A wind storage combined frequency control method considering frequency modulation dead zone

Abstract

The application is a kind of wind storage combined frequency modulation method for setting frequency modulation dead zone of wind turbine and energy storage system, power grid frequency fluctuation, wind turbine detecting whether frequency deviation exceeds wind turbine frequency modulation dead zone, system entering wind turbine frequency modulation response area, energy storage detecting whether frequency deviation exceeds its frequency modulation dead zone, system entering wind storage transition area, system entering energy storage frequency modulation response area, energy storage detecting whether frequency deviation returns to wind turbine frequency modulation area, power grid frequency returning to stability; it can determine wind turbine and energy storage output frequency modulation power, and after wind storage combined frequency modulation starting, wind turbine and energy storage frequency modulation power calculation results are applied to wind turbine and energy storage active power instruction value. The method considers wind turbine and energy storage characteristics and their correlation, simplifies control process and control parameters, from the perspective of frequency modulation dead zone, it can effectively suppress system frequency fluctuation, solve wind turbine stall problem, and further improve energy storage device service life.

Description

Technical Field

[0001] This invention relates to the field of power system frequency control, and is a control method for wind turbines and energy storage systems to jointly participate in system frequency regulation. Specifically, it is a wind-storage joint frequency control method that takes into account the frequency regulation dead zone. Background Technology

[0002] With the large-scale grid connection of new energy power generation, problems have also emerged. Not only do the random fluctuations and intermittent nature of new energy sources cause difficulties for grid operation and dispatch, but the gradual replacement of high-inertia, strongly damped synchronous generators with power electronic grid connection for wind and solar power also weakens the inherent inertial damping effect of the system, leading to a gradual deterioration of the system's frequency indicators and making it highly susceptible to short-term frequency instability issues. Therefore, wind and solar power must gradually assume the primary responsibility for maintaining the safe and stable operation of the power grid, leveraging the flexibility and controllability of converter systems to effectively compensate for insufficient inertial damping in the system, thereby ensuring system frequency stability.

[0003] The kinetic energy contained in the rotor of a doubly-fed induction generator (DFIG) wind turbine can serve as the energy source for frequency regulation. Wind turbine participation in system frequency regulation often involves utilizing its rotor kinetic energy through virtual inertia control, droop control, or a combination of both, to increase or decrease the turbine's output power, thus achieving frequency regulation. Virtual inertia control (D control) uses the rate of frequency change as input, aiming to quickly suppress grid dips / sudden increases in frequency and shorten system frequency fluctuation time. Droop control (P control) uses the frequency deviation as input, improving the system's frequency response's extreme values ​​and recovery speed. Virtual inertia control combines virtual inertia and droop control, using appropriate proportional and derivative coefficients to enable the wind turbine to respond quickly to system frequency changes, reducing the rate of frequency decrease / increase, minimizing the maximum frequency deviation, and improving the system's frequency response characteristics.

[0004] Energy storage systems (ESS) are high-quality frequency-regulating power sources. Facing various disturbances, they can fully leverage their advantages of rapid response and flexible frequency regulation. By quickly processing power, they balance active power on both the source and load sides, maintaining grid frequency stability. In terms of frequency regulation, they offer faster response speed and accuracy than traditional generator sets. Currently, energy storage systems are connected to the external grid through power conversion systems, with their output power controlled by inverters. The main control methods for these inverters include PQ control, VF control, droop control, and virtual synchronous generator control. Each of these four control methods has its advantages and disadvantages, requiring specific analysis based on the specific circumstances.

[0005] Wind turbines utilize their own rotor kinetic energy to adjust the system frequency, mitigating the frequency regulation pressure on synchronous generators during load disturbances by altering grid-connected power. However, the mechanical output of the wind turbine does not increase; in fact, it decreases due to the unit's speed deviating from the optimal value, leading to reduced wind energy utilization. Furthermore, constrained by safe operation, the kinetic energy that the turbine rotor can absorb is limited. Excessive release / absorption of rotor kinetic energy, resulting in excessively low or high speeds, can even cause speed instability. Moreover, sudden increases in power generation / absorption increase the mechanical stress on the turbine's transmission system, exacerbating mechanical fatigue.

