A new energy and flexible direct current coordinated control method and system suitable for power fluctuation

Abstract

The application discloses a new energy and flexible direct current coordinated control method and system suitable for power fluctuation, which comprises the following steps: S1, acquiring the operation state data of new energy units in a flexible direct current power transmission system and a new energy grid-connected system in real time; S2, setting the initial control mode and voltage reference value of the new energy units; setting the initial control mode and initial reactive power value of a flexible direct current converter station; S3, detecting whether a serious fault occurs in the power transmission system; S4, when it is detected that the serious fault occurs, switching the flexible direct current converter station to a constant voltage control mode, and until the voltage is restored to above a preset threshold, executing S2; S5, when there is no serious fault, calculating the power factor of the new energy units; S6, when the power factor is greater than or equal to a preset threshold, then monitoring whether the bus voltage of the flexible direct current converter station exceeds a preset range in real time; S7, when the voltage exceeds the preset range, then adjusting the reactive power reference value of the flexible direct current converter station, and executing S3; and S8, when the voltage does not exceed the preset range, executing S3.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and more specifically, to a method and system for coordinated control of new energy sources and flexible DC power sources that are suitable for power fluctuations. Background Technology

[0002] my country's new energy resources are mainly distributed in remote areas such as the eastern coastal areas and the western inland areas. Moreover, new energy sources themselves exhibit randomness and volatility. Therefore, future power transmission systems should be capable of absorbing large-scale renewable energy. Flexible DC transmission technology has become a suitable power transmission method for integrating new energy into the grid due to its significant advantages in this area.

[0003] In areas where renewable energy is concentrated, the load is typically small. Large-scale wind power integration leads to a larger peak-to-valley difference in the grid's equivalent load. Insufficient reactive power regulation methods make voltage control increasingly difficult, manifesting as higher voltage in some areas during off-peak load periods and lower voltage in others during peak load periods. While the overall grid charging power compensation meets requirements, insufficient compensation in some areas can lead to localized high voltages when the system load is low. Simultaneously, the inherent volatility and randomness of renewable energy pose challenges to the stable operation of the grid, limiting the local grid's capacity to accommodate renewable energy. Under non-fault conditions, the randomness of renewable energy output leads to uncertainty in grid power flow, with large and rapid changes in reactive power demand, resulting in excessive voltage fluctuations. To prevent grid voltage exceeding limits, wind and solar power output is restricted, leading to wind and solar curtailment.

[0004] For scenarios involving the transmission of renewable energy via flexible DC islanding, converter stations need to provide reliable grid-connected voltage for renewable energy units. Therefore, rectifier-side converters typically employ a constant frequency, constant AC voltage amplitude control mode. When significant fluctuations in the active power output of renewable energy at the sending end cause voltage exceedances, the converter's reactive power output increases substantially, limiting the flexible DC transmission capacity. Grid wind turbines can achieve decoupled control of active and reactive power, utilizing their reactive power capacity to provide voltage support. According to GB / T19963-2011 "Technical Regulations for Wind Farm Access to Power Systems," wind turbines can operate within a power factor range of ±0.95, and wind farms can provide voltage regulation to the AC system. However, currently, renewable energy units generally operate at unity power factor during steady-state operation, and their reactive power capacity remains unutilized. Therefore, it is necessary to coordinate the control of reactive power output between renewable energy units and flexible DC converters to improve voltage levels and enhance renewable energy absorption.

[0005] Therefore, a technology is needed to achieve coordinated control of new energy sources and flexible DC power that is suitable for power fluctuations. Summary of the Invention

[0006] The present invention provides a method and system for coordinated control of new energy and flexible DC power generation, applicable to power fluctuations, to solve the problem of coordinated control between new energy generating units and flexible DC converters under the premise of meeting grid voltage requirements.

[0007] To address the aforementioned problems, this invention provides a coordinated control method for new energy sources and flexible DC power sources suitable for power fluctuations, the method comprising:

[0008] S1: Real-time acquisition of operating status data and control parameters of new energy units in flexible DC transmission systems and new energy grid-connected systems;

[0009] S2: Set the initial control mode and voltage reference value of the new energy units in the new energy grid-connected system; set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system;

[0010] S3: Detect whether a serious fault has occurred in the power transmission system;

[0011] S4: When a serious fault is detected in the power transmission system, the reactive power control mode of the flexible DC converter station is switched to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold, and then step S2 is executed.

