A method for suppressing out-of-step oscillations in a wind power system with a high proportion of energy storage participation

Abstract

The present invention discloses a method for suppressing out-of-step oscillations in a high-proportion wind power system with energy storage participation, comprising the following steps: Step S1. Establishing a power system with wind power access and energy storage participation; Step S2. In the power system, collecting the rotational speed of a synchronous machine adjacent to the energy storage and the output power of the wind farm to determine the swing state of the synchronous machine; Step S3. Designing a power angle stability optimization control strategy for each stage of the synchronous machine swing process; Step S4. Analyzing the energy interaction relationship between the energy storage and the synchronous machine to generate correction instructions. Under high-proportion wind power access, the present invention determines the swing state of the synchronous machine, determines the stage and the power angle stability optimization strategy for each stage by comparing the actual value with a threshold, and generates correction instructions; controls the electromagnetic power increment of the synchronous generator by adjusting the active current or active power through emergency control, thereby improving the system power angle stability under different operating characteristics at different stages, thereby achieving the effect of suppressing out-of-step oscillations.

Description

Technical Field

[0001] The present invention relates to the technical field of transient power angle stabilization control of power systems under high-proportion renewable energy access, and in particular to a method for suppressing out-of-step oscillations of power systems under high-proportion wind power access with energy storage participation. Background Art

[0002] The widespread interconnection of power grids presents greater challenges to system stability. The most serious destabilization issue is out-of-step oscillation, which can severely compromise system safety and stability, and even lead to widespread power outages. To prevent these serious grid incidents, power industry professionals have proposed a third line of defense for power systems. Decoupling the out-of-step section during out-of-step conditions is the most fundamental stabilization measure within this third line of defense, effectively eliminating out-of-step oscillations.

[0003] In recent years, both energy storage and wind turbines have experienced rapid development and will play a crucial role in future power grids. As a renewable, clean energy source, wind power has steadily increased its share in the power grid. However, wind turbines are often located at the end of the power grid, resulting in weak grid structures and poor voltage support capabilities. These turbines are highly susceptible to AC system failures, leading to grid disconnection. Furthermore, the integration of high wind power penetration into the grid will reduce the inertia of the existing power system, posing new challenges to the stability control process after out-of-step oscillations. In scenarios with high wind power penetration, preventing further out-of-step oscillations after a grid disturbance is of paramount importance. Furthermore, traditional synchronous generators remain the primary power generation unit in today's large power grids, and synchronous generator generation and renewable energy generation will continue to coexist for a long time. The electromagnetic power of synchronous generators and the active power of energy storage are physically coupled, resulting in an energy interaction between synchronous generators and energy storage. By utilizing this energy interaction, energy storage can quickly adjust the electromagnetic power of the synchronous generator by quickly adjusting its own output or absorbed active power, and then adjust the operating dynamics of the synchronous generator after the system disturbance, ultimately improving the power angle stability of the power system.

[0004] Existing research has simulated and analyzed the impact of factors such as wind farm access method and wind power reactive power control method on system power angle stability, based on actual power grids. However, current research on the impact of wind power access on power grids has mostly focused on the impact on low-frequency oscillations in the system. Relatively few studies have analyzed the impact of high wind power access on actual power grid out-of-step oscillations and related disconnection measures. Regarding the use of energy storage to improve transient power angle stability, some researchers have conducted research on energy storage controllers based on feedback linearization, based on the idea of ​​synergistic interaction between synchronous generators and energy storage. However, detailed modeling and analysis of the energy interaction between energy storage and synchronous generators has not been conducted. Furthermore, given the high degree of nonlinearity and uncertainty in the system dynamics of actual power systems, methods such as sliding mode control are often used for energy storage controllers. However, many power system operating state parameters (such as infinite bus voltage and transmission line impedance) are often difficult to obtain, making it difficult to achieve ideal stability control effects in actual multi-machine power systems. Summary of the Invention

[0005] Based on this, in order to address the transient stability issues of the power system in the current high-proportion wind power access scenario, the present invention proposes a method for suppressing out-of-step oscillations in a high-proportion wind power system with energy storage participation.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for suppressing out-of-step oscillations in a wind power system with a high proportion of energy storage participation comprises the following steps:

[0008] Step S1. Build a power system including wind power access and energy storage participation;

[0009] Step S2. In the power system, the speed of the synchronous machine and the wind farm output power of the energy storage are collected to determine the swing state of the synchronous machine;

[0010] Step S3. Designing a power angle stability optimization control strategy for each stage of the synchronous machine swing process;

[0011] Step S4: Analyze the energy interaction relationship between the energy storage and the synchronous machine, and generate correction instructions.

