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

Abstract

The embodiment of the invention discloses a low-voltage power distribution network master-slave split-phase flexible interconnection control method and system, and the method comprises the steps: carrying out the sequence component decomposition of three-phase currents of two transformer areas, and obtaining a to-be-compensated negative-sequence current and a to-be-compensated zero-sequence current; solving to-be-compensated load current and voltage-stabilized load current according to the target power needing to be transmitted in the two transformer areas; calculating a compensation current reference value according to the to-be-compensated negative sequence current, the to-be-compensated zero sequence current, the to-be-compensated load current and the voltage-stabilized load current; if the compensation current reference value is changed, obtaining a maximum phase compensation current reference value; and performing compensation current control on the master-slave back-to-back voltage source type converter according to the rated current of the master back-to-back voltage source type converter and the maximum phase compensation current reference value. According to the invention, flexible capacity expansion and three-phase imbalance treatment of the power distribution network are synchronously solved at low cost when the overall configuration capacity is relatively low, the problems of light load, heavy load and three-phase imbalance of the transformer area are solved, and the flexibility and expandability of the system are improved through master-slave combined 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-separated 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 transformer light and heavy loads and three-phase imbalance 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 transformer light and heavy loads and three-phase imbalance, and cannot handle them at the same time. Moreover, in the prior art, 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, but the existing flexible interconnection devices are insufficient in flexibility and scalability, and there is a situation where the capacity of the interconnection device is in excess or the capacity does not meet the power supply demand and is difficult to expand. Summary of the invention

[0003] The main purpose of the present application is to provide a low-voltage distribution network master-slave phase-divided flexible interconnection control method and system, which can solve the technical problems in the prior art 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-mentioned object, the first aspect of the present application provides 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 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. The method includes:

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

[0006] Obtaining a target power that needs to be transmitted from the power transmission 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 stabilization 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] According to the negative sequence current to be compensated and the zero sequence current to be compensated in the first and second stations, the load current to be compensated in the power receiving station, and the regulated load current in the power transmitting station, a first compensation current reference value of the power receiving station and a second compensation current reference value of the power transmitting station are calculated;

[0009] If the compensation current reference value changes, 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 is obtained 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, 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.

[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 comprises a back-to-back three-phase full-bridge converter;

[0013] 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;

[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 respectively connected to the neutral line of the first transformer area and the neutral line of the second transformer area;

[0016] The back-to-back single-phase full-bridge converter is also connected to one phase line of the feeder of the first substation through a first three-to-one multi-way switch, and is connected to one phase line of the feeder of the second substation through 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, i.e., a low-cost solution for flexible expansion of distribution network and three-phase imbalance management based on master-slave back-to-back voltage source converters (master-slave BTB-VSCs). All expansion power and a small amount of three-phase imbalance compensation power are transmitted through the master back-to-back voltage source converter (master BTB-VSC); 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 endowed with flexible phase expansion capability, and flexible expansion between substations and high-quality management of three-phase imbalance are realized on the basis of a relatively low overall configuration capacity, effectively and at a low cost, solving the problems of light and heavy loads and three-phase imbalance in the substation area. In addition, the various 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 substations, reduce the cost of management equipment, and promote the interconnection and interoperability of new distribution networks and the consumption 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

[0021] in:

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

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

[0024] Figure 3 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 A schematic diagram of compensation current of a master-slave phase-split flexible interconnection control system of a low-voltage distribution network in an embodiment of the present application;

[0026] Figure 5 This is a diagram showing the effect of compensating current amplification of a master-slave phase-split flexible interconnection control system for a 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 a BTB-VSC (from a back-to-back voltage source converter);

[0030] Fig. 9 The current under the condition of the first load disturbance;

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

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

[0033] In terms of managing the three-phase imbalance in the substation, the main means of management are currently switching capacitors, static VAR compensators, phase converters and other equipment. Switching capacitors is the most common way to compensate for the three-phase unbalanced load in the substation, but the action time is long, the continuous regulation of reactive power cannot be achieved, and there are transient shocks when switching capacitors. Although the static VAR compensator can continuously adjust the reactive power, it still cannot compensate for the active power. The phase converter can control active power and reactive power at the same time, but it requires a lot of investment to achieve the effect of three-phase imbalance management, the cost is high, and the equipment utilization rate is low. In general, the existing three-phase imbalance management methods have problems such as single function, high investment cost, and low efficiency, and cannot take into account the mutual assistance between different substations and the management of light and heavy loads in the substation.

