Current-limiting control method and device for network construction type energy storage converter

Abstract

The invention is suitable for the technical field of electric power, and provides a current-limiting control method and device for a network construction type energy storage converter, and the method comprises the steps: generating the virtual internal potential of the network construction type energy storage converter according to the operation parameters of a power grid; when the power grid breaks down, whether the output current of the grid-forming type energy storage converter exceeds a current rated value or not is judged, and self-adaptive virtual resistance and self-adaptive virtual impedance are determined according to the judgment result and the virtual internal potential; wherein if the output current of the grid-forming type energy storage converter exceeds the current rated value, the fault transient current is limited according to the self-adaptive virtual resistance in the first three power frequency periods of the beginning of the fault, and the fault steady-state current is limited and the power angle curve is remodeled to improve the power angle stability in the later fault time according to the self-adaptive virtual resistance; and calculating a current reference value of the power grid and a voltage reference value of a grid-connected point according to the self-adaptive virtual impedance, and performing switching control on the grid-forming type energy storage converter. According to the invention, safe and stable operation of the network-forming type energy storage converter can be ensured.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and in particular relates to a current limiting control method and device for a grid-type energy storage converter. Background Art

[0002] The construction of new power systems is advancing rapidly. New energy generation based on power electronic converters is gradually replacing traditional synchronous generators. The power system presents the "double high" characteristics of a high proportion of renewable energy and a high proportion of power electronics. New energy generation is random, intermittent and volatile, which leads to serious frequency problems in the power grid. The high proportion of power electronic equipment has led to a significant decrease in the frequency and voltage support capabilities of the power grid, which will bring great challenges to the stability of the power grid. Energy storage has the function of smoothing power fluctuations and peak shaving. The grid-type energy storage converter can also be equivalent to a controllable voltage source according to its control strategy, and has good support capabilities for the voltage and frequency of the power grid. In addition, the grid-type energy storage converter also has good robustness to weak power grids, and is regarded as the most promising solution to solve the frequency and voltage stability of new power systems with "double high" characteristics.

[0003] However, power electronic components are fragile, and their overcurrent capacity is only 1.2-2.0 times the rated current. The grid-type energy storage inverter has a serious overcurrent problem after the grid voltage drops. In addition, the grid-type energy storage inverter simulates the operating characteristics of a synchronous generator, and there is a risk of losing synchronization with the grid after a fault, which will seriously threaten the safe and stable operation of the grid-type energy storage inverter. Therefore, it is urgent to study the current limiting control method of the grid-type energy storage inverter to ensure its safe and stable operation. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a current limiting control method and device for a grid-type energy storage converter to ensure the safe and stable operation of the grid-type energy storage converter.

[0005] A first aspect of an embodiment of the present invention provides a current limiting control method for a grid-type energy storage converter, comprising:

[0006] Obtaining the operating parameters of the power grid;

[0007] According to the operating parameters, a virtual internal potential of the grid-connected energy storage converter is generated by utilizing a virtual synchronous machine control principle;

[0008] When a fault occurs in the power grid, it is determined whether the output current of the grid-type energy storage converter exceeds the allowable current rating, and the adaptive virtual resistance and the adaptive virtual impedance are determined according to the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage converter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time and the power angle curve is reshaped to improve the power angle stability;

[0009] According to the adaptive virtual impedance, the current reference value of the power grid and the grid connection point voltage reference value are calculated, and the switching of the grid-connected energy storage converter is controlled.

[0010] In combination with the first aspect, in a possible implementation manner of the first aspect, determining the adaptive virtual resistance and the adaptive virtual impedance according to the judgment result and the virtual internal potential includes:

[0011] If the output current of the grid-type energy storage converter does not exceed the current rated value, determine that the first virtual resistance and the first virtual impedance are both 0, and select the maximum value of the first virtual resistance and the preset steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the first virtual impedance and the preset steady-state virtual impedance as the adaptive virtual impedance;

[0012] If the output current of the grid-type energy storage converter exceeds the current rating, the second virtual resistance is determined in the first three power frequency cycles after the fault begins. Determine the second virtual impedance to be 0, select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual impedance; during the remaining fault time, determine the third virtual resistance R vadp2 =k R (I s -I n ), determine the third virtual impedance X vadp2 =R vadp2 / σ R / X , selecting the maximum value between the third virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and selecting the maximum value between the third virtual impedance and the steady-state virtual impedance as the adaptive virtual impedance;

[0013] Where E is the virtual internal potential of the grid-type energy storage converter, U g is the effective value of the grid-connected point voltage, δ is the power angle of the grid-connected energy storage converter, I s is the effective value of the output current of the grid-type energy storage converter, I nis the current rating of the grid-type energy storage converter, I lim is the current limit value of the grid-type energy storage converter, k R is the adaptive virtual resistance proportional coefficient, σ R / X is the virtual resistance-to-inductance ratio.