[0012] Furthermore, step S2 includes the following sub-steps:

[0013] Step S2.1. Identify the power angle swing state of the synchronous machine after the power system is disturbed;

[0014] Step S2.2: Set the synchronous machine rotor speed and acceleration thresholds, and determine the stage of the synchronous machine swing process by comparing the actual values ​​of the synchronous machine acceleration and speed with the thresholds.

[0015] Furthermore, the step S2.1 is specifically as follows:

[0016] According to the rotor speed curve of the synchronous machine's swing process, the swing process of each cycle of the synchronous machine is divided into four stages: when the synchronous machine rotor speed is higher than the synchronous speed, the rotor acceleration process is considered the first stage, and the rotor deceleration process is considered the second stage; when the synchronous machine rotor speed is lower than the synchronous speed, the rotor deceleration process is considered the third stage, and the rotor acceleration process is considered the fourth stage;

[0017] According to the second-order integral relationship of rotor acceleration-rotor rotation speed-rotor position / power angle during the synchronous machine swing process, it can be deduced that:

[0018]

[0019] The superscript indicates the swing period of the parameter, and the subscript indicates the swing stage of the synchronous machine in each period. max |、|Δδ min | are the maximum and minimum values ​​of the internal power angle change modulus in each cycle, and a is the rotor equivalent constant acceleration in each stage.

[0020] Furthermore, the step S2.2 is specifically as follows:

[0021] The speed is expanded from the stable equilibrium point to the set synchronous machine rotor speed and acceleration threshold range, and the minimum and maximum speeds are recorded as ω respectively. dmin 、ω dmax The minimum and maximum values ​​of the acceleration range are a dmin 、a dmax After extracting the synchronous machine speed and acceleration and comparing them with the set value, the swing stage of the current synchronous machine can be determined and output.

[0022] Furthermore, in step S2.2, the synchronous machine swing process is at the following stages:

[0023] Stage 1. Acceleration a ≥ a dmax , rotor speed ω≥ω dmax ;

[0024] Stage 2. Acceleration a≤a dmax , rotor speed ω≥ω dmax ;

[0025] Stage 3. Acceleration a ≥ a dmax , rotor speed ω≤ω dmax ;

[0026] Stage 4. Acceleration a≤a dmax , rotor speed ω≤ω dmax .

[0027] Furthermore, the optimization strategy in step S3 is: the constraints of the electromagnetic power variation at each stage are as follows:

[0028]

[0029] Among them, P m is the mechanical power of the synchronous machine, in pu, which is directly controlled by the prime mover input energy control system, P e is the electromagnetic power of the synchronous machine under normal operation, ΔPe is the change in electromagnetic power of the synchronous machine caused by optimization control in each stage, the unit is pu, which depends on the electrical quantity of each node in the power network.

[0030] Furthermore, step S4 includes the following sub-steps:

[0031] Step S4.1. Analyze the interaction between energy storage and synchronous machine energy and determine the indicators to be corrected;

[0032] Step S4.2. Generate correction instructions according to the characteristics of each swing stage of the synchronous machine.

[0033] Furthermore, the power correction instruction is as follows:

[0034]

[0035] Among them: K p represents the proportional coefficient, a represents the acceleration of the system equivalent synchronous machine swing, ΔP min , ΔP max They respectively represent the minimum and maximum power command corrections that the energy storage equipment can withstand.

[0036] Furthermore, the proportional coefficient setting process is as follows:

[0037] First, the grid flow information and typical fault sets of the power system are obtained offline, and the acceleration change and unbalanced power P of the synchronous machine rotor during the first swing period are simulated and analyzed under typical fault instability scenarios or scenarios with low stability margin. m -P e After obtaining multiple sets of data, the linear fitting method is used to process the acceleration change and power change into a linear relationship, that is:

[0038]

[0039] in: They are the average values ​​obtained after multiple measurements of unbalanced power and synchronous machine rotor acceleration.

