Energy storage power station optimization control system and method

Abstract

The invention discloses an energy storage power station optimization control system and method, and belongs to the field of new energy and energy storage, and the system comprises an external power grid, an energy storage power station unit and a line protection unit. The energy storage power station unit comprises an energy storage battery, an energy storage converter and a transformer which are electrically connected in sequence; the line protection unit comprises a bus, a sending-out line, a current transformer, a voltage transformer, a circuit breaker and a protection device; the current transformer and the voltage transformer are respectively used for collecting tie line current and bus voltage, and determining a fault occurrence area according to the relation between the tie line current and the bus voltage; the protection device performs related actions according to the judgment result; the energy storage power station unit is connected to an external power grid through a sending-out line. The system can solve the problem that the complex fault characteristics of the energy storage power station affect the protection performance, and improves the fault response capability of the energy storage power station.

Description

Technical Field

[0001] The present invention belongs to the field of new energy and energy storage, and specifically relates to an optimized control system and method for an energy storage power station. Background Art

[0002] Energy storage, as an indispensable element and important fast and flexible regulation resource in the new power system, plays an important role in aspects such as system peak shaving and valley filling, peak load supply guarantee, safety and stability, frequency modulation and voltage regulation. The special fault characteristics of energy storage power stations change the electrical quantity characteristics after grid faults, subverting the traditional theoretical basis of relay protection based on synchronous machine characteristics. The action performance of existing AC relay protection devices has seriously declined, and there are prominent problems such as refusal to operate, misoperation, and slow operation.

[0003] Affected by the interaction between the energy storage operation state and the control method, the fault characteristics of energy storage show the characteristics of a large and unstable reduction in the steady-state power frequency component when the main protection operates. For the differential protection of the main protection of the power grid, when the energy storage operates in the discharging state after a grid fault, the short-circuit current characteristics provided by the energy storage show a weak-feed characteristic. If the connected power grid is a weak grid and the short-circuit current amplitude provided by the grid side is limited, the sensitivity of the differential protection decreases. When the energy storage operates in the charging state after a grid fault, the short-circuit current provided by the energy storage is an in-drawing current. Whether the connected power grid is a strong grid or a weak grid, the sensitivity of the differential protection decreases. Especially in the case of a weak grid, there may even be a risk of refusal to operate. For the distance protection of the backup protection of the power grid, the phase angle of the short-circuit current provided by the energy storage is controlled after a grid fault, and the additional impedance calculation is inaccurate. There is a risk of refusal to operate for the distance protection on the energy storage side. If the connected power grid is a weak grid, the risk of refusal to operate for the distance protection on the energy storage side is greater. Especially during a fault with a transition resistance when the energy storage operates in the charging state, there is a risk of refusal to operate on both the energy storage side and the system side. That is, there are problems such as low sensitivity of differential protection and possible incorrect operation of distance protection when an electrochemical energy storage power station is connected to the system. At the same time, affected by the interaction between the energy storage operation state and the control method, there are large deviations in the existing steady-state short-circuit current calculation results, and the accuracy of the existing protection setting method has decreased.

[0004] In the prior art, the control and protection of energy storage devices are relatively independent. The time-sequence coupling relationship between the control method of the energy storage converter and the action of the outgoing line protection is not considered. The influence of factors such as the strength of the power grid and the energy storage operation state on the protection setting of the energy storage power station is not fully considered. The coordination and cooperation between the fault control method of the energy storage power station and the traditional outgoing line protection are not considered. Summary of the Invention

[0005] To solve the deficiencies in the prior art, the present invention provides an optimized control system and method for an energy storage power station, which is mainly used to ensure the reliable operation of the outgoing line protection, can solve the problem of the influence of the complex fault characteristics of the energy storage power station on the protection performance, improves the relay protection scheme and fault control method of the energy storage power station, and enhances the fault response ability of the energy storage power station.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an optimized control system for an energy storage power station, including an external power grid, an energy storage power station unit, and a line protection unit; The energy storage power station unit includes an energy storage battery, an energy storage converter, and a transformer that are electrically connected in sequence; The line protection unit includes a bus, a transmission line, a current transformer, a voltage transformer, a circuit breaker, and a protection device; the energy storage power station unit is connected to the external power grid through the transmission line; the current transformer and the voltage transformer are respectively used to collect the tie line current and the bus voltage, and the protection device is used to judge the fault state of the tie line according to the tie line current and the bus voltage, and perform relevant actions according to the judgment result: Based on the judgment result of the tie line fault state, judge the line protection mode, the energy storage operation state, and the strength of the power grid; according to the judgment results of the line protection mode, the energy storage operation state, and the strength of the power grid, perform the response of the action device; perform a closed-loop feedback process based on the response result of the action device.