[0014] In combination with the first aspect, in a possible implementation manner of the first aspect, the adaptive virtual resistance proportional coefficient is calculated by the following formula:

[0015]

[0016] b=2(I lim -I n )X g σ R / X ;

[0017]

[0018] Among them, X g is the equivalent impedance of the power grid.

[0019] In combination with the first aspect, in a possible implementation manner of the first aspect, reshaping the power angle curve to improve power angle stability includes:

[0020] According to the grid parameters and the relevant parameters of the grid-type energy storage converter, solving the maximum output active power expression of the grid-type energy storage converter after the grid voltage drops;

[0021] According to the maximum output active power expression, solving the derivative of active power with respect to the resistance-inductance ratio;

[0022] If the derivative of the active power with respect to the resistance-inductance ratio is greater than 0, the virtual resistance-inductance ratio σ R / X =σ R / X +Δσ R / X If the derivative of the active power with respect to the resistance-inductance ratio is less than 0, the virtual resistance-inductance ratio σ R / X =σ R / X -Δ σR / X ; If the derivative of the active power with respect to the resistance-inductance ratio is equal to 0, then the virtual resistance-inductance ratio σ R / X constant.

[0023] In combination with the first aspect, in a possible implementation manner of the first aspect, the maximum output active power expression is:

[0024]

[0025] In combination with the first aspect, in a possible implementation manner of the first aspect, the derivative of the active power with respect to the resistance-inductance ratio is:

[0026]

[0027] Among them, R v is the adaptive virtual resistance, X v is the adaptive virtual impedance.

[0028] In combination with the first aspect, in a possible implementation manner of the first aspect, before determining the adaptive virtual impedance, it also includes: performing low-pass filtering on the first virtual impedance, the second virtual impedance, and the third virtual impedance.

[0029] In combination with the first aspect, in a possible implementation of the first aspect, the operating parameters of the power grid include: a three-phase power grid voltage and a voltage and current at a three-phase grid connection point;

[0030] The method of generating a virtual internal potential of a grid-connected energy storage converter by using a virtual synchronous machine control principle according to the operating parameters includes:

[0031] Clark transformation and Park transformation are performed on the sampled values ​​of voltage and current to obtain the d-axis and q-axis components of voltage and current;

[0032] According to the d-axis and q-axis components of voltage and current, the active power and reactive power output by the grid-type energy storage converter are calculated;

[0033] According to the active power and the reactive power, a voltage angle and an effective value reference value of a virtual internal potential are generated by utilizing a virtual synchronous machine control principle, and a virtual internal potential vector is synthesized.

[0034] In combination with the first aspect, in a possible implementation manner of the first aspect, the switching control of the grid-type energy storage converter includes:

[0035] According to the current reference value of the power grid and the voltage reference value of the grid connection point, control parameters of the sliding mode control are set, and the switching of the grid-connected energy storage converter is controlled based on the control parameters.

[0036] A second aspect of an embodiment of the present invention provides a current limiting control device for a grid-type energy storage converter, comprising:

[0037] An acquisition module, used to acquire the operating parameters of the power grid;

[0038] A calculation module, used to generate a virtual internal potential of a grid-type energy storage converter using a virtual synchronous machine control principle according to the operating parameters;

[0039] A processing module is used to determine whether the output current of the grid-type energy storage converter exceeds the allowable current rating when a power grid fault occurs, and determine the adaptive virtual resistance and the adaptive virtual impedance according to the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage converter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time and the power angle curve is reshaped to improve the power angle stability;

[0040] The control module is used to calculate the current reference value and the grid connection point voltage reference value of the grid according to the adaptive virtual impedance, and to perform switch control on the grid-connected energy storage converter.

