Low-voltage flexible interconnection device and method

Abstract

The invention relates to a low-voltage flexible interconnection device and a low-voltage flexible interconnection method, which are used for connecting a plurality of transformer areas to a direct-current bus with the same voltage class through an AC / DC bidirectional converter, and the device comprises an alternating-current circuit breaker and an alternating-current fuse which are configured on the wire inlet side of the AC / DC bidirectional converter, and a direct-current circuit breaker and a direct-current fuse which are configured on the wire outlet side of the AC / DC bidirectional converter; the energy storage module is connected with the wire outlet side of the AC / DC bidirectional converter; the control cabinet is respectively connected with the court, the AC / DC bidirectional converter and the energy storage module; the energy management module is integrated in the control cabinet; the device collects electrical data of each module through the energy management module to analyze the heavy overload condition of the low-voltage distribution area, calculates the current needing to be transferred, and issues a control instruction to the AC / DC bidirectional converter; and the AC / DC bidirectional converter realizes energy bidirectional transmission among a plurality of station intervals through bidirectional rectification and inversion of current according to a received control instruction. Compared with the prior art, the method achieves the control purpose of mutual energy assistance and no heavy load of all the transformer areas, and can guarantee the stable operation of all the transformer areas.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution network, and in particular to a low-voltage flexible interconnection device and method. Background Art

[0002] The current passive control distribution equipment can no longer meet the multi-directional flow and flexible conversion power control requirements of multi-category, massive distributed resource access. The continuous increase in power grid transformation investment such as power quality compensation devices, information collection and control secondary equipment cannot fundamentally improve the lack of active control capabilities of the distribution network and cannot meet current requirements. In order to improve the adaptability of active control and digital integration of the distribution network, it is necessary to develop distribution equipment that can achieve flexible interconnection, solve the basic equipment problems at the equipment level of the distribution system, and support the construction of a new distribution system.

[0003] At present, China Electric Power Research Institute has carried out a lot of research on the multi-terminal flexible interconnection of distribution networks, and proposed multi-terminal flexible interconnection equipment for distribution networks - power exchangers and devices. They will replace the rigid equipment of traditional distribution networks, such as distribution transformers, mechanical switches, etc., and have the functions of distributed power grid-connected converters, power flow controllers, distribution automation terminals and power quality controllers, which will greatly reduce the types and quantities of distribution network equipment and make the structure of the distribution network simpler.

[0004] However, the control function of the existing power exchangers is still imperfect, and it is impossible to efficiently and automatically realize the two-way energy transmission in the substation area, and achieve the goals of substation load balancing, heavy overload management, and load transfer. Summary of the invention

[0005] The purpose of the present invention is to provide a low-voltage flexible interconnection device and method in order to overcome the defects of the above-mentioned prior art that it is impossible to efficiently and automatically realize the two-way energy transmission of the substation area and achieve the goals of load balancing, heavy overload management and load transfer in the substation area.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A low-voltage flexible interconnection device is used to connect multiple substations to a DC bus with the same voltage level through an AC / DC bidirectional converter, and the low-voltage flexible interconnection device includes:

[0008] AC circuit breakers and AC fuses configured on the incoming line side of the AC / DC bidirectional converter;

[0009] A DC circuit breaker and a DC fuse are arranged on the outgoing line side of the AC / DC bidirectional converter;

[0010] An energy storage module connected to the output side of the AC / DC bidirectional converter is used to access the DC bus for energy storage and to supply energy to the AC / DC bidirectional converter;

[0011] Control cabinets that connect the substation, AC / DC bidirectional converter and energy storage module respectively;

[0012] The energy management module integrated in the control cabinet is used to monitor and control the operating status of the low-voltage flexible interconnection device in real time and optimize the scheduling of each module in the low-voltage flexible interconnection device;

[0013] The device collects electrical data of the substation, AC / DC bidirectional converter and energy storage module through the energy management module to analyze the heavy overload situation of the low-voltage distribution substation, calculates the current that needs to be transferred, and issues control instructions to the AC / DC bidirectional converter; the AC / DC bidirectional converter controls the PWM signal to the IGBT drive according to the received control instructions, and realizes bidirectional energy transmission between multiple substations through bidirectional rectification and inversion of current.

[0014] Furthermore, there are multiple AC / DC bidirectional converters, each of which is connected to a corresponding substation, and the incoming line side of each AC / DC bidirectional converter is provided with a corresponding AC circuit breaker and AC fuse, and the outgoing line side is provided with a corresponding DC circuit breaker and DC fuse, and the incoming line side of each AC / DC bidirectional converter is connected to a DC bus of the same voltage level.

