Frequency support control method and system for active speed change of combined machine group

Abstract

The invention relates to a combined machine group active speed change frequency support control method, which is used for a dynamic low-frequency wind power system, and comprises the following steps: calculating a power grid frequency deviation signal; if the power grid frequency deviation signal does not exceed the frequency modulation dead zone, outputting 0 as a first power instruction, and if not, performing frequency support power calculation, and outputting a calculation result as the first power instruction; comparing the power grid active power dispatching instruction with the active power calculation value, and outputting a second power instruction; if the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold value, performing power grid frequency support control on the wind power system by using the first power instruction; and if not, performing limited power control on the wind power system by using the second power instruction. Compared with the prior art, active speed increasing and power reducing control of the dynamic low-frequency wind power system can be achieved, more energy reserve can be provided for power grid frequency support while sudden change of the power grid frequency can be rapidly dealt with, and therefore a better power grid support effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of offshore wind power, and in particular to a dynamic low-frequency wind power technology using variable voltage and variable frequency low-frequency AC power transmission, and proposes a frequency support control method and system for active speed change of a combined group of machines. Background Art

[0002] As high-quality offshore wind resources are exhausted, wind power development is gradually moving towards the mid- and far-sea areas. At this time, industrial frequency AC transmission cannot meet the power transmission needs of large-power long-distance wind farms, and DC transmission or low-frequency transmission is required to achieve power transmission.

[0003] At present, wind farms generally use variable speed constant frequency wind turbines. Variable speed constant frequency wind turbines are connected to the AC grid through back-to-back voltage source converters. The power electronic converter decouples the rotor speed of the wind turbine and the frequency of the grid system. The kinetic energy of the wind turbine is "hidden" and cannot provide grid frequency support like traditional synchronous generators when the grid frequency drops. In addition, converter stations used for DC transmission or low-frequency transmission will further increase the inertia barrier between wind turbines and the grid. Therefore, after large-scale wind turbines replace traditional synchronous generators, the effective inertia of the power system will be reduced, making the grid gradually become a "low inertia" system and reducing frequency stability.

[0004] Taking the variable speed constant frequency wind farm as an example, there are four levels of voltage source converters between the wind turbine and the grid, namely the wind turbine side converter, the wind turbine grid side converter, the flexible direct current sending end converter station and the flexible direct current receiving end converter station. Although these voltage source converters composed of fully controlled power electronic devices are flexible to control, too many power electronic devices also bring the following major disadvantages: 1) The initial construction cost of power electronic devices is high and the reliability is low; 2) The interaction of multiple power electronic devices may cause system oscillation; 3) Each level of power electronic power conversion adds one level of decoupling from the grid frequency, making the grid frequency response demand invisible and difficult to respond. In addition, considering that the DC transmission of offshore wind power requires the construction of a high-voltage and large-capacity offshore converter station, the cost is very high. The use of low-frequency transmission has the economic advantage of transmission in COSCO Wind Power 80 to 200 km offshore. Low-frequency transmission can also be used for onshore wind power far away from the load center.

[0005] However, offshore wind farms that use low-frequency power transmission still have a large number of wind turbines with back-to-back voltage source converters scattered on the sea surface at medium and long distances. These converters face greater reliability risks. Once a failure occurs, it will bring huge maintenance costs and downtime losses. In addition, in low-frequency power transmission scenarios, the back-to-back converters of wind turbines will also form a barrier to the grid frequency support. At present, there are two main ways for variable speed constant frequency wind turbines to participate in grid frequency regulation:

[0006] One is for grid-following variable speed constant frequency wind turbines, which usually need to rely on grid frequency detection and generate additional power instructions based on grid frequency signals, usually including virtual inertia control and primary frequency modulation control, see Figure 1 1) The virtual inertia control scheme obtains an additional active reference signal through the differential of the power grid. When the power grid frequency is disturbed, the kinetic energy stored in its own rotor is released to increase the frequency support for the power grid and suppress the drop of the power grid frequency. 2) The primary frequency control introduces the signal of frequency deviation on the basis of the original active reference value, so as to adjust the active reference value in real time according to the change of the power grid frequency and provide power grid frequency support.

