Method and system for determining short-circuit current of power grid and electronic equipment

Abstract

The invention discloses a power grid short-circuit current determination method and system and electronic equipment, and relates to the technical field of power grid data processing. According to the method, the drop degree of the voltage of the grid-connected point is determined by adopting an energy storage grid-connected control strategy, and stage division is performed on the drop degree, so that the constraint condition of the energy storage system in each drop stage is constructed. And determining the fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value, and determining different impedance matrixes based on different fault types so as to determine the short-circuit current of the energy storage system under different faults. And constructing a system equation based on the short-circuit current and the constraint condition of the energy storage system in each drop stage to determine the amplitude and the phase angle of the short-circuit current so as to realize accurate determination of the short-circuit current.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid data processing, and in particular to a method, system and electronic equipment for determining a short-circuit current of a power grid. Background Art

[0002] The main problem, development direction and challenge facing the power grid now is the "double high" power grid. "Double high" refers to a high proportion of clean energy and a high proportion of power electronic devices. With the construction of new power systems, the grid connection of energy storage systems, and the high power electronics of source, grid, load and storage will become the development trend of the power grid. Battery energy storage systems have been rapidly developed and widely used in power systems, but the understanding of the mechanism of battery energy storage systems affecting short-circuit current is not in-depth. The mechanism and key parameters of battery energy storage systems affecting short-circuit current need to be studied urgently. For example, "Research on distribution network flow and short-circuit current calculation considering distributed power sources. Xiao Xinxin. Shanghai Jiaotong University, 2008." This document analyzes the impact of distributed power sources on the short-circuit current of the distribution network and proposes a short-circuit current calculation method based on the improved node admittance matrix, but its power model is not suitable for energy storage systems containing converters. The document "Improved method for short-circuit calculation of distribution network with distributed generation. Wang Chengshan et al. Automation of Electric Power Systems, 2012, 36(23):54-58" proposes an improved algorithm. First, the quantity that cannot change suddenly in the distributed generation during short circuit is obtained by flow calculation, and then the short-circuit current output by the distributed generation is inversely calculated according to the interface type of different distributed generation. However, this method cannot calculate the short-circuit current at the point where the energy storage system is connected to the grid, which has certain limitations. The document "Unified analysis method of flow and short circuit of distribution network with distributed generation. Jiang Xingyue. Tianjin University, 2007" proposes a unified analysis method of three-phase flow and fault calculation of distribution network with distributed generation. The fault compensation circuit is used to form a fault loop, and the fault calculation is converted into a flow calculation under special circumstances. Then the forward and backward flow calculation method is used to calculate the short-circuit current. However, this method is relatively simple in modeling the energy storage system and does not take into account the control method of the converter.

[0003] Traditional short-circuit current calculation is mainly based on power flow calculation and superposition principle. However, when energy storage system is added to the network, the network topology will become complicated. In addition, the energy storage system contains power electronic converters and various related control strategies. The energy storage system cannot be treated as a voltage source with internal impedance for calculation. Based on this, the existing short-circuit current calculation method for distribution network containing energy storage system still has the following problems:

[0004] 1) There is insufficient research on the control strategy for grid-connected energy storage systems. When a distribution network failure occurs, the impact of the control strategy on the short-circuit characteristics is not fully considered.

[0005] 2) The modeling of the energy storage system is overly simplified, ignoring the impact of the power electronic converter, which greatly reduces the accuracy of short-circuit current calculation.

[0006] 3) The impact of low voltage ride-through coordination and control added during a fault to ensure that the energy storage system can continue to operate without being disconnected from the grid is not considered.