[0006] While energy storage systems offer advantages such as precise tracking, rapid response, and bidirectional regulation, resulting in good response speed and accuracy in frequency regulation, frequent charging and discharging can accelerate electrical aging, reduce battery life, and even cause dangerous situations such as drastic fluctuations in bus voltage, rapid decline in capacitance, capacitor bulging or bursting, and damage to electrical insulation. In addition, considering the high cost of energy storage systems, their participation in frequency regulation must take into account their own battery capacity and state of charge to avoid irreversible damage to their service life and improve their frequency regulation economy.

[0007] Currently, wind turbines and energy storage systems have limitations in participating in primary frequency regulation of the power system independently. Existing wind-storage frequency regulation methods only consider the control methods of the wind and storage systems themselves, which not only makes parameter tuning difficult but also makes the control process complex, largely neglecting the inherent characteristics of the wind and storage systems and the coordination between control methods. Therefore, how to coordinate the states of wind turbines and energy storage systems to suppress grid frequency fluctuations when system disturbances occur has become a pressing technical challenge in this field. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the limitations of wind turbines, energy storage, and wind-storage joint participation in primary frequency regulation of power systems. It comprehensively considers the characteristics of wind turbines and energy storage, and combines the control methods of the two to simplify the control process and control parameters. From the perspective of frequency regulation dead zone, it proposes a wind-storage joint frequency control method that can effectively suppress system frequency fluctuations, solve wind turbine stall problems, and thus improve the service life of energy storage devices. This method is scientific, reasonable, highly applicable, and effective.

[0009] The technical solution adopted to solve its technical problem is a wind-storage combined frequency regulation method with a frequency regulation dead zone, characterized in that the method includes the following:

[0010] 1) Set the frequency regulation dead zone for the wind turbine and energy storage system

[0011] Referring to the concept of dead zone setting for synchronous generator sets—synchronous generator sets use small frequency regulation dead zones to participate in primary frequency regulation, while those using large frequency regulation dead zones only respond to large disturbances in grid frequency changes—the frequency regulation dead zones for wind turbines are set smaller than those for energy storage, namely [0,0.01] and [0,0.2], respectively.

[0012] 2) Fluctuations in power grid frequency

[0013] The system detected fluctuations in the power grid frequency;

[0014] 3) Check if the fan's frequency deviation exceeds the fan's frequency adjustment dead zone.

[0015] If the frequency deviation detected by the fan exceeds the frequency dead zone of the fan, proceed to step 4); otherwise, proceed to step 9.

[0016] 4) The system enters the fan frequency regulation response zone.

[0017] The system frequency deviation exceeds the wind turbine's frequency regulation dead zone but not the energy storage's frequency regulation dead zone. Based on the detected grid frequency, the system frequency deviation Δf is calculated, and its absolute value is taken. The specific calculation method for the wind turbine's output frequency regulation power is as follows:

[0018] (1) Collect the current rotor speed of the fan and analyze the rotational kinetic energy capacity stored in the fan rotor based on the current operating status of the fan.

[0019] (2) Calculate the fan frequency regulation coefficient:

[0020] To ensure the wind turbine can fully utilize its frequency regulation potential while maintaining its own stability, a coupling relationship is established between the DFIG frequency regulation coefficient and its effective rotational kinetic energy of the rotor, and its expression is as follows:

[0021]

[0022] Where: K WC K WD These are the frequency modulation coefficients for the fan in the high-frequency and low-frequency stages, respectively; ω r ω is the DFIG rotational speed; min ω max α represents the minimum and maximum rotational speeds of the DFIG, respectively; α is the grid frequency performance adjustment factor.

[0023] (3) Calculate the frequency modulation power output of the fan:

[0024] To avoid noise caused by frequency differentiation, this invention uses droop control. The grid frequency deviation is proportional to the output frequency modulation power, as expressed below:

[0025]

[0026] Where: ΔPWC (t), ΔP WD (t) represents the additional power generated by the wind turbine in the high-frequency and low-frequency stages, respectively; Δf represents the system frequency deviation;

[0027] 5) Whether the frequency deviation of the energy storage exceeds its frequency tuning dead zone.