[0007] The other is for grid-type variable speed constant frequency wind turbines. At this time, the wind turbines can respond autonomously to changes in grid frequency, but multiple grid-type variable speed constant frequency wind turbines may have undesirable interactions. In addition, regardless of whether it is a grid-type variable speed constant frequency wind turbine or a grid-type variable speed constant frequency wind turbine, the grid frequency support usually directly controls the back-to-back converter of the unit.

[0008] It can be seen that the system solution that combines variable speed constant frequency wind turbines with flexible DC transmission or variable speed constant frequency wind turbines with flexible low frequency transmission will face the problems of high cost, low reliability and difficulty in grid frequency support.

[0009] In response to the above problems, studies have proposed a dynamic low-frequency wind power system that integrates centralized frequency conversion and low-frequency AC transmission technology in wind farms. The centralized frequency conversion technology in wind farms adopts the frequency conversion control based on local active power detection disclosed in China's patent CN110247424B, "A communication-free centralized frequency conversion open-loop constant voltage-frequency ratio control method for wind farms", namely "local active power-centralized frequency following control", thereby eliminating the reliance on high-speed communication. In this technical solution, each single unit does not need to be equipped with a back-to-back converter independently. The voltage-frequency conversion control of the common connection point of the wind farm is realized based on the active power-frequency following principle of the low-frequency AC port of the AC-exchange station, thereby providing centralized frequency conversion for the wind turbine group in the wind farm. This control is based on local signal detection and does not require long-distance communication reliance on wind farm information. Through low-frequency AC transmission with voltage conversion and frequency conversion, it simultaneously meets the key requirements of centralized frequency conversion and speed conversion maximum power tracking of the group and low-frequency long-distance transmission. Due to the elimination of back-to-back converters, there are fewer isolation barriers between wind turbines and the grid to achieve frequency support, but at the same time, the controllability of the unit is poor, resulting in challenges for current dynamic low-frequency wind power systems in achieving grid frequency support, and the frequency support technology of variable speed constant frequency wind turbines (variable speed constant frequency wind farms) cannot be directly used.

[0010] Chinese patent CN117595405A, "Grid frequency support control method, equipment, and medium for dynamic low-frequency wind power system" discloses a grid frequency support method for a dynamic low-frequency wind power system. It draws on the frequency support control method of a grid-following variable-speed constant-frequency wind turbine set, uses grid frequency detection, and generates additional power instructions according to the functions of virtual inertia control and primary frequency regulation control. This additional power instruction is directly superimposed on the local active power detection value of the "local active power-centralized frequency following control".

[0011] Although the control method proposed in "Grid frequency support control method, equipment, and medium for dynamic low-frequency wind power system" can extract the power of each wind turbine to improve the grid frequency, the improvement effect is qualitative. Since the process of each wind turbine responding to the grid frequency support under this control method is passive speed change, the effect of the grid frequency support cannot be quantified. Summary of the invention

[0012] The purpose of the present invention is to provide a frequency support control method for active speed change of a combined group of machines, which can realize active speed increase and power reduction control of a dynamic low-frequency wind power system.

[0013] The purpose of the present invention can be achieved by the following technical solutions:

[0014] A frequency support control method for active speed change of a combined group of machines, used in a dynamic low-frequency wind power system, the method comprising:

[0015] Receive three-phase voltage detection signals of the power grid, active power dispatching instructions and thresholds of the power grid;

[0016] Calculate the grid frequency deviation signal using the grid three-phase voltage detection signal and the grid rated frequency;

[0017] If the grid frequency deviation signal does not exceed the frequency modulation dead zone, 0 is output as the first power instruction. If the grid frequency deviation signal exceeds the frequency modulation dead zone, the frequency support power is calculated and the calculation result is output as the first power instruction.