[0012] S5: When no serious fault is detected in the power transmission system, calculate the power factor of the new energy unit based on the operating data;

[0013] S6: When the power factor of the new energy unit is greater than or equal to the preset threshold, the bus voltage of the flexible DC converter station is monitored in real time to see if it exceeds the preset range.

[0014] S7: When the bus voltage of the flexible DC converter station exceeds the preset range, adjust the reactive power reference value of the flexible DC converter station and continue to execute step S3;

[0015] S8: When the bus voltage of the flexible DC converter station does not exceed the preset range, continue to execute step S3.

[0016] Preferably, the setting of the control mode and control parameters for the new energy units in the new energy grid-connected system includes:

[0017] The control mode of the new energy unit is set to constant voltage control mode, and the voltage reference value is the rated voltage of the bus at the grid connection point of the wind farm.

[0018] The control mode and control parameters of the flexible DC converter station at the sending end of the flexible DC transmission system are set, including:

[0019] The active power control mode of the flexible DC converter station is set to constant frequency control mode, and the reactive power control mode is set to constant reactive power control mode.

[0020] Preferably, the serious faults include: a single-circuit fault of a three-permanent-trip line, a double-circuit fault of a three-permanent-trip line, a faultless interruption of a line, and a flexible DC blocking fault.

[0021] Preferably, when the power factor of the new energy unit is less than a preset threshold,

[0022] The power factor is fixed at a preset threshold.

[0023] Preferably, the calculation of the power factor of the new energy unit further includes:

[0024]

[0025] In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

[0026] Preferably, when the bus voltage of the flexible DC converter station exceeds a preset range, the reactive power reference value of the flexible DC converter station is adjusted, and step S3 is continued, including:

[0027] Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria?

[0028] U c <U N -ΔU1 or U c >U N +ΔU2

[0029] △t≥T

[0030] In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU3 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N +ΔU is the time, where T is the set time value.

[0031] Preferably, it further includes:

[0032] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached maxContinue with step S3;

[0033] When U c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max Continue with step S3;

[0034]

[0035] Based on another aspect of the present invention, the present invention provides a coordinated control system for new energy sources and flexible DC power sources suitable for power fluctuations, the system comprising:

[0036] The acquisition unit is used to acquire in real time the operating status data and control parameters of new energy units in the flexible DC transmission system and the new energy grid-connected system.

[0037] The setting unit is used to set the initial control mode and voltage reference value of the new energy units in the new energy grid-connected system; and to set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system.

[0038] The detection unit is used to detect whether a serious fault has occurred in the power transmission system;

[0039] When a serious fault is detected in the power transmission system, the reactive power control mode of the flexible DC converter station is switched to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold. Then, the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system are set.

[0040] When no serious fault is detected in the power transmission system, the power factor of the new energy unit is calculated based on the operating data.

[0041] When the power factor of the new energy unit is greater than or equal to a preset threshold, the bus voltage of the flexible DC converter station is detected in real time to see if it exceeds the preset range.

[0042] When the bus voltage of the flexible DC converter station exceeds the preset range, the reactive power reference value of the flexible DC converter station is adjusted to detect whether a serious fault has occurred in the power transmission system.

[0043] When the bus voltage of the flexible DC converter station does not exceed the preset range, the system is checked to determine whether a serious fault has occurred in the power transmission system.

[0044] Preferably, the setting unit is used to set the control mode and control parameters of the new energy unit in the new energy grid-connected system, and is also used for:

[0045] The control mode of the new energy unit is set to constant voltage control mode, and the voltage reference value is the rated voltage of the bus at the grid connection point of the wind farm.

[0046] The control mode and control parameters of the flexible DC converter station at the sending end of the flexible DC transmission system are set, including:

[0047] The active power control mode of the flexible DC converter station is set to constant frequency control mode, and the reactive power control mode is set to constant reactive power control mode.

[0048] Preferably, the serious faults include: a single-circuit fault of a three-permanent-trip line, a double-circuit fault of a three-permanent-trip line, a faultless interruption of a line, and a flexible DC blocking fault.

[0049] Preferably, the detection unit is further configured to fix the power factor to a preset threshold when the power factor of the new energy unit is less than a preset threshold.

[0050] Preferably, the detection unit is used to calculate the power factor of the new energy unit, and is also used for:

[0051]

[0052] In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

[0053] Preferably, the detection unit is used to adjust the reactive power reference value of the flexible DC converter station when the bus voltage of the flexible DC converter station exceeds a preset range, and to detect whether a serious fault has occurred in the power transmission system. It is also used to:

[0054] Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria?