[0040] Furthermore, the minimum and maximum power command corrections that the energy storage equipment can withstand are:

[0041]

[0042] Where: N is the number of parallel energy storage power stations in the system, P st is the nominal apparent power of each energy storage power station.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The current existing technology focuses on designing specific wind turbine transient optimization control to address the challenges of system transient power angle stability brought about by large-scale wind power grid connection. However, current research on wind turbine transient optimization control pays insufficient attention to wind turbine active current. This invention targets high-proportion wind power access scenarios where the system transient power angle stability challenge is more severe. By comprehensively utilizing the relevant theoretical analysis results of wind turbines, synchronous machines, and energy storage, a specific active current transient optimization control strategy is designed to achieve long-distance wind power transmission.

[0045] 2. Compared with the existing technology that adjusts the transient operating state of the system through wind power, the present invention divides the swing process of each synchronous machine into segments. When judging the swing state of the synchronous machine, it is only necessary to detect the rotor speed of the generator adjacent to the energy storage or the grid-connected bus voltage frequency. On the one hand, it is easy to judge the system operating state. On the other hand, the required detection parameters are easy to obtain through the PMU, avoiding the complicated parameter acquisition and calculation process.

[0046] 3. When the present invention utilizes energy storage emergency control to generate power correction instructions, its control strategy only requires adding a control loop without changing other control modules, making the control process easy to implement.

[0047] 4. The emergency control of energy storage in the present invention is only put into operation after the power system suffers a major disturbance. Its working process only utilizes the remaining capacity of the energy storage, and does not affect other uses of the energy storage module (such as peak shaving and valley filling) when the power system is in a steady state, thereby expanding the application scenarios of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0049] Figure 1 This is a diagram of an improved four-machine, two-area system with energy storage participating in wind power access according to the present invention.

[0050] Figure 2 This is a control block diagram of the method for suppressing out-of-step oscillations of a high-proportion wind power system based on energy storage participation proposed in the present invention.

[0051] Figure 3 It is the equivalent circuit diagram of a single-machine infinite system with energy storage.

[0052] Figure 4 It is the process of generating power correction instructions in each synchronous machine swing phase.

[0053] Figure 5 It is based on the time-varying characteristics of the power angle of each generator in the system under the traditional energy storage vector control strategy.

[0054] Figure 6 It is based on the time-varying characteristics of the speed of each generator in the system under the traditional energy storage vector control strategy.

[0055] Figure 7 It is the time variation characteristic of the power angle of each generator in the system after the out-of-step oscillation suppression method of a high-proportion wind power system based on energy storage participation proposed by the present invention is additionally adopted on the basis of the traditional energy storage control strategy. Specific implementation methods

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0057] To address the transient stability issues of power systems in current scenarios with high wind power integration, the present invention proposes a method for suppressing out-of-step oscillations in high-proportion wind power systems with energy storage. The technical problems to be solved by the present invention can be summarized as follows:

[0058] (1) In the scenario of long-distance wind power transmission, the system faces a more severe challenge of transient power angle stability. Theoretical analysis and actual operation experience of the transient power angle stability of the power system have shown that the increase in transmission distance and transmission capacity will weaken the transient power angle stability of the system. On the other hand, since the transmission capacity of the transmission lines is mostly relatively tight in actual operation, the transmission power is often at a heavy load level close to the stability limit, which further weakens the transient power angle stability of the system. Therefore, in the scenario of high-proportion wind power access, it is necessary to design a reasonable power angle stability optimization control strategy to achieve long-distance wind power transmission.

[0059] (2) In the scenario of high proportion of wind power access, the research on power system oscillation is mostly focused on the impact of wind power access on the low-frequency oscillation of the system. Its application scenario is more suitable for the static stability of the power system when it is subjected to small interference and the power angle is not unstable. However, there are few studies on the method of suppressing out-of-step oscillation when the power system is subjected to large interference under wind power access. Therefore, this invention needs to discuss the changes in transient stability when the power system is subjected to large disturbances under the condition of wind power access, and conduct quantitative and qualitative analysis of the transient swing process of the synchronous machine.