[0028] If the energy storage detects a frequency deviation exceeding its own frequency modulation dead zone, proceed to step 6); otherwise, proceed to step 3.

[0029] 6) The system enters the wind-storage transition zone.

[0030] The system frequency deviation reaches the dead zone boundary of energy storage frequency regulation. Considering the switching phase between wind turbine and energy storage frequency regulation, the wind turbine exits frequency regulation, causing a sudden change in frequency regulation active power. This leads to mechanical fatigue problems at the wind turbine level and increases the system's power deficit at the system level, resulting in mechanical fatigue and frequency drop. Therefore, we assume that the wind turbine smoothly reduces the frequency regulation power, and the calculation is as follows:

[0031] i. Record the time t0 when the system frequency reaches the energy storage dead zone boundary;

[0032] ii. Determine and enter the duration Δt for the fan to exit frequency regulation;

[0033] iii. Calculate the frequency modulation boost power ΔP output when the fan is out of frequency modulation mode. W (t) is the expression in equation (3):

[0034]

[0035] Where: ΔP W0 To increase the frequency modulation power output of the wind turbine at time t0;

[0036] 7) The system enters the energy storage frequency regulation response zone.

[0037] If the system frequency deviation exceeds the energy storage frequency regulation dead zone, the energy storage frequency regulation control system is activated. The energy storage increases its frequency regulation output based on its current state of charge (SOC). The frequency regulation power of the energy storage output is calculated as follows:

[0038] a. Determine the current operating status and SOC of the energy storage, and analyze the potential of the energy storage to release / absorb energy during frequency regulation;

[0039] b. Calculate the frequency modulation power output of the energy storage.

[0040] Considering that the ESS cycle life is closely related to the depth of charge and discharge, the number of cycles, and the operating temperature, during the frequency regulation phase, if the energy storage device is forced to output power when the energy storage SOC value is low, it will cause irreversible damage to the life of the energy storage system. Therefore, a coupling relationship between the energy storage frequency regulation output power and the energy storage SOC is established, and its calculation expression is as follows:

[0041]

[0042] Where: ΔP BC (t) and ΔP BD (t) represents the increased power generation of the energy storage system at high and low frequencies, respectively; k B SOC is a proportional coefficient used to adjust the frequency regulation performance of energy storage; SOC0 is the initial SOC value of the energy storage device; SOC min SOC ma x represents the minimum and maximum SOC of the energy storage device, respectively;

[0043] 8) Has the energy storage detection frequency deviation returned to the wind turbine frequency regulation range?

[0044] If the frequency deviation is detected to return to the fan frequency regulation range, proceed to step 4); otherwise, continue to step 7.

[0045] 9) The power grid frequency has stabilized.

[0046] Through steps 1)-8), the output frequency regulation power of the wind turbine and energy storage is determined, and after the wind-storage joint frequency regulation is started, the calculated results of the frequency regulation power of the wind turbine and energy storage are applied to the active power command values ​​of the wind turbine and energy storage to restore the system frequency to stability.

[0047] The wind-storage combined frequency regulation method proposed in this invention, which takes into account the frequency regulation dead zone, has the following technical advantages compared with the prior art:

[0048] (1) The method of this invention is different from the existing wind and energy storage joint frequency regulation. It proposes a time-sequence frequency regulation control technology scheme of wind turbine first and energy storage later. By reasonably setting the frequency regulation dead zone of wind turbine and energy storage system, it can effectively avoid the stall phenomenon caused by excessive frequency regulation of wind turbine, reduce the number of charging and discharging of energy storage system, improve the cycle efficiency of energy storage system, and reduce maintenance costs.

[0049] (2) The method of the present invention divides the frequency response of the power grid after disturbance into four stages according to the number of frequency changes: namely, no response zone, wind turbine response zone, wind-storage transition zone, and energy storage response zone. The method is designed according to each frequency regulation process. For the wind turbine response zone, the DFIG frequency regulation coefficient is coupled with the effective rotational kinetic energy of its rotor, so that the wind turbine can make full use of its own rotational kinetic energy while ensuring its own stability, thereby suppressing the frequency fluctuation of the system. For the wind-storage transition zone, the mechanical fatigue of the wind turbine rotor is alleviated by making the wind turbine smoothly exit the frequency regulation, which effectively reduces the power deficit of the system and avoids the possibility of a second frequency drop in the system. For the energy storage response zone, the SOC of the energy storage system is coupled with the frequency regulation output power, which effectively avoids the overcharging or over-discharging of the energy storage system and extends the service life of the energy storage system.

