Short-circuit current active suppression method and system for new energy power generation and energy storage system

Abstract

The invention provides a short-circuit current active suppression method and system of a new energy power generation and energy storage system, and belongs to the technical field of short-circuit current suppression of the new energy power generation and energy storage system. In order to solve the problems in the prior art, the invention provides a short-circuit current active suppression method and system of a new energy power generation and energy storage system. According to the technical scheme, grid-connected control is carried out on the new energy power generation and energy storage system by adopting a grid-following type control method and a grid-constructing type control method; when a system fault occurs, a low-voltage ride-through control method is adopted, when the low-voltage ride-through condition of the converter is met, it is guaranteed that the converter does not run off the grid continuously, meanwhile, a short-circuit current active suppression control method is adopted, a new energy power generation and energy storage system is controlled to inject dynamic reactive current meeting the requirement into a power grid, and it is guaranteed that the system does not run off the grid continuously; the active suppression of the short-circuit current is realized; the method is used for actively inhibiting 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 a new energy power generation and energy storage system. Background Art

[0002] A short circuit fault in a power grid refers to a short circuit between transmission lines or between a line and the earth (which may be a small resistance grounding or a metal direct grounding), which results in a huge short circuit current, seriously affecting the safe and stable operation of the power grid, the safety of electrical equipment and personnel. When a short circuit fault occurs in the power grid, the equivalent network impedance of the system will be greatly reduced, resulting in a short circuit current in the system that is much greater than the normal operating current. A high level of short circuit current will pose a huge threat to the safe operation of the system. When the short circuit current exceeds the breaking capacity of the circuit breaker, the circuit breaker cannot disconnect the short circuit current, which may cause a larger and more serious accident in the power grid.

[0003] With the development and construction of new power systems, more and more large-capacity renewable 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 renewable energy power generation and energy storage systems to the power grid is also increasing. In some areas where renewable energy and energy storage systems are connected, the power grid has experienced a serious problem of short-circuit current exceeding the limit at important nodes (220kV), posing a great threat to the safe and stable operation of the power grid.

[0004] At present, the method for suppressing short-circuit current provided by renewable energy power generation and energy storage systems 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: outer loop control and inner loop current control. The outer loop control realizes the output power regulation or stable control of DC voltage of renewable energy power generation and energy storage systems, and the inner loop current control realizes the active and reactive decoupling control and output current limiting functions. It can be seen that the outer loop control and the inner loop current control of the converter will affect the short-circuit current characteristics of renewable energy power generation and energy storage systems. Since the access of large-scale renewable energy power generation and energy storage systems has brought about an increase in the short-circuit current of the power grid, how to control and suppress the short-circuit current provided by the converter in the renewable energy power generation and energy storage system to the power grid is an engineering practical technical problem that needs to be solved urgently.

[0005] At present, the control scheme used to control the short-circuit current of renewable energy power generation and energy storage systems still has the following defects and shortcomings:

[0006] 1. Because the overload capacity of the converter 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 is generally to use an external hardware protection circuit when the output current exceeds the converter threshold current, and directly shut down the power device to make the converter stop running. This method can quickly and effectively protect the converter, but it will cause the key equipment of the non-fault branch to lose power, and the power supply reliability of the new 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 new energy power generation and energy storage system.

[0007] 2. When a short circuit occurs in the power grid, the current limiting device installed in the converter will cause the new energy power generation and energy storage system to output a short-circuit current according to 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, i.e. the maximum value, and the output of active power cannot be adjusted according to the external load demand, causing 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. The control methods commonly used in the current renewable energy power generation and energy storage systems are: the grid-following control method is used in normal operation, and the fault-travel control method is used in the event of a fault. With the development of new power systems, large-scale, large-capacity renewable energy power generation and energy storage systems are increasingly connected to the relatively weak power grid in the Shagohuang area, and the demand for grid-building control methods is increasingly evident. However, there is currently no universal control method that can combine both grid-following and grid-building control methods.