[0060] (3) In the existing technology, most studies on the effects of large-scale wind power on power system out-of-step oscillations improve the transient stability of the power system by changing the type of wind turbines, adjusting the wind power output, etc., which leads to complex coordination problems during power transmission and a complicated parameter setting process. Considering that energy storage not only has good active power control capabilities but can also contribute to the reactive power balance of the system, the present invention improves the transient stability of the system by designing a reasonable energy storage control strategy, while also making the parameter selection process more concise.

[0061] The present invention discloses a method for suppressing out-of-step oscillations in a wind power system with a high proportion of energy storage participation. In a scenario where a high proportion of wind power is connected, the speed or bus voltage frequency of a synchronous generator adjacent to the energy storage is first collected, acceleration and speed thresholds are set, and the swing state of the synchronous machine is judged. By comparing the actual value with the threshold, the stage and the power angle stability optimization strategy of each stage are determined, and a correction instruction is generated; the active current or active power is adjusted through emergency control to control the electromagnetic power increment of the synchronous generator, thereby achieving the improvement of the system power angle stability under different operating characteristics in different stages, thereby achieving the effect of suppressing out-of-step oscillations.

[0062] In order to test the feasibility of the out-of-step oscillation suppression method for high-proportion wind power system with energy storage participation proposed in this invention, a power system with wind power access and energy storage participation based on the classic four-machine two-area system is established in DIgSILENT / PowerFactory. Its structure is shown in the attached figure. Figure 1 As shown in the figure, the classic four-machine two-area system is a typical weak grid with long interconnection lines and heavy loads. Wind power must be transmitted via the long interconnection lines to the load center at the distant No. 9 busbar. Therefore, this test system is a typical long-distance wind power transmission scenario and meets the applicable conditions for optimized control.

[0063] In the improved four-turbine, two-area system, the original four-turbine, two-area system's No. 2 synchronous generator was replaced by a DFIG wind farm. The wind farm consists of 500 1.5MW wind turbines, connected in parallel to the grid via a two-stage step-up transformer. The energy storage device and the wind turbines are connected to bus 6 via a common coupling point to optimize system transient stability. The number of parallel energy storage devices, N, is 3, with each device having a nominal apparent power of 30MVA, resulting in a total storage capacity of 90MVA. During steady-state operation, the total system load is 1800MW, the wind farm generates 500MW of active power, and the electrochemical energy storage device generates no active power. The system's wind power penetration rate is approximately 27.8%.

[0064] The specific steps of using this method to suppress out-of-step oscillations in a wind power system with a high proportion of energy storage are as follows:

[0065] Step S1. Build a power system including wind power access and energy storage participation;

[0066] Step S2. In the power system, the speed of the synchronous machine and the wind farm output power of the energy storage are collected to determine the swing state of the synchronous machine;

[0067] Step 2.1: Identify the power angle swing state of the synchronous machine after the power system is disturbed.

[0068] After the power system suffers a large disturbance, the swing process of the synchronous machine in each cycle can be divided into four stages according to the rotor speed curve of the synchronous machine's swing process: when the synchronous machine rotor speed is higher than the synchronous speed, the rotor acceleration process is regarded as the first stage, and the rotor deceleration process is regarded as the second stage; when the synchronous machine rotor speed is lower than the synchronous speed, the rotor deceleration process is regarded as the third stage, and the rotor acceleration process is regarded as the fourth stage.

[0069] In this embodiment, the disturbance of the power system is set as a three-phase short circuit fault. The fault location is located on bus 8 and is removed by isolating the fault line. The fault duration is 0.2 seconds.

[0070] If the acceleration of the synchronous generator rotor is too large at a certain stage, resulting in an excessively large acceleration area in the power characteristic curve, the system will lose synchronization. Therefore, it is necessary to control the acceleration to a certain extent. Since the evolution relationship between the same type of offset extreme values ​​(such as the maximum value of the synchronous machine speed offset) in two adjacent swing cycles of the synchronous machine is relatively fixed, based on the second-order integral relationship of rotor acceleration-rotor rotation speed-rotor position / power angle during the swing process of the synchronous machine, it can be deduced that:

[0071]

[0072] The superscript indicates the swing period of the parameter, and the subscript indicates the swing stage of the synchronous machine in each period. max |、|Δδ min | are the maximum and minimum values ​​of the internal power angle change modulus in each cycle, and a is the rotor equivalent constant acceleration in each stage.

