Additional control method of variable-speed wind turbine generator for enhancing system synchronization stability

Abstract

The invention discloses a variable-speed wind turbine generator additional control method for enhancing system synchronization stability, which comprises the following steps: S1, selecting a plurality of load nodes in a power system, respectively setting power disturbance, and collecting frequency data of all the nodes and frequency data of a variable-speed wind turbine generator within a period of time; calculating a system inertia center frequency according to the frequency data of the generator set; calculating relevancy according to the frequency data of all the nodes and the corresponding system inertia center frequency so as to determine a system inertia center node; s2, calculating a self-adaptive power modulation coefficient according to the frequency corresponding to the inertia center node of the system, the grid-connected node frequency of the variable-speed wind turbine generator and the operation state of the variable-speed wind turbine generator; and S3, calculating the additional power modulation quantity of the variable-speed wind turbine generator according to the self-adaptive power modulation coefficient so as to carry out an additional control strategy. According to the invention, the number of measurement signals required by transient stability control of the variable-speed wind turbine generator can be greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of logistics and transportation, and in particular relates to an additional control method for a variable-speed wind turbine set for enhancing system synchronization stability. Background Art

[0002] With the continuous increase in system penetration, the impact of wind power grid connection on system synchronization stability is becoming increasingly significant. Variable Speed ​​Wind Turbine (VSWT) based on Voltage Source Converter (VSC) generally adopts Maximum Power Point Tracking (MPPT) control strategy to improve wind energy utilization, but this control strategy will cause variable speed wind turbines to be unable to share the system unbalanced power in transient processes like synchronous generators, which will lead to the deterioration of system synchronization stability.

[0003] Variable speed wind turbines have flexible power modulation capabilities. In the dynamic process, their output power can be quickly adjusted through additional control to increase the system synchronization stability. Analysis through transient energy function is a major method for analyzing system synchronization stability and designing control strategies to improve system synchronization, and is widely used in the design of additional stability control for wind turbines.

[0004] However, the control strategy designed based on the transient energy function requires real-time measurement and transmission of the frequencies of all synchronous generators in the system to calculate the system center of inertia (COI) frequency, which makes the project implementation difficult. In addition, the variable-speed wind turbine mainly completes functional modulation by calling the rotational kinetic energy stored in the wind turbine rotor during the transient process. Since the wind turbine rotor kinetic energy is affected by the operating state of the wind turbine, its modulation capacity is limited by the operating state of the variable-speed wind turbine, that is, the modulation capacity of the unit under different operating states is also different, which easily leads to over-modulation of the wind turbine. Summary of the invention

[0005] In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a practical variable speed wind turbine power control method to overcome the shortcomings and deficiencies of the existing variable speed wind turbine synchronous stability control method designed based on transient energy function, such as the large number of measurement signals and the possible over-modulation of the variable speed wind turbine. In view of the shortcomings of the large number of measurement signals, the system inertia center node frequency is approximately replaced by the system inertia center frequency by selecting the frequency of the key node with the highest correlation with the system inertia center frequency, thereby greatly reducing the number of measurement signals, and by designing an adaptive power modulation coefficient based on the operating state of the variable speed wind turbine, the problem of over-modulation of the unit can be prevented.

[0006] The invention provides an additional control method for a variable speed wind turbine generator set for enhancing system synchronization stability, comprising the following steps: Step S1: Select a node from among multiple nodes in the power system. load nodes, the power system includes generator sets, variable speed wind turbine sets and nodes, wherein the number of the generator sets is n, and the number of the nodes is z; After setting the power disturbance for each load node, the frequency data of all nodes in the system and the frequency data of the generator set are collected at a preset frequency within a preset period of time; Calculate the corresponding system inertia center frequency based on the frequency data of the generator set collected when power disturbance occurs at each load node; According to the frequency data of all nodes collected when power disturbance occurs at each load node and the corresponding system inertia center frequency calculated, the correlation between the frequency of each node and the corresponding system inertia center frequency is calculated, and the node corresponding to the correlation with the largest value among the calculated correlations is the system inertia center node; Step S2: measuring the frequency corresponding to the system inertia center node as the system inertia center node frequency, and measuring the grid-connected node frequency of the variable speed wind turbine generator set at the same time, and calculating the adaptive power modulation coefficient according to the operating state of the variable speed wind turbine generator set, the system inertia center node frequency, and the grid-connected node frequency; Step S3: taking the grid-connected node frequency and the system inertia center frequency as feedback signals, and calculating the additional power modulation amount of the variable speed wind turbine according to the grid-connected node frequency, the system inertia center frequency and the adaptive power modulation coefficient, and performing an additional control strategy for the variable speed wind turbine according to the additional power modulation amount. Furthermore, the calculation formula of the system inertia center frequency when the j-th load node has a power disturbance in step S1 is shown in formula (1): (1) In the formula, represents the system inertia center frequency when the jth load node has a power disturbance, and Expressed in vector form, represents the inertia of the ith generator set, It represents a vector consisting of several frequency data of the ith generator set collected within a preset period of time after a power disturbance occurs at the jth load node, and n is the number of the generator sets.