[0041] In conjunction with the second aspect, in a possible implementation manner of the second aspect, the processing module is specifically configured to:

[0042] If the output current of the grid-type energy storage converter does not exceed the current rated value, determine that the first virtual resistance and the first virtual impedance are both 0, and select the maximum value of the first virtual resistance and the preset steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the first virtual impedance and the preset steady-state virtual impedance as the adaptive virtual impedance;

[0043] If the output current of the grid-type energy storage converter exceeds the current rating, the second virtual resistance is determined in the first three power frequency cycles after the fault begins. Determine the second virtual impedance to be 0, select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual impedance; during the remaining fault time, determine the third virtual resistance R vadp2 =k R (I s -I n ), determine the third virtual impedance X vadp2 =R vadp2 / σ R / X , selecting the maximum value between the third virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and selecting the maximum value between the third virtual impedance and the steady-state virtual impedance as the adaptive virtual impedance;

[0044] Where E is the virtual internal potential of the grid-type energy storage converter, U g is the effective value of the grid-connected point voltage, δ is the power angle of the grid-connected energy storage converter, I s is the effective value of the output current of the grid-type energy storage converter, I n is the current rating of the grid-type energy storage converter, Ilim is the current limit value of the grid-type energy storage converter, k R is the adaptive virtual resistance proportional coefficient, σ R / X is the virtual resistance-to-inductance ratio.

[0045] In combination with the second aspect, in a possible implementation manner of the second aspect, the adaptive virtual resistance proportional coefficient is calculated by the following formula:

[0046]

[0047] b=2(I lim -I n )X g σ R / X ;

[0048]

[0049] Among them, X g is the equivalent impedance of the power grid.

[0050] In conjunction with the second aspect, in a possible implementation manner of the second aspect, reshaping the power angle curve to improve power angle stability includes:

[0051] According to the grid parameters and the relevant parameters of the grid-type energy storage converter, solving the maximum output active power expression of the grid-type energy storage converter after the grid voltage drops;

[0052] According to the maximum output active power expression, solving the derivative of active power with respect to the resistance-inductance ratio;

[0053] If the derivative of the active power with respect to the resistance-inductance ratio is greater than 0, the virtual resistance-inductance ratio σ R / X =σ R / X +Δσ R / X ; If the derivative of the active power with respect to the resistance-inductance ratio is less than 0, then the virtual resistance-inductance ratio σ R / X =σ R / X -Δ σR / X ; If the derivative of the active power with respect to the resistance-inductance ratio is equal to 0, then the virtual resistance-inductance ratio σ R / X constant.

[0054] In combination with the second aspect, in a possible implementation manner of the second aspect, the maximum output active power expression is:

[0055]

[0056] In combination with the second aspect, in a possible implementation manner of the second aspect, the derivative of the active power with respect to the resistance-inductance ratio is:

[0057]

[0058] Among them, R v is the adaptive virtual resistance, X v is the adaptive virtual impedance.

[0059] In combination with the second aspect, in a possible implementation manner of the second aspect, before determining the adaptive virtual impedance, the processing module is further used to: perform low-pass filtering on the first virtual impedance, the second virtual impedance, and the third virtual impedance.

[0060] In combination with the second aspect, in a possible implementation of the second aspect, the operating parameters of the power grid include: a three-phase power grid voltage and a voltage and current at a three-phase grid connection point;

[0061] The calculation module is specifically used for:

[0062] Clark transformation and Park transformation are performed on the sampled values ​​of voltage and current to obtain the d-axis and q-axis components of voltage and current;

[0063] According to the d-axis and q-axis components of voltage and current, the active power and reactive power output by the grid-type energy storage converter are calculated;

[0064] According to the active power and the reactive power, a voltage angle and an effective value reference value of a virtual internal potential are generated by utilizing a virtual synchronous machine control principle, and a virtual internal potential vector is synthesized.

[0065] In conjunction with the second aspect, in a possible implementation manner of the second aspect, the control module is specifically configured to:

[0066] According to the current reference value of the power grid and the voltage reference value of the grid connection point, control parameters of the sliding mode control are set, and the switching of the grid-connected energy storage converter is controlled based on the control parameters.

[0067] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0068] In the embodiment of the present invention, when a fault occurs in the power grid, if the output current of the grid-type energy storage converter exceeds the allowable current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles of the fault, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time. The proposed adaptive virtual resistance technology solves the problem of transient overcurrent caused by the voltage source characteristics of the grid-type energy storage converter during the voltage drop period, and avoids the grid-type converter from being impacted by transient overcurrent. The proposed adaptive virtual impedance technology solves the problem of inaccurate fault steady-state current limiting, avoids overcurrent of the grid-type energy storage converter, and maximizes the efficiency of the overload capacity of the grid-type energy storage converter, thereby ensuring the safe operation of the grid-type energy storage converter. In addition, under the premise of giving priority to the fault current limiting of the grid-type energy storage converter, the power angle curve is reshaped, and the power angle stability of the grid-type energy storage converter is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0070] Figure 1 The following is a schematic diagram of the implementation process of the current limiting control method of the grid-type energy storage converter provided by the embodiment of the present invention. Figure 1 ;

