Method and system for quantitatively evaluating short-circuit ratio of network construction type energy storage access new energy field station

Abstract

The invention discloses a network construction type energy storage access new energy field station short circuit ratio quantitative evaluation method and system, and the method comprises the steps: calculating the equivalent short circuit capacity of an AC system based on the connection mode of network construction type energy storage and a power grid and different access capacities, the connection mode of the network-building type energy storage and the power grid comprises a network-building type energy storage discharging access system and a network-building type energy storage charging access system; based on the equivalent node impedance and the maximum transmission power of the new energy system, calculating a short-circuit ratio and a critical short-circuit ratio of the new energy field station accessed to the network-forming energy storage system; based on the difference value between the short-circuit ratio and the critical short-circuit ratio, calculating the short-circuit ratio margin of the new energy station after the network type energy storage access system is constructed; according to the short-circuit ratio margin index of the network construction type energy storage access new energy field station, the voltage supporting strength of the energy storage access system can be quantitatively evaluated, and reference is provided for planning and operation control of new energy access power grids.

Description

Technical Field

[0001] The present invention relates to an evaluation method and system, and particularly to a quantitative evaluation method and system for the short - circuit ratio of a network - forming energy storage connected to a new - energy power station. Background Art

[0002] The current - bearing capacity of the power converter in new energy is not high and cannot provide sufficient fault current during faults in new - energy power stations. The large - scale grid - connection operation of new energy will reduce the short - circuit ratio of multiple new - energy power stations. Therefore, the short - circuit ratio is an important index to measure the support strength of the power system. By evaluating the short - circuit ratio and critical short - circuit ratio indexes of the power system, the voltage support strength and operation state of the system can be measured.

[0003] Currently, the research focus is on improving the short - circuit ratio to enhance the system support strength. When the grid voltage drops, the DC transmission can achieve pure reactive power output through control strategies to increase the critical short - circuit ratio of the system, but it has little impact on the short - circuit capacity of the system. While the access of distributed small synchronous condensers to system nodes can effectively provide short - circuit capacity, for new - energy users, synchronous condensers are expensive and have low cost - effectiveness. With the development of new energy and energy - storage technologies, in order to provide sufficient voltage - source support, the network - forming control technology of converters will be the future development trend. The network - forming technology can construct a stable - operating self - synchronous power source in each stage before, during, and after disturbances, and can participate in the control of active power imbalance by maintaining the characteristics of potential angle, inertia, and frequency modulation. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a quantitative evaluation method for the short - circuit ratio of a network - forming energy storage connected to a new - energy power station to judge the stability of a multi - fed new - energy system. On the other hand, a quantitative evaluation system for the short - circuit ratio of a network - forming energy storage connected to a new - energy power station is provided.

[0005] Technical Solution: The short - circuit ratio quantitative evaluation method described in the present invention includes the following steps:

[0006] S1. Calculate the equivalent short - circuit capacity of the AC system based on the connection mode of the network - forming energy storage and the power grid and different access capacities. The connection modes of the network - forming energy storage and the power grid include the network - forming energy storage discharging and accessing the system and the network - forming energy storage charging and accessing the system;

[0007] S2. Calculate the short - circuit ratio and critical short - circuit ratio of the new - energy power station after the access of the network - forming energy storage based on the equivalent node impedance and the maximum transmission power of the new - energy system;

[0008] S3. Calculate the short - circuit ratio margin of the new - energy power station after the access of the network - forming energy storage system based on the difference between the short - circuit ratio and the critical short - circuit ratio.

[0009] Preferably, the S1 includes:

[0010] S11. Calculate the apparent power on the energy storage side;

[0011] S12. Charge the energy storage system and calculate the active power and reactive power;

[0012] S13. The grid-forming energy storage system adjusts the power angle and frequency by controlling the active power;

[0013] S14. Adjust the voltage by controlling the reactive power. After grid connection, the grid-forming energy storage can be equivalent to a power source and provide short-circuit capacity to the power grid;

[0014] S15. Calculate the short-circuit capacity after the grid-forming energy storage is connected to the system.