[0007] As a further improvement of the present invention, the protection device is further used to determine the fault occurrence area according to the relationship between the tie line current and the bus voltage.

[0008] As a further improvement of the present invention, the external power grid is divided into a strong power grid and a weak power grid according to different short-circuit ratios.

[0009] As a further improvement of the present invention, the transmission line adopts differential protection as the main protection and distance protection as the backup protection.

[0010] As a further improvement of the present invention, the protection device performs relevant actions according to the judgment result, including: When both the in-zone fault and the differential protection action conditions are met, the main protection is started; when both the in-zone fault and the distance protection action conditions are met, the backup protection is started; when an out-of-zone fault is met, the protection device does not act.

[0011] As a further improvement of the present invention, the transformer device of the line protection unit monitors and collects the electrical characteristic quantities of the tie line and the bus, and the protection device judges whether the current and voltage indicators exceed the limit; if so, a fault occurs in the tie line; if not, the power grid operates normally and the process ends.

[0012] As a further improvement of the present invention, the line protection mode of the protection device is judged according to the magnitude and direction of the setting current, including differential protection and distance protection; when both the in-zone fault and the differential protection action conditions are met, the main protection is started; when both the in-zone fault and the distance protection action conditions are met, the backup protection is started; when an out-of-zone fault is met, the protection device does not act; The energy storage operation state is judged with reference to the charging and discharging of the battery and the reactive power output of the energy storage converter, which is divided into two processes: charging and discharging; the strength of the power grid is judged according to the short-circuit ratio.

[0013] As a further improvement of the present invention, the protection device is further configured to: When the differential protection is activated and the energy storage is operating in the discharging state, if the connected power grid is a strong power grid, the protection device takes priority to act and cut off the power grid fault; if the connected power grid is a weak power grid, the energy storage control responds first and provides active support for the power grid; When the differential protection is activated and the energy storage is operating in the charging state, the energy storage provides a short-circuit current as a drawing current, and the energy storage control responds first and provides active support for the power grid; When the distance protection is activated, the energy storage control responds first and provides active support for the power grid.

[0014] As a further improvement of the present invention, the protection device is further configured to: After a power grid fault, the energy storage provides frequency and voltage support for the power grid by switching the charging and discharging processes and controlling the output power. At the same time, the current transformer device on the line collects electrical characteristic quantities such as current and voltage again to judge whether the index exceeds the limit; if not, the power grid operates normally and the process ends; otherwise, the power grid fault is not lifted and the energy storage output power needs to be further adjusted.

[0015] In a second aspect, the present invention provides an energy storage system optimization control method, including: The current transformer and the voltage transformer are respectively used to collect the tie-line current and the bus voltage, and judge the fault occurrence area according to the relationship between the tie-line current and the bus voltage; the protection device performs relevant actions according to the judgment result.

[0016] As a further improvement of the present invention, it specifically includes: judging the fault state of the tie line; Based on the judgment result of the tie-line fault state, judge the line protection mode, the energy storage operation state and the power grid strength; Based on the judgment results of the line protection mode, the energy storage operation state and the power grid strength, perform the response of the action device; Perform a closed-loop feedback process based on the response result of the action device.

[0017] As a further improvement of the present invention, the judging the fault state of the tie line includes: The transformer device of the line protection unit monitors and collects the electrical characteristic quantities of the tie line and the bus, and judges whether the current and voltage indexes exceed the limit; if so, the tie line has a fault and enters the next step, otherwise the power grid operates normally and the process ends; As a further improvement of the present invention, the judging the line protection mode, the energy storage operation state and the power grid strength includes: The line protection method is judged according to the magnitude and direction of the setting current, including differential protection and distance protection; when both the in-zone fault and the differential protection action conditions are satisfied, the main protection is started; when both the in-zone fault and the distance protection action conditions are satisfied, the backup protection is started; when an out-of-zone fault is satisfied, the protection device does not act.

[0018] The energy storage operation state is judged with reference to the battery charge and discharge and the reactive power output of the energy storage converter, and is divided into two processes: charging and discharging; the strength of the power grid is judged according to the short-circuit ratio.

