High-voltage direct-hanging net-building type energy storage transient power safety domain model construction method considering electric-thermal limit constraint

Abstract

The invention discloses a method for constructing a high-voltage direct-hanging constructed network type energy storage transient power safety domain model considering an electric-thermal limit constraint. According to the method, electric-thermal limit constraints of components of energy storage equipment, system voltage frequency safe operation constraints and small signal stability constraints are comprehensively considered, safe operation requirements of the equipment and the system are considered, and the method for calculating the power safe operation domain before and after transient disturbance when the constructed network type energy storage is connected to the complex power grid is provided. Technical guidance can be provided for safe dispatching operation of the high-voltage direct-hanging network energy storage access high-proportion new energy power system.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and energy storage technology, and in particular relates to a method for constructing a transient power security domain model for high-voltage direct-connected grid-type energy storage that considers electro-thermal limit constraints. Background Technology

[0002] High-voltage direct-connected grid-connected energy storage, as a fast-response and flexible active support resource, can be directly connected to the grid without multi-stage voltage boosting. It features fast dynamic response and strong active support capabilities, significantly improving the safety and stability of the power grid. However, the weak overcurrent and overheating capabilities of power electronic devices in grid-connected energy storage equipment limit its grid support capabilities. Furthermore, under the requirements of safe operation of system voltage and frequency, the transient safety operation boundary of grid-connected energy storage is still unclear. Therefore, it is urgent to study a method for constructing a transient power safety domain model for high-voltage direct-connected grid-connected energy storage that considers electro-thermal limit constraints.

[0003] Patent CN120850549A has established a mathematical correlation model between the overcurrent capacity requirements and the electro-thermal limit parameters of power devices during the transient process of grid-connected energy storage from the perspective of equipment safety. It provides a calculation method for the safe operating range of active and reactive current of grid-connected energy storage equipment under given overcurrent and overheating capacity requirements.

[0004] However, when grid-connected energy storage is connected to complex systems, its safe operating range will be limited by the system frequency and voltage safety offset range and affected by damped oscillation characteristics. Therefore, it is necessary to further calculate the power safe operating domain of grid-connected energy storage from the perspectives of system safety and control characteristics, taking into account the electrical-thermal limit constraints of the equipment, the system voltage and frequency safe operating constraints, and the small-signal stability constraints. This will provide guidance for the selection of operating points and parameter adjustment to better actively support the power grid during transient processes.

[0005] To address the aforementioned issues, this patent proposes a method for constructing a transient power security domain model for high-voltage direct-connected grid-connected energy storage that considers electro-thermal limit constraints. This method can provide theoretical support for the safe and stable operation of high-voltage direct-connected grid-connected energy storage in high-proportion new energy power systems. Summary of the Invention

[0006] This invention discloses a method for constructing a transient power safety domain model for high-voltage direct-connected grid-connected energy storage considering electro-thermal limit constraints. This method comprehensively considers the electro-thermal limit constraints of the energy storage device's own components, the system's voltage and frequency safety operation constraints, and small-signal stability constraints, taking into account the safety operation requirements of both the device and the system. It provides a method for calculating the power safety operation domain before and after transient disturbances when grid-connected energy storage is integrated into a complex power grid, and can provide technical guidance for the safe dispatch and operation of high-voltage direct-connected grid-connected energy storage integrated into high-proportion renewable energy power systems.

[0007] The purpose of this disclosure is achieved through the following technical solution:

[0008] A method for constructing a transient power security domain model for a high-voltage direct-connected grid-type energy storage system considering electro-thermal limit constraints, characterized in that the method includes:

[0009] Determine the topology and baseline operating parameters of the system, and set the input parameters and AC current operating point test range of the model;

[0010] Select an AC current operating point within the test range;

[0011] Calculate the peak current and junction temperature of the power devices in the converter valve arm of the system's direct-connected converter based on the duration of continuous overcurrent before the disturbance;

[0012] Verify whether the peak current and junction temperature of the power device before the disturbance meet the electro-thermal limit constraints.

[0013] If the conditions are met, calculate and record the corresponding power operating point;

[0014] Perform small-signal stability analysis on the power operating point, calculate the damping ratio, and verify whether the small-signal stability constraint is met. If it is met, record the power operating point and the constraint satisfaction status.

