CN115441477A - A method for suppressing out-of-step oscillation of high-proportion wind power system with energy storage participation - Google Patents

Abstract

The invention discloses a method for suppressing step-out oscillation of a high-proportion wind power system with participation of energy storage, which comprises the following steps of: s1, building an electric power system with wind power access and energy storage participation; s2, collecting the rotating speed of an energy storage adjacent synchronous machine and the output power of a wind power plant in the power system, and judging the swing state of the synchronous machine; s3, designing a power angle stability optimization control strategy of each stage in the swing process of the synchronous machine; and S4, analyzing an energy interaction relation between the energy storage and the synchronous machine to generate a correction instruction. Under the condition of high-proportion wind power access, judging the swing state of the synchronous machine, determining the power angle stability optimization strategy of the stage and each stage through the comparison of an actual value and a threshold value, and generating a correction instruction; the electromagnetic power increment of the synchronous generator is controlled by adjusting active current or active power through emergency control, so that the stability of the power angle of the system under different operating characteristics in different stages is improved, and the effect of inhibiting out-of-step oscillation is achieved.

Description

A method for suppressing out-of-step oscillation of a high-ratio wind power system with energy storage participation

technical field

The invention relates to the technical field of transient power angle stability control of a power system under a high proportion of new energy access, in particular to a method for suppressing out-of-step oscillation of a power system when a high proportion of wind power is connected with energy storage.

Background technique

With the large-area interconnection of the power grid, it brings greater challenges to the stable operation of the system. The most serious damage to stability is the out-of-step oscillation of the system. Once the out-of-step oscillation occurs in the system, the safety and stability of the system will be affected. Serious damage, and even lead to large-scale power outages. In order to prevent such serious accidents in the power grid, electric power workers have proposed the third line of defense of the power system. When out of step, disassembling the out-of-step section is the most basic stability control measure in the third line of defense, which can effectively eliminate the system out-of-step oscillations.

In recent years, both energy storage and wind turbines have developed rapidly, and will play a vital role in the future power grid. As a renewable clean energy, the proportion of wind power resources in the power grid has been increasing in recent years. Wind turbines are often located at the end of the power network, the grid frame is relatively weak, and the voltage support capability is poor. network. At the same time, the grid connection of high-penetration wind power will reduce the inertia of the original power system, making the stability control process of the power system after out-of-step oscillation face new challenges. In the high-penetration wind power grid-connected scenario, how to prevent the further expansion of system out-of-step oscillation after the grid is disturbed has very important practical significance. At the same time, in the current large power grid, the traditional synchronous generator is still the main power generation unit, and the synchronous generator power generation and new energy power generation will coexist for a long time. The electromagnetic power of the synchronous generator and the active power of the energy storage have a coupling relationship physically, that is, there is an energy interaction relationship between the synchronous generator and the energy storage. By using this energy interaction, the energy storage can quickly adjust the electromagnetic power of the synchronous generator by quickly adjusting the active power output or absorbed by itself, and then adjust the operating dynamics of the synchronous generator after the system disturbance, and finally improve the power system. Angular stability.

At present, there have been studies combined with the actual power grid to simulate and analyze the influence of factors such as wind farm access mode and wind power reactive power control mode on the system power angle stability. The analysis of the impact of a high proportion of wind power access on the actual power grid out-of-step oscillation and the related decoupling measures are relatively few. In terms of using energy storage to improve transient power angle stability, based on the idea of synchronous generator and energy storage synergistic interaction, some scholars have also carried out research on energy storage controllers based on feedback linearization, but for the energy storage and synchronous generator energy Interactions were not analyzed in detail for modeling. On the other hand, considering the highly nonlinear and uncertain system dynamics in the actual power system, 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, transmission line Impedance, etc.) are often difficult to obtain, and it is also difficult to achieve the ideal stable control effect in the actual multi-machine power system.

Contents of the invention

Based on this, aiming at the transient stability problem existing in the power system under the current high-proportion wind power access scenario, the present invention proposes a method for suppressing out-of-step oscillation of a high-proportion wind power system with the participation of energy storage.