[0050] (3) The method of the present invention uses a linear function to construct the frequency regulation parameters of the wind energy storage system. First, it is simple to construct and easy to implement in hardware. Second, in the face of different engineering needs, the frequency regulation increment can be achieved by adjusting the control parameters, which provides technical support for the engineering application of the energy storage system in the later stage.

[0051] (4) The method of the present invention is scientific, reasonable, highly applicable and effective. Attached Figure Description

[0052] Figure 1 This is a principle block diagram of the wind storage model according to a specific embodiment of the present invention;

[0053] Figure 2 This is a flowchart illustrating the steps of the wind-storage system response in an embodiment of the present invention;

[0054] Figure 3 yes Figure 1 The simulation system model;

[0055] Figure 4 yes Figure 1 The random wind speed image curve;

[0056] Figure 5(a) is a grid frequency curve of Embodiment 1 of the present invention when the wind power penetration rate is 24% and the active power loss is 50MW.

[0057] Figure 5(b) is a wind power frequency regulation output curve of Embodiment 1 of the present invention when the wind power penetration rate is 24% and the active power loss is 50MW.

[0058] Figure 5(c) is a wind turbine speed curve of Embodiment 1 of the present invention when the wind power penetration rate is 24% and the active power loss is 50MW;

[0059] Figure 5(d) is a curve of the wind turbine torque angle in Embodiment 1 of the present invention when the wind power penetration rate is 24% and the active power loss is 50MW.

[0060] Figure 5(e) is a graph showing the change of energy storage SOC in Embodiment 1 of the present invention when the wind power penetration rate is 24% and the active power loss is 50MW.

[0061] Figure 6(a) is a power grid frequency curve of Embodiment 2 of the present invention when the wind power penetration rate is 24% and the active power loss is 80MW;

[0062] Figure 6(b) is a wind power frequency regulation output curve of Embodiment 2 of the present invention when the wind power penetration rate is 24% and the active power loss is 80MW;

[0063] Figure 6(c) is a wind turbine speed curve of Embodiment 2 of the present invention when the wind power penetration rate is 24% and the active power loss is 80MW;

[0064] Figure 6(d) is a curve of the wind turbine torque angle in Embodiment 2 of the present invention when the wind power penetration rate is 24% and the active power loss is 80MW;

[0065] Figure 6(e) is a graph showing the change of energy storage SOC in Embodiment 2 of the present invention when the wind power penetration rate is 24% and the active power loss is 80MW;

[0066] Figure 7(a) is a grid frequency curve of Embodiment 3 of the present invention when the wind power penetration rate is 40% and the active power loss is 80MW.

[0067] Figure 7(b) is a wind-storage frequency regulation output curve of Embodiment 3 of the present invention when the wind power penetration rate is 40% and the active power loss is 80MW.

[0068] Figure 7(c) is a wind turbine speed curve of Embodiment 3 of the present invention when the wind power penetration rate is 40% and the active power loss is 80MW;

[0069] Figure 7(d) is a curve of the wind turbine torque angle in Embodiment 3 of the present invention when the wind power penetration rate is 40% and the active power loss is 80MW.

[0070] Figure 7(e) is a graph showing the change of energy storage SOC in Embodiment 3 of the present invention when the wind power penetration rate is 40% and the active power loss is 80MW. Detailed Implementation

[0071] The following is combined with Figure 1 The present invention will be further described in detail with reference to specific embodiments.