[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 contact 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 comprehensive management effect. However, the light and heavy load / three-phase imbalance management devices in the existing schemes mainly adopt fixed capacity configurations, and the fixed capacity must 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 idle capacity, resulting in relatively high hardware costs. 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 generation consumption.

[0036] like Figure 1 As shown, in one embodiment, a low-voltage distribution network master-slave phase-separated flexible interconnection control method is provided. The low-voltage distribution network master-slave phase-separated flexible interconnection control method specifically includes 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 three-phase imbalance control method of the distribution network 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 management 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 station area 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 three-phase zero-sequence current components to be compensated

[0046] S200: Obtaining a target power that needs to be transmitted from the power transmitting station 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 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 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 station area may also transmit power to the second station area, which will not be described in detail here.

[0052] S300: Calculate the load current to be compensated in the power receiving area and the regulated load current required for voltage stabilization in the 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 voltage-stabilized load current is the load current required for voltage stabilization in the power transmission area. The voltage-stabilized load current includes the a-phase voltage-stabilized load current component, the b-phase voltage-stabilized load current component, and the c-phase voltage-stabilized load current component, namely:

[0055] S400: 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 area and the second area, the load current to be compensated of the power receiving area, and the regulated load current of the power transmitting area.

[0056] 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.

[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 value 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 and the other may not be changed, both may be changed, or neither may be changed.

[0061] If the first compensation current reference value is not changed, the steps S100 - 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 stage are re-executed.

[0063] S600: According to 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 realizes a low-cost solution for flexible capacity expansion and three-phase imbalance management of the distribution network based on the master-slave back-to-back voltage source converter BTB-VSC. The master BTB-VSC transmits all the capacity expansion power and a small amount of three-phase imbalance compensation power; through the cooperation of the slave BTB-VSC and the multi-way switch, the master BTB-VSC is given a flexible phase expansion capability, and the flexible capacity expansion between substations and high-quality management of three-phase imbalance are realized on the basis of a relatively low overall configuration capacity, which effectively and low-costly solves the problems of light and heavy loads and three-phase imbalance in the substation area. In addition, the multiple combination control of the master-slave BTB-VSC improves the flexibility of the device, and when the capacity of the master BTB-VSC converter is insufficient, it can be supplemented by the slave BTB-VSC, and the device or system is more scalable. This embodiment can effectively improve the interconnection and mutual assistance capabilities of the distribution network, reduce the operation loss of the substation area, reduce the cost of the management device, and has a high equipment utilization rate. It efficiently realizes the management of three-phase imbalance, and promotes the interconnection and interoperability of new distribution networks and the process of distributed power consumption, which has great 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-phase compensation current reference values ​​a, b, and c by comparison includes:

[0067] If the first compensation current reference value changes, a first maximum phase compensation current reference value is obtained 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, 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 is obtained 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 adopted to perform first compensation current control on the first side of the main back-to-back voltage source converter and the slave back-to-back voltage source converter according to a comparison between the first rated current of the main 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 main back-to-back voltage source converter connected to the power receiving station area, and the first side is the side connected to the power receiving station area;

[0071] If the second compensation current reference value changes, then 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, 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, 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, and the second side is the side connected to the power transmission station.

[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, then by comparing the three-phase compensation current reference values ​​I a, b, c of the first compensation current reference value 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, then by comparing the three-phase compensation current reference values ​​I a, b, c of the second compensation current reference value 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 adopted to perform a 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 according to 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 main back-to-back voltage source converter, the first side of the slave back-to-back single-phase full-bridge converter is switched to be connected to the first target phase line of the power receiving station through the three-to-one multi-way switch corresponding to the power receiving station, wherein the first target phase line is the 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 main back-to-back voltage source converter is controlled to be the first rated current of the main 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 main 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 the present 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, the 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-select-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 corresponding phase line of 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 main BTB-VSC and the power receiving station area is controlled by the PI closed loop to be the first rated current I of the main BTB-VSC N1 , through PI closed-loop control, the compensation current of the first side connected from the BTB-VSC to 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-to-one multi-way switch corresponding to the power receiving area will switch from the grid connection point of the BTB-VSC to the corresponding phase line connection with the first maximum phase compensation current reference value in the power receiving area, and the compensation current I of the main BTB-VSC is controlled by 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 compensation current I of BTB-VSC c3 is 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 adopted to perform a 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 according to 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 area 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, the 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 multi-way switch corresponding to the power receiving station area remains unchanged, and the compensation current of the first side connected to the power receiving station area by the main back-to-back voltage source converter (main BTB-VSC) through PI closed-loop control is the first maximum phase compensation current reference value, and the compensation current of the first side connected to the power receiving station area by the slave back-to-back voltage source converter (slave BTB-VSC) through PI closed-loop control is 0.