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

A method for suppressing out-of-step oscillation of a high-ratio wind power system involving energy storage, comprising the following steps:

Step S1. Build a power system including wind power access and energy storage;

Step S2. In the power system, collect the rotational speed of the synchronous machine adjacent to the energy storage and the output power of the wind farm, and judge the swing state of the synchronous machine;

Step S3. Designing an optimization control strategy for power angle stability at each stage of the synchronous machine swing process;

Step S4. Analyzing the energy interaction relationship between the energy storage and the synchronous machine, and generating a correction instruction.

Further, the step S2 includes 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 rotor speed and acceleration threshold of the synchronous machine, and determine the phase of the synchronous machine swing process by comparing the actual acceleration and speed of the synchronous machine with the threshold.

Further, the step S2.1 is specifically:

According to the rotor speed curve in the swing process of the synchronous machine, the swing process of each cycle of the synchronous machine is divided into four stages: when the rotor speed of the synchronous machine 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. The second stage; when the rotor speed of the synchronous machine 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;

According to 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:

Among them, the superscript indicates the swing period of the parameter, the subscript indicates the swing stage of the synchronous machine in each period, |Δδ _max |, |Δδ _min | are the maximum and minimum values of the power angle change modulus in each period, respectively, a is the equivalent constant acceleration of the rotor in each stage.

Further, the step S2.2 is specifically:

Extend the rotational speed from the stable equilibrium point to the set rotor rotational speed and acceleration threshold range of the synchronous machine. The minimum and maximum rotational speeds are denoted as ω _dmin and ω _dmax respectively, and the minimum and maximum acceleration ranges are respectively a _dmin and a _dmax . After extracting the rotational speed and acceleration of the synchronous machine and comparing it with the set value, the current swing stage of the synchronous machine can be judged and output.

Further, in the step S2.2, the stages of the synchronous machine swing process are as follows:

Stage 1. Acceleration a≥a _dmax , rotor speed ω≥ω _dmax ;

Stage 2. Acceleration a≤a _dmax , rotor speed ω≥ω _dmax ;

Phase 3. Acceleration a≥a _dmax , rotor speed ω≤ω _dmax ;

Stage 4. Acceleration a≤a _dmax , rotor speed ω≤ω _dmax .

Further, the optimization strategy in the step S3 is: the constraint conditions of the electromagnetic power variation in each stage are as follows:

Among them, P _m is the mechanical power of the synchronous machine, the unit is pu, which is directly controlled by the prime mover input energy control system, Pe is the electromagnetic power of the synchronous machine under normal operation, _ΔPe is the optimal control generated in each stage The electromagnetic power variation of the synchronous machine, unit pu, depends on the electrical quantity of each node in the power network.

Further, the step S4 includes the following sub-steps:

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

Step S4.2. According to the characteristics of each swing stage of the synchronous machine, respectively generate correction instructions.

Further, the power correction command is as follows:

Among them: K _p represents the proportional coefficient, a represents the acceleration of the system equivalent synchronous machine swing, ΔP _min and ΔP _max represent the minimum and maximum power command corrections that the energy storage equipment can withstand, respectively.

Further, the process of setting the proportional coefficient is as follows:

Firstly, the grid power flow information and typical fault sets of the power system are obtained offline, and in the typical fault instability scene or the scene with a low stability margin, the acceleration change and unbalanced power P _m -P during the first swing of the synchronous machine rotor are simulated and analyzed _e , after obtaining multiple sets of data, use the linear fitting method to process the acceleration change and power change into a linear relationship, that is:

分别为多次测量不平衡功率和同步机转子加速度后得到的平均值。in:

are the average values obtained after several measurements of the unbalanced power and the rotor acceleration of the synchronous machine, respectively.

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

Among them: N is the number of parallel energy storage power stations in the system, and P _st is the nominal apparent power of each energy storage power station.

Compared with prior art, the beneficial effect that the present invention produces:

1. At present, the focus of the existing technology to deal with the system transient power angle stability challenge brought by large-scale wind power grid connection is to design the specific transient optimization control of wind turbines, but the current transient optimization control research of wind turbines does not pay enough attention to the active current of wind turbines , the present invention aims at the high-proportion wind power access scenario where the system transient power angle stability is more severe, and comprehensively uses the related theoretical analysis results of wind turbines, synchronous machines and energy storage to design a specific active current transient optimization control strategy, which can Realize long-distance transmission of wind power.

