A wind storage collaborative frequency support control method based on available kinetic energy of a fan and SOC state of energy storage

Abstract

The application discloses a kind of based on fan available kinetic energy and energy storage SOC state of wind storage collaborative frequency support control method, comprising: establishing direct-drive permanent magnet synchronous wind generator grid-connected model;Based on direct-drive permanent magnet synchronous wind generator grid-connected model, in direct current side and into energy storage device and carry out energy storage grid-connected DC / DC converter direct current voltage control design;Design direct-drive permanent magnet synchronous fan side converter and grid-side converter control strategy, combined with direct current side energy storage device constructs wind storage integrated system architecture;According to wind storage integrated system operating condition calculation fan rotor kinetic energy and energy storage available energy, obtain wind storage system total available kinetic energy;Based on wind storage system total available kinetic energy carries out wind storage grid-connected system side converter and grid-side converter control parameter design, proposes wind storage collaborative frequency support grid-connected strategy.The application aims at providing a kind of wind storage collaborative frequency support control method considering operating condition, can significantly improve the frequency stability of high proportion wind power system.

Description

Technical Field

[0001] This invention belongs to the field of power system control technology, specifically relating to a wind-storage coordinated frequency support control method based on the available kinetic energy of wind turbines and the SOC state of energy storage. Background Technology

[0002] With the expansion of renewable energy grid integration, grid stability has become a focal point. The fixed parameter settings of traditional virtual synchronous generator (VSG) control strategies often lead to overdamping or underdamping of the system under different operating conditions, affecting stability. Existing technologies fail to adequately adapt to dynamic changes in power system frequency, potentially reducing system stability, causing issues such as voltage fluctuations and frequency deviations, and even triggering system failures, impacting the reliable operation of the power system. When the grid frequency drops, wind turbines rely on releasing rotor kinetic energy to regulate frequency and increase active power output. However, rotor kinetic energy is limited. Initially, the unit responds to the frequency change by decreasing speed and increasing output power. Subsequently, due to insufficient rotor kinetic energy, as the speed continues to decrease, the power-speed characteristic prevents the power from maintaining the initial level. Furthermore, the decrease in speed also affects wind energy capture efficiency, leading to a further drop in power on top of the already reduced output, resulting in a secondary power drop. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the existing technology, a wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage is provided. This method optimizes the frequency support capability of the wind-storage system under different operating conditions and effectively alleviates the secondary drop problem when the wind turbine participates in frequency regulation, thereby significantly improving the frequency stability of high-proportion wind power systems.

[0004] Technical Solution: To achieve the above objectives, this invention provides a wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, comprising the following steps:

[0005] S1: Establish a grid-connected model for a direct-drive permanent magnet synchronous wind turbine;

[0006] S2: Based on the grid-connected model of a direct-drive permanent magnet synchronous wind turbine, an energy storage device is connected to the DC side and the DC voltage control design of the grid-connected DC / DC converter for energy storage is carried out.

[0007] S3: Design control strategies for the machine-side converter and grid-side converter of direct-drive permanent magnet synchronous wind turbine, and build an integrated wind and energy storage system architecture by combining DC-side energy storage devices;

[0008] S4: Calculate the kinetic energy of the wind turbine rotor and the available energy of the energy storage system based on the operating conditions of the integrated wind and energy storage system, and obtain the total available kinetic energy of the wind and energy storage system.

[0009] S5: Based on the total available kinetic energy of the wind-storage system, the control parameters of the wind-storage grid-connected system's machine-side converter and grid-side converter are designed. A wind-storage coordinated frequency support grid-connected strategy is proposed to effectively allocate the frequency regulation power source under different operating conditions, alleviate secondary drops, and improve the system's frequency support capability.

[0010] Furthermore, the establishment of the grid-connected model for the direct-drive permanent magnet synchronous wind turbine in step S1 includes:

[0011] A1: Establish a complete model of the grid-side inverter: Based on the clear topology of the grid-side inverter, establish the corresponding three-phase voltage equations of the input and output sides and the switching function of the inverter, convert them into a mathematical model in the DQ coordinate system, and then, according to the obtained equations, express the frequency and phase angle of the AC phase voltage of the grid-side inverter, and find the expressions for active power and reactive power.

[0012] A2: Establish a complete model of the generator-side converter: Based on the clear topology of the generator-side converter, establish the corresponding three-phase voltage equations for the input and output sides and the switching function of the converter, convert them into a mathematical model in the DQ coordinate system, and then, based on the obtained equations, represent the equivalent outer loop voltage value and inner loop current value, and calculate the electromagnetic torque of the permanent magnet synchronous generator.

[0013] A3: Establish a complete mathematical model for DC-side energy storage;

[0014] A4: Connect the models in steps A1 to A3 according to the structure of the synchronous generator energy supply system to form a direct-drive permanent magnet synchronous wind turbine grid-connected system model.

[0015] Furthermore, in step S1, the grid-connected model of the direct-drive permanent magnet synchronous wind turbine includes a back-to-back grid-connected converter consisting of a wind turbine, a permanent magnet synchronous generator, a machine-side converter, and a grid-side converter. The wind turbine relies on the collected wind power to drive the blades to rotate, which in turn drives the rotor of the permanent magnet synchronous motor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power point tracking mode to obtain the maximum wind energy resources. The grid-side converter adopts virtual synchronous control to realize active support for the frequency and voltage of the wind turbine.

