Voltage support method for energy storage converter during asymmetric drop fault of power grid

Abstract

The invention discloses a voltage support method for an energy storage converter in an asymmetric drop fault of a power grid, and relates to the technical field of electric energy storage. The method comprises the steps of firstly solving voltage positive and negative sequence components of a target power grid grid-connected point; according to positive and negative sequence voltage component threshold values allowed by the target power grid, judging whether the target power grid has an asymmetric drop fault or not; if yes, a positive and negative sequence reactive current instruction is solved, and the expected reactive power of the energy storage converter is calculated; if the expected reactive power is smaller than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current instruction is injected into the target power grid; and if the expected reactive power is greater than the rated capacity of the energy storage converter, injecting the maximum value of the positive and negative sequence reactive current output by the energy storage converter into the target power grid. According to the scheme, stable power supply of the target power grid during the fault period is guaranteed to the maximum extent, and loss when the power grid breaks down is reduced to the maximum extent.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy storage, and in particular to a voltage support method for an energy storage converter during an asymmetric drop fault in a power grid. Background Art

[0002] In modern power systems, with the large-scale access of renewable energy, the power grid faces more challenges in stability and reliability. Due to the intermittent and uncertain nature of these new energy sources, higher requirements are placed on the safety of the power grid. In particular, when the power grid is subject to asymmetric drop faults (such as single-phase grounding or two-phase short circuit faults), the voltage fluctuations are more severe, which may affect the normal operation of loads and key equipment.

[0003] As the capacity and penetration rate of energy storage systems continue to increase, energy storage systems can also provide some auxiliary services when facing power outages caused by disasters or system failures. In order to further improve the power supply stability of the power grid, large-capacity energy storage systems not only need to maintain a connection with the grid under fault conditions, but also need to actively support the voltage of the grid connection point. This function is achieved by injecting positive and negative sequence reactive currents to increase the voltage of the grid connection point, while suppressing the negative sequence voltage, which is beneficial to the recovery of the grid.

[0004] For large-capacity energy storage systems, traditional grid fault ride-through solutions only consider the positive-sequence component of the grid connection point voltage. When a grid fault occurs, only positive-sequence reactive current is output to support the grid connection point voltage, while the negative-sequence component of the grid connection point is ignored. In actual situations, asymmetric grid faults account for a higher proportion. Therefore, there is an urgent need for a voltage support method for energy storage converters during asymmetric grid drop faults. Summary of the invention

[0005] The object of the present invention is to provide a voltage support method for an energy storage converter during an asymmetric drop fault in a power grid. When an asymmetric fault occurs in a target power grid, the positive sequence current and negative sequence current of the energy storage converter input into the target power grid are adjusted to support the voltage of the grid connection point, so that the target power grid can maintain stable power supply when an asymmetric drop fault occurs and recover to normal from the asymmetric drop fault.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides a method for supporting voltage of an energy storage converter when an asymmetric drop fault occurs in a power grid, the method comprising:

[0008] The positive and negative sequence components of the voltage at the target grid connection point are obtained based on the phase-locked loop and phase sequence separation method;

[0009] According to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target grid, it is determined whether an asymmetric drop fault occurs in the target grid;

[0010] If an asymmetric drop fault occurs in the target power grid, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence components of the voltage at the grid connection point;

[0011] Calculate the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions;

[0012] If the expected reactive power is less than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current commands are injected into the target grid;

[0013] If the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current output by the energy storage converter is determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current is injected into the target power grid.

[0014] In some embodiments, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence voltage components of the grid connection point, including:

[0015] Generate positive and negative sequence command currents according to the reference output current and the positive and negative sequence voltage component thresholds;

[0016] The positive and negative sequence reactive current instructions are obtained according to the droop relationship between the positive and negative sequence command current and the positive and negative sequence components of the voltage at the grid connection point.

[0017] In some embodiments, determining the maximum positive and negative sequence reactive current output by the energy storage converter according to the rated capacity of the energy storage converter includes:

[0018] Calculate the voltage fault critical value of the target power grid according to the rated capacity of the energy storage converter;

[0019] According to the voltage fault critical value, the maximum positive and negative sequence reactive current output by the energy storage converter is determined.

