Frequency-voltage coupling support control method and device for sea wind flexible direct current system based on power grid demand and system support capability

Abstract

The invention discloses a frequency-voltage coupling support control method and device for a sea wind flexible direct current system based on power grid requirements and system support capacity, belongs to the field of power system control, and aims to solve the problem that no method for realizing the frequency-voltage coupling support control method for the sea wind flexible direct current system exists at present. The method comprises the following steps: acquiring voltage and frequency real-time information of a grid-connected point of the sea wind flexible direct current system, and further determining a reactive power support index and an active power support index; then the sea wind flexible direct current system selects a control mode to output active power and reactive power reference values according to the reactive power support index and the active power support index; and finally, the active current and the reactive current are corrected based on the wind power plant regulation capability, the converter station short-time overcurrent capability and the reactive priority principle, the active power reference value and the reactive power reference value are corrected, and then the frequency-voltage coupling support control of the sea wind flexible direct current system is realized.

Description

Technical Field

[0001] This invention belongs to the field of power system control and relates to a frequency-voltage coupling support control method, storage medium and device for a sea wind flexible DC system. Background Technology

[0002] With the rapid increase in the penetration rate of new energy sources and the continuous increase in DC feed-in channels, cascading failures are easily triggered, posing a significant threat to the safe and stable operation of the power grid. Offshore wind-powered flexible DC systems, due to their flexible and diverse control strategies, power decoupling output, and ease of islanded operation, have become a key research direction for active support of new energy sources. The complex interactions between AC and DC systems result in strong coupling characteristics between system frequency and voltage. With the continuous increase in the penetration rate of offshore wind power, the insufficient frequency-voltage coupling support capability of the power system is becoming increasingly prominent. Therefore, it is imperative to propose a frequency-voltage coupling support control method for offshore wind-powered flexible DC systems.

[0003] Currently, there are various methods for frequency and voltage support control research on offshore wind-driven flexible direct current systems, such as:

[0004] 1. Xiong Yongxin's "Active Frequency Support Control for Offshore Wind Power via Multi-Terminal Flexible DC Grid Connection System," 2022, Huazhong University of Science and Technology, proposes active frequency support control for offshore wind power via flexible DC grid connection system. Offshore wind farm frequency control includes rotor kinetic energy control, wind turbine load shedding and backup control, and wind farm cluster control. Flexible DC system frequency control includes DC capacitor energy storage control and multi-terminal flexible DC power distribution control. However, this method does not consider the coordinated frequency regulation control of the offshore wind power via flexible DC system or the quantitative assessment of the frequency regulation capability of offshore wind farms.

[0005] 2. Xu Yanan published "Research on Frequency Support Control and Fault Ride-through Strategy of Offshore Wind Power Through Flexible DC Interconnection System", 2024, Northeast Electric Power University. This article proposes to convert the frequency change of the onshore power grid into the change of DC voltage through droop control, so that the offshore wind farm can participate in frequency regulation, thereby realizing the coordinated active frequency support of the offshore wind flexible DC system. However, this method does not consider the situation where the DC voltage is affected by the voltage fault and transmits incorrect signals, resulting in frequency regulation failure when frequency voltage coupling fault occurs.

[0006] 3. Zhang Jin's article "Research on Grid-Side Voltage Support Strategy of VSC-HVDC for Wind Power Grid Connection" published in 2021 by Shandong University proposes a constant AC voltage switching control. The system operates normally under constant reactive power control. When a voltage fault occurs during grid connection, it switches to constant AC voltage control to provide active voltage support for the system. However, this method does not consider the frequency voltage coupling fault. The offshore wind-flexible DC system has equipment capacity limitations and cannot simultaneously meet the grid frequency voltage coupling support requirements.

[0007] In summary, existing research on support control methods for offshore wind-driven flexible DC systems primarily focuses on frequency or voltage support separately. However, in practical applications, these two disturbances often occur coupled. Therefore, a coupled support control method for offshore wind-driven flexible DC systems is urgently needed to enhance their active frequency and voltage support capabilities. Summary of the Invention

[0008] This invention aims to address the current lack of a method for frequency-voltage coupling support control of a sea-wind flexible direct current system.

[0009] A frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capabilities includes:

[0010] S1. First, obtain the real-time grid voltage and frequency information at the grid connection point of the offshore wind flexible DC system. The real-time grid connection point voltage and frequency information includes: real-time voltage RMS value, voltage fault duration, voltage fault amplitude, voltage change rate, real-time frequency RMS value, frequency fault duration, frequency fault amplitude, and frequency change rate.