2. Compared with the existing technology that adjusts the system’s transient operating state through wind power, the present invention divides the swing process of the synchronous machine in each cycle, and when judging the swing state of the synchronous machine, it only needs to detect the rotor speed or Grid-connected bus voltage and frequency, on the one hand, it is easy to judge the operating state of the system, on the other hand, the required detection parameters are easy to obtain through the PMU, avoiding the complicated parameter acquisition and calculation process.

3. When the present invention utilizes energy storage emergency control to generate power correction commands, its control strategy only needs to add a control loop without changing other control modules, making the control process easy to implement.

4. The emergency control of energy storage in the present invention is only put into operation after the power system suffers a large disturbance, and its working process only utilizes the remaining capacity of the energy storage, and does not affect other uses of the energy storage module when the power system is in a steady state (such as peak shaving and filling). Valley, etc.) have an impact and expand the application scenarios of energy storage.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment, in the accompanying drawing:

Fig. 1 is a diagram of the improved four-machine two-region system with the participation of energy storage under the connection of wind power in the present invention.

Fig. 2 is a control block diagram of the implementation of the out-of-step oscillation suppression method for a high-ratio wind power system based on energy storage participation proposed by the present invention.

Fig. 3 is an equivalent circuit diagram of a stand-alone infinite system with energy storage.

Figure 4 shows the generation process of power correction commands in each synchronous machine swing phase.

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

Figure 6 shows the time-varying characteristics of the rotational speed of each generator in the system based on the traditional energy storage vector control strategy.

Fig. 7 shows the time-varying characteristics of the power angle of each generator in the system after adopting the out-of-step oscillation suppression method based on energy storage participation in a high-ratio wind power system proposed by the present invention on the basis of the traditional energy storage control strategy.

Specific implementation method

In order to make the purpose, technical solution and advantages of the present invention more clear, 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 here are only used to explain the present invention, not to limit the present invention.

Aiming at the transient stability problems existing in the power system under the current high-proportion wind power access scenario, the present invention proposes a method for suppressing out-of-step oscillation of the high-proportion wind power system with the participation of energy storage. Wherein the technical problem to be solved by the present invention can be summarized as follows:

(1) In the scenario of long-distance wind power transmission, the system faces severe challenges of transient power angle stability. The relevant theoretical analysis and practical operation experience of power system transient power angle stability show that the increase of transmission distance and transmission capacity will weaken the transient power angle stability of the system; on the other hand, due to the transmission capacity of transmission lines in actual operation Most of them are relatively tense, and the output 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 of wind power access, it is necessary to design a reasonable power angle stability optimization control strategy to realize long-distance wind power transmission.

(2) In the scenario of a high proportion of wind power access, the research on power system oscillations mostly focuses on the impact of wind power access on the low-frequency oscillation of the system. stable situation; and for the power system under the access of wind power, there are few studies on out-of-step oscillation suppression methods when the power system suffers from large disturbances, so the present invention needs to discuss the transient stability changes of the power system when the power system is subjected to large disturbances under the connection of wind power. Quantitative and qualitative analysis of machine transient swing process.

(3) In the existing technology, most of the researches on the out-of-step oscillation of the power system caused by large-scale wind power increase the transient stability of the power system by changing the type of wind turbines and adjusting the output of wind power. There are complex coordination problems in the power transmission process, and The parameter tuning process is complicated. Considering that the energy storage not only has good active power control capability, but also can make a certain contribution 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, and at the same time, the parameter selection process is more efficient. for brevity.

The invention discloses a method for suppressing out-of-step oscillation of a high-ratio wind power system with energy storage participation. In the scenario of high-ratio wind power access, first collect the speed of the synchronous generator adjacent to the energy storage or the bus voltage frequency, set the acceleration and speed thresholds, and judge In the swing state of the synchronous machine, the stage and the power angle stability optimization strategy of each stage are determined by comparing the actual value with the threshold value, and the correction command is generated; the electromagnetic power increment of the synchronous generator is controlled by adjusting the active current or active power through emergency control, and then Realize the improvement of the power angle stability of the system under different operating characteristics in different stages, and achieve the effect of suppressing out-of-step oscillation.