[0020] In some embodiments, the voltage positive and negative sequence components of the target grid connection point are obtained according to the phase-locked loop and phase sequence separation method, including:

[0021] The three-phase voltage of the target grid connection point is obtained in real time through the voltage sensor;

[0022] According to the three-phase voltage, the positive and negative sequence components of the voltage at the target grid connection point are obtained using a phase-locked loop and phase sequence separation method.

[0023] In some embodiments, judging whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid includes:

[0024] If the positive and negative sequence components of the voltage at the grid connection point are not within the positive and negative sequence voltage component thresholds, it is determined that an asymmetric fault has occurred in the target power grid;

[0025] If the positive and negative sequence components of the voltage at the grid connection point are within the positive and negative sequence voltage component thresholds, it is determined that no asymmetric fault occurs in the target power grid.

[0026] In some embodiments, the method further comprises:

[0027] Obtain the rated voltage of the grid connection point of the target grid under normal operating conditions and the line impedance of the target grid;

[0028] According to the rated voltage and line impedance of the grid connection point, the reference output current of the energy storage inverter is determined.

[0029] In a second aspect, the present invention further provides a voltage support device for an energy storage converter when an asymmetric drop fault occurs in a power grid, the device comprising:

[0030] A voltage determination module, used to obtain the positive and negative sequence components of the voltage at the target grid connection point according to a phase-locked loop and a phase sequence separation method;

[0031] A fault determination module is used to determine whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid;

[0032] The instruction determination module is used to obtain the positive and negative sequence reactive current instructions according to the reference output current of the energy storage converter, the positive and negative sequence voltage component threshold and the positive and negative sequence voltage components of the grid connection point if an asymmetric drop fault occurs in the target power grid;

[0033] A power calculation module, used to calculate the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions;

[0034] A first support module is used to inject positive and negative sequence reactive current instructions into a target power grid if the expected reactive power is less than or equal to the rated capacity of the energy storage converter;

[0035] The second supporting module is used to determine the maximum positive and negative sequence reactive current output by the energy storage converter according to the rated capacity of the energy storage converter if the expected reactive power is greater than the rated capacity of the energy storage converter, and inject the maximum positive and negative sequence reactive current into the target power grid.

[0036] In a third aspect, the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the voltage support method for the energy storage converter during an asymmetric grid drop fault provided in the first aspect is implemented.

[0037] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the voltage support method for the energy storage converter during an asymmetric grid drop fault provided in the first aspect.

[0038] In a fifth aspect, the present invention further provides a computer program product, including a computer program, which, when executed by a processor, implements the voltage support method of the energy storage converter during an asymmetric grid drop fault provided in the first aspect.

[0039] The beneficial effects of the present invention are:

[0040] First, the positive and negative sequence components of the voltage at the target grid connection point are obtained according to the phase-locked loop and phase sequence separation method; then, according to the positive and negative sequence components of the voltage at the connection point and the positive and negative sequence voltage component thresholds allowed by the target grid, it is judged whether an asymmetric drop fault occurs in the target grid; if an asymmetric drop fault occurs in the target grid, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence components of the voltage at the connection point; then, according to the positive and negative sequence reactive current instructions, the expected reactive power of the energy storage converter is calculated; if the expected reactive power is less than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current instructions are injected into the target grid; if the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current output by the energy storage converter is determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current is injected into the target grid. When an asymmetric drop fault occurs in the target power grid, the energy storage converter can input positive and negative sequence reactive current into the target power grid according to its own rated capacity, which maximizes the guarantee that the target power grid can provide stable power supply during the fault and greatly reduces the loss when the power grid fails.

[0041] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of a method for voltage support of an energy storage converter during an asymmetric grid drop fault according to an embodiment of the present invention;

[0043] Figure 2 A schematic diagram of a grid-connected circuit of an energy storage converter and its control structure shown in one embodiment of the present invention;

[0044] Figure 3A control structure block diagram of an energy storage converter for supporting the grid connection point voltage when a grid fault occurs as shown in an embodiment of the present invention, and a segmented droop curve diagram of expected positive and negative sequence currents and first positive and negative sequence voltage components of the grid connection point;

[0045] Figure 4 It is a schematic diagram of a method for selecting a target positive-sequence reactive current and a target negative-sequence reactive current according to an embodiment of the present invention;

