New energy grid-connected converter fault ride-through method and system under asymmetric fault

Abstract

The invention provides a new energy grid-connected converter fault ride-through method and system under an asymmetric fault, and the method comprises the steps: calculating the positive sequence voltage amplitude of a power grid and the voltage unbalance degree of the power grid according to the positive and negative sequence parameters of the power grid; judging whether the power grid is in a normal state or a fault state; when the power grid is in the asymmetric fault state, current amplitude limiting is carried out by adopting a calculation formula of a positive and negative sequence current instruction in the asymmetric fault state based on the related parameters of the power grid fault, and the amplitude limiting value of the positive and negative sequence current instruction of the new energy grid-connected converter in the asymmetric fault state is calculated; feedback control is carried out according to the amplitude limiting values of the positive and negative sequence current instructions, and fault ride-through is completed; according to the method, the current is subjected to amplitude limiting in the calculation formula of the positive and negative sequence current instructions, so that the positive and negative sequence active and reactive current control target can be met to the greatest extent on the premise of ensuring that overcurrent of the converter does not occur, and the power grid supporting capacity during the fault period is improved.

Description

Technical Field

[0001] The patent application of this invention belongs to the technical field of new energy grid-connected control, and specifically relates to a method and system for fault ride-through of a new energy grid-connected converter under asymmetric faults. Background Art

[0002] As the proportion of installed capacity continues to increase, the impact of renewable energy power generation on the safety and stability of the power system is becoming increasingly significant.

[0003] When a power grid fails, in order to ensure the safety and stability of the system, new energy grid-connected converters are required to perform fault ride-through, have a certain ability to operate continuously without disconnecting from the grid, and provide reactive power support to the grid during the fault. Power grid faults can be divided into symmetrical faults (three-phase short circuit faults) and asymmetrical faults (two-phase short circuit faults, single-phase ground short circuit faults, and two-phase ground short circuit faults). Compared with symmetrical faults, asymmetrical faults account for a higher proportion, and single-phase ground short circuit faults alone account for 70%.

[0004] Under asymmetric faults, the power grid will generate negative sequence voltage. For this purpose, some standards have been formulated. For example, the latest wind power grid connection standard "Technical Regulations for Wind Farm Access to Power System (GB / T 19963-2021)" requires that when an asymmetric fault occurs in the power system, the wind farm should have dynamic reactive support capabilities during the low voltage ride-through process. The wind farm should inject positive sequence dynamic reactive current into the grid to support the recovery of positive sequence voltage; it should absorb negative sequence dynamic reactive current from the grid to suppress the increase of negative sequence voltage.

[0005] In response to the above grid-connected requirements, the prior art has proposed dual synchronous decoupled coordinate system phase-locked loops and dual second-order generalized integrator phase-locked loops, which realize the separation of positive and negative sequence of grid voltage and renewable energy output current. The prior art also proposes positive and negative sequence current control algorithms, which realize independent control of positive and negative sequence currents of grid-connected converters.

[0006] However, according to the grid-connected standard requirements, the new energy grid-connected converter has multiple control targets such as injecting positive-sequence dynamic reactive current and absorbing negative-sequence dynamic reactive current under asymmetric faults. In addition, its own active power must be maintained. The above control targets involve multiple current instructions such as positive-sequence reactive current, negative-sequence reactive current, and positive-sequence active current. The overcurrent capacity of the new energy grid-connected converter is limited, and a reasonable current instruction limiting strategy must be formulated to meet the control targets of positive-sequence reactive current, negative-sequence reactive current, and positive-sequence active current to the greatest extent while ensuring that no overcurrent occurs.

[0007] However, under asymmetric faults, the three-phase current of the renewable energy grid-connected converter is unbalanced, and the current limit is determined by the phase with the largest current. The existing fault ride-through method for renewable energy grid-connected converters under asymmetric faults does not consider the problem of three-phase current unbalance and limit, and does not fully utilize the converter's overcurrent capacity, which limits the grid support capacity during faults. Summary of the invention

[0008] In order to overcome the above-mentioned deficiencies of the prior art, the present invention patent application proposes a fault ride-through method for a new energy grid-connected converter under an asymmetric fault, comprising:

[0009] Obtaining positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid;

[0010] According to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage, it is judged whether the power grid is in a normal state or a fault state; the fault state includes an asymmetric fault state;

[0011] When the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the current is limited by using the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state, the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state are calculated, and feedback control is performed according to the limiting values ​​of the positive and negative sequence current instructions to complete fault crossing.

[0012] Preferably, the obtaining of the positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid, comprises:

[0013] The positive and negative sequence parameters of the power grid are obtained through a phase-locked loop with positive and negative sequence separation function;

[0014] Calculating the positive-sequence voltage amplitude and the negative-sequence voltage amplitude of the power grid according to the positive- and negative-sequence parameters of the power grid;

[0015] Calculating the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude;

[0016] Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component.