[0015] Furthermore, each substation is introduced into the low-voltage flexible interconnection device through the ABCN low-voltage line.

[0016] Furthermore, the ABCN low-voltage lines of the substation are respectively connected to a substation master meter, a terminal, a switching switch and a load.

[0017] Furthermore, the energy management module is respectively connected to the area master meter, the switching switch, the AC / DC bidirectional converter and the energy storage module.

[0018] Further, the AC / DC bidirectional converter includes a power electronic power conversion module, a power conversion module controller, a communication module, a power interface module and an embedded energy management system;

[0019] The power conversion module controller is respectively connected to the embedded energy management system, the communication module, the energy storage module and the power electronic power conversion module, and is used for basic control of each power electronic power conversion module to achieve power balance and stable operation of the low-voltage energy router;

[0020] The embedded energy management system is used to optimize the control of the power electronic power conversion module through optimization analysis and decision making;

[0021] The power electronic power conversion module is connected to the energy storage module and the power interface module respectively, and is used to output the converted power through the power interface module.

[0022] Furthermore, the power electronic power conversion module is an AC / DC bidirectional converter with an I-type three-level structure.

[0023] Furthermore, each phase of the power interface module is a T-type three-level circuit topology structure, including a first capacitor C1, a second capacitor C2, a first IGBT tube T1, a second IGBT tube T2, a third IGBT tube T3, a fourth IGBT tube T4, a first diode Da and a second diode Db, the first capacitor C1, the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, the fourth IGBT tube T4 and the second capacitor C2 are connected in series in sequence to form a loop, an input interface O is provided between the first capacitor C1 and the second capacitor C2, and the second IGBT tube T An output interface is provided between the first IGBT tube T1 and the second IGBT tube T2 and the third IGBT tube T3, and the input interface O is divided into two branches, one branch is connected to the connection line of the first IGBT tube T1 and the second IGBT tube T2 through the first diode Da, and the other branch is connected to the connection line of the third IGBT tube T3 and the fourth IGBT tube T4 through the second diode Db; the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, and the fourth IGBT tube T4 are respectively connected in parallel with the first parallel diode D1, the second parallel diode D2, the third parallel diode D3, and the fourth parallel diode D4.

[0024] Furthermore, the working state of the AC / DC bidirectional converter includes:

[0025] State 1: The input grid voltage is positive and the current is positive. At this time, when the input grid voltage is positive, the first IGBT tube T1 is turned on; when the input grid voltage is zero voltage, the first diode Da and the second IGBT tube T2 are used for freewheeling, so that the first IGBT tube T1 has a turn-off voltage spike stress;

[0026] State 2: The input grid voltage is negative and the current is positive. At this time, when the input grid voltage is zero voltage, the first diode Da and the second IGBT tube T2 are used for freewheeling; when the input grid voltage is negative voltage, the third parallel diode D3 and the fourth parallel diode D4 are turned on for freewheeling, so that the second IGBT tube T2 has a turn-off voltage spike stress;

[0027] State 3: the input grid voltage is negative and the current is negative. At this time, when the input grid voltage is zero voltage, the second diode Db and the third IGBT tube T3 are freewheeling; when the input grid voltage is negative voltage, the third IGBT tube T3 and the fourth IGBT tube T4 are freewheeling, so that the fourth IGBT tube T4 has a turn-off voltage spike stress;

[0028] State 4: The input grid voltage is positive and the current is negative. At this time, when the input grid voltage is zero voltage, the third IGBT tube T3 and the second diode Db perform freewheeling; when the input grid voltage is positive voltage, the first parallel diode D1 and the second parallel diode D2 perform freewheeling, so that the third IGBT tube T3 has a turn-off voltage spike stress.

[0029] Furthermore, the energy storage module includes a BCU battery control unit, a DCDC self-locking relay, a control relay, a power-off switch and an emergency stop switch;

[0030] After receiving the power-off switch action instruction and continuing for a first time, the BCU battery control unit delays the second time to disconnect the DCDC self-locking relay, and disconnects the control relay before the second time, so that the components controlled by the energy storage module are powered off, and the energy storage module is powered off after the second time is reached;

[0031] After the BCU battery control unit detects a self-test fault, it delays a third time to disconnect the DCDC self-locking relay, and the energy storage module is powered off;

[0032] After receiving the emergency stop switch action command, the BCU battery control unit disconnects all DCDC self-locking relays and control relays, and the energy storage module is powered off.