[0019] As a further improvement of the present invention, the response of the action device includes: When the differential protection is started and the energy storage is operating in the discharge state, if the connected power grid is a strong power grid, the protection device acts preferentially to cut off the power grid fault; if the connected power grid is a weak power grid, the energy storage control responds preferentially to provide active support for the power grid; When the differential protection is started and the energy storage is operating in the charging state, the energy storage provides a short-circuit current as a drawn current, and the energy storage control responds preferentially to provide active support for the power grid; When the distance protection is started, the energy storage control responds preferentially to provide active support for the power grid.

[0020] As a further improvement of the present invention, the closed-loop feedback process includes: After a power grid fault, the energy storage provides frequency and voltage support for the power grid by switching the charge and discharge processes and controlling the output power. At the same time, the current transformer device on the line collects electrical characteristic quantities such as current and voltage again to judge whether the index exceeds the limit; if not, the power grid operates normally and the process ends; otherwise, the power grid fault is not lifted and the energy storage output power needs to be further adjusted.

[0021] As a further improvement of the present invention, the determination of the fault occurrence area according to the relationship between the tie-line current and the bus voltage includes: Completely identical current transformers are installed at both ends of the line, and the current flowing through the relay is the phasor sum of the currents on both sides; when operating normally or a short-circuit fault occurs outside the line, the current flowing into the relay is 0 and the differential relay does not act; when a fault occurs within the protection range, the current flowing into the relay is the fault current Ik at the short-circuit point. When it is greater than the action current of the differential relay, the relay acts and trips the circuit breakers at both ends of the line; The bus voltage at the protection installation location and the current flowing through the protected line are measured by the impedance relay, and the ratio of the two is the measured impedance Zm; when operating normally, Zm reflects the magnitude and phase of the load impedance; during a fault, Zm reflects the impedance from the fault point to the protection installation location; the fault occurrence point is judged by the change in the magnitude and phase of the impedance.

[0022] As a further improvement of the present invention, the energy storage battery is an electrochemical energy storage. When a short - circuit fault occurs in the power system, causing a voltage dip, the dynamic reactive current injected into the power grid by the electrochemical energy storage system shall satisfy: 1) Starting from the moment when the grid - connected point voltage drops, the response time of the dynamic reactive current shall not be greater than the preset time; 2) From the moment when the dynamic reactive current starts to respond until the voltage recovers to the preset voltage, the dynamic reactive current injected by the energy storage converter into the power system shall track the change of the grid - connected point voltage in real - time and shall satisfy:

[0023] In the formula: is the dynamic reactive current output by the energy storage converter; is the per - unit value of the grid - connected point voltage of the energy storage converter; is the rated current of the energy storage converter; The reference values of the active and reactive currents in the low - voltage ride - through strategy are:

[0024]

[0025] In the formula, and are the reference values of the active current and the reactive current respectively; is the maximum load - carrying current of the energy storage converter; is the rated current of the energy storage converter; is the reference value of the regulating power; is the maximum output power of the energy storage converter; is the voltage at the fault point; is the rated voltage of the grid - connected point of the energy storage converter.

[0026] The beneficial effects of the present invention compared with the prior art are: The present invention provides a fault control system for an energy storage power station that meets the reliable operation requirements of the relay protection of the outgoing line. By combining the fault characteristics of the energy storage power station in different operating states and the impact on the protection performance, it effectively improves the action performance of the protection device and ensures the safe and reliable operation of the power grid. This system takes into account the mutual influence and coupling effect between the control of the energy storage converter and the line protection, which is conducive to giving full play to the fault response redundancy function of the energy storage system and the protection device, and improving the reliability of the energy storage system's participation in actively supporting the power grid service.

[0027] Furthermore, it adapts to the outgoing line protection strategy with rapid switching of operating states, reliably identifies faults, improves the protection action performance of the electrochemical energy storage power station connected to the system, and solves the problems of low sensitivity of differential protection, incorrect operation of distance protection, and decreased adaptability of protection setting calculation methods existing in the electrochemical energy storage power station connected to the system.

[0028] Furthermore, for the typical fault control of the energy storage power station, the present invention considers the fault response during the rapid switching process of the charge and discharge states of the energy storage battery, aiming to improve the fault ride-through ability of the energy storage converter, which helps to improve the operating conditions of the relay protection in the vicinity of the energy storage power station access and increase the correct operation rate of the relay protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following introduces the relevant technical solution drawings in the embodiments of the present invention or the prior art. It should be understood that the drawings below only facilitate the clear expression of some embodiments of the technical solutions in the present invention. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0030] Figure 1 is the topological structure diagram of the energy storage power station; Figure 2 is the interaction action process of energy storage control and protection; Figure 3 is the low voltage ride-through requirement of the electrochemical energy storage system. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention. For the step numbers in the following embodiments, they are only set for the convenience of explanation and no limitation is imposed on the order between the steps. The execution order of each step in the embodiments can be adjusted adaptively according to the understanding of those skilled in the art.

