Wind storage cooperative frequency support control method based on available kinetic energy and energy storage SOC state of draught fan

Abstract

The invention discloses a wind storage cooperative frequency support control method based on available kinetic energy of a fan and an energy storage SOC state. The method comprises the following steps: establishing a direct-driven permanent magnet synchronous wind driven generator grid-connected model; based on a direct-drive permanent magnet synchronous wind driven generator grid-connected model, an energy storage device is connected into a direct current side, and direct current voltage control design of an energy storage grid-connected DC / DC converter is carried out; designing control strategies of a machine-side converter and a grid-side converter of the direct-drive permanent magnet synchronous fan, and constructing a wind storage integrated system architecture in combination with a direct-current side energy storage device; calculating the kinetic energy of a fan rotor and the available energy of stored energy according to the operation condition of the wind storage integrated system, and obtaining the total available kinetic energy of the wind storage system; and designing control parameters of a machine-side converter and a network-side converter of the wind storage grid-connected system based on the total available kinetic energy of the wind storage system, and providing a wind storage cooperative frequency support grid-connected strategy. The invention aims to provide the wind storage cooperative frequency support control method considering the operation condition, and the frequency stability of the high-proportion wind power system can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system control, and specifically relates to a wind-storage coordinated frequency support control method based on the available kinetic energy of a wind turbine and the SOC state of energy storage. Background Art

[0002] With the expansion of renewable energy grid connection, grid stability has become a focus. The fixed parameter settings of traditional virtual synchronous generator (VSG) control strategies often lead to over-damping or under-damping of the system under different working conditions, affecting stability. Existing technologies fail to fully adapt to the dynamic changes in the frequency of the power system, which may reduce the stability of the system, such as voltage fluctuations, frequency deviations, and other problems, and may even cause system failures, affecting the reliable operation of the power system. When the grid frequency drops, wind turbines rely on the release of rotor kinetic energy to adjust the frequency and increase active power output. However, the rotor kinetic energy is limited. At first, the unit responds to frequency changes, the speed decreases, and the output power increases. Later, due to insufficient rotor kinetic energy, as the speed continues to decrease, the power-speed characteristics make it impossible to maintain the initial level of power. In addition, the speed reduction also affects the efficiency of wind energy capture, and the wind energy capture capacity decreases, resulting in a further drop in power on the basis of the already reduced power, resulting in a secondary drop. Summary of the invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, a wind-storage coordinated frequency support control method based on the available kinetic energy of the wind turbine and the SOC status of energy storage is provided to optimize the frequency support capability of the wind-storage system under different working conditions, and effectively alleviate the occurrence of secondary drop problems when the wind turbine participates in frequency modulation, which can significantly improve the frequency stability of high-proportion wind power systems.

[0004] Technical solution: To achieve the above purpose, the present 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 direct-drive permanent magnet synchronous wind turbine generator;

[0006] S2: Based on the direct-drive permanent magnet synchronous wind turbine grid-connected model, an energy storage device is integrated on the DC side and the DC voltage control design of the energy storage grid-connected DC / DC converter is performed;

[0007] S3: Design the control strategy of the machine-side converter and grid-side converter of direct-drive permanent magnet synchronous wind turbine, and build a wind-storage integrated system architecture in combination with DC-side energy storage device;

[0008] S4: Calculate the wind turbine rotor kinetic energy and energy storage available energy according to the operating conditions of the wind-storage integrated system to obtain the total available kinetic energy of the wind-storage system;

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

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

[0011] A1: Establish a complete model of the grid-side inverter: On the basis of clarifying the grid-side inverter topology, establish the corresponding input and output three-phase voltage equations and the inverter switching function, convert them into a mathematical model in the DQ coordinate system, and then express the frequency and phase angle of the grid-side inverter AC phase voltage based on the obtained equation, and find the expressions of active power and reactive power;

[0012] A2: Establish a complete model of the machine-side converter: On the basis of clarifying the topological structure of the machine-side converter, establish the corresponding input and output three-phase voltage equations and the switching function of the converter, convert them into a mathematical model in the DQ coordinate system, and then express the equivalent outer loop voltage value and inner loop current value according to the obtained equation, and calculate the electromagnetic torque of the permanent magnet synchronous generator;

[0013] A3: Establish a complete mathematical model of 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, the unit of the direct-drive permanent magnet synchronous wind turbine grid-connected model in step S1 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 unit relies on the collected wind power to drive the blades to rotate, thereby driving the permanent magnet synchronous motor rotor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power tracking mode to obtain maximum wind energy resources. The grid-side converter adopts virtual synchronous control to achieve active support for the frequency and voltage of the wind turbine unit.