[0087] The state of the three-choice multi-way switch corresponding to the power receiving station area 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 compensation current I of BTB-VSCc3 is 0.

[0088] In one embodiment, if the second compensation current reference value changes, a second strategy is adopted to perform a 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 according to 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 main back-to-back voltage source converter, the second side of the slave back-to-back single-phase full-bridge converter is switched 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;

[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 the master BTB-VSC; the slave back-to-back voltage source converter is the 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, the 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 area will switch from the grid connection point of the BTB-VSC to the corresponding phase line of the second maximum phase compensation current reference value in the power transmission area (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 area 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 area 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-to-one multi-way switch corresponding to the power transmission area will switch from the grid connection point of the 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 adopted to perform a 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 according to 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 stage 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, the 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 main back-to-back voltage source converter (main BTB-VSC) is controlled by the PI closed loop 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 (slave BTB-VSC) is controlled by the PI closed loop to be 0.

[0098] The state of the three-choice multi-way switch corresponding to the power transmission area 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 of the second side of BTB-VSC c4 is 0.

[0099] In one embodiment, in step S400, according to the negative sequence current to be compensated and the zero sequence current to be compensated of the first station area and the second station area, the load current to be compensated of the power receiving station area, and the regulated load current of the power transmission station area, a first compensation current reference value of the power receiving station area and a second compensation current reference value of the power transmission station area are calculated, including:

[0100] Calculate 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 voltage stabilizing load current of the power transmission station area.

[0102] Specifically, taking the transmission of power from the second station area to the first station area as an example, according to the negative sequence current to be compensated in the first station area 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 transformer area 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 power transmission from the first station area to the second station area is similar, which will not be repeated here.

[0105] In one embodiment, 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 by 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 area, respectively. They are the zero-sequence current component to be compensated for phase a, phase b and phase c of the first transformer area, respectively. are respectively the a-phase load current component to be compensated, the b-phase load current component to be compensated, and the c-phase load current component to be compensated of the first station area as the power receiving station area; I ca1_ref ,I cb1_ref ,I cc1_ref The a-phase first compensation current reference value, the b-phase first compensation current reference value and the c-phase first compensation current reference value of the first compensation current reference value of the first station area are respectively;

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

[0109] Specifically, the formula for transmitting power from the first area to the second area 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 of 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 converters in the power transmission section.

[0112] refer to Figure 2 The present application also provides a low-voltage distribution network master-slave phase-split flexible interconnection control system 1, that is, a distribution network three-phase imbalance management device or system based on master-slave back-to-back voltage source converters, the low-voltage distribution network master-slave phase-split flexible interconnection control system 1 comprises: 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 respectively connected to the three phases of the feeder of the first substation and the three phases of the feeder of the second substation;

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

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

[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 a 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 a 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 relatively large capacity, and the slave back-to-back voltage source converter 20 has a relatively small 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 line, phase b phase line, and phase c phase line) through different terminals, and another three-phase full-bridge converter is connected to the three phases of the feeder of the second substation (i.e., phase a phase line, phase b phase line, and phase c phase line) 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 back-to-back voltage source converter 20 includes two back-to-back single-phase full-bridge converters.

[0127] Among them, a single-phase full-bridge converter is connected to the neutral line of the first transformer section, and is also connected to a target phase line in the feeder of the first transformer section through the second connection end of the first three-to-one multi-way switch 30.

[0128] Another single-phase full-bridge converter is connected to the neutral line of the second transformer section, and is also connected to a target phase line in the feeder of the second transformer section through a second connecting 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 comprises three second sub-circuits respectively connected to the three phases of the feeder of the second substation, and each second sub-circuit comprises 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 of which is connected to a phase line of a 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 of which is connected to a phase line of a 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), insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar junction transistor) and MOS (insulated gate field effect transistor). It has the advantages of both MOSFET's high input impedance and GTR's low on-state voltage drop.