[0007] In summary, the main drawback of the prior art is that the energy storage system is oversimplified when calculating the short-circuit current, and the impact of the power electronic converter and control strategy therein is not fully considered, which leads to a large error in the final short-circuit current. Summary of the invention

[0008] In order to solve the above problems existing in the prior art, the present invention provides a method, system and electronic equipment for determining short-circuit current of a power grid.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] A method for determining short-circuit current of a power grid, comprising:

[0011] Adopt energy storage grid-connected control strategy to determine the voltage drop degree at the grid-connected point;

[0012] Dividing the drop degree into four drop stages, and constructing constraint conditions of the energy storage system in each drop stage;

[0013] Obtain the maximum output current of the energy storage system, the rated output current of the energy storage system, and the power reference value;

[0014] Determine a fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value; the fault type includes a symmetrical fault and an asymmetrical fault;

[0015] An impedance matrix is ​​determined based on the fault type, and a short-circuit current of the energy storage system is determined based on the impedance matrix; when the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix; when the fault type is an asymmetrical fault, the impedance matrix includes a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix;

[0016] Constructing a system equation based on the short-circuit current and the constraints of the energy storage system in each drop stage;

[0017] The magnitude and phase angle of the short-circuit current are determined based on the system equations.

[0018] Optionally, the energy storage grid-connected control strategy adopts PQ control.

[0019] Optionally, determining an impedance matrix based on the fault type, and determining a short-circuit current of the energy storage system based on the impedance matrix specifically includes:

[0020] When the fault type of the energy storage system is a symmetrical fault, a node impedance matrix is ​​formed based on the normal voltage component of each node in the energy storage system and the normal operating current of each power supply in the energy storage system;

[0021] Determine a node voltage of the energy storage system and a fault component of the node voltage based on the node impedance matrix;

[0022] A short circuit current of an energy storage system is determined based on the node voltage and a fault component of the node voltage.

[0023] Optionally, determining an impedance matrix based on the fault type, and determining a short-circuit current of the energy storage system based on the impedance matrix specifically includes:

[0024] When the fault type of the energy storage system is an asymmetric fault, a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix are respectively determined based on the positive-sequence component, zero-sequence component, and negative-sequence component of the voltage of each node in the energy storage system and the positive-sequence component, zero-sequence component, and negative-sequence component of the current when each power supply in the energy storage system fails;

[0025] Establish boundary equations based on the fault characteristics of asymmetric faults;

[0026] The short-circuit current of the energy storage system is determined based on the positive-sequence node impedance matrix, the zero-sequence node impedance matrix, the negative-sequence node impedance matrix, and the boundary equation.

[0027] Optionally, the constraints of the energy storage system in the first falling stage are:

[0028]

[0029] The constraints of the energy storage system in the second drop stage are:

[0030]

[0031] The constraints of the energy storage system in the third drop stage are:

[0032]

[0033] The constraints of the energy storage system in the fourth drop stage are:

[0034]

[0035] Where U is the grid connection point voltage of the energy storage system, is the current phase angle provided by the voltage ride-through control strategy when the voltage is lower than the set voltage value, Ic is the current phasor output by the converter, P ref is the power reference value given in PQ control, P is the actual power value of the energy storage system, i q is the actual value of the q-axis current component on the AC side, i d is the actual value of the d-axis current component on the AC side, i qref is the reference value of the q-axis current component of the AC measurement, I max is the maximum output current of the energy storage system, i dref is the reference value of the d-axis current component of the AC measurement, δ is the dynamic adjustment coefficient, f is the frequency of the energy storage system, and f0 is the frequency of the power grid.

[0036] Optionally, the dynamic adjustment coefficient δ is used to reduce frequency fluctuations during fault switching.

[0037] Optionally, the system equation constructed based on the short-circuit current and the constraint conditions of the energy storage system in the first drop stage is:

[0038]

[0039] The system equation constructed based on the constraints of the energy storage system in the short-circuit current and the second drop stage is:

[0040]

[0041] The system equation constructed based on the short-circuit current and the constraints of the energy storage system in the third drop stage is:

[0042]

[0043] The system equation constructed based on the short-circuit current and the constraints of the energy storage system in the fourth drop stage is:

[0044]

[0045] Where U is the grid connection point voltage of the energy storage system, is the current phase angle provided by the voltage ride-through control strategy when the voltage is lower than the set voltage value, I c is the current phasor output by the converter, P ref is the power reference value given in PQ control, i qref is the reference value of the q-axis current component of the AC measurement, I max is the maximum output current of the energy storage system.