[0017] Preferably, the fault state further includes: a high voltage fault state and a three-phase symmetrical fault state; and judging whether the power grid is in a normal state or a fault state according to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage includes:

[0018] When the grid positive sequence voltage amplitude is within a preset grid positive sequence voltage amplitude range, the grid is in a normal state;

[0019] When the positive-sequence voltage amplitude of the power grid is greater than the maximum value of the positive-sequence voltage amplitude interval of the power grid, the power grid is in the high-voltage fault state;

[0020] When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit, the grid is in the three-phase symmetrical fault state;

[0021] When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is greater than the symmetrical fault imbalance limit, the grid is in the asymmetrical fault state.

[0022] Preferably, the calculation formula of the positive and negative sequence current instructions includes: the calculation formula of the positive sequence current q-axis instruction, the calculation formula of the negative sequence current q-axis instruction, the calculation formula of the negative sequence current d-axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d-axis instruction, the positive sequence current q-axis instruction, the negative sequence current d-axis instruction and the negative sequence current q-axis instruction; when the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state is used to perform current amplitude limit, the amplitude limit value of the positive and negative sequence current instructions in the asymmetric fault state is calculated, and feedback control is performed according to the amplitude limit value of the positive and negative sequence current instructions to complete fault crossing, including:

[0023] When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode;

[0024] Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current;

[0025] According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction;

[0026] The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through;

[0027] Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

[0028] Preferably, the calculation formula of the A-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0029]

[0030] Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0031] Preferably, the calculation formula of the B-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0032]

[0033] Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0034] Preferably, the calculation formula of the C phase current amplitude when the positive sequence active current is not injected is as follows:

[0035]

[0036] Among them, I c_noacis the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0037] Preferably, the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction is as follows:

[0038]

[0039] in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

[0040] Preferably, after judging whether the power grid is in a normal state or a fault state according to the power grid positive sequence voltage amplitude and the power grid voltage imbalance, the method further comprises:

[0041] When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions;

[0042] When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions;

[0043] When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

[0044] Based on the same inventive concept, the patent application of the present invention also provides a fault ride-through system for a new energy grid-connected converter under an asymmetric fault, including: a grid voltage related value calculation module, a grid operation state judgment module and an asymmetric fault ride-through module;

[0045] The grid voltage related value calculation module is used to obtain the positive and negative sequence parameters of the grid, and calculate the grid positive sequence voltage amplitude and the grid voltage imbalance according to the positive and negative sequence parameters of the grid;

[0046] The grid operation state judgment module is used to judge whether the grid is in a normal state or a fault state according to the grid positive sequence voltage amplitude and the grid voltage imbalance; the fault state includes an asymmetric fault state;

[0047] The asymmetric fault ride-through module is used to perform current limiting based on the grid fault related parameters when the grid is in the asymmetric fault state, calculate the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state, and perform feedback control according to the limiting values ​​of the positive and negative sequence current instructions to complete fault ride-through.

[0048] Preferably, the grid voltage related value calculation module includes:

[0049] A power grid positive and negative sequence parameter acquisition submodule is used to obtain the positive and negative sequence parameters of the power grid through a phase-locked loop with a positive and negative sequence separation function;

[0050] A grid positive and negative sequence voltage amplitude calculation submodule, used to calculate the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude according to the grid positive and negative sequence parameters;

[0051] A grid voltage imbalance calculation submodule, used to calculate the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude;

[0052] Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component.

[0053] Preferably, the fault state further includes: a high voltage fault state and a three-phase symmetrical fault state; the power grid operation state judgment module includes:

[0054] A normal state confirmation submodule, used for confirming that the power grid is in a normal state when the power grid positive sequence voltage amplitude is within a preset power grid positive sequence voltage amplitude range;

[0055] A high voltage fault state confirmation submodule, used for confirming that the power grid is in the high voltage fault state when the positive sequence voltage amplitude of the power grid is greater than the maximum value of the positive sequence voltage amplitude interval of the power grid;

[0056] A three-phase symmetrical fault state submodule, for when the positive sequence voltage amplitude of the power grid is less than the minimum value of the positive sequence voltage amplitude interval of the power grid, and the power grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit value, the power grid is in the three-phase symmetrical fault state;

[0057] The asymmetric fault state confirmation submodule is configured to determine that when the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval and the grid voltage imbalance is greater than the symmetric fault imbalance limit, the grid is in the asymmetric fault state.

[0058] Preferably, the calculation formula of the positive and negative sequence current instructions includes: the calculation formula of the positive sequence current q axis instruction, the calculation formula of the negative sequence current q axis instruction, the calculation formula of the negative sequence current d axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d axis instruction, the positive sequence current q axis instruction, the negative sequence current d axis instruction and the negative sequence current q axis instruction; the asymmetric fault ride-through module is used to:

[0059] When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode;

[0060] Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current;

[0061] According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction;

[0062] The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through;

[0063] Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

[0064] Preferably, the calculation formula of the A-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0065]

[0066] Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0067] Preferably, the calculation formula of the B-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0068]

[0069] Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0070] Preferably, the calculation formula of the C phase current amplitude when the positive sequence active current is not injected is as follows:

[0071]

[0072] Among them, I c_noac is the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0073] Preferably, the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction is as follows:

[0074]

[0075] in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

[0076] Preferably, it also includes: a fault ride-through module other than asymmetric fault, which is used to:

[0077] When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions;

[0078] When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions;

[0079] When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

[0080] Based on the same inventive concept, the patent application of the present invention also provides an electronic device, comprising: at least one processor and a memory; the memory and the processor are connected via a bus;

[0081] The memory is used to store one or more programs;

[0082] When the one or more programs are executed by the at least one processor, a method for fault ride-through of a new energy grid-connected converter under an asymmetric fault as described above is implemented.