[0016] Furthermore, by configuring energy storage devices on the DC side to assist wind power in frequency support, the parameter design of the machine-side converter and the grid-side converter of the wind-storage system is guided according to the available kinetic energy of the wind turbine and the energy storage, so as to realize the distribution of frequency regulation power of the wind turbine and the energy storage, which can fully utilize the mechanical kinetic energy of the wind turbine rotor for rapid response to frequency disturbances and give play to the large capacity of energy storage to achieve continuous support for frequency over a long time scale.

[0017] Furthermore, the design method of the DC voltage control of the energy storage grid-connected 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 the DC / DC converter, and the DC / DC of the energy storage battery adopts a buck / boost converter with a DC bus voltage outer loop and an inductor current inner loop control; when the wind turbine operates normally, the control target of the energy storage battery is to smooth out the unbalanced power between the wind turbine side and the grid side, and maintain the DC link voltage V dc At its reference value V dc,ref nearby.

[0018] Furthermore, the step S3 specifically includes:

[0019] B1: For wind power systems equipped with energy storage devices, when the energy storage device adopts bus voltage control, the machine-side converter is improved, and the control task of the wind turbine machine-side converter is adjusted so that it can independently respond to the system frequency conversion to increase power. By constructing the system frequency-wind turbine increase power action path in the machine-side speed control loop, the wind turbine rotor kinetic energy can be called when the system frequency is disturbed; in addition, the grid-side controller adopts VSG control to realize active support for the grid frequency;

[0020] B2: Construct an integrated wind-storage system and quantify the operating conditions of the wind-storage system, realize the conversion of complex conditions of the wind-storage system into specific quantitative results, and guide the design of the power allocation strategy of the wind-storage system; specifically, it includes the calculation of the available kinetic energy of the wind-storage system and the frequency regulation energy demand 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 speed limit, and 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, 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 and 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 wind-storage integrated system is insufficient, the droop coefficient is reduced to reduce 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 wind-storage integrated system is large, the droop coefficient is increased so that the wind-storage integrated system can assume more frequency regulation responsibilities in the grid.

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

[0023] Combined with step S3, by designing the inertia transfer gain in the machine-side converter and the grid-side VSG control droop coefficient, the wind-storage integrated system can realize internal power distribution and external frequency regulation tasks, avoiding secondary frequency drops while achieving continuous support for the frequency of the wind-storage system over a long period of time.

[0024] Furthermore, the step S4 specifically includes:

[0025] C1: Quantitative analysis of wind storage operation conditions is carried out, mainly converting the operation conditions of each unit into the available energy of each frequency regulation unit. If the energy is less, it is not suitable for frequency regulation, and if the energy is more, the frequency regulation unit is in a better frequency regulation condition;

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

[0027] The formula for calculating the available kinetic energy of the fan is:

[0028]

[0029] Among them, ω ro is the WTG rotor speed in MPPT mode, ω rmin is the lower limit of rotor speed;

[0030] The calculation formula for the available 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 is the voltage on the energy storage side, i o is the energy storage current, Q N is the total reactive power, γ soc_0 is the conversion coefficient.

[0033] Furthermore, the step S5 specifically includes:

[0034] D1: The total frequency regulation energy required by the system is calculated approximately by assuming the following:

[0035] The present invention makes two assumptions to derive the approximate frequency modulation power consumption E con First, assume that the total power increment of the wind-storage system in the inertia response stage is a linear rising curve. When the curve rises to the incremental power peak DP incm (t ine_m ), it can be seen from the output power transfer function of the machine-side converter that the incremental power peak is essentially caused by the overshoot of the second-order system. Through parameter setting, it can be known that the peak value is usually about 1.2DP inc (t PFR_act ), and 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 inertia response and the energy consumption in the primary frequency regulation process are assumed to be the sum of the area of ​​the shaded trapezoid in the first stage and the area of ​​the shaded rectangle in the second stage;

[0036]