In order to test the feasibility of the high-ratio wind power system out-of-step oscillation suppression method with energy storage participation proposed in the present invention, a system based on the classic four-machine two-zone system was established in D IgS I LENT/PowerFactory, which includes wind power access and energy storage participation. The power system, its structure is shown in Figure 1. Since the classic four-machine two-zone system is a typical long tie-line heavy-load weak grid, the wind power must be sent to the load center at the remote No. 9 bus through the long tie-line. Therefore, this test system is a typical long-distance wind power transmission Scenarios that meet the applicable conditions for optimal control.

In the improved four-machine two-zone system, the No. 2 synchronous generator of the original four-machine two-zone system is replaced by the DF IG wind farm. The wind farm consists of 500 1.5MW wind turbines, which are connected to the grid in parallel through two-stage step-up transformers. The energy storage device and the wind turbine are jointly connected to the bus 6 through the common coupling point, which is used to optimize the transient stability of the system. The number of energy storage devices connected in parallel is N=3, and the nominal apparent power of each energy storage device is 30MVA, that is, the total capacity of the energy storage device is 90MVA. In steady state operation, the total load of the system is 1800MW, the wind farm generates 500MW of active power, and the electrochemical energy storage equipment has no active power output. The wind power penetration rate of the system is about 27.8%.

The specific steps of using this method to suppress the out-of-step oscillation of a high-ratio wind power system with energy storage participation are as follows:

Step S1. Build a power system including wind power access and energy storage;

Step S2. In the power system, collect the rotational speed of the synchronous machine adjacent to the energy storage and the output power of the wind farm, and judge the swing state of the synchronous machine;

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

After the power system suffers a large disturbance, according to the rotor speed curve of the synchronous machine swing process, the swing process of each cycle of the synchronous machine can be divided into four stages: When the rotor speed of the synchronous machine is higher than the synchronous speed, the rotor acceleration process is regarded as the first In the first stage, the rotor deceleration process is regarded as the second stage; when the rotor speed of the synchronous machine 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.

In this embodiment, the disturbance of the power system is set as a three-phase short-circuit fault, the fault location is located on the No. 8 bus, and is removed by isolating the fault line, and the fault lasts for 0.2 seconds.

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

Among them, the superscript indicates the swing period of the parameter, the subscript indicates the swing stage of the synchronous machine in each period, |Δδ _max |, |Δδ _min | are the maximum and minimum values of the power angle change modulus in each period, respectively, a is the equivalent constant acceleration of the rotor in each stage.

Step 2.2: Set the rotor speed and acceleration threshold of the synchronous machine, and determine the stage of the synchronous machine's swing process by comparing the actual acceleration and speed of the synchronous machine with the threshold.

After the sway process of the synchronous machine is divided into four stages, the variation law of the acceleration and rotational speed of the synchronous machine in each stage can be summarized as follows:

Among them, the rotational speed of the stable equilibrium point is taken as 1 (per unit value). Considering the actual operation of the system, the speed threshold is extended from the stable equilibrium point to a small range near the equilibrium point, where the rotor speed and acceleration thresholds set in step 2.2 are the above and below the variation range of the mentioned parameters near the stable equilibrium point Limit value, usually the value of this range is determined according to engineering experience: the minimum and maximum variation range of the acceleration a is usually taken as ±0.004, and the minimum and maximum variation range of the rotor speed is usually taken as ±1.004. Its minimum and maximum values are recorded as ω _dmin and ω _dmax respectively. The minimum and maximum values of the acceleration range are a _dmin and a _dmax , and the actual acceleration value must be outside this range to ensure the normal operation of the system. After extracting the rotational speed and acceleration of the synchronous machine and comparing it with the set value, the current swing stage of the synchronous machine can be judged and output.

In this embodiment, the control block diagram realized by the out-of-step oscillation suppression method based on the participation of energy storage in a high-ratio wind power system proposed by the present invention is shown in Fig. 2 . The completed part of step 1 is the generator power angle swing state identification part in Fig. 2 . First, the rotor speed ω or the bus voltage frequency f of the energy storage adjacent synchronous unit G1 is collected as input to judge the swing stage of the synchronous machine.