[0018] Compare the grid active power dispatch instruction and the active power calculation value, and output a second power instruction;

[0019] If the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold value, the first power instruction is used to perform grid frequency support control on the wind power system;

[0020] If the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is used to perform power limiting control on the wind power system.

[0021] Furthermore, the process of calculating the grid frequency deviation signal includes:

[0022] Calculate the grid frequency using the three-phase voltage detection signal of the grid;

[0023] The grid frequency deviation signal is obtained by subtracting the grid frequency from the grid rated frequency.

[0024] Furthermore, the frequency support power calculation includes an inertia response mode, a primary frequency modulation support mode, and a combined inertia response and primary frequency modulation support mode.

[0025] Furthermore, when a rapid change in grid frequency is detected, the inertia response mode is used for calculation; when it is detected that the grid frequency deviates greatly from the rated value and the frequency needs to be stabilized, the primary frequency regulation support mode is used for calculation; when it is detected that both the rapid change in grid frequency and the large deviation from the rated value need to be considered at the same time, the combined inertia response and primary frequency regulation support mode is used for calculation.

[0026] Furthermore, the calculation formula of the inertia response mode is:

[0027]

[0028] Among them, f g is the grid frequency value, k d1 is the control coefficient, ΔP f1 It is the active power regulation quantity based on the rate of change of grid frequency;

[0029] The calculation formula of the primary frequency modulation support mode is:

[0030] ΔP f2 =-k d2 f(Δf g )·Δf g ,

[0031] Where Δf g k is the frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, d2 is the control coefficient, f(f g ) is the nonlinear variable droop control coefficient, ΔP f2 It is the active power regulation quantity of droop control based on grid frequency deviation;

[0032] The calculation formula of the combined inertia response and primary frequency modulation support mode is:

[0033]

[0034] Among them, f g is the grid frequency value, k d1 is the inertia response control coefficient, k d2 is the primary frequency modulation support control coefficient, Δf gThe frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, f(f g ) is the nonlinear variable droop control coefficient.

[0035] Furthermore, the active power calculation value is obtained by on-site detection and calculation of the AC port on the low-frequency side of the AC-to-AC switching station of the wind farm.

[0036] Further, the process of comparing the grid active dispatch instruction and the active calculated value includes:

[0037] When the grid dispatching instruction is less than the active power calculation value, the output deviation power value is used as the second power instruction;

[0038] When the grid dispatch instruction is greater than the active power calculation value, 0 is output as the second power instruction;

[0039] The deviation power value is the difference between the grid dispatch instruction and the active power calculation value.

[0040] Furthermore, the power grid frequency support control includes:

[0041] Normalize the input first power command;

[0042] The proportional-integral regulator is used to process the normalized power command and output the deviation signal of the concentrated frequency;

[0043] According to the deviation signal of the concentrated frequency, the speed of the wind turbine rotor of the wind power system and the output power of the wind power system are adjusted.

[0044] Furthermore, the power limiting control includes:

[0045] Normalize the input second power command;

[0046] The proportional-integral regulator is used to process the normalized power command and output the deviation signal of the concentrated frequency;

[0047] According to the deviation signal of the concentrated frequency, the speed of the wind turbine rotor of the wind power system is increased and the output power of the wind power system is reduced.

[0048] A frequency support control system for active speed change of a combined group of machines, the system comprising:

[0049] The power-limited operation module compares the grid active dispatch instruction and the active calculation value, and outputs a second power instruction to the speed-changing function selection module;

[0050] The frequency support power calculation module calculates the grid frequency deviation signal using the grid three-phase voltage detection signal and the grid rated frequency, and outputs the result as the first power instruction to the speed change function selection module;

[0051] A speed change function selection module, if the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold, the first power instruction is selected to be output to the active speed change control module; if the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is selected to be output to the active speed change control module;

