corresponding phase line via a common node of two IGBTs connected in series therein.

[0137] IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of a BJT (bipolar junction transistor) and a MOS (insulated gate field effect transistor). It has the advantages of both the high input impedance of a MOSFET and the low on-state voltage drop of a GTR.

[0138] Specific reference Figure 3The back-to-back three-phase full-bridge converter includes 12 IGBT devices S11~S16 and S21~S26, 6 filter inductors L1 and a DC side energy storage capacitor C dc1 .

[0139] Specifically, the first subcircuit includes two IGBTs (S11 and S12) connected in series; the second subcircuit includes two IGBTs (S13 and S14) connected in series; and the third subcircuit includes two IGBTs (S15 and S16) connected in series. The three subcircuits are connected to the corresponding phase lines of the first stage via different filter inductors (L11, L12, and L13).

[0140] The first second subcircuit includes two IGBTs (S21 and S22) connected in series; the second second subcircuit includes two IGBTs (S23 and S24) connected in series; and the third second subcircuit includes two IGBTs (S25 and S26) connected in series. The three second subcircuits are connected to the corresponding phase lines of the second stage via different filter inductors (L21, L22, and L23).

[0141] Two IGBTs connected in series are formed by connecting the emitter node of the first IGBT in series with the collector node of the second IGBT.

[0142] A first DC side energy storage capacitor C is connected in parallel between the first three-phase full-bridge inverter and the second three-phase full-bridge inverter. dc1 .

[0143] DC side energy storage capacitor C dc1 Installed on the DC side of the main back-to-back voltage source converter 10 (i.e., main BTB-VSC), C dc1 The positive electrode of the capacitor is connected to the collector node of the first IGBT (ie, S11, S13, S15, S21, S23, S25) in each of the first and second sub-circuits, C dc1 The negative electrode of the capacitor is connected to the emitter node of the second IGBT (ie, S12, S14, S16, S22, S24, S26) in each of the first and second sub-circuits.

[0144] The functions of the control module are described in detail in the above method and will not be repeated here.

[0145] This embodiment implements a low-cost solution for flexible capacity expansion and three-phase imbalance control in distribution networks based on a master-slave back-to-back voltage source converter (BTB-VSC). The master BTB-VSC transmits all expansion power and a small amount of three-phase imbalance compensation power. By coordinating the slave BTB-VSC with a multi-way switch, the master BTB-VSC is endowed with flexible phase-by-phase capacity expansion capabilities. This allows for flexible capacity expansion between substations and high-quality three-phase imbalance control at a relatively low overall capacity, effectively and cost-effectively addressing light and heavy loads and three-phase imbalance issues in substations. Furthermore, the multiple combined control of the master and slave BTB-VSCs enhances the device's flexibility, and when the master BTB-VSC converter capacity is insufficient, the slave BTB-VSC can supplement it, making the device more scalable. This embodiment effectively improves the interconnectivity and mutual assistance capabilities of distribution networks, reduces substation operating losses, and lowers the cost of control devices. It achieves high equipment utilization, efficiently achieves three-phase imbalance control, and promotes the interconnection and integration of new distribution networks and the integration of distributed power sources, thus possessing significant engineering significance.

[0146] In one embodiment, the back-to-back single-phase full-bridge converter includes two first single-phase full-bridge inverters and a second single-phase full-bridge inverter connected back-to-back and in parallel, and a second DC-side energy storage capacitor connected in parallel and located between the two single-phase full-bridge inverters;

[0147] The first single-phase full-bridge inverter includes two third sub-circuits connected to the neutral line of the first stage and the second connection terminal of the first three-to-one multiplex switch 30 respectively;

[0148] The second single-phase full-bridge inverter includes two fourth sub-circuits connected to the neutral line of the second stage and the second connection end of the second three-to-one multiple-way switch 40 respectively.

[0149] Specifically, the first single-phase full-bridge inverter includes two third subcircuits, one of which is connected to the neutral line of the first stage, and the other is connected to the second connection terminal of the first three-to-one multi-way switch 30 via the filter inductor L1.

[0150] The second single-phase full-bridge inverter includes two fourth subcircuits, one of which is connected to the neutral line of the second stage, and the other is connected to the second connection terminal of the second three-to-one multi-way switch 40 via the filter inductor L2.

[0151] Each of the third sub-circuit and the fourth sub-circuit includes two IGBTs connected in series.

