Power system active power deficiency dynamic change analysis and calculation method considering differences in new energy transient support characteristics

Abstract

The application provides a kind of power system active power shortage dynamic change analytical calculation method considering new energy transient support characteristic difference.The application first measures the voltage drop depth at the moment of fault occurrence, carries out initial correction to system impedance matrix based on equipment equivalent model to calculate the initial value of each node voltage; judge whether new energy equipment enters low voltage ride through state, and introduce state switching judgment mechanism, especially for the deep drop condition of double-fed wind turbine triggering crowbar protection, build complex impedance matrix containing crowbar resistance correction for secondary network order reduction; analyze and calculate the active power output of unit in fault ride through period by time period, and consider the flux linkage reconstruction delay characteristics after fault removal, and synchronously superimpose to obtain the time series of whole network short-time active power shortage. The application effectively considers the rapidity and accuracy of evaluation, realizes the change of active power shortage from single scalar to continuous time sequence trajectory, and can provide reliable basis for high proportion new energy power system safety and stability control strategy making.

Description

Technical Field

[0001] This invention belongs to the field of power system safety and stability control technology, and in particular, it is an analytical calculation method for dynamic changes in active power deficit of power system that takes into account the differences in transient support characteristics of new energy sources. Background Technology

[0002] With the large-scale replacement of traditional synchronous generators by new energy sources in the power grid, the inertia and voltage support capacity of the power system have decreased sharply. When a short-circuit fault in the power grid causes a deep voltage drop in a local area, it can easily trigger a large number of new energy generating units to enter a low-voltage ride-through (LVRT) state. During the LVRT, the active power output of new energy generating units is greatly limited or even drops to zero due to the reactive power priority control strategy and the current limiting constraints of the hardware converter. After the fault is cleared, the active power needs to undergo a slow ramp-up recovery process with a certain slope.

[0003] In actual power grids, there is a wide coexistence of "full-power converter-isolated" equipment, represented by direct-drive wind turbines (PMSG) and photovoltaic inverters (PV), and "partial-power converter-coupled" equipment, represented by doubly-fed induction generators (DFIG). These heterogeneous devices exhibit significant differences in transient response characteristics. Particularly when facing deep voltage dips, DFIGs, in order to protect the rotor-side converter from overcurrent damage, will forcibly trigger a crowbar protection short-circuit to the rotor windings. After the crowbar engages, the DFIG loses control and operates as an asynchronous motor under voltage ride-through, absorbing reactive power from the grid, leading to further voltage deterioration in the surrounding area. This also results in a significant flux linkage rebuilding delay in the recovery trajectory of the DFIG during the later stages of a short-circuit fault.

[0004] The drastic drop in active power and abrupt changes in reactive power characteristics during the aforementioned transient processes can cause severe comprehensive power impacts on the receiving-end power grid, greatly increasing the multiple risks of transient voltage, transient frequency, and power angle instability faced by the system. Therefore, rapid and accurate assessment of the short-term active power deficit caused by faults and its time-series evolution is of great significance for the formulation of safety and stability control strategies for high-proportion renewable energy power systems. Currently, the assessment of short-term active power deficits in renewable energy power systems mainly relies on electromechanical or electromagnetic transient time-domain simulation software. However, time-domain simulation-based methods suffer from large modeling workloads and long computation times, making it difficult to meet the needs of large-scale power grids for rapid online early warning and emergency power control. Analytical calculation-based methods have the advantage of faster computation speed compared to time-domain simulation, and some existing technologies have adopted analytical calculation methods. However, these methods fail to fully account for the differences in transient response characteristics of the aforementioned heterogeneous renewable energy equipment and cannot present continuous time-series evolution trajectories. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing an analytical calculation method for the dynamic changes of active power deficit in power systems that takes into account the differences in transient support characteristics of new energy sources. This method aims to overcome the drawback of long calculation times in traditional time-domain simulation methods, while also compensating for the shortcomings of existing analytical calculations in fully considering the differences in transient responses of heterogeneous new energy sources, particularly the impedance characteristics and flux linkage reconstruction delay after doubly-fed induction generator (DFIG) wind turbines trigger crowbar protection. This invention strives to accurately reconstruct the entire dynamic evolution process of short-term active power deficit in power systems while ensuring calculation speed, transforming the evaluation results from a single maximum deficit scalar to a continuous time-series trajectory, thereby providing efficient and reliable theoretical support for the safe and stable control of high-proportion new energy power systems.

[0006] The technical solution to achieve the purpose of this invention is: a method for analytically calculating the dynamic changes in active power deficit of a power system that takes into account the differences in transient support characteristics of new energy sources, the method comprising the following steps:

[0007] Step 1: Measure the voltage drop depth at the fault point at the instant the fault occurs, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault.

[0008] Step 2: Determine the operating status of the heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for the equipment in different operating states;

[0009] Step 3: Based on the transient equivalent model, perform a second correction on the modified system impedance matrix obtained in Step 1 to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy sources, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly.

[0010] Step 4: Based on the active power recovery strategy of heterogeneous new energy equipment, analyze and calculate the time series of active power deficit for the entire network.

[0011] Furthermore, the heterogeneous new energy equipment mentioned in step 1 includes: direct-drive wind turbines, photovoltaics, and doubly-fed wind turbines; the equivalent model of the heterogeneous new energy equipment is specifically as follows: the direct-drive wind turbine and photovoltaic equipment are equivalent to constant current sources, the doubly-fed wind turbine is equivalent to a transient current source connected in parallel with a transient reactor, and the traditional synchronous generator set is equivalent to a transient current source connected in parallel with a transient reactor.