[0083] Based on the same inventive concept, the patent application of the present invention also provides a readable storage medium on which an execution program is stored. When the execution program is executed, a method for fault crossing of a new energy grid-connected converter under an asymmetric fault as described above is implemented.

[0084] Compared with the closest prior art, the patent application of this invention has the following beneficial effects:

[0085] The patent application of the present invention provides a method and system for fault riding of a new energy grid-connected converter under an asymmetric fault, including: obtaining positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid; judging whether the power grid is in a normal state or a fault state according to the positive sequence voltage amplitude and the unbalance degree of the power grid voltage; the fault state includes an asymmetric fault state; when the power grid is in the asymmetric fault state, based on the power grid fault-related parameters, the current is limited by using the calculation formula of the positive and negative sequence current instructions under the asymmetric fault state. The limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state are calculated, and feedback control is performed according to the limiting values ​​of the positive and negative sequence current instructions to complete fault crossing; the limiting values ​​of the positive and negative sequence current instructions in the present invention are calculated according to the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state, and the current is limited in the calculation formula of the positive and negative sequence current instructions, thereby ensuring that the positive sequence reactive current, negative sequence reactive current, and positive sequence active current control targets can be met to the greatest extent on the premise of ensuring that the converter does not overcurrent, thereby improving the support capacity for the power grid during the fault period. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 A schematic flow chart of a fault ride-through method for a new energy grid-connected converter under an asymmetric fault provided in the patent application of the present invention;

[0087] Figure 2 A schematic diagram of a fault ride-through system for a new energy grid-connected converter under an asymmetric fault provided in the patent application of the present invention;

[0088] Figure 3 A schematic diagram of the structure of an electronic device provided for the patent application of the present invention. DETAILED DESCRIPTION

[0089] The specific implementation methods of the patent application of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0090] Embodiment 1:

[0091] The present invention patent application provides a method for fault ride-through of a new energy grid-connected converter under asymmetric fault. Figure 1 As shown, including:

[0092] Step 1: Obtaining positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid;

[0093] Step 2: judging whether the power grid is in a normal state or a fault state according to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage; the fault state includes an asymmetric fault state;

[0094] Step 3: When the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the current is limited by using the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state, and the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state are calculated. Feedback control is performed according to the limiting values ​​of the positive and negative sequence current instructions to complete fault crossing.

[0095] The above step 1 obtains the positive and negative sequence parameters of the power grid, and calculates the positive sequence voltage amplitude and the power grid voltage imbalance according to the positive and negative sequence parameters of the power grid, including:

[0096] The positive and negative sequence parameters of the power grid are obtained through a phase-locked loop with positive and negative sequence separation function;

[0097] For example, the new energy grid-connected converter obtains the positive sequence voltage phase θ of the power grid through a phase-locked loop with positive and negative sequence separation function + , d-axis component of the grid positive sequence voltage q-axis component of grid positive sequence voltage Output positive sequence current d-axis component Output positive sequence current q-axis component Get the grid negative sequence voltage phase θ - , d-axis component of grid negative sequence voltage q-axis component of negative sequence voltage of power grid Output negative sequence current d-axis component Output negative sequence current q-axis component

[0098] Calculating the positive-sequence voltage amplitude and the negative-sequence voltage amplitude of the power grid according to the positive- and negative-sequence parameters of the power grid;

[0099] For example, the positive sequence voltage amplitude of the power grid The calculation formula is as follows:

[0100]

[0101] in, is the positive sequence voltage amplitude of the power grid, is the d-axis component of the grid positive sequence voltage, is the q-axis component of the grid positive sequence voltage, U nis the rated phase voltage amplitude of the power grid;

[0102] Negative sequence voltage amplitude of power grid The calculation formula is as follows:

[0103]

[0104] in, is the negative sequence voltage amplitude of the power grid, is the d-axis component of the negative sequence voltage of the power grid, is the q-axis component of the negative sequence voltage of the power grid, U n is the rated phase voltage amplitude of the power grid;

[0105] Calculating the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude;

[0106] For example, the calculation formula of the grid voltage unbalance ε is as follows:

[0107]

[0108] Among them, ε is the unbalance degree of grid voltage, is the negative sequence voltage amplitude of the power grid, is the positive sequence voltage amplitude of the power grid;

[0109] Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component; the present invention calculates the grid positive-sequence voltage amplitude and grid voltage imbalance based on the grid positive and negative sequence parameters, providing judgment data support for subsequent judgment of the grid operation status.