[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 first subcircuit includes two IGBTs (S11 and S12) connected in series; the second first subcircuit includes two IGBTs (S13 and S14) connected in series; the third first subcircuit includes two IGBTs (S15 and S16) connected in series. The three first subcircuits are connected to the corresponding phase lines of the first stage through different filter inductors (L11, L12, 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; 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 through different filter inductors (L21, L22, L23).

[0141] Two IGBTs connected in series are connected in series by connecting the emitter node of the first IGBT and 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 (i.e., S11, S13, S15, S21, S23, S25) in each of the first sub-circuit and the second sub-circuit, C dc1 The negative electrode of the capacitor is connected to the emitter node of the second IGBT in each of the first sub-circuit and the second sub-circuit (ie, S12, S14, S16, S22, S24, S26).

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

[0145] This embodiment realizes a low-cost solution for flexible capacity expansion and three-phase imbalance management of the distribution network based on the master-slave back-to-back voltage source converter (BTB-VSC), and transmits all the expansion power and a small amount of three-phase imbalance compensation power through the master BTB-VSC; through the cooperation of the slave BTB-VSC and the multi-way switch, the master BTB-VSC is given flexible phase expansion capability, and the flexible capacity expansion between substations and high-quality management of three-phase imbalance are realized on the basis of a relatively low overall configuration capacity, which effectively and low-costly solves the problems of light and heavy loads and three-phase imbalance in the substation area. In addition, the multiple combination control of the master and slave BTB-VSC improves the flexibility of the device, 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 embodiment can effectively improve the interconnection and mutual assistance capabilities of the distribution network, reduce the operation loss of the substation area, reduce the cost of the management device, and has high equipment utilization. It efficiently realizes the management of three-phase imbalance, and promotes the interconnection and interoperability of new distribution networks and the process of distributed power consumption, which has great engineering significance.

[0146] In one embodiment, 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;

[0147] The first single-phase full-bridge inverter comprises two third sub-circuits respectively connected to the neutral line of the first stage area and the second connection end of the first three-to-one multi-way switch 30;

[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 sub-circuits, one of which is connected to the neutral line of the first stage, and the other is connected to the second connection end 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 sub-circuits, one of which is connected to the neutral line of the second stage, and the other is connected to the second connection end 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), insulated gate bipolar transistor, is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar junction transistor) and MOS (insulated gate field effect transistor). It has the advantages of both MOSFET's high input impedance and GTR's low on-state voltage drop.

[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 third sub-circuit includes two IGBTs (Q11 and Q12) connected in series; the second third sub-circuit includes 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 connected in series by connecting the emitter node of the first IGBT and 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 : 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 currents of the main back-to-back voltage source converter 10 in the first station area are 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 area are I ca2 ,I cb2 ,I cc2 The compensation current from the back-to-back voltage source converter 20 in the first stage is I c3, the compensation current from the back-to-back voltage source converter 20 in the second stage 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 a back-to-back voltage source converter (from BTB-VSC).

[0163] In MATLAB's Simulink, a three-phase unbalanced control method based on master-slave BTB-VSC (master-slave back-to-back voltage source converter) is simulated. The total capacity of area 1 and area 2 is set to 400kVA. Before interconnection, the total load of area 1 is 375kW, the load of phase A is 145kW, the load of phase B is 130kW, and the load of phase C is 105kW. The total load of area 2 is 195kW, the load of phase A is 45kW, the load of phase B is 65kW, and the load of phase C is 85kW. Both areas are in a three-phase unbalanced state, and area 1 is in a heavy load state, resulting in large system losses. A main BTB-VSC is set, where the capacity of each phase of the main BTB-VSC is 25kVA. According to the principle of the three-phase imbalance control method and system based on the master-slave BTB-VSC described above, it can be known that phase A needs to transmit the most power. In the main 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 main BTB-VSC. Therefore, the main BTB-VSC first transmits the power of phases B and C and part 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 part of the current to be compensated of phase A and the current to be compensated of phases B and C in substation 1 is compensated by the main BTB-VSC, and the slave BTB-VSC compensates for the remaining current to be compensated of phase A.

[0164] In the area 2, the A-phase current to be compensated is greater than the rated current of the slave BTB-VSC, so the A-phase transmission current in the master BTB-VSC is the rated current of the slave BTB-VSC, and the transmission current of the slave BTB-VSC is the remaining A-phase current to be compensated. After the value of the current to be compensated changes, the conclusion is the same as above.

[0165] Depend on Figure 6 It can be seen that the three phases are unbalanced before 0.1s, and the current value is relatively high. 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, the load rate is equal, and the overload of substation 1 has been effectively solved.

