Method for controlling transient reactive power support of offshore wind power grid-connected system with participation of energy storage

Abstract

The invention provides a control method for participating in transient reactive power support of an offshore wind power grid-connected system by energy storage and a related device. The control method comprises the following steps: acquiring a voltage deviation value and a voltage change rate of a grid-connected point of the offshore wind power grid-connected system; judging whether the system is in a steady state according to the voltage deviation value; if yes, generating a given reactive power reference value as an energy storage reactive power instruction; if not, double-layer fuzzy control reasoning is carried out based on the voltage deviation value and the voltage change rate, and a dynamic reactive power reference value is obtained to serve as an energy storage reactive power instruction; and performing transient support control of energy storage according to the energy storage reactive instruction until the energy storage is finished, and participating in transient voltage recovery. Through double-layer fuzzy control reasoning, reactive power can be dynamically adjusted in real time according to the power grid state, reactive capacity waste is avoided, and the transient reactive supporting capacity in different transient scenes is improved. Meanwhile, the charge state of energy storage equipment is considered, unreasonable charging and discharging are avoided when the reactive power requirement of a power grid is met, and the energy storage service life is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and in particular relates to a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system. Background Art

[0002] The continuous development of power technology has led to significant progress in both renewable energy generation and power electronics. Renewable energy, with its clean and renewable advantages, is gradually increasing its share in the power system. Simultaneously, various power electronics equipment are becoming widely used in power transmission and distribution. This technological trend is driving the gradual evolution of power systems in my country's coastal regions toward a receiving-end grid structure with a high proportion of renewable energy and power electronics.

[0003] In recent years, offshore wind power, leveraging its abundant resources, has seen rapid growth worldwide. Offshore wind farms typically utilize offshore booster stations, where a high-voltage flexible DC transmission system converts the boosted AC power into DC. This power is then transmitted to land via offshore cables. Onshore converter stations, equipped with extensive power electronics, then convert the DC power into 50Hz AC for grid connection.

[0004] Renewable energy sources have weak reactive power support and interference mitigation capabilities, exposing receiving grids to the risk of transient voltage instability. The dynamic interaction between multiple power electronic devices and the grid complicates the transient voltage response characteristics of receiving grids with a high proportion of renewable energy (such as offshore wind power), leading to significant voltage stability issues. Large-scale offshore wind power grids face difficulties in responding quickly to large transient disturbances, making them prone to grid instability and disconnection. Relying solely on regulating renewable energy output cannot effectively support grid transient stability in extreme situations such as system disturbances and faults, hindering renewable energy absorption. Energy storage systems, with their advantages of flexible installation and efficient charging and discharging, are a growing trend in the power sector. They can smooth out fluctuations in renewable energy output, improving absorption levels and low-voltage ride-through capabilities. However, commonly used control strategies for energy storage systems, such as droop, constant power, and constant voltage, present numerous challenges in emergency situations such as ground faults at energy storage plants. For example, energy storage converters struggle to adjust reactive power in real time, resulting in wasted reactive capacity or limited support capabilities; parameter settings for different transient scenarios are sparse, resulting in insufficient support performance; and the energy storage state of charge is not considered. Summary of the Invention

[0005] In view of this, the present invention provides a control method for energy storage participating in transient reactive power support of offshore wind power grid-connected systems, aiming to at least solve one of the above-mentioned problems existing in the control method adopted when existing energy storage participates in transient reactive power support of offshore wind power grid-connected systems.

[0006] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for controlling energy storage participating in transient reactive power support of an offshore wind power grid-connected system, comprising the following steps:

[0008] Obtain the voltage deviation value and voltage change rate of the offshore wind power grid connection point;

[0009] Determine whether the system is in a steady state based on the voltage deviation value;

[0010] If so, a given reactive power reference value is generated as a stored energy reactive power instruction;

[0011] If not, a two-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive power reference value as the energy storage reactive power instruction. The two-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning. The upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value. The lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive power reference value that changes with time, that is, a dynamic reactive power reference value.

[0012] The transient support control of energy storage is carried out according to the energy storage reactive power instruction until the energy storage is completed and the transient voltage is restored.

[0013] Furthermore, in the upper-level fuzzy control reasoning, the fuzzy control rule table is shown in Table 1 below:

[0014] Table 1 Upper-level fuzzy rule table

[0015]

[0016] Among them, the voltage deviation value and the voltage change rate are divided into 7 areas, including negative large NL, negative medium NM, negative small NS, zero Z, positive small PS, positive medium PM and positive large PL; the reactive power command value is also divided into 7 areas, including negative large NB, negative medium NM, negative small NS, zero Z, positive small PS, positive medium PM and positive large PB.

[0017] Furthermore, in the lower-level fuzzy control reasoning, the fuzzy control rule table is shown in Table 2 below:

[0018] Table 2 Lower layer fuzzy control table

[0019]

[0020] Among them, Q int is the reactive power command value, SOC is the current state of charge of the energy storage, and SOC is divided into three areas, including negative large NL, zero Z and positive large PL.