[0071] Figure 2 The control logic diagram of the current limiting control method of the grid-type energy storage converter provided by the embodiment of the present invention is Figure 1 ;

[0072] Figure 3 The control logic diagram of the current limiting control method of the grid-type energy storage converter provided by the embodiment of the present invention is Figure 2 ;

[0073] Figure 4 The control logic diagram of the current limiting control method of the grid-type energy storage converter provided by the embodiment of the present invention is Figure 3 ;

[0074] Figure 5 The following is a schematic diagram of the implementation process of the current limiting control method of the grid-type energy storage converter provided by the embodiment of the present invention. Figure 2 ;

[0075] Figure 6 It is a structural schematic diagram of a current limiting control device for a grid-type energy storage converter provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0076] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0077] In order to illustrate the technical solution of the present invention, a specific embodiment is provided below for illustration.

[0078] At present, there are literatures that study the fault current limiting and power angle stability improvement methods of grid-type energy storage converters. Switching the converter control strategy from grid-type to grid-following type during a fault is an effective current limiting method, but this method introduces a phase-locked loop in the control strategy, which affects the stability of the converter in a weak grid. In order to ensure the converter's ability to support the grid frequency and voltage, the converter should maintain the grid-type synchronization mode. The current limiting methods for maintaining the grid-type synchronization mode are mainly divided into two categories: one is to limit the current with a current saturator, and the other is to limit the current with a virtual impedance. The current saturator can be divided into three categories: d-axis priority, q-axis priority, and current vector angle priority. Effective current limiting can be achieved by limiting the current reference value. However, the use of a current saturator has the risk that the converter cannot exit the current source mode after the fault ends. In addition, the three current saturators have different reshaping of the power angle curve. The power angle stability of the q-axis priority current saturator is better than that of the d-axis priority and current vector angle priority. However, the q-axis priority may have the stability problem of the q-axis voltage control losing the balance point after the fault. Virtual impedance can also be used to limit fault current. Its principle is to limit fault current by increasing the output impedance of the converter. Compared with the current saturator, the converter remains in voltage source mode. In addition, the virtual impedance method has a larger stability margin and there is no problem of power loop saturation. However, the virtual impedance current limiting method has an irreconcilable contradiction in limiting fault current and enhancing power angle stability. When the virtual impedance is selected to be large, the current limiting effect is good, but the power angle stability will deteriorate. When the virtual impedance is selected to be small, the current limiting effect is poor and the power angle stability is good. Therefore, it is urgent to study an adaptive virtual impedance current limiting method to enhance the power angle synchronization stability of the grid-type energy storage converter while ensuring the limitation of the fault current.

[0079] In view of the problem that a grid-type energy storage converter based on adaptive virtual impedance current limiting is difficult to take into account both fault current limiting and improved power angle synchronization stability when the grid voltage drops, an embodiment of the present invention provides a current limiting control method for a grid-type energy storage converter. Figure 1 This is a flowchart of the implementation of this method. Figure 2 is the logic control diagram of this method. Figure 1 and Figure 2 Provide a description, including:

[0080] Step S101, obtaining the operating parameters of the power grid.

[0081] Here, the operating parameters include: three-phase grid voltage and voltage and current of three-phase grid connection point. Figure 2 , sample the grid voltage, grid connection point voltage and current, and obtain the three-phase grid voltage u ga 、u gb 、u gc , three-phase grid voltage u sa 、u sb 、u sc and three-phase current i sa 、i sb 、i sc .

[0082] Step S102: Generate a virtual internal potential of the grid-connected energy storage converter using the virtual synchronous machine control principle according to the operating parameters.

[0083] In this embodiment, the sampled values ​​of voltage and current can be subjected to Clark transformation and Park transformation to obtain the d-axis and q-axis components u of voltage and current. sd 、u sq 、i sd and i sq Taking the grid connection point voltage as an example, Clark transformation and Park transformation are explained, and the formula is as follows:

[0084]

[0085] In the formula, u sα and u sβ Represents the α and β components of the grid-connected point voltage in the two-phase stationary coordinate system, and θ is the grid-connected point voltage phase angle, which is generated by the grid-connected converter power control loop.

[0086] Then, the active power P and reactive power Q output by the grid-connected converter are calculated as follows:

[0087]

[0088] Finally Figure 2 According to the virtual synchronous machine control principle, the voltage angle θ and the effective value reference value E of the grid-type internal potential are generated, and then the three-phase internal potential vector e is synthesized. aref 、e bref and e cref .

[0089] Step S103, when a fault occurs in the power grid, determine whether the output current of the grid-type energy storage inverter exceeds the allowable current rating, and determine the adaptive virtual resistance and adaptive virtual impedance based on the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage inverter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time and the power angle curve is reshaped to improve the power angle stability.