[0072] This embodiment provides a wind-storage model. In one specific embodiment, the wind turbine model is a simplified model of a doubly-fed induction generator (DFIG) wind turbine. The overall principle block diagram of this invention is as follows: Figure 1 As shown, Figure 1 Middle,U ra U rb U rc and U ga U gb U gcThese represent the A, B, and C phase voltages on the rotor and stator sides of a doubly-fed induction generator (DFIG), respectively; a detailed flowchart is shown below. Figure 2 As shown, it specifically includes:

[0073] 1) Set the frequency regulation dead zone for the wind turbine and energy storage system

[0074] Referring to the concept of dead zone setting for synchronous generator sets—synchronous generator sets use small frequency regulation dead zones to participate in primary frequency regulation, while those using large frequency regulation dead zones only respond to large disturbances in grid frequency changes—the frequency regulation dead zones for wind turbines are set smaller than those for energy storage, namely [0,0.01] and [0,0.2], respectively.

[0075] 2) Fluctuations in power grid frequency

[0076] The system detected fluctuations in the power grid frequency;

[0077] 3) Check if the fan's frequency deviation exceeds the fan's frequency adjustment dead zone.

[0078] If the frequency deviation detected by the fan exceeds the frequency dead zone of the fan, proceed to step 4); otherwise, proceed to step 9.

[0079] 4) The system enters the fan frequency regulation response zone.

[0080] The system frequency deviation exceeds the wind turbine's frequency regulation dead zone but not the energy storage's frequency regulation dead zone. Based on the detected grid frequency, the system frequency deviation Δf is calculated, and its absolute value is taken. The specific calculation method for the wind turbine's output frequency regulation power is as follows:

[0081] (1) Collect the current rotor speed of the fan and analyze the rotational kinetic energy capacity stored in the fan rotor based on the current operating status of the fan.

[0082] (2) Calculate the fan frequency regulation coefficient:

[0083] To ensure the wind turbine can fully utilize its frequency regulation potential while maintaining its own stability, a coupling relationship is established between the DFIG frequency regulation coefficient and its effective rotational kinetic energy of the rotor, and its expression is as follows:

[0084]

[0085] In the formula: K WC K WD These are the frequency modulation coefficients for the fan in the high-frequency and low-frequency stages, respectively; ω r ω is the DFIG rotational speed; min ω max α represents the minimum and maximum rotational speeds of the DFIG, respectively; α is the grid frequency performance adjustment factor.

[0086] (3) Calculate the frequency modulation power output of the fan:

[0087] To avoid noise caused by frequency differentiation, this invention uses droop control. The grid frequency deviation is proportional to the output frequency modulation power, as expressed below:

[0088]

[0089] Where: ΔP WC (t), ΔP WD (t) represents the additional power generated by the wind turbine in the high-frequency and low-frequency stages, respectively; Δf represents the system frequency deviation;

[0090] 5) Whether the frequency deviation of the energy storage exceeds its frequency tuning dead zone.

[0091] If the energy storage detects a frequency deviation exceeding its own frequency modulation dead zone, proceed to step 6); otherwise, proceed to step 3.

[0092] 6) The system enters the wind-storage transition zone.

[0093] The system frequency deviation reaches the dead zone boundary of energy storage frequency regulation. Considering the switching phase between wind turbine and energy storage frequency regulation, the wind turbine exits frequency regulation, causing a sudden change in frequency regulation active power. This leads to mechanical fatigue problems at the wind turbine level and increases the system's power deficit at the system level, resulting in mechanical fatigue and frequency drop. Therefore, we assume that the wind turbine smoothly reduces the frequency regulation power, and the calculation is as follows:

[0094] i. Record the time t0 when the system frequency reaches the energy storage dead zone boundary;

[0095] ii. Determine and enter the duration Δt for the fan to exit frequency regulation;

[0096] iii. Calculate the frequency modulation boost power ΔP output when the fan is out of frequency modulation mode. W (t) is the expression in equation (3):

[0097]

[0098] Where: ΔP W0 To increase the frequency modulation power output of the wind turbine at time t0;

[0099] 7) The system enters the energy storage frequency regulation response zone.

[0100] If the system frequency deviation exceeds the energy storage frequency regulation dead zone, the energy storage frequency regulation control system is activated. The energy storage increases its frequency regulation output based on its current state of charge (SOC). The frequency regulation power of the energy storage output is calculated as follows:

[0101] a. Determine the current operating status and SOC of the energy storage, and analyze the potential of the energy storage to release / absorb energy during frequency regulation;

[0102] b. Calculate the frequency modulation power output of the energy storage.

