A transient synchronous instability determination method suitable for meshed power generation systems

Abstract

The application discloses a kind of suitable for network type power generation system transient synchronous instability determination method, first according to the dynamic reactive power support constraint given in grid connection guide to determine positive sequence, negative sequence reactive power reference value;Subsequently, whether positive sequence system and negative sequence system exist fault operation equilibrium point is examined respectively;If one of positive sequence system and negative sequence system does not exist equilibrium point, then directly determine that system transient synchronous instability.If all exist equilibrium point, then further based on equivalent area relationship establishes transient energy function and obtains equivalent acceleration area and equivalent deceleration area;Again, positive sequence, negative sequence transient synchronous stability criterion is formed by each area quantity and damping energy consumption.It can be respectively outputted that the stability judgment result of two sequence systems under fault condition, for the new energy grid-connected system containing network type inverter to carry out asymmetric fault stability evaluation provides calculable discrimination condition.

Description

Technical Field

[0001] This invention relates to a method for determining transient synchronization instability in grid-connected power generation systems. Specifically, it is a method for judging the positive-sequence and negative-sequence transient operating states of inverters in a power system when an asymmetrical short-circuit fault occurs. The method utilizes the mathematical relationship between the two-sequence power loops and the equal area relationship to form corresponding transient synchronization stability criteria, which belongs to the field of novel power system stability analysis technology. Background Technology

[0002] As the proportion of new energy power sources connected to the grid via power electronic interfaces increases, the ability of grid-connected devices to maintain voltage, frequency, and synchronous operation during disturbances becomes a crucial factor affecting system safety. Grid-connected inverters can actively establish port voltage and frequency, thus undertaking corresponding grid support functions. When an asymmetrical short-circuit fault occurs in the grid, positive and negative sequence components appear in the grid connection point voltage, and low-voltage ride-through requirements cause changes in reactive power support and active power setpoints. These combined changes in electrical state and control setpoints alter the power balance of the grid-connected power generation system, causing its power angle and angular frequency to deviate from the original operating state. Therefore, it is necessary to evaluate the transient synchronous stability during fault transitions. Existing research has mainly formed the following two analytical approaches:

[0003] [1] HART PJ, GONG MZ, LIU HC, et al. Provably-Stable OverloadRide-Through Control for Grid-Forming Inverters Using System-Wide LyapunovFunction Analysis[J]. IEEE Transactions on Energy Conversion, 2022, 37(4):2761-2776.

[0004] [2] PAN DH, WANG XF, LIU FC, et al. Transient Stability ofVoltage-Source Converters with Grid-Forming Control: A Design-Oriented Study[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2020,8(2): 1019-1033.

[0005] Reference [1] provides a stability proof for a grid-type inverter that implements overload ride-through control during a fault using a system-wide Lyapunov function. This study can demonstrate the stability effect of the control strategy when specific constraints are met, but its proof conditions are quite restrictive, and the obtained stability region is difficult to directly reflect the actual achievable stability boundary of the system. Reference [2] takes four types of grid-type control methods as comparison objects, examines the motion trajectory of a voltage source converter after a large disturbance in the phase plane, and discusses the relationship between reactive power droop and reactive power voltage loop parameter changes and power angle stability margin. This study can provide a reference for the selection of control parameters, but its analysis conditions are different from the asymmetrical fault with both positive and negative sequence conditions addressed in this paper. The network model and stability conditions used in the above analysis are mainly for fault conditions where voltage and current remain symmetrical. In asymmetrical short-circuit faults, a negative sequence network is introduced, and positive and negative sequence quantities jointly participate in the formation of port power. Therefore, the original power angle relationship and stability conditions established only based on a single sequence component cannot be directly used for this condition. To obtain judgment results that match the above network structure, it is necessary to characterize the equilibrium points and transient energy changes of the positive-sequence system and the negative-sequence system respectively, and to form a stability discrimination method applicable to asymmetric fault processes. Summary of the Invention

[0006] To address the problem that existing stability criteria based on symmetrical faults cannot directly characterize the two-sequence operating states under asymmetrical faults, this invention provides a method for determining transient synchronization instability in grid-connected power generation systems. This method, for fault networks where both positive and negative sequence components exist simultaneously, establishes an equilibrium point existence judgment and a transient energy judgment, respectively, and accordingly provides the transient synchronization stability result of the system during the fault process.

