Current phase-first current amplitude limiting method and system for grid-forming type energy storage converter

Abstract

The invention belongs to the technical field of converter control, and particularly discloses a current phase-first current amplitude limiting method and system for a grid-forming type energy storage converter. According to the invention, by selecting the appropriate amplitude limiting parameter and changing the dq-axis component of the output current of the converter during the current limiting period, the phase angle of the current vector is fixed preferentially, so that the current vector is not fixed on the d-axis any more. When large disturbance occurs on the power grid side, the current phase is adjusted through the additionally distributed q-axis current, and then the virtual power angle of the converter is changed, so that the transient stability margin of the converter is increased, and the ultimate fault clearing time is prolonged.

Description

Technical Field

[0001] The present application belongs to the field of converter control technology, and more specifically, relates to a current limiting method and system for a grid-type energy storage converter with current phase priority. Background Art

[0002] Due to their voltage source characteristics, grid-connected converters (GCCs) hold significant application potential in renewable energy grid integration scenarios, playing a particularly crucial role in the security and defense systems of large-scale power grids. Their core advantage lies in their ability to provide robust voltage and frequency support, enhancing grid stability and interference resistance. For example, in grids with large-scale renewable energy integration, GCCs, through virtual synchronous generator (VSG) control or droop control, can effectively suppress frequency fluctuations and reduce grid instability caused by renewable energy intermittency. Furthermore, GCCs possess flexible short-circuit current control capabilities, enabling rapid response to grid faults, providing short-circuit capacity support, and enhancing the grid's fault defense capabilities. These characteristics make them a crucial technical support for large-scale power grid security and defense systems.

[0003] In large-scale power grids, current limiting strategies can effectively limit the magnitude of fault currents, preventing equipment damage and grid collapse caused by excessive short-circuit currents. When a large disturbance on the grid side causes a voltage drop, the output current of the grid-connected converter will suddenly increase. When the current rises to a certain level, the excessive output current will seriously threaten the safety of the converter equipment. To protect the converter hardware, a current limiting mechanism is usually required in the converter control process. Its purpose is to limit the converter output current to a safe value when the grid voltage drops.

[0004] The traditional d-axis priority current limiting strategy prioritizes d-axis current during grid voltage drops, ensuring active power output and frequency stability during disturbances. However, this completely sacrifices q-axis current, resulting in significant deficiencies in reactive power and voltage support capabilities. Furthermore, during the limiting period, the converter's output current consists solely of d-axis current, with no q-axis current. This makes it impossible to control the output current phase by controlling the q-axis current. This severely weakens the converter's transient stability margin and increases the risk of transient instability. Summary of the Invention

[0005] In response to the defects of the existing technology, the purpose of this application is to provide a current phase priority grid-type energy storage converter current limiting method and system, aiming to solve the problem that the traditional d-axis priority current limiting strategy seriously weakens the transient stability margin of the grid-type energy storage converter during faults and reduces its transient stability.

[0006] In a first aspect, the present application provides a current phase priority current limiting method for a grid-type energy storage converter, comprising: Monitor the three-phase current at the output of the grid-connected energy storage converter in real time and compare it with the preset current threshold; If the current amplitude of any phase monitored exceeds the preset current threshold, the limiting link is started; The limiting link is located between the voltage outer loop and the current inner loop control loop of the grid-type energy storage converter. By selecting the limiting parameters, the dq axis components of the converter output current during the current limiting period are simultaneously changed, thereby preferentially fixing the phase angle of the current vector.

[0007] Preferably, the d-axis component and the q-axis component of the output current of the converter during the current limiting period are simultaneously changed by selecting the limiting parameters, specifically:

[0008] in, and is the dq axis current reference value output by the voltage outer loop, and is the reference value of the inner loop current after limiting, is the maximum current amplitude allowed by the grid-type energy storage converter equipment, is the limiting parameter.

[0009] It should be noted that the present application prefers the above-mentioned limiting strategy, so that when a large disturbance occurs on the grid side, the current amplitude exceeds the limit, and the inner ring dq axis current reference value after limiting must choose the latter, and the two determine the angle between the current vector and the d axis. , which is related to the limiting parameter The relationship is . Preferably, the limiting parameter The selection of λ follows the following principle: the selected λ increases the transient stability margin of the grid-type energy storage converter while ensuring that active power transmission is not affected.

[0010] It should be noted that the larger the λ is, the more obvious the improvement effect is and the stronger the transient stability of the converter is. However, if the value of λ is too large, the active power transmission of the converter will be weakened. This application prefers the above selection principle, while ensuring the transient stability margin and active power transmission of the grid-type energy storage converter.

[0011] Preferably, the limiting parameter The value range of is as follows:

[0012] in, It is the d-axis component of the output current of the grid-type energy storage converter in rated operation mode.