[0152] Each of the third sub-circuit and the fourth sub-circuit is connected to the neutral line or the second connection terminal via a common node of two IGBTs connected in series therein.

[0153] IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of a BJT (bipolar junction transistor) and a MOS (insulated gate field effect transistor). It has the advantages of both the high input impedance of a MOSFET and the low on-state voltage drop of a GTR.

[0154] Specific reference Figure 3 The back-to-back single-phase full-bridge converter includes 8 IGBT devices Q11~Q14 and Q21~Q24, 2 filter inductors (L1, L2) and a DC side energy storage capacitor C dc2 .

[0155] Specifically, the first and third sub-circuits each include two IGBTs ( Q11 and Q12 ) connected in series; and the second and third sub-circuits each include two IGBTs ( Q13 and Q14 ) connected in series.

[0156] The first fourth sub-circuit includes two IGBTs ( Q21 and Q22 ) connected in series; the second fourth sub-circuit includes two IGBTs ( Q23 and Q24 ) connected in series.

[0157] Two IGBTs connected in series are formed by connecting the emitter node of the first IGBT in series with the collector node of the second IGBT.

[0158] A second DC side energy storage capacitor C is connected in parallel between the first single-phase full-bridge inverter and the second single-phase full-bridge inverter. dc2 .

[0159] In one embodiment, all IGBTs are provided with an anti-parallel diode.

[0160] Specifically, each IGBT includes an anti-parallel diode, which can protect the IGBT.

[0161] Figure 4 A schematic diagram showing the compensation current, Figure 5 The diagram is an enlarged effect diagram of the schematic diagram of the compensation current. Taking the first station area as the power receiving area and the second station area as the power transmission area as an example, the three-phase compensation current of the main back-to-back voltage source converter 10 in the first station area is I ca1 , I cb1 , I cc1 The three-phase compensation currents of the main back-to-back voltage source converter 10 in the second station are I ca2 , I cb2 , I cc2 The compensation current from the back-to-back voltage source converter 20 in the first station is I c3, the compensation current from the back-to-back voltage source converter 20 in the second station is I c4 .

[0162] Figure 6 is the three-phase current under various working conditions in the first transformer area; Figure 7 is the three-phase current under various working conditions in the second substation; Figure 8 Transmits current tracking signals from the back-to-back voltage source converter (slave BTB-VSC).

[0163] In Matlab's Simulink, a three-phase unbalance control method based on the master-slave BTB-VSC (master-slave back-to-back voltage source converter) was simulated. The simulation set the total capacity of substation 1 and substation 2 to 400kVA. Before interconnection, the total load of substation 1 was 375kW, the A phase load was 145kW, the B phase load was 130kW, and the C phase load was 105kW. The total load of substation 2 was 195kW, the A phase load was 45kW, the B phase load was 65kW, and the C phase load was 85kW. Both substations were in a three-phase unbalanced state, and substation 1 was in a heavy load state, resulting in large system losses. A master BTB-VSC is set up, where the capacity of each phase of the master BTB-VSC is 25kVA. According to the principles of the three-phase imbalance control method and system based on the master-slave BTB-VSC described above, it can be seen that phase A needs to transmit the most power. In the master BTB-VSC, the capacity of phase A is less than the power to be transmitted, and the current to be compensated of phase A is greater than the rated current of the master BTB-VSC. Therefore, the master BTB-VSC first transmits the power of phases B and C and a portion of the power of phase A. The remaining power that needs to be transmitted by phase A is transmitted through the slave BTB-VSC, and a portion of the current to be compensated of phase A and the currents to be compensated of phases B and C in substation 1 is compensated by the main BTB-VSC. The slave BTB-VSC compensates for the remaining current to be compensated of phase A.

[0164] In substation 2, the phase A current to be compensated is greater than the rated current of the slave BTB-VSC. Therefore, the current transmitted by the master BTB-VSC for phase A is equal to the rated current of the slave BTB-VSC, and the current transmitted by the slave BTB-VSC is equal to the remaining phase A current to be compensated. The same conclusion holds true if the current to be compensated changes.

[0165] Depend on Figure 6 It can be seen that the three phases are unbalanced and the current value is high before 0.1s. At 0.1s, the main BTB-VSC is put into operation, and it can be seen that the currents of phases B and C are in a balanced state. Due to the insufficient capacity of the main BTB-VSC, the current of phase A is about 100A higher than the current values ​​of phases B and C. At 0.2s, the slave BTB-VSC is put into operation. Figure 6 It can be seen that after this, the A phase current is also well compensated. Figure 8It can be seen that the current tracking signal transmitted from BTB-VSC is good, and after compensation, the three phases A, B, and C are in a three-phase balanced state. Figure 7 Available with Figure 6 The same conclusion is reached, and the current of each phase of the two substations is around the effective value of 431A, with the same load factor. The overload of substation 1 has been effectively resolved.