[0021] Furthermore, transient support control of energy storage is performed according to the energy storage reactive power instruction until energy storage is completed and transient voltage recovery is carried out, including:

[0022] After performing transient support control of energy storage according to the energy storage reactive power instruction, determine whether the system is in a steady state based on the grid connection point voltage;

[0023] If not, the double-layer fuzzy control reasoning is repeated, and the transient support control of energy storage is repeated according to the energy storage reactive power instruction generated by the dynamic reactive power reference value until the system returns to a steady state.

[0024] For a system in steady state, transient support control of energy storage is performed according to the energy storage reactive instruction with a given reactive reference value until the energy storage is completed and participates in transient voltage recovery.

[0025] Furthermore, in transient support control, the following constraints are met:

[0026] Energy storage action interval constraints:

[0027]

[0028] Where, is the grid connection point voltage at time t;

[0029] State of charge constraints:

[0030]

[0031] Where, 、 They are the lower limit and upper limit of energy storage charge state respectively. is the energy storage charge state at time t;

[0032] Energy storage participating in transient voltage recovery power range constraints:

[0033]

[0034]

[0035]

[0036] Where, 、 、 、 They are the total rated power of the energy storage station, the reactive power output of the energy storage station at time t, the active power output of the energy storage station at time t, and the available active power of the energy storage station at time t; is the total active power of the energy storage power station at time t.

[0037] Furthermore, transient support control of energy storage is performed according to the energy storage reactive power instruction, including:

[0038] The reactive power reference value of the energy storage reactive power instruction is multiplied by the set power upper limit to obtain a control signal;

[0039] After the control signal is converted from per-unit value to actual value, it enters the power outer loop and current inner loop to obtain the trigger pulse signal;

[0040] Transient support control is performed based on trigger pulse signals.

[0041] Furthermore, when 0.95U pccN ≤U pcc (t)≤1.05U pccN , the system is judged to be in steady state, where U pcc (t) represents the grid connection point voltage at time t, U pccN Indicates the grid connection point voltage rating.

[0042] In a second aspect, the present invention provides a control device for energy storage participating in transient reactive power support of an offshore wind power grid-connected system, comprising:

[0043] A parameter acquisition module is used to obtain the voltage deviation value and voltage change rate of the grid connection point of the offshore wind power grid connection system;

[0044] An instruction generation module is used to determine whether the system is in a steady state based on the voltage deviation value;

[0045] If so, a given reactive power reference value is generated as a stored energy reactive power instruction;

[0046] If not, a two-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive power reference value as the energy storage reactive power instruction. The two-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning. The upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value. The lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive power reference value that changes with time, that is, a dynamic reactive power reference value.

[0047] The control module is used to perform transient support control of energy storage according to the energy storage reactive power instruction until the energy storage is completed and the transient voltage is restored.

[0048] In a third aspect, the present invention provides a computer device, comprising a processor and a memory:

[0049] The memory is used to store computer programs and send instructions of the computer programs to the processor;

[0050] The processor executes a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system according to the instructions of the computer program as described in the first aspect.

[0051] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system as in the first aspect is implemented.

[0052] In summary, the present invention provides a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system, including obtaining a voltage deviation value and a voltage change rate at a grid-connected point of the offshore wind power grid-connected system; judging whether the system is in a steady state according to the voltage deviation value; if so, generating a given reactive reference value as an energy storage reactive instruction; if not, performing a double-layer fuzzy control reasoning based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive reference value as an energy storage reactive instruction; wherein the double-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning; the upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input, and outputs a reactive power instruction value; the lower-layer fuzzy control reasoning takes the reactive power instruction value and the current charge state of the energy storage as input, and outputs a reactive reference value that changes with time, that is, a dynamic reactive reference value; transient support control of the energy storage is performed according to the energy storage reactive instruction until the energy storage ends and participates in transient voltage recovery. This invention uses dual-layer fuzzy control reasoning to dynamically adjust reactive power in real time based on grid conditions, avoiding reactive capacity waste and improving transient reactive power support capabilities in various transient scenarios. It also takes into account the charge state of the energy storage device, avoiding irrational charging and discharging when meeting the grid's reactive power requirements, and extending the life of the energy storage device.

[0053] The present invention also provides a control device, computer equipment and computer-readable storage medium for energy storage participating in transient reactive support of offshore wind power grid-connected systems, which have similar effects to the above-mentioned method when implemented and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 A flow chart of a control method for energy storage participating in transient reactive power support of an offshore wind power grid-connected system provided by an embodiment of the present invention;

[0056] Figure 2 Offshore wind power grid connection diagram provided by the present invention;

[0057] Figure 3 Reactive capacity diagram under bidirectional operation of energy storage provided by the present invention;

[0058] Figure 4 This is a structural diagram of the equivalent energy storage grid-connected system of the battery provided by the present invention;

[0059] Figure 5 A diagram of common energy storage control methods provided by the present invention;

[0060] Figure 6 This is a model diagram of the traditional droop control structure provided by the present invention;

[0061] Figure 7 A PQ control strategy diagram provided by an embodiment of the present invention;

[0062] Figure 8 A fuzzy control flow chart provided by an embodiment of the present invention;

[0063] Figure 9 A double-layer fuzzy control flow chart provided by an embodiment of the present invention;