[0052] The active speed change module converts the received power command into a deviation signal of the centralized frequency to adjust the speed and output power of the wind power system.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. The present invention is used for dynamic low-frequency wind power systems. By setting a threshold value for comparison with the grid frequency deviation signal, the wind turbine and the grid are monitored in real time, so that the wind turbine can autonomously switch between the two modes of grid frequency support control and power limit control. When the grid active dispatching instruction is lower than the maximum output of the wind farm, it can actively increase the speed and reduce the power. When it is higher than the maximum output of the wind farm, it can maintain maximum power tracking. When faced with sudden changes in grid frequency, the wind turbine can respond quickly through the operation of grid frequency support control, and the grid frequency can be controlled within a safe range. The flexibility and controllability of the wind power system are improved, the operating efficiency of the wind farm is optimized, and the active frequency control also provides more energy reserves for grid frequency support, thereby achieving better frequency support effects.

[0055] 2. The present invention uses a proportional-integral regulator when controlling the speed and output power of the dynamic low-frequency wind power system, which can provide a quantifiable grid frequency support effect according to the preset function;

[0056] 3. The present invention adopts a more concise and efficient control strategy and is designed for dynamic low-frequency wind power systems, which reduces the number of power electronic devices used, reduces the complexity and construction cost of the system. At the same time, the system has a fast response speed and good controllability, and also reduces operation and maintenance costs and failure rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 is a flow chart of the method of the present invention;

[0058] Figure 2 It is a structural diagram of the control system of the present invention. DETAILED DESCRIPTION

[0059] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0060] Example 1

[0061] This embodiment discloses a frequency support control method for active speed change of a combined group of machines, which is used in a dynamic low-frequency wind power system. The method flow chart is as follows: Figure 1 As shown, the specific steps are as follows.

[0062] S1, input, includes receiving the three-phase voltage detection signal of the power grid, the active power dispatching instruction of the power grid and the threshold value. The threshold value here is set manually and can be set to 0 or a specific small positive value. The three-phase voltage detection signal of the power grid and the active power dispatching instruction of the power grid are measured or issued by the local wind power system.

[0063] S2, using the three-phase voltage detection signal of the power grid and the rated frequency of the power grid, calculates the power grid frequency deviation signal.

[0064] In S2, the process of calculating the grid frequency deviation signal includes:

[0065] Calculate the grid frequency using the three-phase voltage detection signal of the grid;

[0066] The grid frequency deviation signal is obtained by subtracting the grid frequency from the grid rated frequency.

[0067] S3, if the grid frequency deviation signal does not exceed the frequency modulation dead zone, then output 0 as the first power command; if the grid frequency deviation signal exceeds the frequency modulation dead zone, then perform frequency support power calculation and output the calculation result as the first power command. Normally, the grid rated frequency f is set. gn The ±0.05Hz range is the frequency modulation dead zone, which is used to detect whether the grid frequency has a sudden change.

[0068] In S3, the frequency support power calculation includes the inertia response mode, the primary frequency modulation support mode, and the combined inertia response and primary frequency modulation support mode;

[0069] When a rapid change in the grid frequency is detected, the inertia response mode is used for calculation; when the grid frequency is detected to deviate greatly from the rated value and the frequency needs to be stabilized, the primary frequency regulation support mode is used for calculation; when it is detected that both the rapid change in the grid frequency and the large deviation from the rated value need to be considered at the same time, the combined inertia response and primary frequency regulation support mode is used for calculation;

[0070] The calculation formula for inertia response mode is:

[0071]

[0072] In the pure inertia response mode, the detected grid frequency f g Differentiate and introduce the grid frequency change rate sf g As the frequency modulation control signal, multiplied by the control coefficient k d1Get the active power regulation ΔP based on the grid frequency change rate f1 ;

[0073] Among them, f g is the grid frequency value, k d1 is the control coefficient, ΔP f1 It is the active power regulation quantity based on the rate of change of grid frequency;

[0074] The calculation formula for the primary frequency modulation support mode is:

