Energy storage converter output control method and system for asymmetric low voltage fault

Abstract

The present application relates to the field of energy storage converter control technology, and specifically provides an energy storage converter output control method and system for a phase-asymmetric low voltage fault, aiming to solve the problem that the current limiting method does not fully utilize the current output capacity of the energy storage converter. To this end, the method includes: obtaining operating information of the energy storage converter, the operating information including the rated current and the positive sequence voltage amplitude of the AC port; when the positive sequence voltage amplitude is less than a preset threshold, calculating the square of the reference current amplitude of phase A, phase B and phase C according to the operating information; calculating the reactive reference current increment and the active reference current amplitude according to the square of the reference current amplitude of phase A, phase B and phase C and the rated current; and controlling the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude. This method can ensure the output of active current as much as possible while satisfying the reactive current output, thereby fully utilizing the current output capacity of the energy storage converter.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage converter control, and in particular to a method and system for controlling the output of an energy storage converter in the face of an asymmetric low voltage fault. Background Art

[0002] Under normal circumstances, the energy storage converter mainly works in the mode of transmitting active power. At this time, the device, i.e., the energy storage converter, only outputs active current. According to the new national standard requirements for electrochemical energy storage converters, in addition to increasing the positive-sequence reactive current, the energy storage converter must also output negative-sequence reactive current during an asymmetric low-voltage fault. The simultaneous output of reactive current and active current may cause the device to output overcurrent, so the current needs to be limited to avoid the occurrence of overcurrent faults. The commonly used solution is to set the active current reference value to a very small value or 0. At this time, the device only outputs positive-sequence reactive current and negative-sequence reactive current, thereby achieving the purpose of limiting the output current. However, this method cannot fully utilize the current output capacity of the device.

[0003] Accordingly, the art needs a new reference current limit calculation solution for phase asymmetric low voltage fault to solve the above problems. Summary of the Invention

[0004] In order to overcome the above-mentioned defects, the present application is proposed to solve or at least partially solve the technical problem that the current method of limiting current by asymmetric low voltage fault ride-through does not fully utilize the current output capacity of the energy storage converter.

[0005] In a first aspect, a method for controlling the output of an energy storage converter facing a phase asymmetric low voltage fault is provided, the method comprising: obtaining operating information of the energy storage converter, the operating information comprising a rated current and a positive-sequence voltage amplitude of an AC port; when the positive-sequence voltage amplitude is less than a preset threshold, calculating the squares of the reference current amplitudes of phases A, B, and C according to the operating information; calculating a reactive reference current increment and an active reference current amplitude according to the squares of the reference current amplitudes of phases A, B, and C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection; and controlling the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude.

[0006] In a technical solution of the above-mentioned method for controlling the output of an energy storage converter in the event of a phase-asymmetric low-voltage fault, the operating information also includes an initial active reference current, and the reactive reference current increment and the active reference current amplitude are calculated based on the squares of the reference current amplitudes of phases A, B, and C and the rated current, including: calculating the initial reactive reference current increment based on the operating information; obtaining the maximum value among the squares of the reference current amplitudes of phases A, B, and C; when the maximum value is less than or equal to the square of the rated current, using the initial reactive reference current increment as the reactive reference current increment; calculating the amplitude range of the active reference current based on the operating information; calculating the active reference current amplitude based on the amplitude range and the initial active reference current; when the maximum value is greater than the square of the rated current, setting the active reference current amplitude to 0; and calculating the reactive reference current increment based on the product of the initial reactive reference current increment and a limiting coefficient, wherein the limiting coefficient is the square root of the ratio of the square of the rated current to the maximum value.

[0007] In a technical solution of the above-mentioned method for controlling the output of an energy storage converter facing a phase-asymmetric low-voltage fault, the amplitude range of the active reference current is calculated based on the operating information, including: calculating the value range of the positive-sequence active reference current amplitudes of phases A, B and C based on the operating information; and selecting the intersection of the value ranges of the positive-sequence active reference current amplitudes of phases A, B and C as the amplitude range of the active reference current.

[0008] In a technical solution of the above-mentioned method for controlling the output of an energy storage converter facing a phase-asymmetric low-voltage fault, the calculation of the active reference current amplitude based on the amplitude range and the initial active reference current includes: obtaining the lower limit value and the upper limit value of the amplitude range; when the amplitude of the initial active reference current is less than the lower limit value, selecting the lower limit value as the active reference current amplitude; when the amplitude of the initial active reference current is greater than the upper limit value, selecting the upper limit value as the active reference current amplitude.

[0009] In one technical solution of the above-mentioned method for controlling the output of an energy storage converter in the event of a phase-asymmetric low-voltage fault, the operating information further includes the rated voltage, the negative-sequence voltage amplitude of the AC port, the positive-sequence reactive current proportional coefficient, and the negative-sequence reactive current proportional coefficient. The initial reactive reference current increment includes an initial positive-sequence reactive reference current increment and an initial negative-sequence reactive reference current increment. Calculating the initial reactive reference current increment based on the operating information includes: calculating the initial positive-sequence reactive reference current increment and the initial negative-sequence reactive reference current increment using the following formula:

[0010] in, Ipq represents the initial positive sequence reactive reference current increment, I nq represents the initial negative sequence reactive reference current increment, k 1 represents the positive sequence reactive current proportional coefficient, k 2 represents the negative sequence reactive current proportional coefficient, U 1 represents the positive sequence voltage amplitude, U 2 represents the negative sequence voltage amplitude, U N Indicates the rated voltage, I N Indicates the rated current, U T Indicates the preset threshold.

[0011] In one technical solution of the above-mentioned method for controlling the output of an energy storage converter in the event of a phase-asymmetric low-voltage fault, the reactive reference current increment includes a positive-sequence reactive reference current increment and a negative-sequence reactive reference current increment. Calculating the reactive reference current increment based on the product of the initial reactive reference current increment and the amplitude limiting coefficient includes: calculating the positive-sequence reactive reference current increment and the negative-sequence reactive reference current increment using the following formula:

[0012] in, represents the positive sequence reactive reference current increment, represents the negative sequence reactive reference current increment, coe represents the clipping coefficient, Represents the maximum value among the squares of the reference current amplitudes of phase A, phase B and phase C.