[0011] Then determine the reactive power support index Q. sp With active power support index P sp :

[0012] 1) Based on the current real-time effective voltage value and the rated voltage U N Lower limit of voltage regulation dead zone U db-min Upper limit of voltage regulation dead zone U db-max Dynamic voltage regulation lower limit U min Dynamic voltage regulation upper limit U max Overvoltage limit value U lim-max Low voltage limit U lim-min Voltage fault status classification is performed based on voltage fault duration T. uf The voltage fault index λ(t) is obtained by combining the real-time effective voltage value U(t) with the voltage change rate and the current voltage state, and the voltage trend index M is obtained based on the voltage change rate and the current voltage state. Q (t); using the voltage fault index λ(t) and the voltage trend index M Q (t) characterizes the severity and trend of grid voltage disturbances, and the reactive power support index Q is obtained by combining the fault status classification results. sp ;

[0013] 2) Based on the current real-time effective frequency value and the frequency rating value f of the frequency classification identifier. N FM dead zone lower limit f db-min FM dead zone upper limit f db-max Dynamic frequency modulation lower limit f min Dynamic frequency modulation upper limit f max High-frequency limit value flim-max Low-frequency limit value f lim-min Frequency fault status classification is performed based on frequency fault duration T. ff The frequency fault index ζ(t) is obtained by combining f(t) with the real-time effective frequency value f(t), and the frequency trend index M is obtained based on the frequency change rate and the current frequency state. P (t); using the frequency state-aware quantization index ζ(t) and the frequency trend index M P (t) characterizes the severity and trend of power grid frequency disturbances. Combining these two factors with the frequency situation classification results, the active power support index P is obtained. sp ;

[0014] S2. The Haifeng Flexible DC system selects the control mode and outputs active and reactive power reference values ​​based on the reactive power support index and the active power support index.

[0015] Based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle, S3 corrects the active and reactive currents to achieve the correction of the active and reactive power reference values, thereby realizing the frequency-voltage coupling support control of the offshore wind-flexible DC system.

[0016] Furthermore, the voltage fault index λ(t) and the voltage trend index M Q (t) is as follows:

[0017] (1)

[0018] (2)

[0019] In the formula, a(T) uf Let b1(U(t)) be the voltage fault time function, b2(U(t)) be the high-voltage fault amplitude function, and b2(U(t)) be the low-voltage fault amplitude function. uf U(t) represents the duration of the voltage drop, U(t) represents the real-time effective voltage value, and t represents time; T umin T umax These are the minimum and maximum values ​​of the voltage drop duration, respectively;

[0020] (3)

[0021] In the formula, dU(t) / dt is the voltage change rate; sgn(·) is the sign function.

[0022] Furthermore, the reactive power support index Q sp as follows:

[0023] (4)

[0024] In the formula, K q1K q2 These are the voltage deviation and the voltage change rate support coefficient, respectively, K. q4 K q5 These are the voltage disturbance and voltage change trend support coefficients, Q. max_MMC This represents the maximum reactive power of the flexible-conductive system.

[0025] Furthermore, the frequency state-aware quantization index ζ(t) and the frequency trend index M P (t) is as follows:

[0026] (5)

[0027] (6)

[0028] In the formula, c(T) ff Let f(t) be the frequency fault time function, d1(f(t)) be the high-frequency fault amplitude function, and d2(f(t)) be the low-frequency fault amplitude function. Duration of frequency fault, T represents the real-time frequency RMS value. min T max These are the minimum and maximum values ​​of the frequency drop duration, respectively;

[0029] (7)

[0030] In the formula, df(t) / dt is the rate of change of frequency.

[0031] Furthermore, the power support index P sp as follows:

[0032] (8)

[0033] In the formula, K p1 K p2 These are the frequency deviation, the support coefficient of the rate of change of frequency, and K. p4 K p5 These are the support coefficients for frequency disturbance and frequency change trend, respectively, P. max_MMC and P 0_MMC These represent the maximum active power and steady-state active power of the flexible DC system, respectively.

[0034] Furthermore, the control mode of the sea breeze flexible vertical rotation system is as follows:

[0035] 1) Unsupported: When Q sp With P sp When both are zero, it indicates that the grid frequency and voltage are in a steady state and there is no support demand. The reference value Q for the offshore wind-flexible DC system is... ref =Q0, P ref=P0, where Q0 and P0 are the steady-state active and reactive power outputs of the sea breeze flexible direct current system, respectively.