[0046] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0047] The present invention adopts an energy storage grid-connected control strategy to determine the voltage drop degree of the grid connection point, and divides the drop degree into stages to construct the constraint conditions of the energy storage system in each drop stage. The fault type of the energy storage system is determined based on the maximum output current, the rated output current and the power reference value, and different impedance matrices are determined based on different fault types to determine the short-circuit current of the energy storage system under different faults. A system equation is constructed based on the short-circuit current and the constraint conditions of the energy storage system in each drop stage to determine the amplitude and phase angle of the short-circuit current, thereby realizing the accurate determination of the short-circuit current.

[0048] Furthermore, the present invention provides a system for determining a short-circuit current of a power grid, the system being used to implement the above-mentioned method for determining a short-circuit current of a power grid; the system comprising:

[0049] The energy storage grid-connected control module is used to determine the voltage drop degree of the grid-connected point by adopting the energy storage grid-connected control strategy;

[0050] A constraint condition construction module, used for dividing the drop degree into four drop stages and constructing the constraint conditions of the energy storage system in each drop stage;

[0051] A data acquisition module, used to obtain the maximum output current of the energy storage system, the rated output current of the energy storage system and the power reference value;

[0052] A fault type determination module, configured to determine a fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value; the fault type includes a symmetrical fault and an asymmetrical fault;

[0053] A short-circuit current determination module, used to determine an impedance matrix based on the fault type, and determine the short-circuit current of the energy storage system based on the impedance matrix; when the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix; when the fault type is an asymmetrical fault, the impedance matrix includes a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix;

[0054] A system equation building module, used for building a system equation based on the short-circuit current and the constraints of the energy storage system in each drop stage;

[0055] An amplitude and phase angle determination module is used to determine the amplitude and phase angle of the short-circuit current based on the system equation.

[0056] Furthermore, the present invention also provides an electronic device, the electronic device comprising:

[0057] Memory for storing computer programs;

[0058] A processor is connected to the memory and is used to retrieve and execute the computer program to implement the above-mentioned method for determining the short-circuit current of the power grid.

[0059] Optionally, the memory is a computer-readable storage medium.

[0060] Since the technical effect achieved by the implementation structure provided by the present invention is the same as the technical effect achieved by the method for determining the short-circuit current of the power grid provided by the present invention, it will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0062] Figure 1 A flow chart of a method for determining short-circuit current of a power grid provided by the present invention;

[0063] Figure 2 A flowchart of the implementation of the method for determining short-circuit current of a power grid provided by the present invention;

[0064] Figure 3 A schematic diagram of PQ control and additional low voltage ride-through control for the grid-connected energy storage system provided by the present invention;

[0065] Figure 4 This is a schematic diagram of an equivalent network for a distribution network fault provided by the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0067] The object of the present invention is to provide a method, system and electronic equipment for determining short-circuit current of a power grid, which can accurately determine the short-circuit current.

[0068] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0069] In order to solve the problems existing in the prior art, the present invention converts the energy storage system into a constant current source and uses the superposition principle to solve the short-circuit current. Under various additional controls (such as low voltage ride-through control, etc.), the reactive power generated by the energy storage system is used as a constraint to calculate the phase angle change of the current and finally obtain the accurate value of the short-circuit current. The specific technical concept and design principle are as follows:

[0070] The energy storage system is processed into a constant current source for calculation, and the equivalent current source coefficient is different according to different battery types (lithium iron phosphate battery, sodium sulfur battery, vanadium flow battery, etc.), which increases the application scenarios. In order to ensure that the energy storage system does not go off the grid in the event of a fault, it will switch from the original PQ control to low voltage ride-through control. There is also a certain time scale in the process of switching control. The fault during this period is equivalent to a large disturbance to the system. In order to maintain the transient stability of the system, a certain frequency support is required. After switching control, the energy storage system will emit reactive power to the outside, resulting in the energy storage system's external output power, voltage, and current cannot be maintained at the reference value. By considering the output power, voltage, current, and frequency as constraints, a reasonable and effective method for calculating the short-circuit current of the power grid containing the energy storage system is obtained.