[0016] Furthermore, by configuring energy storage devices on the DC side to assist wind power in frequency support, the design parameters of the wind-storage system's turbine-side converter and grid-side converter are guided by the available kinetic energy of the wind turbine and energy storage, thereby realizing the allocation of frequency regulation power between the wind turbine and energy storage. This fully utilizes the mechanical kinetic energy of the wind turbine rotor for rapid response to frequency disturbances, while also leveraging the large capacity of energy storage to achieve continuous frequency support over long time scales.

[0017] Furthermore, the design method for the DC voltage control of the grid-connected energy storage DC / DC converter in step S2 is as follows: Based on the establishment of a complete mathematical model of DC-side energy storage, its control principle is clarified. The energy storage device is connected to the DC side of the wind turbine through a DC / DC converter. The energy storage DC / DC converter adopts a buck / boost converter with DC bus voltage outer loop and inductor current inner loop control for the energy storage battery's DC / DC converter. When the wind turbine is running normally, the control objective of the energy storage battery is to smooth the unbalanced power between the wind turbine side and the grid side, and maintain the DC link voltage V. dc In its reference value V dc,ref nearby.

[0018] Furthermore, step S3 specifically includes:

[0019] B1: For wind power systems equipped with energy storage devices, when the energy storage devices are controlled by bus voltage, the turbine-side converter is improved. The control task of the turbine-side converter is adjusted so that it can independently respond to the power increase caused by system frequency changes. By constructing a system frequency-turbine power increase action path within the turbine-side speed control loop, the turbine rotor kinetic energy can be utilized when the system frequency is disturbed. In addition, the grid-side controller uses VSG control to achieve active frequency support for the grid.

[0020] B2: Construct an integrated wind and energy storage system and quantify its operating conditions to convert complex operating conditions into specific quantitative results, guiding the design of power allocation strategies for the wind and energy storage system. Specifically, this includes calculating the available kinetic energy of the wind and energy storage system and the energy demand for frequency regulation under grid frequency disturbances. The available kinetic energy of the wind turbine is mainly calculated based on the current speed of the wind turbine and the set lower limit of the speed. The available energy of the energy storage is calculated based on its SOC observation value.

[0021] B3: Based on the calculation results of available kinetic energy in step B2, an adaptive droop coefficient control method for the grid-side converter of the wind-storage system is designed. The design of the virtual droop coefficient of the grid-side converter VSG is guided by comparing the total available kinetic energy of the wind-storage system with the frequency regulation energy demand under grid frequency disturbances. When the available kinetic energy of the integrated wind-storage system is insufficient, the droop coefficient is reduced to decrease the frequency regulation depth of the wind-storage system and avoid secondary accidents caused by excessive frequency regulation participation. When the available kinetic energy of the integrated wind-storage system is abundant, the droop coefficient is increased, enabling the integrated wind-storage system to assume more frequency regulation responsibility in the grid.

[0022] B4: Based on the calculation results of the available kinetic energy in step B2, design an adaptive inertia coefficient control method for the turbine-side converter of the wind-storage system. Compare the available kinetic energy of the turbine and the energy storage. When the available kinetic energy of the turbine is greater than that of the energy storage, increase the inertia transfer gain of the turbine-side controller to allow the turbine to output more frequency regulation power, while the energy storage outputs less power to ensure that the energy storage operates within the safe operating SOC range. When the available kinetic energy of the energy storage is greater than that of the turbine, decrease the inertia transfer gain to allow the energy storage to output more power to smooth out the DC-side unbalanced voltage and avoid the rapid drop in speed caused by excessive participation of the turbine in frequency regulation.

[0023] Combining step S3, by designing the inertia transfer gain in the generator-side converter and the droop coefficient of the grid-side VSG control, the integrated wind and energy storage system can achieve internal power distribution and external frequency regulation tasks, avoiding secondary frequency drops while ensuring continuous frequency support for the wind and energy storage system over a long time scale.

[0024] Furthermore, step S4 specifically includes:

[0025] C1: Quantitative analysis of wind and storage operation conditions, mainly converting the operation conditions of each unit into the available energy of each frequency regulation unit. If the energy is low, it means that the unit is operating under conditions unsuitable for frequency regulation, while if the energy is high, the frequency regulation unit is operating under better frequency regulation conditions.

[0026] C2: Quantitatively calculate the available kinetic energy of the wind storage system. The available kinetic energy of the wind turbine is mainly calculated based on the rotor speed and the set lower limit of the speed. The available kinetic energy of the energy storage is calculated based on the set minimum SOC point and the current SOC state.

[0027] The formula for calculating the usable kinetic energy of a wind turbine is:

[0028]

[0029] Where, ω ro ω represents the WTG rotor speed in MPPT mode. rmin This is the lower limit of the rotor speed;

[0030] The formula for calculating the usable kinetic energy of energy storage is:

[0031] E ESB_soc =∫u o i o dt=u o Q N γ soc_0

[0032] Among them, u o For the energy storage side voltage, i o Q is the energy storage current. N For the total reactive power, γ soc_0 This is the conversion factor.