[0007] Furthermore, the calculation formula of the correlation between the frequency of each node in step S1 and the system inertia center frequency is as shown in formula (2): (2) In the formula, represents the correlation between the frequency of each node and the center frequency of inertia of the system, Specifically, it refers to the calculation of the vector consisting of several frequency data of the ith node collected within a preset period of time after the power disturbance occurs at the jth load node The corresponding system inertia center frequency The covariance between them is the correlation between the frequency of the i-th node and the corresponding system inertia center frequency when the j-th load node has a power disturbance. Indicates the number of load nodes.

[0008] Furthermore, the operating state of the variable speed wind turbine generator set in step S2 includes an actual operating speed, a minimum allowable operating speed, and a maximum allowable operating speed of the variable speed wind turbine generator set.

[0009] Furthermore, the calculation formula of the adaptive power modulation coefficient in step S2 is shown in formula (3): (3) In the formula, is the adaptive power modulation coefficient, r is the adaptive change coefficient, is a fixed power modulation factor.

[0010] Furthermore, the calculation formula of the adaptive change coefficient is shown in formula (4): (4) In the formula, r is the adaptive change coefficient, is the actual operating speed of the variable speed wind turbine set, is the minimum permissible operating speed of the variable speed wind turbine set, is the maximum allowable operating speed of the variable speed wind turbine set, is the deviation value between the grid-connected node frequency of the variable speed wind turbine and the system inertia center node frequency, that is, , is the grid-connected node frequency of the variable speed wind turbine generator set, is the system inertia center node frequency.

[0011] Furthermore, the calculation formula of the additional power modulation amount in step S3 is shown in formula (5): (5) In the formula, is the output power of the additional controller of the i-th variable speed wind turbine, that is, the additional modulation power, is the adaptive power modulation coefficient, is the grid-connected node frequency of the variable speed wind turbine generator set, is the system inertia center node frequency.

[0012] Furthermore, performing the additional control strategy of the variable speed wind turbine generator set according to the additional power modulation amount specifically includes: adjusting the active power output by the rotor-side frequency converter of the variable speed wind turbine generator set according to the additional power modulation amount.

[0013] The beneficial effects of the present invention are: 1. The present invention adopts the frequency of the key node with the highest correlation with the system inertia center frequency, namely the system inertia center frequency, to approximately replace the system inertia center frequency. It only needs to collect the frequency data of all nodes in the system and the frequency data of the generator set within a short period of time when power disturbance occurs at several load nodes, and then the system inertia center node can be determined by calculation and comparison based on these data. Then, the system inertia center node frequency can be measured based on the system inertia center node, without the need to measure and transmit the frequencies of all synchronous wind turbines in the system in real time to calculate the system inertia center frequency. Therefore, the present invention can greatly reduce the number of measurement signals required for transient stability control of variable speed wind turbines on the basis of ensuring the control effect, thereby greatly saving the communication transmission cost in the installation and control process of the synchronous phasor measurement device, and facilitating engineering implementation.