[0009] 4. Currently, the control of the converter is mainly aimed at grid connection control and low voltage fault ride-through control. There is no control strategy specifically for output short-circuit current suppression. The suppression of short-circuit current is passive or does not consider short-circuit current suppression. This method is applicable in the early scenario where new energy power generation and energy storage systems are not connected to the grid on a large scale. However, with the development of new power systems, large-scale and large-capacity new energy power generation and energy storage systems are increasingly connected to the grid. Due to the lack of active suppression strategies for short-circuit current injected into the grid, some grid connection points have short-circuit currents that exceed the limit. Therefore, the current more common control methods are no longer fully applicable to new operating scenarios.

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

[0011] To sum up, the existing technology can only limit the short-circuit current to a limiting value for the current limiting link, that is, when the short-circuit current is limited to a maximum value, when the current has not reached the maximum value and the short-circuit current can be further actively reduced, the short-circuit current is still output according to the maximum overcurrent capacity of the converter. This may cause the problem of excessive short-circuit current when the new energy power generation and energy storage system is connected to the public grid connection point of the power grid. In addition, the current suppression control methods are all aimed at a single specific application scenario, lack universality, and lack a universal method and system for both grid-following and grid-building 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 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: a short-circuit current active suppression method for a new energy power generation and energy storage system, comprising the following short-circuit current active suppression control steps:

[0014] Step 1: Use the grid-following control method and the grid-building control method to control the grid connection of the new energy power generation and energy storage system;

[0015] When the renewable energy power generation and energy storage system fails, the low voltage ride-through control method is adopted to ensure that the converter does not disconnect from the grid and operates continuously when the low voltage ride-through conditions of the converter are met. At the same time, the short-circuit current active suppression control method is adopted to control the renewable energy power generation and energy storage system to inject dynamic reactive current that meets the requirements into the power grid, ensuring that the renewable energy power generation and energy storage system does not disconnect from the grid and operates continuously, thus realizing active suppression of short-circuit current.

[0016] Step 2: Establish the rated output current I of the new energy power generation and energy storage system for the grid-following control method, grid-building control method, low voltage ride-through control method, and short-circuit current active suppression control method. N The d-axis component i of the actual current output by the system d and the q-axis component i q Mathematical models of relationships;

[0017] Select the network-following control or network-building control method according to the dispatching instruction, and give the control instruction value;

[0018] Step 3: Collect and calculate the voltage per unit value U and the d-axis component u of the voltage at the grid connection point of the new energy power generation and energy storage system respectively d and the q-axis component u q , active power P and reactive power Q, rated output current I of the new energy power generation and energy storage system at the grid connection point N, according to the calculation results, determine whether the new energy power generation and energy storage system has a fault. If no fault occurs, calculate the d-axis component reference value i of the AC side current of the new energy power generation and energy storage system according to normal working conditions dref and the q-axis component reference value i qref , and conduct grid-connected operation control; if the new energy power generation and energy storage system fails, go to step 4;

[0019] Step 4: According to the different current limiting conditions of the converter and the different voltage drop degrees of the grid connection point, set the threshold current kI according to the converter overcurrent capacity and the dispatching demand for short-circuit current suppression. 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 renewable energy generation and energy storage system under fault conditions dref and the q-axis component reference value i qref , and make it satisfy the current constraint condition, the expression is:

[0021] ;

[0022] Among them, I N is the rated output current of the renewable 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, u d is the d-axis component of the voltage;

[0023] Based on the multi-objective function of the optimal short-circuit current, the overcurrent weight coefficient k is corrected in real time and dynamically. The correction equation is:

[0024] ;

[0025] 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 of different k values ​​to the short-circuit current, I k is the short-circuit current of the output of the renewable energy power generation and energy storage system under different k values, I sk is the short-circuit current ratio, σ is the multi-objective weight coefficient;

[0026] Step 5: Determine whether the grid connection point voltage U is greater than 0.85U N , where U N The rated voltage per unit value of the grid connection point is:

[0027] If the grid 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 of the d-axis component of the AC side current of the new energy power generation and energy storage system dref and the q-axis component reference value i qref ;

[0028] If the grid voltage U is less than 0.85U N , then go to step six;

[0029] Step 6: Calculate the current limit value and drop voltage value based on the real-time sampling data, and choose whether to perform active output short-circuit current suppression control based on the dispatching instruction, so as to further reduce the active power value instruction 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, the active power command value of the renewable energy power generation and energy storage system is actively reduced according to the converter overcurrent capacity and control strategy limitation, thereby reducing the output short-circuit current and achieving active suppression of the short-circuit current.