[0033] Furthermore, step S5 specifically includes:

[0034] D1: The total frequency regulation energy requirement of the system is obtained through approximate calculation based on the following assumptions:

[0035] This invention makes two assumptions to derive the approximate frequency modulation power consumption E. con First, it is assumed that during the inertial response phase, the total power increment of the wind-storage system is a linearly increasing curve. When the curve rises to the peak incremental power DP... incm (t ine_m As can be seen from the power transfer function of the generator-side converter, the incremental power peak is essentially caused by the overshoot of the second-order system. Through parameter tuning, the peak value is typically about 1.2DP. inc (t PFR_act Secondly, it is assumed that the incremental power of the wind-storage system during the primary frequency regulation phase is a linearly decreasing curve. Under this assumption, the inertial response and energy consumption during the primary frequency regulation process are assumed to be the sum of the area of ​​the first-stage shaded trapezoid and the area of ​​the second-stage shaded rectangle.

[0036]

[0037] D2: Value determination stage, t PFR_act The value is usually defined empirically as approximately 5 seconds, t ine_m The value of t can be calculated by solving the transfer function. Furthermore, t full By using DP C This is estimated by dividing by the ramp rate of the frequency-regulated generator set, which depends on the unit type and is typically about 1.5% of the capacity of a thermal power generator set. Furthermore, to obtain the maximum energy consumption supported by the frequency, DP... C The value is usually defined as the active power imbalance caused by the most severe unexpected event that can be expected in the power system;

[0038] D3: A wind-storage coordinated grid-connected control architecture with DC-side energy storage batteries was proposed. Based on this architecture, a frequency support coordinated control scheme for the WTG-ESB system was designed: the inertia transfer gain K of the generator-side converter. c K affects the power distribution between wind turbines and energy storage batteries. c The magnitudes of parameters J and J reflect the ratio of the rotational kinetic energy of the wind turbine to the frequency regulation energy of the energy storage battery. Therefore, this invention constructs K... c The relationship between parameters and the available kinetic energy of wind storage depends on the current rotor motion state of the wind turbine and the state of charge (SOC) of the energy storage. The specific calculation formula is as follows:

[0039]

[0040] Among them, E wt_avaE is the available energy for the wind turbine. SB_ava For storing usable energy, λ W-E To enable the wind turbine to participate in the inertial response as much as possible and fully leverage the advantage of the wind turbine rotor's rapid kinetic energy response, a scaling factor needs to be set between the available energy of the wind turbine and the energy storage.

[0041] In the design of the droop control loop, the droop control coefficient reflects the static adjustment capability of the virtual speed governor to frequency deviation, affecting the frequency regulation depth and the active power output of the VSG to the grid. To ensure that the wind turbine and energy storage operate within a reasonable range during frequency support while also considering primary frequency regulation capability, this invention proposes an adaptive droop coefficient K based on the Logistic function. p The droop coefficient can be adjusted in the form of an S-curve based on the total available kinetic energy of the wind-storage system. In the initial stage, the droop coefficient of the Logistic function grows at an approximately exponential rate. As the available kinetic energy gradually saturates, the growth rate of the coefficient slows down, ensuring both smooth power output and the rapid response characteristics of wind-storage systems. The specific formula for calculating the droop coefficient is as follows:

[0042]

[0043] Among them, the droop coefficient K is divided into frequency rise droop coefficient K according to the charging and discharging state. P_dn and frequency decrease coefficient K p_up Maximum adjustment of droop coefficient K max The value is 20. To ensure the safe operation of the wind-storage system, this invention divides the available kinetic energy of the wind-storage system under the current operating conditions into four intervals E. total (E total_min E total_max E total_low E total_high The system adjusts the value of p0 and n within the corresponding range to prevent the wind-storage system from triggering speed protection and causing a secondary drop in system frequency when the available kinetic energy is too low. p0 and n are adaptation factors that determine the shape of the curve.

[0044] This invention addresses the risk of secondary frequency drops in existing wind turbine grid-connected control systems due to insufficient rotor kinetic energy. It proposes a wind power grid-connected architecture with DC-side energy storage and designs a wind-storage grid-connected control scheme within this architecture. This approach balances the rapid inertial response capability of the wind turbine rotor kinetic energy with the continuous primary frequency regulation output capability of the large-capacity energy storage battery. By designing the optimal SOC state of the energy storage and calculating the available kinetic energy of each frequency regulation unit in the wind-storage system based on the lower limit of the wind turbine rotor speed, this invention optimizes the system's frequency support capability under different operating conditions and effectively mitigates the secondary frequency drop problem when the wind turbine participates in frequency regulation.

[0045] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0046] 1. Energy storage shares the frequency regulation output of direct-drive wind turbines by detecting bus voltage fluctuations. Independent control of wind turbine and grid-side VSG frequency regulation is achieved by adding an inertia transfer unit to the wind turbine-side converter. Compared with unified control, the method of this invention makes the power system more resilient to complex changes and improves its adaptability to dynamic events in the power grid.