[0037] D2: value determination stage, t PFR_act The value of t is usually defined empirically as approximately 5 seconds, ine_m The value of can be calculated by solving the transfer function. In addition, t full By adding DP C Divide by the ramp rate of the frequency regulating generator set, which depends on the type of unit and is usually about 1.5% of the capacity of the thermal generator set. And, to obtain the maximum energy consumption for frequency support, DP C The value of is usually defined as the amount of active power imbalance caused by the most serious unexpected event that can be expected in the power system;

[0038] D3: A wind-storage coordinated grid-connected control architecture with energy storage batteries on the DC side is proposed. Based on this architecture, a WTG-ESB system frequency support coordinated control scheme is designed: The inertia transfer gain K of the machine-side converter c Affects the power distribution of wind turbines and energy storage batteries, K c The size of the parameters of and J reflects the ratio of the rotational kinetic energy of the wind turbine to the frequency modulation energy of the energy storage battery. c The relationship between the parameters and the available kinetic energy of wind storage, which depends on the current rotor motion state of the wind turbine and the energy storage SOC state. The specific calculation formula is as follows:

[0039]

[0040] Among them, E wt_avais the available energy of the fan, E SB_ava is the available energy for energy storage, λ W-E In order to make the fan participate in the inertia response as much as possible and give full play to the advantages of the rapid response of the fan rotor kinetic energy, the available energy ratio of the fan and the energy storage needs to be set as a scaling factor.

[0041] In the design of the droop control link, the droop control coefficient reflects the static adjustment ability of the virtual speed regulator to the frequency deviation, which affects the frequency adjustment depth and the active power output of the VSG to the power grid. In order to ensure that the wind turbine and energy storage operate within a reasonable range during the frequency support process while taking into account the primary frequency regulation capability, this paper proposes an adaptive droop coefficient K based on the Logistic function. p , which can be adjusted in the form of an S-curve according to the total available kinetic energy of the wind storage system. In the initial stage, the growth rate of the droop coefficient of the Logistic function is roughly exponential. As the available kinetic energy gradually saturates, the coefficient growth rate slows down, which can ensure the smooth output effect of power while taking into account the rapid response characteristics of wind storage. The specific calculation formula of 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 charge and discharge state P_dn And the frequency reduction coefficient K p_up , maximum adjustable droop coefficient K max To ensure the safe operation of the wind storage system, the present invention divides the available kinetic energy of the wind storage system under the current working condition into 4 intervals E total (E total_min 、E total_max 、E total_low 、E total_high ) value and take action within the corresponding range to prevent the wind storage system from triggering the speed protection when the available kinetic energy is too low, causing the system frequency to drop twice. p0 and n are the adaptive factors that determine the shape of the curve.

[0044] In view of the problem that the existing wind turbine grid-connected control has the risk of secondary drop due to insufficient rotor kinetic energy, the present invention proposes a wind power grid-connected architecture with energy storage configured on the DC side and designs a wind-storage grid-connected control scheme under the architecture, taking into account the rapid inertia response capability of the wind turbine rotor kinetic energy and the continuous primary frequency modulation output capability of the large-capacity energy storage battery. The present invention calculates the available kinetic energy of each frequency modulation unit of the wind-storage system by designing the optimal SOC state of energy storage and the limit amount under the wind turbine rotor speed, and adjusts the control parameters of the machine-side and grid-side converters in real time, thereby optimizing the system frequency support capability of the wind-storage system under different working conditions, and effectively alleviating the occurrence of the secondary drop problem when the wind turbine participates in frequency modulation.

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

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

[0047] 2. The adaptive control strategy optimizes the frequency response and stability by adjusting the system inertia distribution and energy storage droop control coefficient in real time, so that the power grid can better absorb and utilize renewable energy. With the continuous increase in the proportion of renewable energy connected to the grid, the problem of grid frequency fluctuation is becoming more and more serious. The adaptive control method of the present invention can quickly adjust the parameters of the virtual synchronous generator to maintain the stability of the grid frequency when the output of renewable energy is unstable. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a flow chart of the present invention;

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

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

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

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

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

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

[0055] Figure 8 It is the two-stage frequency modulation incremental power curve corresponding to the two assumptions;

[0056] Fig. 9 It is the frequency response curve of the system under high wind speed and high energy storage SOC operating condition;

[0057] Fig.10 It is the frequency response curve of the system under low wind speed and high energy storage SOC operating condition;