[0166] Figure 9 The current under the condition of the first transformer area load disturbance; Figure 10 The tracking signal from the BTB-VSC when the load in the first substation is disturbed.

[0167] Taking Area 1 (the first area) as an example, Figure 10 It can be seen that at 0.3s, the A-phase load in substation 1 was disturbed, and the load power increased by 5kW. At the same time, the A-phase load in substation 2 decreased by 5kW, and the A-phase current to be compensated changed. After balancing, the load rate of the substation did not change. According to the above-described three-phase imbalance control method and system principle based on the master-slave BTB-VSC, the A-phase current to be compensated is still greater than the rated current of the master BTB-VSC, and the A-phase compensation current continues to be transmitted to substation 1 through the slave BTB-VSC. Figure 10 In the example, at 0.35s, the disturbance in phase A was compensated by the BTB-VSC, and the three-phase balance was restored. The same is true for substation 2, which will not be repeated here.

[0168] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, which can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0169] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0170] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A low-voltage distribution network master-slave phase-split flexible interconnection control method, characterized in that: A control module applied to a master-slave split-phase flexible interconnection control system of a low-voltage distribution network, wherein the master-slave split-phase flexible interconnection control system of the low-voltage distribution network also includes a master back-to-back voltage source converter, a slave back-to-back voltage source converter and a three-to-one multi-way switch, wherein the master back-to-back voltage source converter includes a back-to-back three-phase full-bridge converter; the two sides of the back-to-back three-phase full-bridge converter are respectively connected to the three phases of the feeder of the first substation and the three phases of the feeder of the second substation; the slave back-to-back voltage source converter includes a back-to-back single-phase full-bridge converter; the back-to-back single-phase full-bridge converter is respectively connected to the neutral line, The neutral line of the second substation is connected; one side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the first substation through a first three-to-one multi-way switch, wherein the target phase line of the first substation is a phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the first substation; the other side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the second substation through a second three-to-one multi-way switch, wherein the target phase line of the second substation is a phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the second substation, and the method includes: Obtain the three-phase current of the first substation and the three-phase current of the second substation, perform sequence component decomposition calculation on the three-phase current of the first substation and the three-phase current of the second substation, and obtain the negative sequence current to be compensated and the zero sequence current to be compensated of the first substation and the second substation respectively; Obtaining a target power that needs to be transmitted from the power transmitting area to the power receiving area in order to achieve equal load rates between the first area and the second area; Calculating the load current to be compensated of the power receiving section and the regulated load current required for voltage stabilization of the power transmitting section according to the target power, wherein the power receiving section and the power transmitting section are different sections from the first section and the second section; Calculate a first compensation current reference value of the power receiving area and a second compensation current reference value of the power transmitting area according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first and second areas, the load current to be compensated of the power receiving area, and the regulated load current of the power transmitting area; If the compensation current reference value changes, obtaining a maximum compensation current reference value of one phase among the three-phase compensation current reference values ​​a, b, and c of the compensation current reference value by comparison, wherein the compensation current reference value is the first compensation current reference value or the second compensation current reference value; According to the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, corresponding strategies are adopted to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter.

2. The method according to claim 1, characterized in that If the compensation current reference value changes, obtaining the maximum compensation current reference value of one phase among the three-phase compensation current reference values ​​a, b, and c of the compensation current reference value by comparison includes: If the first compensation current reference value changes, obtaining a first maximum phase compensation current reference value by comparing and obtaining a maximum phase compensation current reference value among the three phase compensation current reference values ​​a, b, and c of the first compensation current reference value; If the second compensation current reference value changes, obtaining the maximum phase compensation current reference value among the three-phase compensation current reference values ​​a, b, and c of the second compensation current reference value by comparison to obtain a second maximum phase compensation current reference value; The method of controlling the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter using a corresponding strategy according to the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value includes: If the first compensation current reference value changes, a first strategy is used to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between a first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, wherein the first rated current is the rated current of the side of the master back-to-back voltage source converter connected to the power receiving station, and the first side is the side connected to the power receiving station; If the second compensation current reference value changes, a second strategy is adopted to perform second compensation current control on the second side of the main back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the main back-to-back voltage source converter and the second maximum phase compensation current reference value, wherein the second rated current is the rated current of the side of the main back-to-back voltage source converter connected to the power transmission station area, and the second side is the side connected to the power transmission station area.

