Active Short-Circuit Current Suppression Method and System for New Energy Power Generation and Energy Storage Systems

Abstract

The present invention provides a method and system for actively suppressing short-circuit current in a new energy power generation and energy storage system, belonging to the technical field of short-circuit current suppression in new energy power generation and energy storage systems; in order to solve the problems existing in the prior art, a method and system for actively suppressing short-circuit current in a new energy power generation and energy storage system are provided; the adopted technical solution is: a grid-following control method and a grid-forming control method are used to perform grid connection control on the new energy power generation and energy storage system; during system faults, a low-voltage ride-through control method is adopted. When the low-voltage ride-through conditions of the converter are met, it is ensured that the converter operates continuously without tripping. At the same time, a short-circuit current active suppression control method is adopted to control the new energy power generation and energy storage system to inject dynamic reactive current meeting the requirements into the power grid, ensuring that the system operates continuously without tripping and realizing the active suppression of short-circuit current; the present invention is used to actively suppress the short-circuit current generated by the new energy power generation and energy storage system.

Description

Technical Field

[0001] The present invention provides a method and system for actively suppressing short-circuit current of a new energy power generation and energy storage system, belonging to the technical field of short-circuit current suppression of new energy power generation and energy storage systems. Background Art

[0002] A power grid short-circuit fault refers to a short circuit between lines or between a line and the ground in a transmission line (which may be a small-resistance grounding or a direct metal grounding), thereby forming a huge short-circuit current, seriously affecting the safe and stable operation of the power grid, electrical equipment, and personal safety. When a short-circuit fault occurs in the power grid, the equivalent network impedance of the system will be greatly reduced, resulting in the short-circuit current in the system being much larger than the normal operating current. A high-level short-circuit current poses a huge threat to the safe operation of the system. When the short-circuit current exceeds the breaking capacity of the circuit breaker, since the circuit breaker cannot disconnect the short-circuit current, it may lead to larger and more serious accidents in the power grid.

[0003] With the development and construction of a new power system, more and more large-capacity new energy power generation and energy storage systems are connected to the power grid. When a short-circuit fault occurs in the power grid, the short-circuit current provided by the new energy power generation and energy storage system to the power grid is also increasing. In some regional power grids with new energy and energy storage systems connected, there is a serious problem of short-circuit current exceeding the limit at important nodes (220 kV), posing a great threat to the safe and stable operation of the power grid.

[0004] Currently, for the method of suppressing the short-circuit current provided by new energy power generation and energy storage systems, it mainly depends on the control strategy of the converter control system and the rated capacity of the converter. The control loop of the converter includes two parts: an outer-loop control and an inner-loop current control. The outer-loop control realizes the output power regulation of the new energy power generation and energy storage system or the stable control of the DC voltage. The current inner-loop control realizes the decoupling control of active and reactive power and the current limiting function of the output current. It can be seen that both the outer-loop control and the current inner-loop control of the converter will affect the short-circuit current characteristics of the new energy power generation and energy storage system. Due to the increase in the power grid short-circuit current caused by the access of large-scale new energy power generation and energy storage systems, how to control and suppress the short-circuit current provided by the converter in the new energy power generation and energy storage system to the power grid is an engineering practical technical problem that needs to be solved urgently.

[0005] Currently, the control schemes adopted to control the short-circuit current of new energy power generation and energy storage systems still have the following defects and deficiencies:

[0006] First, because the converter's overload capacity is weak, in order to protect the converter from damage due to overload when a ground short circuit fault occurs in the power grid, the early method generally used an external hardware protection circuit to directly shut down the power devices when the output current exceeded the converter threshold current, causing the converter to exit operation. This method can quickly and effectively protect the converter, but it will cause key equipment in non-fault branches to lose power, and the power supply reliability of the renewable energy power generation and energy storage system cannot be guaranteed. At the same time, it cannot meet the grid connection and low-voltage fault ride-through requirements of the renewable energy power generation and energy storage system.

[0007] Second, when a short circuit occurs in the power grid, the new energy power generation and energy storage system will output a short-circuit current based on the voltage drop at the grid connection point. Due to the action of the current limiting device, the short-circuit current will be limited to the limit value, that is, the maximum value, and the output of active power cannot be adjusted according to the external load demand. This causes the new energy power generation and energy storage system to output unnecessary active power, increase the output short-circuit current, and thus inject a large short-circuit current into the new energy power generation and energy storage system.

[0008] 3. Currently, the control methods commonly used by renewable energy power generation and energy storage systems are: grid-following control during normal operation and fault-ride-through control during faults. With the development of new power systems, large-scale, high-capacity renewable energy power generation and energy storage systems are increasingly connected to the relatively weak power grid in the desert region. The demand for grid-forming control methods is becoming increasingly apparent, but there is currently no universal control method that can combine both grid-following and grid-forming control.