[0058] Fig.11 It is the frequency response curve of the system under high wind speed and low energy storage SOC operating condition;

[0059] Fig.12It is the system frequency response curve of low wind speed and low energy storage SOC operating conditions. DETAILED DESCRIPTION

[0060] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0061] like Figure 1 and Figure 7 As shown, the present 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 direct-drive permanent magnet synchronous wind turbine grid-connected model, including:

[0063] A1: Establish a complete model of the grid-side inverter: On the basis of clarifying the topological structure of the grid-side converter, establish the corresponding input and output three-phase voltage equations:

[0064]

[0065] Where S ga , S gb , S gc is the switching function of the inverter, and its expression is as follows:

[0066]

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

[0068]

[0069] Where: u gd 、u gq are the d and q components of the inverter voltage; i gd 、i gq are the d and q axis components of the three-phase current; ω g is the grid rotation angular velocity, in rad / s.

[0070] According to the above equation, the frequency and phase angle of the AC phase voltage of the grid-side inverter are expressed, and the expressions of active power and reactive power are obtained; the grid-side inverter topology in this embodiment is as follows Figure 2 As shown;

[0071] A2: Establish a complete model of the machine-side converter: On the basis of clarifying the topological structure of the machine-side converter, establish the corresponding input and output three-phase voltage equations:

[0072]

[0073] Switching function S of the bridge arm of the rectifier on the machine side of a direct-drive permanent magnet synchronous fan a , S b , S c The expression is as follows:

[0074]

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

[0076]

[0077] According to the above equations, the equivalent outer loop voltage value and inner loop current value are expressed, and the electromagnetic torque of the permanent magnet synchronous generator is obtained; the topological structure of the machine-side converter in this embodiment is as follows: Figure 3 As shown;

[0078] A3: Establish a complete mathematical model of 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 the DC / DC of the energy storage battery, and adopts a buck / boost converter with DC bus voltage outer loop and inductor current inner loop control; when the wind turbine is operating normally, the control target of the energy storage battery is to smooth out the unbalanced power between the wind turbine side and the grid side, and maintain the DC link voltage V dc At its reference value V dc,ref Nearby; the topological structure of the energy storage grid-connected model in this embodiment 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 unit of the direct-drive permanent magnet synchronous wind turbine grid-connected model 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, and then drives the permanent magnet synchronous motor rotor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power tracking mode to obtain maximum wind energy resources. The grid-side converter adopts virtual synchronous control to achieve active support for the frequency and voltage of the wind turbine.

[0081] By configuring energy storage devices on the DC side to assist wind power in frequency support, the parameter design of the machine-side converter and the grid-side converter of the wind-storage system is guided according to the available kinetic energy of the wind turbine and energy storage, and the frequency regulation power distribution of the wind turbine and energy storage is realized. This not only makes full use of the mechanical kinetic energy of the wind turbine rotor for rapid response to frequency disturbances, but also gives play to the large capacity of energy storage to achieve continuous support for frequency over a long time scale.

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

[0083] S3: Design the control strategy of the direct-drive permanent magnet synchronous wind turbine machine-side converter and grid-side converter, and build a wind-storage integrated system architecture in combination with the DC-side energy storage device, including:

[0084] B1: For wind power systems equipped with energy storage devices, when the energy storage device adopts bus voltage control, the machine-side converter is improved, and the control task of the wind turbine machine-side converter is adjusted so that it can independently respond to the system frequency conversion to increase power. By constructing the system frequency-wind turbine increase power action path in the machine-side speed control loop, the wind turbine rotor kinetic energy can be called when the system frequency is disturbed; in addition, the grid-side controller adopts VSG control to realize active support for the grid frequency;

[0085] B2: Construct an integrated wind and storage system and quantify the operating conditions of the wind and storage system, realize the conversion of complex working conditions of the wind and storage system to specific quantitative results, and guide the design of the power allocation strategy of the wind and storage system. Specifically, it includes the calculation of the available kinetic energy of the wind and storage system and the energy demand for frequency regulation under grid frequency disturbance. The available kinetic energy of the wind turbine is mainly calculated based on the current speed of the wind turbine and the set lower speed limit, and the available energy of the energy storage is calculated based on its SOC observation value;