The rotor acceleration of the synchronous machine is obtained by the differential link of the rotor speed. Considering the engineering practice, the differential link is often difficult to realize. Therefore, the inertia link is adopted in the present invention, namely:

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

In the selection module of the present embodiment, the status of the synchronous machine swing stage is judged as follows:

Step S3. Designing an optimization control strategy for power angle stability at each stage of the synchronous machine swing process;

According to step 2.1, in order to realize the optimal control of synchronous machine power angle stability and reduce the modulus of power angle change, the modulus of the acceleration of the synchronous machine in the first and third stages should be reduced, and the acceleration of the synchronous machine in the second and fourth stages should be increased The modulus value of , that is: optimal control needs to increase the electromagnetic power output by the synchronous machine in the first and second stages of each swing cycle, and reduce the electromagnetic power output by the synchronous machine in the third and fourth stages, namely:

Among them, ΔPe is the electromagnetic power variation of the synchronous machine due to the optimal control in each stage, indicating the impact of the optimal control on the electromagnetic power of the synchronous machine.

In order to ensure that the swing process of the synchronous machine evolves according to the natural order 1-2-3-4-1..., the necessary and sufficient condition is that the signs of the rotor acceleration of the synchronous machine in the first and fourth stages are positive, and the signs of the acceleration in the second and third stages is negative. Combining the above two points, the electromagnetic power constraints at each stage can be obtained as follows:

Among them, P _m is the mechanical power of the synchronous machine, the unit is pu, which is directly controlled by the prime mover input energy control system, Pe is the electromagnetic power of the synchronous machine under normal operation, _ΔPe is the optimal control generated in each stage The electromagnetic power variation of the synchronous machine, unit pu, depends on the electrical quantity of each node in the power network (ie, voltage amplitude and phase angle, etc.).

The relationship between the rotor angular acceleration and power of a synchronous machine is as follows:

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 variation of the synchronous machine due to optimal control in each stage, the unit pu , T _J is the inertial time constant of the synchronous machine.

Based on the above two points, we can see that the constraints on the electromagnetic power variation in each stage are as follows:

Step 4: Analyze the energy interaction relationship between the energy storage and the synchronous machine, and generate a correction instruction.

Step 4.1, analyze the interaction relationship between energy storage and synchronous machine energy, and determine the index to be corrected.

After the energy storage is connected to the power system, the PQ decoupling of the energy storage power is performed in the power control module, and the active and reactive power absorbed by the energy storage is:

P＝v _d i _d +v _q i _q , Q＝v _q i _d -v _d i _q

Among them: v _d , v _q , i _d , i _q represent d-axis voltage, q-axis voltage, d-axis current and q-axis current respectively.

After establishing the local PQ axis with the energy storage terminal voltage as the reference phasor, there are:

v _d =V, v _q =0, i _d =I _d , i _q =I _q

Among them: V is the voltage value of the energy storage terminal, I _d and I _q are the active and reactive currents of the energy storage respectively.

Therefore, after decoupling the active and reactive power of energy storage, it can be expressed as:

P=V×I _d , Q=-V×I _q

The equivalent circuit of the system with energy storage is established. According to the superposition theorem, the electromagnetic power increment ΔP _e of the synchronous generator caused by energy storage is:

Among them: E′ _q ∠(δ-β) is the q-axis transient potential phasor of the synchronous generator; E′ _q is the q-axis transient potential amplitude of the synchronous generator; β is the infinite bus relative to the energy storage terminal voltage Phase angle; δ is the phase angle of the synchronous generator relative to the energy storage terminal voltage; I _d and I _q are the active and reactive currents of the energy storage respectively; ΔI _e is the current increment of the synchronous generator caused by the energy storage; x _d is the d-axis transient reactance of the synchronous generator; x _T is the transmission line reactance. In order to show the flow of current and power in the system more intuitively, Figure 3 shows the equivalent circuit diagram of a stand-alone infinite system with energy storage.