[0007] The technical solution of this invention is implemented as follows:

[0008] A method for determining transient synchronization instability in grid-connected power generation systems, comprising the following steps:

[0009] A1) According to the grid connection guidelines, the reference values ​​for the positive and negative sequence reactive power output of a grid-connected power generation system are set as follows:

[0010]

[0011] In the formula , These represent the positive-sequence and negative-sequence reactive power reference values ​​for a grid-connected power generation system, respectively. , These represent the proportionality coefficients of the positive-sequence and negative-sequence reactive currents, respectively. , These represent the d-axis components of the positive-sequence and negative-sequence voltages at the grid connection point, respectively. The rated current of the system. This is the system's rated voltage;

[0012] A2) Reference values ​​of positive and negative sequence reactive power of grid-connected power generation systems and Input the positive and negative sequence reactive power-voltage control loops respectively. Based on the deviation between the reactive power reference value and the actual reactive power value, calculate the positive and negative sequence voltage command values ​​of the grid-connected power generation system using the following formula:

[0013]

[0014] In the formula , These represent the positive-sequence and negative-sequence voltage command values ​​for a grid-connected power generation system, respectively. and These are the positive-sequence and negative-sequence reactive power droop coefficients, respectively. , These represent the actual values ​​of positive-sequence and negative-sequence reactive power in a grid-type power generation system, respectively.

[0015] A3) Calculate the maximum positive-sequence active power of the grid-connected power generation system during the fault phase using the following formula. and the minimum positive sequence active power :

[0016]

[0017] In the formula This represents the actual value of the positive sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the positive-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle;

[0018] The equilibrium point determination criterion for a positive-sequence system is:

[0019]

[0020] In the formula This represents the positive-sequence active power setpoint during a system fault.

[0021] If the above criteria are met, the positive-order system is determined to have an equilibrium point; if the above criteria are not met, the positive-order system is determined to have no equilibrium point.

[0022] Calculate the maximum negative-sequence active power of a grid-connected power generation system during the fault phase using the following formula. Minimum active power in negative sequence :

[0023]

[0024] In the formula This represents the actual value of the negative sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the negative-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle;

[0025] The equilibrium point determination criterion for a negative-order system is:

[0026]

[0027] In the formula This represents the negative sequence active power setpoint during a system fault.

[0028] If the above criteria are met, the negative-order system is determined to have an equilibrium point; if the above criteria are not met, the negative-order system is determined not to have an equilibrium point.

[0029] If neither the positive nor negative sequence system has an equilibrium point, the grid-connected power generation system is determined to be transiently synchronously unstable; if both the positive and negative sequence systems have equilibrium points, proceed to step A4).

[0030] A4) The transient energy function during a fault in a positive-sequence system is:

[0031]

[0032] In the formula This represents the change in the equivalent kinetic energy of the positive-sequence system. This represents the change in the equivalent potential energy of the positive-sequence system during the transient process of unbalanced power. , These represent the positive-sequence virtual angular frequency and the positive-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the positive-sequence active power of the system; , , These represent the positive sequence work angle, the initial positive sequence work angle, and the final positive sequence work angle during the transient process, respectively. For positive-sequence virtual rotational inertia, Represents the transient energy function of a positive-sequence system;

[0033] The transient energy function during a fault in a negative-sequence system is:

[0034]

[0035] In the formula This represents the change in the equivalent kinetic energy of the negative-order system. This represents the change in the equivalent potential energy of the negative-sequence system during the transient process of unbalanced power. , These represent the negative-sequence virtual angular frequency and the negative-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the negative-sequence active power of the system; , , These represent the negative sequence work angle, the initial negative sequence work angle, and the final negative sequence work angle during the transient process, respectively. For negative-order virtual rotational inertia, Represents the transient energy function of a negative-order system;

[0036] A5) Based on the transient energy function in step A4), the equivalent acceleration area of ​​the positive-sequence system during the fault period. and equivalent deceleration area for:

[0037]

[0038] In the formula , These represent the positive sequence power angle during the fault and the maximum positive sequence power angle after the fault is cleared, respectively.

