Multi-port chained battery energy storage system and fault current limiting method of energy storage system

Abstract

The invention provides a multi-port chain type battery energy storage system and a fault current limiting method of the energy storage system, and relates to the technical field of flexible interconnection power distribution, the system comprises a plurality of power supply modules connected in parallel on a direct current bus, each power supply module comprises a current limiting reactor, a first end of the current limiting reactor is electrically connected with a power supply line, and a second end of the current limiting reactor is electrically connected with the power supply line; the power supply line is used for providing alternating current, and the current limiting reactor is used for inhibiting circulation of short-circuit current under the condition that the energy storage system has a short-circuit fault; the half-bridge power flow control module is provided with a first end, a second end and a third end, the first end of the half-bridge power flow control module and the second end of the half-bridge power flow control module are connected to the direct current bus in parallel, the third end of the half-bridge power flow control module is electrically connected with the second end of the current limiting reactor, and the half-bridge power flow control module is used for controlling the power flow of the energy storage system. According to the system, active suppression of abnormal current is realized, so that voltage sag of a sound port is avoided, and fault ride-through of the device and recovery of a power flow regulation and control function after a fault are realized.

Description

Technical Field

[0001] The present application relates to the field of flexible interconnected power distribution technology, and in particular to a multi-port chain battery energy storage system and a fault current limiting method for the energy storage system. Background Art

[0002] In recent years, with the increasing scarcity of traditional energy and the continuous deterioration of the ecological environment, sustainable development and low-carbon emissions have become the primary goals that countries around the world must achieve while developing their economies, and the global energy structure has undergone major changes. Against this background, the new energy power generation industry has continued to grow and develop with its advantages of low carbon and environmental protection, energy sustainability, and a wide range of energy sources. Distributed power generation represented by wind power and photovoltaic power generation has received more and more attention and widespread application. However, the traditional distribution network architecture is mainly radial, adopting the "closed-loop design, open-loop operation" mode. With the high proportion of new sources and loads connected and increasingly penetrating, the power supply line operation and protection design of the distribution network will face huge challenges, which seriously affects the safe and stable operation of the distribution network.

[0003] At present, there are two main solutions for distribution network optimization: configuring energy storage systems and flexible interconnection technology.

[0004] Energy storage technology has the ability to transfer energy flow at the time level, which can smooth system power fluctuations, reduce peaks and fill valleys, improve power quality, and enhance the grid's ability to absorb new energy. It is an effective solution for the connection of new energy to the grid. However, limited by the radial architecture of the traditional distribution network, large-capacity energy storage currently adopts a chain power conversion topology with a single medium-voltage AC port, which is distributed and connected to different distribution networks. The distributed access solution faces problems such as large battery capacity, low system utilization, high cost, and large floor space. Compared with the flexible interconnection solution, the energy storage system does not have the real-time transfer capability of the load in the distribution network, which restricts the promotion and application of energy storage technology at the medium-voltage distribution level.

[0005] Flexible interconnection technology uses power electronic soft switches to transform the traditional radial distribution network into a new type of ring distribution network with multi-directional power and flexible controllability, giving the distribution system the ability to transfer energy flow at the spatial level. It can effectively deal with a series of problems caused by the large-scale access of new energy and new impact loads, such as power line flow congestion, node voltage exceeding the limit, and insufficient system stability margin. However, the large-scale promotion and application of flexible interconnection technology now also faces two major challenges. On the one hand, when regulating the system flow, it is often constrained by the state of the power grid, the adjustment ability is limited, and compared with the energy storage system, it lacks the ability to transfer energy flow in time; on the other hand, the existing flexible interconnection equipment also needs to add a full-power structure when expanding the port. Like the single-port energy storage system, it also faces the problems of high cost and large size. Summary of the invention

[0006] The main purpose of the present application is to provide a multi-port chain battery energy storage system and a fault current limiting method for the energy storage system, so as to at least solve the problems that the current limiting method of the distribution network in the prior art is constrained by the grid state, the regulation ability is limited, and there is a lack of time transfer capability for the energy flow, and there are high costs and large volumes.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a multi-port chain battery energy storage system is provided, comprising a plurality of power supply modules connected in parallel on a DC bus, wherein the power supply module comprises: a current limiting inductor having a first end and a second end, wherein the first end of the current limiting inductor is electrically connected to a power supply line, wherein the power supply line is used to provide alternating current, and wherein the current limiting inductor is used to suppress the flow of short-circuit current when a short-circuit fault occurs in the energy storage system; and a half-bridge flow control module having a first end, a second end and a third end, wherein the first end of the half-bridge flow control module and the second end of the half-bridge flow control module are connected in parallel on the DC bus, wherein the third end of the half-bridge flow control module is electrically connected to the second end of the current limiting inductor, and wherein the half-bridge flow control module is used to control the flow of the energy storage system.

[0008] Optionally, the power supply module further includes: a thyristor bypass switch, and the thyristor bypass switch is connected in parallel to the first bridge wall of the half-bridge power flow control module.

[0009] Optionally, the half-bridge power flow control module includes a first switch module on the first bridge wall and a second switch module on the second bridge wall, wherein the first switch module has a first end, a second end and a control end, the first end of the first switch module is electrically connected to the DC bus, the second end of the first switch module is electrically connected to the current limiting inductor, and the control end of the first switch module is used to input a first control signal; the second switch module has a first end, a second end and a control end, the first end of the second switch module is electrically connected to the second end of the first switch module and the current limiting inductor respectively, the second end of the second switch module is electrically connected to the DC bus, and the control end of the second switch module is used to input a second control signal.