ΔP _e describes the electrical coupling relationship between the energy storage and the electromagnetic power of the synchronous generator, that is, the energy interaction relationship between the energy storage and the synchronous generator. By controlling the active current of the energy storage, the electromagnetic power of the synchronous machine is changed, and the acceleration of the synchronous machine is further changed, thereby adjusting the power angle stability of the system. At the same time, considering that most of the fans in the long-distance transmission of wind power are located at the end of the long connection line of the transmission channel, the active current behavior has a stronger influence on the synchronous machine. Therefore, the present invention can choose active current or active power as the specific optimization object.

Step 4.2, according to the characteristics of each swing stage of the synchronous machine, respectively generate correction instructions.

According to the constraints in step 3, the optimization control should properly reduce the modulus of the acceleration of the synchronous machine in the first and third stages, and maximize the modulus of the acceleration of the synchronous machine in the second and fourth stages to maximize Make full use of the controllable capacity of the equipment to maximize the stability of the synchronous machine. According to step 3.1, it can be seen that the modulus value of the acceleration is mainly corrected by the active current. Since the PQ decoupling is carried out in the power control link, the correction of the active current can also be carried out directly by correcting the active power.

According to the constraint conditions of the electromagnetic power variation in each stage of step 3, in stage 1 and stage 3, in order to ensure the correct evolution sequence of the synchronous machine swing process, there is a certain limit on the output of the optimal control, and its modulus should be less than |P _m -P _e |. Since the actual value of |P _m -P _e | is usually difficult to measure, according to the relationship between the rotor angular acceleration and power of the synchronous machine in step 3, the acceleration should be proportional to the value of P _m -P _e . Therefore, in this method, according to the acceleration of the synchronous machine swing, a proportional coefficient K _p is added to generate a correction command.

Because in the process of establishing the equivalent circuit, the energy storage absorbs the power as the positive direction of the current. When the phase 1 additional energy storage power correction command is a negative value, it means that the energy storage is absorbing power. At this time, the active current I _d > 0, and the electromagnetic power increment ΔP _e > 0, which is consistent with the change in the phase 1 electromagnetic power in step 3 is a positive constraint requirement; when the phase 3 additional energy storage power correction command is a positive value, it means that the energy storage and the synchronous machine send out power together. At this time, the active current I _d <0, and the electromagnetic power increment ΔP _e <0, conforming to the step In 3, the constraint requirement for the negative value of electromagnetic power variation in stage 3. Therefore, in order to ensure that the correction command is correct, in the additional energy storage power correction command in stages 1 and 3, the added proportional coefficient should be -K _p .

In stage 2 and stage 4, under the action of the power correction command, the variation of electromagnetic power should tend to the positive maximum value or the negative minimum value as much as possible. Considering that the bearing capacity of energy storage equipment has a certain limit, the size of the power correction command is the extreme value of power correction that the energy storage equipment can bear. Among them, the power correction command in stage 2 should tend to the negative minimum value. At this time, the energy storage absorbs power, the active current I _d >0, and the electromagnetic power increment ΔP _e >0, which is consistent with the positive pole of the electromagnetic power change in stage 2 in step 3. Large value constraint requirements; the power correction command in stage 4 should tend to the positive maximum value. At this time, energy storage absorbs power, active current I _d >0, and electromagnetic power increment ΔP _e >0, which is consistent with the phase 2 electromagnetic power in step 3. The constraint requirement that the power variation is a positive maximum value.

In this embodiment, the PQ decoupling of active power is mainly performed through the PQ control module in D IgS I LENT/PowerFactory.

The power correction command is as follows:

Among them: K _p represents the proportional coefficient, a represents the acceleration of the system equivalent synchronous machine swing, ΔP _min and ΔP _max represent the minimum and maximum power command corrections that the energy storage equipment can withstand, respectively.

The time-varying factors that affect the active current of a high-ratio wind power system are mainly changes in system power flow and fault status (fault persistence and fault removal) during the transient process. Therefore, the setting process of the proportional coefficient _Kp can be summarized as follows: First, obtain the power system offline grid power flow information and typical fault sets, and in typical fault instability scenarios or low stability margin scenarios, simulate and analyze the acceleration change and unbalanced power P _m -P _e during the first swing of the rotor of the synchronous machine, and obtain multiple sets of After the data, the linear fitting method is used to process the acceleration change and the power change into a linear relationship, that is:

分别为多次测量不平衡功率和同步机转子加速度后得到的平均值。in:

are the average values obtained after several measurements of the unbalanced power and the rotor acceleration of the synchronous machine, respectively.