[0075] ΔP f2 =-k d2 f(Δf g )·Δf g ,

[0076] In the simple primary frequency regulation support mode, the detected grid frequency value f g The frequency change Δf obtained by subtracting the adjacent grid frequency dead zone value g , and multiply it by the coefficient k d2 , and then multiplied by the nonlinear variable droop control coefficient f(f g ), and the active power regulation value ΔP of droop control based on grid frequency deviation is obtained f2 ;

[0077] Where Δf g k is the frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, d2 is the control coefficient, f(f g ) is the nonlinear variable droop control coefficient, ΔP f2 It is the active power regulation quantity of droop control based on grid frequency deviation;

[0078] The calculation formula for the combined inertia response and primary frequency modulation support mode is:

[0079]

[0080] By adding the regulation values ​​of the above two modes, the total droop control active regulation value P can be obtained. f3 ;

[0081] Among them, f g is the grid frequency value, k d1 is the inertia response control coefficient, k d2 is the primary frequency modulation support control coefficient, Δf g The frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, f(f g ) is the nonlinear variable droop control coefficient.

[0082] S4: If the first power instruction is not 0 and the absolute value of the first power instruction is greater than the threshold, the first power instruction is used as the power instruction to perform grid frequency support control on the wind power system; if the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is used to perform power limiting control on the wind power system.

[0083] The second power instruction is obtained by comparing the grid active power dispatch instruction with the active power calculation value.

[0084] The active power calculation value is obtained by on-site detection and calculation of the AC port on the low-frequency side of the wind farm AC-to-AC switching station.

[0085] The process of comparing the grid active dispatch instruction and the active calculated value specifically includes:

[0086] When the grid dispatching instruction is less than the active power calculation value, the output deviation power value is used as the second power instruction;

[0087] When the grid dispatch instruction is greater than the active power calculation value, 0 is output as the second power instruction;

[0088] The deviation power value is the difference between the grid dispatch instruction and the active power calculation value.

[0089] In S4, the grid frequency support control includes: normalizing the input first power instruction; using a proportional-integral regulator to process the normalized power instruction and output a concentrated frequency deviation signal; adjusting the speed of the wind turbine rotor of the wind power system and the output power of the wind power system according to the concentrated frequency deviation signal, and controlling the speed of the wind turbine rotor of the wind power system to increase or decrease according to the size of the concentrated frequency deviation signal.

[0090] Similarly, the power limiting control includes: normalizing the input second power instruction; using a proportional-integral regulator to process the normalized second power instruction and output a concentrated frequency deviation signal; and according to the concentrated frequency deviation signal, controlling the speed of the wind turbine rotor of the wind power system to increase and reduce the output power of the wind power system.

[0091] The grid frequency support control controls the speed of the wind turbine rotor of the wind power system to increase or decrease the speed according to the size of the deviation signal, while the power limit control only controls the speed of the wind turbine rotor of the wind power system to increase.

[0092] In both control processes, the integrator of the proportional-integral regulator has an upper limit I_lim, which is the rated value of the concentrated frequency f n The deviation from the output frequency value of the centralized frequency control module of the wind farm without communication. This upper limit change limiter can avoid abnormal situations during the operation of the frequency support and power limit control modes and during the switching between the two modes.

[0093] Example 2

[0094] This embodiment discloses a frequency support control system for active speed change of a combined group of machines. Figure 2 As shown, including:

[0095] The power-limited operation module compares the grid active dispatch instruction and the active calculation value, and outputs a second power instruction to the speed-changing function selection module;

[0096] The frequency support power calculation module calculates the grid frequency deviation signal by using the grid three-phase voltage detection signal and the grid rated frequency, and outputs the first power command to the speed change function selection module;

[0097] A speed change function selection module, if the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold, the first power instruction is selected to be output to the active speed change control module; if the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is selected to be output to the active speed change control module;

[0098] The active speed change module converts the received power command into a deviation signal of the centralized frequency to adjust the speed and output power of the wind power system.