[0010] Optionally, the first switch module and the second switch module each include a transistor.

[0011] Optionally, the current limiting reactor is a current limiting inductor.

[0012] According to another aspect of the present application, a fault current limiting method for an energy storage system is provided, the method being used to control any one of the multi-port chain battery energy storage systems, the energy storage system comprising a power supply module, the power supply module comprising a thyristor bypass switch connected in parallel on a first bridge wall of the half-bridge power flow control module, the method comprising: when the energy storage system is in steady-state operation, controlling the power flow of the energy storage system by means of the half-bridge power flow control module; when a short-circuit fault occurs in a target power supply line of the energy storage system and the short-circuit current is less than a maximum threshold current, controlling the thyristor bypass switch corresponding to the target power supply line to be turned on, and controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system.

[0013] Optionally, there are three power supply modules, and controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules includes: controlling the peak voltage of the fundamental frequency component output by all the half-bridge power flow control modules , to control all the half-bridge power flow control modules to operate as dynamic reactive power control modules, wherein, is the peak voltage of the fundamental frequency component output by the half-bridge power flow control module, is the DC bus voltage.

[0014] Optionally, the power supply line includes a first power supply line, a second power supply line and a third power supply line, the power supply modules include three, namely, a first power supply module, a second power supply module and a third power supply module, the target power supply line is the second power supply line, the second power supply line is the target power supply line, and all the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules, including: determining the equivalent voltage source phase angle between the first power supply line and the third power supply line , to control the half-bridge power flow control module of the first power supply module and the half-bridge power flow control module of the third power supply module to operate as a dynamic reactive power control module, wherein the first power supply line is the power supply line of the first power supply module, and the third power supply line is the power supply line of the third power supply module, is the equivalent voltage source phase angle between the first power supply line and the third power supply line, is the equivalent voltage source phase angle of the first power supply line, is the phase angle of the equivalent voltage source of the third power supply circuit; determines the phase angle of the equivalent voltage source of the second power supply circuit , to control the half-bridge power flow control module of the second power supply module to operate as a dynamic reactive power control module, wherein, is the phase angle of the equivalent voltage source of the second power supply line.

[0015] Optionally, there are three power supply modules, namely a first power supply module, a second power supply module and a third power supply module, the power supply line of the first power supply module is a first power supply line, the power supply line of the second power supply module is a second power supply line, the power supply line of the third power supply module is a third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: determining the formula according to the voltage drop , determining the voltage drop of the first power supply line and the voltage drop of the third power supply line, wherein, is the voltage drop of the first power supply line, is the voltage drop of the third power supply line, is the current of the first power supply line, is the current of the third power supply line, jX1 is the equivalent reactance of the first power supply line, and jX3 is the equivalent reactance of the third power supply line.

[0016] Optionally, there are three power supply modules, namely a first power supply module, a second power supply module and a third power supply module, the power supply line of the first power supply module is a first power supply line, the power supply line of the second power supply module is a second power supply line, the power supply line of the third power supply module is a third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: determining a formula according to the power supply port voltage , determining the port voltage of the first power supply line and the port voltage of the third power supply line, wherein, is the port voltage of the first power supply line, is the voltage drop of the first power supply line, is the port voltage of the third power supply line, is the voltage drop of the third power supply line, is the output voltage of the half-bridge modules in series connection of the first power supply circuit, The series-connected half-bridge modules of the third power supply circuit output voltage.

[0017] Applying the technical solution of the present application, the above-mentioned multi-port chain battery energy storage system includes multiple power supply modules connected in parallel on a DC bus, and the power supply module includes: a current limiting inductor having a first end and a second end, the first end of the current limiting inductor being electrically connected to a power supply line, the power supply line being used to provide alternating current, and the current limiting inductor being used to suppress the flow of short-circuit current when a short-circuit fault occurs in the energy storage system; a half-bridge flow control module having a first end, a second end and a third end, the first end of the half-bridge flow control module and the second end of the half-bridge flow control module being connected in parallel on the DC bus, the third end of the half-bridge flow control module being electrically connected to the second end of the current limiting inductor, and the half-bridge flow control module being used to control the flow of the energy storage system. The system analyzes the electrical distribution characteristics of the energy storage device under fault conditions, and combines the unique topological characteristics of the shared energy storage type multi-medium voltage AC port flexible interconnection device to propose an effective flow control module control strategy, which fully utilizes the regulation capability of the power electronic switch to achieve active suppression of abnormal currents, thereby avoiding voltage drops at healthy ports, which is beneficial to achieving fault ride-through of the device and recovery of the flow control function after faults. It solves the problems of the current limiting method of the distribution network in the existing technology being constrained by the grid status, limited regulation capability, lacking the ability to transfer energy flow in time, and having high cost and large size. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 A hardware structure diagram of a multi-port chain battery energy storage system provided in an embodiment of the present application is shown;

[0020] Figure 2 A hardware structure diagram of another multi-port chain battery energy storage system provided in an embodiment of the present application is shown;

[0021] Figure 3 A MACP-CHB-ESS topology diagram provided according to an embodiment of the present application is shown;

[0022] Figure 4 A schematic diagram of an abnormal current path when a MACP-CHB-ESS power supply line fails according to an embodiment of the present application is shown;