[0009] Fourth, current converter control primarily focuses on grid connection and low-voltage fault ride-through control. There are no dedicated control strategies for output short-circuit current suppression. Short-circuit current suppression is passive or not considered. This approach was applicable in early scenarios where renewable energy generation and energy storage systems were not connected to the grid on a large scale. However, with the development of new power systems, large-scale, high-capacity renewable energy generation and energy storage systems are increasingly connected to the grid. Due to the lack of active strategies to suppress short-circuit currents injected into the grid, some grid connection points have experienced short-circuit current exceeding limits. Consequently, the more common control methods currently used are no longer fully applicable to these new operating scenarios.

[0010] 5. Currently, there is no method or system that can be used in new energy power generation and energy storage systems, which has both grid-following and grid-forming control and can actively suppress fault currents. Most of them are designed for a single scenario.

[0011] In summary, in the prior art, for the current limiting link, the short-circuit current can only be limited to the limit value, that is, when the short-circuit current is limited to the maximum value. For the case where the current does not reach the maximum value and can further actively reduce the short-circuit current, the short-circuit current is still output according to the maximum over-current capacity of the converter. This may bring the problem of short-circuit current exceeding the standard when the new energy power generation and energy storage system is connected to the grid common connection point. In addition, the current suppression control means all target single specific application scenarios, lack generality, and lack a general method and system that combines grid-following control and grid-forming control. Summary of the Invention

[0012] In order to solve the problems existing in the prior art, the present invention provides a method and system for actively suppressing the short-circuit current of a new energy power generation and energy storage system.

[0013] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for actively suppressing the short-circuit current of a new energy power generation and energy storage system, including the following steps of actively suppressing the short-circuit current control:

[0014] Step 1: Adopt a grid-following control method and a grid-forming control method to perform grid connection control on the new energy power generation and energy storage system;

[0015] When the new energy power generation and energy storage system fails, adopt a low-voltage ride-through control method. When the low-voltage ride-through conditions of the converter are met, ensure that the converter operates continuously without tripping. At the same time, adopt a short-circuit current active suppression control method to control the new energy power generation and energy storage system to inject dynamic reactive current that meets the requirements into the grid, ensure that the new energy power generation and energy storage system operates continuously without tripping, and achieve active suppression of the short-circuit current;

[0016] Step 2: Respectively establish a mathematical model of the relationship between the rated output current I N of the new energy power generation and energy storage system and the d-axis component i d and the q-axis component i q of the actual current output by the system;

[0017] Select a grid-following control or a grid-forming control method according to the dispatching instruction, and give the control instruction value;

[0018] Step 3: Respectively collect and calculate the per-unit value U of the voltage at the grid connection point of the new energy power generation and energy storage system, the d-axis component u d and the q-axis component u q of the voltage, the active power P and the reactive power Q, and the rated output current I N, determine whether a fault occurs in the new energy power generation and energy storage system according to the calculation results. If no fault occurs, calculate the reference value i of the d-axis component of the AC-side current of the new energy power generation and energy storage system under normal operating conditions dref and the reference value i of the q-axis component qref , and perform grid-connected operation control; if a fault occurs in the new energy power generation and energy storage system, go to Step Four;

[0019] Step Four: For different current limiting conditions of the converter and different degrees of voltage dips at the grid connection point, set the threshold current kI according to the overcurrent capacity of the converter and the demand for short-circuit current suppression by the dispatching N , where k is the overcurrent weight coefficient. When a fault occurs, the overcurrent weight coefficient k is dynamically corrected in real time according to the multi-objective function of the optimal short-circuit current to achieve active short-circuit current suppression control;

[0020] Recalculate the reference value i of the d-axis component of the AC-side current of the new energy power generation and energy storage system under fault conditions dref and the reference value i of the q-axis component qref , and make it satisfy the current constraint condition. The expression is:

[0021]

[0022] where, I N is the rated output current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, U is the per-unit value of the grid connection point voltage, and u d is the d-axis component of the voltage;

[0023] Dynamically correct the overcurrent weight coefficient k in real time based on the multi-objective function of the optimal short-circuit current. The correction equation is:

[0024]

[0025] where, I N is the rated current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, S IK is the contribution degree of different k values to the short-circuit current, I k is the short-circuit current output by the new energy power generation and energy storage system under different k values, I sk is the short-circuit current ratio, and σ is the multi-objective weight coefficient;

[0026] Step Five: Judge whether the grid connection point voltage U is greater than 0.85U N , where U N is the per-unit value of the rated voltage of the grid connection point:

[0027] If the grid connection point voltage U is greater than 0.85U N, the active power command value is adjusted according to the active power required by the power grid, and the reference value i of the d-axis component of the AC-side current of the new energy power generation and energy storage system is recalculated dref and the reference value i of the q-axis component qref ;

[0028] If the grid connection point voltage U is less than 0.85U N , then go to Step 6;

[0029] Step 6: Calculate the current limiting value and the voltage drop value based on the real-time sampling data, and select whether to perform active suppression control of the output short-circuit current according to the dispatching instruction, and further reduce the active power value command issued by the new energy power generation and energy storage system;

[0030] When the voltage drop at the grid connection point does not reach the limit value, limit the amplitude according to the overcurrent capacity of the converter and the control strategy, actively reduce the active power command value of the new energy power generation and energy storage system, and reduce the output short-circuit current to achieve active suppression of the short-circuit current.

[0031] The specific conditions for the low voltage ride-through of the converter satisfied in Step 1 are as follows:

[0032] When the grid connection point voltage drops below the low voltage ride-through standard grid-connected operation curve, the converter exits the grid-connected operation state;

[0033] When the grid connection point voltage drops to 0, the converter can remain connected to the grid and operate continuously for 0.15 s;

[0034] For the converters that are not disconnected during the power system fault, their active power can recover quickly after the fault is cleared. Starting from the moment when the fault is cleared, it recovers to the value before the fault at a power change rate of at least 30% of the rated power per second.

[0035] The dynamic reactive current injected into the power grid that meets the requirements in Step 1, and the calculation method of this current is as follows:

[0036] From the start of the dynamic reactive current response until the voltage recovers to 0.85 p.u., where p.u. is the per-unit value, the reference value i of the q-axis component of the current injected by the converter into the power system qref Tracks the change of the grid connection point voltage in real time and satisfies:

[0037]

[0038] where, I N is the rated output current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, and U is the per-unit value of the grid connection point voltage.

[0039] The specific method for establishing the mathematical model in Step 2 is as follows:

[0040] Calculate the active power P and reactive power Q output by the new energy power generation and energy storage system. The calculation formulas are as follows:

[0041]

[0042] where i d + is the d-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i d - is the d-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i q + is the q-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i q - is the q-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system; u d + is the d-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, and u d - is the d-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, and u q + is the q-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, and u q - is the q-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system;

[0043] Taking the positive-sequence voltage as the reference of the d-axis of the dq synchronous rotating coordinate system, the projection of the positive-sequence voltage on the q-axis is 0, and the expressions of the actual values of the active power and reactive power are simplified as:

[0044]

[0045] Adopt active current suppression control to control the reference value i dref of the d-axis component and the reference value i qref of the q-axis component of the alternating current side current of the new energy power generation and energy storage system. While actively reducing the short-circuit current provided by the new energy power generation and energy storage system to the power grid, low-voltage ride-through control is carried out. At this time, the expressions of the active power and reactive power are:

[0046]

[0047] When it is necessary to minimize the short-circuit current provided by the new energy power generation and energy storage system to the power grid, set the reference value i dref of the d-axis component of the alternating current side current of the converter to 0. At this time, the inner-loop current controller of the converter only provides the reference value i qref of the q-axis component of the alternating current side current.

[0048] A suppression system adopted for the short-circuit current active suppression method of a new energy power generation and energy storage system includes the following suppression control device function modules:

[0049] A field programmable gate array module, which consists of basic programmable logic units, programmable input / output units, programmable wiring resources, memory modules, multiplier modules, and clock frequency division / doubling instruction circuits, is used to run the mathematical model of the converter and the comprehensive control strategy program, including the real-time calculation of grid-following control, grid-forming control, low voltage ride-through control, and short-circuit current active suppression control, real-time updating of the active power, reactive power commands, and short-circuit current suppression commands of the new energy power generation and energy storage system, and real-time simulation and calculation of the general control of the new energy power generation and energy storage system and the active suppression of short-circuit current;

[0050] A central processing unit module, which is used to run the operating system, perform multitask management, and complete the functions of the upper computer application program, communication, and human-machine interaction;

[0051] A digital signal processor module, which is used to implement the functions of collecting electrical quantity data, calculating the dq decomposition task, and exchanging data with the field programmable gate array module and the central processing unit module;

[0052] A memory unit, which is used to implement data reading and writing.