[0046] Figure 5 A diagram showing a process of supporting the grid connection point voltage when a phase A short circuit occurs in the target grid, as shown in an embodiment of the present invention;

[0047] Figure 6 It is a flow chart of another voltage support method of an energy storage converter during an asymmetric grid drop fault shown in one embodiment of the present invention;

[0048] Figure 7 A structural diagram of a voltage support device of an energy storage converter during an asymmetric grid drop fault as shown in one embodiment of the present invention;

[0049] Figure 8 A structural diagram of another voltage support device of an energy storage converter during an asymmetric grid drop fault as shown in one embodiment of the present invention;

[0050] Fig. 9 A schematic diagram of the structure of an electronic device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0051] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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.

[0052] It should be noted that references to "one embodiment", "embodiment", "example embodiment", etc. in this specification refer to the embodiment being described which may include specific features, structures or characteristics, but not every embodiment must include these specific features, structures or characteristics. In addition, such expressions do not refer to the same embodiment. Furthermore, when describing specific features, structures or characteristics in conjunction with an embodiment, whether or not there is an explicit description, it is indicated that incorporating such features, structures or characteristics into other embodiments is within the knowledge of those skilled in the art.

[0053] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] In some embodiments, Figure 1 As shown, a voltage support method for an energy storage converter when an asymmetric drop fault occurs in a power grid is provided, the method comprising:

[0055] S101, obtaining the positive and negative sequence components of the voltage at the target grid connection point according to a phase-locked loop and a phase sequence separation method.

[0056] The grid connection point is the access point where the energy storage converter is connected to the target power grid; the voltage positive and negative sequence components of the grid connection point include a voltage positive sequence component and a voltage negative sequence component.

[0057] Optionally, the three-phase voltage of the target grid connection point is acquired in real time by a voltage sensor; based on the three-phase voltage, the positive and negative sequence components of the voltage at the target grid connection point are obtained by using a phase-locked loop and a phase sequence separation method.

[0058] Specifically, the three-phase voltage of the grid connection point can be sampled in real time by using a voltage sensor, and the phase information of the positive sequence component of the grid connection point voltage can be obtained by using a phase-locked loop based on a second-order generalized integrator. The positive sequence component and negative sequence component of the grid connection point voltage can be extracted by a phase sequence separation method. The specific calculation formulas refer to the following formulas (1)-(2);

[0059]

[0060] in, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, V fa , V fb , V fc is the three-phase voltage at the grid connection point, is the phase information of the positive sequence component at the grid connection point, It is the phase information of the negative sequence component at the grid connection point.

[0061] S102, judging whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid.

[0062] Among them, the positive and negative sequence voltage component thresholds include the minimum positive sequence voltage component and the maximum negative sequence voltage component that can be allowed to pass through the target power grid. They are determined in advance according to relevant regulations. The positive and negative sequence voltage component thresholds can be manually uploaded to the computer's storage system in advance. When an asymmetric drop fault judgment is required, it can be directly retrieved from the storage system.

[0063] Optionally, if the positive and negative sequence components of the voltage at the grid connection point are not within the positive and negative sequence voltage component threshold, it is determined that an asymmetric fault has occurred in the target power grid; if the positive and negative sequence components of the voltage at the grid connection point are within the positive and negative sequence voltage component threshold, it is determined that no asymmetric fault has occurred in the target power grid.

[0064] Specifically, if the positive-sequence component of the voltage at the grid-connected point is less than the minimum value of the positive-sequence voltage component, and / or the negative-sequence component of the voltage at the grid-connected point is greater than the maximum value of the negative-sequence voltage component, it means that the positive-sequence and negative-sequence components of the voltage at the grid-connected point are not within the positive-sequence and negative-sequence voltage component thresholds, and it is determined that an asymmetric fault has occurred in the target power grid; otherwise, it is determined that no asymmetric fault has occurred in the target power grid.

[0065] For example, Figure 2 As shown, Figure 2 This is a schematic diagram of the grid-connected circuit and control structure of the energy storage converter. Figure 2 In the main circuit L 1 is the machine side inductance, C f is the filter capacitor on the AC side, L T is the leakage inductance of the transformer, L l is the line inductance. The leakage inductance of the transformer and the line inductance can be equivalent to the inductance L g , V dc DC bus voltage of energy storage converter, V machine side voltage vector, I f Generator side current vector, V f Capacitor voltage vector, V g is the grid voltage vector, PCC point refers to the grid connection point, and the "Fault" sign represents a grid voltage drop fault.