[0023] Figure 5 A schematic diagram of a system equivalent circuit when a PFCM is used as a dynamic reactive power control device according to an embodiment of the present application is shown;

[0024] Figure 6A schematic diagram of a flow chart of a fault current limiting method for an energy storage system provided according to an embodiment of the present application is shown;

[0025] Figure 7 A schematic diagram of an operation control strategy of a PFCM as a dynamic reactive power control device provided in an embodiment of the present application is shown;

[0026] Figure 8 A current schematic diagram of a first power supply circuit provided according to an embodiment of the present application is shown;

[0027] Fig. 9 A current schematic diagram of a third power supply circuit provided according to an embodiment of the present application is shown;

[0028] Fig.10 A schematic diagram of port voltage of a first power supply module provided according to an embodiment of the present application is shown;

[0029] Fig.11 A schematic diagram of port voltage of a third power supply module provided according to an embodiment of the present application is shown.

[0030] The above drawings include the following reference numerals:

[0031] 10. Power supply module; 11. Current limiting reactor; 111. Current limiting inductor; 12. Half-bridge power flow control module; 121. First switch module; 122. Second switch module; 13. Power supply line; 14. Thyristor bypass switch. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings 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 should fall within the scope of protection of the present application.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] As introduced in the background technology, in the prior art, MACP-CHB-ESS realizes the interconnection of multiple medium-voltage AC ports with the same large-capacity energy storage system. Due to the power interaction between multiple ports, when a power supply line fails, the voltage and current distribution characteristics under the fault state are more complicated. Fault transmission will cause the voltage at the healthy port to drop, which is not conducive to the operation of the system. The following are the main hazards:

[0036] Excessive fault current: A short circuit fault will cause the fault current to increase rapidly, which may exceed the design carrying capacity of the shared energy storage equipment, causing overheating and burning of power electronic components (such as inverters, converters, etc.), and even triggering chain failures.

[0037] Damage to energy storage units: High fault currents may cause overheating, overcurrent, or even thermal runaway or explosion in energy storage units (such as batteries or supercapacitors), seriously damaging the energy storage equipment.

[0038] Voltage sag or fluctuation: A short circuit fault can cause a sudden drop or severe fluctuation in system voltage, affecting the normal operation of other connected equipment and even causing system voltage collapse.

[0039] Local fault extension: Since shared energy storage systems are usually connected to multiple grids or loads, short-circuit faults may spread from the fault point to a wider area, affecting other connected grid parts or users.

[0040] In general, when a short circuit occurs in a shared energy storage flexible interconnection device, the harm is not limited to the device itself, but will also have a profound impact on the stability and safety of the entire power system, which may lead to extensive economic losses and safety hazards. Therefore, it is crucial to adopt effective fault active current limiting measures and protection strategies.

[0041] In order to solve the problems that the current limiting method of the distribution network in the prior art is constrained by the grid status, has limited regulation capability, lacks the ability to transfer energy flow in time, and has high cost and large size, an embodiment of the present application provides a multi-port chain battery energy storage system.

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0043] In this embodiment, a multi-port chain battery energy storage system is provided. Figure 1 is a structural diagram of a multi-port chain battery energy storage system according to an embodiment of the present application. Figure 1 As shown, the system includes a plurality of power supply modules 10 connected in parallel on a DC bus L, wherein the power supply module 10 includes: a current limiting reactor 11 having a first end and a second end, wherein the first end of the current limiting reactor 11 is electrically connected to a power supply line 13, wherein the power supply line 13 is used to provide alternating current, and wherein the current limiting reactor 11 is used to suppress the flow of short-circuit current when a short-circuit fault occurs in the energy storage system; a half-bridge flow control module 12 having a first end, a second end and a third end, wherein the first end of the half-bridge flow control module 12 and the second end of the half-bridge flow control module 12 are connected in parallel to the DC bus L, wherein the third end of the half-bridge flow control module 12 is electrically connected to the second end of the current limiting reactor 11, and wherein the half-bridge flow control module 12 is used to control the flow of the energy storage system.

[0044] The above system can be a multi-AC port flexible interconnection distribution system. The above multi-port chain battery energy storage system is a topological structure based on the multi-port chain battery energy storage system (MACP-CHB-ESS), and proposes a new system combining the idea of ​​"time-space complementarity, flexible storage and use". The system adopts the topological architecture of "series regulation, single parallel support". There is no need to add full-power devices when the port is expanded. It has the characteristics of compactness, low cost and easy expansion, and realizes the mutual assistance and sharing between multi-terminal AC power supply lines and the same energy storage system.

[0045] In the MACP-CHB-ESS topology, each port is equipped with a current-limiting reactor, which can suppress the fault current to a certain extent. However, in order to further improve the fault response capability of the system, the series voltage regulation principle is adopted, and a series regulation type power flow control module is integrated on each power supply line. By implementing an active current limiting control strategy for these modules, they act as dynamic reactive power control devices (such as dynamic voltage regulators DVR) in fault conditions, thereby effectively limiting the magnitude of the fault short-circuit current and improving the voltage stability of the healthy ports during the fault.