[0015] Based on the deviation limit after voltage disturbance, and combined with the reactive power-voltage droop control characteristics and parameters, calculate the corresponding power operating point after voltage disturbance;

[0016] Based on the power operating point after the disturbance, and according to the deviation limit after the frequency disturbance, combined with the active power-frequency droop control characteristics and parameters, the corresponding power operating point after the frequency disturbance is calculated.

[0017] Calculate the current operating point after the disturbance based on the power operating point corresponding to the frequency disturbance, and calculate the peak current and junction temperature of the power device flowing through the converter valve bridge arm of the direct-connected converter after the disturbance by combining the continuous overcurrent time after the disturbance. Verify whether the peak current and junction temperature of the power device after the disturbance simultaneously meet the electro-thermal limit constraint. If they do, record the corresponding power operating point before the disturbance and the constraint satisfaction status.

[0018] Small-signal stability analysis is performed based on the power operating point after the disturbance. The damping ratio is calculated, and it is verified whether the small-signal stability constraints are met. If they are met, the corresponding power operating point before the disturbance and the constraint satisfaction status are recorded.

[0019] Verify whether the traversal process has been completed for all corresponding power operating points within the test range, and construct the energy storage transient power safety domain under the electro-thermal limit constraint.

[0020] Furthermore, the test checks whether the peak current and junction temperature flowing through the power device meet the electro-thermal limit constraints. If they do not meet the constraints, the AC current operating point is reselected within the AC current operating point test range.

[0021] Alternatively, the verification may satisfy the small signal stability constraint. If it does not, the AC current operating point shall be reselected within the AC current operating point test range.

[0022] Alternatively, check whether the traversal process has been completed for all corresponding power operating points within the test range. If not, reselect the AC current operating point within the AC current operating point test range.

[0023] Furthermore, the reference operating parameters include the rated AC voltage, rated DC voltage, and rated AC current of the grid-connected energy storage system, as well as the switching frequency of the power devices. The current operating point test range is selected comprehensively based on the transient time-segmented overcurrent capability requirements to cover all AC power operating point test ranges.

[0024] Furthermore, the input parameters of the model include the electric limit constraint limit: electric limit limit I max Thermal limit constraint limit T IGBT_max Δt before disturbance a System voltage U, system voltage deviation ΔU, system frequency f, system frequency deviation limit Δf, and overcurrent time Δt after disturbance. b Minimum damping ratio threshold ζ min Active power P-frequency f control characteristic parameters, reactive power Q-voltage U control characteristic parameters.

[0025] Furthermore, the verification method for the small-signal stability constraint is as follows:

[0026] First, a state-space model is established using dynamic mathematical models of each component of a grid-type energy storage system:

[0027]

[0028] In the formula: X is the state variable, and U is the input variable.

[0029] Linearizing the above state-space equations yields the small-signal model for grid-type energy storage:

[0030]

[0031] In the formula: A is the state matrix, and B is the input matrix.

[0032] Calculate the eigenvalues ​​of the state matrix of the grid-type energy storage system, and calculate the damping ratio corresponding to all eigenvalues. The calculation formulas are as follows:

[0033]

[0034] In the formula: σ is the real part of the eigenvalue, and ω is the imaginary part of the eigenvalue.

[0035] The minimum damping ratio corresponding to all eigenvalues ​​is compared with the minimum damping ratio threshold ζ. min The comparison is performed to verify whether the small-signal stability constraint is satisfied. The discriminant is as follows: ε>ε min .

[0036] Furthermore, by combining the control method with the grid-type energy storage to set the aforementioned reactive power-voltage droop characteristics and parameters, the reactive power-voltage droop characteristics are as follows:

[0037]

[0038] Where: E is the internal potential output of the grid-type energy storage, K q K is the reactive power droop factor. v Q is the voltage droop factor. ref and V ref These are the reference values ​​for reactive power and AC voltage, respectively, where Q and V are the reactive power and AC voltage, respectively.

[0039] Furthermore, by combining the active power-frequency droop characteristics and parameters of the grid-type energy storage with the control method, the active power-frequency droop characteristics are as follows:

[0040]

[0041] Where: ω is the angular velocity of the grid-type energy storage system, ω ref D is the reference value for the system's angular velocity. p D1 is the primary frequency modulation coefficient, D1 is the damping coefficient, and P is the primary frequency modulation coefficient. ref The active power reference value is given by P, where P is the active power and T is the active power. j is the inertial time constant.