[0073] Step 2.2: Set the synchronous machine rotor speed and acceleration thresholds, and determine the stage of the synchronous machine's swing process by comparing the synchronous machine's acceleration and speed actual values ​​with the thresholds.

[0074] After dividing the synchronous machine swing process into four stages, the change rules of the synchronous machine acceleration and speed in each stage can be summarized as follows:

[0075]

[0076] Among them, the speed of the stable equilibrium point is taken as 1 (standard value). Taking into account the actual operation of the system, the speed threshold is extended from the stable equilibrium point to a small range near the equilibrium point. The rotor speed and acceleration thresholds set in step 2.2 are the upper and lower limits of the variation range of the parameters mentioned near the stable equilibrium point. Usually, the value of this range is determined based on engineering experience: the minimum and maximum values ​​of the variation range of acceleration a are usually taken as ±0.004, and the minimum and maximum values ​​of the rotor speed variation range are usually taken as ±1.004. The minimum and maximum values ​​are respectively denoted as ω dmin 、ω dmax The minimum and maximum values ​​of the acceleration range are a dmin 、a dmax The actual acceleration value must be outside this range to ensure normal system operation. After extracting the synchronous machine speed and acceleration and comparing them with the set values, the current swing stage of the synchronous machine can be determined and output.

[0077] In this embodiment, the control block diagram of the method for suppressing out-of-step oscillation of a high-proportion wind power system based on energy storage participation proposed by the present invention is shown in the attached figure. Figure 2 As shown. The part completed in step 1 is Figure 2 In the generator power angle swing state identification part, the rotor speed ω or bus voltage frequency f of the energy storage adjacent synchronous unit G1 is first collected as input to determine the synchronous machine swing stage.

[0078] The synchronous machine rotor acceleration is obtained by the rotor speed after the differential link. Considering the actual engineering, the differential link is often difficult to implement. Therefore, the inertia link is adopted in the present invention, that is:

[0079]

[0080] In this embodiment, the inertia link time constant T=0.01.

[0081] In the selection module of this embodiment, the status of the synchronous machine during the swing phase is determined as follows:

[0082]

[0083] Step S3. Designing a power angle stability optimization control strategy for each stage of the synchronous machine swing process;

[0084] According to step 2.1, in order to achieve the stable optimization control of the synchronous machine power angle and reduce the power angle variation modulus, the acceleration modulus of the synchronous machine in the first and third stages should be reduced, and the acceleration modulus of the synchronous machine in the second and fourth stages should be increased. That is, the optimization control needs to increase the electromagnetic power output of the synchronous machine in the first and second stages of each swing cycle, and reduce the electromagnetic power output of the synchronous machine in the third and fourth stages, that is:

[0085]

[0086] Wherein, ΔPe is the change in electromagnetic power of the synchronous machine caused by the optimization control in each stage, indicating the impact of the optimization control on the electromagnetic power of the synchronous machine.

[0087] To ensure that the synchronous machine's swing process evolves according to the natural sequence 1-2-3-4-1..., the necessary and sufficient condition is that the sign of the synchronous machine's rotor acceleration is positive in the first and fourth stages, and negative in the second and third stages. Combining these two points, the electromagnetic power constraints for each stage are as follows:

[0088]

[0089] Among them, P m is the mechanical power of the synchronous machine, in pu, which is directly controlled by the prime mover input energy control system, P e is the electromagnetic power of the synchronous machine under normal operation, ΔPe is the change in electromagnetic power of the synchronous machine caused by optimization control in each stage, the unit is pu, which depends on the electrical quantities of each node in the power network (i.e., voltage amplitude and phase angle, etc.).

[0090] The relationship between the synchronous machine rotor angular acceleration and power is as follows:

[0091]

[0092] Among them, P m is the mechanical power of the synchronous machine, unit pu, P e is the electromagnetic power unit pu of the synchronous machine under normal operation, ΔPe is the electromagnetic power change of the synchronous machine caused by optimization control in each stage, unit pu, T J is the inertia time constant of the synchronous machine.