[0071] Based on the above design concept and design principle, the present invention provides a method for determining short-circuit current of a power grid, such as Figure 1 and Figure 2 As shown, the method includes:

[0072] Step 100: Determine the voltage drop degree of the grid connection point by adopting the energy storage grid connection control strategy.

[0073] In actual application, the energy storage grid-connected control strategy adopts PQ control, and in order to ensure that the energy storage system can continue to operate without disconnecting from the grid in the event of a fault, low voltage ride-through control is added. The specific control principle is as follows: Figure 3 When no fault occurs or the voltage drop is very small, the inverter is still controlled by the double closed-loop control strategy, P ref , Q ref are the given power reference values ​​of the power outer loop in PQ control, and P and Q are the actual values ​​of the inverter output power. dref 、i qref are the reference values ​​of the dq axis current components of AC measurement, i d 、i q are the actual values ​​of the dq axis current components on the AC side, u d 、u q are the actual values ​​of the dq axis components of the inverter output voltage, u dl 、u ql are the reference values ​​of the dq axis components of the inverter output voltage, respectively. L is the AC inductance, and θ is the phase angle of the voltage. Figure 3As shown, the power reference value P ref , Q ref The difference between the actual value P and Q is used as the reference value i for the inverter output current through the PI regulator. dref 、i qref , output current reference value i dref 、i qref With the actual value i d 、i q The difference is then output through the PI regulator to output the inverter reference component. At the same time, the actual value of the inverter output voltage and the voltage coupling component ωLi are superimposed. d ωLi q , get the inverter output voltage reference value, and then transform it into abc coordinate components through coordinate transformation to control the inverter. When the voltage drop at the grid connection point is large, the energy storage system power outer loop is locked, and the current reference value is obtained by calculation. The q-axis component reference value of the current is:

[0074]

[0075] Active current command (i.e. current reference value i dref ) take i dref0 and The smaller value between dref0 I is the active current instruction of the inverter current inner loop of the energy storage system before the fault. max is the maximum output current of the energy storage system. N is the rated output current of the energy storage system.

[0076] Step 101: Divide the drop degree into four drop stages, and construct constraint conditions for the energy storage system in each drop stage.

[0077] In actual application, according to the degree of voltage drop at the grid connection point, it is divided into four stages. And in the process of voltage drop and control switching, there is a certain time scale to consider the smoothness of control switching, and to make requirements for the transient stability of the system. The system must have a certain frequency support to resist the large disturbance caused by the fault. Therefore, during the fault switching, the dynamic adjustment coefficient δ should be selected to reduce frequency fluctuations, enhance anti-interference ability, and reduce the impact on the system.

[0078] When the grid connection point voltage drops slightly (i.e. the first drop stage), the converter will not generate reactive power. When the grid connection point voltage fluctuation is small, the energy storage system can transmit active power according to the reference value. At this time, the constraints that the energy storage system needs to meet are:

[0079]

[0080] Where U is the grid connection point voltage of the energy storage system. is the current phase angle provided by the low voltage ride through control strategy. I c is the converter output current phasor.