[0012] Furthermore, in step 1, the power system impedance matrix is ​​corrected based on the equivalent model of heterogeneous new energy equipment, specifically including:

[0013] Step 1-1: Merge the traditional synchronous generator nodes and doubly-fed wind turbine nodes with initial transient support capabilities into a single set of support nodes;

[0014] Steps 1-2 involve iterative calculations using the successive correction method to obtain the corrected system impedance matrix. The specific correction formula is as follows:

[0015]

[0016] In the formula, Let p be the element in the i-th row and j-th column of the corrected system impedance matrix after the p-th correction, where p is the number of iterative correction steps for the matrix, and k is the sequence number of the transient support device currently being processed. In the p-th iteration calculation, the parameters of the k-th device are substituted into the matrix. That is, the upper limit of p is the total number of nodes of traditional synchronous generators and doubly-fed induction generators with initial transient support capability. This represents the element in the i-th row and j-th column of the impedance matrix of the corrected system after the (p-1)-th correction. For the (p-1)th correction, node i in the corrected system impedance matrix and node s participating in the initial transient support equipment connection. k mutual impedance between For node j in the corrected system impedance matrix after the (p-1)th correction, and node s participating in the initial transient support equipment connection... k mutual impedance between For node s, which participates in the initial transient support equipment access after the (p-1)th correction. k Self-impedance, Let j be the equivalent transient reactance of the k-th transient support device to ground at the moment of failure, where j is the imaginary unit.

[0017] Further, in step 1, the initial voltage values ​​of each node in the power system at the instant of the fault are calculated based on the corrected system impedance matrix. The calculation formula is as follows:

[0018]

[0019] In the formula, subscript i represents the node number where the fault occurred, and subscript j represents any node number in the system whose voltage is to be evaluated. This represents the initial transient voltage value at node j after the fault occurs. The steady-state operating voltage of node j before the fault occurred. To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The mutual impedance between node i and node j To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The self-impedance of fault node i in the middle. The voltage drop depth at node i at the instant the fault occurs.

[0020] Furthermore, step 2 specifically includes:

[0021] (1) For the set of direct-drive wind turbines and photovoltaic power generation nodes in the system, based on the initial value of the grid-connected node voltage and the preset threshold of LVRT. Equivalent relationship:

[0022] If the initial value of the grid-connected node voltage is greater than or equal to the preset threshold If the unit is determined not to have entered the low voltage ride-through state (LVRT), the parameters corresponding to that node in the original system impedance matrix are retained.

[0023] If the initial voltage value of the grid-connected node is less than the preset threshold, the unit is determined to enter the LVRT state. According to the reactive power priority support strategy, the dynamic reactive current injected into the node is equivalent to the parallel susceptance. The formula for calculating the per-unit value of the equivalent susceptance is as follows:

[0024]

[0025] In the formula, Let be the per-unit value of the equivalent parallel current of the direct-drive wind turbine or photovoltaic power generation after node j enters the low-voltage ride-through state. The reactive current proportional coefficient set for the control system of new energy generating units. This is the preset per-unit value for the unit's low-voltage ride-through operating voltage threshold. This is the initial value of the transient voltage at node j after the fault occurs.

[0026] (2) For the set of doubly fed wind turbine nodes in the system A dual-state switching determination mechanism based on voltage sag depth is introduced, including:

[0027] Shallow drop conditions: The doubly fed wind turbine behaves as a controlled current source, equivalent to additional susceptance;

[0028] Deep drop condition: The doubly fed wind turbine triggers the crowbar protection and locks out the converter, which is equivalent to a constant complex impedance composed of stator impedance, excitation reactance, rotor resistance and crowbar resistance.

[0029] Furthermore, the additional susceptance is calculated according to the formula for calculating the per-unit value of the equivalent susceptance; the formula for calculating the constant complex impedance is:

[0030]

[0031] In the formula, For a constant complex impedance, For the stator resistance of a doubly-fed fan. For stator leakage reactance, For rotor resistance, For rotor leakage reactance, For the magnetizing reactance, s is the resistance of the crowbar, s is the generator slip, and j is an imaginary number.

[0032] Furthermore, the specific process of the second correction in step 3 includes:

[0033] Step 3-1: Divide the new energy units in the low voltage ride-through (LVRT) state into a set of nodes with equivalent susceptance. and the set of nodes that are equivalent to impedance ;

[0034] Step 3-2, for the set For nodes in the system, their equivalent susceptance is converted to the parallel branch impedance under the system reference capacity; for the set The nodes in the system are converted from their complex impedances to the parallel branch impedances under the system's reference capacity.

[0035] Step 3-3, using the corrected system impedance matrix obtained in Step 1 As the initial iteration matrix, the equivalent parallel branch complex impedances corresponding to the new energy units in the low voltage ride-through state are successively added as branches, and the nodal impedance matrix successive correction method is used to correct the system impedance matrix. The system is iteratively updated; after traversing all unit nodes in the low-voltage ride-through state, the final system impedance matrix, taking into account the dynamic evolution characteristics of heterogeneous new energy sources, is obtained. .

[0036] Furthermore, the active power recovery strategy for heterogeneous new energy equipment in step 4 specifically includes:

[0037] (1) Active power recovery strategy during fault ride-through

[0038] The calculation of active power during fault ride-through includes:

[0039] For the node set equivalent to susceptance Considering the maximum allowable transient overcurrent limit of the converter and the reactive power injection current, calculate the restricted active power.