[0093] Combining the above two points, we can know that the constraints of the electromagnetic power variation in each stage are as follows:

[0094]

[0095] Step 4: Analyze the energy interaction between the energy storage and the synchronous machine, and generate correction instructions.

[0096] Step 4.1: Analyze the interaction between energy storage and synchronous machine energy, and determine the indicators to be corrected.

[0097] After energy storage is connected to the power system, the PQ decoupling of energy storage power is performed in the power control module. The active and reactive power absorbed by the energy storage are:

[0098] P=v d i d +vq i q ,Q=v q i d -v d i q

[0099] Where: v d ,v q ,i d ,i q They represent the d-axis voltage, q-axis voltage, d-axis current, and q-axis current, respectively.

[0100] After establishing the local PQ axis with the energy storage terminal voltage as the reference phasor, we have:

[0101] v d =V,v q =0,i d =I d ,i q =I q

[0102] Where: V is the voltage value of the energy storage terminal, I d , I q are the active and reactive currents of energy storage respectively.

[0103] Therefore, the decoupling of the active and reactive power of energy storage can be expressed as:

[0104] P=V×I d ,Q=-V×I q

[0105] Establish the equivalent circuit of the system with energy storage. According to the superposition theorem, the electromagnetic power increment ΔP of the synchronous generator caused by energy storage is e for:

[0106]

[0107] Where: E′ q ∠(δ-β) is the q-axis transient potential phasor of the synchronous generator; E′ q is the transient potential amplitude of the synchronous generator q axis; β is the phase angle of the infinite busbar relative to the energy storage terminal voltage; δ is the phase angle of the synchronous generator relative to the energy storage terminal voltage; I d , I q are respectively the active and reactive currents of energy storage; ΔI e is the current increment of the synchronous generator caused by energy storage; x d is the d-axis transient reactance of the synchronous generator; x T is the transmission line reactance. To more intuitively show the flow of current and power in the system, Figure 3 The equivalent circuit diagram of a single-machine infinite system with energy storage is given.

[0108] ΔP e This paper describes the electrical coupling relationship between energy storage and the electromagnetic power of synchronous generators, specifically the energy interaction between them. By controlling the active current of the energy storage, the electromagnetic power of the synchronous generator is altered, further changing the acceleration of the synchronous generator's operation, thereby adjusting the system's power angle stability. Furthermore, considering that wind turbines in long-distance wind power transmission scenarios are mostly located at the end of long interconnecting lines, the active current behavior has a greater impact on the synchronous generator. Therefore, the present invention can select active current or active power as the specific optimization target.

[0109] Step 4.2: Generate correction instructions according to the characteristics of each swing stage of the synchronous machine.

[0110] Based on the constraints in step 3, optimal control should appropriately reduce the synchronous machine's acceleration modulus in stages 1 and 3, while maximizing it in stages 2 and 4. This maximizes the use of the equipment's controllable capacity and increases the stability of the synchronous machine. According to step 3.1, the acceleration modulus is primarily corrected via active current. Due to PQ decoupling in the power control link, active current can also be corrected directly by correcting active power.

[0111] According to the constraints of the electromagnetic power variation in each stage of step 3, in order to ensure the correct evolution order of the synchronous machine swing process, the output of the optimization control has certain limitations, and its modulus should be less than |P m -P e |. Due to |P m -P e The actual value of | is usually difficult to measure. According to the relationship between the synchronous machine rotor angular acceleration and power in step 3, the acceleration should be proportional to P m -P e Therefore, this method adds a proportional coefficient K according to the acceleration of the synchronous machine swing. p Generate correction instructions proportionally.

[0112] Since the energy storage absorption power is the positive direction of the current in the process of establishing the equivalent circuit, when the additional energy storage power correction instruction in stage 1 is negative, it means that the energy storage is absorbing power. At this time, the active current I d >0, electromagnetic power increment ΔP e >0, which meets the constraint requirement in step 3 that the change in electromagnetic power in stage 1 is positive; when the additional energy storage power correction instruction in stage 3 is positive, it means that the energy storage and the synchronous machine emit power together. At this time, the active current I d <0, electromagnetic power increment ΔP e<0, which meets the constraint requirement in step 3 that the change in electromagnetic power in stage 3 is negative. Therefore, in order to ensure the correctness of the correction instruction, the added proportional coefficient in the additional energy storage power correction instruction in stages 1 and 3 should be -K p .