[0042] Furthermore, the voltage deviation limit △U and the set K are... q and K v Substituting the reactive power-voltage droop characteristic into the power operating point after voltage disturbance calculation, and based on this, the frequency deviation limit Δf and the set D are applied. p Substituting D1 into the active-frequency droop characteristic calculation, the power operating point after frequency disturbance is obtained. The final active and reactive power at the power operating point after disturbance are as follows:

[0043]

[0044] Among them: (P) u,f Q u,f () represents the power operating point after the disturbance.

[0045] Furthermore, the peak current and junction temperature of the power devices in the converter valve arm of the direct-connected converter after the disturbance are calculated using the current operating point (I) corresponding to the power operating point after the disturbance. d u,f I q u,f Furthermore, the continuous overcurrent time in the model is changed to the perturbed overcurrent time Δt. b The initial temperature is changed to the junction temperature of the power device before the disturbance. Based on this, the power operating point after the disturbance is calculated and judged to meet the electro-thermal limit constraint.

[0046] Furthermore, the transient power safety domain of energy storage under the electro-thermal limit constraint should include: the power operating range that is safe under the electro-thermal limit before the disturbance, the power operating range that can maintain the electro-thermal limit safety after the disturbance, the power operating range that is stable with small signals before the disturbance, and the power operating range that can maintain stable with small signals after the disturbance. Based on the actual needs of the system, these power operating ranges are combined, and the intersection is taken to obtain the final transient power safety domain of energy storage under the electro-thermal limit constraint. Attached Figure Description

[0047] The accompanying drawings illustrate one embodiment of the present disclosure and, together with the description thereof, serve to explain the principles of the present disclosure. These drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification.

[0048] Figure 1 This is a schematic diagram of the process for constructing a transient power safety domain model for high-voltage direct-connected grid-type energy storage that considers electro-thermal limit constraints, as per the present invention. Detailed Implementation

[0049] The present disclosure will now be described in further detail with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure. Furthermore, it should be noted that, for ease of description, only the parts relevant to the present disclosure are shown in the accompanying drawings.

[0050] It should be noted that, where there is no conflict, the embodiments and features described in this disclosure can be combined with each other. The technical solutions of this disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0051] The method for constructing a transient power safety domain model for high-voltage direct-connected grid-type energy storage considering electro-thermal limit constraints, as described in this invention, specifically includes the following steps:

[0052] Step 1: Determine the system topology and baseline operating parameters of high-voltage direct-connected grid-type energy storage, and set the input parameters of the model and the AC current operating point test range according to the system operation requirements;

[0053] The system topology of the high-voltage direct-connected grid-type energy storage mainly includes an energy storage valve and a direct-connected converter. The energy storage valve is composed of multiple battery modules connected in series. Each battery module is connected to the battery unit through the energy storage valve assembly to achieve DC / DC conversion. The direct-connected converter consists of six arms, with each phase having upper and lower arms. Multiple power modules are cascaded in each arm. The DC electrical quantity output from the battery module outlet is sent to each power module inside the direct-connected converter, forming a multi-level electrical quantity interaction path of battery module-power module-direct-connected converter within the grid-type energy storage. Finally, AC power is output to the AC grid at the grid-type energy storage port.

[0054] The aforementioned benchmark operating parameters include system operating parameters such as rated AC voltage, rated DC voltage, and rated AC current of the grid-connected energy storage system, as well as two categories of key parameters for calculating electro-thermal limit constraints, such as the switching frequency of power devices. The AC current operating point test range can be comprehensively selected based on the transient time-segmented overcurrent capacity requirements to cover all requirements. Taking the short-time overcurrent capacity requirement of "having overload capacity of 1.5 times, 2 times, and 3 times the rated current for 10 seconds, 80 milliseconds, and 1 second" as an example, the AC current operating point test range is as follows:

[0055]

[0056] In the formula, I d I q These are the active and reactive currents output from the high-voltage direct-connected grid-connected energy storage converter to the AC grid, respectively; I ac The rated AC current for the AC side of the high-voltage direct-connected grid energy storage direct-connected converter.