[0013] In one technical solution of the above-mentioned method for controlling the output of an energy storage converter in the face of a phase-asymmetric low voltage fault, when the positive sequence voltage amplitude is greater than or equal to a preset threshold, the reactive reference current increment is 0.

[0014] In a second aspect, an output control system for an energy storage converter facing a phase asymmetric low voltage fault is provided, the system comprising: an information acquisition module for acquiring operating information of the energy storage converter, the operating information comprising the rated current and the positive-sequence voltage amplitude of the AC port; an amplitude calculation module for calculating the squares of the reference current amplitudes of phases A, B, and C according to the operating information when the positive-sequence voltage amplitude is less than a preset threshold; a limit calculation module for calculating the reactive reference current increment and the active reference current amplitude according to the squares of the reference current amplitudes of phases A, B, and C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection; and an output control module for controlling the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude.

[0015] In a third aspect, an intelligent device is provided, comprising at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores a computer program, and when the computer program is executed by the at least one processor, the method described in any one of the technical solutions of the above-mentioned method for controlling the output of an energy storage converter with a phase-asymmetric low voltage fault is implemented.

[0016] In a fourth aspect, a computer-readable storage medium is provided, which stores a plurality of program codes, wherein the program codes are suitable for being loaded and run by a processor to execute the method described in any one of the technical solutions of the above-mentioned method for controlling the output of an energy storage converter with a phase-asymmetric low-voltage fault.

[0017] The above one or more technical solutions of this application have at least one or more of the following beneficial effects:

[0018] In implementing the technical solution for calculating the reference current limit for a phase-asymmetric low-voltage fault provided in the present application, by calculating the square of the reference current amplitudes of phases A, B, and C and comparing them with the rated current, the purpose of judging whether the reactive reference current and the active reference current exceed the rated current of the energy storage converter is achieved. Based on the principle of giving priority to ensuring the reactive current, the square of the reference current amplitudes of phases A, B, and C is made not to exceed the rated current. The calculated reactive reference current increment and active reference current amplitude are used to control the energy storage converter, which can ensure the active current output of the energy storage converter as much as possible, thereby making full use of the current output capacity of the device.

[0019] In the technical solution of the present application, by selecting the value closest to the initial active reference current in the amplitude range of the active reference current, the purpose of maintaining the positive-sequence active output before the asymmetric low-voltage fault is achieved, thereby reducing the current mutation when entering and exiting the fault, avoiding output fluctuations near the fault critical point, and facilitating the stable operation of the energy storage converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The disclosure of this application will become more easily understood with reference to the accompanying drawings. Those skilled in the art will readily appreciate that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application. Among them:

[0021] Figure 1 This is a flow chart of the main steps of a method for controlling the output of an energy storage converter in the event of an asymmetric low voltage fault according to an embodiment of the present application;

[0022] Figure 2 This is a schematic diagram of the overall steps of a method for controlling the output of an energy storage converter in the event of an asymmetric low voltage fault according to an embodiment of the present application;

[0023] Figure 3a This is the voltage diagram of the three-phase system under working condition 1;

[0024] Figure 3b This is a schematic diagram of positive sequence voltage and negative sequence voltage in working condition 1;

[0025] Figure 3c This is a schematic diagram of the components of the reference current under working condition 1;

[0026] Figure 3d This is a schematic diagram of the three-phase output current after limiting in working condition 1;

[0027] Figure 3e This is a schematic diagram of the components of the output current after limiting in working condition 1;

[0028] Figure 4a This is the voltage diagram of the three-phase system in working condition 2;

[0029] Figure 4b This is a schematic diagram of positive sequence voltage and negative sequence voltage in working condition 2;

[0030] Figure 4c This is a schematic diagram of the components of the reference current for working condition 2;

[0031] Figure 4d This is a schematic diagram of the three-phase output current after limiting in working condition 2;

[0032] Figure 4e This is a schematic diagram of the components of the output current after limiting in working condition 2;

[0033] Figure 5a This is the voltage diagram of the three-phase system under working condition three;

[0034] Figure 5b This is a schematic diagram of positive sequence voltage and negative sequence voltage in operating condition three;

[0035] Figure 5c This is a schematic diagram of the components of the reference current for working condition three;

[0036] Figure 5d This is a schematic diagram of the three-phase output current after three limiting conditions;

[0037] Figure 5e This is a schematic diagram of the components of the output current after limiting in working condition three;

[0038] Figure 6 This is a schematic diagram of the main structural block diagram of an energy storage converter output control system facing an asymmetric low voltage fault according to an embodiment of the present application;

[0039] Figure 7 This is a schematic diagram of the connection relationship between the processor and memory of a smart device according to an embodiment of the present application.

[0040] Reference numerals:

[0041] 2: Information acquisition module; 4: Amplitude calculation module; 6: Limit calculation module; 11: Memory; 12: Processor. DETAILED DESCRIPTION

[0042] Some embodiments of the present application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and are not intended to limit the scope of protection of the present application.

[0043] In the description of this application, the terms "first", "second", etc. are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way are interchangeable where appropriate so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes 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. The terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or a communication between two elements, a wireless connection, or a wired connection.

[0044] In addition, "module" and "processor" may include hardware, software, or a combination of the two. A module may include hardware circuits, various suitable sensors, communication ports, and memory, and may also include software components, such as program code, or a combination of software and hardware. The processor may be a central processing unit, a microprocessor, an image processor, a digital signal processor, or any other suitable processor. The processor has data and / or signal processing functions. The processor may be implemented in software, hardware, or a combination of the two. Computer-readable storage media include any suitable media that can store program code, such as a magnetic disk, a hard disk, an optical disk, a flash memory, a read-only memory, a random access memory, and the like.