[0081] When the grid-connected point voltage drops to a certain range (i.e., the second drop stage), the grid-connected converter can provide reactive power support for the power system without triggering the current limiter. At this time, the constraints that the energy storage system needs to meet are:

[0082]

[0083] When the voltage drop at the grid connection point is relatively large (i.e., the third drop stage), due to the action of the limiter in the control link, the d-axis component of the converter current cannot reach the reference value, and the active power output of the system cannot reach the reference value. The dynamic adjustment coefficient δ will adjust the frequency to counteract the disturbance. f represents the frequency of the energy storage system, and f0 represents the grid frequency. At this time, the constraints that the energy storage system needs to meet are:

[0084]

[0085] When the grid voltage drops sharply (i.e. the fourth drop stage), the energy storage system can only provide reactive power support for the system with its maximum output current. At this time, the constraints that the energy storage system needs to meet are:

[0086]

[0087] Step 102: Obtain the maximum output current of the energy storage system, the rated output current of the energy storage system, and the power reference value.

[0088] Step 103: Determine the fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value. The fault type includes symmetrical fault and asymmetrical fault.

[0089] Step 104: Determine an impedance matrix based on the fault type, and determine the short-circuit current of the energy storage system based on the impedance matrix. When the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix. When the fault type is an asymmetrical fault, the impedance matrix includes a positive sequence node impedance matrix, a zero sequence node impedance matrix, and a negative sequence node impedance matrix.

[0090] In actual application, in the case of symmetrical and asymmetrical faults in the power grid, there is only a positive sequence current component in the AC side output current of the energy storage system. And in the case of a sudden drop in the voltage at the machine end, the transient process of the fault current output by the energy storage system is short and can be ignored. However, when a fault occurs in the actual power grid, the voltage at the machine end of the energy storage system will not drop suddenly. At the same time, there is a certain delay in the detection of the voltage drop in the power grid. These will bring a certain transient process to the output fault current of the energy storage system, but the transient process will not affect the fault steady-state output current of the energy storage system. That is, in the case of a power grid fault, the fault steady-state current output by the energy storage system only contains a positive sequence component. In addition, even when the voltage at the machine end drops suddenly and the voltage detection delay is not considered, the dq axis component in the fault current output by the energy storage system will not overshoot when tracking the corresponding given signal. Therefore, when the voltage at the machine end does not drop suddenly and there is a voltage detection delay, the magnitude of the fundamental frequency component current output by the energy storage system during the fault transient process will not exceed its fault steady-state current.

[0091] Through the above analysis, and considering the influence of power electronic devices in the energy storage system, it can be known that in the case of a grid fault, the energy storage system can be equivalent to a constant positive sequence current source, and different types of batteries have different output currents. Based on this, the short-circuit fault analysis theory of the grid containing the energy storage system is established. Based on this, the output current of the equivalent positive sequence current source of the energy storage system is:

[0092] I es =K bat K.I N (6)

[0093] Where: I es is the short-circuit current output by the energy storage system. K is the allowable overcurrent multiple, and the value range is usually around 1.2 to 1.5. bat Indicates the output current coefficient of different batteries.

[0094] Then, when the fault type of the energy storage system is a symmetrical fault (for example, a three-phase symmetrical short circuit occurs at point k in the system), the distribution network containing the energy storage system can be operated as follows: Figure 4 A general multi-port network structure is shown.

[0095] Based on this, the normal component of each node voltage can be solved by the node voltage equation of the normal component network. The node voltage equation of the normal component network is:

[0096] U i =ZI S (7)

[0097] Among them: U i is the normal component of each node voltage, is the voltage at point k, k = 1, 2, ..., n. Z is the node impedance matrix. I S is the current of each power supply in the system when it is operating normally, is the current injected by the power supply connected to point k.

[0098] The fault component of each node voltage can be solved by the node voltage equation of the fault component network. The node voltage equation is:

[0099] ΔU i =Z ik I kf (8)

[0100] Where: ΔU i is the fault component of each node voltage. kf Represents the fault injection current of each node. ik Represents the node impedance matrix associated with the fault point. ΔU i ,I kf and Z ik Respectively expressed as:

[0101]

[0102] For the fault point, the voltage at the fault point Expressed as normal component With fault component The superposition of is:

[0103]

[0104] So we have:

[0105]

[0106] In the formula, is the short-circuit current at the fault point, Z kk is the self-impedance when solving the node voltage using the node voltage method, z f is the grounding resistance of the fault point (when the ideal metallic short circuit occurs, z f =0).