[0055] U c <U N -ΔU1 or U c >U N +ΔU2

[0056] △t≥T

[0057] In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU3 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N +ΔU is the time, where T is the set time value.

[0058] Preferably, the detection unit is further configured to:

[0059] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max To detect whether a serious fault has occurred in the power transmission system;

[0060] When U c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max To detect whether a serious fault has occurred in the power transmission system;

[0061]

[0062] This invention provides a method and system for coordinated control of new energy and flexible DC transmission systems, applicable to power fluctuations. The method includes: S1: Real-time acquisition of operating status data and control parameters of new energy units in the flexible DC transmission system and the new energy grid-connected system; S2: Setting the initial control mode and voltage reference value of the new energy units in the new energy grid-connected system; Setting the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system; S3: Detecting whether a serious fault has occurred in the transmission system; S4: When a serious fault is detected in the transmission system, switching the reactive power control mode of the flexible DC converter station to constant. In voltage control mode, step S2 continues until the bus voltage of the flexible DC converter station recovers to above the preset threshold; S5: When no serious fault is detected in the transmission system, the power factor of the new energy unit is calculated based on the operating data; S6: When the power factor of the new energy unit is greater than or equal to the preset threshold, the bus voltage of the flexible DC converter station is monitored in real time to see if it exceeds the preset range; S7: When the bus voltage of the flexible DC converter station exceeds the preset range, the reactive power reference value of the flexible DC converter station is adjusted, and step S3 continues; S8: When the bus voltage of the flexible DC converter station does not exceed the preset range, step S3 continues. This invention provides a coordinated control method between wind turbines and flexible DC converters under the premise of grid voltage compliance, improving the bidirectional reactive power regulation margin of the flexible DC converter and meeting the voltage control requirements under steady-state and transient severe faults in the system. Attached Figure Description

[0063] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0064] Figure 1This is a flowchart of a preferred embodiment of the present invention for a coordinated control method of new energy sources and flexible DC power sources suitable for power fluctuations;

[0065] Figure 2 This is a flowchart of a preferred embodiment of the present invention for a coordinated control method of new energy sources and flexible DC power sources suitable for power fluctuations;

[0066] Figure 3 This is a schematic diagram of the power grid structure of a new energy and flexible DC transmission system according to a preferred embodiment of the present invention;

[0067] Figure 4 This is a schematic diagram of the active power fluctuation curve of a new energy source according to a preferred embodiment of the present invention;

[0068] Figure 5 This is a schematic diagram of the reactive power output of a new energy unit during coordinated control according to a preferred embodiment of the present invention.

[0069] Figure 6 This is a schematic diagram of the reactive power output of a new energy unit without coordinated control according to a preferred embodiment of the present invention.

[0070] Figure 7 This is a schematic diagram of the reactive power output of the converter station during coordinated control according to a preferred embodiment of the present invention.

[0071] Figure 8 A schematic diagram of the reactive power output of a converter station without coordinated control according to a preferred embodiment of the present invention; and

[0072] Figure 9 This is a structural diagram of a new energy and flexible DC coordinated control system suitable for power fluctuations, according to a preferred embodiment of the present invention. Detailed Implementation

[0073] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0074] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0075] Figure 1This is a flowchart illustrating a preferred embodiment of a coordinated control method for new energy sources and flexible DC power sources applicable to power fluctuations according to the present invention. The present invention provides a coordinated control method for new energy sources and flexible DC power sources applicable to power fluctuations, which can quickly and efficiently adjust the reactive power output of new energy power sources and flexible DC converter equipment, suppress grid voltage fluctuations caused by frequent changes in new energy output, and, while ensuring qualified voltage levels, coordinate the flexible DC converter to reserve more reactive power reserve capacity during stable operation, providing reactive voltage support when system faults cause severe voltage drops.

[0076] like Figure 1 As shown, this invention provides a coordinated control method for new energy sources and flexible DC power sources suitable for power fluctuations. The method includes:

[0077] S1: Real-time acquisition of operating status data and control parameters of new energy units in flexible DC transmission systems and new energy grid-connected systems;

[0078] This invention first acquires the operating status and control parameters of new energy units in the flexible DC transmission system and the new energy grid-connected system in real time. The data acquired from the flexible DC transmission system includes: flexible DC control mode, flexible DC rated active power P. d Flexible DC Capacity S c Flexible DC real-time active power transmission P s Flexible DC injection into the AC grid: reactive power Q s The data acquired by the renewable energy grid connection system includes: the active power output P of renewable energy unit i. gi And no effort put in Q gi New energy unit control mode.