[0113] In phase 2 and phase 4, under the action of the power correction instruction, the electromagnetic power variation should be made to tend to the positive maximum or negative minimum as much as possible. Considering that the energy storage equipment has a certain limit to its tolerance, the size of the power correction instruction is the power correction extreme value that the energy storage equipment can withstand. The power correction instruction in phase 2 should tend to the negative minimum value. At this time, the energy storage absorbs power, and the active current I d >0, electromagnetic power increment ΔP e >0, which complies with the constraint requirement in step 3 that the change in electromagnetic power in stage 2 is the positive maximum value; the power correction instruction in stage 4 should tend to the positive maximum value. At this time, the energy storage absorbs power, and the active current I d >0, electromagnetic power increment ΔP e >0, which meets the constraint requirement in step 3 that the change in electromagnetic power in stage 2 is a positive maximum value.

[0114] In this embodiment, the PQ decoupling of active power is mainly performed through the PQ control module in DIgSILENT / PowerFactory.

[0115] The power correction instructions are as follows:

[0116]

[0117] Among them: K p represents the proportional coefficient, a represents the acceleration of the system equivalent synchronous machine swing, ΔP min , ΔP max They respectively represent the minimum and maximum power command corrections that the energy storage equipment can withstand.

[0118] The time-varying factors that affect the active current of high-proportion wind power systems are mainly the changes in system power flow and fault status (fault persistence and fault removal) during transient processes. Therefore, the proportionality coefficient K p The tuning process can be summarized as follows: First, the grid power flow information and typical fault sets of the power system are obtained offline, and the acceleration change and unbalanced power P of the synchronous machine rotor during the first swing period are simulated and analyzed under typical fault instability scenarios or scenarios with low stability margin. m -P e After obtaining multiple sets of data, the linear fitting method is used to process the acceleration change and power change into a linear relationship, that is:

[0119]

[0120] in: They are the average values ​​obtained after multiple measurements of unbalanced power and synchronous machine rotor acceleration.

[0121] The power correction limit that energy storage equipment can withstand is generally expressed as the product of the number of parallel energy storage power stations N and the nominal apparent power of the energy storage, that is:

[0122]

[0123] Where: N is the number of parallel energy storage power stations in the system, P st is the nominal apparent power of each energy storage power station.

[0124] In this embodiment, step 4 corresponds to the following Figure 2 In order to verify the effectiveness of the out-of-step oscillation suppression method for a high-proportion wind power system with energy storage participation proposed in this invention, two different control strategies are adopted for electrochemical energy storage for comparison. The two control strategies are as follows:

[0125] Strategy 1: Electrochemical energy storage adopts the traditional vector control strategy, and the power command value during system disturbances and transients is consistent with that during steady-state operation.

[0126] Strategy 2: Based on the traditional vector control strategy, the high-proportion wind power system out-of-step oscillation suppression power control loop with energy storage participation proposed in this invention is added, and the relevant control parameters are set to K p =1000MW·s2 / m,P max =90MW, P min =-90MW.

[0127] Attachment Figure 5 The following is the time variation law of the power angle of each generator in the system under the control of strategy 1. Figure 6 is the time-varying law of the system generator speed under strategy 1 control. Figure 5 and Figure 6 It can be seen that during the system short circuit, the speed of each generator increased rapidly, with generator G1 experiencing the fastest change. After the fault was cleared, the speed of generator G1 continued to increase, causing relative motion with generators G3 and G4. Generator G1 eventually lost transient stability and the system experienced out-of-step oscillation. During this out-of-step oscillation, G1's power angle rapidly fluctuated between -180° and 180°, causing the voltage and power at various points in the system to continuously oscillate, ultimately affecting the normal operation of various devices and, in severe cases, even causing system failure.

[0128] Attachment Figure 7 is the variation law of the system power angle under strategy 2 control. Figure 7It can be seen that after the system short circuit fault occurs and is cleared, the power angle of generator G1 oscillates significantly, but the power angle amplitude gradually decreases after the fault is cleared, and eventually the power angle of G1 returns to its initial value before the fault. The power angles of generators G3 and G4 do not show any obvious instability and remain stable for a period of time after the fault is cleared. Figure 5 、 Figure 6 By comparing the situations where the system loses step oscillation, it can be seen that the control strategy adopted in the present invention is effective in suppressing the loss-of-step oscillation under large disturbance of the system.

