System transient stability parameter collaborative optimization method after variable speed pumped storage unit is connected

Abstract

The application provides a system transient stability parameter collaborative optimization method after a variable-speed pumped storage unit is connected, comprising the following steps: constructing a system model based on a hybrid pumped storage unit joint sending system to obtain a constant-speed unit electromagnetic power equation and a variable-speed unit grid connection point voltage equation; obtaining a first control parameter affecting system power angle stability according to the constant-speed unit electromagnetic power equation and constructing a first constraint, and obtaining a second control parameter affecting transient overvoltage according to the variable-speed unit grid connection point voltage equation and constructing a second constraint; running the system model under a preset fault, and optimizing the value of the first control parameter according to the first constraint and the value of the second control parameter according to the second constraint based on a first stability criterion, a second stability criterion and a third stability criterion. The application comprehensively considers system transient power angle stability and transient overvoltage suppression, and effectively improves system transient power angle stability and voltage stability by optimizing the fault ride-through performance of the variable-speed pumped storage unit.

Description

Technical Field

[0001] This invention relates to the field of pumped-storage units, specifically to a method for collaborative optimization of system transient stability parameters after a variable-speed pumped-storage unit is connected. Background Technology

[0002] Pumped storage power stations play a role in peak shaving and valley filling. They are currently a mature and cost-effective energy storage technology capable of large-scale storage and long-term discharge, and have broad application prospects in the context of new power systems. However, variable-speed pumped storage systems, when transmitted through weak systems, pose certain safety and stability risks under different fault scenarios. These risks mainly manifest in two ways: first, control switching throughout the fault process can lead to complex changes in system active power, affecting the power angle stability of the near-field synchronous generator; second, inconsistencies in voltage ride-through control parameters under different fault scenarios may cause transient overvoltage problems. Current parameter optimization methods for improving system stability using variable-speed units mainly focus on enhancing system power angle stability.

[0003] Existing technical solutions mainly focus on improving the system's power angle stability. They only consider the effect of the fault ride-through control parameters of the variable speed unit on improving the system's transient stability, without fully considering the coordination of the fault ride-through control parameters of the variable speed unit. This may lead to transient overvoltage problems and affect the safe and stable operation of the system. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a collaborative optimization method for system transient stability parameters after the connection of variable speed pumped-storage units. This method optimizes the fault ride-through performance of variable speed pumped-storage units and effectively improves the transient power angle stability and voltage stability of the system.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for collaborative optimization of system transient stability parameters after the connection of a variable speed pumped storage unit, comprising the following steps: constructing a system model based on a hybrid pumped storage unit joint power transmission system;

[0006] Based on the system model, the electromagnetic power equation of the constant-speed unit and the grid connection voltage equation of the variable-speed unit are obtained.

[0007] The first control parameter is obtained based on the electromagnetic power equation of the constant-speed unit, and the first control parameter is a control parameter that affects the stability of the system power angle; the second control parameter is obtained based on the grid connection point voltage equation of the variable-speed unit, and the second control parameter is a control parameter that affects transient overvoltage.

[0008] A first constraint is constructed based on the first control parameter, and a second constraint is constructed based on the second control parameter.

[0009] The system model is run under a preset fault condition, and a first stability criterion, a second stability criterion, and a third stability criterion are obtained.

[0010] Based on the first stability criterion, the second stability criterion, and the third stability criterion, the value of the first control parameter is optimized according to the first constraint, and the value of the second control parameter is optimized according to the second constraint.

[0011] In some embodiments, the first stability criterion is that the combined pumped storage power generation system does not have a power angle stability problem, the second stability criterion is that the variable speed unit rotor in the combined pumped storage power generation system has no overspeed risk, and the third stability criterion is that the transient overvoltage of the combined pumped storage power generation system meets the requirements.

[0012] In some embodiments, the steps of optimizing the value of the first control parameter according to the first constraint and optimizing the value of the second control parameter according to the second constraint, based on the first stability criterion, the second stability criterion, and the third stability criterion, are as follows:

[0013] Step S1: Obtain the preset step size, the first initial value, and the second initial value, wherein the first initial value is the initial value of the first control parameter, and the second initial value is the initial value of the second control parameter;

[0014] Step S2: Obtain the initial operating condition based on the first initial value and the second initial value; obtain the value of the first control parameter based on the first initial value; and obtain the value of the second control parameter based on the second initial value.