[0045] In addition, if the meaning of "and / or" appears in this application, it includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application. The term "at least one A or B" or "at least one of A and B" has a similar meaning to "A and / or B" and can include only A, only B, or A and B. The singular terms "one" and "this" can also include plural forms.

[0046] Energy storage converters are an essential component of power systems, connecting energy storage units with the grid to achieve efficient energy conversion and transmission. For example, the AC port of an energy storage converter is connected to a three-phase AC power system (the grid), and the DC port is connected to the energy storage system. When the energy storage system releases energy, the converter converts the DC power from the energy storage unit into AC power required by the grid. When the energy storage system stores energy, the converter converts AC power from the grid into DC power and stores it in the energy storage unit. Energy storage converters can monitor input and output voltage and current in real time, adjust the frequency, phase, and amplitude of the output voltage and current, and provide reactive power support. Under normal circumstances, energy storage converters primarily operate in active power transmission mode, outputting only active current. However, when a low voltage fault occurs, they must output reactive current. In actual operation, the incidence of asymmetric low voltage faults is far greater than that of symmetric low voltage faults. The old national standard requires that energy storage converters output positive-sequence reactive current when an asymmetric low voltage fault occurs. The new national standard requires that in addition to increasing the positive-sequence reactive current, energy storage converters also output negative-sequence reactive current when an asymmetric low voltage fault occurs. The output current size is related to the depth of the voltage drop and the degree of imbalance.

[0047] The simultaneous output of reactive current and active current may cause the device to output overcurrent, so the output current needs to be limited to avoid overcurrent faults. Limiting is generally done by limiting the reference current. The reference current includes active and reactive current (components). The old version of the national standard only requires positive-sequence reactive power, because it is orthogonal to the positive-sequence active power. Therefore, the amplitude of the reference current can be directly obtained by taking the square sum and then taking the square root. In this way, it can be calculated whether the reference current exceeds the limit, and the limit of the active current component can be calculated based on the rated current and reactive current. The reference value in the new national standard includes negative-sequence reactive power, which is not orthogonal to the positive-sequence component and will cause the three-phase reference current to be unbalanced. Therefore, the amplitude of the reference current can no longer be directly calculated by taking the square sum method mentioned above. A common solution is to set the active current reference value to a very small value or 0. In this case, the device only outputs positive-sequence reactive current and negative-sequence reactive current. However, this method has the following disadvantages: the current may change significantly when a fault occurs and exits; if the voltage is near the fault threshold, frequent switching of the device's working state may cause output fluctuations; and the device's current output capacity is not fully utilized.

[0048] In view of the above problems, the present application provides an output control method for an energy storage converter in the event of an asymmetric low voltage fault. Figure 1 , Figure 1 This is a flow chart of the main steps of the method for controlling the output of an energy storage converter in the event of an asymmetric low voltage fault according to an embodiment of the present application. Figure 1 As shown, the method mainly includes the following steps S2 to S8:

[0049] Step S2: Acquire operating information of the energy storage converter, where the operating information includes the rated current and the positive sequence voltage amplitude of the AC port.

[0050] In this embodiment, the acquired operating information may include parameter information of the energy storage converter itself or real-time monitoring data, control strategies, environmental parameters, and the like. For example, the energy storage converter's rated voltage and rated current, the AC port's positive-sequence voltage amplitude (obtained by performing positive-negative sequence decomposition of the AC port voltage), the negative-sequence voltage amplitude, the positive-sequence reactive current proportionality coefficient, and the negative-sequence reactive current proportionality coefficient. This embodiment does not impose specific limitations on this information, and it can be configured based on specific needs.

[0051] Step S4: When the positive sequence voltage amplitude is less than a preset threshold, the squares of the reference current amplitudes of phases A, B, and C are calculated according to the operation information.

[0052] In this embodiment, when an asymmetric low voltage fault occurs, the positive-sequence voltage amplitude will usually drop. When the drop rate is small, compensation adjustment can be performed through the preset reactive current of the energy storage converter. When the drop rate is large, that is, the positive-sequence voltage amplitude is less than the preset threshold, it is necessary to control the energy storage converter to provide additional reactive current, that is, the reactive reference current increment to help voltage recovery.

[0053] In one embodiment, when the positive sequence voltage amplitude is greater than or equal to a preset threshold, it indicates that the drop process is small. At this time, compensation adjustment can be performed through the preset reactive current of the energy storage converter, and the reactive reference current increment is 0.

[0054] According to the new national standard, the dynamic reactive power support capability of A1, A2 and B1 energy storage converters during asymmetric low voltage faults should meet the following requirements:

[0055] When the positive-sequence component of the AC port voltage of Class A1 and Class A2 energy storage converters is between 60% and 90% of the rated voltage, or when the positive-sequence component of the AC port voltage of Class B1 energy storage converters is between 60% and 85% of the rated voltage, the energy storage converter can output positive-sequence dynamic reactive current to support positive-sequence voltage recovery and absorb negative-sequence dynamic reactive current from the grid to suppress the increase of negative-sequence voltage.

[0056] Therefore, the preset threshold for A1 and A2 energy storage converters can be 0.9 U N ,in, U N is the rated voltage of the energy storage converter; for the B1 class energy storage converter, the preset threshold value can be 0.85 U N. According to the new national standard, when the positive-sequence voltage amplitude is less than the preset threshold, the energy storage converter is required to output positive-sequence reactive current and negative-sequence reactive current to help the voltage recover. In order to determine whether increasing the reactive current will cause an overcurrent fault, this embodiment calculates the square of the reference current amplitude of phases A, B, and C based on the operating information and compares it with the rated current. It should be noted that the reference current refers to the recommended value (reference value) of the current in a specific situation.