[0031] The low voltage ride-through condition of the converter satisfied in step 1 is specifically:

[0032] When the grid connection point voltage drops to a level outside the low voltage crossing standard grid connection operation curve, the converter exits the grid connection 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 converters that are not cut out during a power system fault, their active power can be quickly restored after the fault is cleared, and from the moment the fault is cleared, it can be restored to the value before the fault at a power change rate of at least 30% of the rated power per second.

[0035] In step 1, the dynamic reactive current of the power grid that meets the requirements is injected, and the current calculation method is:

[0036] From the start of the dynamic reactive current response until the voltage recovers to 0.85 pu, where pu is the per-unit value, the q-axis component reference value i of the current injected into the power system by the converter is qref Real-time tracking of grid connection point voltage changes and meeting:

[0037] ;

[0038] Among them, I N is the rated output current of the renewable 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 of establishing the mathematical model in step 2 is:

[0040] Calculate the active power P and reactive power Q output by the new energy power generation and energy storage system. The calculation formula is:

[0041] ;

[0042] where i d + 、i d - 、i q + 、i q - are the d-axis and q-axis components of the positive-sequence current and negative-sequence current at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively; u d + 、u d - 、u q + 、u q - They are the d-axis and q-axis components of the positive-sequence voltage and negative-sequence voltage at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively;

[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 active power and reactive power are simplified to:

[0044] ;

[0045] Active current suppression control is used to control the reference value i of the d-axis component of the AC side current of the renewable energy power generation and energy storage system dref and the q-axis component reference value i 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 performed. At this time, the expressions of active power and reactive power are:

[0046] ;

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

[0048] The suppression system used to realize the short-circuit current active suppression method of the new energy power generation and energy storage system includes the following suppression control equipment function modules:

[0049] Field programmable gate array module, composed of basic programmable logic unit, programmable input / output unit, programmable wiring resources, memory module, multiplier module, clock frequency division / multiplication instruction circuit, used to run the mathematical model and comprehensive control strategy program of the converter, including real-time calculation of grid-following control, grid-building control, low voltage ride-through control, and short-circuit current active suppression control, real-time update of active power, reactive power instructions, and short-circuit current suppression instructions of new energy power generation and energy storage systems, and real-time simulation and calculation of general control of new energy power generation and energy storage systems and short-circuit current active suppression;

[0050] The central processing unit module is used to run the operating system, perform multi-task management, and complete the host computer application, communication, and human-computer interaction functions;

[0051] Digital signal processor module, used to realize the collection of electrical quantity data, the calculation task of dq decomposition, and the data exchange with the field programmable gate array module and the central processing unit module;

[0052] Memory unit, used to read and write data.

[0053] The beneficial effects of the present invention compared with the prior art are as follows: the method for actively suppressing short-circuit current in a universal renewable energy power generation and energy storage system provided by the present invention does not need to exit the converter operation in the event of a power grid fault, and can switch between the grid-following control method and the grid-forming control method according to scheduling and system requirements, while ensuring the normal low-voltage fault ride-through requirements of the converter, actively reducing and suppressing the impact of renewable energy power generation and energy storage systems on the short-circuit current of the power grid; there is no need to limit the short-circuit current by adding hardware such as a current limiting device in the event of a power grid fault, and the control function of the converter is fully utilized, and an active short-circuit current suppression method is adopted to reduce the impact of renewable energy power generation and energy storage systems on the short-circuit current output of the power grid; The present invention aims to solve the problem that traditional renewable energy power generation and energy storage systems can only passively limit the maximum current by current limiting value and have poor versatility. The present invention can flexibly realize switching between grid-following type and grid-building type control methods under different operating conditions of renewable energy power generation and energy storage systems and different requirements for short-circuit current suppression, and apply active short-circuit current suppression method to ensure that the renewable energy power generation and energy storage system provides the minimum short-circuit current to the power grid under fault ride-through conditions without disconnecting from the grid, so as to meet the requirements for safe and stable operation of the power grid. The active suppression method and system equipment provided by the present invention have good versatility, and can realize real-time switching control of various converter control methods, so as to meet the requirements of real-time control and protection system under normal and fault conditions. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0056] Figure 2 This is a standard schematic diagram of low voltage ride-through of a converter in a new energy station based on the present invention;