3. The method according to claim 2, characterized in that If the first compensation current reference value changes, a first strategy is used to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, including: If the first maximum phase compensation current reference value is greater than the first rated current of the main back-to-back voltage source converter, switching the first side of the back-to-back single-phase full-bridge converter to be connected to a first target phase line of the power receiving station through a three-to-one multi-way switch corresponding to the power receiving station, wherein the first target phase line is a phase line corresponding to the first maximum phase compensation current reference value in the feeder of the power receiving station; The compensation current on the first side of the master back-to-back voltage source converter is controlled to be the first rated current of the master back-to-back voltage source converter, and the compensation current on the first side of the slave back-to-back voltage source converter is controlled to be the difference between the first maximum phase compensation current reference value and the first rated current of the master back-to-back voltage source converter.

4. The method according to claim 2, characterized in that If the first compensation current reference value changes, a first strategy is used to perform first compensation current control on the first side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the first rated current of the master back-to-back voltage source converter and the first maximum phase compensation current reference value, including: If the first maximum phase compensation current reference value is less than the first rated current of the main back-to-back voltage source converter, the three-to-one multi-way switch state corresponding to the power receiving station is controlled to remain unchanged, the compensation current on the first side of the main back-to-back voltage source converter is controlled to be the first maximum phase compensation current reference value, and the compensation current on the first side of the slave back-to-back voltage source converter is controlled to be 0.

5. The method according to claim 2, characterized in that If the second compensation current reference value changes, a second strategy is adopted to perform second compensation current control on the second side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the master back-to-back voltage source converter and the second maximum phase compensation current reference value, including: If the second maximum phase compensation current reference value is greater than the second rated current of the main back-to-back voltage source converter, switching the second side of the back-to-back single-phase full-bridge converter to be connected to the second target phase line of the power transmission section through the three-to-one multi-way switch corresponding to the power transmission section, wherein the second target phase line is the phase line corresponding to the second maximum phase compensation current reference value in the feeder of the power transmission section; The compensation current on the second side of the main back-to-back voltage source converter is controlled to be the second rated current of the main back-to-back voltage source converter, and the compensation current on the second side of the slave back-to-back voltage source converter is controlled to be the difference between the second maximum phase compensation current reference value and the second rated current of the main back-to-back voltage source converter.

6. The method according to claim 2, characterized in that If the second compensation current reference value changes, a second strategy is adopted to perform second compensation current control on the second side of the master back-to-back voltage source converter and the slave back-to-back voltage source converter based on a comparison between the second rated current of the master back-to-back voltage source converter and the second maximum phase compensation current reference value, including: If the second maximum phase compensation current reference value is less than the second rated current of the main back-to-back voltage source converter, the three-to-one multi-way switch state corresponding to the power transmission station is controlled to remain unchanged, the compensation current on the second side of the main back-to-back voltage source converter is controlled to be the second maximum phase compensation current reference value, and the compensation current on the second side of the slave back-to-back voltage source converter is controlled to be 0.

7. The method according to claim 1, characterized in that The calculating of a first compensation current reference value of the power receiving area and a second compensation current reference value of the power transmitting area according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first and second areas, the load current to be compensated of the power receiving area, and the regulated load current of the power transmitting area includes: Calculating a first compensation current reference value of the power receiving station according to the negative sequence current to be compensated, the zero sequence current to be compensated, and the load current to be compensated of the power receiving station; A second compensation current reference value of the power transmission section is calculated according to the negative sequence current to be compensated, the zero sequence current to be compensated and the regulated load current of the power transmission section.