[0057] Since the reference current contains positive sequence components and negative sequence components during a fault, it is assumed that the final three-phase reference current is as shown in formula (1):

[0058] (1)

[0059] in, I ra 、 I rb 、 I rc Respectively represent the reference current of phase A, phase B, and phase C, I 1 and I 2 represent the amplitudes of positive sequence current and negative sequence current respectively, and Represent the initial phases of positive sequence current and negative sequence current respectively, represents the angular frequency, t Represents time. Clarke and Park transformations are performed on formula (1) to obtain the d-axis (direct axis) component and q-axis (quadrature axis) component of the positive-sequence current and negative-sequence current as shown in formula (2):

[0060] (2)

[0061] in, I rpd represents the d-axis component of the positive sequence current, I rpq represents the q-axis component of the positive sequence current, I rnd represents the d-axis component of the negative sequence current, I rnq Represents the q-axis component of the negative sequence current.

[0062] Expand formula (2) and use formula (1) to replace the reference currents of phases A, B, and C. I ra 、 I rb 、 I rc, and filtering out the double frequency, we can obtain the DC values ​​of the positive sequence current and negative sequence current in their respective rotating coordinate systems as shown in formulas (3) and (4):

[0063] (3)

[0064] (4)

[0065] in, It represents the DC value of positive sequence current on the d-axis. It represents the DC quantity of positive sequence current on the q axis, It represents the DC value of negative sequence current on the d-axis. It represents the DC value of negative sequence current on the q axis.

[0066] The above formula (3) and formula (4) are used to further decompose the expression of the three-phase reference current in formula (1), as shown in formula (5) using each sequence component to express I ra 、 I rb 、 I rc :

[0067] (5)

[0068] In the rotating (dq) coordinate system, the d-axis component is usually related to the system's active power, while the q-axis component is related to reactive power. When an asymmetric low voltage fault occurs, the current includes not only the positive sequence active power before the fault, but also the newly added positive sequence reactive power and negative sequence reactive power, but not the negative sequence active power. Therefore, the above formula (5) can be simplified to the following formula (6):

[0069] (6)

[0070] The three-phase reference current I ra 、 I rb 、 I rc The square of the amplitude can be expressed using the following formula (7):

[0071] (7)

[0072] in, I A 、 I B 、 I C Represents the three-phase reference current I ra 、I rb 、 I rc The amplitude of . Formula (7) can be further simplified to the following formula (8):

[0073] (8)

[0074] When limiting the current, based on the reactive power priority strategy, assuming , we can get the square of the reference current amplitude of phase A, phase B and phase C 、 、 As shown in formula (9):

[0075] (9)

[0076] in, It represents the DC quantity of positive sequence current on the q axis, It represents the DC value of negative sequence current on the q axis.

[0077] Step S6, calculating the reactive reference current increment and the active reference current amplitude according to the square of the reference current amplitude of phase A, phase B and phase C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection.

[0078] In this embodiment, the square of the reference current amplitude of phase A, phase B, and phase C in formula (9) is generated by the newly added positive sequence reactive power and negative sequence reactive power. By comparing the square of the reference current amplitude of phase A, phase B, and phase C in formula (9) with the square of the rated current, it can be determined whether any phase reference current generated by the positive sequence reactive power and negative sequence reactive power exceeds the rated current of the energy storage converter. If it exceeds the rated current, it means that the positive sequence active power reference current must be 0 at this time, that is, , and the positive sequence active reference current is required and negative sequence active reference current If the rated current is not exceeded, there is no need to limit the positive sequence active reference current. and negative sequence active reference current Limiting is performed, at which point the (optimal) active reference current amplitude that meets the overcurrent requirement can be calculated .

[0079] Step S8: controlling the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude.

[0080] In this embodiment, a power instruction may be generated based on the reactive reference current increment and the active reference current amplitude calculated in step S6 and sent to the energy storage converter to achieve regulation of the active and reactive power of the power grid.

[0081] Based on the method described in steps S2 to S8 above, by calculating the square of the reference current amplitudes of phases A, B, and C and comparing them with the rated current, the purpose of judging whether the reactive reference current and the active reference current exceed the rated current of the energy storage converter is achieved. Based on the principle of giving priority to ensuring the reactive current, the square of the reference current amplitudes of phases A, B, and C is made not to exceed the rated current. The calculated reactive reference current increment and active reference current amplitude are used to control the energy storage converter, which can ensure the active current output of the energy storage converter as much as possible, thereby fully utilizing the current output capacity of the device.

[0082] In one implementation of the embodiment of the present application, step S6 may further include the following steps S60 to S66:

[0083] Step S60: Calculate the initial reactive reference current increment according to the operation information.

[0084] In this embodiment, the initial reactive reference current increment is a reactive reference value set according to national standards. I pq And the negative sequence reactive reference current increment I nq .

[0085] In one embodiment, the initial positive sequence reactive reference current increment is calculated using the following formula (10): I pq And the initial negative sequence reactive reference current increment I nq :

[0086] (10)

[0087] in, k 1 Indicates the positive sequence reactive current proportional coefficient, k 2 Indicates the negative sequence reactive current proportional coefficient, U 1 represents the positive sequence voltage amplitude, U 2 Indicates the negative sequence voltage amplitude, U N Indicates rated voltage, I N Indicates the rated current, U T Indicates the preset threshold.

[0088] Step S61, obtaining the maximum value of the squares of the reference current amplitudes of phases A, B, and C.

[0089] In this embodiment, the maximum value among the squares of the reference current amplitudes of phases A, B, and C is obtained according to the above formula (9), that is, .

[0090] Step S62: When the maximum value is less than or equal to the square of the rated current, the initial reactive reference current increment is used as the reactive reference current increment.

[0091] In this embodiment, when When , it indicates that the reference current generated by the positive sequence reactive power and the negative sequence reactive power does not exceed the rated current of the energy storage converter. At this time, the initial reactive reference current increment can be used as the reactive reference current increment.

[0092] In one embodiment, assuming that the reference current amplitudes of phase A, phase B, and phase C are positive, and I N Make a comparison.