[0107] Furthermore, when the fault type of the energy storage system is an asymmetric fault (for example, a three-phase asymmetric short circuit occurs in the system at point m), the following positive and negative zero-sequence equations are first established:

[0108]

[0109]

[0110]

[0111]

[0112] In the formula, They represent the positive-sequence component, negative-sequence component and zero-sequence component of each node voltage respectively. Represents the columns in the positive, negative, and zero sequence node impedance matrices associated with the short-circuit point. (1) Represents the positive-sequence node impedance matrix of the network. They represent the positive sequence component, negative sequence component and zero sequence component of the fault current at the fault point respectively.

[0113] Represent the positive and negative zero-sequence self-impedance respectively.

[0114] To solve the three-phase fault current in an asymmetric fault, it is also necessary to establish three boundary equations, namely, the boundary equation of a single-phase grounding fault, the boundary equation of a two-phase short-circuit fault, and the boundary equation of a two-phase grounding short-circuit fault, according to the specific fault characteristics. Among them:

[0115] 1) The boundary equation of single-phase grounding fault is:

[0116]

[0117] 2) The boundary equation of two-phase short circuit fault is:

[0118]

[0119] 3) The boundary equation of two-phase ground short circuit fault is:

[0120]

[0121] Finally, the short-circuit current is calculated based on the short-circuit situation described above.

[0122] Step 105: Constructing system equations based on the short-circuit current and the constraints of the energy storage system in each drop stage.

[0123] In actual applications, due to the low voltage fault ride-through control function, the output current phasor of the energy storage system may not be collinear with the voltage phasor of the grid connection point during the AC main system fault. Based on this, the output short-circuit current can be written as the following phasor equation:

[0124]

[0125]

[0126]

[0127]

[0128] Step 106: Determine the amplitude and phase angle of the short-circuit current based on the system equation. That is, the amplitude and phase angle of the short-circuit current are obtained by solving the above formula (20)-formula (23). The amplitude is obtained by the above method (formula (6)-formula (18)). Amplitude, this value is the sum of the short-circuit current provided by the synchronous motor and the energy storage power station, I c The value of can also be found, and then we get value, The value is the phase angle generated by the energy storage system providing reactive power to the outside. This is the factor that affects the short-circuit current in the control strategy. Adding the phase angle to the basis can obtain a more accurate short-circuit current.

[0129] Based on the above description, compared with the prior art, the present invention has the following advantages:

[0130] 1. The present invention combines the control strategies of the energy storage system under different working conditions to obtain the constraints of the power grid containing the energy storage system after short circuit. When calculating the short-circuit current of the power grid, the influencing factor constraints of different control strategies are considered to obtain more accurate and reasonable calculation results.

[0131] 2. When modeling the energy storage system, the present invention fully considers the characteristics of different energy storage media and improves the applicable scenarios of the proposed short-circuit current calculation method.

[0132] 3. The control strategy for grid-connected energy storage systems is taken into consideration. The present invention divides the short-circuit current output by the energy storage system into four stages according to the voltage drop after a failure of the energy storage system. Different constraints are considered in each stage, and the short-circuit current of the power grid containing the energy storage system is calculated in combination with the constraints, making the calculation result more accurate and reasonable.

[0133] 4. The energy storage system contains a power electronic converter. The present invention fully considers the influence of the power electronic converter in the energy storage system when studying the equivalent model of the energy storage system during short-circuit current calculation, thereby improving the accuracy of short-circuit current calculation.

[0134] 5. Simply equating the energy storage system to a constant current source and then using power flow calculation and superposition principle to calculate the short-circuit current output by the energy storage system cannot completely guarantee accuracy, because the influence of the control method is not fully considered. Therefore, the present invention also considers the influence of the energy storage system's external reactive power output when the voltage drops, and adds the phase angle generated by its external reactive power output into the calculation to ensure the accuracy of the current value calculation.