[0039] Equivalent acceleration area of ​​negative-sequence system during fault and equivalent deceleration area for:

[0040]

[0041] In the formula , These represent the negative sequence power angle during the fault and the maximum negative sequence power angle after the fault is cleared, respectively.

[0042] A6) Based on the equivalent acceleration area and equivalent deceleration area from step A5), solve for the transient synchronization stability criterion of the system during the fault period:

[0043] Criterion for transient synchronization stability of positive-sequence systems:

[0044]

[0045] Criterion for transient synchronization stability of negative-order systems:

[0046]

[0047] In the formula , These represent the energy consumed by damping in a positive-sequence system and the energy consumed by damping in a negative-sequence system, respectively. , These represent the positive-sequence damping coefficient and the negative-sequence damping coefficient, respectively. , These represent the maximum positive sequence work angle and the maximum negative sequence work angle, respectively.

[0048] If both positive and negative sequence systems simultaneously satisfy the above transient synchronization stability criteria, then the grid-type power generation system is transiently synchronized and stable; otherwise, the grid-type power generation system is transiently synchronized and unstable.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] Compared with the analysis method that only establishes a single sequence power angle condition for symmetrical faults, this invention first performs equilibrium point determination on the positive sequence and negative sequence systems respectively, and then combines the acceleration area, deceleration area and damping energy consumption in the two sequence transient processes to complete the stability judgment. This can distinguish the stability constraints of the positive sequence channel and the negative sequence channel on the fault transient process, and provide calculable discrimination conditions for carrying out asymmetrical fault stability assessment of new energy grid-connected systems with grid-connected inverters. Attached Figure Description

[0051] Figure 1 The diagram shows the main circuit topology and control system structure of a grid-type power generation system under asymmetrical short-circuit fault.

[0052] Figure 2 This is a diagram of the power loop control structure for a grid-type power generation system.

[0053] Figure 3 This is a flowchart of the transient stability assessment process for the grid-type power generation system of the present invention.

[0054] Figure 4 The figure shows the simulation results of the grid-type power generation system under different positive sequence damping coefficients.

[0055] Figure 5 The simulation results of the grid-type power generation system under different power command values ​​are shown in the figure.

[0056] Figure 6 The figure shows the simulation results of a grid-connected power generation system under different voltage drop conditions.

[0057] Figure 7 The figure shows the simulation verification results of the negative sequence system of the grid-connected inverter. Detailed Implementation

[0058] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0059] The embodiments of the present invention are based on Figure 1 The main circuit and control structure of the grid-type power generation system shown are the objects of analysis, and are adopted... Figure 2 A transient analysis model is established based on the power loop control relationship shown. Figure 3This is a flowchart of the transient stability assessment process for the grid-connected power generation system of the present invention. During the transient period, the method first determines the reference values ​​of positive-sequence and negative-sequence reactive power based on the dynamic reactive power support constraints given in the grid connection guidelines; then, it checks whether there is a fault operation equilibrium point for the positive-sequence system and the negative-sequence system respectively; for the corresponding sequence system with an equilibrium point, a transient energy function is established based on the equal area relationship, and the equivalent acceleration area and equivalent deceleration area are calculated; then, the positive-sequence and negative-sequence transient synchronous stability criteria are formed by each area quantity and damping energy consumption, thereby outputting the stability judgment results of the two sequence systems under the fault condition respectively. Figures 4-7 Simulation responses are given under different system parameter variations.

[0060] The specific implementation steps of this invention are as follows, and see also... Figure 3 :

[0061] A1) According to the grid connection guidelines, the reference values ​​for the positive and negative sequence reactive power output of a grid-connected power generation system are set as follows:

[0062]

[0063] In the formula , These represent the positive-sequence and negative-sequence reactive power reference values ​​for a grid-connected power generation system, respectively. , These represent the proportionality coefficients of the positive-sequence and negative-sequence reactive currents, respectively. , These represent the d-axis components of the positive-sequence and negative-sequence voltages at the grid connection point, respectively. The rated current of the system. This is the system's rated voltage;

[0064] A2) Reference values ​​of positive and negative sequence reactive power of grid-connected power generation systems and Input the positive and negative sequence reactive power-voltage control loops respectively. Based on the deviation between the reactive power reference value and the actual reactive power value, calculate the positive and negative sequence voltage command values ​​of the grid-connected power generation system using the following formula:

[0065]

[0066] In the formula , These represent the positive-sequence and negative-sequence voltage command values ​​for a grid-connected power generation system, respectively. and These are the positive-sequence and negative-sequence reactive power droop coefficients, respectively. , These represent the actual values ​​of positive-sequence and negative-sequence reactive power in a grid-type power generation system, respectively.