[0040] For the set of nodes that are equivalent to impedance The active power output is considered to be zero;

[0041] (2) Active power recovery strategy after fault clearance

[0042] The calculation of active power recovery after fault clearance includes:

[0043] For sets The unit enters the active power slope recovery process from the moment the fault is cleared, and the slope climbs according to the preset active power recovery rate.

[0044] For sets The doubly fed wind turbine introduces a flux linkage reconstruction delay time. A delay is added to the recovered trajectory, specifically as follows:

[0045] when At that time, active power ;in This is the time when the fault is cleared.

[0046] when At that time, the doubly fed fan completes the magnetic flux reconstruction and begins to recover according to the preset slope.

[0047] Furthermore, in step 4, the active power deficit time series of the entire network is obtained by extracting the total steady-state operating power of the new energy units in the entire network and simultaneously superimposing the dynamic active power curves of the new energy units in the LVRT state of the entire network.

[0048] Furthermore, the time series of the active power deficit across the entire network is represented as follows:

[0049]

[0050] In the formula, N represents the total number of new energy generating units in the entire network. The number of units that can enter low voltage ride-through. This represents the number of normally operating generating units that have not yet entered the low-voltage ride-through phase; t is a time variable, and i is the index of the renewable energy generating unit. This is the time series of short-time active power deficit for the entire network. Let be the initial steady-state active power of the i-th renewable energy unit before the fault occurred. This represents the active power time series of the i-th renewable energy unit that enters low-voltage ride-through after a fault occurs during the transient evolution process.

[0051] Compared with the prior art, the significant advantages of this invention are:

[0052] (1) This invention effectively balances the speed and accuracy of assessment, and realizes the transformation of active power deficit from a single scalar to a continuous time-series trajectory evolution, which can finely depict the attenuation trajectory of active power of the unit being dynamically squeezed out by reactive power during the fault crossing period.

[0053] (2) For the deep voltage drop scenario, the transient equivalent model of the doubly fed wind turbine in the deep voltage drop scenario was improved. By constructing a complex impedance matrix with crowbar resistance correction, the network order was reduced, and the impact of the reactive power absorption characteristics of the unit on the local system voltage drop under this operating condition was quantitatively evaluated.

[0054] (3) The present invention takes into account the flux re-establishment delay characteristics after fault clearing, objectively restores the zero-power delay characteristics of some new energy units in the active power recovery stage, and makes up for the shortcomings of the prior art in not fully considering the flux re-establishment delay.

[0055] (4) In view of the problem that existing methods are difficult to balance the computing speed of large power grids and the micro-transient physical mechanism of heterogeneous new energy, this invention can accurately reproduce the dynamic evolution of short-term active power deficit of power system while ensuring computing speed.

[0056] (5) This invention enables accurate assessment of short-term active power deficit and its temporal evolution, and can provide theoretical support and reliable basis for the formulation of safety and stability control strategies for high-proportion new energy power systems.

[0057] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0058] Figure 1 This is a flowchart of an analytical calculation method for the dynamic change of active power deficit in a power system, taking into account the differences in transient support characteristics of new energy sources, in one embodiment.

[0059] Figure 2 This is a flowchart of the equivalent impedance matrix update for the transient model of heterogeneous new energy equipment in one embodiment.

[0060] Figure 3 This is a transient equivalent circuit diagram of a doubly fed wind turbine in one embodiment when a deep voltage drop triggers the crowbar protection. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0062] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0063] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0064] In one embodiment, a method for dynamically calculating the active power deficit of a power system that takes into account the differences in transient support characteristics of new energy sources is provided. The method includes the following steps:

[0065] Step 1: Measure the voltage drop depth at the fault point at the instant the fault occurs, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault.

[0066] Here, the fault node is node i, and the voltage drop depth is... This indicates that the moment of failure refers to the initial moment of the failure (t=0+), when the new energy transient control module has not yet acted.

[0067] Step 2: Determine the operating status of the heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for the equipment in different operating states;

[0068] Step 3: Based on the transient equivalent model, perform a second correction on the modified system impedance matrix obtained in Step 1 to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy sources, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly.

[0069] Step 4: Based on the active power recovery strategy of heterogeneous new energy equipment, analyze and calculate the time series of active power deficit for the entire network.

[0070] Furthermore, in one embodiment, the heterogeneous new energy equipment mentioned in step 1 includes: a direct-drive wind turbine, a photovoltaic system, and a doubly-fed induction generator (DFIG); the equivalent model of the heterogeneous new energy equipment is specifically as follows: the direct-drive wind turbine and photovoltaic equipment are equivalent to constant current sources, the DFIG is equivalent to a transient current source connected in parallel with a transient reactance, and the traditional synchronous generator set is equivalent to a transient current source connected in parallel with a transient reactance.

[0071] Preferably, in some embodiments, step 1 involves correcting the power system impedance matrix based on the equivalent model of heterogeneous new energy equipment, specifically including:

[0072] Step 1-1: Merge the traditional synchronous generator nodes and doubly-fed wind turbine nodes with initial transient support capabilities into a single set of support nodes;

[0073] Steps 1-2 involve iterative calculations using the successive correction method to obtain the corrected system impedance matrix. The specific correction formula is as follows:

[0074]

[0075] In the formula, Let p be the element in the i-th row and j-th column of the corrected system impedance matrix after the p-th correction, where p is the number of iterative correction steps for the matrix, and k is the sequence number of the transient support device currently being processed. In the p-th iteration calculation, the parameters of the k-th device are substituted into the matrix. That is, the upper limit of p is the total number of nodes of traditional synchronous generators and doubly-fed induction generators with initial transient support capability. This represents the element in the i-th row and j-th column of the impedance matrix of the corrected system after the (p-1)-th correction. For the (p-1)th correction, node i in the corrected system impedance matrix and node s participating in the initial transient support equipment connection. k mutual impedance between For node j in the corrected system impedance matrix after the (p-1)th correction, and node s participating in the initial transient support equipment connection... k mutual impedance between For node s, which participates in the initial transient support equipment access after the (p-1)th correction. k Self-impedance, Let j be the equivalent transient reactance of the k-th transient support device to ground at the moment of failure, where j is the imaginary unit.