[0086] B3: Based on the calculation result 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 and the frequency regulation energy demand under grid frequency disturbance, the design of the virtual droop coefficient of the grid-side converter VSG is guided. When the available kinetic energy of the wind-storage integrated system is insufficient, the droop coefficient is reduced to reduce 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 wind-storage integrated system is large, the droop coefficient is increased so that the wind-storage integrated system assumes more frequency regulation responsibilities in the grid. In this embodiment, the energy storage collaborative control structure is as follows: Figure 5 As shown;

[0087] B4: According to the calculation result of the available kinetic energy in step B2, an adaptive inertia coefficient control method for the machine-side converter of the wind-storage system is designed. 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 the available kinetic energy of the energy storage, increase the inertia transfer gain of the machine-side controller to allow the wind turbine to output more frequency modulation power and the energy storage to output less power to ensure that the energy storage operates in a safe operating SOC range. When the available kinetic energy of the energy storage is greater than that of the wind turbine, reduce the inertia transfer gain so that the energy storage outputs more power to smooth the unbalanced voltage on the DC side and avoid the rapid drop in speed caused by excessive participation of the wind turbine in frequency modulation. Combined with step S3, by designing the inertia transfer gain in the machine-side converter and the design of the grid-side VSG control droop coefficient, the internal power distribution and external frequency modulation task of the wind-storage integrated system are realized, avoiding secondary frequency drops while achieving continuous support for the frequency of the wind-storage system over a long time scale. The inertia transfer link control structure in this embodiment is as follows: Figure 6 As shown;

[0088] S4: Calculate the wind turbine rotor kinetic energy and energy storage available energy according to the operating conditions of the wind-storage integrated system, including:

[0089] C1: Quantitative analysis of wind storage operation conditions is carried out, mainly converting the operation conditions of each unit into the available energy of each frequency regulation unit. If the energy is less, it is not suitable for frequency regulation, and if the energy is more, the frequency regulation unit is in a better frequency regulation condition;

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

[0091] The formula for calculating the available kinetic energy of the fan is:

[0092]

[0093] Among them, ω ro is the WTG rotor speed in MPPT mode, ω rmin is the lower limit of rotor speed;

[0094] The calculation formula for the available 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 is the voltage on the energy storage side, i o is the energy storage current, Q N is the total reactive power, γ soc_0is the conversion coefficient.

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

[0098] D1: The total frequency regulation energy required by the system is calculated approximately by assuming the following:

[0099] The present invention makes two assumptions to derive the approximate frequency modulation power consumption E con ,like Figure 8 As shown in the figure, first assume that the total power increment of the wind storage system in the inertia response stage is a linear rising curve. When the curve rises to the incremental power peak DP incm (t ine_m ), it can be seen from the output power transfer function of the machine-side converter that the incremental power peak is essentially caused by the overshoot of the second-order system. Through parameter setting, it can be known that the peak value is usually about 1.2DP inc (t PFR_act ), and 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 inertia response and the energy consumption in the primary frequency regulation process are assumed to be the sum of the area of ​​the shaded trapezoid in the first stage and the area of ​​the shaded rectangle in the second stage;

[0100]

[0101] D2: value determination stage, t PFR_act The value of t is usually defined empirically as approximately 5 seconds, ine_m The value of can be calculated by solving the transfer function. In addition, t full By adding DP C Divide by the ramp rate of the frequency regulating generator set, which depends on the type of unit and is usually about 1.5% of the capacity of the thermal generator set. And, to obtain the maximum energy consumption for frequency support, DP C The value of is usually defined as the amount of active power imbalance caused by the most serious unexpected event that can be expected in the power system;

[0102] D3: A wind-storage coordinated grid-connected control architecture with energy storage batteries on the DC side is proposed. Based on this architecture, a WTG-ESB system frequency support coordinated control scheme is designed: The inertia transfer gain K of the machine-side converter c Affects the power distribution of wind turbines and energy storage batteries, K c The size of the parameters of and J reflects the ratio of the rotational kinetic energy of the wind turbine to the frequency modulation energy of the energy storage battery. cThe relationship between the parameters and the available kinetic energy of wind storage, which depends on the current rotor motion state of the wind turbine and the energy storage SOC state. The specific calculation formula is as follows:

[0103]

[0104] Among them, E wt_ava is the available energy of the fan, E SB_ava is the available energy for energy storage, λ W-E is the conversion coefficient.