[0015] Step S3: Based on the initial operating conditions, run the system model under the preset fault conditions:

[0016] Step S4: Based on the preset step size, adjust the value of the first control parameter within the first constraint to obtain the first intermediate value;

[0017] Step S5: Based on the first intermediate value, obtain a first judgment according to the first stability criterion:

[0018] If the first judgment determines that the first stability criterion is not true, then a second judgment is obtained based on the second stability criterion:

[0019] If the second determination is that the second stability criterion is true, then update the value of the first control parameter and repeat step S4;

[0020] If the second judgment indicates that the second stability criterion is not valid, then the output optimization result is "no optimization required".

[0021] If the first determination is that the first stability criterion is true, then update the value of the second control parameter according to the first intermediate value and execute step S6;

[0022] Step S6: Based on the preset step size, adjust the value of the second control parameter within the second constraint to obtain a second intermediate value;

[0023] Step S7: Based on the second intermediate value, obtain a third judgment according to the third stability criterion:

[0024] If the third determination indicates that the third stability criterion is not met, update the value of the second control parameter and repeat step S6.

[0025] If the third judgment is true according to the third stability criterion, then the fourth judgment is obtained based on the first stability criterion;

[0026] If the fourth determination is that the first stability criterion is not met, then the value of the first control parameter is updated according to the second intermediate value and step S4 is repeated.

[0027] If the fourth determination is true for the first stability criterion, then update the first intermediate value according to the second intermediate value and execute step S8.

[0028] Step S8: Obtain a first optimized value based on the first intermediate value, and obtain a second optimized value based on the second intermediate value. The first optimized value is the value after optimization of the first control parameter, and the second optimized value is the value after optimization of the second control parameter.

[0029] In some embodiments, the preset fault is an "N-1" fault.

[0030] In some embodiments, the first control parameters include an active current limit 1, an active current limit 2, and a reactive current limit during the low-voltage ride-through of the variable speed unit.

[0031] In some embodiments, the first constraint is:

[0032] ;

[0033] In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. The active current limit for the low voltage ride-through period of the variable speed unit is 2. This refers to the reactive current limit during low-voltage ride-through of the variable speed unit.

[0034] In some embodiments, adjusting the value of the first control parameter within the first constraint based on the preset step size includes:

[0035] The active current limit 1 and the active current limit 2 of the variable speed unit during low voltage ride-through are reduced by the preset step size, and the reactive current limit of the variable speed unit during low voltage ride-through is increased by the preset step size.

[0036] In some embodiments, the second control parameters include an active current limit 1 during the low-voltage ride-through of the variable speed unit, a reactive current limit 1 during the low-voltage ride-through of the variable speed unit, and a voltage threshold for the low-voltage ride-through interval 2.

[0037] In some embodiments, the second constraint is:

[0038] ;

[0039] In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. This refers to the reactive current limit during low-voltage ride-through of variable-speed generator sets. This is the voltage threshold for low-voltage crossing interval 2.

[0040] In some embodiments, adjusting the value of the second control parameter within the second constraint based on the preset step size includes:

[0041] The reactive current limit and the voltage threshold of the low voltage ride-through interval 2 of the variable speed unit are reduced by the preset step size, and the active current limit 1 of the low voltage ride-through interval of the variable speed unit is increased by the preset step size.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This disclosure comprehensively considers the system's transient power angle stability and the suppression of transient overvoltage. Based on relatively independent first and second constraints, it comprehensively optimizes the first control parameter affecting the system's power angle stability and the second control parameter affecting transient overvoltage, thereby solving the coupling problem of transient power angle stability and transient overvoltage after the variable-speed pumped storage unit is connected to the system. Through the coordinated optimization of the variable-speed pumped storage unit parameters, the fault ride-through performance of the variable-speed pumped storage unit is optimized, avoiding the transient overvoltage problem caused by the incoordination of fault ride-through parameters after the variable-speed pumped storage unit is connected to the system. This can effectively improve the system's transient power angle stability and voltage stability. Attached Figure Description

[0044] Figure 1 This is a flowchart illustrating the collaborative optimization method for system transient stability parameters after the connection of the variable-speed pumped-storage unit disclosed in this paper.