[0033] The present invention also provides a station area mutual assistance method of a low-voltage flexible interconnection device as described above, comprising:

[0034] If any of the following conditions are met, the low-voltage flexible interconnection device will not provide mutual assistance between stations:

[0035] 1.1. The load rate of all substations is lower than the preset overload threshold;

[0036] 1.2. The load rate of all substations is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the substation is less than the first deviation threshold;

[0037] 1.3. The load rates of all substations exceed the limit threshold, the load rate deviation of the substation is less than the second deviation threshold, and the second deviation threshold is less than the first deviation threshold;

[0038] The working conditions for low-voltage flexible interconnection devices to carry out mutual assistance between substations are as follows:

[0039] 2.1. The load rate of a certain area exceeds the heavy load threshold and the load rate deviation of the area exceeds the second deviation threshold;

[0040] 2.2. The load rate of the area is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the area is less than the first deviation threshold;

[0041] The mutual assistance adjustment strategy of the low-voltage flexible interconnection device is as follows:

[0042] Calculate the average load rate of each substation and evenly distribute the substation capacity so that the transformers in each substation are not overloaded;

[0043] The restrictions on low voltage flexible interconnection devices are:

[0044] When the capacity to be dispatched exceeds the capacity of the device, the device outputs according to its maximum capacity.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] (1) The present invention realizes bidirectional transmission of energy in each substation by setting up a DC / AC bidirectional converter, and setting up an AC circuit breaker and an AC fuse on the incoming line side, and setting up a DC circuit breaker and a DC fuse on the outgoing line side, and collecting them on the DC bus; and by setting up an energy management module and analyzing the heavy overload situation of the substation according to the power data of each component, the transferred current is automatically calculated, and automatic bidirectional energy transmission between substations is realized, so as to achieve the control purpose of mutual energy assistance and no overload in each substation, and ensure the optimized operation of each substation.

[0047] (2) The present invention optimizes and selects the structure of the AC / DC bidirectional converter. Different circuit topologies have a direct impact on the efficiency, heat generation, and ripple of the power conversion unit. The present invention adopts a T-type three-level circuit topology structure, which implements a certain turn-off voltage peak stress on each IGBT tube, making the flexible interconnection device with frequent commutation more stable and reliable.

[0048] (3) The present invention fully and completely defines the working conditions, non-working conditions, adjustment strategies, restriction conditions and power transfer strategies of mutual assistance between substations, and can ensure the stable operation of each substation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of the principle of a low-voltage flexible interconnection device provided in an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of an application structure of a low-voltage flexible interconnection device provided in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of a communication route of an energy management module provided in an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of an embodiment of the present invention provided in an embodiment of the present invention;

[0053] Figure 5 A schematic diagram of the operating principle of an AC / DC bidirectional converter state 1 provided in an embodiment of the present invention;

[0054] Figure 6 A schematic diagram of the operating principle of state 2 of an AC / DC bidirectional converter provided in an embodiment of the present invention;

[0055] Figure 7 A schematic diagram of the operating principle of state 3 of an AC / DC bidirectional converter provided in an embodiment of the present invention;

[0056] Figure 8 Schematic diagram of the operating principle of state 4 of an AC / DC bidirectional converter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0058] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0060] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0061] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0062] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0063] Example 1

[0064] like Figure 1 and Figure 2 As shown, this embodiment provides a low-voltage flexible interconnection device for connecting multiple substations to a DC bus of the same voltage level through an AC / DC bidirectional converter. The low-voltage flexible interconnection device includes:

[0065] AC circuit breakers and AC fuses configured on the incoming line side of the AC / DC bidirectional converter;

[0066] A DC circuit breaker and a DC fuse are arranged on the outgoing line side of the AC / DC bidirectional converter;

[0067] An energy storage module connected to the output side of the AC / DC bidirectional converter is used to access the DC bus for energy storage and to supply energy to the AC / DC bidirectional converter;

[0068] Control cabinets for connecting AC / DC bidirectional converters and energy storage modules respectively;

[0069] The energy management module integrated in the control cabinet is used to monitor and control the operating status of the low-voltage flexible interconnection device in real time, and to optimize the scheduling of each module in the low-voltage flexible interconnection device.

[0070] A DC interface is reserved on the DC bus for subsequent configuration of charging piles to meet the charging needs of electric vehicles in scenic areas.