[0036] 2) Dynamic voltage support: When Q sp Non-zero, P sp When the value is zero, it indicates that the power grid frequency is in a steady state. If a voltage fault occurs, the system only has voltage support demand, which is based on the reactive power support index Q. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0;

[0037] 3) Dynamic frequency support: When Q sp P is zero. sp When the value is non-zero, it indicates that the grid voltage is in a steady state, a frequency fault occurs, and the system only has frequency support demand, which is based on the active power support index P. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0, P ref =P0+P sp ;

[0038] 4) Frequency-voltage coupling support: When Q sp P sp When both are non-zero, it indicates a voltage-frequency coupled fault in the power grid, where both system frequency and voltage have support requirements, based on the active power support index P. sp and reactive power support index Q sp To provide frequency and voltage coupling support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0+P sp .

[0039] Furthermore, the corrected active and reactive currents described in S3 are as follows:

[0040] (16)

[0041] (17)

[0042] In the formula, I n The rated current of the grid-side MMC; i d_ref i q_ref These are the d-axis and q-axis current command values ​​for the grid-side MMC, respectively; i q_sq i d0 and These are the reactive power support current, steady-state active current, and corrected active power support current, respectively, denoted by Q. sq P 0_MMC and Calculated based on the current PCC point voltage; K ol T ol and T ol_lim These represent the short-term overcurrent coefficient, overcurrent duration implementation, and overcurrent time limit of MMC, respectively.

[0043] Furthermore, in the process of correcting active and reactive currents based on wind farm regulation capabilities, converter station short-time overcurrent capabilities, and the reactive power priority principle, it is also necessary to correct the power support indicators, including:

[0044] Wind turbines achieve power reserve through overspeed load reduction control and pitch angle load reduction control. The regulation capability of the entire wind farm is quantified from two aspects: available kinetic energy and reserve power, as follows:

[0045] (13)

[0046] (14)

[0047] In the formula, ΔE k_wfu and ΔE k_wfd These represent the total available kinetic energy of the wind farm during the periods of active power increase and decrease; ΔP o_deli Let ΔP be the standby power of the i-th overspeed generator unit. p_delj These represent the standby power of the j-th pitch angle reduction turbine unit; ΔP del_wf ΔP u_wf and ΔP d_wf These are the total reserve power, the upper limit of total active power regulation, and the lower limit of the wind farm, respectively.

[0048] Then the corrected active power support index is obtained:

[0049] .

[0050] A computer storage medium storing at least one instruction, which is loaded and executed by a processor to implement the frequency-voltage coupling support control method for a wind-driven flexible DC system based on grid demand and system support capability.

[0051] A frequency-voltage coupling support control device for a flexible DC-DC system based on grid demand and system support capability is disclosed. The device includes a processor and a memory. The memory stores at least one instruction, which is loaded and executed by the processor to implement the frequency-voltage coupling support control method for the flexible DC-DC system based on grid demand and system support capability.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] To address frequency-voltage coupling faults in the power grid, a frequency-voltage coupling support control method for offshore wind-flexible DC systems is proposed, based on grid demand and system support capabilities. First, reactive / active power support indices are constructed to quantify grid support requirements. Then, the control mode of the offshore wind-flexible DC system is selected based on these indices. Finally, the reference values ​​for active and reactive power are corrected based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle. This method provides a basis for the offshore wind-flexible DC system to participate in system frequency-voltage coupling support control by quantifying the system's grid support requirements. It achieves coupled control and equipment safety of the offshore wind-flexible DC system based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle. While being easily implemented in engineering, this method significantly improves the frequency-voltage coupling support capability of the offshore wind-flexible DC system and enhances the safe operation level of the power grid. Furthermore, the coupling control approach provided by this method has strong versatility and can be applied to multi-terminal offshore flexible DC grid-connected systems and onshore flexible DC grid-connected systems, and is not limited to wind farms and other new energy power plants. Attached Figure Description

[0054] Figure 1 A schematic diagram of a frequency-voltage coupling support control method for a marine wind-flexible DC system based on grid demand and system support capability;

[0055] Figure 2 This is a schematic diagram of voltage status classification;

[0056] Figure 3 This is a schematic diagram of frequency situation classification;

[0057] Figure 4 This is a schematic diagram of the frequency-voltage coupling support control logic for MMC-HVDC. Detailed Implementation