[0047] 2. The adaptive control strategy optimizes frequency response and stability by adjusting the system inertia distribution and energy storage droop control coefficient in real time, thereby enabling the power grid to better absorb and utilize renewable energy. As the proportion of renewable energy connected to the grid continues to increase, the problem of grid frequency fluctuations is becoming increasingly serious. Applying the adaptive control method of this invention can quickly adjust the parameters of the virtual synchronous generator to maintain grid frequency stability when renewable energy output is unstable. Attached Figure Description

[0048] Figure 1 This is a flowchart of the present invention;

[0049] Figure 2 This is a diagram of the grid-side converter control structure of the present invention;

[0050] Figure 3 This is a diagram of the machine-side converter control structure of the present invention;

[0051] Figure 4 This is a grid-connected structure diagram of the energy storage battery system of the present invention;

[0052] Figure 5 This is a diagram of the energy storage collaborative control structure of the present invention;

[0053] Figure 6 This is a control structure diagram of the inertia transfer link of the present invention;

[0054] Figure 7 This is a structural diagram of the wind-storage collaborative control model of the present invention;

[0055] Figure 8 This is a graph showing the two-stage frequency modulation incremental power curves corresponding to the two assumptions.

[0056] Figure 9 This is a frequency response curve of a high-wind-speed, high-energy-storage SOC operating system.

[0057] Figure 10 This is a frequency response curve of a system operating under low wind speed and high energy storage SOC conditions.

[0058] Figure 11 This is a frequency response curve of a system operating under high wind speed and low energy storage SOC conditions.

[0059] Figure 12This is a frequency response curve of a system operating under low wind speed and low energy storage SOC conditions. Detailed Implementation

[0060] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0061] like Figure 1 and Figure 7 As shown, this invention provides a wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, comprising the following steps:

[0062] S1: Establish a grid-connected model for a direct-drive permanent magnet synchronous wind turbine, specifically including:

[0063] A1: Establish a complete model of the grid-side inverter: Based on a clear understanding of the grid-side inverter topology, establish the corresponding three-phase voltage equations for the input and output sides:

[0064]

[0065] In the formula S ga S gb S gc The switching function for the inverter is expressed as follows:

[0066]

[0067] The mathematical model of the inverter voltage equation in the dq0 coordinate system can be obtained using the Park transformation, as follows:

[0068]

[0069] In the formula: u gd u gq For the inverter voltage d and q components; i gd i gq ω represents the d-axis and q-axis components of the three-phase current. g The angular velocity of the power grid rotation is expressed in rad / s.

[0070] Based on the above equations, the frequency and phase angle of the AC phase voltage of the grid-side inverter are expressed, and the expressions for active power and reactive power are derived. In this embodiment, the grid-side inverter topology is as follows: Figure 2 As shown;

[0071] A2: Establish a complete model of the machine-side converter: Based on a clear understanding of the topology of the machine-side converter, establish the corresponding three-phase voltage equations for the input and output sides:

[0072]

[0073] Direct-drive permanent magnet synchronous wind turbine side rectifier bridge arm switching function S a S b S c The expression is as follows:

[0074]

[0075] Using the Park transformation, the mathematical model expression for the voltage equation of the direct-drive wind turbine's machine-side rectifier in the dq0 coordinate system can be obtained as follows:

[0076]

[0077] Based on the above equations, the equivalent outer loop voltage and inner loop current values ​​are expressed, and the electromagnetic torque of the permanent magnet synchronous generator is calculated. In this embodiment, the generator-side converter topology is as follows: Figure 3 As shown;

[0078] A3: Establish a complete mathematical model for DC-side energy storage: Clarify its control principle. The energy storage device is connected to the DC side of the wind turbine through a DC / DC converter. The energy storage DC / DC converter adopts a buck / boost converter with DC bus voltage outer loop and inductor current inner loop control for the energy storage battery's DC / DC converter. When the wind turbine is running normally, the control objective of the energy storage battery is to smooth the unbalanced power between the wind turbine side and the grid side, and maintain the DC link voltage V. dc In its reference value V dc,ref Nearby; in this embodiment, the energy storage grid-connected model topology is as follows: Figure 4 As shown;

[0079] A4: Connect the models in steps A1 to A3 according to the structure of the synchronous generator energy supply system to form a direct-drive permanent magnet synchronous wind turbine grid-connected system model.

[0080] The grid-connected model of a direct-drive permanent magnet synchronous wind turbine generator includes a back-to-back grid-connected converter consisting of a wind turbine, a permanent magnet synchronous generator, a machine-side converter, and a grid-side converter. The wind turbine generator relies on the collected wind power to drive the blades to rotate, which in turn drives the rotor of the permanent magnet synchronous motor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power point tracking mode to obtain the maximum wind energy resources. The grid-side converter adopts virtual synchronous control to realize active support for the frequency and voltage of the wind turbine generator.

[0081] By configuring energy storage devices on the DC side to assist wind power in frequency support, and using the available kinetic energy of the wind turbine and energy storage to guide the design of the turbine-side converter and grid-side converter parameters of the wind-storage system, the frequency regulation power of the wind turbine and energy storage can be allocated. This fully utilizes the mechanical kinetic energy of the wind turbine rotor for rapid response to frequency disturbances, and leverages the large capacity of energy storage to achieve continuous frequency support over a long period of time.

[0082] S2: Construct a grid-connected model of a DC-side energy storage device and design the DC voltage control of the grid-connected DC / DC converter for energy storage.