[0014] 2. When calculating the adaptive power modulation coefficient, the present invention refers to the operating status data of the variable-speed wind turbine including the actual operating speed, the minimum operating speed and the maximum allowable operating speed, and then calculates the additional modulation power through the calculated adaptive power modulation coefficient. Finally, additional control of the variable-speed wind turbine is performed according to the additional modulation power. In other words, the present invention adopts the variable-speed wind turbine to adjust the control coefficient value in real time based on its own operating dynamics, which can effectively avoid excessive modulation of the wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 It is a schematic diagram of IEEE10-machine 39-node power system; Figure 3 A schematic diagram of additional control of a variable speed wind turbine generator system according to the present invention; DETAILED DESCRIPTION In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0016] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0017] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0018] like Figure 1 As shown, the present invention provides an additional control method for a variable speed wind turbine set for enhancing system synchronization stability, comprising the following steps: Step S1: Select a node from among multiple nodes in the power system. load nodes, the power system includes generator sets, variable speed wind turbine sets and nodes, where the number of variable speed wind turbine sets is m and the number of nodes is z; After setting the power disturbance for each load node, the frequency data of all nodes in the system and the frequency data of the variable speed wind turbines are collected at a preset frequency within a preset period of time; Calculate the corresponding system inertia center frequency based on the frequency data of the generator set collected when power disturbance occurs at each load node; According to the frequency data of all nodes collected when power disturbance occurs at each load node and the corresponding system inertia center frequency calculated, the correlation between the frequency of each node and the corresponding system inertia center frequency is calculated, and the node corresponding to the largest correlation value among the calculated correlations is the system inertia center node.

[0019] Specifically, in this embodiment, the power system includes a generator set, a variable speed wind turbine set and a node. The generator set is a combination of equipment that converts various energy sources (such as water energy, wind energy, heat energy generated by fuel combustion, etc.) into electrical energy. The generator set in this embodiment is a wind turbine set, which is a device that converts wind energy into electrical energy. When working, the generator drives the generator rotor to rotate through the prime mover to generate electrical energy. The control system in the power system will detect the voltage, frequency and other parameters of the power grid. After ensuring that the grid connection conditions are met, the generator set will be connected to the grid and start generating electricity. During the grid-connected power generation process, the control system will automatically adjust the excitation current and the power output of the prime mover according to the grid load demand and the operating status of the generator set to keep the voltage and frequency of the generator stable, while the variable speed wind turbine captures wind energy through the wind wheel and converts it into mechanical energy, and then converts the mechanical energy into electrical energy through the generator set. The two work together in the power system to provide a stable and reliable power supply to the power grid. The node is used to connect different power equipment and grid lines to ensure the transmission and distribution of electrical energy.

[0020] Specifically, in the actual working process, the control system will also perform additional control on the variable speed wind turbine. The additional control can more effectively adjust its output power, thereby enhancing the stability of the power system. For example, when the system frequency drops, the additional control can quickly provide active reference instructions according to the system frequency change rate, so that the wind turbine can provide power support to the system, which is conducive to the frequency recovery and stability of the system. At the same time, the additional control of the variable speed wind turbine can optimize its power output, especially when the wind speed changes. Through precise control strategies, it can be ensured that the wind turbine can improve the energy conversion efficiency as much as possible when the wind speed is below the rated wind speed, and when the wind speed is above the rated wind speed, the output power is controlled by adjusting the pitch angle and the generator torque to avoid overload and excessive mechanical stress. In addition, variable speed wind turbines usually operate in complex natural environments, and meteorological conditions such as wind speed and wind direction are random and discontinuous. Additional control can enable wind turbines to better adapt to these changes, ensuring stable operation and output of high-quality electricity under various working conditions. In addition, through additional control, variable speed wind turbines can achieve decoupling control of active and reactive power, and improve the flexibility of power system regulation. This is of great significance for the optimized operation and dispatch of power systems.

[0021] There are usually multiple generator sets and variable speed wind turbine sets in the power system, and there are also multiple nodes. In this embodiment, the number of generator sets is defined as m, and the number of nodes is defined as z.

[0022] like Figure 2As shown in the figure, this is an IEEE 10-machine 39-node power system (i.e., the New England 39-node power system). The IEEE 10-machine 39-node power system is a power system consisting of 39 nodes. It is a power system model established by manual interaction. It is a power system simulation model with high quality and stable performance. It can be used for transient simulation research and other related analysis of power systems.

[0023] In this embodiment, the IEEE 10-machine 39-node power system is used as the simulation of the power system, which includes 10 generator sets, 39 nodes, and a variable-speed wind turbine set is connected to node 16, that is, n=10, z=39. The variable-speed wind turbine set is an equivalent unit of a wind farm, with a capacity of 600MW and an output active power of 500MW.