[0058] To address frequency-voltage coupling faults in offshore wind power systems, this invention quantifies grid support requirements by constructing a system reactive / active power support index. This index is used to adjust the active and reactive power reference values ​​of the offshore wind-powered flexible DC system. Furthermore, the active / reactive power reference values ​​are corrected using wind farm regulation capabilities, converter station short-time overcurrent capabilities, and a reactive power priority principle. This proposes a frequency-voltage coupling support control method for offshore wind-powered flexible DC systems based on grid demand and system support capabilities. This support control method is simple and flexible, significantly improving the frequency-voltage coupling support capability of offshore wind power systems connected to the grid via flexible DC, thereby enhancing the safe operation of the grid and the stability of offshore wind farms. The main collaborative control strategies of this invention are as follows:

[0059] The coupled support control method mainly includes the following steps: First, obtain real-time grid voltage and frequency information at the grid connection point of the offshore wind-flexible DC system, and construct a reactive power support index Q that considers fault time, fault depth, and fault trend. sp With active power support index Psp The grid support requirements are quantified. Then, the offshore wind-flexible DC system selects the control mode and outputs active and reactive power reference values ​​based on the reactive power support indicators and active power support indicators. Finally, the active and reactive power reference values ​​are corrected based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle.

[0060] The frequency-voltage coupling support control method for offshore wind-flexible DC systems, based on grid demand and system support capabilities, primarily targets frequency-voltage coupling faults in the grid system, but is also applicable to single-frequency or single-voltage faults. First, a reactive power support index Q is constructed, considering fault time, fault depth, and fault trend. sp With active power support index P sp The system quantifies the power grid's support requirements under different fault scenarios. Based on these support requirement commands, the offshore wind-flexible DC system selects the control mode.

[0061] Pattern 1: When Q sp With P sp When both are zero, it indicates that the system has no support requirements and the system remains in a steady state.

[0062] Mode 2: When Q sp Non-zero, P sp When Q is zero, it indicates that the power grid frequency is in a steady state. A voltage fault occurs, and the system only requires voltage support. The offshore wind-flexible DC system is based on Q... sp The indicator provides voltage support;

[0063] Mode 3: When Q sp P is zero. sp When the voltage is non-zero, it indicates that the grid voltage is in a steady state, a frequency fault occurs, and the system only has frequency support requirements. The offshore wind-flexible DC system is based on P sp Indicators provide frequency support;

[0064] Pattern 4: When Q sp P sp When both are non-zero, it indicates a voltage-frequency coupling fault in the power grid, where both system frequency and voltage have support requirements. The offshore wind-flexible DC system is based on Q... sp P sp The indicators provide frequency-voltage coupling support. Finally, based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle, the active and reactive power reference values ​​are corrected to achieve frequency-voltage coupling support for the offshore wind-flexible DC system. The invention will now be described in conjunction with specific implementation methods. Specific implementation method one:

[0066] Combination Figure 1This embodiment describes a frequency-voltage coupling support control method for a wind-driven flexible DC system based on grid demand and system support capability. The method includes the following steps:

[0067] S1. First, obtain the real-time grid voltage and frequency information of the grid connection point of the Haifeng Flexible DC system. The real-time grid connection point voltage and frequency information includes: real-time voltage effective value, voltage fault duration, voltage fault amplitude, voltage change rate, real-time frequency effective value, frequency fault duration, frequency fault amplitude, and frequency change rate.

[0068] Then, a reactive power support index Q is constructed that considers fault time, fault depth, and fault trend. sp With active power support index P sp Quantifying the power grid support requirements. This includes constructing a reactive power support index Q that considers fault time, fault depth, and fault trend. sp With active power support index P sp The process includes:

[0069] 1) Reactive power support index Q sp :like Figure 2 As shown, based on the current real-time effective voltage value and voltage classification indicator, the fault condition can be classified into four conditions: voltage regulation dead zone, steady-state voltage regulation, dynamic voltage regulation, and emergency reactive power support. The voltage classification indicator U... N U db-min U db-max U min U max U lim-max U lim-min These include the rated voltage, lower limit of the voltage regulation dead zone, upper limit of the voltage regulation dead zone, lower limit of dynamic voltage regulation, upper limit of dynamic voltage regulation, overvoltage limit, and undervoltage limit; the classification labels can be set according to national standards or equipment characteristics. Based on the voltage fault time T... uf (t) and the real-time effective voltage value U(t) are used to construct the voltage fault index λ(t):

[0070] (1)

[0071] (2)

[0072] In the formula, a(T) uf Let b1(U(t)) be the voltage fault time function, b2(U(t)) be the high-voltage fault amplitude function, and b2(U(t)) be the low-voltage fault amplitude function. uf U(t) represents the duration of the voltage drop, U(t) represents the real-time effective voltage value, and t represents time; T umin T umaxThese are the minimum and maximum values ​​of the voltage drop duration, respectively.