[0045] Figure 2 This is a system model constructed by our company based on a hybrid pumped storage unit combined power transmission system;

[0046] Figure 3 This is a fault ride-through characteristic diagram of a variable speed unit;

[0047] Figure 4 The effects of the active current limit 1 and the reactive current limit 1 during the low voltage ride-through of the variable speed unit on transient overvoltage;

[0048] Figure 5 The impact of reactive current limits on transient overvoltages during low-voltage ride-through of variable-speed generator sets;

[0049] Figure 6 The effects of the voltage thresholds in low-voltage ride-through interval 2 and low-voltage ride-through interval 1 on transient overvoltages;

[0050] Figure 7 The impact of active current limit 1 and active current limit 2 during low voltage ride-through of variable speed generator sets on transient overvoltage.

[0051] Figure 8 The power angle characteristic curves of constant speed generators under different active currents of variable speed generators;

[0052] Figure 9 The power angle characteristic curves of constant-speed generators under different reactive currents of variable-speed generators;

[0053] Figure 10 The system power angle curves before and after control parameter optimization in Example 1 are shown.

[0054] Figure 11 The overvoltage curves at the generator terminals of the variable speed unit before and after optimization of control parameters in Example 1;

[0055] Figure 12 The system power angle curves before and after control parameter optimization in Example 2 are shown.

[0056] Figure 13 The overvoltage curves at the generator terminals of the variable speed unit before and after the control parameters were optimized in Example 2. Detailed Implementation

[0057] To clearly illustrate the technical features of this solution, the implementation methods of this application will be described in detail below with reference to the accompanying drawings and embodiments. This will allow for a full understanding and implementation of how this application uses technical means to solve technical problems and achieve corresponding technical effects. The embodiments of this application and the various features within them can be combined with each other without conflict, and the resulting technical solutions are all within the protection scope of this application.

[0058] See Figure 1 This disclosure provides a method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit, including the following steps: constructing a system model based on a hybrid pumped-storage unit joint power transmission system, see [link to relevant documentation]. Figure 2 Hybrid pumped storage units include constant-speed pumped storage units and variable-speed pumped storage units. Figure 2 middle: The voltage is an infinite bus voltage, and this bus is used as the voltage phase reference point. The potential amplitude within the constant-speed generator unit. The internal potential power angle of a constant-speed generator unit; For the grid connection voltage of the variable speed unit, The voltage power angle at the grid connection point of the variable speed unit; Transient Reactors for Constant Speed ​​Units Reactance of step-up transformer The sum of For the step-up transformer reactor of the variable speed unit, This is the equivalent reactance of a single-circuit transmission line; For the output current of the constant speed generator unit, The power angle of the output current of the constant speed generator unit. This refers to the output current of the variable speed unit. The power angle of the output current of the variable speed unit. For transmitting current in a double-circuit transmission line, The current-carrying angle for a double-circuit transmission line;

[0059] The electromagnetic power equation of the constant-speed unit and the grid connection voltage equation of the variable-speed unit are obtained based on the system model.

[0060] The voltage equation for the grid connection point of the variable speed unit is:

[0061] ;

[0062] ;

[0063] In the formula, For the equivalent reactance of a double-circuit transmission line, To output active current for the variable speed generator unit. To output reactive current for the variable speed unit;

[0064] The electromagnetic power equation for a constant-speed generator set is:

[0065] ;

[0066] In the formula, For the electromagnetic power of the constant speed unit, This is the first intermediate expression. This is the second intermediate expression;

[0067] ;

[0068] ;

[0069] During steady state, the variable speed unit only outputs active power, which can be approximated as... and In phase, that is ;

[0070] If the requirement is that the variable speed unit should only output reactive current to maintain the common bus voltage during a fault, and the fault period is not considered... Dynamic changes can be obtained during the fault period If the variable speed unit outputs active current simultaneously during the fault, then ,in, , This indicates the angle by which the phase angle of the variable speed unit's current lags behind the phase angle of the grid-connected voltage during the fault period.