[0135] Furthermore, the present invention provides a system for determining short-circuit current of a power grid, which is used to implement the above-mentioned method for determining short-circuit current of a power grid. The system includes: an energy storage grid-connected control module, a constraint condition building module, a data acquisition module, a fault type determination module, a short-circuit current determination module, a system equation building module, and an amplitude and phase angle determination module.

[0136] The energy storage grid-connected control module is used to determine the voltage drop degree of the grid-connected point by adopting the energy storage grid-connected control strategy.

[0137] The constraint condition building module is used to divide the drop degree into four drop stages and build the constraint conditions of the energy storage system in each drop stage.

[0138] The data acquisition module is used to obtain the maximum output current of the energy storage system, the rated output current of the energy storage system and the power reference value.

[0139] The fault type determination module is used to determine the fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value. The fault type includes symmetrical fault and asymmetrical fault.

[0140] The short-circuit current determination module is used to determine the impedance matrix based on the fault type, and determine the short-circuit current of the energy storage system based on the impedance matrix. When the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix. When the fault type is an asymmetrical fault, the impedance matrix includes a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix.

[0141] The system equation building module is used to build the system equation based on the short-circuit current and the constraints of the energy storage system in each drop stage.

[0142] The amplitude and phase angle determination module is used to determine the amplitude and phase angle of the short-circuit current based on the system equation.

[0143] Furthermore, the present invention also provides an electronic device, which includes: a memory and a processor.

[0144] Memory, used to store computer programs.

[0145] The processor is connected to the memory and is used to retrieve and execute a computer program to implement the above-mentioned method for determining the short-circuit current of the power grid.

[0146] In addition, when the computer program in the above-mentioned memory is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory, a random access memory, a magnetic disk or an optical disk.

[0147] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0148] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for determining short-circuit current of a power grid, characterized in that: include: Adopt energy storage grid-connected control strategy to determine the voltage drop degree at the grid-connected point; Dividing the drop degree into four drop stages, and constructing constraint conditions of the energy storage system in each drop stage; Obtain the maximum output current of the energy storage system, the rated output current of the energy storage system, and the power reference value; Determine a fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value; the fault type includes a symmetrical fault and an asymmetrical fault; Determine an impedance matrix based on the fault type, and determine a short-circuit current of an energy storage system based on the impedance matrix; When the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix; When the fault type is an asymmetric fault, the impedance matrix includes a positive sequence node impedance matrix, a zero sequence node impedance matrix and a negative sequence node impedance matrix; Constructing a system equation based on the short-circuit current and the constraints of the energy storage system in each drop stage; The magnitude and phase angle of the short-circuit current are determined based on the system equations.

2. The method for determining short-circuit current of a power grid according to claim 1, characterized in that: The energy storage grid-connected control strategy adopts PQ control.

3. The method for determining short-circuit current of a power grid according to claim 1, characterized in that: Determining an impedance matrix based on the fault type, and determining a short-circuit current of an energy storage system based on the impedance matrix, specifically includes: When the fault type of the energy storage system is a symmetrical fault, a node impedance matrix is ​​formed based on the normal voltage component of each node in the energy storage system and the normal operating current of each power supply in the energy storage system; Determine a node voltage of the energy storage system and a fault component of the node voltage based on the node impedance matrix; A short circuit current of an energy storage system is determined based on the node voltage and a fault component of the node voltage.

4. The method for determining short-circuit current of a power grid according to claim 1, characterized in that: Determining an impedance matrix based on the fault type, and determining a short-circuit current of an energy storage system based on the impedance matrix, specifically includes: When the fault type of the energy storage system is an asymmetric fault, a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix are respectively determined based on the positive-sequence component, zero-sequence component, and negative-sequence component of the voltage of each node in the energy storage system and the positive-sequence component, zero-sequence component, and negative-sequence component of the current when each power supply in the energy storage system fails; Establish boundary equations based on the fault characteristics of asymmetric faults; The short-circuit current of the energy storage system is determined based on the positive-sequence node impedance matrix, the zero-sequence node impedance matrix, the negative-sequence node impedance matrix, and the boundary equation.