[0015] Preferably, the calculation formula in S11 is as follows:

[0016]

[0017] Where, P x represents the active power on the energy storage side, Q x represents the reactive power on the energy storage side, U x represents the grid voltage, U t represents the energy storage grid connection voltage, P x represents the active power, Q x represents the reactive power, δ represents the power angle, R represents the resistance, and X represents the reactance.

[0018] Preferably, the calculation formula in S15 is as follows:

[0019]

[0020] Where, S' a represents the short-circuit capacity after the grid-forming energy storage discharges and is connected to the system, S″ a represents the short-circuit capacity after the grid-forming energy storage charges and is connected to the system, U N represents the rated voltage. After the energy storage discharges and is connected to node n, the equivalent impedance matrix Z Eq becomes the equivalent node impedance matrix Z' Eq ; after the energy storage charges and is connected to node n, the equivalent impedance matrix Z Eq becomes the equivalent node impedance matrix Z″ Eq , Z Eq represents the multi-port Thevenin equivalent impedance.

[0021] Preferably, the S2 includes:

[0022] S21. Calculate the short-circuit ratio of a new energy single power station after the grid-forming energy storage discharges and charges and is connected to the system;

[0023] S22. Calculate the short-circuit ratio of a new energy multi-power station after the grid-forming energy storage is connected;

[0024] S23. Calculate the maximum transmission power of the new energy system;

[0025] S24. Calculate the critical short - circuit ratio of the multi - station new energy system after the grid - forming energy storage discharges and charges are connected.

[0026] Preferably, the calculation formula is:

[0027]

[0028]

[0029] Among them, P N represents the rated capacity of new energy at the grid connection point, SCR1 represents the short - circuit ratio of a single new - energy station after the grid - forming energy storage discharge is connected, S' a represents the short - circuit capacity of the system after the grid - forming energy storage discharge is connected to the system; SCR2 represents the short - circuit ratio of a single new - energy station after the grid - forming energy storage charge is connected, S″ a represents the short - circuit capacity of the system after the grid - forming energy storage charge is connected to the system; G MRSCR represents the critical short - circuit ratio of the multi - station new energy system after the grid - forming energy storage is connected, U i represents the operating voltage of node i, Z Eqii and Z Eqij respectively represent the self - impedance and mutual - impedance of the corresponding nodes in the equivalent impedance matrix on the grid side, P i represents the active power of new energy injected into node i, P j represents the active power of new energy injected into node j; P Gmax represents the maximum transmission power of the system after the energy storage is connected, C MRSCR1 represents the critical short - circuit ratio of the multi - station new energy system after the grid - forming energy storage discharge is connected, C MRSCR2 represents the critical short - circuit ratio of the multi - station new energy system after the grid - forming energy storage charge is connected.

[0030] Preferably, the said S3 includes:

[0031] S31. Calculate the short - circuit ratio margin of a single new - energy station in the system after the grid - forming energy storage is connected;

[0032] S32. Judge the stability of the single - feed - in new - energy system in the system after the grid - forming energy storage is connected;

[0033] S33. Calculate the short - circuit ratio margin of the multi - station new energy system after the grid - forming energy storage discharges and charges are connected to the system;

[0034] S34. Judge the stability of the multi - feed - in new - energy system in the system after the grid - forming energy storage is connected.

[0035] 11. Preferably, the calculation formula of S31 is:

[0036]

[0037] Among them, Q represents the equivalent reactive power transmitted from the new energy to the AC system.

[0038] The stability judgment condition described in S32 is:

[0039] If SCR < C MRSCR , that is, η s < 0, the new energy grid-connected system is in an unstable state;

[0040] If SCR > C MRSCR , that is, η s > 0, the new energy grid-connected system is in a stable state.