[0129] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing out-of-step oscillations in a wind power system with a high proportion of energy storage participation, characterized in that: The steps include: Step S1. Build a power system including wind power access and energy storage participation; Step S2. In the power system, the speed of the energy storage adjacent synchronous machine and the wind farm output power are collected to determine the swing state of the synchronous machine; including the following sub-steps: Step S2.

1. Identify the power angle swing state of the synchronous machine after the power system is disturbed; Step S2.

2. Set the synchronous machine rotor speed and acceleration thresholds, and determine the stage of the synchronous machine swing process by comparing the actual values ​​of the synchronous machine acceleration and speed with the thresholds; Step S2.1 is specifically as follows: According to the rotor speed curve of the synchronous machine's swing process, the swing process of each cycle of the synchronous machine is divided into four stages: when the synchronous machine rotor speed is higher than the synchronous speed, the rotor acceleration process is considered the first stage, and the rotor deceleration process is considered the second stage; when the synchronous machine rotor speed is lower than the synchronous speed, the rotor deceleration process is considered the third stage, and the rotor acceleration process is considered the fourth stage; According to the second-order integral relationship of rotor acceleration-rotor rotation speed-rotor position / power angle during the synchronous machine swing process, it can be deduced that: The superscript indicates the swing period of the parameter, and the subscript indicates the swing stage of the synchronous machine in each period. 、 are the maximum and minimum values ​​of the internal power angle change modulus in each cycle, and a is the rotor equivalent constant acceleration in each stage; Step S2.2 is specifically as follows: The speed is expanded from the stable equilibrium point to the set synchronous machine rotor speed and acceleration threshold range, and the minimum and maximum speeds are recorded as 、 The minimum and maximum values ​​of the acceleration range are 、 After extracting the synchronous machine speed and acceleration and comparing them with the set value, the swing stage of the synchronous machine can be determined and output; Step S3. Design an optimization control strategy for the power angle stability of each stage of the synchronous machine swing process; the optimization strategy is: the constraints on the electromagnetic power variation at each stage are as follows: in, P m is the mechanical power of the synchronous machine, in pu, which is directly controlled by the prime mover input energy control system. P e is the electromagnetic power of the synchronous machine under normal operation, The change in electromagnetic power of the synchronous machine due to optimization control in each stage, in units of pu, depends on the electrical quantity of each node in the power network; Step S4: Analyze the energy interaction between the energy storage and the synchronous machine and generate a correction instruction; including the following sub-steps: Step S4.

1. Analyze the interaction between energy storage and synchronous machine energy to determine the indicators to be corrected; Step S4.

2. Generate correction instructions based on the characteristics of each swing phase of the synchronous machine; the power correction instructions are as follows: in: represents the proportionality coefficient, represents the acceleration of the system equivalent synchronous machine swing, 、 They respectively represent the minimum and maximum power command corrections that the energy storage equipment can withstand; The proportional coefficient adjustment process is as follows: First, the grid flow information and typical fault sets of the power system are obtained offline, and the acceleration change and unbalanced power of the synchronous machine rotor during the first swing period are simulated and analyzed in typical fault instability scenarios or scenarios with low stability margin. P m -P e After obtaining multiple sets of data, the linear fitting method is used to process the acceleration change and power change into a linear relationship, that is: in: 、 are the average values ​​obtained after multiple measurements of unbalanced power and synchronous machine rotor acceleration; The minimum and maximum power command corrections that the energy storage equipment can withstand are: in: N is the number of parallel energy storage power stations in the system, is the nominal apparent power of each energy storage power station.

2. The method for suppressing out-of-step oscillation of a wind power system with a high proportion of energy storage participation according to claim 1 is characterized in that: In step S2.2, the synchronous machine swing process is at the following stages: Stage 1. Acceleration a ≥ , rotor speed ≥ ; Phase 2. Acceleration a ≤ , rotor speed ≥ ; Stage 3. Acceleration a ≥ , rotor speed ≤ ; Stage 4. Acceleration a ≤ , rotor speed ≤ .

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