5. The method for determining short-circuit current of a power grid according to claim 2, characterized in that: The constraints of the energy storage system in the first drop stage are: The constraints of the energy storage system in the second drop stage are: The constraints of the energy storage system in the third drop stage are: The constraints of the energy storage system in the fourth drop stage are: Where U is the grid connection point voltage of the energy storage system, is the current phase angle provided by the voltage ride-through control strategy when the voltage is lower than the set voltage value, I c is the current phasor output by the converter, P ref is the power reference value given in PQ control, P is the actual power value of the energy storage system, i q is the actual value of the q-axis current component on the AC side, i d is the actual value of the d-axis current component on the AC side, i qref is the reference value of the q-axis current component of the AC measurement, I max is the maximum output current of the energy storage system, i dref is the reference value of the d-axis current component of the AC measurement, δ is the dynamic adjustment coefficient, f is the frequency of the energy storage system, and f0 is the frequency of the power grid.

6. The method for determining the short-circuit current of a power grid according to claim 5, characterized in that: The dynamic adjustment coefficient δ is used to reduce frequency fluctuation during fault switching.

7. The method for determining short-circuit current of a power grid according to claim 1, characterized in that: The system equation constructed based on the short-circuit current and the constraints of the energy storage system in the first drop stage is: The system equation constructed based on the constraints of the energy storage system in the short-circuit current and the second drop stage is: The system equation constructed based on the short-circuit current and the constraints of the energy storage system in the third drop stage is: The system equation constructed based on the short-circuit current and the constraints of the energy storage system in the fourth drop stage is: Where U is the grid connection point voltage of the energy storage system, is the current phase angle provided by the voltage ride-through control strategy when the voltage is lower than the set voltage value, I c is the current phasor output by the converter, P ref is the power reference value given in PQ control, i qref is the reference value of the q-axis current component of the AC measurement, I max is the maximum output current of the energy storage system.

8. A system for determining short-circuit current of a power grid, characterized in that: The system is used to implement the method for determining the short-circuit current of a power grid according to any one of claims 1 to 7; the system comprises: The energy storage grid-connected control module is used to determine the voltage drop degree of the grid-connected point by adopting the energy storage grid-connected control strategy; A constraint condition construction module, used for dividing the drop degree into four drop stages and constructing the constraint conditions of the energy storage system in each drop stage; A data acquisition module, used to obtain the maximum output current of the energy storage system, the rated output current of the energy storage system and the power reference value; A fault type determination module, configured to determine a fault type of the energy storage system based on the maximum output current, the rated output current and the power reference value; the fault type includes a symmetrical fault and an asymmetrical fault; A short-circuit current determination module, used to determine an impedance matrix based on the fault type, and determine the short-circuit current of the energy storage system based on the impedance matrix; when the fault type is a symmetrical fault, the impedance matrix is ​​a node impedance matrix; when the fault type is an asymmetrical fault, the impedance matrix includes a positive-sequence node impedance matrix, a zero-sequence node impedance matrix, and a negative-sequence node impedance matrix; A system equation building module, used for building a system equation based on the short-circuit current and the constraints of the energy storage system in each drop stage; An amplitude and phase angle determination module is used to determine the amplitude and phase angle of the short-circuit current based on the system equation.

9. An electronic device, characterized in that: include: Memory for storing computer programs; A processor, connected to the memory, is used to retrieve and execute the computer program to implement the method for determining the short-circuit current of the power grid as described in any one of claims 1 to 7.

10. The electronic device according to claim 9, characterized in that: The memory is a computer-readable storage medium.

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