[0105] In the design of the droop control link, the droop control coefficient reflects the static adjustment ability of the virtual speed regulator to the frequency deviation, which affects the frequency adjustment depth and the active power output of the VSG to the power grid. In order to ensure that the wind turbine and energy storage operate within a reasonable range during the frequency support process while taking into account the primary frequency regulation capability, this paper proposes an adaptive droop coefficient K based on the Logistic function. p , which can be adjusted in the form of an S-curve according to the total available kinetic energy of the wind storage system. In the initial stage, the growth rate of the droop coefficient of the Logistic function is roughly exponential. As the available kinetic energy gradually saturates, the coefficient growth rate slows down, which can ensure the smooth output effect of power while taking into account the rapid response characteristics of wind storage. The specific calculation formula of 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 charge and discharge state P_dn And the frequency reduction coefficient K p_up , maximum adjustable droop coefficient K max To ensure the safe operation of the wind storage system, the present invention divides the available kinetic energy of the wind storage system under the current working condition into 4 intervals E total (E total_min 、E total_max 、E total_low 、E total_high ) value and take action within the corresponding range to prevent the wind storage system from triggering the speed protection when the available kinetic energy is too low, causing the system frequency to drop twice. p0 and n are the adaptive factors that determine the shape of the curve.

[0108] In order to verify the effectiveness and effect of the control method of the present invention, the performance data of the power grid under the control method of the present invention and the existing control method are compared and analyzed in this embodiment, as follows:

[0109] 1. High wind speed and high energy storage SOC operating conditions: wind speed is 12m / s, initial energy storage charge state is 0.8, wind turbine output power before disturbance is 260MW, total system load is 2921MW, wind power penetration is 20.55%. At time t = 2 seconds, the 680MW generator G1 tripped and lost 9.9% of the power system power generation.

[0110] The system frequency response of high wind speed and high energy storage SOC operating conditions is as follows: Fig. 9 As shown in the figure, it can be seen that when the wind-storage coordinated control under the framework proposed by the present 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 provided more by the energy storage device. Since the system takes into account the available kinetic energy on the source side during the frequency regulation process, compared with the traditional control of the wind turbine frequency regulation alone, the energy storage shares the frequency regulation task of the wind turbine, and the system has enough kinetic energy to complete the entire frequency support process and avoid speed limit exceeding.

[0111] 2. Low wind speed and high energy storage SOC operating conditions: The wind speed is 8m / s, the initial state of charge of the energy storage is 0.8, the output power of the wind turbine before the system disturbance is 224.4MW, and the total system load is 1856MW. Therefore, the wind power penetration rate is 32.33%. At time t = 2 seconds, the generator G1 with a capacity of 680MW tripped and lost 9.9% of the power system power generation.

[0112] The system frequency response of low wind speed and high energy storage SOC operating condition is as follows: Fig.10 As shown in the figure, it can be seen that the solution proposed in the present invention does not excessively call upon the kinetic energy of the wind turbine rotor at low wind speeds, so that the speed of the wind turbine rotor is in a normal operating state throughout the frequency disturbance stage.

[0113] 3. High wind speed and low energy storage SOC operating conditions: The wind speed is 12m / s, the initial state of charge of the energy storage is 0.4, the output power of the wind turbine before the system disturbance is 459MW, and the total system load is 1460MW. Therefore, the wind power penetration rate is 41.1%. At time t=2s, the generator G1 with a capacity of 650MW tripped and lost 9.48% of the power system power generation.

[0114] The system frequency response of high wind speed and low energy storage SOC operating conditions is as follows: Fig.11 As shown in the figure, it can be seen that in the initial stage of frequency drop, the frequency change speed and the lowest frequency point of the scheme proposed in the present invention are similar to those of other schemes, but 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 the present invention mainly undertakes the task of inertia support in the initial stage of frequency disturbance, avoiding the rapid deterioration of frequency.

[0115] 4. Low wind speed and low energy storage SOC operating conditions: The wind speed is 8m / s, the initial state of charge of the energy storage is 0.4, the output power of the wind turbine before the system disturbance is 224.4MW, and the total system load is 1856MW. Therefore, the wind power penetration rate is 32.33%. At time t=2s, the generator G2 with a capacity of 680MW tripped and lost 9.9% of the power system power generation.