The power correction limit borne by energy storage equipment is generally expressed by the product of the number N of parallel energy storage power stations and the nominal apparent power of the energy storage, namely:

Among them: N is the number of parallel energy storage power stations in the system, and P _st is the nominal apparent power of each energy storage power station.

In this embodiment, step 4 corresponds to the control module for generating the correction instruction in FIG. 2 . In order to verify the effectiveness of the out-of-step oscillation suppression method for high-ratio wind power systems with energy storage participation proposed in the present invention, two different control strategies are used for electrochemical energy storage for comparison. The two control strategies are as follows:

Strategy 1: Electrochemical energy storage adopts the traditional vector control strategy, and the power command value during the system disturbance and transient state is consistent with the steady state operation.

Strategy 2: On the basis of the traditional vector control strategy, add the out-of-step oscillation suppression power control loop of the high proportion wind power system with the participation of energy storage proposed by the present invention, and set the relevant control parameters as K _p =1000MW·s2/m, P _max = 90 MW, P _min = -90 MW.

Figure 5 shows the power angle of each generator in the system changing with time under the control of strategy 1, and Figure 6 shows the changing law of the system generator speed with time under the control of strategy 1. It can be seen from Figure 5 and Figure 6 that when the system is short-circuited, the speed of each generator increases rapidly, and the speed of generator G1 changes the fastest; after the fault is cleared, the speed of generator G1 continues to increase, which is the same as that of generator G3. Relative motion occurs between generator G1 and G4, the generator G1 eventually loses its transient stability, and the system undergoes out-of-step oscillation. During the out-of-step oscillation, the power angle of G1 changes rapidly between -180° and 180°, which causes the voltage and power of each point in the system to continuously oscillate, eventually affecting the normal operation of each device, and even causing the system to collapse in severe cases.

Accompanying drawing 7 is the change rule of the power angle of the system under the control of strategy 2. It can be seen from Figure 7 that after the system short-circuit fault occurs and is cleared, the power angle of generator G1 obviously oscillates, but after the fault is cleared, the amplitude of the power angle gradually decreases, and finally the power angle of G1 returns to the initial value before the fault, and the power angle of the generator There is no obvious instability in the power angles of G3 and G4, and they all remain stable after a period of time when the fault is cleared. Compared with the situation of out-of-step oscillation in the system shown in Fig. 5 and Fig. 6, it can be seen that the control strategy adopted in the present invention is effective in suppressing out-of-step oscillation under large disturbance of the system.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. A high-proportion wind power system out-of-step oscillation suppression method with participation of energy storage is characterized by comprising the following steps:

s1, building an electric power system with wind power access and energy storage participation;

s2, collecting the rotating speed of an energy storage adjacent synchronous machine and the output power of a wind power plant in the power system, and judging the swing state of the synchronous machine;

s3, designing a power angle stability optimization control strategy of each stage in the swing process of the synchronous machine;

and S4, analyzing an energy interaction relation between the energy storage and the synchronous machine to generate a correction instruction.

2. The method for suppressing step-out oscillation of a high-proportion wind power system with participation of stored energy according to claim 1, wherein the step S2 comprises the following substeps:

s2.1, identifying the swing state of a power angle of the synchronous machine after the power system is disturbed;

and S2.2, setting the rotating speed and the acceleration threshold of the rotor of the synchronous machine, and determining the swing process stage of the synchronous machine by comparing the actual values of the acceleration and the rotating speed of the synchronous machine with the threshold.