[0110] The step 2 described above of judging whether the power grid is in a normal state or a fault state according to the power grid positive sequence voltage amplitude and the power grid voltage imbalance includes:

[0111] When the grid positive sequence voltage amplitude is within a preset grid positive sequence voltage amplitude range, the grid is in a normal state;

[0112] For example, determine the positive sequence voltage amplitude of the power grid Is it satisfied? If U + satisfy It is determined that there is no fault in the power grid and the power grid is in normal condition.

[0113] When the positive-sequence voltage amplitude of the power grid is greater than the maximum value of the positive-sequence voltage amplitude interval of the power grid, the power grid is in the high-voltage fault state;

[0114] For example, determine the positive sequence voltage amplitude of the power grid Is it satisfied? If U + satisfy It is determined that a high voltage fault occurs in the power grid.

[0115] When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit, the grid is in the three-phase symmetrical fault state;

[0116] For example, determine the positive sequence voltage amplitude of the power grid And whether the imbalance degree ε satisfies like and ε satisfies Determine whether a three-phase symmetrical fault occurs in the power grid, where ε limit is the symmetrical fault imbalance limit;

[0117] When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is greater than the symmetrical fault imbalance limit, the grid is in the asymmetrical fault state.

[0118] For example, determine the positive sequence voltage amplitude of the power grid And whether the imbalance degree ε satisfies like and ε satisfies Determine whether an asymmetric fault has occurred in the power grid; the present invention can determine the operating state of the power grid according to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage, so as to facilitate subsequent processing of the power grid in each state.

[0119] In one implementation, after judging whether the power grid is in a normal state or a fault state according to the power grid positive sequence voltage amplitude and the power grid voltage imbalance, the method further includes:

[0120] When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions;

[0121] For example, in normal mode, in order to suppress the three-phase current imbalance, the negative sequence current dq axis command is set to 0; the positive sequence current d axis command is set to 0. Positive sequence current q-axis command Negative sequence current d-axis command Negative sequence current q-axis command The calculation is as follows:

[0122]

[0123] in, is the positive sequence current d-axis command, is the positive sequence current q axis command, is the negative sequence current d-axis command, is the negative sequence current q axis command, is the positive sequence current d-axis command before the fault, It is the q-axis instruction of the positive sequence current before the fault;

[0124] When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions;

[0125] For example, in high voltage ride-through mode, the positive sequence current d-axis command Positive sequence current q-axis command Negative sequence current d-axis command Negative sequence current q-axis command The calculation is as follows:

[0126]

[0127] in, is the positive sequence current q axis command, is the q-axis command of the positive sequence current before the fault, K UI1 To balance the dynamic reactive current proportionality coefficient under fault conditions, is the positive sequence voltage amplitude of the power grid, I n is the rated phase current amplitude of the new energy grid-connected converter, is the positive sequence current d-axis command, is the positive sequence current d-axis command before the fault, I max is the maximum current amplitude of the new energy grid-connected converter, is the negative sequence current d-axis command, is the negative sequence current q axis instruction;

[0128] When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

[0129] For example, the new energy grid-connected converter operates in the symmetrical fault low voltage ride-through mode; in the symmetrical fault low voltage ride-through mode, the positive sequence current d-axis instruction Positive sequence current q-axis command Negative sequence current d-axis command Negative sequence current q-axis command The calculation is as follows:

[0130]

[0131] in, is the positive sequence current d-axis command, is the positive sequence current q axis command, is the negative sequence current d-axis command, is the negative sequence current q axis command, is the q-axis command of the positive sequence current before the fault, K UI1 To balance the dynamic reactive current proportionality coefficient under fault conditions, is the positive sequence voltage amplitude of the power grid, I n is the rated phase current amplitude of the new energy grid-connected converter, is the positive sequence current d-axis command before the fault, I max is the maximum current amplitude of the new energy grid-connected converter;

[0132] The calculation formula of the positive and negative sequence current instructions in the above step 3 includes: the calculation formula of the positive sequence current q-axis instruction, the calculation formula of the negative sequence current q-axis instruction, the calculation formula of the negative sequence current d-axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d-axis instruction, the positive sequence current q-axis instruction, the negative sequence current d-axis instruction and the negative sequence current q-axis instruction; when the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state is used to perform current amplitude limit, the amplitude limit value of the positive and negative sequence current instructions in the asymmetric fault state is calculated, and feedback control is performed according to the amplitude limit value of the positive and negative sequence current instructions to complete fault crossing, including:

[0133] When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode;

[0134] For example, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode. In the asymmetric fault low voltage ride-through mode, the positive sequence current q-axis command is calculated Negative sequence current d-axis command Negative sequence current q-axis command The calculation formula is as follows:

[0135]

[0136] in, is the positive sequence current q axis command, is the negative sequence current d-axis command, is the negative sequence current q axis command, is the q-axis command of the positive sequence current before the fault, K UI2 is the dynamic reactive current proportional coefficient under unbalanced fault, is the positive sequence voltage amplitude of the power grid, I n is the rated phase current amplitude of the new energy grid-connected converter, is the negative sequence voltage amplitude of the power grid.