[0041] Preferably, the calculation formula described in S33 is:

[0042]

[0043]

[0044] Among them, Z o represents the equivalent impedance of the grid-forming energy storage;

[0045] The stability judgment condition described in S34 is:

[0046] If G' MRSCR < C MRSCR1 or G” MRSCR < G MRSCR2 , that is, η M < 0, the new energy station access system is in an unstable state;

[0047] If G' MRSCR > C MRSCR1 or G” MRSCR > C MRSCR2 , that is, η M > 0, the new energy station access system is in a stable state.

[0048] A quantitative evaluation system for the short-circuit ratio of a grid-forming energy storage connected to a new energy station according to the present invention includes:

[0049] An equivalent short-circuit capacity calculation module, configured to calculate the equivalent short-circuit capacity of the AC system based on the connection mode of the grid-forming energy storage and the power grid and different access capacities, where the connection mode of the grid-forming energy storage and the power grid includes the grid-forming energy storage discharging and accessing the system and the grid-forming energy storage charging and accessing the system;

[0050] A short-circuit ratio and critical short-circuit ratio calculation module, configured to calculate the short-circuit ratio and critical short-circuit ratio of the new energy station after accessing the grid-forming energy storage based on the equivalent node impedance and the maximum transmission power of the new energy system;

[0051] A short-circuit ratio margin calculation module is used to calculate the short-circuit ratio margin of a new energy power station after the grid-forming energy storage is connected to the system based on the difference between the short-circuit ratio and the critical short-circuit ratio.

[0052] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: By calculating the difference between the short-circuit ratio of the new energy power station after the grid-forming energy storage is connected and the critical short-circuit ratio, the short-circuit ratio margin control is determined, so as to judge the safety and stability of the new energy multi-infeed system, providing an intuitive method for the real-time evaluation of the stability of the new energy grid-connected system, and having important significance for ensuring the safe and stable operation of the new energy grid-connected system. Description of the Drawings

[0053] Figure 1 It is a schematic flow diagram of the present invention;

[0054] Figure 2 It is a schematic diagram of the grid-connected equivalent circuit of the grid-forming energy storage system of the present invention;

[0055] Figure 3 It is a schematic diagram of the equivalent model of the system after the grid-forming energy storage is connected according to the present invention. Specific Embodiments

[0056] Next, with reference to the drawings, the technical solutions of the present invention will be described in detail.

[0057] A method for quantitatively evaluating the short-circuit ratio of a grid-forming energy storage connected to a new energy power station includes the following steps:

[0058] S1. Calculate the equivalent short-circuit capacity of the AC system based on the connection mode between the grid-forming energy storage and the power grid and different access capacities.

[0059] The connection modes between the grid-forming energy storage and the power grid include the grid-forming energy storage discharging and connecting to the system and the grid-forming energy storage charging and connecting to the system:

[0060] (1) Calculate the apparent power on the energy storage side.

[0061]

[0062] Among them, S x represents the apparent power on the energy storage side, p x represents the active power on the energy storage side, Q x represents the reactive power on the energy storage side, U x represents the grid voltage, U t represents the energy storage grid-connected voltage, P x represents the active power, Q x represents the reactive power, I represents the current, Z represents the equivalent impedance, δ represents the power angle, * represents the conjugate, and j represents the imaginary number.

[0063] (2) Charge the energy storage system and calculate the active power and reactive power.

[0064]

[0065] Let \(Z\cos\theta = R\) and \(Z\sin\theta = X\), where \(R\) represents resistance and \(X\) represents reactance. Then the active power and reactive power can be expressed as:

[0066]

[0067] After simplification, it is expressed as:

[0068]

[0069] From the above derivation, it can be seen that the grid-forming energy storage system can dynamically adjust the power angle by controlling the active power, thereby adjusting the frequency; and dynamically adjust the voltage by controlling the reactive power. Therefore, the overall grid-forming energy storage after grid connection can be equivalently regarded as a traditional power source, providing short-circuit capacity to the power grid.