[0093] Step S63: Calculate the amplitude range of the active reference current according to the operation information.

[0094] In this embodiment, the amplitude range of the active reference current is derived from the expression of the three-phase reference current amplitude in formula (8).

[0095] Specifically, the above step S63 may further include the following steps S631 and S632:

[0096] Step S631 , calculating the value range of the positive-sequence active reference current amplitude of phases A, B, and C according to the operation information.

[0097] In this embodiment, the amplitudes of the active reference currents of phases A, B, and C are calculated according to the above formula (8): I pda 、 I pdb 、 I pdc Range, as shown in formula (11):

[0098] (11)

[0099] Then use the rated current of the energy storage converter I N Substituting the amplitudes of the reference currents of phases A, B, and C, we obtain the following formula (12):

[0100] (12)

[0101] in, 、 、 Respectively represent the active reference current (amplitude) range of phase A, phase B, and phase C. The minimum and maximum values ​​of the active components of the three-phase reference current are shown in formulas (13) to (15):

[0102] (13)

[0103] (14)

[0104] (15)

[0105] in, and Respectively represent the minimum and maximum values ​​of the active reference current of phase A, and Respectively represent the minimum and maximum values ​​of the active reference current of phase B, and Respectively represent the minimum and maximum values ​​of the active reference current of phase C. Using formula (10) I pq 、 I nq The calculation result is replaced by 、 , get the minimum and maximum values ​​of the reference currents of phase A, phase B and phase C.

[0106] Step S632: Select the intersection of the value ranges of the positive-sequence active reference current amplitudes of phases A, B, and C as the amplitude range of the active reference current.

[0107] In this embodiment, the minimum value among the maximum values ​​of the three-phase active reference current and the maximum value among the minimum values ​​of the three-phase active reference current are taken as the upper limit and lower limit of the amplitude range, that is, the intersection of the active reference current ranges of phases A, B, and C is selected as the amplitude range, as shown in formulas (16) and (17):

[0108] (16)

[0109] (17)

[0110] in, Indicates the maximum value among the minimum values ​​of the three-phase active reference current, that is, the lower limit of the amplitude range. Indicates the minimum value among the maximum values ​​of the three-phase active reference current, that is, the upper limit of the amplitude range.

[0111] Step S64: Calculate the active reference current amplitude according to the amplitude range and the initial active reference current.

[0112] In this embodiment, since a sudden change in the active reference current is not conducive to stable operation of the system, this embodiment selects an active reference current amplitude closest to the amplitude before the fault within the amplitude range of the active reference current, thereby achieving the purpose of avoiding overcurrent problems and ensuring stable and reliable operation of the system.

[0113] In an optional implementation, the above step S64 includes the following steps S641 to S643:

[0114] Step S641, obtaining the lower limit value and the upper limit value of the amplitude range.

[0115] In this embodiment, the lower limit and upper limit of the amplitude range are and .

[0116] Step S642: When the amplitude of the initial active reference current is less than the lower limit, the lower limit is selected as the active reference current amplitude.

[0117] In this embodiment, in order to ensure the stable and reliable operation of the system, when the amplitude of the initial active reference current is less than the lower limit When selecting As the active reference current amplitude.

[0118] Step S643: When the amplitude of the initial active reference current is greater than the upper limit value, the upper limit value is selected as the amplitude of the active reference current.

[0119] In this embodiment, in order to ensure the stable and reliable operation of the system, when the amplitude of the initial active reference current is greater than the upper limit When selecting As the active reference current amplitude.

[0120] It is understandable that when the amplitude of the initial active reference current is within the amplitude range, it can be directly output as the original value.

[0121] Step S65: When the maximum value is greater than the square of the rated current, the active reference current amplitude is set to 0.

[0122] In this embodiment, when When , it means that the reference current of a phase generated by positive sequence reactive power and negative sequence reactive power has exceeded the rated current of the energy storage converter. At this time, based on the reactive power priority strategy, the positive sequence active component of the reference current is Set to 0.

[0123] Step S66 , calculating the reactive reference current increment according to the product of the initial reactive reference current increment and the amplitude limiting coefficient, where the amplitude limiting coefficient is the square root of the ratio of the square of the rated current to the maximum value.

[0124] In this embodiment, the limiting coefficient is shown in formula (18):

[0125] (18)

[0126] in, coe represents the limiting coefficient, I N Indicates the rated current, It represents the maximum value among the squares of the reference current amplitudes of phases A, B, and C, and can be determined by formulas (9) and (10).

[0127] Then the reactive reference current increment can be calculated according to the following formula (19):

[0128] (19)

[0129] in, Indicates the positive sequence reactive reference current increment, Indicates the negative sequence reactive reference current increment, It represents the DC quantity of positive sequence current on the q axis, represents the DC amount of negative sequence current on the q axis, which is the result of formula (10). coe Indicates the limiting coefficient.

[0130] In implementing the technical solution of the present application, the value range of the three-phase positive-sequence active current is first calculated based on the rated current, positive-sequence reactive power, and negative-sequence reactive power reference values, and the minimum range is taken as the amplitude range of the active reference current. If the active current reference value before the fault (active reference current amplitude) is within this range, the output remains unchanged; otherwise, it is limited. This method, while meeting the requirements of the new national standard on positive-sequence reactive power and negative-sequence reactive power, tries to maintain the output of positive-sequence active power before the fault, reduces the sudden change of the energy storage converter current when the fault enters and exits, avoids voltage fluctuations near the fault criticality, is conducive to the stable operation of the energy storage converter, and can maximize the output capacity of the energy storage converter.

[0131] In an application scenario according to an embodiment of the present application, taking A1 and A2 energy storage converters as an example, the steps of how to limit the current during asymmetric low voltage fault ride-through are described. Specifically, Figure 2 This is a schematic diagram of the overall steps of the output control method of the energy storage converter in the face of an asymmetric low voltage fault according to an embodiment of the present application. Figure 2 As shown, the method mainly includes the following steps:

[0132] Step S20, calculate the per-unit value of the positive sequence voltage, that is, .