[0083] S3: Design control strategies for the machine-side converter and grid-side converter of a direct-drive permanent magnet synchronous wind turbine, and construct an integrated wind and energy storage system architecture by combining it with a DC-side energy storage device. Specifically, this includes:

[0084] B1: For wind power systems equipped with energy storage devices, when the energy storage devices are controlled by bus voltage, the turbine-side converter is improved. The control task of the turbine-side converter is adjusted so that it can independently respond to the power increase caused by system frequency changes. By constructing a system frequency-turbine power increase action path within the turbine-side speed control loop, the turbine rotor kinetic energy can be utilized when the system frequency is disturbed. In addition, the grid-side controller uses VSG control to achieve active frequency support for the grid.

[0085] B2: Construct an integrated wind and energy storage system and quantify its operating conditions. This involves converting complex operating conditions into concrete quantitative results to guide the design of power allocation strategies for the wind and energy storage system. Specifically, this includes calculating the available kinetic energy of the wind and energy storage system and the energy demand for frequency regulation under grid frequency disturbances. The available kinetic energy of the wind turbine is mainly calculated based on the current turbine speed and the set lower speed limit, while the available energy of the energy storage is calculated based on its observed SOC value.

[0086] B3: Based on the calculation results of available kinetic energy in step B2, an adaptive droop coefficient control method for the grid-side converter of the wind-storage system is designed. The design of the virtual droop coefficient of the grid-side converter VSG is guided by comparing the total available kinetic energy of the wind-storage system with the frequency regulation energy demand under grid frequency disturbances. When the available kinetic energy of the integrated wind-storage system is insufficient, the droop coefficient is reduced to decrease the frequency regulation depth of the wind-storage system and avoid secondary accidents caused by excessive participation in frequency regulation. When the available kinetic energy of the integrated wind-storage system is abundant, the droop coefficient is increased, allowing the integrated wind-storage system to assume more frequency regulation responsibility in the grid. In this embodiment, the energy storage collaborative control structure is as follows: Figure 5 As shown;

[0087] B4: Based on the calculation results of available kinetic energy in step B2, an adaptive inertia coefficient control method for the wind-storage system's turbine-side converter is designed. Comparing the available kinetic energy of the wind turbine and the energy storage, when the available kinetic energy of the wind turbine is greater than that of the energy storage, the inertia transfer gain of the turbine-side controller is increased to allow the wind turbine to output more frequency regulation power, while the energy storage outputs less power to ensure that the energy storage operates within the safe operating SOC range. When the available kinetic energy of the energy storage is greater than that of the wind turbine, the inertia transfer gain is decreased to allow the energy storage to output more power to smooth out the DC-side unbalanced voltage and prevent the wind turbine from excessively participating in frequency regulation, thus avoiding a rapid drop in speed. Combined with step S3, through the design of the inertia transfer gain in the turbine-side converter and the design of the grid-side VSG control droop coefficient, the integrated wind-storage system achieves internal power distribution and external frequency regulation tasks, avoiding secondary frequency drops while ensuring continuous frequency support over long time scales. The control structure of the inertia transfer link in this embodiment is as follows: Figure 6 As shown;

[0088] S4: Calculate the kinetic energy of the wind turbine rotor and the available energy storage based on the operating conditions of the integrated wind and energy storage system, specifically including:

[0089] C1: Quantitative analysis of wind and storage operation conditions, mainly converting the operation conditions of each unit into the available energy of each frequency regulation unit. If the energy is low, it means that the unit is operating under conditions unsuitable for frequency regulation, while if the energy is high, the frequency regulation unit is operating under better frequency regulation conditions.

[0090] C2: Quantitative calculation of available kinetic energy for wind storage system. Wind turbine is mainly calculated based on rotor speed and set lower speed limit. Energy storage is calculated based on set minimum SOC point and current SOC state.

[0091] The formula for calculating the usable kinetic energy of a wind turbine is:

[0092]

[0093] Where, ω ro ω represents the WTG rotor speed in MPPT mode. rmin This is the lower limit of the rotor speed;

[0094] The formula for calculating the usable kinetic energy of energy storage is:

[0095] E ESB_soc =∫u o i o dt=u o Q N γ soc_0

[0096] Among them, u o For the energy storage side voltage, i o Q is the energy storage current. N For the total reactive power, γ soc_0This is the conversion factor.

[0097] S5: Based on the available kinetic energy of each frequency regulation unit obtained from the operating condition calculation of the integrated wind and energy storage system, the control parameters of the turbine-side converter and grid-side converter of the wind and energy storage grid-connected system are designed, and a wind and energy storage coordinated frequency support grid connection strategy is proposed, specifically including:

[0098] D1: The total frequency regulation energy requirement of the system is obtained through approximate calculation based on the following assumptions:

[0099] This invention makes two assumptions to derive the approximate frequency modulation power consumption E. con ,like Figure 8 As shown, it is first assumed that the total power increment of the wind-storage system during the inertial response phase is a linearly increasing curve. When the curve rises to the peak incremental power DP... incm (t ine_m As can be seen from the power transfer function of the generator-side converter, the incremental power peak is essentially caused by the overshoot of the second-order system. Through parameter tuning, the peak value is typically about 1.2DP. inc (t PFR_act Secondly, it is assumed that the incremental power of the wind-storage system during the primary frequency regulation phase is a linearly decreasing curve. Under this assumption, the inertial response and energy consumption during the primary frequency regulation process are assumed to be the sum of the area of ​​the first-stage shaded trapezoid and the area of ​​the second-stage shaded rectangle.