[0032] In the description of the present invention, unless otherwise clearly defined, words such as "set", "installed", and "connected" should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0033] The present invention proposes an optimized control system for an energy storage power station to meet the reliable operation requirements of the outgoing line protection. It includes an external power grid, an energy storage power station unit, and a line protection unit. As Figure 1 shown, the energy storage power station is connected to the power grid through an outgoing line.

[0034] Specifically, the energy storage power station unit is composed of an energy storage battery, an energy storage converter, and a transformer. According to different operating modes, the energy storage power station is divided into two states: charging and discharging.

[0035] The line protection unit includes protection devices such as busbars, outgoing lines, current transformers, voltage transformers, and circuit breakers. The energy storage power station is connected to the power grid through the power transmission line, and the outgoing line is connected to protection devices such as current transformers and circuit breakers.

[0036] Among them, the external power grid can be divided into a strong power grid and a weak power grid according to different short-circuit ratios; the energy storage power station is divided into a charging state and a discharging state according to different operating modes; the 110kV centralized outgoing line usually uses differential protection as the main protection and distance protection as the backup protection.

[0037] In the power system, it is crucial to protect the safe and stable operation of equipment. Differential protection and distance protection are two common protection methods, which each undertake different protection responsibilities and jointly ensure the reliable operation of the power system.

[0038] Furthermore, differential protection is a protection method based on the principle of current difference. It detects faults by comparing the current differences at the incoming and outgoing terminals of electrical equipment (such as transformers, generators, etc.). When the equipment is operating normally, the currents at the incoming and outgoing terminals should be equal, and the differential current is zero or close to zero. Once a fault occurs inside the equipment, such as a phase-to-phase short circuit or a ground short circuit, the currents at the incoming and outgoing terminals will no longer be balanced, generating a differential current. The differential protection device can quickly detect this current difference and issue a trip signal to cut off the faulty equipment, thereby preventing the expansion of the fault and protecting the safety of the equipment and the system. Differential protection has the advantages of high sensitivity, fast operating speed, and good selectivity, so it is usually used as the main protection. It can quickly and accurately locate and cut off the faulty equipment, reducing the impact of the fault on the system.

[0039] Furthermore, distance protection is a protection method based on the impedance principle. It determines the location of the fault by measuring the impedance (or distance) from the fault point to the protection installation point and decides whether to issue a trip signal according to the preset setting value. Distance protection can reflect various types of faults on the line, including phase-to-phase short circuits, ground short circuits, etc. Compared with differential protection, the operating speed of distance protection may be slower, but it has the advantages of a wide coverage range and the ability to protect the entire length of the line. Therefore, distance protection is usually used as the backup protection. When the main protection (such as differential protection) fails to operate correctly for some reason, distance protection can provide an additional protection level to ensure the safe and stable operation of the system.

[0040] Even further, differential protection, as the main protection, can quickly and accurately locate and cut off the faulty equipment; while distance protection, as the backup protection, provides an additional protection level for the system to ensure the safe and stable operation of the system when the main protection fails to operate correctly. The mutual cooperation of these two protection methods jointly constitutes the safety defense line of the power system.

[0041] Preferably, the protection device is used to judge the fault state of the tie line according to the tie line current and the bus voltage, and perform relevant actions according to the judgment result: based on the judgment result of the tie line fault state, judge the line protection mode, the energy storage operation state, and the strength of the power grid; according to the judgment results of the line protection mode, the energy storage operation state, and the strength of the power grid, perform the response of the action device; based on the response result of the action device, perform a closed-loop feedback process.

[0042] Among them, the protection device performs relevant actions according to the judgment result, including: When both the in-zone fault and the differential protection action conditions are met, the main protection is started; when both the in-zone fault and the distance protection action conditions are met, the backup protection is started; when an out-of-zone fault is met, the protection device does not act.

[0043] Furthermore, the transformer device of the line protection unit monitors and collects the electrical characteristic quantities of the tie line and the bus, and the protection device judges whether the current and voltage indexes exceed the limit; if so, a fault occurs on the tie line; if not, the power grid operates normally, and the process ends.