[0071] The first control parameter is obtained based on the electromagnetic power equation of the constant-speed generator set. This first control parameter is a control parameter that affects the stability of the system's power angle. In some embodiments, the first control parameter includes an active current limit of 1 during the low-voltage ride-through of the variable-speed generator set. Active current limit during low voltage ride-through of variable speed unit 2 Reactive current limits during low voltage ride-through of variable speed units ;

[0072] The second control parameter is obtained based on the voltage equation at the grid connection point of the variable speed unit. This second control parameter is a control parameter affecting transient overvoltage. In some embodiments, the second control parameter includes an active current limit of 1 during the low-voltage ride-through of the variable speed unit. Reactive current limits during low voltage ride-through of variable speed units and the voltage threshold of low voltage crossover interval 2 ;

[0073] Fault ride-through characteristics of the transmission unit during a fault, such as Figure 3 As shown; Figure 3 In the middle, when the grid voltage is lower than the voltage threshold of the low voltage crossing interval 2. When the variable speed unit enters the low-voltage control phase, the output active current of the variable speed unit does not exceed the output active current limit. The output reactive current of the variable speed unit shall not exceed the output reactive current limit. When the grid voltage is lower than the voltage threshold of low voltage crossing interval 1 V LVL1 At that time, the output active current of the variable speed unit is 1 times the active current limit during the low voltage ride-through period of the variable speed unit. The reactive current output of the variable speed unit is the reactive current limit during the low voltage ride-through period of the variable speed unit. .

[0074] Active current limit during fault for:

[0075] ;

[0076] In the formula, This is the third intermediate expression. , This refers to the voltage measurement at the grid connection point during the fault period;

[0077] Reactive current limit during fault for:

[0078] ;

[0079] In the formula, This is the fourth intermediate expression. ;

[0080] It can be seen that when the grid voltage drops to different depths, the fault ride-through control strategy of the variable speed unit is at different levels.

[0081] When the fault zone is located in the low-voltage crossing zone 1, the voltage at the grid connection point of the transmission unit after the fault is cleared is:

[0082] ;

[0083] ;

[0084] In the formula, A This is the fifth intermediate expression;

[0085] At this time, the transient overvoltage is mainly affected by the fault control parameters of the variable speed unit, specifically the active current limit 1 during the low voltage ride-through of the variable speed unit. I pLV1 Reactive current limits during low voltage ride-through of variable speed units I qLV1 The impact. The fault control parameters of the variable speed unit were changed, and the active current limit during the low voltage ride-through of the variable speed unit was set to 1. I pLV1 Reactive current limits during low voltage ride-through of variable speed units I qLV1 Observe the voltage at the grid connection point of the variable speed unit. U p Changes, such as Figure 4 As shown;

[0086] from Figure 4It can be seen that when the fault interval is located in the low-voltage ride-through interval 1, the transient overvoltage is mainly affected by the active current limit 1 during the low-voltage ride-through of the variable speed unit, which is a fault control parameter of the variable speed unit. I pLV1 Reactive current limits during low voltage ride-through of variable speed units I qLV1 The impact of fault control parameters on the variable speed unit, including the active current limit during low voltage ride-through of the variable speed unit, is 1. I pLV1 The increase in voltage at the grid connection point of the variable speed unit U p The more active current the variable-speed pumped storage unit generates during low-voltage ride-through, the smaller the peak transient overvoltage at the grid connection point after fault clearance; and the lower the reactive current limit during low-voltage ride-through of the variable-speed unit. I qLV1 The increase in voltage at the grid connection point of the variable speed unit U p The more reactive current the variable-speed pumped storage generates during low-voltage ride-through, the greater the peak transient overvoltage at the grid connection point after the fault is cleared.