[0099] If the active speed change module receives the first power instruction, the wind turbine is increased or decreased in speed according to the first power instruction to provide frequency support for the power grid. If the active speed change module receives the second power instruction, the wind turbine is increased in speed and decreased in power.

[0100] Figure 2 The part other than the above four parts is the conventional dynamic low-frequency wind power system, which has been disclosed in the technology, and includes the main circuit, the non-communication wind farm centralized frequency control module and the converter station control module. The main circuit includes the wind farm, the wind farm booster station, the transformer-frequency low-frequency transmission line, the AC-exchange station and the industrial frequency power grid. The non-communication wind farm centralized frequency control module obtains the active power calculation value P according to the on-site detection of the AC port on the low-frequency side of the AC-exchange station. wf Determine the optimal reference frequency f in the maximum power point tracking mode of the wind farm opt The converter station control module includes a converter station low-frequency port control module and a converter station power frequency port control module. The technical solution of the present invention only improves the converter station low-frequency port control module to generate a centralized frequency deviation signal Δf cyca The frequency reference signal f is superimposed on the output of the centralized frequency conversion control module of the non-communication wind farm. opt The new frequency reference signal f is obtained ref , f ref As the input of the low-frequency port control module of the converter station.

[0101] The system of the present invention is used for simulation verification, and two situations are set to test the power grid frequency support control and the power limit control respectively.

[0102] The dynamic low-frequency wind power system is connected to the power grid and operates according to the active power dispatching instructions of the power grid under random wind speed. When the active power dispatching instructions of the power grid are lower than the maximum output of the wind farm, it can actively increase the speed and reduce the power. When the active power dispatching instructions of the power grid are higher than the maximum output of the wind farm, it can maintain maximum power tracking.

[0103] By setting different grid frequency mutation conditions, 30MW of load was switched on and off respectively. It can be seen from the operation results that the use of inertia response control, primary frequency regulation control and 'inertia response + primary frequency regulation control' can all achieve active speed change and provide quantifiable grid frequency support effects, thereby enhancing grid frequency stability.

[0104] The specific control effect is as follows: when the grid frequency drops suddenly, the virtual inertia control module outputs the transmission frequency adjustment value f of the low-frequency wind power system cycd , timely adjust the dynamic transmission frequency f cyc The active power P output by the wind farm wf Increase; droop control module outputs the active power control system command active power regulation amount P f , the active power control system is used to first reduce the pitch angle of the wind farm unit, and then reduce the transmission frequency f when the pitch angle is zero. cyc , tracking the target power to increase the wind farm output active power P wf ; Ultimately, the drop of the grid frequency is slowed down, the lowest point of the grid frequency is raised, and the grid frequency is controlled within a safe range. When the grid frequency suddenly rises, the virtual inertia control module adjusts the dynamic transmission frequency to increase, so that the active power output of the wind farm decreases; the droop control module reduces the command active power of the active control system, first increasing the transmission frequency f cyc , reaching the rated transmission frequency f cycn Then increase the pitch angle of the wind farm unit and reduce the wind farm output active power P wf ; Ultimately, slow down the rise of grid frequency, reduce the maximum point of grid frequency, and control the grid frequency within a safe range.

[0105] The specific details of the above modules can be understood by referring to the relevant descriptions and effects in Example 1.

[0106] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A frequency support control method for active speed change of a combined group of machines, used in a dynamic low-frequency wind power system, characterized in that: The method comprises: Receive three-phase voltage detection signals of the power grid, active power dispatching instructions and thresholds of the power grid; Calculate the grid frequency deviation signal using the grid three-phase voltage detection signal and the grid rated frequency; If the grid frequency deviation signal does not exceed the frequency modulation dead zone, 0 is output as the first power instruction. If the grid frequency deviation signal exceeds the frequency modulation dead zone, the frequency support power is calculated and the calculation result is output as the first power instruction. Compare the grid active power dispatch instruction and the active power calculation value, and output a second power instruction; If the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold value, the first power instruction is used to perform grid frequency support control on the wind power system; If the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is used to perform power limiting control on the wind power system.