[0071] The working process of the above device is as follows: the electrical data of the distribution transformer, energy storage module, DC / AC bidirectional converter, and DC / DC conversion port are collected through the local energy management module. The energy management module analyzes the heavy overload situation of the low-voltage distribution station area and issues instructions to the DC / AC bidirectional converter. Then, the energy management module calculates the current that needs to be transferred. The DC / AC bidirectional converter controls the PWM signal to the IGBT drive according to the received control instruction, and realizes the bidirectional energy transmission of the station area through bidirectional rectification and inversion of the current.

[0072] Flexible interconnection principle Figure 1 The flexible interconnection device connects the interconnected substations to the DC bus of the same voltage level through an AC / DC bidirectional converter to perform energy management.

[0073] There are multiple AC / DC bidirectional converters, each of which is connected to a corresponding substation. The incoming line side of each AC / DC bidirectional converter is provided with a corresponding AC circuit breaker and AC fuse, and the outgoing line side is provided with a corresponding DC circuit breaker and DC fuse. The incoming line side of each AC / DC bidirectional converter is connected to a DC bus of the same voltage level.

[0074] In this embodiment, a low-voltage flexible interconnection device is provided for the flexible interconnection of the three stations, such as Figure 2 As shown in the figure, the ABCN low-voltage lines of the three substations are introduced into the flexible DC interconnection system box, and are converted into DC±375V through three AC / DC bidirectional converters and then merged into the DC bus. The AC / DC inlet side is equipped with an AC circuit breaker and an AC fuse, and the outlet side is equipped with a DC circuit breaker and a DC fuse to achieve fault protection and fault isolation. The energy storage module has a capacity of 50kWh, and comes with a BMS battery management system, fire protection, air conditioning, etc., and is connected to the DC bus through a DC / DC.

[0075] The device is equipped with an energy management module, which is integrated in the flexible interconnection equipment control cabinet to monitor and control the operation status of the flexible interconnection equipment in the distribution area in real time. At the same time, based on the built-in algorithm and control logic, it optimizes the scheduling instructions for each module of the interconnection system. Figure 3 shown.

[0076] Figure 4 The system structure of the AC / DC bidirectional converter includes a power electronic power conversion module, a power conversion module controller, an energy storage module, a communication module, a power interface module, and an embedded energy management system. Figure 2 The AC / DC converter, DC / DC converter and power conversion module controller shown in the figure realize the basic control of each power electronic conversion module, and realize the power balance and stable operation of the low-voltage energy router; the embedded energy management system optimizes the control of the power electronic conversion module through optimization analysis and decision-making, and realizes the operation optimization of the low-voltage energy router.

[0077] The following is a detailed description of each component:

[0078] 1. AC / DC bidirectional converter

[0079] Principle topology: Different circuit topologies have a direct impact on the efficiency, heat generation, and ripple of the power conversion unit. Each phase of the power interface module adopted in this solution is a T-type three-level circuit topology structure, including a first capacitor C1, a second capacitor C2, a first IGBT tube T1, a second IGBT tube T2, a third IGBT tube T3, a fourth IGBT tube T4, a first diode Da, and a second diode Db. The first capacitor C1, the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, the fourth IGBT tube T4, and the second capacitor C2 are connected in series in sequence to form a loop. The first capacitor C1 and the second capacitor C2 are connected in series. An input interface O is provided, and an output interface is provided between the second IGBT tube T2 and the third IGBT tube T3. The input interface O is divided into two branches, one branch is connected to the connection line between the first IGBT tube T1 and the second IGBT tube T2 through the first diode Da, and the other branch is connected to the connection line between the third IGBT tube T3 and the fourth IGBT tube T4 through the second diode Db; the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, and the fourth IGBT tube T4 are respectively connected in parallel with the first parallel diode D1, the second parallel diode D2, the third parallel diode D3, and the fourth parallel diode D4.

[0080] Working principle of AC / DC bidirectional converter.

[0081] 1) State 1: Grid voltage is positive, current is positive

[0082] At this time, there are two states, namely, IGBT T1 is turned on, the output level is DC+; IGBT T1 is turned off, the output level is 0. That is, when the voltage is positive, T1 and T2 are turned on; when the voltage is 0, D a , T2 continues current. Among them: T1, D a There is commutation. The commutation process is caused by the shutdown of T1. The devices involved in the commutation process are mainly C1, T1 and D a , which is also what we often call a small commutation circuit. According to the size of the commutation circuit inductance, T1 will have a certain turn-off voltage spike stress. Figure 5 shown.