[0079] S2: Set the initial control mode and voltage reference value of the new energy units in the new energy grid-connected system; set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system;

[0080] Preferably, the control mode and control parameters of the new energy units in the new energy grid-connected system are set, including:

[0081] The control mode of the new energy unit is set to constant voltage control mode, and the voltage reference value is the rated voltage of the bus at the grid connection point of the wind farm.

[0082] The control mode and control parameters of the flexible DC converter station at the sending end of the flexible DC transmission system are set, including:

[0083] The active power control mode of the flexible DC converter station is set to constant frequency control mode, and the reactive power control mode is set to constant reactive power control mode.

[0084] This invention sets the wind turbines within the region to a constant voltage control mode, with the voltage reference value being the rated voltage of the wind farm's grid connection point bus. The active power control mode of the flexible direct-transmission converter is set to constant frequency control, and the reactive power control mode is set to constant reactive power control. The reactive power command is divided into n levels, each with a capacity of ±ΔQ. c + represents capacitive reactive power, - represents inductive reactive power, and the initial reactive power command value is zero.

[0085] S3: Detect whether a serious fault has occurred in the power transmission system; preferably, serious faults include: single circuit fault of three permanent line trip, double circuit fault of three permanent line trip, faultless line interruption, and flexible DC blocking fault.

[0086] The severe fault types in this invention include: single-circuit fault of three permanent line trips, double-circuit fault of three permanent line trips, faultless line interruption, and flexible DC blocking fault.

[0087] S4: When a serious fault is detected in the power transmission system, switch the reactive power control mode of the flexible DC converter station to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold, and then continue to execute step S2.

[0088] In this invention, when a severe system fault disturbance is detected, the flexible DC reactive power control mode switches to constant voltage control mode, with the voltage reference value being the rated voltage of the flexible DC converter station bus. When the flexible DC converter station bus voltage recovers to above 0.9 pu, the process returns to step S2. If no system fault is detected, step S5 is executed.

[0089] S5: When no serious fault is detected in the power transmission system, calculate the power factor of the new energy unit based on the operating data;

[0090] Preferably, calculating the power factor of the new energy unit further includes:

[0091]

[0092] In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

[0093] S6: When the power factor of the new energy unit is greater than or equal to the preset threshold, the bus voltage of the flexible DC converter station is monitored in real time to see if it exceeds the preset range; preferably, when the power factor of the new energy unit is less than the preset threshold, the power factor is fixed at the preset threshold.

[0094] If the cosφ of the new energy unit is ≥0.95, step S7 is executed. If the cosφ of the new energy unit is <0.95 and the reactive power output is positive, the control mode of the new energy unit is switched to constant power factor control, with a power factor of 0.95 (leading). If the cosφ of the new energy unit is <0.95 and the reactive power output is negative, the control mode of the new energy unit is switched to constant power factor control, with a power factor of 0.95 (lagging). If the voltage fluctuation at the grid connection point of the unit is less than 2% within 1 minute, the wind turbine control mode is switched to constant voltage control.

[0095] S7: When the bus voltage of the flexible DC converter station exceeds the preset range, adjust the reactive power reference value of the flexible DC converter station and continue to execute step S3;

[0096] S8: If the bus voltage of the flexible DC converter station does not exceed the preset range, continue to execute step S3.

[0097] Preferably, when the bus voltage of the flexible DC converter station exceeds a preset range, the reactive power reference value of the flexible DC converter station is adjusted, and step S3 is continued, including:

[0098] Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria?

[0099] U c <U N -ΔU1 or U c >U N +ΔU2

[0100] △t≥T

[0101] In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU3 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N +ΔU is the time, where T is the set time value.

[0102] Preferably, it further includes:

[0103] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max Continue with step S3;

[0104] When U c >U N+ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max Continue with step S3;

[0105]

[0106] If the criteria are met, adjust the flexible DC reactive power reference value. The adjustment method for the flexible DC reactive power reference value is as follows:

[0107] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max Return to step S3; when U c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max Return to step S3.

[0108]

[0109] If the criterion is not met, return to step S3.

[0110] This invention provides a coordinated control method between wind turbines and flexible DC converters under the premise of meeting grid voltage requirements. It improves the bidirectional reactive power regulation margin of the flexible DC converter and meets the voltage control requirements under both steady-state and transient severe fault conditions. This invention can reduce the workload of grid dispatching personnel in steady-state voltage regulation and improve the absorption rate of new energy sources while ensuring grid security.