[0067] A3) Calculate the maximum positive-sequence active power of the grid-connected power generation system during the fault phase using the following formula. and the minimum positive sequence active power :

[0068]

[0069] In the formula This represents the actual value of the positive sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the positive-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle;

[0070] The equilibrium point determination criterion for a positive-sequence system is:

[0071]

[0072] In the formula This represents the positive-sequence active power setpoint during a system fault.

[0073] If the above criteria are met, the positive-order system is determined to have an equilibrium point; if the above criteria are not met, the positive-order system is determined to have no equilibrium point.

[0074] Calculate the maximum negative-sequence active power of a grid-connected power generation system during the fault phase using the following formula. Minimum active power in negative sequence :

[0075]

[0076] In the formula This represents the actual value of the negative sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the negative-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle;

[0077] The equilibrium point determination criterion for a negative-order system is:

[0078]

[0079] In the formula This represents the negative sequence active power setpoint during a system fault.

[0080] If the above criteria are met, the negative-order system is determined to have an equilibrium point; if the above criteria are not met, the negative-order system is determined not to have an equilibrium point.

[0081] If neither the positive nor negative sequence system has an equilibrium point, the grid-connected power generation system is determined to be transiently synchronously unstable; if both the positive and negative sequence systems have equilibrium points, proceed to step A4).

[0082] A4) The transient energy function during a fault in a positive-sequence system is:

[0083]

[0084] In the formula This represents the change in the equivalent kinetic energy of the positive-sequence system. This represents the change in the equivalent potential energy of the positive-sequence system during the transient process of unbalanced power. , These represent the positive-sequence virtual angular frequency and the positive-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the positive-sequence active power of the system; , , These represent the positive sequence work angle, the initial positive sequence work angle, and the final positive sequence work angle during the transient process, respectively. For positive-sequence virtual rotational inertia, Represents the transient energy function of a positive-sequence system;

[0085] The transient energy function during a fault in a negative-sequence system is:

[0086]

[0087] In the formula This represents the change in the equivalent kinetic energy of the negative-order system. This represents the change in the equivalent potential energy of the negative-sequence system during the transient process of unbalanced power. , These represent the negative-sequence virtual angular frequency and the negative-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the negative-sequence active power of the system; , , These represent the negative sequence work angle, the initial negative sequence work angle, and the final negative sequence work angle during the transient process, respectively. For negative-order virtual rotational inertia, Represents the transient energy function of a negative-order system;

[0088] A5) Based on the transient energy function in step A4), the equivalent acceleration area of ​​the positive-sequence system during the fault period. and equivalent deceleration area for:

[0089]

[0090] In the formula , These represent the positive sequence power angle during the fault and the maximum positive sequence power angle after the fault is cleared, respectively.

[0091] Equivalent acceleration area of ​​negative-sequence system during fault and equivalent deceleration area for:

[0092]

[0093] In the formula , These represent the negative sequence power angle during the fault and the maximum negative sequence power angle after the fault is cleared, respectively.

[0094] A6) Based on the equivalent acceleration area and equivalent deceleration area from step A5), solve for the transient synchronization stability criterion of the system during the fault period:

[0095] Criterion for transient synchronization stability of positive-sequence systems:

[0096]

[0097] Criterion for transient synchronization stability of negative-order systems:

[0098]

[0099] In the formula , These represent the energy consumed by damping in a positive-sequence system and the energy consumed by damping in a negative-sequence system, respectively. , These represent the positive-sequence damping coefficient and the negative-sequence damping coefficient, respectively. , These represent the maximum positive sequence work angle and the maximum negative sequence work angle, respectively.