[0083] 2) State 2: Grid voltage is negative and current is positive

[0084] At this time, there are two states, namely, IGBT T2 is turned on, the output level is 0; IGBT T2 is turned off, IGBT D3D4 continues to flow, and the output level is DC-. That is, when the voltage is 0, D a , T2 continues to flow; when the voltage is negative, D4 ​​and D3 continue to flow; among them: T2, D3 and D4 have commutation. The commutation process is caused by the shutdown of T2. The devices involved in the commutation process are mainly C2, D a, T2, D3 and D4, which is also what we often call a large commutation circuit. According to the size of the commutation circuit inductance, T2 will have a certain turn-off voltage spike stress. Figure 6 shown.

[0085] 3) State 3: Grid voltage is negative and current is negative

[0086] At this time, there are two states, namely, IGBT T4 is turned on, and the output level is negative; IGBT T4 is turned off, IGBT T3 and diode Db continue to flow, and the output level is 0. That is: when the voltage is 0, Db and T3 continue to flow; when the voltage is negative, T3 and T4 continue to flow; among them: T4, Db, and D4 are commutating. The commutation process is caused by the shutdown of T4. The devices involved in the commutation process are mainly C2, Db and T4. This is also a small commutation circuit. According to the size of the commutation circuit inductance, T4 will have a certain turn-off voltage spike stress. Figure 7 shown.

[0087] 4) State 4: Grid voltage is positive and current is negative

[0088] At this time, there are two states, namely, IGBT T3 is turned on, and the output level is 0; IGBT T3 is turned off, and the parasitic diodes D1D2 of the IGBT continue to flow, and the output level is positive. That is: when the voltage is 0, T3 and Db continue to flow; when the voltage is positive, D2 and D1 continue to flow. Among them: T3, D1, and D2 are commutating. The commutation process is caused by the shutdown of T3. The devices involved in the commutation process are mainly C1, D1, D2, T3 and Db. This is a large commutation circuit. According to the size of the commutation circuit inductance, T3 will have a certain turn-off voltage spike stress. For example Figure 8 shown.

[0089] Specific parameters are shown in Table 1:

[0090] Table 1 AC / DC bidirectional converter parameters

[0091]

[0092]

[0093] 2. Energy storage module

[0094] Principle topology: When the energy storage module is powered on, the circuit breaker is closed, the self-reset switch is pressed to short-circuit the DC / DC latching relay, and the DCDC outputs 24V to power the BCU. After the BCU wakes up, the DCDC latching relay is closed and the display screen is powered on to light up. At this point, the battery system is powered on at low voltage.

[0095] After the above actions are completed, the BCU performs self-inspection. If there is no fault in the self-inspection, the pre-charge relay and the main negative relay are closed to perform pre-charge power-on. After the pre-charge is completed, the main positive relay is closed, the pre-charge relay is disconnected, and the high-voltage power-on is completed.

[0096] There are three situations in which the energy storage module is powered off:

[0097] (1) After the BCU is powered on at low voltage for 10 seconds, press the power-off switch for 1 second. The BCU will delay for 2 seconds to disconnect the DCDC self-latching relay. Before the DCDC self-latching relay is disconnected, disconnect the main positive and negative relays and other relay drivers, and power off the system at high voltage. After all relay drivers except the DCDC self-latching relay are disconnected, disconnect the DCDC self-latching relay, power off the system at low voltage, and open the circuit breaker. At this point, the system is powered off.

[0098] (2) When the BCU self-test fault is triggered, the self-locking relay is disconnected after a delay of 15S+500ms, and the system is powered off;

[0099] (3) When the emergency stop switches K2 and K3 are pressed, the low-voltage power supply to the BCU is cut off, all relays are disconnected, and the system is powered off.

[0100] The specific parameters of the energy storage module are shown in Table 2:

[0101] Table 4-2 Energy storage module parameters

[0102]

[0103] 3. Energy management module

[0104] The energy management module uses a domestically produced industrial-grade quad-core ARM processor based on the Cortex-A7 architecture and a main frequency of 1.2GHz. It adopts a modular structure design, supports multiple functional modules, and has hardware interface scalability. The operating system uses the unified operating system of the Measurement Alliance. Based on the unified software architecture of the alliance, it has strong independence and flexible scalability. The energy management module has powerful edge computing functions and supports functions such as mutual aid equipment scheduling, photovoltaic group scheduling and group control.

[0105] The specific parameters of the energy management module are shown in Table 3:

[0106] Table 3 Energy management module parameters

[0107]

[0108] 4. DC / DC conversion port

[0109] Principle topology: Each phase adopts an I-type three-level circuit topology, also called a T-type three-level circuit topology. The advantages of the T-type three-level circuit are: (1) Lower conduction loss and higher overall efficiency; (2) Single commutation circuit, convenient for debugging and optimization; (3) Simplified switching timing and timely fault protection; (4) Eliminate voltage equalization resistors and simplify peripheral circuits; (5) Uniform loss and maximize chip area utilization; (6) Power terminals are connected in parallel to reduce parasitic resistance losses in the package and improve current carrying capacity.