[0111] Figure 2 This is a flowchart of a preferred embodiment of the present invention for a coordinated control method of new energy sources and flexible DC power sources suitable for power fluctuations.

[0112] like Figure 2 As shown, the present invention (1) first obtains the operating status of flexible DC and new energy sources:

[0113] This invention acquires in real time the operating status and control parameters of new energy units in flexible DC transmission systems and new energy grid-connected systems. The data acquired from the flexible DC transmission system includes: flexible DC control mode, and the rated active power P of the flexible DC transmission system. d Flexible DC Capacity S c Flexible DC real-time active power transmission P s Flexible DC injection into the AC grid: reactive power Q sThe data acquired by the renewable energy grid connection system includes: the active power output P of renewable energy unit i. gi And no effort put in Q gi New energy unit control mode.

[0114] (2) Initialization settings:

[0115] This invention sets the wind turbines within the region to a constant voltage control mode, with the voltage reference value being the rated voltage of the wind farm's grid connection point bus. The active power control mode of the flexible direct-transmission converter is set to constant frequency control, and the reactive power control mode is set to constant reactive power control. The reactive power command is divided into n levels, each with a capacity of ±ΔQ. c + represents capacitive reactive power, - represents inductive reactive power, and the initial reactive power command value is zero.

[0116] (3) Determine if a serious malfunction has occurred:

[0117] In this invention, when a severe system fault disturbance is detected, the flexible DC reactive power control mode switches to constant voltage control mode, with the voltage reference value being the rated voltage of the flexible DC converter station bus. When the flexible DC converter station bus voltage recovers to above 0.9 pu, the process returns to step (2). If no system fault is detected, step (4) is executed.

[0118] Serious fault types include: single-circuit fault of three permanent lines tripping, double-circuit fault of three permanent lines tripping, faultless interruption of lines, and flexible DC blocking fault.

[0119] (4) Coordinated control strategy for new energy sources and flexible DC transmission:

[0120] Step (4-1): Calculate the power factor of the new energy units. Calculate the power factor cosφ of all new energy units at the sending end using the following formula.

[0121]

[0122] In the formula, P gi and Q gi The active and reactive power outputs of the new energy unit i.

[0123] In this invention, if the cosφ of the new energy unit is ≥0.95, step (4-2) is executed. If the cosφ of the new energy unit is <0.95 and the reactive power output is positive, the control mode of the new energy unit is switched to constant power factor control, with a power factor of 0.95 (leading); if the cosφ of the new energy unit is <0.95 and the reactive power output is negative, the control mode of the new energy unit is switched to constant power factor control, with a power factor of 0.95 (lagging); if the voltage fluctuation at the grid connection point of the unit is less than 2% within 1 minute, the wind turbine control mode is switched to constant voltage control.

[0124] Step (4-2): Adjustment of flexible DC operation conditions. Real-time monitoring of the bus voltage U of the flexible DC converter station. c Changes, determine U c Does it meet the following criteria?

[0125] U c <U N -ΔU1 or U c >U N +ΔU2

[0126] △t≥T

[0127] In the formula, U N ΔU1 represents the rated voltage of the converter station bus, ΔU2 represents the minimum allowable voltage deviation of the converter station, and ΔU3 represents the maximum allowable voltage deviation of the converter station. Δt represents U... c Continuously less than U N -ΔU or U c Persistently greater than U N The time for +ΔU, where T is a set value.

[0128] If the criteria are met, adjust the flexible DC reactive power reference value. The adjustment method for the flexible DC reactive power reference value is as follows:

[0129] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max Return to step (3); when U c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max Return to step (3).

[0130]

[0131] If the criterion is not met, return to step (3).

[0132] This embodiment uses a real power grid as an example to illustrate the implementation steps of a coordinated control method for new energy sources and flexible DC power transmission that is suitable for power fluctuations:

[0133] (1) Obtain the operating status of flexible DC transmission and new energy sources:

[0134] This invention establishes a system based on a regional renewable energy and flexible DC islanding transmission system as an example. Figure 3The illustrated centralized renewable energy transmission system connects to a region with concentrated wind power resources at the sending end of the grid. Wind power is collected at 500kV collection stations 1, 2, and 3, and each station connects to a flexible DC converter station at the sending end via a 50km 500kV line. The installed capacity of renewable energy is approximately 6000MW. All wind turbines and the flexible DC power grid at the sending end are considered as coordinated control objects.