8. The method according to claim 7, characterized in that If the first station area is a power receiving station area and the second station area is a power transmitting station area, the first compensation current reference value and the second compensation current reference value are calculated using the following formula: in, They are the negative sequence current component to be compensated for phase a, phase b and phase c of the first transformer substation, respectively. They are the zero-sequence current component of phase a to be compensated, the zero-sequence current component of phase b to be compensated, and the zero-sequence current component of phase c to be compensated in the first transformer substation, respectively. are the load current component of phase a to be compensated, the load current component of phase b to be compensated, and the load current component of phase c to be compensated in the power receiving station area respectively; I ca1_ref , I cb1_ref , I cc1_ref The first compensation current reference value of phase a, the first compensation current reference value of phase b and the first compensation current reference value of phase c are respectively the first compensation current reference values ​​of the first station area; They are the negative sequence current component to be compensated for phase a, phase b and phase c of the second transformer substation, respectively. They are the zero-sequence current component of phase a to be compensated, the zero-sequence current component of phase b to be compensated, and the zero-sequence current component of phase c to be compensated in the second substation, respectively. are the a-phase regulated load current component, b-phase regulated load current component and c-phase regulated load current component of the power transmission station; I ca2_ref , I cb2_ref , I cc2_ref The second compensation current reference value of the second stage area are respectively the a-phase second compensation current reference value, the b-phase second compensation current reference value and the c-phase second compensation current reference value.

9. A low-voltage distribution network master-slave phase-split flexible interconnection control system, characterized in that: The system comprises: a master back-to-back voltage source converter, a slave back-to-back voltage source converter, a first three-to-one multiplexer, a second three-to-one multiplexer and a control module; The main back-to-back voltage source converter comprises a back-to-back three-phase full-bridge converter; Both sides of the back-to-back three-phase full-bridge converter are respectively connected to the three phases of the feeder of the first substation and the three phases of the feeder of the second substation; The slave back-to-back voltage source converter comprises a back-to-back single-phase full-bridge converter; The back-to-back single-phase full-bridge converters are connected to the neutral line of the first transformer area and the neutral line of the second transformer area respectively; One side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the first substation through a first three-to-one multi-way switch, wherein the target phase line of the first substation is a phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the first substation; The other side of the back-to-back single-phase full-bridge converter can be connected to the target phase line in the feeder of the second substation through a second three-to-one multi-way switch, wherein the target phase line of the second substation is a phase line corresponding to the maximum single-phase compensation current reference value among the compensation current reference values ​​of the second substation; The control module is used to obtain the three-phase current of the first substation and the three-phase current of the second substation, perform sequence component decomposition calculation on the three-phase current of the first substation and the three-phase current of the second substation, and obtain the negative sequence current to be compensated and the zero sequence current to be compensated of the first substation and the second substation respectively; Obtaining a target power that needs to be transmitted from the power transmitting area to the power receiving area in order to achieve equal load rates between the first area and the second area; Calculating the load current to be compensated of the power receiving section and the regulated load current required for voltage stabilization of the power transmitting section according to the target power, wherein the power receiving section and the power transmitting section are different sections from the first section and the second section; Calculate a first compensation current reference value of the power receiving area and a second compensation current reference value of the power transmitting area according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first and second areas, the load current to be compensated of the power receiving area, and the regulated load current of the power transmitting area; If the compensation current reference value changes, obtaining a maximum compensation current reference value of one phase among the three-phase compensation current reference values ​​a, b, and c of the compensation current reference value by comparison, wherein the compensation current reference value is the first compensation current reference value or the second compensation current reference value; According to the rated current of the master back-to-back voltage source converter and the maximum single-phase compensation current reference value, corresponding strategies are adopted to control the compensation current of the master back-to-back voltage source converter and the slave back-to-back voltage source converter.

10. The system according to claim 9, characterized in that The back-to-back three-phase full-bridge converter comprises two first three-phase full-bridge inverters and a second three-phase full-bridge inverter connected back-to-back and in parallel, and a first DC-side energy storage capacitor connected in parallel and located between the two three-phase full-bridge inverters; The first three-phase full-bridge inverter comprises three first sub-circuits respectively connected to the three phases of the feeder of the first substation, and each first sub-circuit comprises two IGBTs connected in series; The second three-phase full-bridge inverter includes three second sub-circuits respectively connected to the three phases of the feeder of the second substation, and each second sub-circuit includes two IGBTs connected in series; The back-to-back single-phase full-bridge converter comprises two first single-phase full-bridge inverters and a second single-phase full-bridge inverter connected back-to-back and in parallel, and a second DC-side energy storage capacitor connected in parallel and located between the two single-phase full-bridge inverters; The first single-phase full-bridge inverter includes two third sub-circuits respectively connected to the neutral line of the first stage and the second connection end of the first three-to-one multiple-way switch; The second single-phase full-bridge inverter includes two fourth sub-circuits respectively connected to the neutral line of the second stage and the second connection end of the second three-to-one multiple-way switch.

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