[0053] The beneficial effects of the present invention compared with the prior art are as follows: The method for actively suppressing short-circuit current of the general-purpose new energy power generation and energy storage system provided by the present invention does not require the converter to exit operation under grid fault conditions. It can switch between the grid-following control and grid-forming control methods according to the dispatching and system requirements. When ensuring the normal low voltage fault ride-through requirements of the converter, it can actively reduce and suppress the impact of the new energy power generation and energy storage system on the grid short-circuit current; nor does it require adding hardware such as current limiting devices to limit the short-circuit current under grid fault conditions. It makes full use of the control function of the converter and adopts the active short-circuit current suppression method to reduce the impact of the new energy power generation and energy storage system on the grid output short-circuit current. Aiming at the problems of the traditional new energy power generation and energy storage system that can only passively limit the maximum current by the current limiting value and has poor versatility, the present invention can flexibly switch between the grid-following and grid-forming control methods under different operating conditions of the new energy power generation and energy storage system and different requirements for short-circuit current suppression, and apply the active short-circuit current suppression method to ensure that the new energy power generation and energy storage system provides the minimum short-circuit current to the grid under the fault ride-through condition without tripping, so as to meet the requirements of the safe and stable operation of the grid. Moreover, the active suppression method and system equipment provided by the present invention have good versatility and can realize the real-time switching control of various converter control methods, meeting the requirements of the real-time control and protection system under normal and fault conditions. Description of the Drawings

[0054] The present invention will be further described below with reference to the accompanying drawings:

[0055] Figure 1 It is a structural block diagram of the general short-circuit current active suppression control method proposed by the present invention;

[0056] Figure 2 It is a standard schematic diagram of the low-voltage ride-through of the converter in the new energy power station according to the present invention;

[0057] Figure 3 It is a flowchart of the implementation steps of the general short-circuit current active suppression method proposed by the present invention;

[0058] Figure 4 It is a structural schematic diagram of the general short-circuit current active suppression system proposed by the present invention. Specific implementation manners

[0059] As Figures 1 to 4 shown, the present invention proposes a general control method and system equipment for short-circuit current suppression applicable to new energy power generation and energy storage systems. Through the designed general control method and control system architecture, the method and system equipment have both universality and real-time performance. While meeting the requirements of different operating conditions such as grid-connected operation and fault operation of new energy power generation and energy storage systems, it can effectively reduce the short-circuit current provided by new energy power generation and energy storage systems to the power grid, maximize the use of the self-regulation ability of new energy power generation and energy storage systems, and effectively suppress the short-circuit current provided by them without adding other equipment. It can not only ensure the economic and stable operation of new energy power generation and energy storage systems, but also have the function of active current suppression, and ensure the safe and stable operation of the converter and the power grid under fault operating conditions.

[0060] Based on the traditional grid-connected control of new energy power generation and energy storage systems, the present invention provides a general real-time system with both grid-following and grid-forming control methods. When a grid fault occurs, a short-circuit current active suppression method is introduced, real-time simulation and calculation are carried out according to the fault situation, the active power and reactive power output commands of new energy power generation and energy storage systems are modified in real time, and the current commands are calculated and adjusted in real time, which can minimize the short-circuit current output by new energy power generation and energy storage systems to the power grid to ensure the safe operation of the converter and the power grid.

[0061] The grid-connected control of the converter mainly includes grid-following control and grid-forming control. The differences between the two controls are mainly reflected in the outer-loop controller. The present invention is applicable to different types of new energy power generation and energy storage systems, including grid-following active power and reactive power (PQ) control, grid-forming voltage / frequency (V / f) control, droop control, low-voltage ride-through control, high-voltage ride-through control, general short-circuit current active suppression control and other methods. The structural diagram of the general short-circuit current active suppression method is asFigure 1 as shown

[0062] In engineering, the constant active power and constant reactive power control methods are usually adopted, that is, the grid-connected control strategy of the new energy power generation and energy storage system adopts active power and reactive power control. To ensure that the new energy power generation and energy storage system can operate continuously without disconnecting from the grid under fault conditions, low voltage ride-through control is added. According to the technical specification requirements: when a fault occurs in the power system, if the grid-connected point voltage of the converter is all within the area above the voltage profile line required for the low voltage ride-through of the converter, the converter should ensure continuous operation without disconnecting from the grid; otherwise, the converter is allowed to withdraw from grid-connected operation. The standards and voltage profile lines for low voltage ride-through are as Figure 2 shown, and the specific standards and requirements for the low voltage ride-through of the converter are as follows:

[0063] (1) When the grid-connected point voltage of the converter drops to 0, the converter can ensure continuous operation without disconnecting from the grid for 0.15 s;

[0064] (2) When the grid-connected point voltage of the converter drops below the curve, the converter can be disconnected from the power grid;

[0065] (3) For the converters that are not disconnected during the power system fault, their active power should be able to recover quickly after the fault is cleared. Starting from the moment when the fault is cleared, it should recover to the value before the fault at a power change rate of at least 30% of the rated power per second.

[0066] To implement the general active short-circuit current suppression method of the present invention, the general short-circuit current active suppression method and steps adopted by the present invention are as Figure 3 shown.