[0044] Furthermore, the line protection mode of the protection device is judged according to the magnitude and direction of the setting current, including differential protection and distance protection; when both the in-zone fault and the differential protection action conditions are met, the main protection is started; when both the in-zone fault and the distance protection action conditions are met, the backup protection is started; when an out-of-zone fault is met, the protection device does not act; The energy storage operation state is judged with reference to the charging and discharging of the battery and the reactive power output of the energy storage converter, and is divided into two processes: charging and discharging; the strength of the power grid is judged according to the short-circuit ratio.

[0045] Optionally, the protection device is further used for: When the differential protection is started and the energy storage is operating in the discharge state, if the connected power grid is a strong power grid, the protection device acts preferentially to cut off the power grid fault; if the connected power grid is a weak power grid, the energy storage control responds preferentially to provide active support for the power grid; When the differential protection is started and the energy storage is operating in the charging state, the energy storage provides a short-circuit current as a drawn current, and the energy storage control responds preferentially to provide active support for the power grid; When the distance protection is started, the energy storage control responds preferentially to provide active support for the power grid.

[0046] Optionally, the protection device is further used for: After the power grid fails, the energy storage provides frequency and voltage support for the power grid by switching the charging and discharging processes and controlling the output power. At the same time, the transformer device on the line collects electrical characteristic quantities such as current and voltage again to judge whether the indexes exceed the limit; if not, the power grid operates normally and the process ends; otherwise, the power grid fault is not lifted and the energy storage output power needs to be further adjusted.

[0047] For a 110 kV centralized outgoing line, the present invention adopts differential protection as the main protection and distance protection as the backup protection. Current transformers and voltage transformers are respectively used to collect the current of the tie line and the bus voltage, and the fault occurrence area is determined according to the relationship between the tie line current and the bus voltage; when the conditions of in-zone fault and differential protection action are satisfied simultaneously, the main protection is started; when the conditions of in-zone fault and distance protection action are satisfied simultaneously, the backup protection is started; when an out-of-zone fault is satisfied, the protection device does not act.

[0048] In the embodiment of the present invention, the external power grid can be divided into a strong power grid and a weak power grid according to different short-circuit ratios.

[0049] Under fault conditions, the setting method and reliable operation of the energy storage power station protection device are affected by multiple factors such as the strength of the power grid, the line protection method, and the energy storage operation state. Considering the time-sequence coupling relationship between the energy storage converter control method and the outgoing line protection action, the energy storage output is controlled with the reliable action of the protection device as the goal, and the coordination and cooperation between the energy storage power station fault control method and the traditional outgoing line protection are realized.

[0050] Specifically, the present invention provides an energy storage power station fault control method that meets the reliable operation requirements of the outgoing line relay protection. By introducing the energy storage converter control method, combining the fault characteristics under different operation states of the energy storage power station and the influence on the protection performance, the coordination and cooperation between the energy storage power station fault control method and the traditional outgoing line protection are strengthened, the action performance of the protection device is effectively improved, and the safe and reliable operation of the power grid is guaranteed.

[0051] Current transformers and voltage transformers respectively collect the current of the tie line and the bus voltage, and the fault occurrence area is determined according to the relationship between the tie line current and the bus voltage; when the conditions of in-zone fault and differential protection action are satisfied simultaneously, the main protection is started; when the conditions of in-zone fault and distance protection action are satisfied simultaneously, the backup protection is started; when an out-of-zone fault is satisfied, the protection device does not act. The fault area judgment method is as follows: (1) Differential protection: Identical current transformers are installed at both ends of the line, and the current flowing through the relay is the phasor sum of the currents on both sides. During normal operation or when a short-circuit fault occurs outside the line, the current flowing into the relay is 0, and the differential relay does not act. When a fault occurs within the protection range, the current flowing into the relay is the fault current Ik at the short-circuit point. When it is greater than the action current of the differential relay, the relay acts and trips the circuit breakers at both ends of the line.

[0052] (2) Distance protection: The bus voltage at the protection installation location and the current flowing through the protected line are measured by an impedance relay, and the ratio of the two is the measured impedance Zm. During normal operation, Zm reflects the magnitude and phase of the load impedance; during a fault, Zm reflects the impedance from the fault point to the protection installation location. The fault occurrence point is judged by the change in impedance magnitude and phase.