[0100]

[0101] D2: Value determination stage, t PFR_act The value is usually defined empirically as approximately 5 seconds, t ine_m The value of t can be calculated by solving the transfer function. Furthermore, t full By using DP C This is estimated by dividing by the ramp rate of the frequency-regulated generator set, which depends on the unit type and is typically about 1.5% of the capacity of a thermal power generator set. Furthermore, to obtain the maximum energy consumption supported by the frequency, DP... C The value is usually defined as the active power imbalance caused by the most severe unexpected event that can be expected in the power system;

[0102] D3: A wind-storage coordinated grid-connected control architecture with DC-side energy storage batteries was proposed. Based on this architecture, a frequency support coordinated control scheme for the WTG-ESB system was designed: the inertia transfer gain K of the generator-side converter. c K affects the power distribution between wind turbines and energy storage batteries. c The magnitudes of parameters J and J reflect the ratio of the rotational kinetic energy of the wind turbine to the frequency regulation energy of the energy storage battery. Therefore, this invention constructs K... cThe relationship between parameters and the available kinetic energy of wind storage depends on the current rotor motion state of the wind turbine and the state of charge (SOC) of the energy storage. The specific calculation formula is as follows:

[0103]

[0104] Among them, E wt_ava E is the available energy for the wind turbine. SB_ava For storing usable energy, λ W-E This is the conversion factor.

[0105] In the design of the droop control loop, the droop control coefficient reflects the static adjustment capability of the virtual speed governor to frequency deviation, affecting the frequency regulation depth and the active power output of the VSG to the grid. To ensure that the wind turbine and energy storage operate within a reasonable range during frequency support while also considering primary frequency regulation capability, this invention proposes an adaptive droop coefficient K based on the Logistic function. p The droop coefficient can be adjusted in the form of an S-curve based on the total available kinetic energy of the wind-storage system. In the initial stage, the droop coefficient of the Logistic function grows at an approximately exponential rate. As the available kinetic energy gradually saturates, the growth rate of the coefficient slows down, ensuring both smooth power output and the rapid response characteristics of wind-storage systems. The specific formula for calculating the droop coefficient is as follows:

[0106]

[0107] Among them, the droop coefficient K is divided into frequency rise droop coefficient K according to the charging and discharging state. P_dn and frequency decrease coefficient K p_up Maximum adjustment of droop coefficient K max The value is 20. To ensure the safe operation of the wind-storage system, this invention divides the available kinetic energy of the wind-storage system under the current operating conditions into four intervals E. total (E total_min E total_max E total_low E total_high The system adjusts the value of p0 and n within the corresponding range to prevent the wind-storage system from triggering speed protection and causing a secondary drop in system frequency when the available kinetic energy is too low. p0 and n are adaptation factors that determine the shape of the curve.

[0108] To verify the effectiveness and impact of the control method of the present invention, this embodiment compares and analyzes the power grid performance data under existing control methods, as follows:

[0109] I. High Wind Speed ​​and High Energy Storage SOC Operating Condition: The wind speed is 12 m / s, the initial state of charge of the energy storage is 0.8, the output power of the wind turbine generator before the disturbance is 260 MW, the total system load is 2921 MW, and the wind power penetration rate is 20.55%. At time t = 2 seconds, the 680 MW generator G1 tripped and lost 9.9% of the power system's generating capacity.

[0110] The specific frequency response of the system under high wind speed and high energy storage SOC operating conditions is as follows: Figure 9 As shown in the figure, when the wind-storage coordinated control under the framework proposed in this invention is adopted, the speed deviation decreases. As the frequency deviation increases, when the available kinetic energy of the energy storage is greater than that of the wind turbine, the kinetic energy of the wind-storage system is mostly provided by the energy storage device. Because the system considers the available kinetic energy on the source side during frequency regulation, compared with the traditional control of wind turbine frequency regulation alone, the energy storage shares the frequency regulation task of the wind turbine. The system has sufficient kinetic energy to complete the frequency support throughout the process, avoiding speed exceeding the limit.

[0111] II. Low Wind Speed, High Energy Storage State of Charge (SOC) Operating Condition: Wind speed is 8 m / s, initial state of charge of energy storage is 0.8, wind turbine output power before system disturbance is 224.4 MW, and total system load is 1856 MW. Therefore, wind power penetration is 32.33%. At time t = 2 seconds, generator G1 with a capacity of 680 MW tripped, resulting in a loss of 9.9% of the power system's generating capacity.

[0112] The specific frequency response of the system under low wind speed and high energy storage SOC operating conditions is as follows: Figure 10 As shown in the figure, the proposed solution does not excessively utilize the kinetic energy of the wind turbine rotor at low wind speeds, ensuring that the wind turbine rotor speed remains in normal operating condition throughout the entire frequency disturbance phase.