[0067] First, according to the instructions of the system and dispatching, select the grid-following control or grid-forming control instruction.

[0068] The operation data of the new energy power generation and energy storage system, including active power, reactive power, grid-connected point voltage, and current, are collected in real time through the data acquisition system and are subjected to dq decomposition.

[0069] Apply dq decomposition to establish the mathematical relationship between the output current I of the new energy power generation and energy storage system and the d-axis component i d and the q-axis component i q . The specific method is as follows:

[0070] According to the instantaneous power theory, the expressions of the actual values of the active power and reactive power at the bus of the new energy power generation and energy storage system are as shown in the following formula (1):

[0071]

[0072] where, i d +is the d-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, i d - is the d-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system, i q + is the q-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, i q - is the q-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system; u d + is the d-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u d - is the d-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u q + is the q-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u q - is the q-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system;

[0073] When the d-axis of the dq synchronous rotating coordinate system is based on the positive-sequence voltage, the projection of the positive-sequence voltage on the q-axis is 0, and at this time, Equation (1) can be simplified to Equation (2):

[0074]

[0075] It can be seen from Equation (2) that by separately controlling the d-axis component of the AC-side current and the q-axis component of the negative-sequence current of the new energy power generation and energy storage system, the active power and reactive power transmitted by the new energy power generation and energy storage system can be adjusted.

[0076] Under normal operating conditions, the output active power is controlled according to actual needs, and the reactive power is set to 0. Since Equation (3) is satisfied:

[0077]

[0078] Therefore, the current I output by the new energy power generation and energy storage system at this time is the same as i d i q is 0.

[0079] When a short-circuit fault occurs in the power grid and causes a voltage dip, the dynamic reactive power injected into the power grid by the new energy power generation and energy storage system through the converter. From the start of the dynamic reactive current response until the voltage recovers to 0.85 p.u., where p.u. is the per-unit value, the reference value i of the q-axis component of the current injected by the converter into the power system qref tracks the change of the grid-connected point voltage in real time and satisfies Equation (4):

[0080]

[0081] Among them, I N is the rated current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, and U is the per-unit value of the grid connection point voltage.

[0082] For different current limiting conditions of the converter and different degrees of voltage dips at the grid connection point, the threshold current kI is set according to the overcurrent capacity of the converter and the demand for short-circuit current suppression by the dispatching N , and the value range of the overcurrent weight coefficient k is 0.8 - 3.0 (when operating in normal grid connection, the grid-following control takes 1.2, and the grid-forming control takes 1.2 - 3.0 according to the command. When a fault occurs, the k value is dynamically adjusted according to the optimal short-circuit current correction equation to achieve active short-circuit current suppression control); further calculate the reference value i dref of the d-axis component and the reference value i qref of the q-axis component of the alternating current side current of the new energy power generation and energy storage system, and make them satisfy the current constraint conditions. The calculation formula and constraint conditions are as shown in Equation (5):

[0083]

[0084] Among them, I N is the rated output current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, U is the per-unit value of the grid connection point voltage, and u d is the d-axis component of the voltage.

[0085] Based on the multi-objective function of the optimal short-circuit current, the overcurrent weight coefficient k is corrected in real time dynamically. The correction equation is as shown in the following Equation (6):

[0086]

[0087] Among them, I N is the rated current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, S IK is the contribution degree of different k values to the short-circuit current, I k is the short-circuit current output by the new energy power generation and energy storage system under different k values, and σ is the multi-objective weight coefficient, which is taken as 0.5 here and can be further optimized in actual applications.

[0088] Adopt active current suppression control to control the reference value i dref of the d-axis component and the reference value i qref of the q-axis component of the alternating current side current of the new energy power generation and energy storage system. In this way, the short-circuit current provided by the energy storage system to the power grid can be actively reduced while realizing the low voltage ride-through control. The active power and reactive power of the system are as shown in the following Equation (7):

[0089]

[0090] As can be seen from Equation (7), by separately controlling the d-axis component and q-axis component of the output current of the new energy power generation and energy storage system, the active power and reactive power transmitted by the new energy power generation and energy storage system can be adjusted.