[0057] The input parameters of the model include the electric limit constraint limit: electric limit limit I max Thermal limit constraint limit T IGBT_max Δt before disturbance a System voltage U, system voltage deviation ΔU, system frequency f, system frequency deviation limit Δf, and overcurrent time Δt after disturbance. b Minimum damping ratio threshold ζ min Active power P-frequency f control characteristic parameters, reactive power Q-voltage U control characteristic parameters.

[0058] Step 2: Select an AC current operating point within the test range, input it and the continuous overcurrent time before the disturbance into the electro-thermal model to calculate the peak value of the converter valve arm current and the junction temperature of the power device of the direct-connected converter, and verify whether the current operating point simultaneously meets the electro-thermal limit constraint. If it does not meet the constraint, return to select the next current operating point. If it does meet the constraint, calculate the corresponding power operating point and record it.

[0059] This embodiment uses IGBTs as power devices for illustration. The specific calculation steps for calculating the peak value of the converter valve arm current of the direct-connected converter using an electro-thermal model and verifying whether the operating point meets the electrical limit constraint are as follows:

[0060] (1) Calculate the effective value of the AC current on the grid side:

[0061]

[0062] (2) Ignoring converter losses and assuming that the DC power of the energy storage valve is approximately equal to the active power at the converter outlet, calculate the DC current on the DC side:

[0063]

[0064] In the formula, U d U q For the active and reactive components of the AC voltage on the AC side of the high-voltage direct-connected grid energy storage converter, U dc This refers to the rated DC voltage on the DC side of the high-voltage direct-connected grid energy storage converter.

[0065] (3) Calculate the effective and peak values ​​of the converter valve arm current of the direct-connected converter and the current flowing through the IGBT in the power module. Taking the upper arm current of phase A as an example, the formula for calculating the effective value of the arm current is as follows:

[0066]

[0067] The formula for calculating the peak current of the bridge arm is as follows:

[0068]

[0069] The expression for the current flowing through the IGBT is as follows:

[0070]

[0071] In the formula, ω is the power factor angle; ω is the angular velocity.

[0072] (4) The electric limit constraint is satisfied when the peak current flowing through the IGBT is less than the maximum allowable turn-off current of the IGBT device. The criterion is as follows:

[0073] I arm,peak max

[0074] In the formula, I max This is the maximum allowable turn-off current for IGBT devices in a high-voltage direct-connected grid energy storage converter, i.e., the electrical constraint limit.

[0075] ​The specific calculation steps for using an electro-thermal model to calculate the junction temperature of the IGBT device in the converter valve of a direct-connected converter and to verify whether the operating point meets the thermal limit constraint are as follows:

[0076] (1) Calculate the average on-state loss of the IGBT device in a direct-connected converter during one switching cycle.

[0077] P cond =U ce (t)i(t)δ(t)

[0078] In the formula, δ(t) is the duty cycle of the IGBT switching period; U ce i(t) is the forward on-state voltage drop of the IGBT, which can be obtained from the device datasheet; i(t) is the collector current.

[0079] (2) Calculate the average turn-on loss P of the IGBT device in the direct-connected converter during one switching cycle. on With average turn-off loss P off

[0080]

[0081] In the formula, f sw E is the switching frequency. sw_on E sw_off These are the turn-on and turn-off power consumption of the IGBT under rated conditions; T / I N U dc / U N These are the current and voltage conversion factors for the IGBT, respectively; K Rg_on K Rg_off For the driving resistor R g The influence coefficient of turn-on energy consumption and turn-off energy consumption; K Tj Temperature coefficient of junction temperature on switching losses

[0082] (3) Calculate the average power loss of the IGBT device in the direct-connected converter during one switching cycle.

[0083] P sw =P on +P off

[0084] P IGBT =P cond +P sw

[0085] In the formula, P sw P represents the average switching loss over one switching cycle. IGBT This represents the average power loss of an IGBT device over one switching cycle.

[0086] (4) Calculate the junction temperature of IGBT devices in a direct-connected converter

[0087]

[0088] ΔT jm (t)=P IGBT Z jc (t)

[0089] T IGBT (t)=T a +ΔT jm

[0090] In the formula, Z jc (t) represents the junction-shell transient thermal impedance in the IGBT module, τ i With R i These are the thermal time constant and thermal resistance constant of the IGBT, respectively, ΔT jm (t) represents the temperature rise; T a The ambient temperature; T IGBT (t) represents the IGBT junction temperature, T IGBT_max This is the maximum allowable operating junction temperature for IGBT devices.