[0053] The present invention also proposes an optimized control method for an energy storage system to meet the reliable operation requirements of outgoing line protection, such as Figure 2 shown. Among them, the line protection method is judged according to the magnitude and direction of the setting current, including differential protection and distance protection; the energy storage operation state is judged with reference to the battery charge and discharge and the reactive power output of the energy storage converter, and is divided into two processes: charging and discharging; the strength of the power grid is judged according to the short-circuit ratio. The action device response can be divided into the action of the protection device to cut off the fault, or the energy storage control response to provide active support.

[0054] Specifically, it includes four steps: judging the line protection method, judging the energy storage operation state, judging the strength of the power grid, and the response of the action device. The specific steps are as follows: 1) Judge the fault state of the tie line. The transformer device of the line protection unit monitors and collects the electrical characteristic quantities of the tie line and the bus, and judges whether the current and voltage indicators exceed the limit; if so, the tie line fails, and proceed to the next step, otherwise the power grid operates normally and the process ends.

[0055] 2) Judge the line protection method, energy storage operation state and power grid strength. The line protection method is judged according to the magnitude and direction of the setting current, including differential protection and distance protection; when both the in-zone fault and the differential protection action conditions are met, the main protection is started; when both the in-zone fault and the distance protection action conditions are met, the backup protection is started; when an out-of-zone fault is met, the protection device does not act. The energy storage operation state is judged with reference to the battery charge and discharge and the reactive power output of the energy storage converter, and is divided into two processes: charging and discharging. The strength of the power grid is judged according to the short-circuit ratio.

[0056] 3) Action device response.

[0057] 31) When the main protection differential protection is started and the energy storage is in the discharging state, if the connected power grid is a strong power grid, the protection device acts first to cut off the power grid fault; if the connected power grid is a weak power grid, the sensitivity of the differential protection decreases, and the energy storage control responds first to provide active support for the power grid.

[0058] 32) When the main protection differential protection is started and the energy storage is in the charging state, the energy storage provides a short-circuit current as a drawn current. Whether the connected power grid is a strong power grid or a weak power grid, the sensitivity of the differential protection decreases. Especially in the case of a weak power grid, there may even be a risk of refusal to act. Therefore, the energy storage control responds first to provide active support for the power grid.

[0059] 33) When the backup protection distance protection is started, regardless of the operation state of the energy storage and the power grid strength, there is a risk of refusal to act for the distance protection. Therefore, the energy storage control responds first to provide active support for the power grid.

[0060] 4) Closed-loop feedback process. After a power grid fault, the energy storage provides frequency and voltage support for the power grid by switching the charge and discharge process and controlling the output power. At the same time, the current transformer device on the line collects electrical characteristic quantities such as current and voltage again to determine whether the indicators exceed the limit. If not, the power grid operates normally and the process ends; otherwise, the power grid fault is not lifted and the output power of the energy storage needs to be further adjusted.

[0061] Among them, the normal operating range of voltage is (0.9, 1.1) p.u., and the normal operating range of frequency is (49.5, 50.5) Hz; in this embodiment, the energy storage power station needs to have the low voltage ride-through ability. When a low voltage ride-through fault occurs in the power grid, it outputs specific fault characteristic electrical quantities as required, and the output response delay does not exceed 30 ms.

[0062] GB / T 36547-2024 "Technical Regulations for the Connection of Electrochemical Energy Storage Power Stations to the Power Grid" and GB / T 34120-2023 "Technical Requirements for the Energy Storage Inverters of Electrochemical Energy Storage Systems" stipulate that electrochemical energy storage systems connected to the public power grid through voltage levels of 10(6) kV and above should have the Figure 3 low voltage ride-through ability as shown, Figure 3 which is the low voltage ride-through requirement for electrochemical energy storage systems.

[0063] When the grid-connected point voltage is Figure 3 above the contour line of curve 1 in, the electrochemical energy storage system should operate continuously without disconnecting from the grid; otherwise, the electrochemical energy storage system is allowed to disconnect from the grid.

[0064] When a short-circuit fault in the power system causes a voltage drop, the dynamic reactive current injected by the electrochemical energy storage system into the power grid should meet the following requirements: 1) Starting from the moment when the grid-connected point voltage drops, the response time of the dynamic reactive current is not greater than 30 ms; 2) From the start of the dynamic reactive current response until the voltage recovers to 0.85 (p.u.), the dynamic reactive current injected by the energy storage inverter into the power system should track the change of the grid-connected point voltage in real time and should meet Equation (1): (1) In the formula: is the dynamic reactive current output by the energy storage inverter; is the per-unit value of the grid-connected point voltage of the energy storage inverter; is the rated current of the energy storage inverter.