[0110] The specific parameters of the energy management module are shown in Table 4:

[0111] Table 4 DC / DC conversion port parameters

[0112]

[0113] Example 2

[0114] This embodiment provides a station area mutual assistance method of the above-mentioned low-voltage flexible interconnection device, including:

[0115] If any of the following conditions are met, the low-voltage flexible interconnection device will not provide mutual assistance between stations:

[0116] 1.1. The load rate of all substations is lower than the preset overload threshold;

[0117] 1.2. The load rate of all substations is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the substation is less than the first deviation threshold;

[0118] 1.3. The load rates of all substations exceed the limit threshold, the load rate deviation of the substation is less than the second deviation threshold, and the second deviation threshold is less than the first deviation threshold;

[0119] The working conditions for low-voltage flexible interconnection devices to carry out mutual assistance between substations are as follows:

[0120] 2.1. The load rate of a certain area exceeds the heavy load threshold and the load rate deviation of the area exceeds the second deviation threshold;

[0121] 2.2. The load rate of the area is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the area is less than the first deviation threshold;

[0122] The mutual assistance adjustment strategy of the low-voltage flexible interconnection device is as follows:

[0123] Calculate the average load rate of each substation and evenly distribute the substation capacity so that the transformers in each substation are not overloaded;

[0124] The restrictions on low voltage flexible interconnection devices are:

[0125] When the capacity to be dispatched exceeds the capacity of the device, the device outputs according to its maximum capacity.

[0126] Specifically, in this embodiment, the operation mode of the low-voltage flexible interconnection device is:

[0127] 1. Local autonomy model - mutual assistance among regions

[0128] 1) Mutual assistance among substations: The three substations are interconnected by DC through the flexible DC interconnection system. When the load rate of any substation exceeds the overload threshold, other substations supply power to the substation through the DC interconnection system to achieve no overload in the substation.

[0129] 2) Energy storage control: When the substation is overloaded, the energy storage device is discharged to alleviate the overload situation in the substation. When the substation is lightly loaded, the energy storage device is charged to store electrical energy.

[0130] 2. Load transfer mode

[0131] If two substations are normal and one substation is out of power, you can enable the load transfer mode by clicking on the microgrid controller screen to supply power to the out-of-power substation and ensure power supply to important loads. After power supply is restored, you need to exit the load transfer mode and enable the local autonomy mode by clicking on the microgrid controller screen.

[0132] The mutual assistance strategy of the low-voltage flexible interconnection device is:

[0133] (1) If any of the following conditions are met, mutual aid will not work.

[0134] All load factors are below 70% (overload threshold, adjustable)

[0135] The load factor of all stations is greater than 70% and less than 85% (adjustable), and the load factor deviation (maximum-minimum) of the stations is less than 20%.

[0136] All load factors exceed 85%, and the load factor deviation of each area is less than 10%.

[0137] The load rate refers to the ratio of the load power of the substation (including the power provided by the transformer and the power provided by the mutual aid equipment. The mutual aid equipment is divided into positive and negative, and the energy provided to the substation is positive) to the capacity of the transformer.

[0138] (2) Mutual Aid Working Conditions

[0139] When the load factor of a certain area exceeds 85% and the load factor difference (maximum load factor - minimum load factor) exceeds 10%

[0140] The load factor of the substation exceeds 70% and is less than 85%, and the load factor difference exceeds 20%.

[0141] (3) Adjustment strategy

[0142] The transformer is not overloaded according to the strategy. The adjustment target is that the transformer is not overloaded (load rate is less than 70%).

[0143] The microgrid controller calculates the average load rate of each substation. If the average load rate is heavy, the load rate balancing strategy ① is implemented; if the average load rate is light, the substation with the lowest load rate first provides power to the heavy-loaded substation. The power required to be dispatched when the load rate of the heavy-loaded substation is less than 70% is the total dispatch power. The principle of evenly distributing the substation capacity is that the load rates of the three substations are close.

[0144] The specific implementation is: the heavy-loaded area draws the actually required power from the bus, and the actual output power of each light-loaded area is min (total dispatching power, (light-loaded area load + total dispatching power)), and then the light-loaded area load rate balances the power required for dispatching.

[0145] (4) Repeat 1 / 2

[0146] (5) Restrictions

[0147] When the capacity to be dispatched exceeds the capacity of the device, the device outputs according to its maximum capacity.