[0135] This invention acquires data from a flexible DC transmission system in real time under a certain operating mode, including the rated active power P of the flexible DC transmission system. d The flexible DC capacity is 6000MW. c For 6500MVA, flexible DC transmission active power P s For 6000MW of flexible DC power injection into the AC grid, reactive power Q is injected. s The power output is 0 Mvar. The sending-end converter station of the flexible DC transmission system uses constant frequency control and constant AC voltage control, while the receiving-end converter station uses constant DC voltage control and constant reactive power control. In the renewable energy grid-connected system, the total active power output of the wind turbines is 6000 MW, and the total reactive power output is 0 Mvar. The wind turbine control mode is constant power factor control, with a power factor of 1.

[0136] (2) Initialization settings:

[0137] This invention sets the wind turbines within the region to a constant voltage control mode, with the voltage reference value being the rated voltage of the wind farm's grid connection point bus, 690V. The active power control mode of the flexible DC sending-end converter is set to constant frequency control, with the frequency reference value being the converter station bus frequency. The reactive power control mode is set to constant reactive power control, dividing the reactive power command into 15 levels, each with a capacity of ±200Mvar. + represents capacitive reactive power, - represents inductive reactive power, and the initial reactive power command value is zero.

[0138] (3) Coordinated control strategy for new energy and flexible DC:

[0139] This invention simulates the changes in active power output of wind power throughout the day, such as... Figure 4 As shown. During the period from 0:00 to 8:00, as the active power output of wind power increases, the voltage of the sending-end grid decreases. The power factor cosφ of the wind turbines in the calculation area is used. Under constant voltage control, the wind turbines increase capacitive reactive power to suppress voltage fluctuations. Around 4:00, the power factor of the wind turbines at the sending-end Denghui wind farm decreases to 0.95 (leading). The wind turbine control mode is then switched to constant power factor control, and the power factor is set to 0.95. The bus voltage U of the flexible DC converter station is monitored in real time. c Changes, determine U c Does it satisfy the following formula?

[0140] U c<525kV-15kV or U c >525kV+10kV

[0141] △t≥2

[0142] In the formula, the rated voltage of the converter station bus is 525kV, the minimum allowable voltage deviation of the converter station is 15kV, and the maximum allowable voltage deviation of the converter station is 10kV. The voltage over-limit duration is set to 2 seconds.

[0143] As wind power continued to increase, the converter station bus voltage Uc decreased to 510kV and remained there for more than 2 seconds, meeting the criterion. The converter's reactive power reference value was increased by 150Mvar. After four adjustments, the converter's reactive power reference value was adjusted to 600Mvar, generating capacitive reactive power to the AC system. Between 16:00 and 24:00, as wind power active power decreased, the sending-end grid voltage increased. The renewable energy units rapidly increased their inductive reactive power output to suppress voltage fluctuations. Around 18:00, the power factor of the wind turbines at the sending-end Denghui Wind Farm decreased to 0.95 (lagging), and the turbine control mode was switched to constant power factor control, with the power factor set to 0.95. As wind power continued to decrease, the converter station bus voltage Uc rose to 535kV and lasted for more than 2 seconds. The reactive power reference value of the converter was reduced by 150Mvar. After 4 adjustments, the reactive power reference value of the converter was adjusted to 0Mvar.

[0144] Figures 5-8 To achieve coordinated control of reactive power output from the wind turbines and flexible DC converter station, the following approach is adopted. If independent control is used instead, the wind turbines and flexible DC converter will have zero reactive power output between 8:00 and 16:00, while the flexible DC converter's reactive power output will reach its maximum capacity limit of 2500 Mvar, exceeding its reactive power voltage regulation limit. Since the flexible DC converter can output a large amount of reactive power during transient processes, providing stronger support for the main grid voltage, it is desirable for the flexible DC converter to reserve more reactive power capacity during steady-state operation, providing more dynamic reactive power support during severe voltage drops caused by system faults. Using the coordinated control method provided in this invention, the wind turbine's reactive power output reaches its maximum value of 0.33 pu for most of the day, while the flexible DC converter's reactive power output will not exceed 25% of its total capacity, providing more reactive power reserves to address potential voltage stability issues after severe faults.

[0145] Figure 9 This is a structural diagram of a new energy and flexible DC coordinated control system suitable for power fluctuations, according to a preferred embodiment of the present invention. Figure 9 As shown, this invention provides a coordinated control system for new energy sources and flexible DC power transmission suitable for power fluctuations. The system includes:

[0146] The acquisition unit 901 is used to acquire in real time the operating status data and control parameters of new energy units in the flexible DC transmission system and the new energy grid-connected system.