[0070] (3) Calculate the short-circuit capacity after the grid-forming energy storage is connected to the system.

[0071] The short-circuit capacity in the AC power grid is as follows:

[0072]

[0073] Among them, \(U\) N represents the rated voltage, and \(Z\) Eq represents the multi-port Thevenin equivalent impedance;

[0074] After the energy storage discharges and is connected to node \(n\), the equivalent impedance matrix \(Z\) Eq becomes the equivalent node impedance matrix \(Z'\) Eq ; after the energy storage charges and is connected to node \(n\), the equivalent impedance matrix \(Z\) Eq becomes the equivalent node impedance matrix \(Z''\) Eq , and their expressions are respectively:

[0075]

[0076] Among them, represents the transpose of \(z\) n , \(Z\) n is the \(n\)-th row vector of the equivalent impedance matrix \(Z\) Eq , and \(Z\) o represents the equivalent impedance of the grid-forming energy storage;

[0077] Expanding the above formula, we can get:

[0078]

[0079] The short-circuit capacity after the grid-forming energy storage discharges and connects to the system is:

[0080]

[0081] The short-circuit capacity after the grid-forming energy storage charges and connects to the system is:

[0082]

[0083] S2. Calculate the short-circuit ratio and critical short-circuit ratio of the new energy power station after connecting the grid-forming energy storage based on the equivalent node impedance and the maximum transmission power of the new energy system.

[0084] (1) Calculate the short-circuit ratios of the new energy single power station after the grid-forming energy storage discharges and charges and connects, which are respectively:

[0085]

[0086] Among them, P N represents the rated capacity of new energy at the point of common coupling, SCR1 represents the short-circuit ratio of the new energy single power station after the grid-forming energy storage discharges and connects, S' a represents the short-circuit capacity after the grid-forming energy storage discharges and connects to the system; SCR2 represents the short-circuit ratio of the new energy single power station after the grid-forming energy storage charges and connects, S″ a represents the short-circuit capacity after the grid-forming energy storage charges and connects to the system;

[0087] ; P Gmax represents the maximum transmission power of the system after the energy storage connects, C MRSCR1 represents the critical short-circuit ratio of the new energy multi-power station after the grid-forming energy storage discharges and connects, C MRSCR2 represents the critical short-circuit ratio of the new energy multi-power station after the grid-forming energy storage charges and connects

[0088] (2) Calculate the short-circuit ratio of the new energy multi-power station after the grid-forming energy storage connects.

[0089] Assume U i =U j , that is, the voltage phase angles between the new energy power stations are equal. The short-circuit ratio of the new energy multi-power station can be expressed as:

[0090]

[0091] Substitute Z Eqij ', Z Eqij " into the above formula, and the short-circuit ratios of the i-th new energy power station node at the energy storage discharge and charge connection node n can be obtained as:

[0092]

[0093]

[0094] Among them, U i represents the operating voltage of node i, and Z Eqii , Z Eqij respectively represent the self-impedance and mutual-impedance of the corresponding nodes in the equivalent impedance matrix on the grid side, P i represents the active power of new energy injected into node i, and P j represents the active power of new energy injected into node j;

[0095] (3) Calculate the maximum transmission power of the new energy system.

[0096] The quadratic equation about the grid connection point voltage is:

[0097]

[0098] It is deduced that the maximum transmission power of the system after the energy storage is connected is:

[0099]

[0100] (4) Calculate the critical short-circuit ratio of multiple new energy stations after the grid-forming energy storage discharges and charges are connected:

[0101]

[0102] (5) Based on the difference between the short-circuit ratio and the critical short-circuit ratio, calculate the short-circuit ratio margin of the new energy station after the grid-forming energy storage is connected to the system, so as to quantitatively evaluate the stability of the new energy fed into the system.

[0103] S3. Based on the difference between the short-circuit ratio and the critical short-circuit ratio, calculate the short-circuit ratio margin of the new energy station after the grid-forming energy storage is connected to the system.