2. A frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The process of calculating the grid frequency deviation signal comprises: Calculate the grid frequency using the three-phase voltage detection signal of the grid; The grid frequency deviation signal is obtained by subtracting the grid frequency from the grid rated frequency.

3. The frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The frequency support power calculation includes an inertia response mode, a primary frequency modulation support mode, and a combined inertia response and primary frequency modulation support mode.

4. A frequency support control method for active speed change of a combined group of machines according to claim 3, characterized in that: When a rapid change in grid frequency is detected, the inertia response mode is used for calculation; when it is detected that the grid frequency deviates greatly from the rated value and the frequency needs to be stabilized, the primary frequency regulation support mode is used for calculation; when it is detected that both the rapid change in grid frequency and the large deviation from the rated value need to be considered at the same time, the combined inertia response and primary frequency regulation support mode is used for calculation.

5. A frequency support control method for active speed change of a combined group of machines according to claim 4, characterized in that: The calculation formula of the inertia response mode is: Among them, f g is the grid frequency value, k d1 is the control coefficient, ΔP f1 It is the active power regulation quantity based on the rate of change of grid frequency; The calculation formula of the primary frequency modulation support mode is: ΔP f2 =-k d2 f(Δf g )·Δf g , Where Δf g k is the frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, d2 is the control coefficient, f(f g ) is the nonlinear variable droop control coefficient, ΔP f2 It is the active power regulation quantity of droop control based on grid frequency deviation; The calculation formula of the combined inertia response and primary frequency modulation support mode is: Among them, f g is the grid frequency value, k d1 is the inertia response control coefficient, k d2 is the primary frequency modulation support control coefficient, Δf g The frequency change obtained by subtracting the detected grid frequency value from the adjacent grid frequency dead zone value, f(f g ) is the nonlinear variable droop control coefficient.

6. A frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The active power calculation value is obtained by on-site detection and calculation of the low-frequency side AC port of the wind farm AC-exchange station.

7. A frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The process of comparing the grid active dispatch instruction and the active calculated value includes: When the grid dispatching instruction is less than the active power calculation value, the output deviation power value is used as the second power instruction; When the grid dispatch instruction is greater than the active power calculation value, 0 is output as the second power instruction; The deviation power value is the difference between the grid dispatch instruction and the active power calculation value.

8. The frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The grid frequency support control includes: Normalize the input first power command; The proportional-integral regulator is used to process the normalized power command and output the deviation signal of the concentrated frequency; According to the deviation signal of the concentrated frequency, the rotation speed of the wind turbine rotor of the wind power system and the output power of the wind power system are adjusted.

9. The frequency support control method for active speed change of a combined group of machines according to claim 1, characterized in that: The power limiting control comprises: Normalize the input second power command; The proportional-integral regulator is used to process the normalized power command and output the deviation signal of the concentrated frequency; According to the deviation signal of the concentrated frequency, the speed of the wind turbine rotor of the wind power system is increased and the output power of the wind power system is reduced.

10. A frequency support control system for active speed change of a combined group of machines, characterized in that: The system comprises: The power-limited operation module compares the grid active dispatch instruction and the active calculation value, and outputs a second power instruction to the speed-changing function selection module; The frequency support power calculation module calculates the grid frequency deviation signal using the grid three-phase voltage detection signal and the grid rated frequency, and outputs the calculation result as the first power instruction to the speed change function selection module; A speed change function selection module, if the first power instruction is not 0 and the absolute value of the first power instruction is greater than a threshold, the first power instruction is selected to be output to the active speed change control module; if the first power instruction is 0 or the absolute value of the first power instruction is less than the threshold, the second power instruction is selected to be output to the active speed change control module; The active speed change module converts the received power command into a deviation signal of the centralized frequency to adjust the speed and output power of the wind power system.

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