[0064] Figure 10 A diagram of an energy storage station configured for offshore wind power grid connection according to an embodiment of the present invention;

[0065] Figure 11 A flow chart of energy storage actions under transient processes provided by an embodiment of the present invention;

[0066] Figure 12 An upper-layer fuzzy control graph provided by an embodiment of the present invention;

[0067] Figure 13 The lower fuzzy control graph provided by the embodiment of the present invention;

[0068] Figure 14 A diagram showing the voltage change at the grid connection point in simulation 1 provided by an embodiment of the present invention;

[0069] Figure 15 A diagram showing the voltage change at the grid connection point in the second simulation provided by an embodiment of the present invention;

[0070] Figure 16 A diagram showing the voltage change at the grid connection point in simulation 3 provided by an embodiment of the present invention;

[0071] Figure 17 A block diagram of a control device for energy storage participating in transient reactive power support of an offshore wind power grid-connected system provided by an embodiment of the present invention;

[0072] Figure 18 A block diagram of a computer device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the purposes, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0074] See also Figure 1-8 , Figure 1 The flow chart of a control method for energy storage participating in transient reactive support of offshore wind power grid-connected system is shown. Figure 2-8 right Figure 1 The background of the control method shown is introduced in detail.

[0075] like Figure 2 As shown in the figure, the offshore wind farm transmits power to the onshore grid via a high-voltage flexible direct current (HVDC) transmission system after passing through an offshore booster station. The HVDC system converts the boosted AC power into DC power, which is then transmitted over the sea via cables. Onshore, an onshore converter station, equipped with extensive power electronics, converts the transmitted DC power into 50Hz AC power for subsequent connection to the grid. Therefore, the sending end refers to the offshore wind farm, while the receiving end refers to the AC grid.

[0076] In extreme situations such as system disturbances and faults, regulating renewable energy (offshore wind power) output alone cannot effectively support the transient stability of the power grid, hindering the reliable absorption of renewable energy. To address this issue, reactive power compensation devices are often installed to support bus voltage. Compared to traditional capacitor compensation devices, energy storage systems, as a flexible regulatory resource, are becoming a future development trend in the power sector. Energy storage systems (ESS), with their flexible installation, diverse forms, and efficient charging and discharging, can effectively smooth out fluctuations in renewable energy output, significantly improve renewable energy absorption, and, to a certain extent, enhance the low-voltage and ride-through capabilities of grid-connected renewable energy power generation systems. Therefore, it is urgent to develop a control strategy for energy storage inverters that fully taps the reactive power regulation potential of large-scale energy storage power stations and effectively improves the transient voltage response characteristics of the system.

[0077] When connected to the grid, the energy storage system exhibits bidirectional transmission characteristics, meaning it can simultaneously emit and absorb active or reactive power. When a power shortfall occurs at the energy storage system's grid connection point (PCC), the energy storage battery discharges to compensate for the shortfall. When a power surplus occurs at the PCC, the surplus power is supplied to the energy storage battery for charging. Within the permitted state of charge (SOC) range, the reactive power support potential of the energy storage system during bidirectional charging and discharging is determined by the apparent power and active power, specifically expressed as:

[0078] (1)

[0079] Where: 、 ——The upper and lower limits of the reactive power of energy storage at time t; ——Apparent power of energy storage system; ——The active power of the energy storage system at time t. When the energy storage system operates under charging and discharging conditions, the output active power and reactive power range is as follows: Figure 3 shown.

[0080] The equivalent energy storage grid-connected system structure of the battery is as follows: Figure 4 As shown, the system consists of four components: an energy storage unit, a converter (i.e., a power conversion system (PCS)), a control system, and a measurement system. In a grid-connected energy storage system, the measurement system extracts the operating status information of the energy storage battery unit, converts it, and transmits it to the control system. Based on this status information and a given control strategy, the control system generates control signals for the PCS. Based on these control signals, the PCS controls the bidirectional energy transfer of the energy storage unit by changing the switching state of the power electronic devices (inverter). During transient conditions, to improve transient voltage stability, the energy storage system must output reactive power to compensate for insufficient reactive power in the grid or absorb excess reactive power. (In a grid, excessive reactive power increases voltage, while insufficient reactive power decreases voltage.)

[0081] In recent years, research on grid-connected inverter control strategies aimed at improving transient voltage support capabilities has attracted much attention. Under transient conditions, droop control, constant power, and constant voltage control strategies are currently commonly used as control methods for transient support.

[0082] Common controls such as Figure 5 As shown, it is described as follows (only for reactive power control):

[0083] ① Droop control

[0084] The commonly used droop control strategy is mainly based on reactive power-voltage droop control, as shown below:

[0085] (2)

[0086] Where, ——droop coefficient; ——voltage amplitude / effective value; ——Reference voltage amplitude / effective value.

[0087] Traditional droop control structure model such as Figure 6 As shown, where the given reference voltage amplitude / effective value U refThen get the voltage amplitude / effective value U, subtract the two, and multiply by the droop coefficient KQ to get the reactive reference value Q ref , Q ref Subtract the reactive power Qt controlled by the energy storage converter PCS and obtain the q-axis current reference value I after the PI link. qref Then it enters the current and voltage double closed-loop control link, and then obtains the SPWM signal that the PCS needs to control the inverter to open and close. The inverter is turned on and off according to the SPWM signal, thereby controlling the reactive power Q t Output.