[0133] Step S21, determine whether the positive sequence voltage per unit value is less than 0.9, that is, determine whether the positive sequence voltage per unit value is less than 0.9. If not, execute step S22 and step S23; if yes, execute step S24.

[0134] Step S22, positive sequence reactive power increment = 0.

[0135] Step S23, negative sequence reactive power increment=0.

[0136] It is understandable that when When the voltage drop is small, it means that the voltage drop is small. At this time, the preset reactive current of the energy storage converter can be used for compensation adjustment, and there is no need to provide additional reactive reference current. That is to say, the positive sequence reactive increment and the negative sequence reactive increment are 0.

[0137] Step S24, calculate the negative sequence voltage per unit value, that is .

[0138] Step S25: Calculate the initial positive-sequence reactive reference current and negative-sequence reactive reference current. The calculation method can be found in Formula (10) in step S60 and will not be repeated here. It should be noted that the positive-sequence reactive reference current and negative-sequence reactive reference current are current reference values ​​calculated based on the new national standard. By substituting these values ​​into the preset three-phase reference currents, it is possible to determine whether an overcurrent has occurred and calculate the appropriate active reference current amplitude.

[0139] Step S26, calculate the maximum value of the square of the three-phase reference current amplitude I max . I max Right now For details, please refer to step S4 in the above embodiment, which will not be repeated here.

[0140] Step S27, determine I max Is it less than the square of the rated current, that is, to judge If not, execute step S28 and step S29; if yes, execute step S30.

[0141] Step S28, calculate the derating factor coe .

[0142] Step S29, set the active reference current to 0, and multiply the initial reactive reference current by coe .like , indicating that the reference current of a phase generated by positive sequence reactive power and negative sequence reactive power has exceeded the rated current of the energy storage converter. At this time, based on the reactive power priority strategy, the positive sequence active component of the reference current is ( I pd) is set to 0; the positive sequence reactive reference current increment and the negative sequence reactive reference current increment are multiplied by the derating factor (limiting factor) respectively coe For details, please refer to step S66 in the above embodiment, which will not be described again here.

[0143] Step S30, calculate the three-phase active reference current range. , indicating that the reference current generated by the positive-sequence reactive and negative-sequence reactive power does not exceed the rated current of the energy storage converter. At this point, there is no need to limit the reactive reference current. In other words, the initial reactive reference current increment is used as the final reactive reference current increment. The three-phase active reference current range is then calculated based on the reactive reference current increment, thereby deriving the appropriate active reference current amplitude.

[0144] Step S31: Determine the amplitude range according to the three-phase active reference current range. The detailed calculation method of the amplitude range can be found in step S632 in the above embodiment, which will not be repeated here.

[0145] Step S32: Determine the active reference current amplitude based on the amplitude range. After calculating the amplitude range, the active reference current amplitude that meets the overcurrent requirement can be determined based on the amplitude range and the amplitude of the initial active reference current. For details, see step S64 in the above embodiment and will not be repeated here.

[0146] In one embodiment, in order to verify the correctness of the above method, an asymmetric low voltage fault is simulated under different voltage drop conditions, and the reference current is limited using the above method to check whether overcurrent occurs. For the convenience of observation, all voltages and currents are displayed in per-unit values. Assuming that the positive sequence active component is 0.6 and the positive sequence reactive component is 0 during normal operation, the positive sequence reactive current proportional coefficient of the reference value is calculated during an asymmetric low voltage fault. k 1 =1.5, negative sequence reactive current proportional coefficient k 2 =1.5, and conduct the following three working condition tests:

[0147] Working condition 1: Ua=1.0, Ub=0.6, Uc=0.6.

[0148] In working condition 1, the voltage drop is shallow, and the amplitude of the three-phase reference current is less than the rated current, so the positive sequence reactive power and the negative sequence reactive power do not need to be limited. The positive sequence active power is within the limit range and can be output according to the reference value before the fault. Figures 3a to 5e In the figure, the horizontal axis represents the time axis (which can be selected according to the needs, such as setting the start time to 0.35s and the time interval to 0.05s, which is not specifically limited in this embodiment), and the vertical axis represents the voltage per unit value or the current per unit value. Specifically, Figure 3aThis is a schematic diagram of the three-phase system voltage under working condition 1. The three curves represent the per-unit voltage values ​​of phases A, B, and C respectively. Figure 3b The positive-sequence voltage and negative-sequence voltage obtained by performing positive- and negative-sequence decomposition on the three-phase system voltage are shown. Figure 3c It is a schematic diagram of the components of the reference current under working condition 1. The three curves represent the positive-sequence active component of the reference current, the positive-sequence reactive component of the reference current, and the negative-sequence reactive component of the reference current, respectively. Figure 3d The three-phase output current after limiting by the method of the present application is shown. The three curves represent the per-unit values ​​of the output currents of phases A, B, and C, respectively. It can be seen that no overcurrent occurs in phases A, B, and C. Figure 3e The three curves in the middle represent the output current positive sequence active component, output current positive sequence reactive component, and output current negative sequence reactive component respectively. Figure 3e and Figure 3c , you can observe the limiting conditions of the positive-sequence active power, positive-sequence reactive power and negative-sequence reactive power components.

[0149] Working condition 2: Ua=1.0, Ub=0.3, Uc=0.3.