[0024] Select the power system load nodes, specifically, all load nodes in the system where power disturbance may occur are selected. In this embodiment, four nodes, 8, 18, 23, and 39, are selected as load nodes in the IEEE 10-machine 39-node power system.

[0025] A power disturbance is set for each load node. Specifically, a small power disturbance for increasing power is applied to each load node. In this embodiment, the small power disturbance is increased by 30MW.

[0026] The frequency data of all nodes in the system and the frequency data of the generator set are collected at a preset frequency within a preset period of time, wherein the frequency data of all nodes can be marked as f i (i=1,…,z), the frequency data of the generator set can be marked as f Gi (i=1,…,n).

[0027] In this embodiment, by equipping each node with a phase measurement unit PMU, its frequency data can be collected for transient stability control. The use of PMU to collect frequency data is an existing conventional technology, so its operation process and principle are not described here. In this embodiment, a preset time is selected as 5 seconds, and the preset frequency of collection is set to 100 Hz, that is, 500 times of collection.

[0028] Then, the corresponding system inertia center frequency is calculated according to the frequency data of the variable speed wind turbines collected when the power disturbance occurs at each load node. Specifically, the calculation formula of the system inertia center frequency when the power disturbance occurs at the jth load node is shown in formula (1): (1) In the formula, represents the system inertia center frequency when the jth load node has a power disturbance, and Expressed in vector form, represents the inertia of the ith generator set, It represents a vector consisting of several frequency data of the ith generator set collected within a preset period of time after a power disturbance occurs at the jth load node, where n is the number of generator sets.

[0029] Specifically, in the above calculation, the The 500-order value is converted into a vector and then calculated. The calculated system inertia center frequency will also be expressed in the form of a vector. The reason for converting to a vector for calculation is to prepare for the subsequent calculation of the correlation between the frequency of each node and the system inertia center frequency.

[0030] In this embodiment, the inertia of the generator set is Usually refers to the inertia of synchronous generator sets, which refers to the ability of the unit to resist speed changes when disturbed. It is an important parameter in the operation of the power system, which determines whether the unit can maintain stable operation when disturbed. Inertia can be understood as a measure of system inertia, reflecting the inertial response characteristics of the system in dynamic changes.

[0031] In practical applications, the value of the moment of inertia of a generator set is usually obtained by referring to the design documents or technical manuals of the generator set, or the moment of inertia is estimated based on the design parameters of the generator set (such as rotor mass, radius, material, etc.) and operating conditions (such as speed, load, etc.). Since the inertia of a generator set is usually a fixed value, and the calculation method of the inertia of a generator set is an existing conventional method, how to calculate the inertia of a generator set will not be described in detail here.

[0032] After calculating the system inertia center frequency corresponding to the frequency data of the generator set collected when the power disturbance occurs at each load node, the correlation between the frequency of each node and the corresponding system inertia center frequency is calculated, and the node corresponding to the correlation with the largest value among the calculated correlations is the system inertia center node.

[0033] Specifically, the calculation formula for the correlation between the frequency of each node and the center frequency of the system inertia is as shown in formula (2): (2) In the formula, represents the correlation between the frequency of each node and the center frequency of inertia of the system, Specifically, it refers to the calculation of the vector consisting of several frequency data of the ith node collected within a preset period of time after the power disturbance occurs at the jth load node The corresponding system inertia center frequency The covariance between them is the correlation between the frequency of the i-th node and the corresponding system inertia center frequency when the j-th load node has a power disturbance. Indicates the number of load nodes.

[0034] Specifically, in this embodiment and They are all in vector form. Only in vector form can the correlation be easily calculated. In addition, in this embodiment, the sum of the covariances between the frequency of each node and the corresponding system inertia center frequency under different disturbance conditions is divided by the number of load nodes to obtain a relatively average and more reliable correlation value.

[0035] Specifically, in probability theory and statistics, covariance is used to measure the overall error of two variables, and the expected values ​​are and The covariance between two real random variables X and Y Defined as: - , and the calculation formula of mathematical expectation can be expressed as: , that is, the sum of all possible values ​​and the corresponding probability products, the expected frequency of each node and the expected center frequency of the system inertia can be calculated through the previously collected multiple data. The calculation of mathematical expectation and covariance is existing conventional knowledge and will not be repeated here. In this embodiment, =4.