[0148] The load transfer strategy of the low voltage flexible interconnection device is:

[0149] The load transfer control logic (load transfer in one area) is as follows:

[0150] (1) Receive the transfer instruction issued by the screen and determine the transfer conditions;

[0151] (2) Detect the state of the intelligent switching circuit breaker. If the circuit breaker is 0, go to step 4; if the circuit breaker is 1, go to step 2;

[0152] (3) Send the intelligent switching circuit breaker opening command; (reservation remote tripping is executed immediately NN = 0)

[0153] (4) Detect the operation status word of the intelligent switching circuit breaker; (A.20 operation status word remote trip Bit1 = 0;)

[0154] (5) Select rectifier equipment and equipment mode control;

[0155] (6) Instructions on charging pile power limit, mutual assistance equipment, and energy storage power control are issued;

[0156] (7) Determination of transfer conditions;

[0157] (8) Repeat steps 6-7 until load transfer is terminated;

[0158] (9) Receive the exit transfer instruction sent by the screen;

[0159] (10) Select rectifier equipment and equipment mode control;

[0160] (11) Check whether the operation mode conversion of the mutual aid equipment is successful. If successful, proceed to step 13. Otherwise, repeat the mode conversion command and check whether the conversion is successful. If it exceeds 5 times, the corresponding mutual aid equipment is shut down. If more than 2 mutual aid equipment are shut down, all equipment are shut down.

[0161] (12) Close the intelligent switching circuit breaker;

[0162] (13) Equipment power control;

[0163] (14) Exit the supply transfer mode.

[0164] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A low voltage flexible interconnection device, characterized in that: Used to connect multiple substations to a DC bus of the same voltage level through an AC / DC bidirectional converter, the low-voltage flexible interconnection device includes: AC circuit breakers and AC fuses configured on the incoming line side of the AC / DC bidirectional converter; A DC circuit breaker and a DC fuse are arranged on the outgoing line side of the AC / DC bidirectional converter; An energy storage module connected to the output side of the AC / DC bidirectional converter is used to access the DC bus for energy storage and to supply energy to the AC / DC bidirectional converter; Control cabinets that connect the substation, AC / DC bidirectional converter and energy storage module respectively; The energy management module integrated in the control cabinet is used to monitor and control the operating status of the low-voltage flexible interconnection device in real time and optimize the scheduling of each module in the low-voltage flexible interconnection device; The device collects electrical data of the substation, AC / DC bidirectional converter and energy storage module through the energy management module to analyze the heavy overload situation of the low-voltage distribution substation, calculates the current that needs to be transferred, and issues control instructions to the AC / DC bidirectional converter; the AC / DC bidirectional converter controls the PWM signal to the IGBT drive according to the received control instructions, and realizes bidirectional energy transmission between multiple substations through bidirectional rectification and inversion of current.

2. A low voltage flexible interconnection device according to claim 1, characterized in that: There are multiple AC / DC bidirectional converters, each of which is connected to a corresponding substation. The incoming line side of each AC / DC bidirectional converter is provided with a corresponding AC circuit breaker and AC fuse, and the outgoing line side is provided with a corresponding DC circuit breaker and DC fuse. The incoming line side of each AC / DC bidirectional converter is connected to a DC bus of the same voltage level.

3. A low voltage flexible interconnection device according to claim 1, characterized in that: Each substation is introduced into the low-voltage flexible interconnection device through the ABCN low-voltage line.

4. A low voltage flexible interconnection device according to claim 1, characterized in that: The ABCN low-voltage lines in the substation are respectively connected with a substation master meter, a terminal, a switching switch and a load.

5. A low voltage flexible interconnection device according to claim 4, characterized in that: The energy management module is respectively connected to the area master meter, the switching switch, the AC / DC bidirectional converter and the energy storage module.

6. A low voltage flexible interconnection device according to claim 1, characterized in that: The AC / DC bidirectional converter includes a power electronic power conversion module, a power conversion module controller, a communication module, a power interface module and an embedded energy management system; The power conversion module controller is respectively connected to the embedded energy management system, the communication module, the energy storage module and the power electronic power conversion module, and is used for basic control of each power electronic power conversion module to achieve power balance and stable operation of the low-voltage energy router; The embedded energy management system is used to optimize the control of the power electronic power conversion module through optimization analysis and decision making; The power electronic power conversion module is connected to the energy storage module and the power interface module respectively, and is used to output the converted power through the power interface module.