[0065] Therefore, the reference values of the active and reactive currents in the low voltage ride-through strategy are as shown in Equations (2) and (3).

[0066] (2) (3) Wherein, and are the reference values of the active current and the reactive current respectively; is the maximum load current of the energy storage converter; is the rated current of the energy storage converter; is the reference value of the regulation power; is the maximum output power of the energy storage converter; is the voltage at the fault point; is the rated voltage of the grid connection point of the energy storage converter.

[0067] The energy storage power station fault control method and system provided by the present invention meet the reliable operation requirements of the relay protection of the outgoing line, fully consider the coordination and cooperation between the energy storage power station fault control method and the traditional outgoing line protection, effectively improve the action performance of the protection device, and ensure the safe and reliable operation of the power grid.

[0068] Obviously, the described embodiments are only partial embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced, and any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. An energy storage power station optimization control system, characterized in that: It includes energy storage power station unit and line protection unit; The energy storage power station unit comprises an energy storage battery, an energy storage converter and a transformer which are electrically connected in sequence; The line protection unit includes a busbar, an outgoing line, a current transformer, a voltage transformer, a circuit breaker and a protection device; the energy storage power station unit is connected to the external power grid through the outgoing line; the current transformer and the voltage transformer are used to collect the tie line current and the bus voltage respectively, and the protection device is used to judge the tie line fault state according to the tie line current and the bus voltage, and perform relevant actions according to the judgment result: Based on the results of the tie line fault status judgment, the line protection mode, the energy storage operation status and the strength of the power grid are judged; according to the results of the line protection mode, the energy storage operation status and the strength of the power grid, the action device responds; A closed-loop feedback process is performed based on the response results of the action device.

2. The energy storage power station optimization control system according to claim 1, characterized in that: The protection device is also used to determine the fault occurrence area based on the relationship between the tie line current and the bus voltage.

3. The energy storage power station optimization control system according to claim 1, characterized in that: The external power grid is divided into a strong power grid and a weak power grid according to different short-circuit ratios.

4. The energy storage power station optimization control system according to claim 1, characterized in that: The transmission line adopts differential protection as the main protection and distance protection as the backup protection.

5. The energy storage power station optimization control system according to claim 3, characterized in that: The protection device performs relevant actions according to the judgment result, including: When the conditions for the in-zone fault and differential protection action are met at the same time, the main protection is started; when the conditions for the in-zone fault and distance protection action are met at the same time, the backup protection is started; when the out-of-zone fault occurs, the protection device does not act.

6. The energy storage power station optimization control system according to claim 1, characterized in that: The mutual inductor device of the line protection unit monitors and collects the electrical characteristic quantities of the tie line and the busbar, and the protection device determines whether the current and voltage indicators are out of limit; if so, the tie line fails; if not, the power grid operates normally and the process ends.

7. The energy storage power station optimization control system according to claim 1, characterized in that: The line protection mode of the protection device is determined according to the size and direction of the setting current, including differential protection and distance protection; when the fault in the zone and the differential protection action conditions are met at the same time, the main protection is started; when the fault in the zone and the distance protection action conditions are met at the same time, the backup protection is started; when the fault outside the zone is met, the protection device does not act; The energy storage operation status is judged by referring to the battery charging and discharging and the reactive output of the energy storage converter, which is divided into two processes: charging and discharging. The strength of the power grid is judged based on the short-circuit ratio.

8. The energy storage power station optimization control system according to claim 1, characterized in that: The protection device is also used for: When the differential protection is activated and the energy storage is in the discharge state, if the connected grid is a strong grid, the protection device will take priority to cut off the grid fault; if the connected grid is a weak grid, the energy storage control will take priority to respond and provide active support for the grid; When the differential protection is activated and the energy storage is operating in the charging state, the energy storage provides short-circuit current as the draw current, and the energy storage control responds first, providing active support for the grid; When distance protection is activated, energy storage control responds first and provides active support for the power grid.

9. The energy storage power station optimization control system according to claim 1, characterized in that: The protection device is also used for: After a grid failure, the energy storage provides frequency and voltage support for the grid by switching the charging and discharging process and controlling the output power. At the same time, the transformer device on the line collects electrical characteristic quantities such as current and voltage again to determine whether the indicators are out of limit. If not, the grid operates normally and the process ends. Otherwise, the grid failure has not been resolved and the energy storage output power needs to be further adjusted.