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

[0167] Taking area 1 (the first area) as an example, Fig.10 It can be seen that at 0.3s, the A-phase load in substation 1 was disturbed, increasing the load power by 5kW, and at the same time, the A-phase load in substation 2 was reduced by 5kW, so the A-phase current to be compensated changed, and the load rate of the substation did not change after balancing. According to the above-described three-phase imbalance control method and system principle based on master-slave BTB-VSC, at this time, 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. Fig.10 In the figure, at 0.35s, the disturbance in phase A was compensated by BTB-VSC, and the three-phase balance was restored. The same is true for area 2, which will not be repeated here.

[0168] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program 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 may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an 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 may 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-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A low-voltage distribution network master-slave phase-separated flexible interconnection control method, characterized in that: A control module applied to a low-voltage distribution network master-slave split-phase flexible interconnection control system, wherein the low-voltage distribution network master-slave split-phase flexible interconnection control system further comprises a master back-to-back voltage source converter, a slave back-to-back voltage source converter and a three-to-one multi-way switch, and the method comprises: Obtain the three-phase current of the first transformer substation and the three-phase current of the second transformer substation, perform sequence component decomposition calculation on the three-phase current of the first transformer substation and the three-phase current of the second transformer substation respectively, and obtain the negative sequence current to be compensated and the zero sequence current to be compensated of the first transformer substation and the second transformer substation respectively; Obtaining a target power that needs to be transmitted from the power transmission area to the power receiving area in order to achieve equal load rates between the first area and the second area; Solve the load current to be compensated of the power receiving area and the regulated load current required for voltage stabilization of the power transmission area according to the target power, wherein the power receiving area and the power transmission area are different areas of the first area and the second area; According to the negative sequence current to be compensated and the zero sequence current to be compensated of the first and second stations, the load current to be compensated of the power receiving station, and the regulated load current of the power transmitting station, a first compensation current reference value of the power receiving station and a second compensation current reference value of the power transmitting station are calculated; If the compensation current reference value changes, 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 is obtained 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, 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.

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, a first maximum phase compensation current reference value is obtained 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, 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 is obtained 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 by adopting 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 comprises: If the first compensation current reference value changes, a first strategy is adopted to perform first compensation current control on the first side of the main back-to-back voltage source converter and the slave back-to-back voltage source converter according to a comparison between the first rated current of the main 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 main back-to-back voltage source converter connected to the power receiving station area, and the first side is the side connected to the power receiving station area; If the second compensation current reference value changes, then 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, 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, 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, and the second side is the side connected to the power transmission station.

3. The method according to claim 2, characterized in that If the first compensation current reference value changes, a first strategy is adopted to perform a 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 according to 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, the first side of the slave back-to-back single-phase full-bridge converter is switched to be connected to the first target phase line of the power receiving station through the three-to-one multi-way switch corresponding to the power receiving station, wherein the first target phase line is the 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 main back-to-back voltage source converter is controlled to be the first rated current of the main 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 main 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 adopted to perform a 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 according to 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 area 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 according to 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, the second side of the slave back-to-back single-phase full-bridge converter is switched 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 according to 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 stage 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 method of calculating 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 comprises: Calculate 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; 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 voltage stabilizing 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 by 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 area, respectively. They are the zero-sequence current component to be compensated for phase a, phase b and phase c of the first transformer area, 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 the a-phase, the first compensation current reference value of the b-phase and the first compensation current reference value of the c-phase 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 area, respectively. They are the zero-sequence current component to be compensated for phase a, phase b and phase c of the second transformer area, 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 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.

9. A low-voltage distribution network master-slave phase-separated 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 multi-way switch, a second three-to-one multi-way switch 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 station area and the three phases of the feeder of the second station area; 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 respectively connected to the neutral line of the first transformer area and the neutral line of the second transformer area; One side of the back-to-back single-phase full-bridge converter can be connected to a 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 control three-phase imbalance according to the low-voltage distribution network master-slave phase-separated flexible interconnection control method according to any one of claims 1-8.

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 stage, and each first sub-circuit comprises two IGBTs connected in series; The second three-phase full-bridge inverter comprises three second sub-circuits respectively connected to the three phases of the feeder of the second substation, and each second sub-circuit comprises 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 comprises two third sub-circuits respectively connected to the neutral line of the first stage area and the second connection end of the first three-to-one multi-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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