7. A low voltage flexible interconnection device according to claim 6, characterized in that: Each phase of the power interface module is a T-type three-level circuit topology structure, including a first capacitor C1, a second capacitor C2, a first IGBT tube T1, a second IGBT tube T2, a third IGBT tube T3, a fourth IGBT tube T4, a first diode Da and a second diode Db. The first capacitor C1, the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, the fourth IGBT tube T4 and the second capacitor C2 are connected in series in sequence to form a loop. An input interface O is provided between the first capacitor C1 and the second capacitor C2. The second IGBT tube T2 and An output interface is provided between the first and second IGBT tubes T3, and the input interface O is divided into two branches, one branch is connected to the connection line between the first IGBT tube T1 and the second IGBT tube T2 through the first diode Da, and the other branch is connected to the connection line between the third IGBT tube T3 and the fourth IGBT tube T4 through the second diode Db; the first IGBT tube T1, the second IGBT tube T2, the third IGBT tube T3, and the fourth IGBT tube T4 are respectively connected in parallel with the first parallel diode D1, the second parallel diode D2, the third parallel diode D3, and the fourth parallel diode D4.

8. A low voltage flexible interconnection device according to claim 7, characterized in that: The working state of the AC / DC bidirectional converter includes: State 1: The input grid voltage is positive and the current is positive. At this time, when the input grid voltage is positive, the first IGBT tube T1 is turned on; when the input grid voltage is zero voltage, the first diode Da and the second IGBT tube T2 are used for freewheeling, so that the first IGBT tube T1 has a turn-off voltage spike stress; State 2: The input grid voltage is negative and the current is positive. At this time, when the input grid voltage is zero voltage, the first diode Da and the second IGBT tube T2 are used for freewheeling; when the input grid voltage is negative voltage, the third parallel diode D3 and the fourth parallel diode D4 are turned on for freewheeling, so that the second IGBT tube T2 has a turn-off voltage spike stress; State 3: the input grid voltage is negative and the current is negative. At this time, when the input grid voltage is zero voltage, the second diode Db and the third IGBT tube T3 are freewheeling; when the input grid voltage is negative voltage, the third IGBT tube T3 and the fourth IGBT tube T4 are freewheeling, so that the fourth IGBT tube T4 has a turn-off voltage spike stress; State 4: The input grid voltage is positive and the current is negative. At this time, when the input grid voltage is zero voltage, the third IGBT tube T3 and the second diode Db perform freewheeling; when the input grid voltage is positive voltage, the first parallel diode D1 and the second parallel diode D2 perform freewheeling, so that the third IGBT tube T3 has a turn-off voltage spike stress.

9. The low voltage flexible interconnection device according to claim 1, characterized in that: The energy storage module includes a BCU battery control unit, a DCDC self-locking relay, a control relay, a power-off switch and an emergency stop switch; After receiving the power-off switch action instruction and continuing for a first time, the BCU battery control unit delays the second time to disconnect the DCDC self-locking relay, and disconnects the control relay before the second time, so that the components controlled by the energy storage module are powered off, and the energy storage module is powered off after the second time is reached; After the BCU battery control unit detects a self-test fault, it delays a third time to disconnect the DCDC self-locking relay, and the energy storage module is powered off; After receiving the emergency stop switch action command, the BCU battery control unit disconnects all DCDC self-locking relays and control relays, and the energy storage module is powered off.

10. A station area mutual assistance method for a low voltage flexible interconnection device as claimed in claim 1, characterized in that: include: If any of the following conditions are met, the low-voltage flexible interconnection device will not provide mutual assistance between stations: 1.

1. The load rate of all substations is lower than the preset overload threshold; 1.

2. The load rate of all substations is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the substation is less than the first deviation threshold; 1.

3. The load rates of all substations exceed the limit threshold, the load rate deviation of the substation is less than the second deviation threshold, and the second deviation threshold is less than the first deviation threshold; The working conditions for low-voltage flexible interconnection devices to carry out mutual assistance between substations are as follows: 2.

1. The load rate of a certain area exceeds the heavy load threshold and the load rate deviation of the area exceeds the second deviation threshold; 2.

2. The load rate of the area is greater than the heavy load threshold and less than the limit threshold, and the load rate deviation of the area is less than the first deviation threshold; The mutual assistance adjustment strategy of the low-voltage flexible interconnection device is as follows: Calculate the average load rate of each substation and evenly distribute the substation capacity so that the transformers in each substation are not overloaded; The restrictions on low voltage flexible interconnection devices are: When the capacity to be dispatched exceeds the capacity of the device, the device outputs according to its maximum capacity.

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