[0073] A voltage trend index M is constructed based on the voltage change rate and the current voltage state. Q (t):

[0074] (3)

[0075] In the formula, dU(t) / dt is the voltage change rate; sgn(·) is the sign function.

[0076] Regarding reactive power, the voltage fault index λ(t) and the voltage trend index M Q (t) can respectively characterize the severity and trend of grid voltage disturbances. Combining the two with voltage status classification, a reactive power support index Q is proposed. sp As shown in equation (4):

[0077] (4)

[0078] In the formula, K q1 K q2 These are the voltage deviation and the voltage change rate support coefficient, respectively, K. q4 K q5 These are the voltage disturbance and voltage change trend support coefficients, Q. max_MMC This represents the maximum reactive power of the flexible-conductive system.

[0079] 2) Active power support command P sp Similarly, such as Figure 3 As shown, the fault status is classified based on the current real-time effective frequency value and the frequency classification identifier. The frequency classification identifier f N f db-min f db-max f min f max f lim-max f lim-min These include the rated frequency, lower limit of FM dead zone, upper limit of FM dead zone, lower limit of dynamic FM, upper limit of dynamic FM, high-frequency limit, and low-frequency limit; the frequency classification label can be set according to national standards or equipment characteristics; based on the frequency fault time T... ff The frequency fault index ζ(t) is constructed by combining f(t) with the real-time effective frequency value, as shown below:

[0080] (5)

[0081] (6)

[0082] In the formula, c(T) ffLet f(t) be the frequency fault time function, d1(f(t)) be the high-frequency fault amplitude function, and d2(f(t)) be the low-frequency fault amplitude function. Duration of frequency fault, T represents the real-time frequency RMS value. min T max These are the minimum and maximum values ​​of the frequency drop duration, respectively.

[0083] Similarly, construct the frequency trend indicator M. P (t), as shown in equation (7):

[0084] (7)

[0085] In the formula, df(t) / dt is the rate of change of frequency.

[0086] In terms of active power, the frequency state-aware quantification index ζ(t) and the frequency trend index M P (t) can respectively characterize the severity and trend of power grid frequency disturbances. Combining the two with frequency situation classification, an active power support index P is proposed. sp :

[0087] (8)

[0088] In the formula, K p1 K p2 These are the frequency deviation, the support coefficient of the rate of change of frequency, and K. p4 K p5 These are the support coefficients for frequency disturbance and frequency change trend, respectively, P. max_MMC and P 0_MMC These represent the maximum active power and steady-state active power of the flexible DC system, respectively.

[0089] S2, the Haifeng Flexible DC system selects the control mode and outputs reference values ​​for active and reactive power based on the reactive power support index and the active power support index.

[0090] The control modes of the Haifeng Flexible Straight Line System are as follows:

[0091] 1) Unsupported: When Q sp With P sp When both are zero, it indicates that the grid frequency and voltage are in a steady state and there is no support demand. The reference value Q for the offshore wind-flexible DC system is... ref =Q0, P ref =P0, where Q0 and P0 are the steady-state active and reactive power outputs of the sea breeze flexible direct current system, respectively.

[0092] 2) Dynamic voltage support: When Q sp Non-zero, P spWhen the value is zero, it indicates that the power grid frequency is in a steady state. If a voltage fault occurs, the system only has voltage support demand, which is based on the reactive power support index Q. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0.

[0093] 3) Dynamic frequency support: When Q sp P is zero. sp When the value is non-zero, it indicates that the grid voltage is in a steady state, a frequency fault occurs, and the system only has frequency support demand, which is based on the active power support index P. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0, P ref =P0+P sp .

[0094] 4) Frequency-voltage coupling support: When Q sp P sp When both are non-zero, it indicates a voltage-frequency coupled fault in the power grid, where both system frequency and voltage have support requirements, based on the active power support index P. sp and reactive power support index Q sp To provide frequency and voltage coupling support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0+P sp .

[0095] S3. Based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle, the active current and reactive current are corrected to achieve the correction of the active power and reactive power reference values.