[0090] See also Figure 3 As shown, first determine the output current effective value I of the grid-type energy storage converter s Whether it exceeds the rated current I of the grid-connected energy storage converter n .

[0091] If the rated current is not exceeded, I s ≤I n , it is determined that the output current of the grid-type energy storage converter is not overcurrent, and the first virtual resistance R vadp =0.0, the first virtual impedance X vadp =0.0, and select the first virtual resistor R vadp and the preset steady-state virtual resistance R vss The maximum value in is the adaptive virtual resistance R v , select the first virtual impedance X vadp and the preset steady-state virtual impedance X vss The maximum value in is the adaptive virtual impedance X v . Generally, R vss =0.01pu,X vss =0.09pu, therefore, when the output current of the grid-type energy storage converter is not overcurrent, the virtual impedance uses the steady-state setting value.

[0092] If the output current of the grid-type energy storage converter exceeds the current rating, the second virtual resistor is determined in the first three power frequency cycles after the fault begins. Determine the second virtual impedance as X vadp1 =0.0, select the second virtual resistor R vadp1 and the steady-state virtual resistance R vss The maximum value in is the adaptive virtual resistance R v , select the second virtual impedance X vadp1 and the steady-state virtual impedance X vss The maximum value in is the adaptive virtual impedance X v ; During the remaining fault time, determine the third virtual resistor R vadp2 =k R (I s -I n ), determine the third virtual impedance Xvadp2 =R vadp2 / σ R / X , select the third virtual resistor R vadp2 and the steady-state virtual resistance R vss The maximum value in is the adaptive virtual resistance R v , select the third virtual impedance X vadp2 and the steady-state virtual impedance X vss The maximum value in is the adaptive virtual impedance X v Among them, E is the virtual internal potential of the grid-type energy storage converter, U g is the effective value of the grid-connected point voltage, δ is the power angle of the grid-connected energy storage converter, k R is the adaptive virtual resistance proportional coefficient, σ R / X is the virtual resistance-to-inductance ratio.

[0093] Where:

[0094]

[0095]

[0096] b=2(I lim -I n )X g σ R / X ;

[0097]

[0098] Among them, X g is the equivalent impedance of the power grid.

[0099] In the control principle of adaptive virtual impedance, a low-pass filter is also added to filter out the high-frequency components generated during the adaptive virtual impedance change process, see Figure 4 As shown, the transfer function of the low-pass filter can be expressed as:

[0100]

[0101] In the formula, ω f is the cutoff frequency of the low-pass filter, ω f =5Hz.

[0102] In this embodiment, when the fault current exceeds the current rating, an adaptive virtual resistor is used to limit the fault transient current in the first three power frequency cycles after the fault begins, and the virtual resistance-inductance ratio is set equal to 0. During the remaining fault time, an adaptive virtual impedance is used to limit the fault steady-state current and reshape the power angle curve to improve the power angle stability. The virtual resistance-inductance ratio is set to the optimal virtual resistance-inductance ratio for power angle stability.

[0103] Therefore, this embodiment designs an adaptive resistance-to-sensitivity ratio σ R / XTo reshape the power angle curve and enhance the power angle stability of the grid-connected converter, the following steps are included:

[0104] (1) According to the grid parameters and the relevant parameters E, δ, I of the grid-type energy storage converter lim ,I n ,I s , σ R / X and U g , solve the maximum output active power expression of the grid-type energy storage converter after the grid voltage drops:

[0105]

[0106] (2) According to the maximum output active power expression, solve the derivative of active power with respect to the resistance-inductance ratio:

[0107]

[0108] Among them, R v is the adaptive virtual resistance, X v is the adaptive virtual impedance.

[0109] (3) If the derivative of active power with respect to the resistance-inductance ratio is greater than 0, then the virtual resistance-inductance ratio σ R / X =σ R / X +Δσ R / X ; If the derivative of active power with respect to the resistance-inductance ratio is less than 0, then the virtual resistance-inductance ratio σ R / X =σ R / X -Δ σR / X ; If the derivative of active power with respect to the resistance-inductance ratio is equal to 0, then the virtual resistance-inductance ratio σ R / X constant.

[0110] Step S104, calculating the current reference value of the power grid and the grid connection point voltage reference value according to the adaptive virtual impedance, and performing switch control on the grid-connected energy storage converter.