[0113] III. High Wind Speed ​​and Low Energy Storage State of Charge (SOC) Operating Condition: Wind speed is 12 m / s, initial state of charge of energy storage is 0.4, wind turbine output power before system disturbance is 459 MW, and total system load is 1460 MW. Therefore, wind power penetration rate is 41.1%. At time t = 2 s, generator G1 with a capacity of 650 MW tripped, resulting in a loss of 9.48% of the power system's generating capacity.

[0114] The specific frequency response of the system under high wind speed and low energy storage SOC operating conditions is as follows: Figure 11 As shown in the figure, in the early stage of frequency drop, the frequency change rate and the lowest frequency point of the proposed scheme are similar to those of other schemes. However, after 5.54 seconds, the steady-state deviation of the system is larger than that of other schemes. At this time, the wind storage system proposed in this invention mainly undertakes the task of inertia support in the early stage of frequency disturbance, thus avoiding rapid frequency deterioration.

[0115] IV. Low Wind Speed ​​and Low Energy Storage State of Charge (SOC) Operating Conditions: Wind speed is 8 m / s, initial state of charge of energy storage is 0.4, wind turbine output power before system disturbance is 224.4 MW, and total system load is 1856 MW. Therefore, wind power penetration is 32.33%. At time t = 2 s, generator G2 with a capacity of 680 MW tripped, resulting in a loss of 9.9% of the power system's generating capacity.

[0116] The specific frequency response of the system under low wind speed and low energy storage SOC operating conditions is as follows: Figure 12 As shown in the figure, the wind turbine output is reduced under the method proposed in this invention. Although the frequency recovery time is relatively long, it can still suppress the rapid change of frequency in the early stage of disturbance and effectively alleviate the secondary drop in frequency.

Claims

1. A wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the state of charge (SOC) of the energy storage, characterized in that, Includes the following steps: S1: Establish a grid-connected model for a direct-drive permanent magnet synchronous wind turbine; S2: Based on the grid-connected model of a direct-drive permanent magnet synchronous wind turbine, an energy storage device is connected to the DC side and the DC voltage control design of the grid-connected DC / DC converter for energy storage is carried out. S3: Design control strategies for the machine-side converter and grid-side converter of direct-drive permanent magnet synchronous wind turbine, and build an integrated wind and energy storage system architecture by combining DC-side energy storage devices; S4: Calculate the kinetic energy of the wind turbine rotor and the available energy of the energy storage system based on the operating conditions of the integrated wind and energy storage system, and obtain the total available kinetic energy of the wind and energy storage system. S5: Based on the total available kinetic energy of the wind-storage system, design the control parameters of the machine-side converter and grid-side converter of the wind-storage grid-connected system, and propose a wind-storage coordinated frequency support grid-connection strategy; Step S5 specifically includes: D1: The total frequency regulation energy requirement of the system is obtained through approximate calculation based on the following assumptions: Two assumptions were made to derive the approximate frequency modulation power consumption. First, it is assumed that during the inertial response phase, the total power increment of the wind-storage system is a linearly increasing curve. When the curve rises to the peak value of the incremental power... As can be seen from the power transfer function of the generator-side converter, the incremental power peak is essentially caused by the overshoot of the second-order system. Secondly, it is assumed that the incremental power of the wind-storage system in the primary frequency regulation stage is a linearly decreasing curve. Under this assumption, the inertial response and energy consumption in the primary frequency regulation process are assumed to be the sum of the area of ​​the first-stage shadow trapezoid and the area of ​​the second-stage shadow rectangle. ； D2: Value determination stage, The value is defined empirically; furthermore... By It is estimated by dividing by the ramp rate of the frequency-controlled generator set; and, in order to obtain the maximum energy consumption supported by the frequency, The value is usually defined as the active power imbalance caused by the most severe unexpected event that can be expected in the power system; D3: A wind-storage coordinated grid-connected control architecture with DC-side energy storage batteries was proposed, and a frequency support coordinated control scheme for the WTG-ESB system was designed based on this architecture. Machine-side converter inertia transfer gain It affects the power distribution between the wind turbine and the energy storage battery. and The parameter values ​​reflect the ratio of the rotational kinetic energy of the wind turbine to the frequency regulation energy of the energy storage battery; a system was constructed. The relationship between parameters and the available kinetic energy of wind storage depends on the current rotor motion state of the wind turbine and the state of charge (SOC) of the energy storage. The specific calculation formula is as follows: ； in, For the energy available to the wind turbine, For storing usable energy, This is the conversion factor.

2. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 1, is characterized in that... The establishment of the grid-connected model for the direct-drive permanent magnet synchronous wind turbine in step S1 includes: A1: Establish a complete model of the grid-side inverter: Based on the clear topology of the grid-side inverter, establish the corresponding three-phase voltage equations of the input and output sides and the switching function of the inverter, convert them into a mathematical model in the DQ coordinate system, and then, according to the obtained equations, express the frequency and phase angle of the AC phase voltage of the grid-side inverter, and find the expressions for active power and reactive power. A2: Establish a complete model of the generator-side converter: Based on the clear topology of the generator-side converter, establish the corresponding three-phase voltage equations for the input and output sides and the switching function of the converter, convert them into a mathematical model in the DQ coordinate system, and then, based on the obtained equations, represent the equivalent outer loop voltage value and inner loop current value, and calculate the electromagnetic torque of the permanent magnet synchronous generator. A3: Establish a complete mathematical model for DC-side energy storage; A4: Connect the models in steps A1 to A3 according to the structure of the synchronous generator energy supply system to form a direct-drive permanent magnet synchronous wind turbine grid-connected system model.

3. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 2, is characterized in that... In step S1, the grid-connected model of the direct-drive permanent magnet synchronous wind turbine includes a back-to-back grid-connected converter consisting of a wind turbine, a permanent magnet synchronous generator, a machine-side converter, and a grid-side converter. The wind turbine relies on the collected wind power to drive the blades to rotate, which in turn drives the rotor of the permanent magnet synchronous motor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power point tracking mode to obtain the maximum wind energy resources. The grid-side converter adopts virtual synchronous control to realize active support for the frequency and voltage of the wind turbine.

4. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 1, is characterized in that... The design method for DC voltage control of the grid-connected energy storage DC / DC converter in step S2 is as follows: Based on the establishment of a complete mathematical model of DC-side energy storage, its control principle is clarified. The energy storage device is connected to the DC side of the wind turbine through a DC / DC converter. The energy storage DC / DC converter adopts a buck / boost converter with DC bus voltage outer loop and inductor current inner loop control for the energy storage battery's DC / DC converter. When the wind turbine is running normally, the control objective of the energy storage battery is to smooth the unbalanced power between the wind turbine side and the grid side and maintain the DC link voltage. In its reference value nearby.

5. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 1, is characterized in that... Step S3 specifically includes: B1: For wind power systems equipped with energy storage devices, when the energy storage devices are controlled by bus voltage, the turbine-side converter is improved. The control task of the turbine-side converter is adjusted so that it can independently respond to the power increase caused by system frequency changes. By constructing a system frequency-turbine power increase action path within the turbine-side speed control loop, the turbine rotor kinetic energy can be utilized when the system frequency is disturbed. In addition, the grid-side controller uses VSG control to achieve active frequency support for the grid. B2: Construct an integrated wind and energy storage system and quantify its operating conditions to convert complex operating conditions into specific quantitative results, guiding the design of power allocation strategies for the wind and energy storage system; specifically including the calculation of available kinetic energy of the wind and energy storage system and the frequency regulation energy demand under grid frequency disturbances. B3: Based on the calculation results of available kinetic energy in step B2, design an adaptive droop coefficient control method for the grid-side converter of the wind-storage system: By comparing the total available kinetic energy of the wind-storage system with the frequency regulation energy demand under grid frequency disturbance, guide the design of the virtual droop coefficient of the grid-side converter VSG. When the available kinetic energy of the integrated wind-storage system is insufficient, reduce the droop coefficient to reduce the frequency regulation depth of the wind-storage system. When the available kinetic energy of the integrated wind-storage system is large, increase the droop coefficient. B4: Based on the calculation results of the available kinetic energy in step B2, design an adaptive inertia coefficient control method for the turbine-side converter of the wind-storage system; compare the available kinetic energy of the wind turbine and the energy storage. When the available kinetic energy of the wind turbine is greater than that of the energy storage, increase the inertia transfer gain of the turbine-side controller to allow the wind turbine to output more frequency regulation power, while the energy storage outputs less power to ensure that the energy storage operates within the safe operating SOC range. When the available kinetic energy of the energy storage is greater than that of the wind turbine, decrease the inertia transfer gain to allow the energy storage to output more power to smooth out the DC side unbalanced voltage and avoid the wind turbine's excessive participation in frequency regulation, which could cause a rapid drop in speed.

6. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 1, is characterized in that... Step S4 specifically includes: C1: Perform quantitative analysis of the wind storage operation conditions and convert the operation conditions of each unit into the available energy of each frequency regulation unit; C2: Quantitatively calculate the available kinetic energy of the wind-storage system. The available kinetic energy of the wind turbine is calculated based on the rotor speed and the set lower speed limit. The available kinetic energy of the energy storage is calculated based on the set minimum SOC point and the current SOC state.

7. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 6, is characterized in that... The formula for calculating the usable kinetic energy of the wind turbine in step C2 is as follows: ； in, This refers to the WTG rotor speed in MPPT mode. This is the lower limit of the rotor speed.

8. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 6, is characterized in that... The formula for calculating the usable kinetic energy stored in step C2 is as follows: ； in, This is the voltage on the energy storage side. For energy storage current, Total reactive power This is the conversion factor.

9. The wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC state of the energy storage, as described in claim 1, is characterized in that... In the design of the droop control mechanism in step S5, an adaptive droop coefficient based on the Logistic function is proposed. The droop coefficient can be adjusted in the form of an S-curve based on the total available kinetic energy of the wind-storage system; the specific calculation formula for the droop coefficient is as follows: ； ； Among them, the droop coefficient Based on the charging and discharging state, it is divided into frequency rise and droop coefficient. and frequency decrease coefficient Maximum adjustment of droop coefficient The value is 20; to ensure the safe operation of the wind storage system, the available kinetic energy under the current operating conditions of the wind storage system is divided into 4 intervals. ( , , , The system will adjust the value and take action within the corresponding range to prevent the wind-storage system from triggering speed protection and causing a secondary drop in system frequency when the available kinetic energy is too low. and It is the adaptive factor that determines the shape of the curve.

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