[0057] Figure 3 A flowchart of the implementation steps of the universal short-circuit current active suppression method proposed by the present invention;

[0058] Figure 4 This is a schematic diagram of the structure of the universal short-circuit current active suppression system proposed by the present invention. DETAILED DESCRIPTION

[0059] like Figures 1 to 4 As shown, the present invention proposes a universal control method and system equipment suitable for short-circuit current suppression of renewable energy power generation and energy storage systems. The method and system equipment have both universality and real-time performance through the designed universal control method and control system architecture. While meeting the requirements of different operating conditions such as grid-connected operation and fault operation of renewable energy power generation and energy storage systems, the short-circuit current provided by renewable energy power generation and energy storage systems to the power grid can be effectively reduced, and the self-regulation ability of renewable energy power generation and energy storage systems can be utilized to the maximum extent. Without adding other equipment, the short-circuit current provided by them can be effectively suppressed, which can not only ensure the economic and stable operation of renewable energy power generation and energy storage systems, but also have the function of active current suppression, and ensure the safe and stable operation of converters and power grids under fault operating conditions.

[0060] Based on the traditional grid-connected control of renewable energy power generation and energy storage systems, the present invention provides a universal real-time system with both grid-following and grid-building control methods. When a grid fault occurs, an active short-circuit current suppression method is introduced to perform real-time simulation and calculation according to the fault condition, and the active power and reactive power output instructions of the renewable energy power generation and energy storage systems are modified in real time. The current instructions are calculated and adjusted in real time, which can minimize the short-circuit current output by the renewable energy power generation and energy storage systems to the grid, so as to ensure the safe operation of the converter and the grid.

[0061] There are two main grid-connected control methods for converters: grid-following control and grid-forming control. The difference between the two types of control is mainly reflected in the outer loop controller. The present invention is applicable to different types of renewable 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, and general short-circuit current active suppression control. The structural diagram of the general short-circuit current active suppression method is shown in FIG. Figure 1 shown.

[0062] In engineering, active power and reactive power control are usually used, that is, the grid-connected control strategy of new energy power generation and energy storage system adopts active power and reactive power control, and low voltage ride-through control is added to ensure that the new energy power generation and energy storage system can continue to operate without disconnecting from the grid in the event of a fault. According to the technical specifications: When a fault occurs in the power system, if the grid connection point voltage is all within the voltage contour line required by the converter low voltage ride-through and above, the converter should ensure continuous operation without disconnecting from the grid; otherwise, the converter is allowed to exit the grid-connected operation. The standards and voltage contour lines of low voltage ride-through are as follows: Figure 2 As shown in the figure, the specific standards and requirements for converter low voltage ride-through are as follows:

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

[0064] (2) When the voltage at the inverter grid connection point drops below the curve, the inverter can be disconnected from the grid;

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

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

[0067] First, according to the system and scheduling instructions, select network-following control or network-building control instructions.

[0068] The data acquisition system collects real-time operating data of new energy power generation and energy storage systems, including active power, reactive power, grid connection point voltage and current, and performs dq decomposition.

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

[0070] According to the instantaneous power theory, the actual values ​​of active power and reactive power at the bus of the renewable energy power generation and energy storage system are expressed as follows (1):

[0071] (1);

[0072] where i d + 、i d - 、i q + 、iq - are the d-axis and q-axis components of the positive-sequence current and negative-sequence current at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively; u d + 、u d - 、u q + 、u q - They are the d-axis and q-axis components of the positive-sequence voltage and negative-sequence voltage at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively;

[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. At this time, equation (1) can be simplified to equation (2):

[0074] (2);

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

[0076] Under normal operating conditions, the output active power is controlled according to actual demand, and the reactive power is set to 0, since equation (3) is satisfied:

[0077] (3);

[0078] Therefore, the current I and i output by the new energy power generation and energy storage system are d Same, i q is 0.