[0066] S103, if an asymmetric drop fault occurs in the target power grid, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence voltage components of the grid connection point.

[0067] The reference output current is the reference value of the output current of the energy storage converter when a drop fault occurs in the target power grid.

[0068] Optionally, the rated voltage of the target grid at the grid connection point and the line impedance of the target grid under normal operating conditions may be obtained first, and then the reference output current of the energy storage converter may be determined according to the rated voltage and line impedance of the grid connection point. The specific calculation formula is referred to in the following formula (3);

[0069]

[0070] Among them, I q0 is the reference output current, V N is the rated voltage of the grid connection point, Z g is the line impedance.

[0071] According to the reference output current of the target power grid, the positive and negative sequence voltage component thresholds and the positive and negative sequence voltage components of the grid connection point, the positive and negative sequence reactive current instructions are calculated. The specific calculation formulas refer to the following formulas (4)-(5);

[0072]

[0073] in, is the positive sequence reactive current command, is the negative sequence reactive current instruction, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, is the maximum value of the negative sequence voltage component, I q0 is the reference output current.

[0074] Optionally, the positive and negative sequence command currents may be generated based on the reference output current and the positive and negative sequence voltage component thresholds; and the positive and negative sequence reactive current commands may be obtained based on the droop relationship between the positive and negative sequence command currents and the positive and negative sequence components of the voltage at the grid connection point.

[0075] Specifically, the positive and negative sequence command currents are generated according to the reference output current and the positive and negative sequence voltage component thresholds. The specific expressions of the droop relationship between the positive and negative sequence command currents and the positive and negative sequence components of the voltage at the grid connection point can be referred to the following formulas (6)-(7):

[0076]

[0077] in, is the positive sequence command current, is the negative sequence command current, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, is the maximum value of the negative sequence voltage component, I q0 is the reference output current.

[0078] For example, Figure 3 The control structure diagram of the energy storage converter to achieve grid connection point voltage support when the grid fails and the expected positive and negative sequence current The first positive and negative sequence voltage components of the grid-connected point and The piecewise droop curve diagram.

[0079] S104, calculating the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions.

[0080] Specifically, the expected reactive power of the energy storage converter is calculated according to the positive-sequence reactive current command and the negative-sequence reactive current command. The specific calculation formula is shown in the following formula (8);

[0081]

[0082] Among them, Q ref (t) is the expected reactive power, is the positive sequence reactive current command, is the negative sequence reactive current instruction, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, It is the maximum value of negative sequence voltage component.

[0083] S105: If the expected reactive power is less than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current instructions are injected into the target power grid.

[0084] Specifically, if the expected reactive power is less than or equal to the rated capacity of the energy storage converter, it means that the energy storage converter can fully support the target power grid at this time, and the positive-sequence reactive current command and the negative-sequence reactive current command can be directly input into the target power grid, that is, the support for the target power grid can be completed.

[0085] S106, if the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current output by the energy storage converter is determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current is injected into the target power grid.

[0086] Optionally, the voltage fault critical value of the target power grid can be calculated according to the rated capacity of the energy storage converter, and then the maximum positive and negative sequence reactive current output by the energy storage converter can be determined according to the voltage fault critical value.

[0087] Among them, the voltage fault critical value of the target power grid is the voltage critical value that the target power grid can withstand without a fault, the voltage fault critical value includes a first voltage critical value and a second voltage critical value, and the positive and negative sequence reactive current maximum values ​​include a positive sequence reactive current maximum value and a negative sequence reactive current maximum value.

[0088] Specifically, when the expected reactive power is greater than the rated capacity of the energy storage converter, it means that the energy storage converter can no longer fully support the target power grid. At this time, it is necessary to provide maximum power support to the target power grid. The voltage fault critical value can be calculated according to the following formulas (9)-(12), and the maximum value of the positive and negative sequence reactive current can be calculated:

[0089]

[0090] in, is the maximum value of positive sequence reactive current, is the maximum value of negative sequence reactive current, n 0 and M is the transition parameter, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, is the maximum value of the negative sequence voltage component, I q0 is the reference output current, S N is the capacity of the energy storage converter, V N is the rated voltage of the grid connection point, is the first voltage threshold, is the second voltage threshold.