[0104] (1) Calculate the short-circuit ratio margin of a single new energy station after the grid-forming energy storage is connected to the system:

[0105]

[0106] Among them, Q represents the equivalent reactive power transmitted by the new energy to the AC system.

[0107] (2) Stability criterion of a single new energy feed-in system after the grid-forming energy storage is connected to the system:

[0108] If SCR < C MRSCR , that is, η s < 0, the new energy grid-connected system is in an unstable state;

[0109] If SCR > C MRSCR , that is, η s > 0, the new energy grid-connected system is in a stable state.

[0110] (3) Short-circuit ratio margin of multiple new energy power stations after the grid-forming energy storage is connected to the system for discharging and charging:

[0111]

[0112]

[0113] Among them, Z o represents the equivalent impedance of the grid-forming energy storage.

[0114] (4) Stability criterion of the new energy multi-infeed system after the grid-forming energy storage is connected to the system:

[0115] If G' MRSCR < C MRSCR1 or G” MRSCR < G MRSCR2 , that is, when η M < 0, the new energy power station connected to the system is in an unstable state;

[0116] If G' MRSCR > C MRSCR1 or G” MRSCR > C MRSCR2 , that is, when η M > 0, the new energy power station connected to the system is in a stable state.

Claims

1. A quantitative evaluation method for the short-circuit ratio of a network-forming energy storage connected to a new energy power station, characterized in that, It includes the following steps: S1. Calculate the equivalent short-circuit capacity of the AC system based on the connection mode between the network-forming energy storage and the power grid and different access capacities. The connection modes between the network-forming energy storage and the power grid include the network-forming energy storage discharging and accessing the system and the network-forming energy storage charging and accessing the system; S2. Calculate the short-circuit ratio and critical short-circuit ratio of the new energy power station after accessing the network-forming energy storage based on the equivalent node impedance and the maximum transmission power of the new energy system; S3. Calculate the short-circuit ratio margin of the new energy power station after the network-forming energy storage is connected to the system based on the difference between the short-circuit ratio and the critical short-circuit ratio.

2. The short-circuit ratio quantitative evaluation method according to claim 1, wherein S1 includes: S11. Calculate the apparent power on the energy storage side; S12. Charge the energy storage system and calculate the active power and reactive power; S13. The network-forming energy storage system adjusts the power angle and frequency by controlling the active power; S14. Adjust the voltage by controlling the reactive power. After grid connection, the network-forming energy storage can be equivalent to a power source and provide short-circuit capacity to the power grid; S15. Calculate the short-circuit capacity after the network-forming energy storage is connected to the system.

3. The short-circuit ratio quantitative evaluation method according to claim 2, wherein The calculation formula of S11 is as follows: Among them, P x represents the active power on the energy storage side, Q x represents the reactive power on the energy storage side, U x represents the grid voltage, U t represents the energy storage grid-connected voltage, P x represents the active power, Q x represents the reactive power, δ represents the power angle, R represents the resistance, and X represents the reactance.

4. The short-circuit ratio quantitative evaluation method according to claim 2, wherein The calculation formula of S15 is as follows: Among them, S' a represents the short-circuit capacity after the grid-forming energy storage discharges and is connected to the system. S' a ' represents the short-circuit capacity after the grid-forming energy storage charges and is connected to the system. U N represents the rated voltage. After the energy storage discharges and is connected to node n, the equivalent impedance matrix Z Eq becomes the equivalent node impedance matrix Z'. Eq After the energy storage charges and is connected to node n, the equivalent impedance matrix Z Eq becomes the equivalent node impedance matrix Z". Eq Z Eq represents the multi-port Thevenin equivalent impedance.