[0013] It should be noted that the present application prefers the above value range to ensure that the d-axis component of the converter output current during current limiting is not less than its rated value.

[0014] Preferably, the calculation formula of the transient stability margin is as follows:

[0015] in, is the transient stability margin of the grid-type energy storage converter operating in rated mode. is the grid-side reactance, The PCC point voltage of the grid-type energy storage converter operating in rated mode is: is the angle between the current vector and the d-axis, , It is the virtual power angle of the grid-type energy storage converter operating in rated mode.

[0016] It should be noted that the present application preferably uses the above formula to calculate the transient stability margin and provides a quantitative method for the transient stability margin, which is related to the current vector angle. The larger the λ, the larger the current vector angle, the more obvious the improvement effect, and the stronger the transient stability of the converter.

[0017] Preferably, the calculation formula for the PCC point voltage when the grid-type energy storage converter operates in rated mode is as follows:

[0018] in, It is the grid voltage when the grid-type energy storage converter operates in rated mode.

[0019] In the second aspect, the present application provides a current phase priority grid-type energy storage converter current limiting system, comprising: at least one memory for storing programs; at least one processor for entering the program stored in the memory, and when the program stored in the memory is entered, the processor is used to enter the current limiting method as described in the first aspect.

[0020] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0021] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies: This application proposes a current-phase-prioritized current-limiting method for grid-type energy storage converters. By selecting appropriate limiting parameters and simultaneously changing the dq-axis components of the converter's output current during the current-limiting period, the phase angle of the current vector is prioritized, eliminating the current vector's d-axis fixation. When a large disturbance occurs on the grid side, the current phase is adjusted using the additionally allocated q-axis current, thereby changing the converter's virtual power angle. This increases the converter's transient stability margin and prolongs the ultimate fault clearance time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of a current limiting method for a grid-type energy storage converter with current phase priority provided in an embodiment of the present application.

[0023] Figure 2 This is a structural diagram of a single-mechanism grid-type energy storage converter grid-connected system provided in an embodiment of the present application.

[0024] Figure 3 This is a schematic diagram of the position of the current limiting link provided in an embodiment of the present application.

[0025] Figure 4 This is a vector diagram of system operation in the rated mode and with the d-axis priority limiting scheme provided in an embodiment of the present application.

[0026] Figure 5 This is a vector diagram of system operation under the d-axis priority limiting scheme provided in the embodiment of the present application when a fault occurs.

[0027] Figure 6 This is a system operation vector diagram under the power angle priority limiting scheme provided in an embodiment of the present application.

[0028] Figure 7 This is a system operation vector diagram under the power angle priority limiting scheme provided in the embodiment of the present application when a fault occurs. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0030] The term "and / or" in this application describes an association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, or B exists alone. The symbol " / " in this application indicates that the associated objects are in an "or" relationship, for example, A / B means A or B.

[0031] In the specification and claims of this application, the terms "first" and "second" are used to distinguish different objects, rather than to describe a specific order of objects. For example, "first response message" and "second response message" are used to distinguish different response messages, rather than to describe a specific order of response messages.

[0032] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0033] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more, for example, multiple processing units means two or more processing units, etc.; multiple elements means two or more elements, etc.

[0034] like Figure 1 As shown, the present application provides a current phase priority grid-type energy storage converter current limiting method, including: Monitor the three-phase current at the output of the grid-connected energy storage converter in real time and compare it with the preset current threshold; If the current amplitude of any phase monitored exceeds the preset current threshold, the limiting link is started; The limiting link is located between the voltage outer loop and the current inner loop control loop of the grid-type energy storage converter. By selecting the limiting parameters, the dq axis components of the converter output current during the current limiting period are simultaneously changed, thereby preferentially fixing the phase angle of the current vector.

[0035] Preferably, the d-axis component and the q-axis component of the output current of the converter during the current limiting period are simultaneously changed by selecting the limiting parameters, specifically:

[0036] in, and is the dq axis current reference value output by the voltage outer loop, and is the reference value of the inner loop current after limiting, is the maximum current amplitude allowed by the grid-type energy storage converter equipment, is the limiting parameter. The value of is determined by the equipment's tolerance. This application selects 1.2 times the rated output current, i.e. I lim =1.2I N .

[0037] It can be seen from the above formula that when the output current amplitude of the converter exceeds I lim When the current is in the range of 0 to 100, the limiting link will adjust the dq axis current according to the set limiting parameters in order to maintain the relative balance between active power-frequency stability and reactive power-voltage support.

[0038] Preferably, the limiting parameter The selection of λ follows the following principle: the selected λ increases the transient stability margin of the grid-type energy storage converter while ensuring that active power transmission is not affected.