[0100] If both positive and negative sequence systems simultaneously satisfy the above transient synchronization stability criteria, then the grid-type power generation system is transiently synchronized and stable; otherwise, the grid-type power generation system is transiently synchronized and unstable.

[0101] Description of the effects of this invention:

[0102] according to Figure 1 The main circuit shown and Figure 2 A simulation model of the power loop control structure is established, and a single-phase ground fault condition is set. The aforementioned criteria are verified by comparing whether each condition satisfies the positive-sequence or negative-sequence transient synchronous stability criterion and its corresponding power, frequency, and power angle responses.

[0103] Figure 4The system response under different positive-sequence damping conditions is presented. Under conditions with larger positive-sequence damping, the system satisfies the positive-sequence transient synchronous stability criterion; the output power, frequency, and power angle gradually converge after the transient process, and the system remains transiently synchronous and stable. Under conditions with smaller positive-sequence damping, the system does not satisfy the positive-sequence transient synchronous stability criterion; the output power, frequency, and power angle fail to converge, and the system experiences transient synchronous instability. The simulation results under both conditions are consistent with the determination results of the positive-sequence transient synchronous stability criterion, indicating that the criterion can effectively determine the transient synchronous stability state of a positive-sequence system.

[0104] Figure 5 The system response under different active power given conditions during a fault is presented. Under a lower active power given condition, the system satisfies the positive-sequence transient synchronous stability criterion and can recover stability after the transient process. However, when the active power given level is increased during the fault, the system no longer satisfies the positive-sequence transient synchronous stability criterion; the output power, frequency, and power angle fail to converge, and the system experiences transient synchronous instability. The simulation results under both conditions are consistent with the determination results of the positive-sequence transient synchronous stability criterion, indicating that the criterion can effectively determine the transient synchronous stability state of a positive-sequence system.

[0105] Figure 6 The system response under different voltage dip conditions is presented. Under shallow voltage dip conditions, the system satisfies the positive-sequence transient synchronous stability criterion; the output power, frequency, and power angle gradually converge after the transient process, and the system remains transiently synchronous and stable. Under deep voltage dip conditions, the system does not satisfy the positive-sequence transient synchronous stability criterion; the system frequency and power angle fail to converge, and the system experiences transient synchronous instability. The simulation results under both conditions are consistent with the determination results of the positive-sequence transient synchronous stability criterion, indicating that the criterion can effectively determine the transient synchronous stability state of a positive-sequence system.

[0106] Figure 7 The system response under different negative-sequence damping conditions is presented. Under conditions of large negative-sequence damping, the system satisfies the negative-sequence transient synchronous stability criterion; the output power, frequency, and power angle gradually converge after the transient process, and the negative-sequence system remains transiently synchronously stable. Under conditions of small negative-sequence damping, the system does not satisfy the negative-sequence transient synchronous stability criterion; the output power, frequency, and power angle fail to converge, and the negative-sequence system experiences transient synchronous instability. The simulation results under both conditions are consistent with the determination results of the negative-sequence transient synchronous stability criterion, indicating that the criterion can effectively determine the transient synchronous stability state of the negative-sequence system.

[0107] The above simulation response based on the asymmetric short-circuit fault of the power grid corresponds to the criterion calculation results under various operating conditions, indicating that the positive-sequence system transient synchronization stability criterion and negative-sequence system transient synchronization stability criterion established in this invention can be used to determine the transient synchronization stability of grid-type power generation systems under asymmetric short-circuit faults.