[0111] In this embodiment, the proposed grid-type energy storage converter control method has no current inner loop, and the reference current is tracked based on sliding mode control. The current reference value can be calculated based on the virtual impedance method, and the grid connection point voltage reference value can be calculated based on the virtual impedance method. The current reference value can directly output an on-off signal after sliding mode control and hysteresis modulation to control the on-off of the switch tube of the power device.

[0112] The specific steps are as follows:

[0113] (1) Calculate the current reference value based on the virtual impedance value calculated above:

[0114]

[0115] (2) The grid connection point voltage reference value is calculated based on Kirchhoff's voltage law and virtual impedance. The specific calculation formula is as follows:

[0116] u sref =e ref -Z v i s

[0117] (3) Set the sliding mode control sliding surface as:

[0118] S=αx 1 +x 2 +βx 3

[0119] In the formula, α=1400, β=13000.

[0120] (4) Set the sliding mode control approach rate as:

[0121]

[0122] Where +h and -h are the upper and lower bounds of the hysteresis comparison link designed to avoid high switching frequency.

[0123] (5) Set the sliding mode control rate to u is the on-off signal of the switch tube. Controlling the on-off of the switch tube based on the on-off signal can realize the closed-loop control of the proposed control strategy.

[0124] In combination with the above content, an overall control process of this embodiment can be seen in Figure 5 As shown. The present invention proposes an adaptive virtual resistance technology, which solves the problem of transient overcurrent caused by the voltage source characteristics of the grid-type energy storage inverter during voltage drops, and avoids the grid-type energy storage inverter from being impacted by transient overcurrent. The problem of inaccurate steady-state current limiting during faults is solved, and while avoiding overcurrent of the grid-type energy storage inverter, the overload capacity of the grid-type energy storage inverter is utilized with maximum efficiency, ensuring the safe operation of the grid-type energy storage inverter. By reshaping the power angle curve of the grid-type energy storage inverter on the basis of the proposed adaptive virtual impedance current limiting method, it is ensured that the grid-type energy storage inverter can output active power at its maximum capacity during grid voltage drops, and the power angle stability of the grid-type energy storage inverter is improved while taking into account fault current limiting.

[0125] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0126] Figure 6 Schematic diagram of the structure of a current limiting control device 60 for a grid-type energy storage converter provided in an embodiment of the present invention, including:

[0127] The acquisition module 61 is used to acquire the operating parameters of the power grid.

[0128] The calculation module 62 is used to generate the virtual internal potential of the grid-connected energy storage converter according to the operating parameters by using the virtual synchronous machine control principle.

[0129] The processing module 63 is used to determine whether the output current of the grid-type energy storage inverter exceeds the allowable current rating when a power grid fault occurs, and determine the adaptive virtual resistance and the adaptive virtual impedance based on the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage inverter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time and the power angle curve is reshaped to improve the power angle stability.

[0130] The control module 64 is used to calculate the current reference value of the power grid and the grid connection point voltage reference value according to the adaptive virtual impedance, and to perform switching control on the grid-connected energy storage converter.

[0131] As a possible implementation manner, the processing module 63 is specifically used for:

[0132] If the output current of the grid-type energy storage converter does not exceed the current rated value, the first virtual resistance and the first virtual impedance are determined to be 0, and the maximum value of the first virtual resistance and the preset steady-state virtual resistance is selected as the adaptive virtual resistance, and the maximum value of the first virtual impedance and the preset steady-state virtual impedance is selected as the adaptive virtual impedance;

[0133] If the output current of the grid-type energy storage converter exceeds the current rating, the second virtual resistor is determined in the first three power frequency cycles after the fault begins. Determine the second virtual impedance to be 0, select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual impedance; during the remaining fault time, determine the third virtual resistance R vadp2 =k R (I s -I n ), determine the third virtual impedance X vadp2 =R vadp2 / σ R / X , selecting the maximum value between the third virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and selecting the maximum value between the third virtual impedance and the steady-state virtual impedance as the adaptive virtual impedance;

[0134] Where E is the virtual internal potential of the grid-type energy storage converter, U gis the effective value of the grid-connected point voltage, δ is the power angle of the grid-connected energy storage converter, I s is the effective value of the output current of the grid-type energy storage converter, I n is the current rating of the grid-type energy storage converter, I lim is the current limit value of the grid-type energy storage converter, k R is the adaptive virtual resistance proportional coefficient, σ R / X is the virtual resistance-to-inductance ratio.

[0135] As a possible implementation, the adaptive virtual resistance proportionality factor is calculated by the following formula:

[0136]

[0137] b=2(I lim -I n )X g σ R / X ;

[0138]

[0139] Among them, X g is the equivalent impedance of the power grid.