[0039] Preferably, the limiting parameter The value range of is as follows:

[0040] in, It is the d-axis component of the output current of the grid-type energy storage converter in rated operation mode.

[0041] Preferably, the calculation formula of the transient stability margin is as follows:

[0042] in, is the transient stability margin of the grid-type energy storage converter operating in rated mode. is the grid-side reactance, The PCC point voltage (the node where the energy storage system is connected to the grid or load) of the grid-type energy storage converter operating in rated mode is is the angle between the current vector and the d-axis, , It is the virtual power angle of the grid-type energy storage converter operating in rated mode.

[0043] Preferably, the calculation formula for the PCC point voltage when the grid-type energy storage converter operates in rated mode is as follows:

[0044] in, It is the grid voltage when the grid-type energy storage converter operates in rated mode.

[0045] Example This embodiment involves Figure 2 The single-mechanism grid-type energy storage converter grid-connected system shown in FIG2 is set to five modes as shown in Table 1 for performance comparison and analysis.

[0046]

[0047] Table 1 The current limiting link is set at the output end of the voltage outer loop, and the current reference value is limited and fed into the current inner loop, such as Figure 3 The d-axis priority limiting strategy is shown in the following formula:

[0048] in, i Ld,ref and iLq,ref is the dq axis current reference value output by the outer loop, and is the reference value of the inner loop current after limiting, I lim The maximum current amplitude allowed by the converter equipment is 1.2 times the rated output current, that is, I lim =1.2I N From the above formula, it can be seen that when the output current amplitude of the converter exceeds I lim When , the limiting link will give priority to maintaining the d-axis current amplitude and completely sacrifice the q-axis current, sacrificing the reactive power and voltage support capabilities to ensure active power transmission and frequency stability.

[0049] For the convenience of calculation, the power, voltage and reactance in the following formula are all in per unit value. The power and grid voltage in the rated operation mode are used as the reference values. The active power P output by the converter in the rated operation mode is TN =1.0pu, the grid voltage U when the converter operates in rated mode g,N =1.0pu.

[0050] Mode 1: When the d-axis priority current limiting scheme is adopted, the operating vector diagram of the converter in the rated current limiting mode is as follows: Figure 4 In mode 1, the converter output active power and various parameters are shown in the following formula:

[0051] in, U PCC,d For this mode, the PCC point voltage is is the initial phase offset of the power angle sine function caused by the d-axis priority limiting strategy, δ N It is the virtual power angle when the converter operates in rated mode.

[0052] The transient stability margin of the converter in mode 1 can be obtained from the above equation: , as shown below:

[0053] Mode 2: When the d-axis priority current limiting scheme is adopted, the converter triggers the limiting link under fault conditions, and the operating vector diagram is as follows: Figure 5 As shown. In mode 2, the converter output active power is:

[0054] in, U PCC,dF is the PCC point voltage at the moment of fault occurrence, is the virtual power angle of the converter at the moment of fault occurrence. Figure 5 The vector geometric relationship of the above formula can be obtained U PCC,dF and :

[0055] Mode 3: When the power angle priority current limiting scheme is adopted, the operating vector diagram of the converter in the rated current limiting mode is as follows: Figure 6 In mode 3, the converter output active power and various parameters are shown in the following formula:

[0056] in, U PCC,λ For this mode, the PCC point voltage is is the initial phase offset of the power angle sine function caused by the power angle priority limiting strategy, is the angle between the current vector and the d-axis.

[0057] The transient stability margin of the converter in mode 3 can be obtained from the above equation: :

[0058] Mode 4: When the power angle priority current limiting scheme is adopted, the converter triggers the limiting link under fault conditions, and the operating vector diagram is as follows: Figure 7 As shown. In mode 4, the converter output active power is:

[0059] in, U PCC,λF is the grid connection point voltage at the moment the fault occurs, is the virtual power angle of the converter at the moment of fault occurrence. Figure 7 The vector geometric relationship can be obtained U PCC,λF and :

[0060] Mode 5: Without the limiter link, the converter operates at the rated state. According to the equal area rule, the transient stability limit fault removal angle of the converter without the limiter link is , at this time the transient stability margin of the converter is It can be given by the following formula:

[0061] in, U PCC,N is the grid connection point voltage in rated operation mode.

[0062] The transient stability margin of the converter in each mode is compared below, as shown in Table 2.

[0063]

[0064] Table 2 In order to verify whether the transient stability margin is improved after adopting the power angle priority limiting scheme, mathematical verification is required. With style , it can be proved that U PCC,λ > U PCC,d , and then from the expression of transient stability margin in Table 2, it can be obviously deduced that .