[0076] Here are the detailed steps:

[0077] Assume the full-dimensional nodal impedance matrix used for initial power flow calculations is as follows: Let the set of traditional synchronous generator nodes participating in the initial transient support within the system be . The corresponding subtransient reactance set is Meanwhile, let the set of doubly-fed wind turbine nodes in the system be... The corresponding set of equivalent transient reactances is denoted as The two types of nodes with initial transient support capabilities are merged into a single set of support nodes. The total number of nodes is The corresponding set of ground-supporting reactances is uniformly denoted as... .

[0078] For the k-th node in the total set of support nodes ( Its correction formula is:

[0079]

[0080] In the formula, Let p be the element in the i-th row and j-th column of the corrected system impedance matrix after the p-th correction, where p is the number of iterative correction steps for the matrix, and k is the sequence number of the transient support device currently being processed. In the p-th iteration calculation, the parameters of the k-th device are substituted into the matrix. That is, the upper limit of p is the total number of nodes of traditional synchronous generators and doubly-fed induction generators with initial transient support capability. This represents the element in the i-th row and j-th column of the impedance matrix of the corrected system after the (p-1)-th correction. For the (p-1)th correction, node i in the corrected system impedance matrix and node s participating in the initial transient support equipment connection. k mutual impedance between For node j in the corrected system impedance matrix after the (p-1)th correction, and node s participating in the initial transient support equipment connection... k mutual impedance between For node s, which participates in the initial transient support equipment access after the (p-1)th correction. k Self-impedance, Let be the equivalent transient reactance to ground of the k-th transient support device at the moment of failure, where j is the imaginary unit. After K iterations of calculation, the improved impedance matrix considering the combined effect of the initial transient support of the entire grid's synchronous generators and doubly-fed induction generators is obtained, denoted as . .

[0081] Preferably, in some embodiments, in step 1, the initial voltage values ​​of each node in the power system at the moment of fault are calculated based on the corrected system impedance matrix, and the calculation formula is as follows:

[0082]

[0083] In the formula, subscript i represents the node number where the fault occurred, and subscript j represents any node number in the system whose voltage is to be evaluated. This represents the initial transient voltage value at node j after the fault occurs. The steady-state operating voltage of node j before the fault occurred. To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The mutual impedance between node i and node j To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The self-impedance of fault node i in the middle. The voltage drop depth at node i at the instant the fault occurs.

[0084] Furthermore, in one embodiment, step 2 specifically includes:

[0085] (1) For the set of direct-drive wind turbines and photovoltaic power generation nodes in the system, based on the initial value of the grid-connected node voltage and the preset threshold of LVRT. Equivalent relationship:

[0086] If the initial value of the grid-connected node voltage is greater than or equal to the preset threshold If the unit is determined not to have entered the low voltage ride-through (LVRT) state, the parameters corresponding to that node in the original system impedance matrix are retained; preferably, the preset threshold... The value can be, but is not limited to, 0.9pu.

[0087] If the initial voltage value of the grid-connected node is less than the preset threshold, the unit is determined to enter the LVRT state. According to the reactive power priority support strategy, the dynamic reactive current injected into the node is equivalent to the parallel susceptance. The formula for calculating the per-unit value of the equivalent susceptance is as follows:

[0088]

[0089] In the formula, Let be the per-unit value of the equivalent parallel current of the direct-drive wind turbine or photovoltaic power generation after node j enters the low-voltage ride-through state. The reactive current proportional coefficient set for the control system of new energy generating units. This is the preset per-unit value for the unit's low-voltage ride-through operating voltage threshold. This is the initial value of the transient voltage at node j after the fault occurs.

[0090] (2) For the set of doubly fed wind turbine nodes in the system A dual-state switching determination mechanism based on voltage sag depth is introduced, including:

[0091] Shallow drop condition: The rotor-side converter does not trigger the crowbar protection. At this time, the doubly fed wind turbine behaves as a controlled current source, which is equivalent to additional susceptance.

[0092] Deep drop condition: The doubly fed wind turbine is forced to trigger the crowbar protection and lock the converter, which is equivalent to a constant complex impedance composed of stator impedance, excitation reactance, rotor resistance and crowbar resistance.

[0093] Preferably, in some embodiments, the additional susceptance is calculated according to the formula for calculating the per-unit value of the equivalent susceptance; the formula for calculating the constant complex impedance is:

[0094]

[0095] In the formula, For a constant complex impedance, For the stator resistance of a doubly-fed fan. For stator leakage reactance, For rotor resistance, For rotor leakage reactance, For the magnetizing reactance, s is the resistance of the crowbar, s is the generator slip, and j is an imaginary number.

[0096] Furthermore, in one embodiment, the specific process of the secondary correction in step 3 includes:

[0097] Step 3-1: Divide the new energy units in the low voltage ride-through (LVRT) state into a set of nodes with equivalent susceptance. (Including direct-drive / photovoltaic and shallow-drop double-fed) and the set of nodes equivalent to impedance. (Including a double-fed deep-drop triggered crowbar);

[0098] Step 3-2, for the set For nodes in the system, their equivalent susceptance is converted to the parallel branch impedance under the system reference capacity; for the set The nodes in the system are converted from their complex impedances to the parallel branch impedances under the system's reference capacity.