10. A method for optimizing and controlling an energy storage system, characterized in that: include: The current transformer and voltage transformer collect the tie line current and bus voltage respectively, and determine the fault occurrence area based on the relationship between the tie line current and bus voltage; The protection device takes relevant actions according to the judgment results, including: Determine the fault status of the contact line; Based on the results of the tie line fault status judgment, determine the line protection mode, energy storage operation status and power grid strength; The action device responds according to the line protection mode, energy storage operation status and grid strength judgment results; A closed-loop feedback process is performed based on the response results of the action device.

11. The energy storage system optimization control method according to claim 10, characterized in that: Determining the fault status of the tie line includes: The transformer device of the line protection unit monitors and collects the electrical characteristics of the tie line and busbar to determine whether the current and voltage indicators are out of limit; if so, the tie line has a fault; if not, the power grid operates normally and the process ends.

12. The energy storage system optimization control method according to claim 10, characterized in that: The determination of line protection mode, energy storage operation status and power grid strength includes: The line protection mode is determined according to the size and direction of the set current, including differential protection and distance protection. When the fault conditions within the zone and the differential protection action conditions are met at the same time, the main protection is started; when the fault conditions within the zone and the distance protection action conditions are met at the same time, the backup protection is started; when the fault conditions outside the zone are met, the protection device does not operate. The energy storage operation status is judged by referring to the battery charging and discharging and the reactive output of the energy storage converter, which is divided into two processes: charging and discharging. The strength of the power grid is judged based on the short-circuit ratio.

13. The energy storage system optimization control method according to claim 10, characterized in that: The action device responds, including: When the differential protection is activated and the energy storage is in the discharge state, if the connected grid is a strong grid, the protection device will take priority to cut off the grid fault; if the connected grid is a weak grid, the energy storage control will take priority to respond and provide active support for the grid; When the differential protection is activated and the energy storage is operating in the charging state, the energy storage provides short-circuit current as the draw current, and the energy storage control responds first, providing active support for the grid; When distance protection is activated, energy storage control responds first and provides active support for the power grid.

14. The energy storage system optimization control method according to claim 10, characterized in that: The closed-loop feedback process includes: After a grid failure, the energy storage provides frequency and voltage support for the grid by switching the charging and discharging process and controlling the output power. At the same time, the transformer device on the line collects electrical characteristic quantities such as current and voltage again to determine whether the indicators are out of limit. If not, the grid operates normally and the process ends. Otherwise, the grid failure has not been resolved and the energy storage output power needs to be further adjusted.

15. The energy storage system optimization control method according to claim 10, characterized in that: Determining the fault occurrence area according to the relationship between the tie line current and the bus voltage includes: Identical current transformers are installed at both ends of the line, and the current flowing through the relay is the sum of the current phases on both sides; during normal operation or a short circuit fault occurs outside the line, the current flowing into the relay is 0, and the differential relay does not operate; when a fault occurs within the protection range, the current flowing into the relay is the fault current Ik at the short-circuit point. When it is greater than the differential relay operating current, the relay operates and trips the circuit breakers at both ends of the line; The bus voltage at the protection installation and the current flowing through the protected line are measured through the impedance relay, and the ratio of the two is the measurement impedance. During normal operation, the measured impedance reflects the size and phase of the load impedance. In the event of a fault, the measured impedance reflects the impedance from the fault point to the protection installation. The fault occurrence point is determined by the impedance size and phase changes.

16. The energy storage system optimization control method according to claim 10, characterized in that: The energy storage battery is an electrochemical energy storage. When a short circuit fault occurs in the power system and causes a voltage drop, the dynamic reactive current injected into the power grid by the electrochemical energy storage system should meet the following requirements: 1) From the moment the grid voltage drops, the response time of the dynamic reactive current shall not exceed the preset time; 2) From the start of the dynamic reactive current response until the voltage returns to the preset voltage, the dynamic reactive current injected into the power system by the energy storage converter should track the voltage change at the grid connection point in real time and meet the following requirements: Where: It is the dynamic reactive current output by the energy storage converter; is the per unit voltage of the energy storage converter grid connection point; is the rated current of the energy storage converter; The reference values ​​of active and reactive currents in the low voltage ride-through strategy are: In the formula, and They are active current reference value and reactive current reference value respectively; is the maximum load current of the energy storage converter; is the rated current of the energy storage converter; To adjust the power reference value; is the maximum output power of the energy storage converter; is the fault point voltage; It is the rated voltage of the grid-connected point of the energy storage converter.

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