[0087] When the fault zone is located in low-voltage crossing zone 2, the voltage at the grid connection point of the transmission unit after the fault is cleared is:

[0088] ;

[0089] ;

[0090] In the formula, B This is the sixth intermediate expression;

[0091] At this time, the transient overvoltage is mainly affected by the fault control parameters of the variable speed unit, specifically the reactive current limit during the low voltage ride-through of the variable speed unit. I qLV1 Voltage threshold of low voltage crossing interval 1 V LVL1 Voltage threshold of low voltage crossover zone 2 V LVL2 、 Active current limit 1 during low voltage ride-through of variable speed unit I pLV1 Active current limit during low voltage ride-through of variable speed unit 2 I pLV2 The impact of changing the fault control parameters of the above-mentioned variable speed unit is observed. The voltage at the grid connection point of the variable speed unit is then monitored. U p Changes, such as Figure 5-7 As shown;

[0092] from Figure 5-7As can be seen from this, when the fault interval is located in the low-voltage ride-through interval 2, the transient overvoltage is mainly affected by the reactive current limit during the low-voltage ride-through of the variable speed unit. I qLV1 Voltage threshold of low voltage crossing interval 1 V LVL1 The impact of low voltage crossing range 1 on the voltage threshold V LVL1 The increase in voltage at the grid connection point of the variable speed unit U p The greater the reactive current generated by the variable-speed pumped-storage unit during the low-voltage ride-through period, the smaller the peak transient overvoltage at the grid connection point after fault clearance; with the increase of the reactive current limit during the low-voltage ride-through period of the variable-speed unit... I qLV1 The increase in voltage at the grid connection point of the variable speed unit U p The more reactive current the variable-speed pumped storage generates during the low-voltage period, the greater the peak value of the transient overvoltage at the grid connection point after the fault is cleared.

[0093] Based on the electromagnetic power equation of a constant-speed generator set, plot the curves of electromagnetic power as a function of power angle under the active power output of different variable-speed generator sets, such as... Figure 8 As shown; based on the electromagnetic power equation of a constant-speed generator set, plot the curves of electromagnetic power as a function of power angle under reactive power output of different variable-speed generator sets, as follows. Figure 9 As shown;

[0094] Depend on Figure 8 It can be seen that as the active power output of the variable speed unit decreases, the electromagnetic power curve of the constant speed unit shifts upward, and the corresponding acceleration area decreases during the fault period. This is beneficial to the power angle stability of the constant speed unit and reduces the active current limit during the low voltage ride-through of the variable speed unit. I pLV1 This can improve the transient stability of the system. After the fault is cleared, as the variable speed unit exits low-voltage ride-through control as the voltage recovers, active power gradually recovers, reducing the active current limit of the variable speed unit during low-voltage ride-through by 2. I pLV2 It can reduce the active power output of the variable speed unit during the recovery period and increase the active power output of the constant speed unit. The corresponding reduction area is increased, which is beneficial to the stability of the power angle of the constant speed unit.

[0095] Depend on Figure 9 It can be seen that as the reactive power output of the variable speed unit decreases during a fault, the electromagnetic power curve of the constant speed unit shifts upward, and the corresponding acceleration area decreases during the fault, which is beneficial to the power angle stability of the constant speed unit. Therefore, it is appropriate to increase the reactive current limit of the variable speed unit during low voltage ride-through. I qLV1 It can improve the transient stability of the system.

[0096] A first constraint is constructed based on the first control parameter, and a second constraint is constructed based on the second control parameter.

[0097] Parameters that have a significant impact on the system's power angle stability are selected as the first control parameters, and the constraint range of these parameters is set to construct the first constraint; in some embodiments, the first constraint is:

[0098] ;

[0099] In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. The active current limit for the low voltage ride-through period of the variable speed unit is 2. This refers to the reactive current limit during low-voltage ride-through of the variable speed unit.

[0100] Parameters that have a significant impact on transient overvoltages are selected as second control parameters, and the constraint ranges of these parameters are set to construct the second constraint; in some embodiments, the second constraint is:

[0101] ;

[0102] In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. This refers to the reactive current limit during low-voltage ride-through of variable-speed generator sets. This is the voltage threshold for low-voltage crossing interval 2.

[0103] The system model is run under a preset fault. In some embodiments, the preset fault is an "N-1" fault, and a first stability criterion, a second stability criterion, and a third stability criterion are obtained. The first stability criterion is that there is no power angle stability problem in the hybrid pumped storage unit combined power transmission system. The second stability criterion is that the rotor of the variable speed unit in the hybrid pumped storage unit combined power transmission system has no overspeed risk. The third stability criterion is that the transient overvoltage of the hybrid pumped storage unit combined power transmission system meets the requirements.