[0099] Specifically, for example:

[0100] For sets At node t, its equivalent susceptance is converted to the parallel branch impedance under the system reference capacity. :

[0101]

[0102] For sets Node p in the system is converted to its complex impedance as a parallel branch impedance under the system's reference capacity. :

[0103]

[0104] In the formula, As the system's baseline capacity, , These represent the number of turbine units at the station corresponding to nodes t and p, respectively. , These represent the single-machine capacities corresponding to nodes t and p, respectively. This represents the per-unit value of the equivalent parallel current of the direct-drive wind turbine or photovoltaic power generation after entering the low-voltage ride-through state at node t. The transient equivalent impedance of the doubly fed wind turbine at node p when a deep voltage drop triggers the crowbar protection.

[0105] Step 3-3, using the corrected system impedance matrix obtained in Step 1 As the initial iteration matrix, the equivalent parallel branch complex impedances corresponding to the new energy units in the low voltage ride-through state are successively added as branches, and the nodal impedance matrix successive correction method is used to correct the system impedance matrix. The system is iteratively updated; after traversing all unit nodes in the low-voltage ride-through state, the final system impedance matrix, taking into account the dynamic evolution characteristics of heterogeneous new energy sources, is obtained. .

[0106] Furthermore, in one embodiment, step 3 is based on the final system impedance matrix. Calculate the transient equivalent voltage of each node during the fault ride-through period after the reactive power response of the new energy unit is triggered by a short-circuit fault. The calculation formula is:

[0107]

[0108] In the formula, The mutual impedance between fault node i and node j in the final system impedance matrix is ​​given. This represents the self-impedance of fault node i in the final system impedance matrix.

[0109] Furthermore, in one embodiment, the active power recovery strategy for heterogeneous new energy devices in step 4 specifically includes:

[0110] (1) Active power recovery strategy during fault ride-through

[0111] The calculation of active power during fault ride-through includes:

[0112] For the node set equivalent to susceptance Considering the maximum allowable transient overcurrent limit of the converter and the reactive power injection current, calculate the restricted active power.

[0113] For the set of nodes that are equivalent to impedance The active power output is considered to be zero;

[0114] Specifically:

[0115] Considering the new energy unit nodes entering LVRT state, for the node set equivalent to susceptance During a fault, the active power output is not only limited by the converter's hardware overload capacity and reactive power priority strategy, but also by the physical constraints of the prime mover's (or primary energy source) input power. Considering that the prime mover's mechanical power cannot change abruptly during a transient period, the actual active current output by the unit... The expression depends on the smaller of the current required for the prime mover to deliver energy and the available active current limit of the converter:

[0116]

[0117] In the formula, This is the transient equivalent voltage during the fault ride-through period. This is the maximum permissible transient overcurrent limit for the converter; The reactive current injected is required according to the grid connection guidelines. This represents the steady-state active power before the fault occurred. Finally, considering the dynamic deviation caused by internal control transients within the converter, its active power... The calculation formula is:

[0118]

[0119] in, The active transient decay coefficient is... The time when the fault occurred.

[0120] For the set of nodes N that is equivalent to impedance Z Because it forcibly locks out the rotor-side converter, it loses its active power output capability, and its active power is considered zero during this period:

[0121]

[0122] (2) Active power recovery strategy after fault clearance

[0123] The calculation of active power recovery after fault clearance includes:

[0124] For sets The unit enters the active power slope recovery process from the moment the fault is cleared, and the slope climbs according to the preset active power recovery rate.

[0125] For sets The doubly fed wind turbine introduces a flux linkage reconstruction delay time. A delay is added to the recovered trajectory, specifically as follows:

[0126] when At that time, active power ;in This is the time when the fault is cleared.

[0127] when At that time, the doubly fed fan completes the magnetic flux reconstruction and begins to recover according to the preset slope.

[0128] Specifically:

[0129] For the node set equivalent to susceptance For units in the process, after a fault is cleared, they directly enter the active power slope recovery process. The calculation formula is:

[0130]

[0131] in, The active power at the moment of fault clearing. For active power recovery rate, This represents the steady-state active power before the fault occurred.

[0132] For the set of nodes that are equivalent to impedance In doubly-fed wind turbines, the removal of the crowbar and restoration of converter control require a specific physical transition process, introducing a flux linkage reconstruction delay time. Add this delay element to its recovery trajectory: when At that time, the wind turbine was still in the preparation stage for restarting, and the active power remained at a low level.

[0133]

[0134] when At that time, the wind turbine completes the magnetic flux reconstruction and begins to recover at the given slope:

[0135]

[0136] Furthermore, in one embodiment, in step 4, the total active power deficit time series of the entire network is obtained by extracting the total steady-state operating power of all new energy units in the entire network. The dynamic active power curves of new energy units in LVRT state across the entire network are simultaneously superimposed and calculated.

[0137] Preferably, in some embodiments, the time series of the total network active power deficit is represented as follows:

[0138]

[0139] In the formula, N represents the total number of new energy generating units in the entire network. The number of units that can enter low voltage ride-through. This represents the number of normally operating generating units that have not yet entered the low-voltage ride-through phase; t is a time variable, and i is the index of the renewable energy generating unit. This is the time series of short-time active power deficit for the entire network. Let be the initial steady-state active power of the i-th renewable energy unit before the fault occurred. This is the active power time series of the i-th renewable energy unit that enters low-voltage ride-through after a fault, during its transient evolution. This characterizes the entire dynamic evolution of the short-term active power deficit caused by the fault at the system level.