[0103] Considering that the ESS cycle life is closely related to the depth of charge and discharge, the number of cycles, and the operating temperature, during the frequency regulation phase, if the energy storage device is forced to output power when the energy storage SOC value is low, it will cause irreversible damage to the life of the energy storage system. Therefore, a coupling relationship between the energy storage frequency regulation output power and the energy storage SOC is established, and its calculation expression is as follows:

[0104]

[0105] Where: ΔP BC (t) and ΔP BD (t) represents the increased power generation of the energy storage system at high and low frequencies, respectively; k B SOC is a proportional coefficient used to adjust the frequency regulation performance of energy storage; SOC0 is the initial SOC value of the energy storage device; SOC min SOC ma x represents the minimum and maximum SOC of the energy storage device, respectively;

[0106] 8) Has the energy storage detection frequency deviation returned to the wind turbine frequency regulation range?

[0107] If the frequency deviation is detected to return to the fan frequency regulation range, proceed to step 4); otherwise, continue to step 7.

[0108] 9) The power grid frequency has stabilized.

[0109] Through steps 1)-8), the output frequency regulation power of the wind turbine and energy storage is determined, and after the wind-storage joint frequency regulation is started, the calculated results of the frequency regulation power of the wind turbine and energy storage are applied to the active power command values ​​of the wind turbine and energy storage to restore the system frequency to stability.

[0110] The technical effects of this invention will be explained in detail below with reference to simulation examples.

[0111] This invention utilizes the EMTP-RV simulation platform to build an IEEE 14-node simulation system with varying wind power penetration rates for verification. The simulation system includes a DFIG aggregated wind farm with a storage capacity of 40MW / 6MW·h, five synchronous generator units, and a static load of 600MW. Figure 3 As shown.

[0112] To mitigate the reduced lifespan and mechanical fatigue issues caused by frequent frequency adjustments in the wind-storage system, referencing the synchronous machine's frequency dead-time setting, the dead-times for the wind turbine and ESS are set to 0.01Hz < Δf < 0.2Hz and Δf > 0.2Hz, respectively. α is set to 46.6, Δt to 5 seconds, and k... B Set it to 300.

[0113] Considering actual operation, wind speed fluctuations are the main disturbance factor causing frequency fluctuations. Therefore, varying wind speeds are incorporated throughout the simulation, as shown in the wind speed graph. Figure 4 As shown, the synchronous SG2 was disconnected as a high-power disturbance excitation during the simulation process for 130 seconds. The effectiveness of the proposed method was verified under wind turbine-only, energy storage-only, and wind-storage frequency regulation methods, respectively. The specific example settings are shown in Table 1 and Table 2, respectively.

[0114] Table 1 Example Settings

[0115]

[0116] Table 2 Frequency modulation method settings

[0117]

[0118] Example 1: Wind power penetration rate 24%, active power loss 50MW

[0119] Figure 5 shows that, during the period from 60s to 130s, affected by wind speed changes, the maximum positive and negative frequency deviations of the non-frequency control method are 0.21Hz and 0.19Hz, respectively; at 130s, affected by the synchro going offline, the grid frequency drops to a minimum of 59.40Hz.

[0120] During periods of wind speed variation alone, Method 2 effectively suppressed frequency fluctuations, with the maximum positive and negative frequency deviations reduced to 0.15Hz and 0.15Hz, respectively. This was mainly because the wind turbine participated in frequency regulation by absorbing and discharging kinetic energy through its rotor. After the synchronous machine went offline, the lowest frequency point increased to 59.54Hz. This was because the wind turbine increased the depth of its kinetic energy utilization, with the maximum frequency regulation power reaching 24.62MW. This resulted in an increase in the torque angle of the transmission system to 0.44°, increasing mechanical stress. At the same time, the lowest rotational speed reached 0.79 pu, posing a risk of wind turbine stall.

[0121] In scenarios involving only wind speed variations and synchronous generator shutdown, Method 3 achieves almost the same frequency regulation performance as Method 2 through the charging and discharging of energy storage. However, when frequency fluctuations are small due to wind speed variations, the ESS participates in frequency regulation through six shallow charges and discharges. The long-term accumulation of frequent charging and discharging will inevitably reduce the service life of the energy storage device.