[0091] (5) The thermal limit constraint condition is that the operating junction temperature of the IGBT device shall not exceed the maximum allowable operating junction temperature under any operating condition; when the converter is overcurrent output (such as short-term output of 3 times the rated current), it must also be ensured that the junction temperature does not exceed the limit within a specified duration (such as 80 milliseconds). The specific discrimination formula is as follows:

[0092] T IGBT (Δt a ) <T IGBT_max

[0093] In the formula, T IGBT_max Δt is the maximum allowable operating junction temperature of the IGBT device. a The duration of the overcurrent before the disturbance.

[0094] Step 3: Perform small-signal stability analysis based on the power operating point obtained in Step 2, calculate the damping ratio, and check whether the small-signal stability constraint is met. If not, return to Step 2 to select the next AC current operating point. If it is met, record the power operating point and the constraint satisfaction status.

[0095] The verification process for small-signal stability constraints is as follows:

[0096] (1) First, a state-space model is established using dynamic mathematical models of each link in a grid-type energy storage system:

[0097]

[0098] In the formula: X is the state variable, and U is the input variable.

[0099] (2) Linearize the above state-space equations to obtain the small-signal model of grid-type energy storage:

[0100]

[0101] In the formula: A is the state matrix, and B is the input matrix.

[0102] (3) Calculate the eigenvalues ​​of the state matrix of the grid-type energy storage system, and calculate the damping ratio corresponding to all eigenvalues. The calculation formula is as follows:

[0103]

[0104] In the formula: σ is the real part of the eigenvalue, and ω is the imaginary part of the eigenvalue.

[0105] (4) Compare the minimum damping ratio corresponding to all eigenvalues ​​with the minimum damping ratio threshold ζmin to verify the small-signal stability constraint is satisfied. The discriminant is as follows:

[0106] ε>ε min

[0107] Step 4: Based on the power operating point obtained in Step 3, calculate the corresponding power operating point after voltage disturbance according to the deviation limit after voltage disturbance, combined with the reactive power-voltage droop control characteristics and parameters. Then, based on the operating point after disturbance, calculate the corresponding power operating point after frequency disturbance according to the deviation limit after frequency disturbance, combined with the active power-frequency droop control characteristics and parameters.

[0108] The reactive power-voltage droop characteristics and parameters mentioned above need to be set in conjunction with the specific control method adopted for grid-type energy storage. Taking conventional virtual synchronous machine control as an example, its reactive power-voltage droop characteristics are as follows:

[0109]

[0110] Where: E is the internal potential output of the grid-type energy storage, K q K is the reactive power droop factor. v Q is the voltage droop factor. ref and V ref These are the reactive power reference value and the AC voltage reference value, respectively.

[0111] The active power-frequency droop characteristics and parameters need to be set in conjunction with the specific control method adopted for grid-type energy storage. Taking conventional virtual synchronous machine control as an example, its active power-frequency droop characteristics are as follows:

[0112]

[0113] Where: ω is the angular velocity of the grid-type energy storage system, ωref D is the reference value for the system's angular velocity. p D1 is the primary frequency modulation coefficient, D1 is the damping coefficient, and P is the primary frequency modulation coefficient. ref T is the active power reference value. j is the inertial time constant.

[0114] Set the voltage deviation limit ΔU and the set K q and K v Substituting the reactive power-voltage droop characteristic into the power operating point after voltage disturbance calculation, and based on this, the frequency deviation limit Δf and the set D are... p Substituting D1 into the active-frequency droop characteristic calculation, the power operating point after frequency disturbance is obtained. The final active and reactive power at the power operating point after disturbance are as follows:

[0115]

[0116] Among them: (P) u,f Q u,f () represents the power operating point after the disturbance.

[0117] Step 5: Calculate the current operating point after the disturbance based on the power operating point obtained in Step 4, and input it along with the continuous overcurrent time after the disturbance into the electro-thermal model. Calculate the peak value of the converter valve arm current and the junction temperature of the IGBT device after the disturbance. Verify whether the current operating point simultaneously meets the electro-thermal limit constraint. If it does not meet the constraint, return to Step 2 to select the next current operating point. If it does meet the constraint, record the corresponding power operating point before the disturbance and the constraint satisfaction status.