[0116] The system frequency response of low wind speed and low energy storage SOC operating conditions is as follows: Fig.12 As shown in the figure, it can be seen that the fan output is reduced under the method proposed in the present invention. Although the time for the frequency to return to a steady state is relatively long, the rapid change of the frequency can still be suppressed in the early stage of the disturbance, and the secondary drop of the frequency can also be effectively alleviated.

Claims

1. A wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state, characterized in that: The steps include: S1: Establish a grid-connected model for direct-drive permanent magnet synchronous wind turbine generator; S2: Based on the direct-drive permanent magnet synchronous wind turbine grid-connected model, an energy storage device is integrated on the DC side and the DC voltage control design of the energy storage grid-connected DC / DC converter is performed; S3: Design the control strategy of the machine-side converter and grid-side converter of direct-drive permanent magnet synchronous wind turbine, and build a wind-storage integrated system architecture in combination with DC-side energy storage device; S4: Calculate the wind turbine rotor kinetic energy and energy storage available energy according to the operating conditions of the wind-storage integrated system to obtain the total available kinetic energy of the wind-storage system; S5: Based on the total available kinetic energy of the wind-storage system, the control parameters of the machine-side converter and the grid-side converter of the wind-storage grid-connected system are designed, and a wind-storage coordinated frequency support grid-connected strategy is proposed.

2. According to claim 1, a wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state is characterized in that: The establishment of the direct-drive permanent magnet synchronous wind turbine grid-connected model in step S1 includes: A1: Establish a complete model of the grid-side inverter: On the basis of clarifying the grid-side inverter topology, establish the corresponding input and output three-phase voltage equations and the inverter switching function, convert them into a mathematical model in the DQ coordinate system, and then express the frequency and phase angle of the grid-side inverter AC phase voltage based on the obtained equation, and find the expressions of active power and reactive power; A2: Establish a complete model of the machine-side converter: On the basis of clarifying the topological structure of the machine-side converter, establish the corresponding input and output three-phase voltage equations and the switching function of the converter, convert them into a mathematical model in the DQ coordinate system, and then express the equivalent outer loop voltage value and inner loop current value according to the obtained equation, and calculate the electromagnetic torque of the permanent magnet synchronous generator; A3: Establish a complete mathematical model of 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 according to claim 2 is characterized in that: The unit of the direct-drive permanent magnet synchronous wind turbine grid-connected model in step S1 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, thereby driving the permanent magnet synchronous motor rotor to rotate, converting wind energy into electrical energy. The machine-side converter is used to control the wind turbine to operate in maximum power tracking mode to obtain maximum wind energy resources. The grid-side converter adopts virtual synchronous control to achieve active support for the frequency and voltage of the wind turbine.

4. The wind-storage coordinated frequency support control method considering operating conditions according to claim 1 is characterized in that: The design method of the DC voltage control of the energy storage grid-connected 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, and the DC / DC of the energy storage battery adopts a buck / boost converter with a DC bus voltage outer loop and an inductor current inner loop control; when the wind turbine is operating normally, the control target of the energy storage battery is to smooth out the unbalanced power between the wind turbine side and the grid side, and maintain the DC link voltage V dc At its reference value V dc,ref nearby.

5. The wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state according to claim 1 is characterized in that: The step S3 specifically includes: B1: For wind power systems equipped with energy storage devices, when the energy storage device adopts bus voltage control, the machine-side converter is improved, and the control task of the wind turbine machine-side converter is adjusted so that it can independently respond to the system frequency conversion to increase power. By constructing the system frequency-wind turbine increase power action path in the machine-side speed control loop, the wind turbine rotor kinetic energy can be called when the system frequency is disturbed; in addition, the grid-side controller adopts VSG control to realize active support for the grid frequency; B2: Construct an integrated wind-storage system and quantify the operating conditions of the wind-storage system, realize the conversion of complex working conditions of the wind-storage system to specific quantitative results, and guide the design of the power allocation strategy of the wind-storage system; specifically, it includes the calculation of the available kinetic energy of the wind-storage system and the frequency regulation energy demand under grid frequency disturbance; B3: Based on the calculation result of the available kinetic energy in step B2, the adaptive droop coefficient control method of the grid-side converter of the wind-storage system is designed: by comparing the total available kinetic energy of the wind-storage system and the frequency regulation energy demand under the grid frequency disturbance, the design of the virtual droop coefficient of the grid-side converter VSG is guided. When the available kinetic energy of the wind-storage integrated system is insufficient, the droop coefficient is reduced to reduce the frequency regulation depth of the wind-storage system. When the available kinetic energy of the wind-storage integrated system is more, the droop coefficient is increased. B4: Based on the calculation result of the available kinetic energy in step B2, design an adaptive inertia coefficient control method for the machine-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 the available kinetic energy of the energy storage, increase the inertia transfer gain of the machine-side controller to allow the wind turbine to output more frequency modulation power and the energy storage to output less power to ensure that the energy storage operates in a safe operating SOC range. When the available kinetic energy of the energy storage is greater than that of the wind turbine, reduce the inertia transfer gain so that the energy storage outputs more power to smooth the unbalanced voltage on the DC side and avoid a rapid drop in speed caused by excessive participation of the wind turbine in frequency modulation.