[0150] The drop in working condition 2 is deeper. The amplitude of the reference current of a certain phase calculated by the above method is already greater than the rated current. Therefore, while first satisfying the positive sequence reactive power and negative sequence reactive power output, a certain limit is applied to the positive sequence active power so that the three-phase current output does not flow, and the maximum current is the rated current (for detailed calculation method, please refer to the above step S63). Specifically, Figure 4a This is the voltage diagram of the three-phase system under working condition 2. The three curves represent the per-unit voltage values ​​of phases A, B, and C respectively. Figure 4b The positive-sequence voltage and negative-sequence voltage obtained by performing positive- and negative-sequence decomposition on the three-phase system voltage are shown. Figure 4c It is a schematic diagram of the components of the reference current under working condition 2. The three curves represent the positive-sequence active component of the reference current, the positive-sequence reactive component of the reference current, and the negative-sequence reactive component of the reference current, respectively. Figure 4d The three-phase output current after limiting by the method of the present application is shown. The three curves represent the per-unit values ​​of the output currents of phases A, B, and C, respectively. It can be seen that no overcurrent occurs in phases A, B, and C. Figure 4e The three curves in the middle represent the output current positive sequence active component, output current positive sequence reactive component, and output current negative sequence reactive component respectively. Figure 4e and Figure 4c , you can observe the limiting conditions of the positive-sequence active power, positive-sequence reactive power and negative-sequence reactive power components.

[0151] Working condition three: Ua=0.8, Ub=0.1, Uc=0.1.

[0152] The drop in working condition 3 is very deep. The calculated positive sequence reactive power (current) and negative sequence reactive power (current) have made the current amplitude of a phase greater than the rated current. Therefore, the positive sequence active power is set to 0, and the positive sequence reactive power and negative sequence reactive power components are synchronously limited. Similarly, when the three-phase current output is not flowing, the maximum current is the rated current. Specifically, Figure 5a This is a schematic diagram of the three-phase system voltage under working condition three. The three curves represent the per-unit voltage values ​​of phases A, B, and C respectively. Figure 5b The positive-sequence voltage and negative-sequence voltage obtained by performing positive-negative sequence decomposition on the three-phase voltage are shown. Figure 5c Schematic diagram of the reference current components for operating condition three. The three curves represent the positive-sequence active component of the reference current, the positive-sequence reactive component of the reference current, and the negative-sequence reactive component of the reference current, respectively. Figure 5d The three-phase output current after limiting by the method of the present application is shown. The three curves represent the per-unit values ​​of the output currents of phases A, B, and C, respectively. It can be seen that no overcurrent occurs in phases A, B, and C. Figure 5e The three curves in the middle represent the output current positive sequence active component, output current positive sequence reactive component, and output current negative sequence reactive component respectively. Figure 5e and Figure 5c , you can observe the limiting conditions of the positive-sequence active power, positive-sequence reactive power and negative-sequence reactive power components.

[0153] In summary, the method in this embodiment can accurately calculate the amplitude limit value of each component when an asymmetric low voltage fault occurs, thereby improving the current output capability while avoiding overcurrent.

[0154] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effect of the present application, different steps do not have to be performed in such an order. They can be performed simultaneously (in parallel) or in other orders. These adjusted solutions are equivalent to the technical solutions described in this application, and therefore will also fall within the scope of protection of this application.

[0155] Another aspect of the present application also provides an energy storage converter output control system for a phase asymmetric low voltage fault, such as Figure 6As shown, the system includes: an information acquisition module 2, which is used to obtain the operating information of the energy storage converter, and the operating information includes the rated current and the positive sequence voltage amplitude of the AC port; an amplitude calculation module 4, which is used to calculate the square of the reference current amplitude of phase A, phase B and phase C according to the operating information when the positive sequence voltage amplitude is less than a preset threshold; a limit calculation module 6, which is used to calculate the reactive reference current increment and the active reference current amplitude according to the square of the reference current amplitude of phase A, phase B and phase C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection; an output control module 8, which is used to control the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude.

[0156] It is understandable that the above-mentioned energy storage converter output control system for the asymmetric low voltage fault is used to perform Figure 1 The embodiment of the energy storage converter output control method for facing asymmetric low voltage fault is shown in the figure. The technical principles, technical problems solved and technical effects produced by the two are similar. Those skilled in the art can clearly understand that for the convenience and conciseness of description, the specific working process and related instructions of the system can refer to the contents described in the embodiment of the method, and will not be repeated here.

[0157] Another aspect of the present application provides a computer-readable storage medium.

[0158] It will be understood by those skilled in the art that all or part of the processes in the method for implementing the above embodiment of the present application can also be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above-mentioned various method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file or some intermediate form. The computer-readable storage medium may include: any entity or device, medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electric carrier signal, telecommunication signal and software distribution medium, etc. that can carry the computer program code.

[0159] Another aspect of the present application provides a computer-readable storage medium.

[0160] In an embodiment of a computer-readable storage medium according to the present application, the computer-readable storage medium can be configured to store a program for executing the method for controlling the output of an energy storage converter in the event of a phase-asymmetric low-voltage fault according to the above-mentioned method embodiment. The program can be loaded and executed by a processor to implement the method for controlling the output of an energy storage converter in the event of a phase-asymmetric low-voltage fault. For ease of explanation, only the parts related to the embodiment of the present application are shown. For specific technical details not disclosed, please refer to the method section of the embodiment of the present application. The computer-readable storage medium can be a storage device formed by various electronic devices. Optionally, the computer-readable storage medium in the embodiment of the present application is a non-transitory computer-readable storage medium.

[0161] Another aspect of the present application provides a smart device.

[0162] In an embodiment of a smart device according to the present application, the smart device may include at least one processor; and a memory in communication with the at least one processor; wherein the memory stores a computer program, and when the computer program is executed by the at least one processor, the method described in any of the above embodiments is implemented. Figure 7 , Figure 7 exemplarily shows that the memory 11 and the processor 12 are communicatively connected via a bus.

[0163] In some embodiments of the present application, the smart device may further include at least one sensor for sensing information. The sensor is communicatively coupled to any of the processors described herein. Optionally, the smart device described herein may be, but is not limited to, a mobile phone, tablet computer, desktop computer, laptop computer, handheld computer, notebook computer, in-vehicle device, or ultra-mobile personal computer (UMPC), etc., and the embodiments of the present application are not limiting in this regard.

[0164] Thus far, the technical solution of the present application has been described in conjunction with an embodiment shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present application is obviously not limited to these specific embodiments. Without departing from the principles of the present application, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present application.