3. The method for suppressing the out-of-step oscillation of the high-proportion wind power system with participation of stored energy according to claim 2, wherein the step S2.1 specifically comprises the following steps:

according to the rotor speed curve of the swing process of the synchronous machine, the swing process of the synchronous machine in each period is divided into four stages: when the rotating speed of the rotor of the synchronous machine is higher than the synchronous speed, the acceleration process of the rotor is regarded as a first stage, and the deceleration process of the rotor is regarded as a second stage; when the rotating speed of the rotor of the synchronous machine is lower than the synchronous speed, the rotor deceleration process is regarded as a third stage, and the rotor acceleration process is regarded as a fourth stage;

according to the second-order integral relation of rotor acceleration, rotor rotation speed, rotor position and power angle in the swing process of the synchronous machine, the following can be obtained:

wherein, the superscript represents the swing cycle of the parameter, the subscript represents the swing phase of the synchronous machine in each cycle, | Δ δ _max |、|Δδ _min And l is respectively the maximum and minimum values of the power angle change module value in each period, and a is the equivalent normal acceleration of the rotor in each stage.

4. The method for suppressing the out-of-step oscillation of the high-proportion wind power system with participation of stored energy according to claim 2, wherein the step S2.2 is specifically as follows:

extending the rotation speed from a stable equilibrium point toThe set rotating speed and acceleration threshold range of the rotor of the synchronous machine, and the minimum value and the maximum value of the rotating speed are respectively marked as omega _dmin 、ω _dmax The minimum and maximum values of the acceleration range are a _dmin 、a _dmax After the rotating speed and the acceleration of the synchronous machine are extracted, the rotating speed and the acceleration are compared with set values, and then the swing stage of the current synchronous machine can be judged and output.

5. The method for suppressing step-out oscillation of a high-proportion wind power system with participation of stored energy according to claim 4, wherein in the step S2.2, the swing process of the synchronous machine is in the following stage:

stage one, acceleration a is more than or equal to a _dmax The rotor speed omega is not less than omega _dmax ；

Stage two, acceleration a is less than or equal to a _dmax The rotor speed omega is not less than omega _dmax ；

Stage three, acceleration a is more than or equal to a _dmax The rotation speed omega of the rotor is less than or equal to omega _dmax ；

Stage four, acceleration a is less than or equal to a _dmax The rotor speed omega is less than or equal to omega _dmax 。

6. The method for suppressing the out-of-step oscillation of the high-proportion wind power system with participation of stored energy according to claim 1, wherein the optimization strategy in the step S3 is as follows: the constraint conditions of the electromagnetic power variation of each stage are as follows:

wherein, P _m For synchronizing mechanical power of machines in p.u., directly controlled by a prime mover input energy control system, P _e For the electromagnetic power of the synchronous machine under the normal operation condition, Δ Pe is the electromagnetic power variation of the synchronous machine generated by performing optimization control in each stage, and the unit is p.u., and depends on the electrical quantity of each node in the power network.

7. The method for suppressing step-out oscillation of a high-proportion wind power system with participation of stored energy according to claim 1, wherein the step S4 comprises the following substeps:

s4.1, analyzing the interaction relation between the energy storage and the synchronous energy, and determining an index to be corrected;

and S4.2, respectively generating correction instructions according to the characteristics of each swing stage of the synchronous machine.

8. The method for suppressing step-out oscillation of a high-proportion wind power system with participation of stored energy according to claim 7,

the power correction command is as follows:

wherein: k _p Expressing the proportionality coefficient, a the acceleration of the system isodyne swing, Δ P _min 、ΔP _max Representing the minimum and maximum power command corrections, respectively, that the energy storage equipment can withstand.

9. The method for suppressing step-out oscillation of a high-proportion wind power system with participation of stored energy according to claim 8, wherein the scaling factor setting process is as follows:

firstly, net rack tide information and a typical fault set of a power system are acquired off line, and acceleration change and unbalanced power P during rotor head swing of a synchronous machine are simulated and analyzed in a typical fault instability scene or a scene with low stability margin _m -P _e After acquiring multiple groups of data, processing the acceleration variation and the power variation into a linear relation by adopting a linear fitting method, namely:

wherein:

the average values are obtained after the unbalance power and the synchronous machine rotor acceleration are measured for multiple times respectively.

10. The method for suppressing step-out oscillation of a high-proportion wind power system participating in energy storage according to claim 8, wherein the minimum and maximum power command corrections that the energy storage equipment can bear are:

wherein: n is the number of energy storage power stations connected in parallel in the system, P _st The nominal apparent power of each energy storage plant.

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