[0104] Based on the first stability criterion, the second stability criterion, and the third stability criterion, the value of the first control parameter is optimized according to the first constraint, and the value of the second control parameter is optimized according to the second constraint.

[0105] In some embodiments, the steps of optimizing the value of the first control parameter according to the first constraint and optimizing the value of the second control parameter according to the second constraint based on the first stability criterion, the second stability criterion, and the third stability criterion are as follows:

[0106] Step S1: Obtain the preset step size, the first initial value, and the second initial value. The first initial value is the initial value of the first control parameter, and the second initial value is the initial value of the second control parameter.

[0107] Step S2: Obtain the initial operating conditions based on the first initial value and the second initial value; obtain the value of the first control parameter based on the first initial value; and obtain the value of the second control parameter based on the second initial value.

[0108] Step S3: Based on the initial operating conditions, run the system model under preset fault conditions:

[0109] Step S4: Based on a preset step size, adjust the value of the first control parameter within the first constraint to obtain a first intermediate value; in some embodiments, adjusting the value of the first control parameter within the first constraint based on a preset step size includes:

[0110] The active current limit 1 and the active current limit 2 during the low voltage ride-through of the variable speed unit are reduced by a preset step size, and the reactive current limit during the low voltage ride-through of the variable speed unit is increased by a preset step size.

[0111] Step S5: Based on the first intermediate value, obtain the first judgment according to the first stability criterion:

[0112] If the first criterion for stability is not met, then the second criterion for stability is used to obtain the second criterion for stability:

[0113] If the second judgment is true and the second stability criterion is met, then update the value of the first control parameter and repeat step S4.

[0114] If the second judgment indicates that the second stability criterion is not valid, then the output optimization result is "no optimization required".

[0115] If the first judgment is true and the first stability criterion is met, then update the value of the second control parameter according to the first intermediate value and execute step S6.

[0116] Step S6: Based on a preset step size, adjust the value of the second control parameter within the second constraint to obtain a second intermediate value; in some embodiments, adjusting the value of the second control parameter within the second constraint based on a preset step size includes:

[0117] The reactive current limit and voltage threshold of the low voltage ride-through interval 2 of the variable speed unit are reduced by a preset step size, and the active current limit 1 of the low voltage ride-through interval of the variable speed unit is increased by a preset step size.

[0118] Step S7: Based on the second intermediate value, obtain the third judgment according to the third stability criterion:

[0119] If the third judgment determines that the third stability criterion is not valid, update the value of the second control parameter and repeat step S6.

[0120] If the third judgment is true according to the third stability criterion, then the fourth judgment is obtained according to the first stability criterion.

[0121] If the fourth judgment determines that the first stability criterion is not met, then update the value of the first control parameter according to the second intermediate value and repeat step S4.

[0122] If the fourth judgment is true for the first stability criterion, then update the first intermediate value according to the second intermediate value and execute step S8.

[0123] Step S8: Obtain the first optimized value based on the first intermediate value, and obtain the second optimized value based on the second intermediate value. The first optimized value is the value after optimization of the first control parameter, and the second optimized value is the value after optimization of the second control parameter.

[0124] The system performs an N-1 fault scan under the extreme power transmission conditions of the pumped storage power station. Under the premise of satisfying the first constraint, the active current limit during the low-voltage ride-through of the variable-speed generator is reduced by a fixed step size (i.e., a preset step size). I pLV1 Active current limit 2 during low voltage ride-through of variable speed unit I pLV2 The value was increased, and the reactive current limit during low-voltage ride-through of the variable speed unit was raised. I qLV1 This provides reactive power support. Next, the system is verified for power angle stability issues. If a power angle stability issue exists, the speed of the transmission unit needs further inspection to determine if it exceeds its specified range, in order to assess the risk of instability. If the speed exceeds the specified range, it indicates a risk of speed instability, and further parameter optimization is unnecessary; if the speed is within the specified range, it indicates no risk of instability, and the optimization process should be repeated. If the system does not have a power angle stability issue, the parameter optimization phase for suppressing transient overvoltages can proceed.