Claims

1. A method for controlling the output of an energy storage converter in the event of an asymmetric low voltage fault, characterized in that: The method comprises: Acquiring operating information of the energy storage converter, wherein the operating information includes a rated current and a positive sequence voltage amplitude of an AC port; When the positive sequence voltage amplitude is less than a preset threshold, calculating the squares of the reference current amplitudes of phases A, B, and C according to the operation information; Calculating a reactive reference current increment and an active reference current amplitude according to the square of the reference current amplitudes of phases A, B, and C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection. Based on the principle of giving priority to ensuring reactive current, the square of the reference current amplitudes of phases A, B, and C is generated by newly added positive-sequence reactive power and negative-sequence reactive power. If the reference current of any phase does not exceed the rated current, there is no need to limit the positive-sequence active reference current and the negative-sequence active reference current. If the reference current of any phase exceeds the rated current, it is necessary to limit the positive-sequence active reference current and the negative-sequence active reference current. The output of the energy storage converter is controlled according to the reactive reference current increment and the active reference current amplitude.

2. The method according to claim 1, characterized in that The operation information further includes an initial active reference current, and the calculation of a reactive reference current increment and an active reference current amplitude based on the squares of the reference current amplitudes of phases A, B, and C and the rated current includes: Calculating an initial reactive reference current increment according to the operating information; Obtaining the maximum value among the squares of the reference current amplitudes of phase A, phase B, and phase C; When the maximum value is less than or equal to the square of the rated current, using the initial reactive reference current increment as the reactive reference current increment; Calculating an amplitude range of active reference current according to the operating information; Calculating the active reference current amplitude according to the amplitude range and the initial active reference current; When the maximum value is greater than the square of the rated current, setting the active reference current amplitude to 0; The reactive reference current increment is calculated according to the product of the initial reactive reference current increment and a limiting coefficient, where the limiting coefficient is the square root of the ratio of the square of the rated current to the maximum value.

3. The method according to claim 2, characterized in that The calculating the amplitude range of the active reference current according to the operation information includes: Calculate the value range of the positive sequence active reference current amplitude of phase A, phase B and phase C according to the operating information; The intersection of the value ranges of the positive-sequence active reference current amplitudes of phases A, B and C is selected as the amplitude range of the active reference current.

4. The method according to claim 2 or 3, characterized in that The calculating the active reference current amplitude according to the amplitude range and the initial active reference current includes: Obtaining the lower limit and upper limit of the amplitude range; When the amplitude of the initial active reference current is less than the lower limit, selecting the lower limit as the amplitude of the active reference current; When the amplitude of the initial active reference current is greater than the upper limit value, the upper limit value is selected as the active reference current amplitude.

5. The method according to claim 2, characterized in that The operation information further includes the rated voltage, the negative-sequence voltage amplitude of the AC port, the positive-sequence reactive current proportional coefficient, and the negative-sequence reactive current proportional coefficient. The initial reactive reference current increment includes the initial positive-sequence reactive reference current increment and the initial negative-sequence reactive reference current increment. Calculating the initial reactive reference current increment based on the operation information includes: The following formula is used to calculate the initial positive sequence reactive reference current increment and the initial negative sequence reactive reference current increment: in, I pq represents the initial positive sequence reactive reference current increment, I nq represents the initial negative sequence reactive reference current increment, k 1 represents the positive sequence reactive current proportional coefficient, k 2 represents the negative sequence reactive current proportional coefficient, U 1 represents the positive sequence voltage amplitude, U 2 represents the negative sequence voltage amplitude, U N Indicates the rated voltage, I N Indicates the rated current, U T Indicates the preset threshold.

6. The method according to claim 5, characterized in that The reactive reference current increment includes a positive-sequence reactive reference current increment and a negative-sequence reactive reference current increment, and calculating the reactive reference current increment based on the product of the initial reactive reference current increment and the amplitude limiting coefficient includes: The positive-sequence reactive reference current increment and the negative-sequence reactive reference current increment are calculated using the following formula: in, represents the positive sequence reactive reference current increment, represents the negative sequence reactive reference current increment, coe represents the clipping coefficient, Represents the maximum value among the squares of the reference current amplitudes of phase A, phase B and phase C.

7. The method according to claim 1, characterized in that When the positive sequence voltage amplitude is greater than or equal to a preset threshold, the reactive reference current increment is 0.

8. An output control system for an energy storage converter in the face of an asymmetric low voltage fault, characterized in that: The system comprises: An information acquisition module is used to obtain operating information of the energy storage converter, wherein the operating information includes the rated current and the positive sequence voltage amplitude of the AC port; an amplitude calculation module, configured to calculate the squares of the reference current amplitudes of phases A, B, and C according to the operation information when the positive sequence voltage amplitude is less than a preset threshold; A limiting calculation module is used to calculate the reactive reference current increment and the active reference current amplitude based on the square of the reference current amplitudes of phases A, B, and C and the rated current, wherein the reactive reference current increment and the active reference current amplitude meet the requirements of asymmetric low voltage fault ride-through and overcurrent protection. Based on the principle of giving priority to ensuring reactive current, the square of the reference current amplitudes of phases A, B, and C is generated by the newly added positive-sequence reactive power and negative-sequence reactive power. If the reference current of any phase does not exceed the rated current, there is no need to limit the positive-sequence active reference current and the negative-sequence active reference current. If the reference current of any phase exceeds the rated current, it is necessary to limit the positive-sequence active reference current and the negative-sequence active reference current. The output control module is used to control the output of the energy storage converter according to the reactive reference current increment and the active reference current amplitude.

9. A smart device, characterized in that: include: at least one processor; and, a memory communicatively coupled to the at least one processor; The memory stores a computer program, and when the computer program is executed by the at least one processor, the method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium storing a plurality of program codes, characterized in that: The program code is suitable for being loaded and executed by a processor to perform the method according to any one of claims 1 to 7.

Images