[0137] Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current;

[0138] According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction;

[0139] The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through;

[0140] For example, the positive sequence current d-axis command Positive sequence current q-axis command Negative sequence current d-axis command Negative sequence current q-axis command As the reference value, the d-axis component of the output positive sequence current is Output positive sequence current q-axis component Output negative sequence current d-axis component Output negative sequence current q-axis component Feedback control is carried out to realize fault ride-through of the renewable energy grid-connected converter under unbalanced fault.

[0141] Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

[0142] In one implementation, the calculation formula of the A-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0143]

[0144] Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0145] In one implementation, the calculation formula of the B-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0146]

[0147] Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0148] In one implementation, the calculation formula of the C phase current amplitude when the positive sequence active current is not injected is as follows:

[0149]

[0150] Among them, I c_noac is the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0151] In one implementation, the calculation formula of the amplitude limit value of the positive sequence current d-axis command is as follows:

[0152]

[0153] in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

[0154] For example, the positive sequence current d-axis command is calculated based on the residual current margin When no positive sequence active current is injected, the current amplitude of any phase is greater than or equal to I max hour, Set to 0; when no positive sequence active current is injected, the amplitudes of the three-phase currents are all less than I max hour, Calculated according to the residual current margin of the phase with the largest current;

[0155] In the calculation formula of the limit value of the positive sequence current d-axis command, δ l The calculation of is as follows:

[0156]

[0157] Among them, δ l is the phase angle difference between the positive and negative sequence currents of the maximum phase in the three-phase current amplitude when no positive sequence active current is injected, θ + is the grid positive sequence voltage phase, θ -is the negative-sequence voltage phase of the power grid, l is the phase with the maximum three-phase current amplitude when the positive-sequence active current is not injected, A is phase A, B is phase B, and C is phase C; the present invention can complete the operation of three-phase current unbalanced amplitude limiting in the fault crossing method of the new energy grid-connected converter under asymmetric faults through the calculation formula of the amplitude limit value of the positive-sequence current d-axis instruction, and then, on the premise of ensuring that the converter does not overcurrent, it can meet the positive-sequence reactive current, negative-sequence reactive current, and positive-sequence active current control targets to the greatest extent, thereby improving the support capacity of the power grid during the fault period; the present invention first calculates the positive-sequence voltage amplitude, negative-sequence voltage amplitude and imbalance of the power grid , determine the type of power grid fault; secondly, according to the type of power grid fault and the grid-connected standard requirements, calculate the positive and negative sequence current instructions of the new energy grid-connected converter; then, under an asymmetric power grid fault, calculate the maximum current amplitude in the three phases according to the positive and negative sequence current instructions; finally, according to the maximum current amplitude in the three phases, limit the positive and negative sequence current instructions to obtain the positive and negative sequence current instruction limiting values. Therefore, under an unbalanced power grid fault, the present invention can limit the current instruction according to the phase with the largest current, and under the premise of ensuring that the converter does not overcurrent, the positive sequence reactive current, negative sequence reactive current, and positive sequence active current control targets are met to the greatest extent.

[0158] Embodiment 2:

[0159] Based on the same inventive concept, the present invention patent application also provides a fault ride-through system for a new energy grid-connected converter under an asymmetric fault. Figure 2 As shown, it includes: a grid voltage related value calculation module, a grid operation status judgment module and an asymmetric fault ride-through module;

[0160] The grid voltage related value calculation module is used to obtain the positive and negative sequence parameters of the grid, and calculate the grid positive sequence voltage amplitude and the grid voltage imbalance according to the positive and negative sequence parameters of the grid;

[0161] The grid operation state judgment module is used to judge whether the grid is in a normal state or a fault state according to the grid positive sequence voltage amplitude and the grid voltage imbalance; the fault state includes an asymmetric fault state;

[0162] The asymmetric fault ride-through module is used to perform current limiting based on the grid fault related parameters when the grid is in the asymmetric fault state, calculate the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state, and perform feedback control according to the limiting values ​​of the positive and negative sequence current instructions to complete fault ride-through.

[0163] Preferably, the grid voltage related value calculation module includes:

[0164] A power grid positive and negative sequence parameter acquisition submodule is used to obtain the positive and negative sequence parameters of the power grid through a phase-locked loop with a positive and negative sequence separation function;

[0165] A grid positive and negative sequence voltage amplitude calculation submodule, used to calculate the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude according to the grid positive and negative sequence parameters;

[0166] A grid voltage imbalance calculation submodule, used to calculate the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude;

[0167] Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component.