[0108] Finally, it should be noted that the above examples of the present invention are merely illustrative and not intended to limit the implementation of the invention. Although the applicant has described the present invention in detail with reference to preferred embodiments, those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for determining transient synchronization instability in grid-connected power generation systems, characterized in that: The specific steps are as follows: A1) According to the grid connection guidelines, the reference values ​​for the positive and negative sequence reactive power output of a grid-connected power generation system are set as follows: In the formula , These represent the positive-sequence and negative-sequence reactive power reference values ​​for a grid-connected power generation system, respectively. , These represent the proportionality coefficients of the positive-sequence and negative-sequence reactive currents, respectively. , These represent the d-axis components of the positive-sequence and negative-sequence voltages at the grid connection point, respectively. The rated current of the system. This is the system's rated voltage; A2) Reference values ​​of positive and negative sequence reactive power of grid-connected power generation systems and Input the positive and negative sequence reactive power-voltage control loops respectively. Based on the deviation between the reactive power reference value and the actual reactive power value, calculate the positive and negative sequence voltage command values ​​of the grid-connected power generation system using the following formula: In the formula , These represent the positive-sequence and negative-sequence voltage command values ​​for a grid-connected power generation system, respectively. and These are the positive-sequence and negative-sequence reactive power droop coefficients, respectively. , These represent the actual values ​​of positive-sequence and negative-sequence reactive power in a grid-type power generation system, respectively. A3) Calculate the maximum positive-sequence active power of the grid-connected power generation system during the fault phase using the following formula. Minimum positive sequence active power : In the formula This represents the actual value of the positive sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the positive-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle; The equilibrium point determination criterion for a positive-sequence system is: In the formula This represents the positive-sequence active power setpoint during a system fault. If the above criteria are met, the positive-order system is determined to have an equilibrium point; if the above criteria are not met, the positive-order system is determined to have no equilibrium point. Calculate the maximum negative-sequence active power of a grid-connected power generation system during the fault phase using the following formula. Minimum active power in negative sequence : In the formula This represents the actual value of the negative sequence voltage at the power grid fault point. , These represent the magnitudes of the equivalent admittances of the negative-sequence composite sequence network at the machine end and the fault point, respectively. for The corresponding admittance angle; The equilibrium point determination criterion for a negative-order system is: In the formula This represents the negative sequence active power setpoint during a system fault. If the above criteria are met, the negative-order system is determined to have an equilibrium point; if the above criteria are not met, the negative-order system is determined not to have an equilibrium point. If neither the positive nor negative sequence system has an equilibrium point, the grid-connected power generation system is determined to be transiently synchronously unstable; if both the positive and negative sequence systems have equilibrium points, proceed to step A4). A4) The transient energy function during a fault in a positive-sequence system is: In the formula This represents the change in the equivalent kinetic energy of the positive-sequence system. This represents the change in the equivalent potential energy of the positive-sequence system during the transient process of unbalanced power. , These represent the positive-sequence virtual angular frequency and the positive-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the positive-sequence active power of the system; , , These represent the positive sequence work angle, the initial positive sequence work angle, and the final positive sequence work angle during the transient process, respectively. For positive-sequence virtual rotational inertia, Represents the transient energy function of a positive-sequence system; The transient energy function during a fault in a negative-sequence system is: In the formula This represents the change in the equivalent kinetic energy of the negative-order system. This represents the change in the equivalent potential energy of the negative-sequence system during the transient process of unbalanced power. , These represent the negative-sequence virtual angular frequency and the negative-sequence rated angular frequency of the power grid, respectively. This represents the actual value of the negative-sequence active power of the system; , , These represent the negative sequence work angle, the initial negative sequence work angle, and the final negative sequence work angle during the transient process, respectively. For negative-order virtual rotational inertia, Represents the transient energy function of a negative-order system; A5) Based on the transient energy function in step A4), the equivalent acceleration area of ​​the positive-sequence system during the fault period. and equivalent deceleration area for: In the formula , These represent the positive sequence power angle during the fault and the maximum positive sequence power angle after the fault is cleared, respectively. Equivalent acceleration area of ​​negative-sequence system during fault and equivalent deceleration area for: In the formula , These represent the negative sequence power angle during the fault and the maximum negative sequence power angle after the fault is cleared, respectively. A6) Based on the equivalent acceleration area and equivalent deceleration area from step A5), solve for the transient synchronization stability criterion of the system during the fault period: Criterion for transient synchronization stability of positive-sequence systems: Criterion for transient synchronization stability of negative-order systems: In the formula , These represent the energy consumed by damping in a positive-sequence system and the energy consumed by damping in a negative-sequence system, respectively. , These represent the positive-sequence damping coefficient and the negative-sequence damping coefficient, respectively. , These represent the maximum positive sequence work angle and the maximum negative sequence work angle, respectively. If both positive and negative sequence systems simultaneously satisfy the above transient synchronization stability criteria, then the grid-type power generation system is transiently synchronized and stable; otherwise, the grid-type power generation system is transiently synchronized and unstable.

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