[0088] ②PQ control

[0089] Compared with the droop control strategy, the previous voltage closed loop is omitted and the reactive reference value Q is directly given. ref , the subsequent operations are the same.

[0090] ③Constant voltage control

[0091] Compared with the droop control strategy, given the reference voltage amplitude / effective value U ref Then, we get the voltage amplitude / effective value U, subtract the two, and perform PI adjustment to get the reactive reference value Q ref , the subsequent operations are the same.

[0092] When a large-scale energy storage power station faces an emergency threat such as a ground fault, conventional control methods have the following disadvantages:

[0093] 1. When using droop control with fixed droop characteristics or other traditional control methods, it is difficult for the energy storage converter to adjust reactive power in real time based on the current system power output. This results in wasted reactive capacity of the energy storage system participating in grid voltage regulation, or the transient reactive power support capability provided is limited, further threatening the safe operation of the power system.

[0094] 2. Conventional control methods use a single parameter setting for different transient scenarios, such as transient undervoltage and transient overvoltage. This can result in excellent transient reactive power support performance in one transient scenario, but inadequate in another. (Good transient voltage support performance means the ability to fully control reactive power output or absorption based on the current grid state.)

[0095] 3. Conventional control methods only consider the reactive power output value and do not consider the state of charge (SOC) of the energy storage device, that is, the remaining power, which represents the ratio of the remaining power of the lithium battery to the fully charged power, usually as a percentage. SOC = 0 represents full discharge, and SOC = 1 represents a fully charged battery. The state of charge of the energy storage device should not be too high or too low. When the SOC is too low, the battery is deeply discharged, which may lead to incomplete chemical reactions or internal short circuits, thereby reducing the battery life. Excessively high SOC puts the battery in a saturated state, which may cause the chemical substances in the battery to be unable to effectively store more energy, reducing the battery's operating efficiency. Therefore, it is necessary to consider reducing the power emitted / absorbed when the state of charge of the energy storage device is too high or too low.

[0096] In view of the above problems, an embodiment of the present invention provides a control method for energy storage participating in transient reactive support of offshore wind power grid-connected system, the steps of which are as follows: Figure 1 As shown, including:

[0097] S1: Obtain the voltage deviation value and voltage change rate of the grid connection point of the offshore wind power grid connection system;

[0098] S2: Determine whether the system is in a steady state based on the voltage deviation value;

[0099] S3: If yes, generate a given reactive power reference value as the energy storage reactive power instruction;

[0100] S4: If not, a two-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive power reference value as the energy storage reactive power instruction. The two-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning. The upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value. The lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive power reference value that changes with time, i.e., a dynamic reactive power reference value.

[0101] It can be understood that after the energy storage reactive instruction generated by the dynamic reactive reference value in this step is used for transient reactive support control, if the system returns to steady state, the energy storage reactive instruction is adjusted to the energy storage reactive instruction generated by the given reactive reference value to continue control.

[0102] S5: Perform transient support control of energy storage according to the energy storage reactive power instruction until the energy storage is completed and the transient voltage is restored.

[0103] The following combination Figure 7-9 The control method proposed in this embodiment is introduced in detail.

[0104] Figure 7 This is the conventional PQ control strategy diagram: First, the active power set value P is given refand reactive power given value Q ref , then enters the PQ outer-loop control. This converts electrical quantities (current, voltage, etc.) from the three-phase stationary coordinate system into the rotating dq coordinate system, subsequently obtaining the d-axis and q-axis current reference values. This then leads to the current inner-loop control. Due to the coupling between the dq axes, the active and reactive power responses are determined by both the d-axis and q-axis currents. To effectively independently control the active power (P) and reactive power (Q), a feedforward decoupling strategy is often employed within the current inner-loop control to decouple the dq axes. The dq coordinate system is then converted back to the abc three-phase coordinate system to generate an SPWM signal. The SPWM generates a pulse signal that is transmitted to the energy storage converter (PCS). The PCS uses this signal to control the inverter's on / off state, achieving active and reactive power output.

[0105] When a transient occurs in the grid, the voltage will exceed the given range. If energy storage is involved in voltage regulation, the given reactive power value Q ref , which can easily lead to the problem of excess or insufficient output / absorption power. Therefore, the reactive power given value Q ref It needs to be dynamically adjusted according to the grid voltage information, just like droop control and other methods.

[0106] The reactive power support problem is a complex nonlinear problem, and this study considered using fuzzy control to solve it. Fuzzy control is a control method based on fuzzy logic that uses fuzzy reasoning and fuzzy rules to process and control complex, nonlinear systems. Unlike traditional control methods (such as PID control), fuzzy control does not require precise mathematical models, but instead makes decisions based on empirical rules. This makes fuzzy control highly advantageous when dealing with system uncertainty, complexity, and dynamic changes, making it particularly suitable for systems that are difficult to model.