[0140] In one embodiment, a power system active power deficit dynamic change analytical calculation system considering the differences in transient support characteristics of new energy sources is provided, the system comprising:

[0141] The first module is used to: measure the voltage drop depth at the fault point at the instant of the fault, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault.

[0142] The second module is used to: determine the operating status of heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for equipment in different operating states;

[0143] The third module is used to: perform a second correction on the modified system impedance matrix obtained by the first module based on the transient equivalent model, to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly.

[0144] The fourth module is used to: analyze and calculate the time series of active power deficit for the entire network based on the active power recovery strategy of heterogeneous new energy equipment.

[0145] Specific limitations regarding the dynamic analysis and calculation system for the active power deficit of the power system taking into account the differences in transient support characteristics of new energy sources can be found in the limitations on the dynamic analysis and calculation method for the active power deficit of the power system taking into account the differences in transient support characteristics of new energy sources mentioned above, and will not be repeated here. Each module in the aforementioned dynamic analysis and calculation system for the active power deficit of the power system taking into account the differences in transient support characteristics of new energy sources can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the corresponding operations of each module.

[0146] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements:

[0147] Step 1: Measure the voltage drop depth at the fault point at the instant the fault occurs, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault.

[0148] Step 2: Determine the operating status of the heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for the equipment in different operating states;

[0149] Step 3: Based on the transient equivalent model, perform a second correction on the modified system impedance matrix obtained in Step 1 to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy sources, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly.

[0150] Step 4: Based on the active power recovery strategy of heterogeneous new energy equipment, analyze and calculate the time series of active power deficit for the entire network.

[0151] For specific limitations on each step, please refer to the limitations on the dynamic change analysis calculation method of the power system active power deficit considering the differences in the transient support characteristics of new energy sources mentioned above, which will not be repeated here.

[0152] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, the computer program being implemented when executed by a processor:

[0153] Step 1: Measure the voltage drop depth at the fault point at the instant the fault occurs, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault.

[0154] Step 2: Determine the operating status of the heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for the equipment in different operating states;

[0155] Step 3: Based on the transient equivalent model, perform a second correction on the modified system impedance matrix obtained in Step 1 to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy sources, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly.

[0156] Step 4: Based on the active power recovery strategy of heterogeneous new energy equipment, analyze and calculate the time series of active power deficit for the entire network.

[0157] For specific limitations on each step, please refer to the limitations on the dynamic change analysis calculation method of the power system active power deficit considering the differences in the transient support characteristics of new energy sources mentioned above, which will not be repeated here.

[0158] As a specific example, in some embodiments, the present invention will be further verified and described in conjunction with the accompanying drawings.

[0159] Example 1

[0160] The following is combined with Figures 1 to 3 The invention also provides a detailed explanation of the dynamic evolution assessment method for short-term active power deficit of the system provided by this invention, using a specific example of a power system containing a high proportion of heterogeneous new energy sources.

[0161] Assume the test system includes a conventional synchronous generator set, a direct-drive wind farm (PMSG), a photovoltaic power plant (PV), and a doubly-fed induction generator (DFIG). The system baseline capacity is set to S. bs The specific implementation steps are as follows:

[0162] S1 measures the voltage drop depth at the fault point at the instant the fault occurs. For example... Figure 1As shown, the initial power flow operating parameters and the full-dimensional node impedance matrix Z of the system are obtained. Assume that a three-phase short-circuit fault occurs at a bus node i at time t=0, and the voltage at the fault point drops instantaneously from its rated value. The actual voltage drop depth ΔU is measured. i At this time, the new energy transient control module has not yet activated.

[0163] S2, Initial transient support assessment and initial voltage value calculation. The subtransient reactance of the synchronous generator providing initial transient support and the equivalent transient reactance of the doubly-fed wind farm are included in the support node set S. sup Photovoltaic and direct-drive wind turbines, due to converter isolation, do not provide initial inherent reactive power support and are considered constant current sources. Using the formula... The successive correction method involves iteratively reducing the order of the original impedance matrix Z by K iterations based on the support reactance, to obtain the corrected impedance matrix Z' taking into account the initial physical support. Using the formula... The initial voltage values ​​of all renewable energy grid-connected nodes across the entire network were calculated analytically at the instant of a short-circuit fault, before the control system responded. .

[0164] S3, Heterogeneous New Energy Status Determination and Impedance Matrix Secondary Correction. Assume the initial values ​​of the grid connection point voltages for the photovoltaic power plant and the direct-drive wind farm. It is determined that it has entered the low voltage ride-through (LVRT) state; since it is a full-power converter isolated device, according to the reactive power priority strategy, using the formula Calculate its dynamic reactive equivalent susceptance And it is included in the set of susceptance nodes. .

[0165] For DFIG wind farms, further judgment is made based on the drop-off depth at the grid connection point. If the drop-off is extremely deep, causing rotor overcurrent and forcibly triggering the crowbar protection, the DFIG abruptly changes from a controlled current source to an uncontrollable inductive impedance. In this case, combined with... Figure 3 The equivalent circuit diagram, using the formula Calculate the resistance R of the crowbar cb stator and rotor leakage reactance and magnetizing reactance X m Complex impedance Z df And classify them into the impedance node set. .

[0166] Using formula and formula set and The susceptance and impedance in the equation are converted to a unified system reference and then the formula is used again. Iterative updates yield the final system impedance matrix Z'', which reflects the heterogeneous transient evolution characteristics. The equivalent parallel branch complex impedance of the k-th device currently being updated is given by the value described above. or Subsequently, through the formula Calculate the transient equivalent voltage of each node during the fault ride-through period. .