5. The short-circuit ratio quantitative evaluation method according to claim 1, characterized in that S2 includes: S21. Calculate the short-circuit ratio of a single new energy power station after the network-forming energy storage discharges and charges and accesses the system; S22. Calculate the short-circuit ratio of multiple new energy power stations after the network-forming energy storage is connected; S23. Calculate the maximum transmission power of the new energy system; S24. Calculate the critical short-circuit ratio of multiple new energy power stations after the network-forming energy storage discharges and charges and accesses.

6. The short-circuit ratio quantitative evaluation method according to claim 5, wherein The calculation formula is: Among them, P N represents the rated capacity of new energy at the grid connection point, SCR1 represents the short-circuit ratio of a single new energy power station after the connection of the network-forming energy storage during discharge, and S' a represents the short-circuit capacity of the system after the connection of the network-forming energy storage during discharge; SCR2 represents the short-circuit ratio of a single new energy power station after the connection of the network-forming energy storage during charging, and S” a represents the short-circuit capacity of the system after the connection of the network-forming energy storage during charging; G MRSCR represents the short-circuit ratio of multiple new energy power stations after the connection of the network-forming energy storage, U i represents the operating voltage of node i, Z Eqii and Z Eqij respectively represent the self-impedance and mutual-impedance of the corresponding nodes in the equivalent impedance matrix on the grid side, P i represents the active power of new energy injected into node i, P j represents the active power of new energy injected into node j; P Gmax represents the maximum transmission power of the system after the connection of the energy storage, C MRSCR1 represents the critical short-circuit ratio of multiple new energy power stations after the connection of the network-forming energy storage during discharge, C MRSCR2 represents the critical short-circuit ratio of multiple new energy power stations after the connection of the network-forming energy storage during charging.

7. The short-circuit ratio quantitative evaluation method according to claim 1, wherein S3 includes: S31. Calculate the short-circuit ratio margin of a single new energy power station after the network-forming energy storage is connected to the system; S32. Judge the stability of the single-feed new energy system after the network-forming energy storage is connected to the system; S33. Calculate the short-circuit ratio margin of multiple new energy power stations after the network-forming energy storage discharges and charges and accesses the system; S34. Judge the stability of the multi-feed new energy system after the network-forming energy storage is connected to the system.

8. The short-circuit ratio quantitative evaluation method according to claim 7, characterized in that The calculation formula of S31 is: Among them, Q represents the equivalent reactive power transmitted by the new energy to the AC system. The stability judgment condition of S32 is: If SCR < C MRSCR , that is, η s < 0, the new energy grid-connected system is in an unstable state; If SCR > C MRSCR , that is, η s > 0, the new energy grid-connected system is in a stable state.

9. The short-circuit ratio quantitative evaluation method according to claim 6, characterized in that The calculation formula of S33 is: Among them, Z o represents the equivalent impedance of the network-forming energy storage; The stability judgment condition of S34 is: If G' MRSCR <C MRSCR1 or G'' MRSCR <C MRSCR2 , that is, when η M < 0, the new energy power station access system is in an unstable state; If G' MRSCR > C MRSCR1 or G'' MRSCR > C MRSCR2 , that is, when η M > 0, the access system of the new new energy power station is in a stable state.

10. A quantitative evaluation system for the short-circuit ratio of a grid-forming energy storage connected to a new energy power station, characterized in that, It includes: An equivalent short-circuit capacity calculation module, which is used to calculate the equivalent short-circuit capacity of the AC system based on the connection mode between the network-forming energy storage and the power grid and different access capacities. The connection modes between the network-forming energy storage and the power grid include the network-forming energy storage discharging and accessing the system and the network-forming energy storage charging and accessing the system; A short-circuit ratio and critical short-circuit ratio calculation module, which is used to calculate the short-circuit ratio and critical short-circuit ratio of the new energy power station after accessing the network-forming energy storage based on the equivalent node impedance and the maximum transmission power of the new energy system; A short-circuit ratio margin calculation module, which is used to calculate the short-circuit ratio margin of the new energy power station after the network-forming energy storage is connected to the system based on the difference between the short-circuit ratio and the critical short-circuit ratio.

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