[0036] After calculating the multiple correlations, the values ​​of the multiple correlations are compared, and the node corresponding to the correlation with the largest value can be determined as the system inertia center node.

[0037] In one embodiment, ignoring the grid-connected node of the generator set, the calculation results of the other 29 nodes in the system are shown in Table 1 below.

[0038] Table 1 Calculation results of the correlation between the frequencies of the other 29 nodes in the system except the grid-connected node of the generator set and the corresponding system inertia center frequency From Table 1, we can see the correlation between the frequency of node 18 and the corresponding system inertia center frequency. The value of is the largest, so node 18 is selected as the system inertia center node.

[0039] Step S2: measuring the frequency corresponding to the system inertia center node as the system inertia center node frequency, and measuring the grid-connected node frequency of the variable speed wind turbine generator set at the same time, and calculating the adaptive power modulation coefficient according to the operating state of the variable speed wind turbine generator set, the system inertia center node frequency, and the grid-connected node frequency; Specifically, the operating state of the variable speed wind turbine generator set includes the actual operating speed, the minimum allowable operating speed, and the maximum allowable operating speed of the variable speed wind turbine generator set, which can be marked as , , The system inertia center node frequency is marked as , the grid-connected node frequency of the variable speed wind turbine is marked as .

[0040] Variable-speed wind turbines have the ability to adjust wind speed and output power, so they will have a certain impact on the frequency of the power grid after being connected to the grid. The grid-connected node frequency of variable-speed wind turbines refers to the frequency value that is consistent with the power grid system when the variable-speed wind turbines are connected to the power grid. The grid-connected node frequency of variable-speed wind turbines is of great significance in ensuring the stability of the power grid, improving energy utilization efficiency, promoting the development of wind power grid-connected technology, and promoting the development of the power system. In most power systems, the grid-connected node frequency value is fixed, usually 50Hz or 60Hz, depending on the power standards in the area, or it can be measured by using high-precision frequency measuring instruments such as phase measurement units (PMUs) or other professional frequency meters to ensure the accuracy of the measurement.

[0041] The specific calculation formula for calculating the adaptive power modulation coefficient is shown in formula (3) according to the operating status of the variable speed wind turbine, the system inertia center node frequency, and the grid-connected node frequency: (3) In the formula, is the adaptive power modulation coefficient, r is the adaptive change coefficient, is a fixed power modulation coefficient. Specifically, K is a relatively fixed value. In this embodiment, K=30.

[0042] The calculation formula of the adaptive change coefficient is shown in formula (4): (4) In the formula, r is the adaptive change coefficient, is the actual operating speed of the variable speed wind turbine set, is the minimum permissible operating speed of the variable speed wind turbine. is the maximum allowable operating speed of the variable speed wind turbine. is the deviation between the grid-connected node frequency of the variable-speed wind turbine and the system inertia center node frequency, that is, , is the grid-connected node frequency of the variable speed wind turbine, is the system inertia center node frequency.

[0043] Specifically, when the grid-connected node frequency of the variable-speed wind turbine is greater than the system inertia center node frequency, it means that the grid-connected node frequency of the variable-speed wind turbine needs to be reduced to reach a level consistent with the system inertia center node frequency of the generator set, otherwise the grid-connected node frequency needs to be increased.

[0044] Step S3: taking the grid-connected node frequency and the system inertia center frequency as feedback signals, and calculating the additional power modulation amount of the variable speed wind turbine according to the grid-connected node frequency, the system inertia center frequency and the adaptive power modulation coefficient, and performing an additional control strategy for the variable speed wind turbine according to the additional power modulation amount.

[0045] Specifically, the calculation formula of the additional power modulation amount in step S3 is shown in formula (5): (5) In the formula, is the output power of the additional controller of the i-th variable speed wind turbine, that is, the additional modulation power, is the adaptive power modulation coefficient, is the grid-connected node frequency of the variable speed wind turbine, is the system inertia center node frequency.