[0107] Fuzzy control process such as Figure 8 As shown, including:

[0108] Input Settings: When designing a fuzzy controller, if only one input or output parameter is used, the performance of the controlled object cannot be accurately simulated. However, if too many input and output parameters are used, the number of rules in the fuzzy inference rule base will increase exponentially, resulting in a massive computational load and excessive time consumption during the simulation process. This is a significant drawback for time-sensitive control systems. Therefore, when designing a fuzzy controller, a two-input, one-output fuzzy controller is generally preferred.

[0109] Fuzzy control setting: simulate various possible situations of input parameters, set the fuzzy reasoning results corresponding to each output, and finally obtain the fuzzy control rules.

[0110] Simulation accuracy setting: Simulation accuracy is mainly determined by the number of divisions of the parameter change area. The more divisions there are for each input and output parameter interval, the higher the simulation accuracy will be, but the complexity will also be higher and it will be difficult to set. Generally, the division area is 3-7 intervals.

[0111] This embodiment comprehensively considers the voltage deviation value , voltage change rate The reactive power reference value Q is obtained by fuzzy control of the SOC value. ref (t), the overall process is as follows Figure 9 shown.

[0112] The input of the upper fuzzy control is the voltage deviation value , voltage change rate , the output is the reactive power command value Q int (t), the lower fuzzy control is based on the reactive power command value Q int (t) and SOC(t) are used as inputs, and the output reactive power reference value Q ref (t).

[0113] This embodiment provides a control method for energy storage participating in transient reactive power support for offshore wind power grid-connected systems. This method differs from traditional control methods in that it performs double-layer fuzzy control reasoning based on the grid connection point voltage deviation value and voltage change rate, allowing the reactive power setpoint to be dynamically adjusted based on the grid connection point voltage conditions, rather than adopting a fixed strategy.

[0114] In one embodiment of the present invention, transient support control of energy storage is performed according to the energy storage reactive power instruction until energy storage is completed and transient voltage recovery is participated in, including:

[0115] After performing transient support control of energy storage according to the energy storage reactive power instruction, determine whether the system is in a steady state based on the grid connection point voltage;

[0116] If not, the double-layer fuzzy control reasoning is repeated, and the transient support control of energy storage is repeated according to the energy storage reactive power instruction generated by the dynamic reactive power reference value until the system returns to a steady state.

[0117] For a system in steady state, transient support control of energy storage is performed according to the energy storage reactive instruction with a given reactive reference value until the energy storage is completed and participates in transient voltage recovery.

[0118] In one embodiment of the present invention, performing transient support control of energy storage according to energy storage reactive power instructions includes:

[0119] The reactive power reference value of the energy storage reactive power instruction is multiplied by the set power upper limit to obtain a control signal;

[0120] After the control signal is converted from per-unit value to actual value, it enters the power outer loop and current inner loop to obtain the trigger pulse signal;

[0121] Transient support control is performed based on trigger pulse signals.

[0122] like Figure 9 As shown, the output reactive power reference value Q ref (t), multiply it by the set power limit K n , convert the control signal from the per-unit value to the actual value, and then enter the power outer loop and current inner loop to obtain the trigger pulse signal.

[0123] In one embodiment of the present invention, when 0.95U pccN ≤U pcc (t)≤1.05U pccN , the system is judged to be in steady state, where U pcc (t) represents the grid connection point voltage at time t, U pccN Indicates the grid connection point voltage rating.

[0124] Taking the transient support control process and steady-state judgment of the above embodiment as an example, in the double-layer fuzzy control, the grid connection point voltage Upccref=1p.u. is set as the reference value, and the grid connection point voltage U pcc (t) Subtract to get the voltage deviation value , the reference value of the voltage deviation value is set to 0, and the voltage deviation value Subtraction forms a closed loop control. Figure 10 As shown, the energy storage action process in the entire transient process is as follows Figure 11 As shown, the steps are as follows:

[0125] Step 1: Monitor the voltage at the grid connection point to determine whether the system is in a steady state:

[0126] If the grid voltage is 0.95U pccN ≤U pcc (t)≤1.05U pccN , then the system is judged to be in steady state;

[0127] Step 2: When the voltage drops below 0.95U pccN or higher than 1.05U pccN :

[0128] The energy storage switching control strategy enters the fuzzy reasoning stage, comprehensively considers the reactive power demand and the current state of charge, and gives the reactive power dynamic instruction Q ref (t), the energy storage starts to generate reactive power;

[0129] Step 3: Monitor the voltage at the grid connection point to determine if the system has reached a steady state:

[0130] If the grid voltage U pcc (t) is in the steady-state range, and the voltage change rate is close to 0, then the energy storage gives the reactive power instruction Q ref (t)=0;

[0131] If the grid voltage U pcc (t) is in the transient interval, then according to the grid voltage U pcc (t) Real-time status, dynamic adjustment of reactive power instruction Q ref (t).