[0147] Setting unit 902 is used to set the initial control mode and voltage reference value of new energy units in the new energy grid-connected system; and to set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system.

[0148] Preferably, the setting unit 902 is used to set the control mode and control parameters of the new energy unit in the new energy grid-connected system, and is also used for:

[0149] The control mode of the new energy unit is set to constant voltage control mode, and the voltage reference value is the rated voltage of the bus at the grid connection point of the wind farm.

[0150] The control mode and control parameters of the flexible DC converter station at the sending end of the flexible DC transmission system are set, including:

[0151] The active power control mode of the flexible DC converter station is set to constant frequency control mode, and the reactive power control mode is set to constant reactive power control mode.

[0152] The detection unit 903 is used to detect whether a serious fault has occurred in the power transmission system;

[0153] When a serious fault is detected in the power transmission system, the reactive power control mode of the flexible DC converter station is switched to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold. Then, the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system are set.

[0154] When no serious fault is detected in the power transmission system, the power factor of the new energy units is calculated based on the operating data;

[0155] When the power factor of the new energy unit is greater than or equal to the preset threshold, the bus voltage of the flexible DC converter station is detected in real time to see if it exceeds the preset range.

[0156] When the bus voltage of the flexible DC converter station exceeds the preset range, the reactive power reference value of the flexible DC converter station is adjusted, and the transmission system is checked for serious faults. Preferably, serious faults include: single circuit fault of three permanent line trip, double circuit fault of three permanent line trip, faultless line interruption, and flexible DC blocking fault.

[0157] When the bus voltage of the flexible DC converter station does not exceed the preset range, the system is checked to see if a serious fault has occurred in the power transmission system.

[0158] Preferably, the detection unit 903 is further configured to fix the power factor to the preset threshold when the power factor of the new energy unit is less than the preset threshold.

[0159] Preferably, the detection unit is used to calculate the power factor of the new energy unit, and also for:

[0160]

[0161] In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

[0162] Preferably, the detection unit 903 is used to adjust the reactive power reference value of the flexible DC converter station when the bus voltage of the flexible DC converter station exceeds a preset range, to detect whether a serious fault has occurred in the power transmission system, and is also used to:

[0163] Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria?

[0164] U c <U N -ΔU1 or U c >U N +ΔU2

[0165] △t≥T

[0166] In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU3 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N +ΔU is the time, where T is the set time value.

[0167] Preferably, the detection unit 903 is further used for:

[0168] When U c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max To detect whether a serious fault has occurred in the power transmission system;

[0169] When U c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached maxTo detect whether a serious fault has occurred in the power transmission system;

[0170]

[0171] The preferred embodiment of the present invention provides a new energy and flexible DC coordinated control system 900 suitable for power fluctuations, which corresponds to the preferred embodiment of the present invention provides a new energy and flexible DC coordinated control method 100 suitable for power fluctuations, and will not be described in detail here.

[0172] The invention has been described with reference to a few embodiments. However, as will be known to those skilled in the art, and as defined in the appended claims, other embodiments besides those disclosed above fall equivalently within the scope of the invention.

[0173] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless otherwise expressly defined herein. All references to “a / / the [device, component, etc.]” ​​are openly interpreted as at least one instance of the device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein are not necessarily to be performed in the exact order disclosed, unless explicitly stated otherwise.

Claims

1. A method for coordinated control of new energy sources and flexible DC power sources suitable for power fluctuations, the method comprising: S1: Real-time acquisition of operating status data and control parameters of new energy units in flexible DC transmission systems and new energy grid-connected systems; S2: Set the initial control mode and voltage reference value of the new energy units in the new energy grid-connected system; set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system; The setting of the initial control mode and voltage reference value of the new energy unit in the new energy grid-connected system includes: setting the initial control mode of the new energy unit to a constant voltage control mode, and the voltage reference value being the rated voltage of the bus at the grid connection point of the wind farm; setting the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system includes: setting the active power control mode of the flexible DC converter station to a constant frequency control mode and the reactive power control mode to a constant reactive power control mode. S3: Detect whether a serious fault has occurred in the power transmission system; S4: When a serious fault is detected in the power transmission system, the reactive power control mode of the flexible DC converter station is switched to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold, and then step S2 is executed. S5: When no serious fault is detected in the power transmission system, calculate the power factor of the new energy unit based on the operating status data; S6: When the power factor of the new energy unit is greater than or equal to the preset threshold, the bus voltage of the flexible DC converter station is monitored in real time to see if it exceeds the preset range. S7: When the bus voltage of the flexible DC converter station exceeds the preset range, adjust the reactive power reference value of the flexible DC converter station and continue to execute step S3, including: Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria? U c N -ΔU1 or U c >U N +ΔU2​ △t≥T In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU2 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N The time for +ΔU, where T is the set time value; WhenU c N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max Continue with step S3;​ WhenU c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max Continue with step S3; Among them, S c For flexible DC capacity, P s This represents the real-time active power transmission of flexible DC. S8: When the bus voltage of the flexible DC converter station does not exceed the preset range, continue to execute step S3.