6. The wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state according to claim 1 is characterized in that: The step S4 specifically includes: C1: Quantitatively analyze the wind storage operation conditions and convert the operation conditions of each unit into the available energy of each frequency modulation 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, and the available kinetic energy of the energy storage is calculated based on the set SOC minimum point and the current SOC state.

7. A wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state according to claim 6, characterized in that: The calculation formula of the available kinetic energy of the fan in step C2 is: Among them, ω ro is the WTG rotor speed in MPPT mode, ω rmin is the lower limit of rotor speed.

8. The wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state according to claim 6 is characterized in that: The calculation formula of the available kinetic energy of energy storage in step C2 is: E ESB_soc =∫u o i o dt=u o Q N γ soc_0 Among them, u o is the voltage on the energy storage side, i o is the energy storage current, Q N is the total reactive power, γ soc_0 is the conversion coefficient.

9. The wind-storage coordinated frequency support control method based on wind turbine available kinetic energy and energy storage SOC state according to claim 1 is characterized in that: The step S5 specifically includes: D1: The total frequency regulation energy required by the system is calculated approximately by assuming the following: Two assumptions are made to derive the approximate FM power consumption E con First, assume that the total power increment of the wind-storage system in the inertia response stage is a linear rising curve. When the curve rises to the incremental power peak DP incm (t ine_m ), it can be seen from the output power transfer function of the machine-side converter that the incremental power peak is essentially caused by the overshoot of the second-order system. Through parameter setting, it can be known that the peak value is usually about 1.2DP inc (t PFR_act ), and 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 inertia response and the energy consumption in the primary frequency regulation process are assumed to be the sum of the area of ​​the shaded trapezoid in the first stage and the area of ​​the shaded rectangle in the second stage; D2: value determination stage, t PFR_act The value of is defined empirically, t ine_m The value of is obtained by solving the transfer function; in addition, t full By using DP C divided by the ramp rate of the frequency-regulated generator set; and, to obtain the maximum energy consumption for frequency support, DP C The value of is usually defined as the amount of active power imbalance caused by the most serious unexpected event that can be expected in the power system; D3: A wind-storage coordinated grid-connected control architecture with energy storage batteries on the DC side is proposed. Based on this architecture, a WTG-ESB system frequency support coordinated control scheme is designed: Machine-side converter inertia transfer gain K c Affects the power distribution of wind turbines and energy storage batteries, K c The size of the parameters of and J reflects the ratio of the rotational kinetic energy of the wind turbine and the frequency modulation energy of the energy storage battery; K c The relationship between the parameters and the available kinetic energy of wind storage, which depends on the current rotor motion state of the wind turbine and the energy storage SOC state. The specific calculation formula is as follows: Among them, E wt_ava is the available energy of the fan, E SB_ava is the available energy for energy storage, λ W-E is the conversion coefficient. In the design of droop control link, an adaptive droop coefficient K based on Logistic function is proposed p , which can be adjusted in the form of an S-shaped curve according to 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 K is divided into frequency rise droop coefficient K according to the charge and discharge state P_dn And the frequency reduction coefficient K p_up , maximum adjustable droop coefficient K max is 20; in order to ensure the safe operation of the wind storage system, the available kinetic energy of the wind storage system under the current working conditions is divided into 4 intervals E total (E total_min 、E total_max 、E total_low 、E total_high ) value and act within the corresponding range to prevent the wind storage system from triggering the speed protection when the available kinetic energy is too low, causing the system frequency to drop twice. p0 and n are the adaptive factors that determine the shape of the curve.

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