[0079] When a short circuit occurs in the power grid and causes a voltage drop, the dynamic reactive power injected into the power grid by the new energy generation and energy storage system through the converter is from the dynamic reactive current response until the voltage recovers to 0.85pu, where pu is the per-unit value, and the q-axis component reference value i of the current injected into the power system by the converter is qref Track the voltage change of the grid connection point in real time and satisfy equation (4):

[0080] (4);

[0081] Among them, I N is the rated current of the renewable 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] According to the different current limiting conditions of the converter and the different voltage drop degrees of the grid connection point, the threshold current kI is set according to the converter overcurrent capacity and the dispatching demand for short-circuit current suppression. N, the value range of the overcurrent weight coefficient k is 0.8-3.0 (1.2 for grid-following control during normal grid-connected operation, 1.2-3.0 for grid-building control according to instructions, and the k value is dynamically adjusted according to the optimal short-circuit current correction equation when a fault occurs to achieve active short-circuit current suppression control); further 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 dref and the q-axis component reference value i qref , and make it meet the current constraint conditions. The calculation formula and constraint conditions are shown in formula (5):

[0083] (5);

[0084] Among them, I N is the rated output current of the renewable 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, 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 and dynamically. The correction equation is shown in the following equation (6):

[0086] (6);

[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 of different k values ​​to the short-circuit current, I k is the short-circuit current of the output of the renewable energy power generation and energy storage system under different k values, σ is the multi-objective weight coefficient, which is taken as 0.5 here, and the value can be further optimized in practical applications.

[0088] Active current suppression control is used to control the reference value i of the d-axis component of the AC side current of the renewable energy power generation and energy storage system dref and the q-axis component reference value i qref , which can actively reduce the short-circuit current provided by the energy storage system to the grid and realize low voltage ride-through control. The active power and reactive power of the system are shown in the following formula (7):

[0089] (7);

[0090] It can be seen from formula (7) that by controlling the d-axis component and q-axis component of the output current of the renewable energy power generation and energy storage system respectively, the active power and reactive power delivered by the renewable energy power generation and energy storage system can be adjusted.

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

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

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

[0094] (9);

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

[0096] 0.2≤U≤0.85 (10); where 0.2 and 0.85 are per unit values ​​of 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 current d-axis component reference value i dref and the q-axis component reference value i qref , the calculation formula is shown in formula (11);

[0098] (11);

[0099] When it is necessary to minimize the short-circuit current provided by the energy storage system to the grid, the converter active power current command i dref Set to 0, and then obtain the reference value i of the d-axis component of the output current of the new energy power generation and energy storage system dref and the q-axis component reference value i qref , as shown in the following formula (12):

[0100] (12);

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

[0102] U<0.2(13);0.2 is the per unit value of 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 q-axis component reference value i qref , as shown in the following formula (14):

[0104] (14);

[0105] It can be seen from equations (4) to (14) that when the renewable 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 overcurrent weight coefficient k is dynamically adjusted in real time, and the power generated by the renewable energy power generation and energy storage system is controlled according to the short-circuit current suppression requirements, thereby realizing the active suppression control of the short-circuit current.

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

[0107] (15);

[0108] Among them, u d It is the d-axis component of the actual value of the grid-connected point voltage during a fault.

[0109] Taking a 200MW energy storage system as an example, when the overcurrent weight coefficient k is 1.2, the grid voltage U drops to 0.82, and the active power generated by the renewable energy power generation and energy storage system can reach the rated value. The voltage operating range of this 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 per unit values ​​of voltage;

[0111] That is, in this voltage range, the short-circuit current output by the renewable 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.

[0112] When the overcurrent 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 operating range of this 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 voltage;

[0114] That is, in this voltage range, the short-circuit current output by the renewable 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.

[0115] Therefore, the short-circuit current active suppression control method is adopted within this voltage range, 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 active suppression effect of short-circuit current.