[0091] That is, if the expected reactive power is greater than the rated capacity of the energy storage converter, and The input injection into the target grid has completed the support of the target grid.

[0092] For example, Figure 4 As shown, the process in S105-S106 is described in detail. Figure 4 According to the capacity S of the energy storage converter N And the first positive and negative sequence voltage components during grid fault right Figure 3 middle and and its corresponding and Schematic diagram of the selection method.

[0093] According to the capacity of the converter S N Determine the combination of grid fault conditions that can support the grid connection point within the normal range of the grid For the specific expression, refer to formula (13):

[0094]

[0095] Simplified to obtain formula (14):

[0096]

[0097] The expression of M is formula (15):

[0098]

[0099] From this, we can get the capacity constraint curve of the energy storage converter and The expression of is formula (16):

[0100]

[0101] According to the positive and negative sequence components of the grid connection point voltage when the grid fault occurs, the positive and negative sequence reactive current ratio curve n required to support the grid connection point within the normal range is drawn -=n 0 , the specific expression is formula (17):

[0102]

[0103] Capacity Constraint Curve The positive-negative sequence reactive current ratio curve n required to support the grid connection point within the normal range under fault conditions - =n 0 The intersection point is the best combination, and its corresponding maximum positive and negative sequence reactive current The expression of is formula (18)-(19):

[0104]

[0105] in, is the maximum value of positive sequence reactive current, is the maximum value of negative sequence reactive current, n 0 and M is the transition parameter, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, is the maximum value of the negative sequence voltage component, I q0 is the reference output current, S N is the capacity of the energy storage converter, V N is the rated voltage of the grid connection point, is the first voltage threshold, is the second voltage threshold.

[0106] In summary, after an asymmetric drop fault occurs in the target grid, the target positive sequence current and target negative sequence current injected into the target grid by the energy storage converter can be referred to the following formulas (20)-(21):

[0107]

[0108] in, is the maximum value of positive sequence reactive current, is the maximum value of negative sequence reactive current, is the positive sequence component of the voltage at the grid connection point, is the negative sequence component of the voltage at the grid connection point, is the minimum value of the positive sequence voltage component, is the maximum value of the negative sequence voltage component, is the first voltage threshold, is the second voltage threshold, is the positive sequence reactive current command, It is the negative sequence reactive current command.

[0109] In specific operations, the target positive-sequence current and target negative-sequence current obtained above can be used as the input of the current controller of the energy storage converter, and the output signal of the controller can be used as the modulation signal of the converter switch tube. After carrier comparison and power amplification, the switch tube is driven to work, and finally the voltage of the grid connection point can be supported in the event of a grid failure.

[0110] For example, Figure 5 As shown, Figure 5 This is a diagram of the process of supporting the grid connection point voltage when phase A is short-circuited to ground in the target grid; during the phase A short-circuit fault, the energy storage converter Figure 3 The droop curve and Figure 4 The target positive and negative sequence reactive current selection method is adopted to inject the target positive and negative sequence reactive current into the target power grid, thereby making full use of the capacity of the energy storage converter to support the grid connection point voltage.

[0111] Figure 5 Sub-figure (a) is a voltage waveform diagram when a grid fault occurs and when the fault is cleared, sub-figure (b) is a waveform diagram of the output current of the energy storage converter during the target grid fault period and when it returns to normal, sub-figure (c) is a diagram showing the change process of the first positive and negative sequence voltage components when a grid fault occurs and when the fault is cleared, and sub-figure (d) is a diagram showing the change of the target positive and negative sequence reactive current instructions when a grid fault occurs and when the fault is cleared.

[0112] Depend on Figure 5 -b and Figure 5 -d, it can be seen that when the power grid is normal and allowed, the energy storage converter outputs 1pu of positive sequence active current i dp When a fault occurs in the power grid, the energy storage converter enters the fault ride-through mode, stops the active output, and outputs the corresponding positive sequence reactive current i qp and negative sequence reactive current i qn When the grid fault is cleared, the converter outputs 1pu positive sequence active current i again. dp , positive sequence reactive current i qp and negative sequence reactive current i qn All dropped to 0.