[0132] In one embodiment of the present invention, the upper fuzzy control reasoning is as follows Figure 12 As shown, the fuzzy control rule table is shown in Table 1 below:

[0133] Table 1 Upper-level fuzzy rule table

[0134]

[0135] Assuming the grid voltage parameters are divided into seven regions, the fuzzy control rules require 7*7=49 rules. The voltage deviation value and voltage change rate are both divided into seven regions: negative (large) NL, negative (medium) NM, negative (small) NS, zero (Z), positive (small) PS, positive (medium) PM, and positive (large) PL. The reactive power command value is also divided into seven regions: negative (large) NB, negative (medium) NM, negative (small) NS, zero (Z), positive (small) PS, positive (medium) PM, and positive (large) PB. The fuzzy control rules are roughly explained as follows:

[0136] ① Voltage deviation is less than -0.05:

[0137] When the voltage drops and the voltage deviation is less than -0.05, the rate of change is negative, and a reactive power command is issued to the energy storage station. As the voltage deviation increases and the voltage change first increases and then decreases, the reactive power output command should be increased. When the voltage deviation does not change much after a period of time, the voltage change rate is close to 0, the voltage drops to the lowest point, and the reactive power output command should be the maximum value of the set range. When the voltage change rate starts to be positive and the voltage deviation decreases to a certain extent, it is in the voltage recovery stage, and the reactive power output command should be gradually reduced from the maximum value of the set range.

[0138] ②The voltage deviation is between -0.05 and 0.05:

[0139] If the voltage deviation is between -0.05 and 0, but the voltage change rate is still large, a small amount of reactive output command should be continuously guaranteed at this time; if the voltage deviation is between -0.05 and 0.05 and the voltage change rate is close to 0, the reactive command becomes 0; if the voltage deviation is between 0 and 0.05 and the voltage change rate is a positive value not close to 0, the reactive command should first ensure a small amount of reactive absorption command; if the voltage deviation is between 0 and 0.05 and the voltage change rate is a negative value not close to 0, the reactive command should first become 0.

[0140] ③The voltage deviation is greater than 0.05:

[0141] If the voltage deviation is greater than 0.05 and the voltage change rate is still a positive value not close to 0, a transient overvoltage occurs and the reactive absorption instruction should be gradually increased; if the voltage deviation is greater than 0.05 and the voltage change rate is close to 0, it is at the maximum transient overvoltage and the reactive absorption instruction should be the maximum value of the set range; if the voltage deviation is greater than 0.05 and the voltage change rate is negative, the reactive absorption instruction should be gradually reduced.

[0142] In one embodiment of the present invention, the lower level fuzzy control reasoning is as follows Figure 13 As shown, the fuzzy control rule table is shown in Table 2 below:

[0143] Table 2 Lower layer fuzzy control table

[0144]

[0145] Among them, Q int is the reactive power command value, SOC is the current state of charge of the energy storage, and SOC is divided into three areas, including negative large NL, zero Z and positive large PL. Output Q int If (t) is positive, it means that reactive power is absorbed and the output Q int If (t) is negative, it means reactive power is being generated.

[0146] In one embodiment of the present invention, in transient support control, the following constraints are met:

[0147] Energy storage action interval constraints:

[0148] (3)

[0149] Where, is the grid connection point voltage at time t;

[0150] State of charge constraints:

[0151] (4)

[0152] Where, 、 They are the lower limit and upper limit of energy storage charge state respectively. is the energy storage charge state at time t;

[0153] Energy storage participating in transient voltage recovery power range constraints:

[0154] (5)

[0155] (6)

[0156] (7)

[0157] Where, 、 、 、 They are the total rated power of the energy storage station, the reactive power output of the energy storage station at time t, the active power output of the energy storage station at time t, and the available active power of the energy storage station at time t; is the total active power of the energy storage power station at time t.

[0158] The above method is verified by combining a numerical example. The simulation settings of the numerical example are as follows:

[0159] Offshore wind power grid-connected energy storage configuration Figure 10 The offshore wind farm utilizes a multi-input system, with 60 turbines rated at 5MW each. Each wind farm has a transmission capacity of 300MW. With four wind farms, the total offshore wind power grid-connected is 1,200MW, connected to the 220kV AC grid via flexible direct current transmission lines. Energy storage is also configured to be 200MVA.

[0160] In simulation 1, a three-phase ground short circuit fault lasting 0.5 seconds occurs on the AC line of the offshore wind power grid at t=1.5 seconds, and the voltage drops to 0.22pu. The upper limit of the energy storage power is set to 0.6Sn. The voltage change at the grid connection point is as follows: Figure 14 As shown, the transient voltage recovery analysis is as follows:

[0161] The double-layer fuzzy control strategy proposed in the present invention can reduce the transient overvoltage peak from 1.36pu to 1.08pu. At the same time, compared with other methods, the strategy proposed in the present invention can better reduce the transient overvoltage peak and accelerate the transient voltage recovery speed after improving the fuzzy control rules.

[0162] Simulation 2: On the AC line of offshore wind power grid connection, a three-phase ground short circuit fault lasting 0.5 seconds occurs at t=1.5 seconds. The upper limit of energy storage power is set to 0.6Sn. The voltage change at the grid connection point under different SOC states is studied. Figure 15 As shown, the transient voltage stability analysis is as follows:

[0163] In the double-layer fuzzy control strategy proposed in this invention, U pcc,max (15%)>U pcc,max (90%)>U pcc,max (50%), that is, when the SOC is close to 90% or close to 10%, the energy storage station considers its own SOC state and changes the reactive power command value Q ref (t), while satisfying the dynamic reactive power support as much as possible, the reactive power command value is reduced to avoid reducing the service life.