[0125] Under the premise of satisfying the second constraint, the reactive current limit during the low voltage ride-through of the variable speed unit is reduced by a fixed step size, i.e., a preset step size. I qLV1 Voltage threshold of low voltage crossover interval 2 V LVL2 At the same time, the active current limit during low-voltage ride-through of variable speed units is increased by 1. I pLV1 Verify if the system has a transient overvoltage problem. If a transient overvoltage problem exists, continue the optimization process. If no transient overvoltage problem exists, continue to verify if the system has a power angle stability problem and repeat the optimization of the transient power angle stability component. If no power angle stability problem exists, stop the optimization. This result is the parameter result after optimization under the current operating conditions.

[0126] The above describes the optimization of control parameters for variable-speed pumped storage units using a fixed-step iterative method. Alternatively, a multi-objective optimization function with power angle and overvoltage constraints can be established, and optimization algorithms can be used to optimize the control parameters of variable-speed pumped storage units.

[0127] Calculation example 1

[0128] Taking a pumped storage power station in northern Hebei as an example, a detailed system model was built in BPA, and the parameters of the variable-speed pumped storage units were optimized using the method proposed in this paper. The pumped storage power station includes 10 constant-speed pumped storage units with a capacity of 300MW and 2 variable-speed pumped storage units with a capacity of 300MW. The system model parameter settings are shown in Table 1.

[0129] Table 1 System Model Parameter Settings

[0130]

[0131] The pumped storage power station is configured to transmit power via a 500kV line over a distance of 200km. A three-phase short-circuit fault is assumed to occur at the end of the 500kV line. Table 2 shows the parameters for the variable speed unit's fault-crossing control before and after optimization. The system power angle curves and the variable speed unit's overvoltage curves before and after control parameter optimization are also provided in the table. Figure 10 , 11 ;

[0132] Table 2 Parameters before and after fault ride-through control optimization for the variable speed unit in Example 1

[0133]

[0134] Depend on Figure 10 , 11 It is evident that the system experienced power angle instability before the optimization of the fault control parameters of the variable speed unit, and the system power angle gradually stabilized after the optimization of the fault control parameters; the power at the grid connection point when the fault was cleared met the overvoltage requirements, and no optimization was needed.

[0135] Calculation example 2

[0136] Taking a pumped storage power station in northern Hebei Province as an example, a detailed model was built in BPA, and the parameters of the variable-speed pumped storage units were optimized using the method proposed in this paper. The pumped storage power station includes five 300MW constant-speed pumped storage units and seven 300MW variable-speed pumped storage units. The system model parameter settings are shown in Table 1.

[0137] The pumped storage power station is configured to transmit power via a 500kV line over a distance of 200km. A three-phase short-circuit fault is assumed to occur at the end of the 500kV line. Table 3 shows the parameters for the variable speed unit's fault-crossing control before and after optimization. The system power angle curves and the variable speed unit's overvoltage curves before and after control parameter optimization are also provided in Table 3. Figure 12 , 13 ;

[0138] Table 3. Parameters before and after fault ride-through control optimization for the variable speed unit in Example 2.

[0139]

[0140] Depend on Figure 12 , 13 It is evident that overvoltage occurred at the grid connection point before the optimization of the fault control parameters of the variable speed unit, but no overvoltage occurred at the grid connection point after the optimization; the system power angle meets the power angle stability condition and no optimization is required.