[0167] S4, constructs and aggregates active power time-series trajectories in different time periods for evaluation. During fault ride-through, for the set... In direct-drive / photovoltaic systems, reactive current preempts converter margin, using the formula... Calculate its constrained active power output; for the set The active power output of the doubly fed fan that triggers the Crowbar is approximately zero.

[0168] During the recovery period after fault clearance, collection The generating units in the middle restore active power according to the set slope, that is And set N Z The doubly fed wind turbine in the middle needs to wait for Δt delay The flux linkage rebuilding is delayed and maintains an active power of approximately 0 before active power ramp-up recovery begins. The active power calculation formula for the recovery phase is as follows: .

[0169] Finally, the active power trajectories of all new energy generating units in LVRT state across the entire network are synchronously superimposed on the time axis and substituted into the formula. The total short-time active power deficit time series ΔP(t) of the system is obtained. This curve can be directly used to formulate power grid security and stability control strategies.

[0170] Example 2

[0171] To highlight the advantages of the present invention in refining modeling to eliminate the inaccuracies of traditional analytical models, this embodiment focuses on the extreme condition of deep voltage drop in the local power system where a doubly fed wind farm (DFIG) is located, and provides a detailed explanation of the generation and characteristics of the active power deficit time series curve ΔP(t).

[0172] In the fault scenario of this embodiment, assuming that the fault point is very close to the DFIG wind farm, the grid connection point voltage measured and calculated using the corrected system impedance matrix drops sharply to 0.15 pu.

[0173] Due to the deep fall, the DFIG forcibly triggered the crowbar protection. In the evaluation method of this invention, the wind farm was accurately determined to have experienced a transient model switch and was categorized into set N. Z By introducing Figure 3 The equivalent circuit and formula shown This method will reduce the resistance R of the crowbar. cbIncorporating complex impedance Z df The calculations are then used to perform a secondary correction of the network impedance matrix. This objectively reveals the physical fact that during a fault, the wind farm not only failed to output active power but also absorbed a large amount of reactive power, leading to further deterioration of the grid voltage.

[0174] The active power evolution trajectory of the wind farm output by this method exhibits zero-power trough and delayed recovery characteristics: during the fault period, affected by the crowbar lockout, the active power drops sharply and remains at a near-zero trough. Although the grid voltage begins to recover initially after the fault is cleared, this method takes into account the physical delay Δt necessary for DFIG crowbar removal and flux linkage reconstruction. delay During this delay period, the unit's active power remained at zero. Only after the flux linkage was rebuilt did the unit slowly recover to its pre-fault steady-state output P according to the set active power ramp-up rate. 0i .

[0175] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention without departing from its spirit and scope should be included within the protection scope of the present invention.

Claims

1. A method for analytically calculating the dynamic changes in active power deficit in a power system, taking into account the differences in transient support characteristics of new energy sources, characterized in that, The method includes the following steps: Step 1: Measure the voltage drop depth at the fault point at the instant the fault occurs, correct the system impedance matrix based on the equivalent model of heterogeneous new energy equipment, and calculate the initial voltage value of each node in the system at the instant of the fault. Step 2: Determine the operating status of the heterogeneous new energy equipment based on the initial voltage value, and match the corresponding transient equivalent model for the equipment in different operating states; Step 3: Based on the transient equivalent model, perform a second correction on the modified system impedance matrix obtained in Step 1 to obtain the final system impedance matrix that takes into account the dynamic evolution characteristics of heterogeneous new energy sources, and calculate the transient equivalent voltage of each node during the fault ride-through period accordingly. Step 4: Based on the active power recovery strategy of heterogeneous new energy equipment, analyze and calculate the time series of active power deficit for the entire network.

2. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 1, is characterized in that... The heterogeneous new energy equipment mentioned in step 1 includes: direct-drive wind turbines, photovoltaics, and doubly-fed wind turbines; the equivalent model of the heterogeneous new energy equipment is as follows: the direct-drive wind turbine and photovoltaic equipment are equivalent to constant current sources, the doubly-fed wind turbine is equivalent to a transient current source connected in parallel with a transient reactor, and the traditional synchronous generator set is equivalent to a transient current source connected in parallel with a transient reactor.

3. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 2, is characterized in that... Step 1 involves correcting the power system impedance matrix based on the equivalent model of heterogeneous new energy equipment, specifically including: Step 1-1: Merge the traditional synchronous generator nodes and doubly-fed wind turbine nodes with initial transient support capabilities into a single set of support nodes; Steps 1-2 involve iterative calculations using the successive correction method to obtain the corrected system impedance matrix. The specific correction formula is as follows: In the formula, Let p be the element in the i-th row and j-th column of the corrected system impedance matrix after the p-th correction, where p is the number of iterative correction steps for the matrix, and k is the sequence number of the transient support device currently being processed. In the p-th iteration calculation, the parameters of the k-th device are substituted into the matrix. That is, the upper limit of p is the total number of nodes of traditional synchronous generators and doubly-fed induction generators with initial transient support capability. This represents the element in the i-th row and j-th column of the impedance matrix of the corrected system after the (p-1)-th correction. For the (p-1)th correction, node i in the corrected system impedance matrix and node s participating in the initial transient support equipment connection. k mutual impedance between For node j in the corrected system impedance matrix after the (p-1)th correction, and node s participating in the initial transient support equipment connection... k mutual impedance between For node s, which participates in the initial transient support equipment access after the (p-1)th correction. k Self-impedance, Let j be the equivalent transient reactance of the k-th transient support device to ground at the moment of failure, where j is the imaginary unit.

4. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 1, is characterized in that... In step 1, the initial voltage values ​​of each node in the power system at the instant of the fault are calculated based on the corrected system impedance matrix. The calculation formula is as follows: In the formula, subscript i represents the node number where the fault occurred, and subscript j represents any node number in the system whose voltage is to be evaluated. This represents the initial transient voltage value at node j after the fault occurs. The steady-state operating voltage of node j before the fault occurred. To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The mutual impedance between node i and node j To correct the system impedance matrix after taking into account the initial transient support effect of the generator set The self-impedance of fault node i in the middle. The voltage drop depth at node i at the instant the fault occurs.

5. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 2, is characterized in that... Step 2 specifically includes: (1) For the set of direct-drive wind turbines and photovoltaic power generation nodes in the system, based on the initial value of the grid-connected node voltage and the preset threshold of LVRT. Equivalent relationship: If the initial value of the grid-connected node voltage is greater than or equal to the preset threshold If the unit is determined not to have entered the low voltage ride-through state (LVRT), the parameters corresponding to that node in the original system impedance matrix are retained. If the initial voltage value of the grid-connected node is less than the preset threshold, the unit is determined to enter the LVRT state. According to the reactive power priority support strategy, the dynamic reactive current injected into the node is equivalent to the parallel susceptance. The formula for calculating the per-unit value of the equivalent susceptance is as follows: In the formula, Let be the per-unit value of the equivalent parallel current of the direct-drive wind turbine or photovoltaic power generation after node j enters the low-voltage ride-through state. The reactive current proportional coefficient set for the control system of new energy generating units. This is the preset per-unit value for the unit's low-voltage ride-through operating voltage threshold. The initial transient voltage value of node j after the fault occurs. (2) For the set of doubly fed wind turbine nodes in the system A dual-state switching determination mechanism based on voltage sag depth is introduced, including: Shallow drop conditions: The doubly fed wind turbine behaves as a controlled current source, equivalent to additional susceptance; Deep drop condition: The doubly fed wind turbine triggers the crowbar protection and locks out the converter, which is equivalent to a constant complex impedance composed of stator impedance, excitation reactance, rotor resistance and crowbar resistance.

6. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 5, is characterized in that... The additional susceptance is calculated according to the formula for calculating the per-unit value of the equivalent susceptance; the formula for calculating the constant complex impedance is: In the formula, For a constant complex impedance, For the stator resistance of a doubly-fed fan. For stator leakage reactance, For rotor resistance, For rotor leakage reactance, For the magnetizing reactance, s is the resistance of the crowbar, s is the generator slip, and j is an imaginary number.

7. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 5, is characterized in that... The specific process of the second correction in step 3 includes: Step 3-1: Divide the new energy units in the low voltage ride-through (LVRT) state into a set of nodes with equivalent susceptance. and the set of nodes that are equivalent to impedance ; Step 3-2, for the set For nodes in the system, their equivalent susceptance is converted to the parallel branch impedance under the system reference capacity; for the set The nodes in the system are converted from their complex impedances to the parallel branch impedances under the system's reference capacity. Step 3-3, using the corrected system impedance matrix obtained in Step 1 As the initial iteration matrix, the equivalent parallel branch complex impedances corresponding to the new energy units in the low voltage ride-through state are successively added as branches, and the nodal impedance matrix successive correction method is used to correct the system impedance matrix. The system is iteratively updated; after traversing all unit nodes in the low-voltage ride-through state, the final system impedance matrix, taking into account the dynamic evolution characteristics of heterogeneous new energy sources, is obtained. .

8. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 7, is characterized in that... The active power recovery strategy for heterogeneous renewable energy equipment in step 4 specifically includes: (1) Active power recovery strategy during fault ride-through The calculation of active power during fault ride-through includes: For the node set equivalent to susceptance Considering the maximum allowable transient overcurrent limit of the converter and the reactive power injection current, calculate the restricted active power. For the set of nodes that are equivalent to impedance The active power output is considered to be zero; (2) Active power recovery strategy after fault clearance The calculation of active power recovery after fault clearance includes: For sets The unit enters the active power slope recovery process from the moment the fault is cleared, and the slope climbs according to the preset active power recovery rate. For sets The doubly fed wind turbine introduces a flux linkage reconstruction delay time. A delay is added to the recovered trajectory, specifically as follows: when At that time, active power ;in This is the time when the fault is cleared. when At that time, the doubly fed fan completes the magnetic flux reconstruction and begins to recover according to the preset slope.

9. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 1, is characterized in that... In step 4, the active power deficit time series of the entire network is obtained by extracting the total steady-state operating power of the new energy units in the entire network and simultaneously superimposing the dynamic active power curves of the new energy units in the LVRT state of the entire network.

10. The analytical calculation method for dynamic changes in active power deficit of power system considering the differences in transient support characteristics of new energy sources, as described in claim 9, is characterized in that... The time series of the active power deficit across the entire network is represented as follows: In the formula, N represents the total number of new energy generating units in the entire network. The number of units that can enter low voltage ride-through. This represents the number of normally operating generating units that have not yet entered the low-voltage ride-through phase; t is a time variable, and i is the index of the renewable energy generating unit. This is the time series of short-time active power deficit for the entire network. Let be the initial steady-state active power of the i-th renewable energy unit before the fault occurred. This represents the active power time series of the i-th renewable energy unit that enters low-voltage ride-through after a fault occurs during the transient evolution process.

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