[0140] As a possible implementation method, reshaping the power angle curve can improve the power angle stability, including:

[0141] According to the grid parameters and the related parameters of the grid-type energy storage converter, the maximum output active power expression of the grid-type energy storage converter after the grid voltage drops is solved;

[0142] According to the expression of maximum output active power, solve the derivative of active power with respect to resistance-inductance ratio;

[0143] If the derivative of active power with respect to the resistance-inductance ratio is greater than 0, the virtual resistance-inductance ratio σ R / X =σ R / X +Δσ R / X ; If the derivative of active power with respect to the resistance-inductance ratio is less than 0, then the virtual resistance-inductance ratio σ R / X =σ R / X -Δ σR / X ; If the derivative of active power with respect to the resistance-inductance ratio is equal to 0, then the virtual resistance-inductance ratio σ R / X constant.

[0144] As a possible implementation method, the maximum output active power expression is:

[0145]

[0146] As a possible implementation, the derivative of active power with respect to the resistance-inductance ratio is:

[0147]

[0148] Among them, R v is the adaptive virtual resistance, X v is the adaptive virtual impedance.

[0149] As a possible implementation manner, before determining the adaptive virtual impedance, the processing module 63 is further configured to: perform low-pass filtering on the first virtual impedance, the second virtual impedance and the third virtual impedance.

[0150] As a possible implementation method, the operating parameters of the power grid include: the voltage of the three-phase power grid and the voltage and current of the three-phase grid connection point;

[0151] The calculation module 62 is specifically used for:

[0152] Clark transformation and Park transformation are performed on the sampled values ​​of voltage and current to obtain the d-axis and q-axis components of voltage and current;

[0153] According to the d-axis and q-axis components of voltage and current, the active power and reactive power output by the grid-type energy storage converter are calculated;

[0154] According to the active power and reactive power, the voltage angle and effective value reference value of the virtual internal potential are generated by utilizing the virtual synchronous machine control principle, and the virtual internal potential vector is synthesized.

[0155] As a possible implementation manner, the control module 64 is specifically used for:

[0156] According to the current reference value of the power grid and the voltage reference value of the grid connection point, the control parameters of the sliding mode control are set, and the switching of the grid-connected energy storage converter is controlled based on the control parameters.

[0157] In the embodiment of the present invention, when a fault occurs in the power grid, if the output current of the grid-type energy storage converter exceeds the allowable current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles of the fault, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time. The proposed adaptive virtual resistance technology solves the problem of transient overcurrent caused by the voltage source characteristics of the grid-type energy storage converter during the voltage drop period, and avoids the grid-type converter from being impacted by transient overcurrent. The proposed adaptive virtual impedance technology solves the problem of inaccurate fault steady-state current limiting, avoids overcurrent of the grid-type energy storage converter, and maximizes the efficiency of the overload capacity of the grid-type energy storage converter, thereby ensuring the safe operation of the grid-type energy storage converter. In addition, under the premise of giving priority to the fault current limiting of the grid-type energy storage converter, the power angle curve is reshaped, and the power angle stability of the grid-type energy storage converter is enhanced.

[0158] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0159] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0160] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned embodiments of the current limiting control method of each grid-type energy storage converter. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0161] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A current limiting control method for a grid-type energy storage converter, characterized in that: include: Acquire the operating parameters of the power grid; and generate the virtual internal potential of the grid-connected energy storage converter using the virtual synchronous machine control principle according to the operating parameters; When a fault occurs in the power grid, it is determined whether the output current of the grid-type energy storage inverter exceeds the allowable current rating, and the adaptive virtual resistance and adaptive virtual impedance are determined based on the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage inverter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance during the subsequent fault time and the power angle curve is reshaped to improve the power angle stability; based on the adaptive virtual impedance, the current reference value of the power grid and the grid connection point voltage reference value are calculated, and the switching of the grid-type energy storage inverter is controlled.