[0046] The above-mentioned multi-port chain battery energy storage system of the present application includes a plurality of power supply modules connected in parallel on a DC bus, and the power supply module includes: a current limiting inductor having a first end and a second end, the first end of the current limiting inductor being electrically connected to a power supply line, the power supply line being used to provide alternating current, and the current limiting inductor being used to suppress the flow of short-circuit current in the event of a short-circuit fault in the energy storage system; a half-bridge flow control module having a first end, a second end and a third end, the first end of the half-bridge flow control module and the second end of the half-bridge flow control module being connected in parallel on the DC bus, the third end of the half-bridge flow control module being electrically connected to the second end of the current limiting inductor, and the half-bridge flow control module being used to control the flow of the energy storage system. The system analyzes the electrical distribution characteristics of the energy storage device under fault conditions, and combines the unique topological characteristics of the shared energy storage type multi-medium voltage AC port flexible interconnection device to propose an effective flow control module control strategy, which fully utilizes the regulation capability of the power electronic switch to achieve active suppression of abnormal currents, thereby avoiding voltage drops at healthy ports, which is beneficial to achieving fault ride-through of the device and recovery of the flow control function after faults. It solves the problems of the current limiting method of the distribution network in the existing technology being constrained by the grid status, limited regulation capability, lacking the ability to transfer energy flow in time, and having high cost and large size.

[0047] In some instances, such as Figure 2 As shown, the power supply module 10 further includes: a thyristor bypass switch 14 , which is connected in parallel to the first bridge wall of the half-bridge power flow control module 12 .

[0048] Among them, the thyristor bypass switch is used to bypass the switching devices of the half-bridge power flow control module (PFCM) when the corresponding power supply line fails. This eliminates the need to bypass all half-bridge power flow control modules, effectively reducing abnormal currents in the system and ensuring the safe operation of power electronic equipment and relay protection systems.

[0049] In some instances, such as Figure 2 As shown, the half-bridge power flow control module 12 includes a first switch module 121 on the first bridge wall and a second switch module 122 on the second bridge wall, wherein the first switch module 121 has a first end, a second end and a control end, the first end of the first switch module 121 is electrically connected to the DC bus L, the second end of the first switch module 121 is electrically connected to the current limiting reactor 11, and the control end of the first switch module 121 is used to input a first control signal; the second switch module 122 has a first end, a second end and a control end, the first end of the second switch module 122 is electrically connected to the second end of the first switch module 121 and the current limiting reactor 11 respectively, the second end of the second switch module 122 is electrically connected to the DC bus L, and the control end of the second switch module 122 is used to input a second control signal.

[0050] Among them, by controlling the output voltage of the half-bridge power flow control module connected in series in the AC power supply line, effective regulation of the power flow can be achieved.

[0051] In some instances, such as Figure 2 As shown, the first switch module 121 and the second switch module 122 each include a transistor.

[0052] In some instances, such as Figure 2 As shown, the above-mentioned current limiting reactor 11 is a current limiting inductor 111.

[0053] In the prior art, when a fault occurs in the AC power supply line, the power electronic switch device responds much faster than the sectional switch on the power supply line. In order to protect the switch device of the device, the energy storage power module is often bypassed for protection. Since power electronic devices are more sensitive to abnormal voltage and abnormal current, and have lower tolerance to overvoltage and overcurrent, most existing intelligent soft switches use bypass to prevent abnormal current from damaging the power electronic switch. However, under this method, the device will completely stop working, the device utilization rate is low, and it is not conducive to the recovery of the power flow control function after the fault.

[0054] In the MACP-CHB-ESS system of the present application, each port is equipped with a current-limiting reactor. By utilizing its unique topological structure, these reactors significantly suppress the short-circuit current flowing through each port in the event of a fault.

[0055] In some instances, such as Figure 3 As shown, taking phase A and three power supply ports as an example, a mechanical circuit breaker is installed in each power supply line between the port inductor and the common connection point (PCC), and in the half-bridge power flow control module (PFCM), the lower IGBT module is installed with a thyristor bypass switch (TBS). The above power flow control modules are all connected in parallel to the common DC bus, and a DC unloading circuit is connected in parallel to the DC bus. In the connected chain energy storage system, a fast mechanical switch is connected between the midpoints of the two bridge arms of each energy storage power unit, and a DC unloading circuit is connected in parallel on the DC side of the energy storage battery. Among them, Figure 3 The multi-port chain battery energy storage system in the embodiment includes a CHB-ESS module, which is composed of multiple sub-modules connected in parallel. The structure of the sub-modules of the CHB-ESS module is as follows: Figure 3 As shown in the structure in A, Figure 3 B is a fast mechanical switch, and transistors Q1, Q2, Q3, Q4 and fast mechanical switch B together form a power supply module. The power supply module is also connected in parallel with a battery for charging and discharging. The specific structure of the thyristor bypass switch is as follows: Figure 3 As shown in Figure C, the thyristor bypass switch consists of two thyristors connected in reverse parallel. Figure 2 , Figure 3 and Figure 4 As shown. When a short circuit fault occurs and the current does not exceed the carrying capacity of the switching device, the MACP-CHB-ESS system will actively respond, first by locking the control signals of all switches and activating the thyristor bypass switch (TBS). When the TBS is activated, the voltage of the MACP-CHB-ESS system in series with the power supply line is quickly clamped to a position close to 0V. For the parallel part of the CHB-ESS, since the sum of the DC voltages of each phase is higher than the phase voltage amplitude at the grid connection point during design, when the CHB-ESS is locked, the sum of the DC voltages exceeds the phase voltage amplitude, and the diode is therefore subjected to reverse voltage and is turned off, causing the current to drop to zero.