[0118] Among them, the peak value of the converter valve arm current and the junction temperature of the IGBT device in the direct-connected converter are calculated using an electro-thermal model, and the current operating point (I0) corresponding to the power operating point after the disturbance is used. d u,f I q u,f Furthermore, the continuous overcurrent time in the electro-thermal model needs to be changed to the perturbation-induced overcurrent time Δt. b The initial temperature is changed to the junction temperature of the IGBT device before the disturbance, and on this basis, the power operating point after the disturbance is calculated and judged to meet the electro-thermal limit constraint.

[0119] Step 6: Based on the power operating point after the disturbance obtained in Step 5, perform small-signal stability analysis, calculate the damping ratio, and check whether the small-signal stability constraints are met. If not, return to Step 2 to select the next current operating point. If the constraints are met, record the corresponding power operating point before the disturbance and the constraint satisfaction status.

[0120] The small-signal stability analysis is based on the power operating point (P) after the disturbance. u,f Q u,fThe damping ratio is calculated and compared with the minimum damping ratio threshold ζ. min Compare and verify whether the small-signal stability constraints are satisfied.

[0121] Step 7: Verify whether the traversal process has been completed for all corresponding power operating points within the test range. If not, return to Step 2 to select the next current operating point. If so, integrate all recorded power operating points and constraint satisfaction status to construct the energy storage transient power safety domain under the electro-thermal limit constraint.

[0122] The transient power safety domain of energy storage under the electro-thermal limit constraint shall include: 1) the power operating range that is safe under the electro-thermal limit before the disturbance; 2) the power operating range that can maintain the electro-thermal limit safety after the disturbance; 3) the power operating range that is stable with small signals before the disturbance; and 4) the power operating range that can maintain stable with small signals after the disturbance. The final transient power safety domain of energy storage under the electro-thermal limit constraint can be obtained by combining these power operating ranges according to the actual needs of the system and taking their intersection.

[0123] In the description of this specification, the references to terms such as "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., refer to specific features, structures, or characteristics described in connection with that embodiment / mode or example, which are included in at least one embodiment / mode or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0124] Those skilled in the art should understand that the above embodiments are merely for illustrating the present disclosure and are not intended to limit the scope of the disclosure. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present disclosure.

Claims

1. A method for constructing a transient power security region model of a high-voltage direct-coupled grid-forming energy storage system considering electro-thermal limit constraints, characterized in that, The method comprises: determining the topology of the system and the benchmark operating parameters, setting the input parameters of the model and the alternating current operating point test range; selecting an alternating current operating point in the test range; calculating the current peak value and junction temperature of the power device of the converter valve bridge arm of the converter directly connected to the system based on the duration of overcurrent before disturbance; checking whether the current peak value and junction temperature of the power device meet the electro-thermal limit constraint condition; if yes, calculating the corresponding power operating point and recording it; performing small signal stability analysis on the power operating point, calculating the damping ratio, checking whether the small signal stability constraint is met, and if yes, recording the power operating point and the constraint satisfaction condition; calculating the corresponding power operating point after voltage disturbance according to the voltage deviation limit value, combining the reactive power-voltage droop control characteristics and parameters; calculating the corresponding power operating point after frequency disturbance based on the power operating point after disturbance, according to the frequency deviation limit value, combining the active power-frequency droop control characteristics and parameters; calculating the current operating point after disturbance based on the corresponding power operating point after frequency disturbance, and combining the duration of overcurrent after disturbance to calculate the current peak value and junction temperature of the power device of the converter valve bridge arm directly connected to the converter, checking whether the current peak value and junction temperature of the power device after disturbance meet the electro-thermal limit constraint, and if yes, recording the corresponding power operating point before disturbance and the constraint satisfaction condition; performing small signal stability analysis based on the power operating point after disturbance, calculating the damping ratio, checking whether the small signal stability constraint is met, and if yes, recording the corresponding power operating point before disturbance and the constraint satisfaction condition; checking whether the traversal process for all corresponding power operating points in the test range is completed, and constructing the power storage transient power safety domain under the electro-thermal limit constraint.

2. The method of claim 1, wherein the method is characterized by, The method comprises: checking whether the current peak value and junction temperature of the power device meet the electro-thermal limit constraint condition, and if not, reselecting the alternating current operating point in the alternating current operating point test range; or, checking whether the small signal stability constraint is met, and if not, reselecting the alternating current operating point in the alternating current operating point test range; 3. The method of claim 1, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. or, checking whether the traversal process for all corresponding power operating points in the test range is completed, and if not, reselecting the alternating current operating point in the alternating current operating point test range.