2. The current limiting control method for a grid-type energy storage converter according to claim 1, characterized in that: The step of determining the adaptive virtual resistance and the adaptive virtual impedance according to the judgment result and the virtual internal potential includes: If the output current of the grid-type energy storage converter does not exceed the current rated value, determine that the first virtual resistance and the first virtual impedance are both 0, and select the maximum value of the first virtual resistance and the preset steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the first virtual impedance and the preset steady-state virtual impedance as the adaptive virtual impedance; If the output current of the grid-type energy storage converter exceeds the current rating, the second virtual resistance is determined in the first three power frequency cycles after the fault begins. Determine the second virtual impedance to be 0, select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and select the maximum value of the second virtual resistance and the steady-state virtual resistance as the adaptive virtual impedance; during the remaining fault time, determine the third virtual resistance R vadp2 =k R (I s -I n ), determine the third virtual impedance X vadp2 =R vadp2 / σ R / X , selecting the maximum value between the third virtual resistance and the steady-state virtual resistance as the adaptive virtual resistance, and selecting the maximum value between the third virtual impedance and the steady-state virtual impedance as the adaptive virtual impedance; Where E is the virtual internal potential of the grid-type energy storage converter, U g is the effective value of the grid-connected point voltage, δ is the power angle of the grid-connected energy storage converter, I s is the effective value of the output current of the grid-type energy storage converter, I n is the current rating of the grid-type energy storage converter, I lim is the current limit value of the grid-type energy storage converter, k R is the adaptive virtual resistance proportional coefficient, σ R / X is the virtual resistance-to-inductance ratio.

3. The current limiting control method for a grid-type energy storage converter according to claim 2, characterized in that: The adaptive virtual resistance proportionality coefficient is calculated by the following formula: b=2(I lim -I n )X g σ R / X ; Among them, X g is the equivalent impedance of the power grid.

4. The current limiting control method for a grid-type energy storage converter according to claim 3, characterized in that: The reshaping of the power angle curve to improve the power angle stability includes: According to the grid parameters and the relevant parameters of the grid-type energy storage converter, solving the maximum output active power expression of the grid-type energy storage converter after the grid voltage drops; According to the maximum output active power expression, solving the derivative of active power with respect to the resistance-inductance ratio; If the derivative of the active power with respect to the resistance-inductance ratio is greater than 0, the virtual resistance-inductance ratio σ R / X =σ R / X +Δσ R / X ; If the derivative of the active power with respect to the resistance-inductance ratio is less than 0, then the virtual resistance-inductance ratio σ R / X =σ R / X -Δ σR / X ; If the derivative of the active power with respect to the resistance-inductance ratio is equal to 0, then the virtual resistance-inductance ratio σ R / X constant.

5. The current limiting control method for a grid-type energy storage converter according to claim 4, characterized in that: The maximum output active power expression is:

6. The current limiting control method for a grid-type energy storage converter according to claim 4, characterized in that: The derivative of the active power with respect to the resistance-inductance ratio is: Among them, R v is the adaptive virtual resistance, X v is the adaptive virtual impedance.

7. The current limiting control method of a grid-type energy storage converter according to claim 2, characterized in that: Before determining the adaptive virtual impedance, the method further includes: performing low-pass filtering on the first virtual impedance, the second virtual impedance and the third virtual impedance.

8. The current limiting control method for a grid-type energy storage converter according to claim 1, characterized in that: The operating parameters of the power grid include: the voltage of the three-phase power grid and the voltage and current of the three-phase grid connection point; The method of generating a virtual internal potential of a grid-connected energy storage converter by using a virtual synchronous machine control principle according to the operating parameters includes: Clark transformation and Park transformation are performed on the sampled values ​​of voltage and current to obtain the d-axis and q-axis components of voltage and current; According to the d-axis and q-axis components of voltage and current, the active power and reactive power output by the grid-type energy storage converter are calculated; According to the active power and the reactive power, a voltage angle and an effective value reference value of a virtual internal potential are generated by utilizing a virtual synchronous machine control principle, and a virtual internal potential vector is synthesized.

9. The current limiting control method for a grid-type energy storage converter according to claim 1, characterized in that: The switching control of the grid-type energy storage converter includes: According to the current reference value of the power grid and the voltage reference value of the grid connection point, control parameters of the sliding mode control are set, and the switching of the grid-connected energy storage converter is controlled based on the control parameters.

10. A current limiting control device for a grid-type energy storage converter, characterized in that: include: An acquisition module, used to acquire the operating parameters of the power grid; A calculation module, used to generate a virtual internal potential of a grid-type energy storage converter using a virtual synchronous machine control principle according to the operating parameters; A processing module is used to determine whether the output current of the grid-type energy storage converter exceeds the allowable current rating when a power grid fault occurs, and determine the adaptive virtual resistance and the adaptive virtual impedance according to the judgment result and the virtual internal potential; wherein, if the output current of the grid-type energy storage converter exceeds the current rating, the fault transient current is limited according to the adaptive virtual resistance in the first three power frequency cycles after the fault begins, and the fault steady-state current is limited according to the adaptive virtual impedance in the subsequent fault time and the power angle curve is reshaped to improve the power angle stability; The control module is used to calculate the current reference value and the grid connection point voltage reference value of the grid according to the adaptive virtual impedance, and to perform switch control on the grid-connected energy storage converter.

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