[0096] The control logic of MMC-HVDC is as follows: Figure 4 As shown: Based on S1, the grid support requirements are quantified; based on S2, the system output mode is determined; and finally, the active power and reactive power reference values ​​are corrected based on the wind farm regulation capability, the converter station short-time overcurrent capability, and the reactive power priority principle.

[0097] 1) Wind turbines achieve power reserve through overspeed load reduction control and pitch angle load reduction control, quantifying the wind farm's regulation capability from the perspectives of available kinetic energy and reserve power.

[0098] For wind turbines operating in overspeed unloading mode, the rotor kinetic energy can be utilized by adjusting the rotor speed, while simultaneously adjusting the input mechanical power. This adjustment capability can be quantified as follows:

[0099] (9)

[0100] (10)

[0101] In the formula, ΔE k_ui and ΔE k_di ω represents the available kinetic energy of the i-th overspeed unit during the active power increase and decrease periods, respectively; J is the moment of inertia of the wind turbine, and d is the load reduction coefficient; 0i ω opt and ω max These represent the steady-state, optimal, and maximum speeds of the i-th overspeed unit, respectively; ΔP o_deli P opti and P o_deli Let ΔP be the standby power, active power before load reduction, and active power after load reduction of the i-th overspeed generator unit. o_ui and ΔP o_di Let ΔP be the upper and lower limits of the active power regulation of the i-th overspeed generator unit, respectively. o_ui Equal to reserve power P o_deli ΔP o_di Usually equal to -ΔP o_deli It can also be determined according to actual needs.

[0102] For wind turbines operating in pitch angle load reduction mode, the input mechanical power is mainly adjusted by regulating the pitch angle, and the adjustment capability can be quantified as follows:

[0103] (11)

[0104] (12)

[0105] In the formula, ΔE k_j and ΔP p_delj These represent the available kinetic energy and reserve power of the j-th pitch angle reduction turbine unit, respectively; P optj and P p_delj These are the active power of the j-th pitch angle turbine unit before and after load reduction, respectively; ΔP p_uj and ΔP p_dj These are the upper and lower limits of the active power regulation for the j-th overspeed generator unit, respectively, and their values ​​are similar to those of the overspeed unloading generator unit.

[0106] The combined formulas (9)-(12) can quantify the regulation capacity of the entire wind farm:

[0107] (13)

[0108] (14)

[0109] In the formula, ΔE k_wfu and ΔE k_wfd These represent the total available kinetic energy of the wind farm during the periods of active power increase and decrease; ΔPdel_wf ΔP u_wf and ΔP d_wf These are the total reserve power, the upper limit of total active power regulation, and the lower limit of the wind farm, respectively.

[0110] Since the actual active power regulation capability of the MMV-HVDC system originates from the wind farm, the system's active power support index needs further correction based on the above formula to avoid the support command exceeding the actual regulation capability. The corrected active power support index is as follows:

[0111] (15)

[0112] 2) To leverage the short-time overcurrent capability of the MMC, an improved reactive power priority control is proposed, with the active and reactive currents modified as follows:

[0113] (16)

[0114] (17)

[0115] In the formula, I n The rated current of the grid-side MMC; i d_ref i q_ref These are the d-axis and q-axis current command values ​​for the grid-side MMC, respectively; i q_sq i d0 and These are the reactive power support current, steady-state active current, and corrected active power support current, respectively, denoted by Q. sq P 0_MMC and Calculated based on the current PCC point voltage; K ol T ol and T ol_lim These represent the short-term overcurrent coefficient, overcurrent duration implementation, and overcurrent time limit of MMC, respectively.

[0116] The coupled control approach provided by this method has strong versatility and can be applied to various electromagnetic transient modeling and control methods, such as Simulink and PSCAD simulation software. It is not limited by the type of wind turbine in wind farms and can also be applied to other new energy power plants such as photovoltaic and hydropower. Specific Implementation Method Two:

[0118] This embodiment is a computer storage medium that stores at least one instruction. The at least one instruction is loaded and executed by a processor to implement the frequency-voltage coupling support control method for a flexible DC-DC system based on grid demand and system support capability.