[0164] Simulation 3: At the offshore wind power grid connection point, a reactive load disturbance lasting 0.5 seconds occurs at t=1.5 seconds. Under different control strategies, the upper limit of the energy storage power is set to 0.6Sn. The voltage change at the grid connection point is as follows: Figure 16 As shown, the transient voltage recovery analysis is as follows:

[0165] The dual-layer fuzzy control strategy proposed in this paper effectively improves transient low voltage during reactive load disturbances, raising the voltage from 0.895 pu to approximately 0.924 pu. Furthermore, by incorporating the voltage change rate as a research objective, the control rules enable continuous reactive power output during the voltage recovery phase to accelerate voltage recovery.

[0166] Based on the above embodiments, the control method proposed in the present invention has the following advantages:

[0167] 1. In the control strategy of the present invention, the reactive power setpoint is dynamically adjusted according to the voltage condition at the grid connection point;

[0168] 2. Consider the state of charge of the energy storage device and adjust the fuzzy rules. When it is at the charge boundary, the reactive output / absorption of the energy storage device is reduced. While satisfying the dynamic reactive support as much as possible, the reactive power command value is reduced to avoid reducing the service life of the energy storage (most dynamic adjustment strategies are only dynamically adjusted according to the grid connection point, and the voltage deviation value is comprehensively considered). , voltage change rate There is no fuzzy control of SOC);

[0169] 3. Divide fuzzy control into two layers to reduce the complexity of rule formulation and the amount of algorithm calculation;

[0170] 4. Under the fuzzy control strategy, the final reactive power demand is determined by fuzzy control rules, which can increase the upper limit. Using voltage deviation and voltage rate of change as dynamic indicators, this strategy not only meets reactive power requirements during transient low voltage conditions, but also effectively addresses reactive power requirements during overvoltage regulation and transient overvoltage conditions, thus adapting to various transient voltage stability issues. (Control strategies such as droop control, which include a PI component, can effectively address reactive power requirements during transient low voltage conditions by adjusting PI parameters. However, their single parameter setting does not necessarily provide adequate transient voltage support for overvoltage regulation and transient overvoltage conditions.)

[0171] Based on the same inventive concept, an embodiment of the present application further provides a control device for energy storage participating in transient reactive power support of an offshore wind power grid-connected system, which is used to implement the aforementioned control method for energy storage participating in transient reactive power support of an offshore wind power grid-connected system. The solution provided by this device is similar to the solution described in the aforementioned method. Therefore, the specific limitations of the embodiment of the control device for energy storage participating in transient reactive power support of an offshore wind power grid-connected system provided below can be found in the limitations of the control method for energy storage participating in transient reactive power support of an offshore wind power grid-connected system described above, and will not be repeated here.

[0172] See also Figure 17 The present invention provides a control device for energy storage participating in transient reactive power support of an offshore wind power grid-connected system, comprising:

[0173] A parameter acquisition module is used to obtain the voltage deviation value and voltage change rate of the grid connection point of the offshore wind power grid connection system;

[0174] An instruction generation module is used to determine whether the system is in a steady state based on the voltage deviation value;

[0175] If so, a given reactive power reference value is generated as a stored energy reactive power instruction;

[0176] If not, a two-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive power reference value as the energy storage reactive power instruction. The two-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning. The upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value. The lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive power reference value that changes with time, that is, a dynamic reactive power reference value.

[0177] The control module is used to perform transient support control of energy storage according to the energy storage reactive power instruction until the energy storage is completed and the transient voltage is restored.

[0178] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0179] Reference Figure 18 An embodiment of the present invention further provides a computer device, comprising: a memory and a processor, and a computer program stored in the memory. When the computer program is executed on the processor, a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system as described in any one of the above methods is implemented.

[0180] The computer device may be a desktop computer, notebook computer, PDA, cloud server or other computing device. The computer device may include, but is not limited to, a processor and a memory. It will be understood by those skilled in the art that Figure 18 The computer device is merely an example and does not constitute a limitation on the computer device. The computer device may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, etc.

[0181] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0182] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard drive or memory of the computer device. In other embodiments, the memory may also be an external storage device of the computer device, such as a plug-in hard drive, a Smart Media Card (SMC), a Secure Digital (SD) card, a flash memory card, etc. equipped with the computer device. Furthermore, the memory may include both an internal storage unit of the computer device and an external storage device. The memory is used to store an operating system, application programs, a boot loader, data, and other programs, such as the program code of the computer program. The memory may also be used to temporarily store data that has been output or is about to be output.

[0183] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system as described in any one of the above methods is implemented.

[0184] In this embodiment, if the integrated unit is implemented as a software functional unit and sold or used as a standalone product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application can implement all or part of the process steps in the above-mentioned method embodiments by using a computer program to instruct the relevant hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of each of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file, or some intermediate form. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a camera / terminal device, recording medium, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signals, telecommunication signals, and software distribution media. Examples include USB flash drives, removable hard drives, magnetic disks, or optical disks. In some jurisdictions, based on legislation and patent practice, computer-readable media cannot be electric carrier signals or telecommunication signals.