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

[0117] The multi-module architecture design adopts field-programmable gate array (FPGA), central processing unit (CPU), digital signal processor (DSP), and corresponding memory units. The FPGA+DSP+CPU system architecture structure and module logic relationship are as follows Figure 4 shown.

[0118] The storage unit can be configured as single-port mode, simple dual-port mode, full dual-port mode, shift register mode, read-only memory mode, First In First Out (FIFO) mode, etc. according to the needs, so as to complete high-speed reading and writing of data.

[0119] 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 / multiplication circuits, etc. Since FPGA has a highly configurable parallel hardware structure, distributed memory and pipeline architecture, it is suitable for highly parallel large-scale numerical calculations. Therefore, the system equipment has high-speed parallel computing capabilities.

[0120] FPGA, as the underlying computing hardware, has the characteristics of high parallelism, high throughput, low latency, high flexibility, and strong expansion capability due to its highly parallel hardware structure, pipeline computing architecture, rich I / O interfaces, and distributed data storage. The mathematical model and comprehensive control strategy of the converter are run 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 at the moment of short-circuit fault, so as to carry out real-time simulation and calculation of general control and short-circuit current active suppression methods of new energy power generation and energy storage systems, and meet the needs of real-time control and protection of the system.

[0121] 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 collection and dq decomposition.

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

[0123] According to the voltage drop of the grid connection point after a fault and the system's requirement for short-circuit current limitation, the present invention preferentially adopts a short-circuit current active suppression control method to reduce the total current output by the renewable energy power generation and energy storage system through voltage and short-circuit current interval judgment, while ensuring that the renewable energy power generation and energy storage system does not go off the grid, thereby achieving the purpose of suppressing the output short-circuit current of the renewable energy power generation and energy storage system. The present invention is suitable for grid-following and grid-building converters, and the control system equipment hardware architecture adopts the DSP+FPGA+CPU architecture, and has the functions of microsecond-level real-time parallel calculation, control and synchronous simulation, and has good real-time 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to 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 in a new energy power generation and energy storage system, characterized in that: The short-circuit current active suppression control steps include the following: Step 1: Use the grid-following control method and the grid-building control method to control the grid connection of the new energy power generation and energy storage system; When the renewable energy power generation and energy storage system fails, the low voltage ride-through control method is adopted to ensure that the converter does not disconnect from the grid and operates continuously when the low voltage ride-through conditions of the converter are met. At the same time, the short-circuit current active suppression control method is adopted to control the renewable energy power generation and energy storage system to inject dynamic reactive current that meets the requirements into the power grid, ensuring that the renewable energy power generation and energy storage system does not disconnect from the grid and operates continuously, thus realizing active suppression of short-circuit current. Step 2: Establish the rated output current I of the new energy power generation and energy storage system for the grid-following control method, grid-building control method, low voltage ride-through control method, and short-circuit current active suppression control method. N The d-axis component i of the actual current output by the system d and the q-axis component i q Mathematical models of relationships; Select the network-following control or network-building control method according to the dispatching instruction, and give the control instruction value; Step 3: Collect and calculate the voltage per unit value U and the d-axis component u of the voltage at the grid connection point of the new energy power generation and energy storage system respectively d and the q-axis component u q , active power P and reactive power Q, rated output current I of the new energy power generation and energy storage system at the grid connection point N , according to the calculation results, determine whether the new energy power generation and energy storage system has a fault. If no fault occurs, calculate the d-axis component reference value i of the AC side current of the new energy power generation and energy storage system according to normal working conditions dref and the q-axis component reference value i qref , and conduct grid-connected operation control; if the new energy power generation and energy storage system fails, go to step 4; Step 4: According to the different current limiting conditions of the converter and the different voltage drop degrees of the grid connection point, set the threshold current kI according to the converter overcurrent capacity and the dispatching demand for short-circuit current suppression. 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; Recalculate the reference value i of the d-axis component of the AC side current of the renewable energy generation and energy storage system under fault conditions dref and the q-axis component reference value i qref , and make it satisfy the current constraint condition, the expression is: ； Among them, I N is the rated output current of the renewable 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, 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 and dynamically. 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 of different k values ​​to the short-circuit current, I k is the short-circuit current of the output of the renewable energy power generation and energy storage system under different k values, I sk is the short-circuit current ratio, σ is the multi-objective weight coefficient; Step 5: Determine whether the grid connection point voltage U is greater than 0.85U N , where U N The rated voltage per unit value of the grid connection point is: If the grid 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 of the d-axis component of the AC side current of the new energy power generation and energy storage system dref and the q-axis component reference value i qref ; If the grid voltage U is less than 0.85U N , then go to step six; Step 6: Calculate the current limit value and drop voltage value based on the real-time sampling data, and choose whether to perform active output short-circuit current suppression control based on the dispatching instruction, so as to further reduce the active power value instruction issued by the new energy power generation and energy storage system; When the voltage drop at the grid connection point does not reach the limit value, the active power command value of the renewable energy power generation and energy storage system is actively reduced according to the converter overcurrent capacity and control strategy limitation, thereby reducing the output short-circuit current and achieving active suppression of the short-circuit current.