[0168] Preferably, the fault state further includes: a high voltage fault state and a three-phase symmetrical fault state; the power grid operation state judgment module includes:

[0169] A normal state confirmation submodule, used for confirming that the power grid is in a normal state when the power grid positive sequence voltage amplitude is within a preset power grid positive sequence voltage amplitude range;

[0170] A high voltage fault state confirmation submodule, used for confirming that the power grid is in the high voltage fault state when the positive sequence voltage amplitude of the power grid is greater than the maximum value of the positive sequence voltage amplitude interval of the power grid;

[0171] A three-phase symmetrical fault state submodule, for when the positive sequence voltage amplitude of the power grid is less than the minimum value of the positive sequence voltage amplitude interval of the power grid, and the power grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit value, the power grid is in the three-phase symmetrical fault state;

[0172] The asymmetric fault state confirmation submodule is configured to determine that when the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval and the grid voltage imbalance is greater than the symmetric fault imbalance limit, the grid is in the asymmetric fault state.

[0173] Preferably, the calculation formula of the positive and negative sequence current instructions includes: the calculation formula of the positive sequence current q axis instruction, the calculation formula of the negative sequence current q axis instruction, the calculation formula of the negative sequence current d axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d axis instruction, the positive sequence current q axis instruction, the negative sequence current d axis instruction and the negative sequence current q axis instruction; the asymmetric fault ride-through module is used to:

[0174] When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode;

[0175] Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current;

[0176] According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction;

[0177] The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through;

[0178] Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

[0179] Preferably, the calculation formula of the A-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0180]

[0181] Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0182] Preferably, the calculation formula of the B-phase current amplitude when the positive-sequence active current is not injected is as follows:

[0183]

[0184] Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0185] Preferably, the calculation formula of the C phase current amplitude when the positive sequence active current is not injected is as follows:

[0186]

[0187] Among them, I c_noac is the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

[0188] Preferably, the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction is as follows:

[0189]

[0190] in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

[0191] Preferably, it also includes: a fault ride-through module other than asymmetric fault, which is used to:

[0192] When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions;

[0193] When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions;

[0194] When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

[0195] Example 3

[0196] like Figure 3 As shown, the present invention also provides an electronic device, which may be a computer device, a single-chip device, an intelligent mobile device, etc. The electronic device in this embodiment may include a processor, a memory, a transceiver component, etc. The memory, the processor, and the transceiver component are connected via a bus; the memory may be used to store an execution program, and an exemplary execution program may include instructions; the processor is used to execute the instructions stored in the memory. The memory may also be used to store data, which may be called and / or modified when the instructions are executed.

[0197] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in a storage medium to implement a corresponding method flow or a corresponding function, so as to implement the steps of a method for fault crossing of a new energy grid-connected converter under an asymmetric fault in the above-mentioned embodiment.

[0198] Example 4

[0199] Based on the same inventive concept, the present invention also provides a readable storage medium, specifically an electronic device readable storage medium (Memory), which is a memory device in an electronic device for storing programs and data. It can be understood that the storage medium here can include both built-in storage media in electronic devices and, of course, extended storage media supported by electronic devices. The storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more execution programs (including program codes). It should be noted that the storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor loads and executes one or more instructions stored in the storage medium, which can implement the steps of a method for fault crossing of a new energy grid-connected converter under an asymmetric fault in the above embodiment.

[0200] It should be understood by those skilled in the art that the embodiments of the present invention patent application can be provided as methods, systems, or computer program products. Therefore, the present invention patent application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention patent application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0201] The present invention patent application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present invention patent application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0202] These computer program instructions may also be stored in a computer readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0203] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0204] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the patent application of the present invention rather than to limit its protection scope. Although the patent application of the present invention is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the patent application of the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the protection scope of the claims to be approved.

Claims

1. A fault ride-through method for a new energy grid-connected converter under an asymmetric fault, characterized in that: include: Obtaining positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid; According to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage, it is judged whether the power grid is in a normal state or a fault state; the fault state includes an asymmetric fault state; When the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the current is limited by using the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state, the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state are calculated, and feedback control is performed according to the limiting values ​​of the positive and negative sequence current instructions to complete fault crossing.

2. The method according to claim 1, characterized in that The obtaining of the positive and negative sequence parameters of the power grid, and calculating the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage according to the positive and negative sequence parameters of the power grid, comprises: The positive and negative sequence parameters of the power grid are obtained through a phase-locked loop with positive and negative sequence separation function; Calculating the positive-sequence voltage amplitude and the negative-sequence voltage amplitude of the power grid according to the positive- and negative-sequence parameters of the power grid; Calculating the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude; Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component.

3. The method according to claim 1, characterized in that The fault state also includes: a high voltage fault state and a three-phase symmetrical fault state; judging whether the power grid is in a normal state or a fault state according to the positive sequence voltage amplitude of the power grid and the unbalance degree of the power grid voltage includes: When the grid positive sequence voltage amplitude is within a preset grid positive sequence voltage amplitude range, the grid is in a normal state; When the positive-sequence voltage amplitude of the power grid is greater than the maximum value of the positive-sequence voltage amplitude interval of the power grid, the power grid is in the high-voltage fault state; When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit, the grid is in the three-phase symmetrical fault state; When the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval, and the grid voltage imbalance is greater than the symmetrical fault imbalance limit, the grid is in the asymmetrical fault state.