[0091] When the voltage U at the grid connection point satisfies the relational expression (8):

[0092] U > 0.85 (8); where 0.85 is the per-unit value of the voltage;

[0093] The new energy power generation and energy storage system does not generate reactive power, and the reference value i of the d-axis component of the output current of the new energy power generation and energy storage system is obtained dref and the reference value i of the q-axis component qref , as shown in the following Equation (9), and the short-circuit current of the output is effectively suppressed by dynamically adjusting the overcurrent weighting coefficient k:

[0094]

[0095] When the voltage U at the grid connection point satisfies the relational expression (10):

[0096] 0.2 ≤ U ≤ 0.85 (10); where 0.2 and 0.85 are the per-unit values of the voltage;

[0097] During the low voltage ride-through control and short-circuit current active suppression control of the converter, the VSC inner-loop current controller provides the reference value i of the d-axis component of the current dref and the reference value i of the q-axis component qref , and the calculation formula is as shown in the following Equation (11);

[0098]

[0099] When it is necessary to minimize the short-circuit current provided by the energy storage system to the power grid, the active power current command i of the converter can be set to 0 according to the dispatching instruction or system demand, and then the reference value i of the d-axis component of the output current of the new energy power generation and energy storage system is obtained dref and the reference value i of the q-axis component dref and the reference value i of the q-axis component qref , as shown in the following Equation (12):

[0100]

[0101] When the voltage U at the grid connection point satisfies the relational expression (13):

[0102] U < 0.2 (13); where 0.2 is the per-unit value of the voltage;

[0103] At this time, the new energy power generation and energy storage system does not provide active power, and the reference value i of the d-axis component of the output current of the new energy power generation and energy storage system is obtained dref and the reference value i of the q-axis componentqref , as shown in the following formula (14):

[0104]

[0105] It can be seen from formulas (4) to (14) that when the new energy power generation and energy storage system enters the low-voltage ride-through control process, due to the adoption of the short-circuit current active suppression method, the over-current weight coefficient k is dynamically and real-time adjusted, and the power generated by the new energy power generation and energy storage system is controlled according to the short-circuit current suppression requirement, so as to realize the active suppression control of the short-circuit current.

[0106] In addition, during the low-voltage ride-through control process, when it is necessary for the new energy power generation and energy storage system to provide a certain amount of active power, when the over-current capacity of the converter is kI N , the current that the new energy power generation and energy storage system can output is as shown in the following formula (15), and at this time the short-circuit current is not the minimum short-circuit current:

[0107]

[0108] where u d is the d-axis component of the actual value of the grid connection point voltage during the fault.

[0109] Taking a 200MW energy storage system as an example, when the over-current weight coefficient k is 1.2, the grid connection point voltage U drops to 0.82, and the active power generated by the new energy power generation and energy storage system can reach the rated value. The voltage operation range of this working condition can be obtained as shown in the following formula (16):

[0110] 0.82 ≤ U ≤ 0.85 (16); where 0.82 and 0.85 are the per-unit values of the voltage;

[0111] That is, in this voltage range, the short-circuit current output by the new energy power generation and energy storage system will reach the limit value, that is, the maximum value. If the active current suppression method is not adopted, the system will provide the maximum short-circuit current to the short-circuit point at this time.

[0112] When the over-current weight coefficient k is 1.5, the grid connection point voltage U drops to 0.67, and the active power generated by the new energy power generation and energy storage system can reach the rated value. The voltage operation range of this working condition can be obtained as shown in the following formula (17):

[0113] 0.67 ≤ U ≤ 0.85 (17); where 0.67 and 0.85 are the per-unit values of the voltage;

[0114] That is, in this voltage range, the short-circuit current output by the new energy power generation and energy storage system will reach the limit value, that is, the maximum value. If the active current suppression method is not adopted, the system will provide the maximum short-circuit current to the short-circuit point at this time.

[0115] Therefore, in this voltage range, the active short-circuit current suppression control method is adopted, and the active power output of the new energy power generation and energy storage system is flexibly adjusted within this range, which can effectively achieve the effect of active short-circuit current suppression.

[0116] The present invention also provides a general-purpose and real-time active short-circuit current suppression system, which mainly includes the following modules:

[0117] A multi-module architecture design is adopted, which includes a field-programmable gate array (FPGA), a central processing unit (CPU), a digital signal processor (DSP), and corresponding memory units. The FPGA+DSP+CPU system architecture and the module logic relationship are as Figure 4 shown.

[0118] According to requirements, the storage unit can configure the memory as a single-port mode, a simple dual-port mode, a full dual-port mode, a shift register mode, a read-only memory mode, a first-in-first-out queue (FIFO), etc., so as to complete the high-speed reading and writing of data.

[0119] The FPGA is mainly composed of a large number of basic programmable logic units, programmable input / output units, programmable wiring resources, memory modules, DSP multiplier modules, clock frequency division / doubling circuits, etc. Since the FPGA has a highly configurable parallel hardware structure, distributed memory, and a pipeline architecture, which is suitable for large-scale numerical operations with high parallelism. Therefore, the system equipment has the ability of high-speed parallel computing.