[0122] When using Method 4 for the wind-storage system, when only wind speed changes, the frequency does not exceed the energy storage frequency regulation dead zone under wind turbine frequency regulation, which avoids frequent participation of energy storage in frequency regulation and is beneficial to its cycle life. After the synchronous machine goes offline, the frequency drops out of the energy storage frequency regulation dead zone. By establishing a wind-storage transition zone, the wind turbine smoothly exits frequency regulation and returns to MPPT operation mode. In addition, the lowest grid frequency point is 0.02Hz higher than that of Method 3. This is because wind and energy storage participate in frequency regulation simultaneously for a short period of time, and the maximum frequency regulation power is 6.41MW higher than that of Method 3. Subsequently, the ESS (Energy Storage System) undertakes the frequency regulation task alone, maintaining the excellent frequency regulation characteristics of Method 3, while avoiding the risk of wind turbine stall due to excessively low speed. Although the energy storage SOC of Method 4 is 0.12% lower than that of Method 3, the impact on the ESS is not significant.

[0123] If the wind storage system participates in frequency regulation when wind speed changes, it can effectively smooth out frequency fluctuations. However, the frequent charging and discharging of energy storage seriously affects its operational lifespan.

[0124] Example 2: Wind power penetration rate 24%, active power loss 80MW

[0125] Within the wind speed variation range, wind-storage frequency regulation systems using methods 2, 3, and 4 achieve similar frequency regulation effects. However, the frequent charging and discharging of the energy storage system in method 3 is detrimental to its service life.

[0126] During the offline range of the synchronous generator unit, the lowest frequency points for methods 2, 3, and 4 are 59.30, 59.35, and 59.36 Hz, respectively. Compared to Example 1, methods 2, 3, and 4 increase the maximum frequency regulation output by 9.4, 9.97, and 12.36 MW, respectively, thus improving the frequency regulation effect to varying degrees, as shown in Figure 6. Method 2 is more susceptible to disturbances, releasing more rotor kinetic energy to participate in frequency regulation, causing the lowest speed to reach 0.77 pu, increasing the risk of turbine stall. Method 4 maintains the excellent frequency regulation capability of Example 1.

[0127] Example 3: Wind power penetration rate 40%, active power loss 80MW

[0128] As wind power penetration increases, system inertia and frequency regulation decrease. Although each method maintains frequency regulation capability under low penetration, the problems of wind turbine stall risk in Method 2 and reduced energy storage life in Method 3 have not been improved. However, Method 4 can still achieve complementary advantages through wind-storage system timing control and maintain excellent frequency regulation capability, as shown in Figure 7.

[0129] The simulation results show that the method of this invention can effectively utilize the frequency regulation characteristics of wind turbines and energy storage. From the perspective of the wind turbines and energy storage themselves, it avoids the stall phenomenon caused by excessive release of the wind turbine's rotor kinetic energy, while reducing the number of charge-discharge cycles of the energy storage system and improving its cycle efficiency. From the perspective of the power system, it improves the stability of the system frequency under the background of high wind power grid connection. This proves the feasibility and effectiveness of the wind-storage joint frequency regulation method that takes into account the frequency regulation dead zone described in this invention.

[0130] The specific embodiments of the present invention are not exhaustive. Any reproduction and improvement by those skilled in the art without creative effort based on the teachings of the present invention are within the scope of protection of the present invention.