4. The method according to claim 3, characterized in that The calculation formula of the positive and negative sequence current instructions includes: the calculation formula of the positive sequence current q-axis instruction, the calculation formula of the negative sequence current q-axis instruction, the calculation formula of the negative sequence current d-axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d-axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d-axis instruction, the positive sequence current q-axis instruction, the negative sequence current d-axis instruction and the negative sequence current q-axis instruction; when the power grid is in the asymmetric fault state, based on the power grid fault related parameters, the calculation formula of the positive and negative sequence current instructions in the asymmetric fault state is used to perform current amplitude limit, the amplitude limit value of the positive and negative sequence current instructions in the asymmetric fault state is calculated, and feedback control is performed according to the amplitude limit value of the positive and negative sequence current instructions to complete fault crossing, including: When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode; Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current; According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction; The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through; Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

5. The method according to claim 4, characterized in that The calculation formula for the A phase current amplitude when no positive sequence active current is injected is as follows: Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

6. The method according to claim 4, characterized in that The calculation formula for the B phase current amplitude when no positive sequence active current is injected is as follows: Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

7. The method according to claim 4, characterized in that The calculation formula of the C phase current amplitude when no positive sequence active current is injected is as follows: Among them, I c_noac is the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

8. The method according to claim 4, characterized in that The calculation formula of the amplitude limit value of the positive sequence current d-axis command is as follows: in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

9. The method according to claim 3, characterized in that After judging whether the power grid is in a normal state or a fault state according to the power grid positive sequence voltage amplitude and the power grid voltage imbalance, the method further includes: When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions; When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions; When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

10. A fault ride-through system for a new energy grid-connected converter under asymmetric faults, characterized in that: include: Grid voltage related value calculation module, grid operation status judgment module and asymmetric fault ride-through module; The grid voltage related value calculation module is used to obtain the positive and negative sequence parameters of the grid, and calculate the grid positive sequence voltage amplitude and the grid voltage imbalance according to the positive and negative sequence parameters of the grid; The grid operation state judgment module is used to judge whether the grid is in a normal state or a fault state according to the grid positive sequence voltage amplitude and the grid voltage imbalance; the fault state includes an asymmetric fault state; The asymmetric fault ride-through module is used to perform current limiting based on grid fault related parameters when the power grid is in the asymmetric fault state, calculate the limiting values ​​of the positive and negative sequence current instructions of the new energy grid-connected converter in the asymmetric fault state, and perform feedback control according to the limiting values ​​of the positive and negative sequence current instructions to complete fault ride-through.

11. The system according to claim 10, characterized in that The grid voltage related value calculation module comprises: A power grid positive and negative sequence parameter acquisition submodule is used to obtain the positive and negative sequence parameters of the power grid through a phase-locked loop with a positive and negative sequence separation function; A grid positive and negative sequence voltage amplitude calculation submodule, used to calculate the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude according to the grid positive and negative sequence parameters; A grid voltage imbalance calculation submodule, used to calculate the grid voltage imbalance according to the grid positive sequence voltage amplitude and the grid negative sequence voltage amplitude; Among them, the voltage and current parameters include at least one or more of the following: grid positive-sequence voltage phase, grid positive-sequence voltage d-axis component, grid positive-sequence voltage q-axis component, output positive-sequence current d-axis component, output positive-sequence current q-axis component, grid negative-sequence voltage phase, grid negative-sequence voltage d-axis component, grid negative-sequence voltage q-axis component, output negative-sequence current d-axis component and output negative-sequence current q-axis component.

12. The system according to claim 10, characterized in that The fault state also includes: a high voltage fault state and a three-phase symmetrical fault state; the power grid operation state judgment module includes: A normal state confirmation submodule, used for confirming that the power grid is in a normal state when the power grid positive sequence voltage amplitude is within a preset power grid positive sequence voltage amplitude range; A high voltage fault state confirmation submodule, used for confirming that the power grid is in the high voltage fault state when the positive sequence voltage amplitude of the power grid is greater than the maximum value of the positive sequence voltage amplitude interval of the power grid; A three-phase symmetrical fault state submodule, for when the positive sequence voltage amplitude of the power grid is less than the minimum value of the positive sequence voltage amplitude interval of the power grid, and the power grid voltage imbalance is less than or equal to the symmetrical fault imbalance limit value, the power grid is in the three-phase symmetrical fault state; The asymmetric fault state confirmation submodule is configured to determine that when the grid positive sequence voltage amplitude is less than the minimum value of the grid positive sequence voltage amplitude interval and the grid voltage imbalance is greater than the symmetric fault imbalance limit, the grid is in the asymmetric fault state.