[0120] Due to its highly parallel hardware structure, pipeline computing architecture, rich I / O interfaces, and distributed data storage, the FPGA has the characteristics of high parallelism, high throughput, low latency, high flexibility, and strong expansion ability as the underlying computing hardware. Running the mathematical model and comprehensive control strategy of the converter in the FPGA system, through microsecond-level high-speed parallel computing, the active power, reactive power, and short-circuit current suppression instructions of the control system are calculated and updated in real time to meet the real-time switching of different control functions and control instructions of the system during the short-circuit fault moment, so as to perform real-time simulation and calculation of the general control of the new energy power generation and energy storage system and the active short-circuit current suppression method, and meet the requirements of system real-time control and protection.

[0121] The DSP is a signal processor unit that processes and converts the collected relevant electrical quantities, and mainly completes the calculation tasks of conventional electrical quantity data acquisition and dq decomposition.

[0122] The CPU is a general - purpose processor unit, including functions such as general - purpose algorithms, operating system and application communication, human - machine interaction, and post - period data analysis and processing.

[0123] According to the voltage drop condition of the grid - connection point after a fault and the requirements of the system for short - circuit current limitation, the present invention, while ensuring that the new - energy power generation and energy - storage system does not disconnect from the grid, adopts a short - circuit current active suppression control method preferentially through voltage and short - circuit current interval criteria to reduce the total current output by the new - energy power generation and energy - storage system, thereby achieving the purpose of suppressing the short - circuit current output by the new - energy power generation and energy - storage system. The present invention is applicable to grid - following and grid - forming converters. The hardware architecture of the control system equipment adopts the architecture of DSP + FPGA + CPU, and at the same time has the functions of micro - second - level real - time parallel computing, control, and synchronous simulation, with good real - time performance and versatility.

[0124] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent substitutions on some or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for actively suppressing short-circuit current of a new energy power generation and energy storage system, characterized in that: It includes the following active short-circuit current suppression control steps: Step 1: Adopt the grid-following control method and grid-forming control method to conduct grid connection control on the new energy power generation and energy storage system; when a fault occurs in the new energy power generation and energy storage system, adopt the low-voltage ride-through control method. When the low-voltage ride-through conditions of the converter are met, ensure that the converter operates continuously without disconnecting from the grid. At the same time, adopt the active short-circuit current suppression control method to control the new energy power generation and energy storage system to inject dynamic reactive current that meets the requirements into the grid, ensure that the new energy power generation and energy storage system operates continuously without disconnecting from the grid, and achieve active suppression of the short-circuit current; Step 2: Establish a mathematical model for the relationship between the rated output current I of the new energy power generation and energy storage system and the d-axis component i and q-axis component i of the actual current output by the system, respectively, for the grid-following control method, grid-forming control method, low-voltage ride-through control method, and short-circuit current active suppression control method. N of the actual current output by the system. d and the q-axis component i q of the actual current output by the system. Select the grid-following control or grid-forming control method according to the dispatching instruction and give the control instruction value; Step 3: Collect and calculate the per-unit value U of the voltage, the d-axis component u of the voltage, d and the q-axis component u q , the active power P, the reactive power Q, and the rated output current I of the new energy power generation and energy storage system at the grid connection point. Determine whether the new energy power generation and energy storage system has a fault according to the calculation results. If there is no fault, calculate the reference value i of the d-axis component of the AC-side current of the new energy power generation and energy storage system N and the reference value i of the q-axis component according to the normal operating conditions dref for grid-connected operation control; if the new energy power generation and energy storage system has a fault, go to Step 4; qref ​ Step 4: For different current limiting conditions of the converter and different degrees of voltage dips at the grid connection point, set the threshold current kI according to the overcurrent capacity of the converter and the demand of the dispatching for short-circuit current suppression N , where k is the overcurrent weight coefficient. During a fault, the overcurrent weight coefficient k is dynamically corrected in real time according to the multi-objective function of the optimal short-circuit current to achieve active short-circuit current suppression control; Recalculate the reference value of the d-axis component i of the AC-side current of the new energy power generation and energy storage system under fault conditions dref and the reference value of the q-axis component i qref , and make it satisfy the current constraint condition. The expression is as follows: Among them, I N is the rated output current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, U is the per-unit value of the grid connection point voltage, and u d is the d-axis component of the voltage; Based on the multi-objective function of the optimal short-circuit current, the overcurrent weight coefficient k is corrected in real time dynamically, and the correction equation is: Among them, I N is the rated current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, S IK is the contribution degree of different k values to the short-circuit current, I k is the short-circuit current output by the new energy power generation and energy storage system under different k values, I sk is the short-circuit current ratio, and σ is the multi-objective weight coefficient; Step Five: Determine whether the grid connection point voltage U at this time is greater than 0.85U N , where U N is the per-unit value of the rated voltage at the grid connection point: If the grid connection point voltage U is greater than 0.85U N , then adjust the active power command value according to the active power required by the power grid, and recalculate the reference value i dref of the d-axis component and the reference value i qref of the q-axis component of the alternating current side current of the new energy power generation and energy storage system; If the grid connection point voltage U is less than 0.85U N , then proceed to Step 6; Step 6: Calculate the current limiting value and the voltage drop value according to the real-time sampling data, and select whether to perform active short-circuit current suppression control according to the dispatching instruction, and further reduce the active power value instruction issued by the new energy power generation and energy storage system; when the grid connection point voltage drop does not reach the limit value, limit according to the overcurrent capacity and control strategy of the converter, actively reduce the active power instruction value of the new energy power generation and energy storage system, and reduce the output short-circuit current to achieve active suppression of the short-circuit current.