[0046] like Figure 3 As shown, the grid-connected node frequency and the system inertia center frequency are used as feedback signals, and the output power of the additional controller of the variable-speed wind turbine is calculated. The additional control strategy of the variable-speed wind turbine is carried out according to the additional power modulation. Specifically, the active power output of the rotor-side inverter of the variable-speed wind turbine is adjusted according to the additional power modulation. Specifically, the additional output modulation power, i.e. It is superimposed on the active power reference value of the variable speed wind turbine rotor converter to adjust the wind turbine output power during a fault and enhance the system synchronization stability.

[0047] Specifically, taking the case where the grid-connected node frequency of the variable-speed wind turbine is greater than the system inertia center node frequency, the adaptive change coefficient is calculated based on the difference between the maximum allowable operating speed and the actual operating speed of the variable-speed wind turbine, and finally the required adaptive power modulation coefficient is obtained by multiplying the adaptive change coefficient with the fixed power modulation coefficient. is a positive value, , the output power of the additional controller , that is, the output power of the variable speed wind turbine needs to be increased. The increase in output power depends on the increase in the wind speed of the variable speed wind turbine. As the wind speed increases, the adaptive change coefficient r decreases. , Therefore, in this embodiment, by using the variable speed wind turbine to adjust the control coefficient value in real time based on its own operating dynamics including actual operating speed, minimum allowable operating speed, maximum allowable operating speed, etc., it is possible to effectively avoid over-modulation of the variable speed wind turbine.

[0048] In summary, the present invention adopts the frequency of the key node with the highest correlation with the system inertia center frequency, that is, the system inertia center frequency, to approximately replace the system inertia center frequency. It only needs to collect the frequency data of all nodes in the system and the frequency data of the variable speed wind turbines in a short period of time when power disturbance occurs at several load nodes, and the system inertia center node can be determined by calculation and comparison based on these data. Then, the system inertia center node frequency can be measured based on the system inertia center node, without the need to measure and transmit the frequencies of all synchronous wind turbines in the system in real time to calculate the system inertia center frequency. Therefore, on the basis of ensuring the control effect, the number of measurement signals required for transient stability control of variable speed wind turbines can be greatly reduced. After that, it is only necessary to measure the frequency of the system inertia center node through a synchronous phasor measurement device, so the communication transmission cost in the installation and control process of the synchronous phasor measurement device can be greatly saved, which is convenient for engineering implementation.

[0049] In this embodiment, the following power small disturbances are set for the following four situations: variable speed wind turbines are configured with additional control and use an adaptive power modulation coefficient and a system inertia center node frequency; variable speed wind turbines are configured with additional control and use a system inertia center frequency; variable speed wind turbines are configured with additional control and use a fixed modulation coefficient and a system inertia center node frequency; and variable speed wind turbines are not configured with additional control: (1) A three-phase short circuit fault occurs at the midpoint of line 25-26; (2) A three-phase short circuit fault occurs at the midpoint of line 14-15.

[0050] The results are shown in Table 2 below: Table 2 The limit removal time of the system after power disturbance is set for four configurations of variable speed wind turbines The critical clearing time (CCT) of the system is an important quantitative indicator in transient stability analysis. The critical clearing time refers to the maximum time allowed for fault clearing in order to maintain the transient stability of the system when the system fails. That is, the system can maintain transient stability only when the actual fault clearing time is less than the critical clearing time. Therefore, if the critical clearing time is larger, the time left for modulation is longer, which is more conducive to ensuring the synchronous stability of the system.

[0051] It can be seen from Table 1 above that when the variable-speed wind turbine is configured with additional control and uses a fixed modulation coefficient and the system inertia center node frequency, after setting a small power disturbance, its limit cut-off time is less than the limit cut-off time without additional control, resulting in the modulation time exceeding the limit cut-off time, resulting in over-modulation of the variable-speed wind turbine. During the transient process, the protection action of the unit is triggered due to excessive speed, resulting in the cut-off of the variable-speed wind turbine, further deteriorating the system synchronization stability.

[0052] It can also be seen that the variable-speed wind turbine is configured with additional control and uses an adaptive power modulation coefficient and a system inertia center node frequency. Compared with the configuration of additional control and the use of the system inertia center frequency, the control effect is basically the same. However, when the system inertia center node frequency is used, the measurement burden of the control can be greatly reduced while avoiding over-modulation of the wind turbine.

[0053] Therefore, the present invention adopts a variable speed wind turbine to adjust the control coefficient value in real time based on its own operating dynamics, which can effectively avoid over-modulation of the wind turbine while ensuring the control effect, while greatly reducing the control measurement burden.