2. The method according to claim 1, wherein the serious fault includes: Line 3 permanent trip single circuit fault, Line 3 permanent trip double circuit fault, Line no fault interruption or flexible DC blocking fault.

3. According to the method of claim 1, when the power factor of the new energy unit is less than a preset threshold, the power factor is fixed to the preset threshold.

4. The method according to claim 1, wherein calculating the power factor of the new energy unit further includes: In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

5. A coordinated control system for new energy sources and flexible DC power sources suitable for power fluctuations, the system comprising: The acquisition unit is used to acquire in real time the operating status data and control parameters of new energy units in the flexible DC transmission system and the new energy grid-connected system. The setting unit is used to set the initial control mode and voltage reference value of the new energy unit in the new energy grid-connected system; set the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system; and is also used to: set the initial control mode of the new energy unit to a constant voltage control mode, with the voltage reference value being the rated voltage of the bus at the wind farm grid connection point. Setting the initial control mode and control parameters of the flexible DC converter station at the sending end of the flexible DC transmission system includes: setting the active power control mode of the flexible DC converter station to a constant frequency control mode and the reactive power control mode to a constant reactive power control mode. The detection unit is used to detect whether a serious fault has occurred in the power transmission system; When a serious fault is detected in the power transmission system, the reactive power control mode of the flexible DC converter station is switched to the constant voltage control mode until the bus voltage of the flexible DC converter station recovers to above the preset threshold. Then, the initial control mode and initial reactive power value of the flexible DC converter station at the sending end of the flexible DC transmission system are set. When no serious fault is detected in the power transmission system, the power factor of the new energy unit is calculated based on the operating status data. When the power factor of the new energy unit is greater than or equal to a preset threshold, the bus voltage of the flexible DC converter station is detected in real time to see if it exceeds the preset range. When the bus voltage of the flexible DC converter station exceeds the preset range, the reactive power reference value of the flexible DC converter station is adjusted to detect whether a serious fault has occurred in the power transmission system. When the bus voltage of the flexible DC converter station does not exceed the preset range, it is necessary to detect whether a serious fault has occurred in the power transmission system. The detection unit is used to adjust the reactive power reference value of the flexible DC converter station when the bus voltage of the flexible DC converter station exceeds a preset range, and to detect whether a serious fault has occurred in the power transmission system. It is also used to: Monitoring the bus voltage U of the flexible DC converter station c Changes, determine U c Does it meet the following criteria? U c N -ΔU1 or U c >U N +ΔU2​ △t≥T In the formula, U N ΔU1 is the rated voltage of the converter station bus, ΔU2 is the minimum allowable voltage deviation of the converter station, ΔU2 is the maximum allowable voltage deviation of the converter station, and Δt is the voltage deviation of U. c Continuously less than U N -ΔU or U c Persistently greater than U N The time for +ΔU, where T is the set time value; The detection unit is also used for: WhenU c <U N -ΔU increases the reactive power reference value level by one level, increasing the reactive power value by ΔQ. c Until the maximum converter capacity Q is reached max To detect whether a serious fault has occurred in the power transmission system; WhenU c >U N +ΔU lowers the reactive power reference value level by one level, resulting in a decrease in reactive power value of ΔQ. c Until the maximum converter capacity Q is reached max To detect whether a serious fault has occurred in the power transmission system; Among them, S c For flexible DC capacity, P s This refers to the real-time active power transmission of flexible DC.

6. The system according to claim 5, wherein the serious fault includes: Line 3 permanent trip single circuit fault, Line 3 permanent trip double circuit fault, Line no fault interruption or flexible DC blocking fault.

7. The system according to claim 5, wherein the detection unit is further configured to fix the power factor to the preset threshold when the power factor of the new energy unit is less than the preset threshold.

8. The system according to claim 5, wherein the detection unit is used to calculate the power factor of the new energy unit, and is further used to: In the formula, P gi and Q gi These are the active and reactive power outputs of the new energy unit i, respectively.

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