2. The method for actively suppressing short-circuit current of the new energy power generation and energy storage system according to claim 1, characterized in that: The specific low-voltage ride-through conditions of the converter satisfied in Step 1 are: When the grid connection point voltage drops outside the low-voltage ride-through standard grid connection operation curve, the converter exits the grid connection operation state; When the grid connection point voltage drops to 0, the converter can maintain continuous operation without disconnecting from the grid for 0.15 s; For the converters that are not cut out during the power system fault, their active power can be quickly restored after the fault is cleared. Starting from the moment when the fault is cleared, it is restored to the value before the fault at a power change rate of at least 30% of the rated power per second.

3. The active short-circuit current suppression method for the new energy power generation and energy storage system according to claim 2, wherein: The dynamic reactive current injected into the grid that meets the requirements in Step 1, and the calculation method of this current is: During the period from the start of the automatic dynamic reactive current response until the voltage recovers to 0.85 p.u., where p.u. is the per-unit value, the reference value of the q-axis component of the current injected by the converter into the power system is i qref Track the changes in the grid-connected point voltage in real time and satisfy: Among them, I N is the rated output current of the new energy power generation and energy storage system, k is the overcurrent weight coefficient, and U is the per-unit value of the grid connection point voltage.

4. The method for actively suppressing short-circuit current of the new energy power generation and energy storage system according to claim 3, wherein: The specific method for establishing the mathematical model in Step 2 is: Calculate the active power P and reactive power Q output by the new energy power generation and energy storage system, and the calculation formulas are: wherein, i d + is the d-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i d - is the d-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i q + is the q-axis component of the positive-sequence current at the grid-connected bus of the new energy power generation and energy storage system, and i q - is the q-axis component of the negative-sequence current at the grid-connected bus of the new energy power generation and energy storage system; u d + is the d-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u d - is the d-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u q + is the q-axis component of the positive-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system, u q - is the q-axis component of the negative-sequence voltage at the grid-connected bus of the new energy power generation and energy storage system; Taking the positive-sequence voltage as the reference of the d-axis of the dq synchronous rotating coordinate system, the projection of the positive-sequence voltage on the q-axis is 0, and the expressions of the actual values of the active power and reactive power are simplified to: Adopt active current suppression control to control the reference value i of the d-axis component of the AC-side current of the new energy power generation and energy storage system dref and the reference value i of the q-axis component qref . While actively reducing the short-circuit current provided by the new energy power generation and energy storage system to the power grid, low-voltage ride-through control is carried out. At this time, the expressions of active power and reactive power are as follows: When it is necessary to minimize the short-circuit current provided by the new energy power generation and energy storage system to the power grid, the reference value i of the d-axis component of the AC-side current of the converter is set to 0. At this time, the inner-loop current controller of the converter only provides the reference value i of the q-axis component of the AC-side current. dref qref .​ 5. The suppression system adopted for the method of actively suppressing short-circuit current of the new energy power generation and energy storage system described in claim 1, characterized in that: It includes the following suppression control equipment function modules: Field Programmable Gate Array (FPGA) module, which consists of basic programmable logic units, programmable input / output units, programmable wiring resources, memory modules, multiplier modules, and clock frequency division / doubling instruction circuits, and is used to run the mathematical model of the converter and the comprehensive control strategy program, including real-time calculations of grid-following control, grid-forming control, low-voltage ride-through control, and active short-circuit current suppression control, real-time update of the active power, reactive power instruction, and short-circuit current suppression instruction of the new energy power generation and energy storage system, and conduct real-time simulation and calculation of the general control of the new energy power generation and energy storage system and the active short-circuit current suppression; Central Processing Unit (CPU) module, which is used to run the operating system, conduct multi-task management, and complete the functions of the upper computer application program, communication, and human-computer interaction; A digital signal processor module, which is used to implement the functions of collecting electrical quantity data, calculating the dq decomposition, and exchanging data with a field programmable gate array module and a central processing unit module; A memory unit, which is used to implement the reading and writing of data.

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