Claims

1. A wind-storage combined frequency regulation control method considering frequency regulation dead zone, characterized in that, The method Includes the following: 1) Set the frequency regulation dead zone for the wind turbine and energy storage system; The frequency regulation dead zone of the wind turbine is set to be smaller than that of the energy storage frequency regulation dead zone, which are [0,0.01] and [0,0.2] respectively; 2) Fluctuations in power grid frequency; The system detected fluctuations in the power grid frequency; 3) Check if the frequency deviation of the fan exceeds the frequency dead zone of the fan; If the fan detection frequency deviation exceeds the fan frequency adjustment dead zone, proceed to step 4); otherwise, proceed to step 9). 4) The system enters the fan frequency regulation response zone; The system frequency deviation exceeds the wind turbine frequency regulation dead zone but does not exceed the energy storage frequency regulation dead zone. Based on the detected grid frequency, the system frequency deviation ∆ is calculated. f The absolute value of the calculated frequency modulation power output of the fan is as follows: 4.1 Collect the current rotor speed of the fan and analyze the rotational kinetic energy capacity stored in the fan rotor based on the current operating status of the fan; 4.2 Calculate the fan frequency regulation coefficient: To ensure the wind turbine can fully utilize its frequency regulation potential while maintaining its own stability, a coupling relationship is established between the DFIG frequency regulation coefficient and its effective rotational kinetic energy of the rotor, and its expression is as follows: （1） In the formula: K WC , K WD These are the frequency modulation coefficients of the fan in the high-frequency and low-frequency stages, respectively; ω r For DFIG rotational speed; ω min , ω max These are the minimum and maximum speeds of the DFIG, respectively; α This is a power grid frequency performance adjustment factor. 4.3 Calculate the frequency modulation power output of the fan: To avoid noise caused by frequency differentiation, droop control is used. The grid frequency deviation is proportional to the output frequency modulation power, and its expression is as follows: （2） In the formula: Δ P WC ( t ), Δ P WD ( t ) represent the increased power output of the wind turbine in the high-frequency and low-frequency phases, respectively; ∆ f This refers to the system frequency deviation. 5) Whether the frequency deviation of the energy storage detection exceeds its frequency tuning dead zone; If the energy storage detects a frequency deviation exceeding its own frequency modulation dead zone, proceed to step 6); otherwise, proceed to step 3). 6) The system enters the wind-storage transition zone; The system frequency deviation reaches the dead zone boundary of energy storage frequency regulation. Considering the switching phase between wind turbine and energy storage frequency regulation, the wind turbine exits frequency regulation, causing a sudden change in frequency regulation active power. This leads to mechanical fatigue problems at the wind turbine level and increases the system's power deficit at the system level, resulting in mechanical fatigue and frequency drop. Therefore, we assume that the wind turbine smoothly reduces the frequency regulation power, and the calculation is as follows: 6.1 Record the moment when the system frequency reaches the energy storage dead zone boundary. t 0 ; 6.2 Determine and input the duration Δ for the fan to exit frequency regulation. t ; 6.3 Calculate the frequency modulation boost power Δ when the fan is out of frequency modulation mode. P W ( t Equation (3) is given by: （3） In the formula: Δ P W0 For the wind turbine t Output frequency modulation power at time 0; 7) The system enters the energy storage frequency regulation response zone; If the system frequency deviation exceeds the energy storage frequency regulation dead zone, the energy storage frequency regulation control system is activated. The energy storage increases its frequency regulation output based on its current state of charge (SOC). The frequency regulation power of the energy storage output is calculated as follows: 7.1 Determine the current operating status and SOC of the energy storage, and analyze the potential of the energy storage to release / absorb energy during frequency regulation; 7.2 Calculate the frequency modulation power output of the energy storage; The coupling relationship between the frequency regulation output power of energy storage and the state of energy storage (SOC) is established, and its calculation expression is as follows: （4） In the formula: Δ P BC ( t ) and Δ P BD ( t These represent the increased power generation of the energy storage system at high and low frequencies, respectively. k B SOC is a proportional coefficient used to adjust the frequency regulation performance of energy storage; SOC0 is the initial SOC value of the energy storage device; SOC min SOC ma x represents the minimum and maximum SOC of the energy storage device, respectively; 8) Whether the energy storage detection frequency deviation has returned to the fan frequency regulation range; If the frequency deviation is detected to have returned to the fan frequency regulation range, proceed to step 4); otherwise, continue to step 7). 9) The power grid frequency has stabilized; By determining the output frequency regulation power of the wind turbine and energy storage through steps 1)-8), and applying the calculated frequency regulation power of the wind turbine and energy storage to the active power command values ​​of the wind turbine and energy storage after the joint frequency regulation of wind and energy storage is started, the system frequency is restored to stability.

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