[0056] At this time, it is not necessary to bypass all PFCMs. Instead, their output voltage can be controlled to be opposite to the system power supply, so that their output characteristics can operate as a dynamic reactive power control device, further limiting abnormal current. When the PFCM operates in dynamic reactive power control mode, the equivalent circuit of the system is as shown in the following figure. Figure 5 This active fault current limiting strategy effectively reduces the abnormal current in the system and ensures the safe operation of power electronic equipment and relay protection systems.

[0057] An embodiment of the present application also provides a fault current limiting method for an energy storage system, which is used to control any of the above-mentioned multi-port chain battery energy storage systems, wherein the energy storage system includes a power supply module, and the power supply module includes a thyristor bypass switch connected in parallel on the first bridge wall of the above-mentioned half-bridge current control module.

[0058] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0059] Figure 6 is a flow chart of a fault current limiting method for an energy storage system according to an embodiment of the present application. Figure 6 As shown, the method comprises the following steps:

[0060] Step S101, when the energy storage system is in steady-state operation, controlling the power flow of the energy storage system through a half-bridge power flow control module;

[0061] Step S102, when a short-circuit fault occurs in the target power supply line of the energy storage system and the short-circuit current is less than the maximum threshold current, the thyristor bypass switch corresponding to the target power supply line is controlled to be turned on, and all the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system.

[0062] Specifically, the above steps propose a fault active current limiting strategy for a "shared energy storage" distribution system based on MACP-CHB-ESS. This strategy analyzes the electrical distribution characteristics of a shared energy storage multi-terminal flexible interconnected device under fault conditions, and combines the unique topological structure of MACP-CHB-ESS to develop an effective power flow control module control scheme. By giving full play to the regulation capability of power electronic switches, the amplitude of the fault current is actively limited, thereby reducing the drop voltage of the healthy power supply port and enhancing the fault ride-through capability and anti-interference performance of the energy storage system.

[0063] In the steady-state operation stage, MACP-CHB-ESS realizes effective regulation of power flow by controlling the output voltage of the PFCM module connected in series in the AC power supply line.

[0064] When a fault occurs in the AC power supply line, when a short circuit occurs and the current does not exceed the carrying capacity of the switch device, the MACP-CHB-ESS system will actively respond, first by locking the control signals of all switches and activating the thyristor bypass switch (TBS). When the TBS is activated, the voltage of the MACP-CHB-ESS system in series with the power supply line is quickly clamped to a position close to 0V.

[0065] Among them, there are three power supply modules, which control all the half-bridge power flow control modules to operate as dynamic reactive power control modules, including: controlling the peak voltage of the base frequency component output by all the half-bridge power flow control modules , to control all the above half-bridge power flow control modules to operate as dynamic reactive power control modules, wherein, is the peak voltage of the fundamental frequency component output by the above half-bridge power flow control module, is the DC bus voltage.

[0066] Specifically, under the SPWM modulation mode, the peak voltage of the fundamental frequency component that the power flow control module can output satisfies In order to achieve the best fault current suppression effect for the output voltage of the power flow control module, make full use of its modulation degree, establish a dq rotating coordinate system synchronized with the node voltage of each sound power supply line, and realize the peak output of the base frequency AC component voltage of the three-terminal series power flow control module by giving the maximum value of the d-axis component reference value, that is, , where V c1 、V c2 、V c3 It is the effective value of the fundamental AC component that can be output by the half-bridge module in the three power supply lines.

[0067] In this system, when a power supply line fails, the reference value of the d-axis component will be in opposite phase to the reference value of the d-axis component of a normal and healthy line. At the same time, the phase-locked loop is used to obtain the first power supply line ( Figure 4 The power supply line 1) and the third power supply line ( Figure 4 The node voltage phase of the power supply line 3) in the middle is used to ensure that the voltage phase angle output by the power flow regulation module matches the node voltage phase angle of the connected power supply line, thereby maximizing the use of the output voltage of the series power flow regulation module on the healthy line. Under normal circumstances, the node voltage of each power supply port is relatively consistent with the parameters of the power supply line, that is, Assuming that the power supply ports in steady state are numbered from 1 to n, the phase angle of the equivalent voltage source of the power supply line connected to the n healthy ports can be expressed as formula (1):

[0068] (1)

[0069] in, The phase angle of the equivalent voltage source of the power supply line, The voltage source phase angle of the power supply port number i, is the node voltage phase angle of power supply ports 1 and 3.

[0070] In order to maximize the use of the output voltage of the PFCM power flow control module in the faulty power supply line, the phase of its output voltage should be synchronized with the equivalent power phase of the healthy power supply line. Based on this idea, a control strategy is proposed, as shown in the attached figure. Figure 7 As shown, it is used to convert the PFCM into a dynamic reactive power control device under fault conditions, thereby achieving accurate regulation of reactive power during the fault period to maintain system stability.