[0185] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0186] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0187] In the embodiments disclosed in the present application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely schematic. For example, the division of the modules or units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0188] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A control method for energy storage participating in transient reactive support of offshore wind power grid-connected system, characterized in that: The steps include: Obtain the voltage deviation value and voltage change rate of the offshore wind power grid connection point; determining whether the system is in a steady state according to the voltage deviation value; If so, a given reactive power reference value is generated as a stored energy reactive power instruction; If not, a double-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive reference value as the energy storage reactive instruction; wherein the double-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning; the upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value; the lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive reference value that changes with time, that is, the dynamic reactive reference value; The transient support control of energy storage is performed according to the energy storage reactive instruction until the energy storage is completed and the transient voltage is restored.

2. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 1 is characterized in that: In the upper-level fuzzy control reasoning, the fuzzy control rule table is shown in Table 1 below: Table 1 Upper-level fuzzy rule table Among them, the voltage deviation value and the voltage change rate are divided into 7 regions, including negative large NL, negative medium NM, negative small NS, zero Z, positive small PS, positive medium PM and positive large PL; the reactive power instruction value is also divided into 7 regions, including negative large NB, negative medium NM, negative small NS, zero Z, positive small PS, positive medium PM and positive large PB.

3. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 2 is characterized in that: In the lower-level fuzzy control reasoning, the fuzzy control rule table is shown in Table 2 below: Table 2 Lower layer fuzzy control table Among them, Q int is the reactive power command value, SOC is the current state of charge of the energy storage, and SOC is divided into three areas, including negative large NL, zero Z and positive large PL.

4. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 1, characterized in that: Performing transient support control of energy storage according to the energy storage reactive power instruction until energy storage is completed and participating in transient voltage recovery includes: After performing transient support control of energy storage according to the energy storage reactive power instruction, determining whether the system is in a steady state according to the grid connection point voltage; If not, the double-layer fuzzy control reasoning is performed again, and the transient support control of the energy storage is performed again according to the energy storage reactive instruction generated by the dynamic reactive reference value until the system returns to a steady state; For a system in a steady state, transient support control of energy storage is performed according to the energy storage reactive instruction with a given reactive reference value until energy storage is completed and transient voltage recovery is participated in.

5. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 1 or 4, characterized in that: In the transient support control, the following constraints are met: Energy storage action interval constraints: Where, is the grid connection point voltage at time t; State of charge constraints: Where, 、 They are the lower limit and upper limit of energy storage charge state respectively. is the energy storage charge state at time t; Energy storage participating in transient voltage recovery power range constraints: Where, 、 、 、 They are the total rated power of the energy storage station, the reactive power output of the energy storage station at time t, the active power output of the energy storage station at time t, and the available active power of the energy storage station at time t; is the total active power of the energy storage power station at time t.

6. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 1 or 4, characterized in that: Performing transient support control of energy storage according to the energy storage reactive power instruction includes: Multiplying the reactive power reference value of the energy storage reactive power instruction by a set power upper limit to obtain a control signal; After the control signal is converted from a per-unit value to an actual value, it enters the power outer loop and the current inner loop to obtain a trigger pulse signal; Transient support control is performed based on the trigger pulse signal.

7. The control method for energy storage participating in transient reactive support of offshore wind power grid-connected system according to claim 1, characterized in that: When 0.95U pccN ≤U pcc (t)≤1.05U pccN , the system is judged to be in steady state, where U pcc (t) represents the grid connection point voltage at time t, U pccN Indicates the grid connection point voltage rating.

8. A control device for energy storage participating in transient reactive power support of offshore wind power grid-connected system, characterized in that: include: A parameter acquisition module is used to obtain the voltage deviation value and voltage change rate of the grid connection point of the offshore wind power grid connection system; An instruction generating module is used to determine whether the system is in a steady state according to the voltage deviation value; If so, a given reactive power reference value is generated as a stored energy reactive power instruction; If not, a double-layer fuzzy control reasoning is performed based on the voltage deviation value and the voltage change rate to obtain a dynamic reactive reference value as the energy storage reactive instruction; wherein the double-layer fuzzy control reasoning includes an upper-layer fuzzy control reasoning and a lower-layer fuzzy control reasoning; the upper-layer fuzzy control reasoning takes the voltage deviation value and the voltage change rate as input and outputs a reactive power instruction value; the lower-layer fuzzy control reasoning takes the reactive power instruction value and the current state of charge of the energy storage as input and outputs a reactive reference value that changes with time, that is, the dynamic reactive reference value; The control module is used to perform transient support control of energy storage according to the energy storage reactive power instruction until energy storage is completed and participates in transient voltage recovery.

9. A computer device, characterized in that: The device includes a processor and a memory: The memory is used to store the computer program and send instructions of the computer program to the processor; The processor executes a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system according to any one of claims 1 to 7 according to instructions of the computer program.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, which, when executed by a processor, implements a control method for energy storage participating in transient reactive support of an offshore wind power grid-connected system according to any one of claims 1 to 7.

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