2. The short-circuit current active suppression method of the new energy power generation and energy storage system according to claim 1 is characterized by: The low voltage ride-through condition of the converter satisfied in step 1 is specifically: When the grid connection point voltage drops to a level outside the low voltage crossing 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 remain connected to the grid and operate continuously for 0.15 s; For converters that are not cut out during a power system fault, their active power can be quickly restored after the fault is cleared, and from the moment the fault is cleared, it can be restored to the value before the fault at a power change rate of at least 30% of the rated power per second.

3. The short-circuit current active suppression method of the new energy power generation and energy storage system according to claim 2 is characterized by: In step 1, the dynamic reactive current of the power grid that meets the requirements is injected, and the current calculation method is: From the start of the dynamic reactive current response until the voltage recovers to 0.85 pu, where pu is the per-unit value, the q-axis component reference value i of the current injected into the power system by the converter is qref Real-time tracking of grid connection point voltage changes and meeting: ； Among them, I N is the rated output current of the renewable 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 short-circuit current active suppression method of the new energy power generation and energy storage system according to claim 3 is characterized by: The specific method of 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. The calculation formula is: ； where i d + 、i d - 、i q + 、i q - are the d-axis and q-axis components of the positive-sequence current and negative-sequence current at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively; u d + 、u d - 、u q + 、u q - They are the d-axis and q-axis components of the positive-sequence voltage and negative-sequence voltage at the grid-connected busbar of the renewable energy power generation and energy storage system, respectively; 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 active power and reactive power are simplified to: ； Active current suppression control is used to control the reference value i of the d-axis component of the AC side current of the renewable energy power generation and energy storage system dref and the q-axis component reference value i 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 performed. At this time, the expressions of active power and reactive power are: ； When it is necessary to minimize the short-circuit current provided by the renewable energy generation and energy storage system to the power grid, the AC side current d-axis component reference value i dref =0, at this time, the converter inner loop current controller only provides the AC side current q-axis component reference value i qref .

5. A suppression system for implementing the short-circuit current active suppression method of the new energy power generation and energy storage system as claimed in claim 1, characterized in that: The following inhibition control equipment functional modules are included: Field programmable gate array module, composed of basic programmable logic unit, programmable input / output unit, programmable wiring resources, memory module, multiplier module, clock frequency division / multiplication instruction circuit, used to run the mathematical model and comprehensive control strategy program of the converter, including real-time calculation of grid-following control, grid-building control, low voltage ride-through control, and short-circuit current active suppression control, real-time update of active power, reactive power instructions, and short-circuit current suppression instructions of new energy power generation and energy storage systems, and real-time simulation and calculation of general control of new energy power generation and energy storage systems and short-circuit current active suppression; The central processing unit module is used to run the operating system, perform multi-task management, and complete the host computer application, communication, and human-computer interaction functions; Digital signal processor module, used to realize the collection of electrical quantity data, the calculation task of dq decomposition, and the data exchange with the field programmable gate array module and the central processing unit module; Memory unit, used to read and write data.

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