13. The system of claim 12, wherein: The calculation formula of the positive and negative sequence current instructions includes: the calculation formula of the positive sequence current q axis instruction, the calculation formula of the negative sequence current q axis instruction, the calculation formula of the negative sequence current d axis instruction and the calculation formula of the amplitude limit value of the positive sequence current d axis instruction; the positive and negative sequence current instructions include: the amplitude limit value of the positive sequence current d axis instruction, the positive sequence current q axis instruction, the negative sequence current d axis instruction and the negative sequence current q axis instruction; the asymmetric fault ride-through module is used to: When the power grid is in the asymmetric fault state, the new energy grid-connected converter operates in the asymmetric fault low voltage ride-through mode, and based on the power grid fault related parameters, the positive sequence current q-axis instruction calculation formula, the negative sequence current q-axis instruction calculation formula and the negative sequence current d-axis instruction calculation formula are used to calculate the positive sequence current q-axis instruction, the negative sequence current q-axis instruction and the negative sequence current d-axis instruction in the asymmetric fault low voltage ride-through mode; Based on the positive-sequence current q-axis command, the negative-sequence current q-axis command, the grid positive-sequence voltage phase, and the grid negative-sequence voltage phase, the three-phase current amplitude is calculated without injecting the positive-sequence active current; According to the maximum current amplitude of one phase among the three-phase current amplitudes when no positive-sequence active current is injected and the maximum current amplitude of the new energy grid-connected converter, the calculation formula of the limit value of the positive-sequence current d-axis instruction is used to obtain the limit value of the positive-sequence current d-axis instruction; The positive-sequence current q-axis instruction, the negative-sequence current q-axis instruction, the negative-sequence current d-axis instruction and the amplitude limit value of the positive-sequence current d-axis instruction are used as reference values ​​to respectively perform feedback control on the output positive-sequence current d-axis component, the output positive-sequence current q-axis component, the output negative-sequence current d-axis component and the output negative-sequence current q-axis component to complete fault ride-through; Among them, the power grid fault related parameters include at least one or more of the following: the positive-sequence current d-axis instruction before the fault, the positive-sequence current q-axis instruction before the fault, the dynamic reactive current proportional coefficient under balanced fault, the maximum current amplitude of the new energy grid-connected converter, the rated phase current amplitude of the new energy grid-connected converter, the symmetrical fault imbalance limit, and the dynamic reactive current proportional coefficient under unbalanced fault; the three-phase current amplitude without injecting positive-sequence active current includes at least one or more of the following: the A-phase current amplitude without injecting positive-sequence active current, the B-phase current amplitude without injecting positive-sequence active current, and the C-phase current amplitude without injecting positive-sequence active current.

14. The system of claim 13, wherein: The calculation formula for the A phase current amplitude when no positive sequence active current is injected is as follows: Among them, I a_noac is the current amplitude of phase A without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

15. The system of claim 13, wherein: The calculation formula for the B phase current amplitude when no positive sequence active current is injected is as follows: Among them, I b_noac is the current amplitude of phase B without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

16. The system of claim 13, wherein: The calculation formula of the C phase current amplitude when no positive sequence active current is injected is as follows: Among them, I c_noac is the current amplitude of phase C without injecting positive sequence active current, is the negative sequence current q axis command, is the positive sequence current q-axis command, θ + is the grid positive sequence voltage phase, θ - is the negative sequence voltage phase of the power grid.

17. The system of claim 13, wherein: The calculation formula of the amplitude limit value of the positive sequence current d-axis command is as follows: in, is the limit value of the positive sequence current d-axis command, I a_noac is the current amplitude of phase A without injecting positive sequence active current, I b_noac is the current amplitude of phase B without injecting positive sequence active current, I c_noac is the current amplitude of phase C without injecting positive sequence active current, I max is the maximum current amplitude of the new energy grid-connected converter, I l_noac is the maximum current amplitude of one phase among the three-phase current amplitudes when no positive sequence active current is injected, δ l It is the phase angle difference between the maximum positive and negative sequence currents in the three-phase current amplitude without injecting positive sequence active current.

18. The system of claim 12, wherein: Also includes: Fault ride-through modules other than asymmetric faults are used for: When the power grid is in the normal state, the new energy grid-connected converter operates in the normal mode, calculates the positive and negative sequence current instructions in the normal mode, and completes the fault ride-through according to the positive and negative sequence current instructions; When the power grid is in the high voltage fault state, the new energy grid-connected converter operates in the high voltage ride-through mode, and based on the grid fault related parameters, the positive and negative sequence current instructions in the high voltage ride-through mode are calculated using the calculation formula, and the fault ride-through is completed according to the positive and negative sequence current instructions; When the power grid is in the three-phase symmetrical fault state, the new energy grid-connected converter operates in a symmetrical fault low voltage ride-through mode. Based on the grid fault related parameters, the calculation formula of the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode is adopted to calculate the positive and negative sequence current instructions of the symmetrical fault low voltage ride-through mode, and complete the fault ride-through according to the positive and negative sequence current instructions.

19. An electronic device, characterized in that: include: at least one processor and memory; The memory and the processor are connected via a bus; The memory is used to store one or more programs; When the one or more programs are executed by the at least one processor, a fault ride-through method for a new energy grid-connected converter under an asymmetric fault as described in any one of claims 1 to 9 is implemented.

20. A readable storage medium, characterized in that: An execution program is stored thereon, and when the execution program is executed, a fault ride-through method for a new energy grid-connected converter under an asymmetric fault as described in any one of claims 1 to 9 is implemented.

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