[0054] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A variable speed wind turbine additional control method for enhancing system synchronization stability, characterized in that: The following steps are involved: Step S1: Select a node from among multiple nodes in the power system. load nodes, the power system includes generator sets, variable speed wind turbine sets and nodes, wherein the number of the generator sets is n, and the number of the nodes is z; After setting the power disturbance for each load node, the frequency data of all nodes in the system and the frequency data of the generator set are collected at a preset frequency within a preset period of time; Calculate the corresponding system inertia center frequency based on the frequency data of the generator set collected when power disturbance occurs at each load node; According to the frequency data of all nodes collected when power disturbance occurs at each load node and the corresponding system inertia center frequency calculated, the correlation between the frequency of each node and the corresponding system inertia center frequency is calculated, and the node corresponding to the correlation with the largest value among the calculated correlations is the system inertia center node; Step S2: measuring the frequency corresponding to the system inertia center node as the system inertia center node frequency, and measuring the grid-connected node frequency of the variable speed wind turbine generator set at the same time, and calculating the adaptive power modulation coefficient according to the operating state of the variable speed wind turbine generator set, the system inertia center node frequency, and the grid-connected node frequency; Step S3: taking the grid-connected node frequency and the system inertia center frequency as feedback signals, and calculating the additional power modulation amount of the variable speed wind turbine according to the grid-connected node frequency, the system inertia center frequency and the adaptive power modulation coefficient, and performing an additional control strategy for the variable speed wind turbine according to the additional power modulation amount.

2. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 1, characterized in that: The calculation formula of the system inertia center frequency when the j-th load node has a power disturbance in step S1 is shown in formula (1): （1） In the formula, represents the system inertia center frequency when the jth load node has a power disturbance, and Expressed in vector form, represents the inertia of the ith generator set, It represents a vector consisting of several frequency data of the ith generator set collected within a preset period of time after a power disturbance occurs at the jth load node, and n represents the number of the generator sets.

3. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 2, characterized in that: The calculation formula of the correlation between the frequency of each node in the step S1 and the center frequency of the system inertia is as shown in formula (2): （2） In the formula, represents the correlation between the frequency of each node and the center frequency of inertia of the system, Specifically, it refers to the calculation of the vector consisting of several frequency data of the ith node collected within a preset period of time after the power disturbance occurs at the jth load node The corresponding system inertia center frequency The covariance between them is the correlation between the frequency of the i-th node and the corresponding system inertia center frequency when the j-th load node has a power disturbance. is the number of the load nodes.

4. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 3, characterized in that: The operating state of the variable speed wind turbine generator set in step S2 includes the actual operating speed, the minimum allowable operating speed, and the maximum allowable operating speed of the variable speed wind turbine generator set.

5. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 4, characterized in that: The calculation formula of the adaptive power modulation coefficient in step S2 is shown in formula (3): （3） In the formula, is the adaptive power modulation coefficient, r is the adaptive change coefficient, is a fixed power modulation factor.

6. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 5, characterized in that: The calculation formula of the adaptive change coefficient is shown in formula (4): （4） In the formula, r is the adaptive change coefficient, is the actual operating speed of the variable speed wind turbine set, is the minimum permissible operating speed of the variable speed wind turbine set, is the maximum allowable operating speed of the variable speed wind turbine set, is the deviation value between the grid-connected node frequency of the variable speed wind turbine and the system inertia center node frequency, that is, , is the grid-connected node frequency of the variable speed wind turbine generator set, is the system inertia center node frequency.

7. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 6, characterized in that: The calculation formula of the additional power modulation amount in step S3 is shown in formula (5): （5） In the formula, is the output power of the additional controller of the i-th variable speed wind turbine, that is, the additional modulation power, is the adaptive power modulation coefficient, is the grid-connected node frequency of the variable speed wind turbine generator set, is the system inertia center node frequency.

8. The additional control method for variable speed wind turbines for enhancing system synchronization stability according to claim 1, characterized in that: The additional control strategy for the variable speed wind turbine generator set according to the additional power modulation amount specifically includes: adjusting the active power output by the rotor-side frequency converter of the variable speed wind turbine generator set according to the additional power modulation amount.

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