[0119] It should be understood that the instructions include computer program products, software, or computerized methods corresponding to any method described in this invention; the instructions can be used to program computer systems or other electronic devices. Computer storage media may include readable media on which instructions are stored, and may include, but are not limited to, magnetic storage media, optical storage media; magneto-optical storage media include read-only memory (ROM), random access memory (RAM), erasable programmable memory (e.g., EPROM and EEPROM), and flash memory layers, or other types of media suitable for storing electronic instructions. Specific implementation method three:

[0121] This embodiment is a frequency-voltage coupling support control device for a wind-driven flexible DC system based on grid demand and system support capability. The device includes a processor and a memory. It should be understood that this includes any device with a processor and a memory described in this invention. The device may also include other units or modules that perform display, interaction, processing, control, and other functions through signals or instructions.

[0122] The memory stores at least one instruction, which is loaded and executed by the processor to implement the frequency-voltage coupling support control method for a flexible DC-DC transmission system based on grid demand and system support capability.

[0123] Those skilled in the art will understand that at least one stored instruction constitutes a computer program product corresponding to a method or system. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0124] This application is described with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products according to embodiments of this application, and can also be used with corresponding devices. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0125] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0126] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0127] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0128] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

[0129] The above examples of the present invention are merely illustrative of the computational model and process of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A frequency-voltage coupling support control method for offshore wind-driven flexible DC systems based on grid demand and system support capabilities, characterized in that, include: S1. First, obtain the real-time grid voltage and frequency information at the grid connection point of the offshore wind flexible DC system. The real-time grid connection point voltage and frequency information includes: real-time voltage RMS value, voltage fault duration, voltage fault amplitude, voltage change rate, real-time frequency RMS value, frequency fault duration, frequency fault amplitude, and frequency change rate. Then determine the reactive power support index Q. sp With active power support index P sp : 1) Based on the current real-time effective voltage value and the rated voltage U N Lower limit of voltage regulation dead zone U db-min Upper limit of voltage regulation dead zone U db-max Dynamic voltage regulation lower limit U min Dynamic voltage regulation upper limit U max Overvoltage limit value U lim-max Low voltage limit U lim-min Voltage fault status classification is performed based on voltage fault duration T. uf The voltage fault index λ(t) is obtained by combining the real-time effective voltage value U(t) with the voltage change rate and the current voltage state, and the voltage trend index M is obtained based on the voltage change rate and the current voltage state. Q (t); using the voltage fault index λ(t) and the voltage trend index M Q (t) characterizes the severity and trend of grid voltage disturbances, and the reactive power support index Q is obtained by combining the fault status classification results. sp ; 2) Based on the current real-time effective frequency value and the frequency rating value f of the frequency classification identifier. N FM dead zone lower limit f db-min FM dead zone upper limit f db-max Dynamic frequency modulation lower limit f min Dynamic frequency modulation upper limit f max High-frequency limit value f lim-max Low-frequency limit value f lim-min Frequency fault status classification is performed based on frequency fault duration T. ff The frequency fault index ζ(t) is obtained by combining f(t) with the real-time effective frequency value f(t), and the frequency trend index M is obtained based on the frequency change rate and the current frequency state. P (t); using the frequency state-aware quantization index ζ(t) and the frequency trend index M P (t) characterizes the severity and trend of power grid frequency disturbances. Combining these two factors with the frequency situation classification results, the active power support index P is obtained. sp ; S2. The Haifeng Flexible DC system selects the control mode and outputs active and reactive power reference values ​​based on the reactive power support index and the active power support index. Based on the wind farm's regulation capability, the converter station's short-time overcurrent capability, and the reactive power priority principle, S3 corrects the active and reactive currents to achieve the correction of the active and reactive power reference values, thereby realizing the frequency-voltage coupling support control of the offshore wind flexible DC system.

2. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 1, characterized in that, The voltage fault index λ(t) and voltage trend index M Q (t) is as follows: (1) (2) In the formula, a(T) uf Let b1(U(t)) be the voltage fault time function, b2(U(t)) be the high-voltage fault amplitude function, and b2(U(t)) be the low-voltage fault amplitude function. uf (t) represents the duration of the voltage drop, U(t) represents the real-time effective voltage value, and t represents time; T umin T umax These are the minimum and maximum values ​​of the voltage drop duration, respectively; (3) In the formula, dU(t) / dt is the voltage change rate; sgn(·) is the sign function.

3. The frequency-voltage coupling support control method for offshore wind-driven flexible DC systems based on grid demand and system support capability as described in claim 2, characterized in that, The reactive power support index Q sp as follows: (4) In the formula, K q1 K q2 These are the voltage deviation and the voltage change rate support coefficient, respectively, K. q4 K q5 These are the voltage disturbance and voltage change trend support coefficients, Q. max_MMC This represents the maximum reactive power of the flexible-conductive system.

4. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 3, characterized in that, The frequency state perception quantization index ζ(t) and frequency trend index M P (t) is as follows: (5) (6) In the formula, c(T) ff Let f(t) be the frequency fault time function, d1(f(t)) be the high-frequency fault amplitude function, and d2(f(t)) be the low-frequency fault amplitude function. Duration of frequency fault, T represents the real-time frequency RMS value. min T max These are the minimum and maximum values ​​of the frequency drop duration, respectively; (7) In the formula, df(t) / dt is the rate of change of frequency.

5. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 4, characterized in that, The power support index P sp as follows: (8) In the formula, K p1 K p2 These are the frequency deviation, the support coefficient of the rate of change of frequency, and K. p4 K p5 These are the support coefficients for frequency disturbance and frequency change trend, respectively, P. max_MMC and P 0_MMC These represent the maximum active power and steady-state active power of the flexible DC system, respectively.

6. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 5, characterized in that, The control mode of the sea breeze flexible vertical system is as follows: 1) Unsupported: When Q sp With P sp When both are zero, it indicates that the grid frequency and voltage are in a steady state and there is no support demand. The reference value Q for the offshore wind-flexible DC system is... ref =Q0, P ref =P0, where Q0 and P0 are the steady-state active and reactive power outputs of the sea breeze flexible straight system, respectively; 2) Dynamic voltage support: When Q sp Non-zero, P sp When the value is zero, it indicates that the power grid frequency is in a steady state. If a voltage fault occurs, the system only has voltage support demand, which is based on the reactive power support index Q. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0; 3) Dynamic frequency support: When Q sp P is zero. sp When the value is non-zero, it indicates that the grid voltage is in a steady state, a frequency fault occurs, and the system only has frequency support demand, which is based on the active power support index P. sp To provide voltage support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0, P ref =P0+P sp ; 4) Frequency-voltage coupling support: When Q sp P sp When both are non-zero, it indicates a voltage-frequency coupled fault in the power grid, where both system frequency and voltage have support requirements, based on the active power support index P. sp and reactive power support index Q sp To provide frequency and voltage coupling support for the system, the reference value Q for the offshore flexible DC system is... ref =Q0+Q sp P ref =P0+P sp .

7. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 6, characterized in that, The corrected active and reactive currents described in S3 are as follows: (16) (17) In the formula, I n The rated current of the grid-side MMC; i d_ref i q_ref These are the d-axis and q-axis current command values ​​for the grid-side MMC, respectively; i q_sq i d0 and These are the reactive power support current, steady-state active current, and corrected active power support current, respectively, denoted by Q. sq P 0_MMC and Calculated based on the current PCC point voltage; K ol T ol and T ol_lim These represent the short-term overcurrent coefficient, overcurrent duration implementation, and overcurrent time limit of MMC, respectively.

8. The frequency-voltage coupling support control method for offshore wind-flexible DC systems based on grid demand and system support capability as described in claim 7, characterized in that, In the process of adjusting active and reactive currents based on wind farm regulation capabilities, converter station short-time overcurrent capabilities, and the reactive power priority principle, it is also necessary to correct the power support indicators, including: Wind turbines achieve power reserve through overspeed load reduction control and pitch angle load reduction control. The regulation capability of the entire wind farm is quantified from two aspects: available kinetic energy and reserve power, as follows: (13) (14) In the formula, ΔE k_wfu and ΔE k_wfd These represent the total available kinetic energy of the wind farm during the periods of active power increase and decrease; ΔP o_deli Let ΔP be the standby power of the i-th overspeed generator unit. p_delj These represent the standby power of the j-th pitch angle reduction turbine unit; ΔP del_wf ΔP u_wf and ΔP d_wf These are the total reserve power, the upper limit of total active power regulation, and the lower limit of the wind farm, respectively. Then the corrected active power support index is obtained: 。 9. A computer storage medium, characterized in that, The storage medium stores at least one instruction, which is loaded and executed by a processor to implement the frequency-voltage coupling support control method for a flexible DC-DC system based on grid demand and system support capability, as described in any one of claims 1 to 8.

10. A frequency-voltage coupling support control device for a marine wind-driven flexible DC system based on grid demand and system support capabilities, characterized in that, The device includes a processor and a memory, the memory storing at least one instruction, which is loaded and executed by the processor to implement the frequency-voltage coupling support control method for a flexible DC-DC system based on grid demand and system support capability as described in any one of claims 1 to 8.

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