4. The method of claim 1, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The input parameters of the model include electrode limit constraint limit value: electric limit constraint limit value I max , thermal limit constraint limit value T IGBT_max , disturbance before overcurrent time Δt a , system voltage U, system voltage deviation value ΔU, system frequency f, system frequency deviation limit value Δf, disturbance after overcurrent time Δt b , minimum damping ratio threshold ζ min , active P-frequency f control characteristic parameters, reactive Q-voltage U control characteristic parameters.

5. The method of claim 1, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The benchmark operating parameters include the rated alternating current voltage, rated direct current voltage and rated alternating current of the grid-connected energy storage system, and the switching frequency of the power device, and the alternating current operating point test range is comprehensively selected according to the transient time period overcurrent capacity requirement index to cover the full requirement of the alternating current power operating point test range. The checking method of the small signal stability constraint is as follows: First, the state space model is established by using the dynamic mathematical model of each link of the grid-connected energy storage: In the formula, X is the state variable, and U is the input variable. The state space equation is linearized to obtain the small signal model of the grid-connected energy storage: In the formula, A is the state matrix, and B is the input matrix. The eigenvalues of the state matrix of the grid-connected energy storage are calculated, and the damping ratio corresponding to all eigenvalues is calculated, and the calculation formula is as follows: In the formula, σ is the real part of the eigenvalue, and ω is the imaginary part of the eigenvalue. Compare the minimum damping ratio corresponding to all the characteristic values with the minimum damping ratio threshold ζ min , check the satisfaction of the small signal stability constraint, and the discriminant is as follows: ε>ε min .

6. The method of claim 1, wherein the method further comprises: The reactive-voltage droop characteristic and parameters are set in combination with a control mode of the network-constructed energy storage, and the reactive-voltage droop characteristic is: Wherein: E is the internal potential of network-type energy storage output, K q is the reactive droop coefficient, K v is the voltage droop coefficient, Q ref and V ref are the reactive power reference value and AC voltage reference value respectively, Q and V are the reactive power and AC voltage respectively.

7. The method of claim 6, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The active-frequency droop characteristic and parameters are set in combination with a control mode of the network-constructed energy storage, and the active-frequency droop characteristic is: Wherein: ω is the network type energy storage system angular velocity, ω ref is the system angular velocity reference value, D p is the first frequency modulation coefficient, D1 is the damping coefficient, P ref is the active power reference value, P is the active power, T j is the inertia time constant.

8. The method of claim 7, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The voltage deviation limit value ΔU and the set K q and K v The reactive power-frequency droop characteristic is substituted into the post-disturbance power operating point calculated by the reactive power-voltage droop characteristic, and on this basis, the frequency deviation limit Δf and the set D p and D1 are substituted into the active power-frequency droop characteristic to calculate the post-disturbance power operating point, and the active power and the reactive power of the final post-disturbance power operating point are respectively: where: (P u,f , Q u,f ) is the post-disturbance power operating point.

9. The method of claim 8, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The peak value of the current of the power device in the bridge arm of the direct hanging converter valve after the disturbance and the junction temperature are calculated by using the current operating point (I d u,f , I q u,f ) corresponding to the power operating point after the disturbance, the overcurrent time in the model is changed to the overcurrent time △t b after the disturbance, and the initial temperature is changed to the junction temperature of the power device before the disturbance, and then whether the power operating point after the disturbance meets the electro-thermal limit constraint is calculated and judged.

10. The method of claim 9, wherein the method further comprises: determining the transient power security region of the high-voltage direct-coupled grid-tied energy storage system based on the electrical-thermal limit constraints. The internal of the energy storage transient power safety domain under the electric-thermal limit constraint should include: a power operation range before the disturbance that is safe to the electric-thermal limit, a power operation range after the disturbance that can maintain the electric-thermal limit safety, a power operation range before the disturbance that is small signal stable, a power operation range after the disturbance that can maintain the small signal stability, and the final electric-thermal limit constraint under the energy storage transient power safety domain is obtained by comprehensively taking the intersection of the above-mentioned power operation ranges according to actual needs of the system.

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