[0065] In fact, the operating vector diagram of the converter also shows that the transient stability margin is improved after adopting the power angle priority limiting scheme. Compared with the zero initial phase power angle curve under the rated operating state, the d-axis priority limiting scheme will make the power angle curve in this mode have a positive initial phase, causing the power angle curve to shift to the left as a whole, resulting in the unstable equilibrium point in mode 1 being close to the stable equilibrium point in the rated mode, and the transient stability margin is reduced; while the power angle priority limiting scheme will make the power angle curve in this mode have a negative initial phase, causing the power angle curve to shift to the right as a whole, causing the unstable equilibrium point in mode 3 to be far away from the stable equilibrium point in the rated mode, and the transient stability margin is increased.

[0066] It should be understood that the above-mentioned device is used to execute the method in the above-mentioned embodiment. The implementation principle and technical effect of the corresponding program module in the device are similar to those described in the above-mentioned method. The working process of the device can refer to the corresponding process in the above-mentioned method and will not be repeated here.

[0067] Based on the methods in the above embodiments, embodiments of the present application provide an electronic device that may include: a processor, a communications interface, a memory, and a communication bus, wherein the processor, the communications interface, and the memory communicate with each other via the communication bus. The processor may invoke logic instructions in the memory to execute the methods in the above embodiments.

[0068] In addition, the logical instructions in the above-mentioned memory can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present application, or the part that contributes to the existing technology, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application.

[0069] Based on the method in the above embodiment, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program runs on a processor, the processor executes the method in the above embodiment.

[0070] Based on the method in the above embodiment, an embodiment of the present application provides a computer program product. When the computer program product runs on a processor, the processor executes the method in the above embodiment.

[0071] It is understood that the processor in the embodiments of the present application may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0072] The method steps in the embodiments of the present application can be implemented by hardware or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, which can be stored in random access memory (RAM), flash memory, read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, mobile hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be an integral part of the processor. The processor and storage medium can be located in an ASIC.

[0073] The above embodiments can be implemented in whole or in part using software, hardware, firmware, or any combination thereof. When implemented using software, they can be implemented in whole or in part in the form of a computer program product. The computer program product comprises one or more computer instructions. When loaded and executed on a computer, the computer program instructions fully or partially produce the processes or functions described in the embodiments of this application. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted via the computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible by a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be magnetic media (e.g., floppy disk, hard disk, tape), optical media (e.g., DVD), or semiconductor media (e.g., solid-state drive (SSD)).

[0074] It will be understood that the various numerical numbers involved in the embodiments of the present application are merely distinctions for the convenience of description and are not intended to limit the scope of the embodiments of the present application.

[0075] It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A current limiting method for a grid-type energy storage converter with current phase priority, characterized in that: include: Monitor the three-phase current at the output of the grid-type energy storage converter in real time and compare it with the preset current threshold; If the current amplitude of any phase monitored exceeds the preset current threshold, the limiting link is started; The limiting link is located between the voltage outer loop and the current inner loop control loop of the grid-type energy storage converter. By selecting the limiting parameters, the dq axis components of the converter output current during the current limiting period are simultaneously changed, thereby preferentially fixing the phase angle of the current vector.

2. The current limiting method according to claim 1, wherein: The d-axis component and q-axis component of the output current of the converter during the current limiting period are simultaneously changed by selecting the limiting parameters, specifically: in, and is the dq axis current reference value output by the voltage outer loop, and is the reference value of the inner loop current after limiting, is the maximum current amplitude allowed by the grid-type energy storage converter equipment, is the limiting parameter.

3. The current limiting method according to claim 1, wherein: Limiting parameters The selection of λ follows the following principle: the selected λ increases the transient stability margin of the grid-type energy storage converter while ensuring that active power transmission is not affected.

4. The current limiting method according to claim 3, wherein: Limiting parameters The value range of is as follows: in, It is the d-axis component of the output current of the grid-type energy storage converter in rated operation mode.

5. The current limiting method according to claim 3, wherein: The calculation formula of the transient stability margin is as follows: in, is the transient stability margin of the grid-type energy storage converter operating in rated mode. is the grid-side reactance, The PCC point voltage of the grid-type energy storage converter operating in rated mode is: is the angle between the current vector and the d-axis, , It is the virtual power angle of the grid-type energy storage converter operating in rated mode.

6. The current limiting method according to claim 5, wherein: The calculation formula for the PCC point voltage of the grid-type energy storage converter operating in rated mode is as follows: in, It is the grid voltage when the grid-type energy storage converter operates in rated mode.

7. A current phase priority grid-type energy storage converter current limiting system, characterized in that: include: at least one memory for storing a program; At least one processor is configured to enter the program stored in the memory, and when the program stored in the memory is entered, the processor is configured to enter the current limiting method according to any one of claims 1 to 6.

Images