[0071] The power supply line includes a first power supply line, a second power supply line and a third power supply line. The power supply modules include three, namely, a first power supply module, a second power supply module and a third power supply module. The second power supply line is used as the target power supply line, and the second power supply line is used as the power supply line of the second power supply module. Controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules includes the following steps:

[0072] Step S201, determining the equivalent voltage source phase angle between the first power supply circuit and the third power supply circuit , to control the half-bridge power flow control module of the first power supply module and the half-bridge power flow control module of the third power supply module to operate with a dynamic reactive power control module, wherein the first power supply line is the power supply line of the first power supply module, and the third power supply line is the power supply line of the third power supply module, is the equivalent voltage source phase angle between the first power supply line and the third power supply line, is the equivalent voltage source phase angle of the first power supply circuit, is the equivalent voltage source phase angle of the third power supply line;

[0073] Step S202, determining the phase angle of the equivalent voltage source of the second power supply circuit , to control the half-bridge power flow control module of the second power supply module to operate as a dynamic reactive power control module, wherein, is the phase angle of the equivalent voltage source of the second power supply line.

[0074] Specifically, referring to formula (1), the equivalent voltage source phase angle formula of the first power supply line and the third power supply line can be obtained: , so that in the three-port MACP-CHB-ESS, the phase angle of the equivalent voltage source of the power supply line connected to the fault port can be , to achieve maximum utilization of the output voltage of the power flow control module connected to the faulty power supply line and the sound power supply line. is the equivalent voltage source phase angle of the first power supply circuit, is the equivalent voltage source phase angle of the third power supply line; Indicates the power supply line connected to the faulty port ( Figure 4 The phase angle of the equivalent voltage source in the power supply line 2).

[0075] Specifically, the fault active current limiting strategy of the multi-medium voltage AC port shared energy storage type flexible interconnection device proposed in the above embodiment can actively limit the fault current increase when a fault occurs in the AC power supply line connected to the MACP-CHB-ESS, thereby improving the voltage level of the healthy port, preventing the expansion of local faults from affecting the normal operation of other power supply ports, helping the device to remain stable during the fault and quickly restore the power flow control function after the fault is eliminated.

[0076] The active current limiting strategy of the above-mentioned multi-medium voltage AC port shared energy storage flexible interconnection device fully utilizes the potential advantages of the MACP-CHB-ESS device in current limiting, enhances the response capability of power electronic devices in the event of a fault, and provides technical support for the protection strategy of MACP-CHB-ESS in future engineering applications.

[0077] After the PFCM is put into operation, various asymmetric short-circuit faults can be analyzed by the symmetrical component method. The system parameters and the currents of the three power supply lines under the short-circuit fault condition can be calculated as shown in formula (2):

[0078] (2)

[0079] in, , , Respectively represent the first power supply line (i.e. Figure 4 The second power supply line (i.e. Figure 4 The power supply line 2), the third power supply line (i.e. Figure 4 The current in the power supply line 3).

[0080] Among them, there are three power supply modules, namely the first power supply module, the second power supply module and the third power supply module, the power supply line of the first power supply module is the first power supply line, the power supply line of the second power supply module is the second power supply line, the power supply line of the third power supply module is the third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: determining the formula according to the voltage drop , determine the voltage drop of the first power supply line and the voltage drop of the third power supply line, wherein, is the voltage drop of the first power supply line, is the voltage drop of the third power supply line, is the current of the first power supply line, is the current of the third power supply line, jX1 is the equivalent reactance of the first power supply line, and jX3 is the equivalent reactance of the third power supply line.

[0081] Specifically, according to formula (2) and the voltage drop determination formula, the voltage drop on two healthy power supply lines can be obtained as shown in formula (3):

[0082] (3)

[0083] Among them, there are three power supply modules, namely the first power supply module, the second power supply module and the third power supply module. The power supply line of the first power supply module is the first power supply line, the power supply line of the second power supply module is the second power supply line, the power supply line of the third power supply module is the third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: determining the formula according to the power supply port voltage , determine the port voltage of the first power supply line and the port voltage of the third power supply line, wherein, is the port voltage of the first power supply line, is the voltage drop of the first power supply line, is the port voltage of the third power supply line, is the voltage drop of the third power supply line, is the output voltage of the half-bridge module in series with the first power supply circuit, The output voltage of the half-bridge modules connected in series on the third power supply circuit.

[0084] Specifically, according to formula (2), the voltage drop determination formula and the power supply port voltage determination formula, the voltage at the healthy power supply port of MACP-CHB-ESS is obtained as shown in formula (4):

[0085] (4)

[0086] in, is the port voltage of the first power supply line, is the voltage drop of the first power supply line, is the port voltage of the third power supply line, is the voltage drop of the third power supply line, is the output voltage of the half-bridge module in series with the first power supply circuit, The output voltage of the half-bridge modules connected in series on the third power supply circuit.

[0087] The fault current limiting method of the energy storage system of the present application is used to control any of the multi-port chain battery energy storage systems mentioned above, the energy storage system includes a power supply module, the power supply module includes a thyristor bypass switch connected in parallel on the first bridge wall of the half-bridge power flow control module, the method first controls the power flow of the energy storage system through the half-bridge power flow control module when the energy storage system is in steady state operation; then, when a short-circuit fault occurs in the target power supply line of the energy storage system and the short-circuit current is less than the maximum threshold current, the thyristor bypass switch corresponding to the target power supply line is controlled to be turned on, and all the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system. The method can actively limit the fault current increase when a fault occurs in the AC power supply line connected to the MACP-CHB-ESS, thereby increasing the voltage level of the healthy port and preventing the local fault from expanding and affecting the normal operation of other power supply ports. It helps the device to remain stable during the fault and quickly restore the power flow regulation function after the fault is eliminated. It utilizes the potential advantages of the MACP-CHB-ESS device in current limiting, enhances the response capability of power electronic devices in the event of a fault, and solves the problems of the current limiting method of the distribution network in the prior art being constrained by the grid state, limited regulation capability, lacking the time transfer capability of the energy flow, and having high cost and large size.