[0141] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit, characterized in that: Includes the following steps: A system model was constructed based on the combined power transmission system of hybrid pumped storage units. Based on the system model, the electromagnetic power equation of the constant-speed unit and the grid connection voltage equation of the variable-speed unit are obtained. The first control parameter is obtained based on the electromagnetic power equation of the constant-speed unit, and the first control parameter is a control parameter that affects the stability of the system power angle; the second control parameter is obtained based on the grid connection point voltage equation of the variable-speed unit, and the second control parameter is a control parameter that affects transient overvoltage. A first constraint is constructed based on the first control parameter, and a second constraint is constructed based on the second control parameter. The system model is run under a preset fault condition, and a first stability criterion, a second stability criterion, and a third stability criterion are obtained. Based on the first stability criterion, the second stability criterion, and the third stability criterion, the value of the first control parameter is optimized according to the first constraint, and the value of the second control parameter is optimized according to the second constraint; Based on the first stability criterion, the second stability criterion, and the third stability criterion, the steps of optimizing the value of the first control parameter according to the first constraint and optimizing the value of the second control parameter according to the second constraint are as follows: Step S1: Obtain the preset step size, the first initial value, and the second initial value, wherein the first initial value is the initial value of the first control parameter, and the second initial value is the initial value of the second control parameter; Step S2: Obtain the initial operating condition based on the first initial value and the second initial value; obtain the value of the first control parameter based on the first initial value; and obtain the value of the second control parameter based on the second initial value. Step S3: Based on the initial operating conditions, run the system model under the preset fault conditions: Step S4: Based on the preset step size, adjust the value of the first control parameter within the first constraint to obtain the first intermediate value; Step S5: Based on the first intermediate value, obtain a first judgment according to the first stability criterion: If the first determination is that the first stability criterion is true, then update the value of the second control parameter according to the first intermediate value and execute step S6; Step S6: Based on the preset step size, adjust the value of the second control parameter within the second constraint to obtain a second intermediate value; Step S7: Based on the second intermediate value, obtain a third judgment according to the third stability criterion: If the third judgment is true according to the third stability criterion, then the fourth judgment is obtained based on the first stability criterion; If the fourth determination is that the first stability criterion is not met, then the value of the first control parameter is updated according to the second intermediate value and step S4 is repeated. If the fourth determination is true for the first stability criterion, then update the first intermediate value according to the second intermediate value and execute step S8. Step S8: Obtain a first optimized value based on the first intermediate value, and obtain a second optimized value based on the second intermediate value. The first optimized value is the value after optimization of the first control parameter, and the second optimized value is the value after optimization of the second control parameter.

2. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 1, characterized in that: The first stability criterion is that there is no power angle stability problem in the combined pumped storage power generation system; the second stability criterion is that the rotor of the variable speed unit in the combined pumped storage power generation system has no overspeed risk; and the third stability criterion is that the transient overvoltage of the combined pumped storage power generation system meets the requirements.

3. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 2, characterized in that: In step S5: If the first judgment determines that the first stability criterion is not true, then a second judgment is obtained based on the second stability criterion: If the second determination is that the second stability criterion is true, then update the value of the first control parameter and repeat step S4; If the second judgment indicates that the second stability criterion is not valid, then the output optimization result is "no optimization required". In step S7: If the third determination indicates that the third stability criterion is not met, update the value of the second control parameter and repeat step S6.

4. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 3, characterized in that: The preset fault is "N-1" fault.

5. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 3, characterized in that: The first control parameters include the active current limit 1, the active current limit 2, and the reactive current limit during the low voltage ride-through of the variable speed unit.

6. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 5, characterized in that: The first constraint is: ； In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. The active current limit for the low voltage ride-through period of the variable speed unit is 2. This refers to the reactive current limit during low-voltage ride-through of the variable speed unit.

7. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 6, characterized in that: Adjusting the value of the first control parameter within the first constraint based on the preset step size includes: The active current limit 1 and the active current limit 2 of the variable speed unit during low voltage ride-through are reduced by the preset step size, and the reactive current limit of the variable speed unit during low voltage ride-through is increased by the preset step size.

8. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 3, characterized in that: The second control parameters include the active current limit 1 during the low voltage ride-through of the variable speed unit, the reactive current limit during the low voltage ride-through of the variable speed unit, and the voltage threshold of the low voltage ride-through interval 2.

9. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 8, characterized in that: The second constraint is: ； In the formula, The active current limit during low voltage ride-through of the variable speed unit is 1. This refers to the reactive current limit during low-voltage ride-through of variable-speed generator sets. This is the voltage threshold for low-voltage crossing interval 2.

10. The method for collaborative optimization of system transient stability parameters after the connection of a variable-speed pumped-storage unit according to claim 9, characterized in that: Adjusting the value of the second control parameter within the second constraint based on the preset step size includes: The reactive current limit and the voltage threshold of the low voltage ride-through interval 2 of the variable speed unit are reduced by the preset step size, and the active current limit 1 of the low voltage ride-through interval of the variable speed unit is increased by the preset step size.

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