[0113] Depend on Figure 5 -c shows that when a short circuit occurs to the ground in phase A of the power grid, the positive sequence component of the grid connection point voltage drops from 1pu to 0.67pu, and the negative sequence component increases from 0pu to 0.33pu. When the energy storage converter starts the fault ride-through mode, the positive sequence component of the grid connection point voltage increases to 0.88pu, and the negative sequence component drops to 0.17pu. When the grid voltage returns to normal, the converter stops the fault ride-through mode and switches to the normal grid connection mode.

[0114] In the above embodiment, the positive and negative sequence components of the voltage at the target grid connection point are first obtained according to the phase-locked loop and phase sequence separation method; then, according to the positive and negative sequence components of the voltage at the connection point and the positive and negative sequence voltage component thresholds allowed by the target grid, it is determined whether an asymmetric drop fault occurs in the target grid; if an asymmetric drop fault occurs in the target grid, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence components of the voltage at the connection point; then, according to the positive and negative sequence reactive current instructions, the expected reactive power of the energy storage converter is calculated; if the expected reactive power is less than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current instructions are injected into the target grid; if the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current output by the energy storage converter is determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current is injected into the target grid. When an asymmetric drop fault occurs in the target power grid, the energy storage converter can input positive and negative sequence reactive current into the target power grid according to its own rated capacity, which maximizes the guarantee that the target power grid can provide stable power supply during the fault and greatly reduces the loss when the power grid fails.

[0115] In order to more comprehensively demonstrate this solution, this embodiment provides an optional method for voltage support of an energy storage converter when an asymmetric drop fault occurs in the power grid, such as Figure 6 As shown:

[0116] S201, obtaining the rated voltage of the grid connection point of the target grid under normal operating conditions and the line impedance of the target grid.

[0117] S202, determining a reference output current of the energy storage converter according to the rated voltage of the grid connection point and the line impedance.

[0118] S203, obtaining the three-phase voltage of the target power grid connection point in real time through a voltage sensor.

[0119] S204, according to the three-phase voltage, using a phase-locked loop and a phase sequence separation method to obtain the positive and negative sequence components of the voltage at the target grid connection point.

[0120] S205: If the positive and negative sequence voltage components of the grid connection point are not within the positive and negative sequence voltage component thresholds, it is determined that an asymmetric fault has occurred in the target power grid.

[0121] S206: If the positive and negative sequence voltage components of the grid connection point are within the positive and negative sequence voltage component thresholds, it is determined that no asymmetric fault occurs in the target power grid.

[0122] S207, generating positive and negative sequence command currents according to the reference output current and the positive and negative sequence voltage component thresholds.

[0123] S208, obtaining positive and negative sequence reactive current instructions according to the droop relationship between the positive and negative sequence instruction currents and the positive and negative sequence components of the voltage at the grid connection point.

[0124] S209, calculating the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions.

[0125] S210: If the expected reactive power is less than or equal to the rated capacity of the energy storage converter, the positive and negative sequence reactive current instructions are injected into the target power grid.

[0126] S211, if the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current output by the energy storage converter is determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current is injected into the target power grid.

[0127] The specific process of S201-S211 above can refer to the description of the above method embodiment, and its implementation principle and technical effect are similar, which will not be repeated here.

[0128] Based on the same inventive concept, the embodiment of the present application also provides a voltage support device for an energy storage converter during an asymmetric grid drop fault, which is used to implement the voltage support method for an energy storage converter during an asymmetric grid drop fault. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of the voltage support device for an energy storage converter during an asymmetric grid drop fault provided below can refer to the limitations of the voltage support method for an energy storage converter during an asymmetric grid drop fault in the above text, and will not be repeated here.