[0088] According to the current distribution coefficient, and considering the power supply line current distributed according to the natural flow of the node voltage of each power supply line before the short-circuit fault, the current of the three power supply lines after the attenuation of the non-periodic component can be further obtained. As the current of the healthy power supply line increases, the voltage drop on the power supply line also increases. Compared with the fault active current limiting strategy suitable for multi-medium voltage AC port shared energy storage type flexible interconnection device. It can be seen that after the PFCM is put into operation as a dynamic reactive power control device, the abnormal increase in current has been significantly suppressed, and the healthy port voltage has increased to more than 80% of the rated voltage, which is conducive to assisting the system to achieve fault crossing.

[0089] In the three-terminal power supply line flexible interconnection system, the second power supply line of MACP-CHB-ESS (i.e. Figure 4 A three-phase short circuit fault occurs in the power supply line 2), and the abnormal current limiting strategy of the present invention is used to actively limit the short circuit abnormal current of the system. The simulation timing is set as follows: the fault occurs at t=0.05s, and the PFCM is first bypassed through the TBS. At this time, the abnormal increase in current is only limited by the current limiting reactor of the power supply port of the MACP-CHB-ESS. At 0.5s, the PFCM control strategy is put into operation to make it work in the dynamic reactive power control device operation state, further limiting the abnormal current.

[0090] The following is a further explanation of the application of the above structure and method in conjunction with a specific simulation example; in conjunction with the above embodiment, the following uses MATLAB / Simulink software to perform simulation verification for the normal working condition and the fault working condition of the system, respectively. The specific simulation parameters are shown in Table 1, and Appendix Figure 8 , Fig. 9 , Fig.10 as well as Fig.11 is the simulation waveform. Among them, Figure 8 Where Ia1, Ib1, and Ic1 are the abc three-phase currents of the first power supply line, Fig. 9 Where Ia3, Ib3, and Ic3 are the abc three-phase currents of the third power supply line, Fig.10 Where Va1, Vb1, and Vc1 are the abc three-phase port voltages of the first power supply module, Fig.11 Where Va3, Vb3, and Vc3 are the abc three-phase port voltages of the third power supply module respectively.

[0091] Table 1. Simulation model parameters

[0092]

[0093] The simulation results show that when a fault occurs in an AC power supply line, by controlling the PFCM to operate as a dynamic reactive power control device, the abnormal current and the voltage drop at the healthy port outlet can be effectively suppressed, which is beneficial to the fault ride-through of the device and the recovery of the power flow control function after the fault.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0095] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0096] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0097] 1) The above-mentioned multi-port chain battery energy storage system of the present application includes a plurality of power supply modules connected in parallel on a DC bus, and the power supply module includes: a current limiting inductor having a first end and a second end, the first end of the current limiting inductor being electrically connected to a power supply line, the power supply line being used to provide alternating current, and the current limiting inductor being used to suppress the flow of short-circuit current in the event of a short-circuit fault in the energy storage system; a half-bridge flow control module having a first end, a second end and a third end, the first end of the half-bridge flow control module and the second end of the half-bridge flow control module being connected in parallel on the DC bus, the third end of the half-bridge flow control module being electrically connected to the second end of the current limiting inductor, and the half-bridge flow control module being used to control the flow of the energy storage system. The system analyzes the electrical distribution characteristics of the energy storage device under fault conditions, and combines the unique topological characteristics of the shared energy storage type multi-medium voltage AC port flexible interconnection device to propose an effective flow control module control strategy, which fully utilizes the regulation capability of the power electronic switch to achieve active suppression of abnormal currents, thereby avoiding voltage drops at healthy ports, which is beneficial to achieving fault ride-through of the device and recovery of the flow control function after faults. It solves the problems of the current limiting method of the distribution network in the existing technology being constrained by the grid status, limited regulation capability, lacking the ability to transfer energy flow in time, and having high cost and large size.

[0098] 2) The fault current limiting method of the energy storage system of the present application is used to control any of the multi-port chain battery energy storage systems mentioned above, the energy storage system includes a power supply module, the power supply module includes a thyristor bypass switch connected in parallel on the first bridge wall of the half-bridge power flow control module, the method first controls the power flow of the energy storage system through the half-bridge power flow control module when the energy storage system is in steady state operation; then, when a short-circuit fault occurs in the target power supply line of the energy storage system and the short-circuit current is less than the maximum threshold current, the thyristor bypass switch corresponding to the target power supply line is controlled to be turned on, and all the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system. The method can actively limit the fault current increase when a fault occurs in the AC power supply line connected to the MACP-CHB-ESS, thereby increasing the voltage level of the healthy port and preventing the local fault from expanding and affecting the normal operation of other power supply ports. It helps the device to remain stable during the fault and quickly restore the power flow regulation function after the fault is eliminated. It utilizes the potential advantages of the MACP-CHB-ESS device in current limiting, enhances the response capability of power electronic devices in the event of a fault, and solves the problems of the current limiting method of the distribution network in the prior art being constrained by the grid state, limited regulation capability, lacking the time transfer capability of the energy flow, and having high cost and large size.

[0099] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-port chain battery energy storage system, characterized in that: It includes a plurality of power supply modules connected in parallel on a DC bus, and the power supply module includes: A current limiting reactor having a first end and a second end, wherein the first end of the current limiting reactor is electrically connected to a power supply line, the power supply line is used to provide alternating current, and the current limiting reactor is used to suppress the flow of short-circuit current when a short-circuit fault occurs in the energy storage system; A half-bridge flow control module has a first end, a second end and a third end. The first end of the half-bridge flow control module and the second end of the half-bridge flow control module are connected in parallel to the DC bus, and the third end of the half-bridge flow control module is electrically connected to the second end of the current limiting inductor. The half-bridge flow control module is used to control the flow of the energy storage system.

2. The multi-port chain battery energy storage system according to claim 1, characterized in that: The power supply module also includes: A thyristor bypass switch is connected in parallel to the first bridge wall of the half-bridge power flow control module.

3. The multi-port chain battery energy storage system according to claim 1, characterized in that: The half-bridge power flow control module includes a first switch module on a first bridge wall and a second switch module on a second bridge wall, wherein: The first switch module has a first end, a second end and a control end, the first end of the first switch module is electrically connected to the DC bus, the second end of the first switch module is electrically connected to the current limiting reactor, and the control end of the first switch module is used to input a first control signal; The second switch module has a first end, a second end and a control end. The first end of the second switch module is electrically connected to the second end of the first switch module and the current limiting inductor respectively, the second end of the second switch module is electrically connected to the DC bus, and the control end of the second switch module is used to input a second control signal.

4. The multi-port chain battery energy storage system according to claim 3, characterized in that: The first switch module and the second switch module each include a transistor.

5. The multi-port chain battery energy storage system according to claim 1, characterized in that: The current limiting reactor is a current limiting inductor.

6. A fault current limiting method for an energy storage system, characterized in that: The method is used to control the multi-port chain battery energy storage system according to any one of claims 1 to 5, the energy storage system comprising a power supply module, the power supply module comprising a thyristor bypass switch connected in parallel on the first bridge wall of the half-bridge power flow control module, and the method comprises: When the energy storage system is in steady state operation, the power flow of the energy storage system is controlled by a half-bridge power flow control module; When a short-circuit fault occurs in the target power supply line of the energy storage system and the short-circuit current is less than the maximum threshold current, the thyristor bypass switch corresponding to the target power supply line is controlled to be turned on, and all the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system.

7. The method according to claim 6, characterized in that The power supply modules have three components, and control all the half-bridge power flow control modules to operate as dynamic reactive power control modules, including: Control the peak voltage of the fundamental frequency component output by all the half-bridge power flow control modules , to control all the half-bridge power flow control modules to operate as dynamic reactive power control modules, wherein, is the peak voltage of the fundamental frequency component output by the half-bridge power flow control module, is the DC bus voltage.

8. The method according to claim 6, characterized in that The power supply line includes a first power supply line, a second power supply line and a third power supply line. The power supply modules include three, namely, a first power supply module, a second power supply module and a third power supply module. The second power supply line is used as the target power supply line, and the second power supply line is used as the power supply line of the second power supply module. All the half-bridge power flow control modules are controlled to operate as dynamic reactive power control modules, including: Determine the equivalent voltage source phase angle between the first power supply line and the third power supply line , to control the half-bridge power flow control module of the first power supply module and the half-bridge power flow control module of the third power supply module to operate as a dynamic reactive power control module, wherein the first power supply line is the power supply line of the first power supply module, and the third power supply line is the power supply line of the third power supply module, is the equivalent voltage source phase angle between the first power supply line and the third power supply line, is the equivalent voltage source phase angle of the first power supply line, is the equivalent voltage source phase angle of the third power supply circuit; Determine the phase angle of the equivalent voltage source of the second power supply line , to control the half-bridge power flow control module of the second power supply module to operate as a dynamic reactive power control module, wherein, is the phase angle of the equivalent voltage source of the second power supply line.

9. The method according to claim 6, characterized in that There are three power supply modules, namely a first power supply module, a second power supply module and a third power supply module. The power supply line of the first power supply module is a first power supply line, the power supply line of the second power supply module is a second power supply line, the power supply line of the third power supply module is a third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: Determine the formula based on the pressure drop , determining the voltage drop of the first power supply line and the voltage drop of the third power supply line, wherein, is the voltage drop of the first power supply line, is the voltage drop of the third power supply line, is the current of the first power supply line, is the current of the third power supply line, jX1 is the equivalent reactance of the first power supply line, and jX3 is the equivalent reactance of the third power supply line.

10. The method according to claim 6, characterized in that There are three power supply modules, namely a first power supply module, a second power supply module and a third power supply module. The power supply line of the first power supply module is a first power supply line, the power supply line of the second power supply module is a second power supply line, the power supply line of the third power supply module is a third power supply line, and the target power supply line is the second power supply line. After controlling all the half-bridge power flow control modules to operate as dynamic reactive power control modules to reduce the short-circuit current in the energy storage system, the method further includes: Determine the formula based on the power supply port voltage , determining the port voltage of the first power supply line and the port voltage of the third power supply line, wherein, is the port voltage of the first power supply line, is the voltage drop of the first power supply line, is the port voltage of the third power supply line, is the voltage drop of the third power supply line, is the output voltage of the half-bridge modules in series connection of the first power supply circuit, The series-connected half-bridge modules of the third power supply circuit output voltage.

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