[0129] In one embodiment, Figure 7 As shown, a voltage support device for an energy storage converter in the event of an asymmetric drop fault in a power grid is provided, the device comprising:

[0130] A voltage determination module 30, used to obtain the positive and negative sequence components of the voltage at the target grid connection point according to a phase-locked loop and a phase sequence separation method;

[0131] A fault determination module 31 is used to determine whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid;

[0132] The instruction determination module 32 is used to obtain the positive and negative sequence reactive current instructions according to the reference output current of the energy storage converter, the positive and negative sequence voltage component threshold and the positive and negative sequence voltage components of the grid connection point if an asymmetric drop fault occurs in the target power grid;

[0133] A power calculation module 33, used to calculate the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions;

[0134] A first support module 34 is used to inject positive and negative sequence reactive current instructions into the target power grid if the expected reactive power is less than or equal to the rated capacity of the energy storage converter;

[0135] The second support module 35 is used to determine the maximum positive and negative sequence reactive current output by the energy storage converter according to the rated capacity of the energy storage converter if the expected reactive power is greater than the rated capacity of the energy storage converter, and inject the maximum positive and negative sequence reactive current into the target power grid.

[0136] In another embodiment, the voltage determination module 30 in the above embodiment is specifically used for:

[0137] The three-phase voltage of the target grid connection point is obtained in real time through the voltage sensor; based on the three-phase voltage, the positive and negative sequence components of the voltage at the target grid connection point are obtained using the phase-locked loop and phase sequence separation method.

[0138] In another embodiment, the fault determination module 31 in the above embodiment is specifically used for:

[0139] If the positive and negative sequence components of the voltage at the grid connection point are not within the positive and negative sequence voltage component threshold, it is determined that an asymmetric fault has occurred in the target power grid; if the positive and negative sequence components of the voltage at the grid connection point are within the positive and negative sequence voltage component threshold, it is determined that no asymmetric fault has occurred in the target power grid.

[0140] In another embodiment, the instruction determination module 32 in the above embodiment is specifically used for:

[0141] The positive and negative sequence command currents are generated according to the reference output current and the positive and negative sequence voltage component thresholds; the positive and negative sequence reactive current commands are obtained according to the droop relationship between the positive and negative sequence command currents and the positive and negative sequence components of the voltage at the grid connection point.

[0142] In another embodiment, the second support module 35 in the above embodiment is specifically used for:

[0143] According to the rated capacity of the energy storage converter, the voltage fault critical value of the target power grid is calculated; according to the voltage fault critical value, the maximum positive and negative sequence reactive current output by the energy storage converter is determined.

[0144] In another embodiment, Figure 8 As shown, the voltage support device of the energy storage converter during an asymmetric drop fault of the power grid also includes:

[0145] An information acquisition module 36 is used to obtain the rated voltage of the grid connection point of the target grid under normal working conditions and the line impedance of the target grid;

[0146] The current determination module 37 is used to determine the reference output current of the energy storage converter according to the rated voltage of the grid connection point and the line impedance.

[0147] The present application also provides an electronic device, in some implementations, referring to Fig. 9 As shown, the electronic device 700 includes an input unit 710, a memory 720, a processor 730, and an output unit 740. The memory 720 stores program instructions that can be run on the processor 730, and the processor 730 calls the program instructions to execute the voltage support method and / or technical solution of the energy storage converter when the power grid asymmetric drop fault occurs based on the aforementioned embodiment. The electronic device 700 can be a mobile terminal device such as a mobile phone and a computer.

[0148] In addition, an embodiment of the present application further provides a computer-readable storage medium for storing a computer program for executing a voltage support method for an energy storage converter during an asymmetric drop fault in a power grid. For example, a computer program instruction, when executed by a computer, can call or provide a method and / or technical solution according to the present application through the operation of the computer. The program instructions for calling the method of the present application may be stored in a fixed or removable storage medium, and / or transmitted through a data stream in a broadcast or other signal-bearing medium and / or stored in a storage medium that runs according to the program instructions.

[0149] Obviously, those skilled in the art should understand that the above modules or steps of the present application can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. In this way, the present application is not limited to any specific combination of hardware and software.

[0150] The technical features of the above embodiments may be arbitrarily integrated. To make the description concise, not all possible integrations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the integration of these technical features, they should be considered to be within the scope of this specification.

[0151] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A voltage support method for an energy storage converter during an asymmetric drop fault in a power grid, characterized in that: The method comprises: The positive and negative sequence components of the voltage at the target grid connection point are obtained based on the phase-locked loop and phase sequence separation method; According to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target grid, determining whether an asymmetric drop fault occurs in the target grid; If an asymmetric drop fault occurs in the target power grid, the positive and negative sequence reactive current instructions are obtained according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence components of the voltage at the grid connection point; Calculating the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions; If the expected reactive power is less than or equal to the rated capacity of the energy storage converter, injecting the positive and negative sequence reactive current instructions into the target power grid; If the expected reactive power is greater than the rated capacity of the energy storage converter, the maximum positive and negative sequence reactive current values ​​output by the energy storage converter are determined according to the rated capacity of the energy storage converter, and the maximum positive and negative sequence reactive current values ​​are injected into the target power grid.

2. The voltage support method of the energy storage converter during an asymmetric drop fault of the power grid as claimed in claim 1, characterized in that: According to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence voltage components of the grid connection point, the positive and negative sequence reactive current instructions are obtained, including: Generate positive and negative sequence command currents according to the reference output current and the positive and negative sequence voltage component thresholds; The positive and negative sequence reactive current instructions are obtained according to the droop relationship between the positive and negative sequence instruction currents and the positive and negative sequence components of the voltage at the grid connection point.

3. The voltage support method of the energy storage converter during an asymmetric drop fault of the power grid as claimed in claim 1, characterized in that: Determining the maximum positive and negative sequence reactive current output by the energy storage converter according to the rated capacity of the energy storage converter includes: Calculating a voltage fault critical value of the target power grid according to the rated capacity of the energy storage converter; The maximum values ​​of the positive and negative sequence reactive current output by the energy storage converter are determined according to the voltage fault critical value.

4. The voltage support method of the energy storage converter during an asymmetric drop fault of the power grid as claimed in claim 1, characterized in that: The positive and negative sequence components of the voltage at the target grid connection point are obtained based on the phase-locked loop and phase sequence separation method, including: Acquire the three-phase voltage of the target power grid connection point in real time through a voltage sensor; According to the three-phase voltage, the positive and negative sequence components of the voltage at the target grid connection point are obtained by using a phase-locked loop and a phase sequence separation method.

5. The voltage support method of the energy storage converter during an asymmetric drop fault of the power grid as claimed in claim 4, characterized in that: Judging whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid, including: If the positive and negative sequence voltage components of the grid connection point are not within the positive and negative sequence voltage component thresholds, it is determined that an asymmetric fault has occurred in the target power grid; If the positive and negative sequence components of the voltage at the grid connection point are within the positive and negative sequence voltage component thresholds, it is determined that no asymmetric fault occurs in the target power grid.

6. The voltage support method of the energy storage converter during an asymmetric drop fault of the power grid as claimed in claim 1, characterized in that: The method further comprises: Obtaining the rated voltage of the grid connection point of the target grid under normal operating conditions and the line impedance of the target grid; A reference output current of the energy storage converter is determined according to the rated voltage of the grid connection point and the line impedance.

7. A voltage support device for an energy storage converter during an asymmetric drop fault in a power grid, characterized in that: The device comprises: A voltage determination module, used to obtain the positive and negative sequence components of the voltage at the target grid connection point according to a phase-locked loop and a phase sequence separation method; A fault determination module, used for determining whether an asymmetric drop fault occurs in the target power grid according to the positive and negative sequence voltage components of the grid connection point and the positive and negative sequence voltage component thresholds allowed by the target power grid; An instruction determination module is used to obtain positive and negative sequence reactive current instructions according to the reference output current of the energy storage converter, the positive and negative sequence voltage component thresholds and the positive and negative sequence voltage components of the grid connection point if an asymmetric drop fault occurs in the target power grid; A power calculation module, used for calculating the expected reactive power of the energy storage converter according to the positive and negative sequence reactive current instructions; A first support module, configured to inject the positive and negative sequence reactive current instructions into the target power grid if the expected reactive power is less than or equal to the rated capacity of the energy storage converter; The second supporting module is used to determine the maximum positive and negative sequence reactive current output by the energy storage inverter according to the rated capacity of the energy storage inverter if the expected reactive power is greater than the rated capacity of the energy storage inverter, and inject the maximum positive and negative sequence reactive current into the target power grid.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, a voltage support method for an energy storage converter during an asymmetric grid drop fault is implemented according to any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the voltage support method of the energy storage converter during an asymmetric grid drop fault according to any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the voltage support method of the energy storage converter during an asymmetric grid drop fault according to any one of claims 1 to 6 is implemented.

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