Transition process simulation method for water-electricity-electricity long-time and short-time step length coupling of variable-speed pumped storage power station

Abstract

The invention relates to the technical field of pumped storage power station simulation, and particularly provides a transition process simulation method for water-electricity-electricity long-time and short-time step length coupling of a variable-speed pumped storage power station, which comprises the following steps: establishing a simulation model comprising a water delivery and power generation system pipeline, a pump turbine, a doubly-fed motor and a converter of the doubly-fed motor; carrying out hydro-electro-mechanical steady-state calculation on the variable-speed pumped storage power station system; electrical system short-time step transition process calculation and pump turbine and speed regulator and water delivery pipeline system long-time step transition process calculation are carried out, in the electrical short-time step calculation process, the rotating speed of a unit is kept unchanged, and the calculation result of the last short-time step is substituted into a rotor motion equation; and repeating the transition process calculation step until the calculation is finished. According to the invention, the simulation efficiency of the whole system can be effectively improved, and the simulation precision of each subsystem is ensured; the simulation method is not influenced by the arrangement of a complex pipeline system, and has wide application potential.

Description

Technical Field

[0001] The invention belongs to the technical field of simulation of pumped storage power stations, and in particular relates to a transient process simulation method for coupling long and short time steps of hydro-mechanical electricity in variable-speed pumped storage power stations. Background Art

[0002] As the proportion of installed capacity of new energy in my country continues to increase, its volatility and intermittent characteristics have brought peak load regulation and absorption problems to the power grid, and pumped storage power stations are an important mitigation measure. Compared with traditional fixed-speed pumped storage power stations, double-fed variable-speed pumped units are more flexible and efficient, especially capable of tracking the grid frequency and regulating the water pump input under pumping conditions, which has great potential for improving the stability of the power grid. my country has already put many variable-speed pumped storage units into operation.

[0003] At present, the research on variable speed pumped storage system mainly relies on numerical simulation technology, which requires the establishment of complete dynamic models for multiple systems. Generally speaking, the electrical system generally requires a lower simulation step to ensure the accuracy of the simulation. When the same time step is used for the refined simulation model, the resources and time required for calculation are greatly increased. The existing methods more or less require the simplification of water pipelines, mechanical systems or power systems. Therefore, how to establish a refined dynamic model of the variable speed pumped storage system and reduce the resources required for calculation is a difficult problem to be solved. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems of a variable-speed pumped-storage power station, thereby establishing a precise dynamic model of the variable-speed pumped-storage system and greatly improving the simulation efficiency.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a transient process simulation method for the long-short time step coupling of the hydro-mechanical and electrical systems of a variable-speed pumped storage power station, comprising the following steps: Step 1: Establish a simulation model: Establish a simulation model including the water transmission and power generation system pipeline, pump-turbine, doubly-fed generator and its converter. According to the actual power station parameters, input the basic parameters of the variable-speed pumped storage power station into the simulation model, including the water transmission and power generation system pipeline parameters, pump-turbine basic parameters, doubly-fed generator and its machine-side converter parameters; Step 2: Calculation of hydro-mechanical steady-state of variable-speed pumped-storage power station system: Use NURBS surface to express the full characteristics of the pump-turbine, and interpolate the unit flow, working head and turbine torque at the corresponding opening according to the actual opening of the pump-turbine; Substitute the obtained turbine unit flow and working head into the finite element method to calculate the flow of each pipeline and the pressure of each node in the pipeline system of the variable-speed pumped-storage power station; Substitute the obtained turbine torque value into the basic equation of the doubly-fed generator, and use the Newton-Raphson iteration method to obtain the stator and rotor voltage, current and output active power of the doubly-fed generator; Step 3: Initialization of hydraulic system transient process calculation: assign the flow rate of each pipeline and the pressure of each node obtained by steady-state calculation to each node in the pipeline through interpolation; set the regulation target of the pump turbine and converter, that is, the target speed and target output; set the calculation step size of the doubly fed generator and converter ; Set the calculation step size of the water pipeline system and the pump turbine ; Set the total calculation length T ; Step 4: Calculation of electrical system short time step transient process: Calculation , , …, , The transient process parameters of the doubly fed machine and the converter at the moment include the stator and rotor voltage, the stator and rotor current and the intermediate parameters of the converter. The stator and rotor active and reactive power and the electromagnetic torque are calculated through the stator and rotor voltage and current. The number of calculation steps is Step 1, in calculating During the process of adjusting the electrical parameters, the speed of the pump turbine is constant. The value of the moment; Step 5: Calculation of long-time step transition process of pump-turbine: Substitute the electromagnetic torque into the solution process of pump-turbine and solve The transient process parameters of the pump-turbine at each moment include the unit speed, flow rate, volute end pressure and draft tube inlet pressure; Step 6: Calculation of long-time step transition process of water pipeline system: Substitute the flow rate through the machine, the pressure at the end of the volute and the pressure at the inlet of the draft tube into the solution process of the pipeline system transition process to solve Transition process parameters of each node of the pipeline system at each moment; Step 7: Update the calculation results: The transient process parameters of the doubly-fed machine and converter, the transient process parameters of the pump-turbine, and the transient process parameters of each node of the pipeline system at the moment are used as Solving for known values ​​at time; Step 8: Iterative calculation: Repeat steps 4 to 7 until the calculation is completely completed.

[0006] In the preferred scheme, in step 1, the pipeline parameters of the water transmission and power generation system include the length and diameter of each pipeline, and the topological relationship of the water transmission pipeline; the basic parameters of the pump turbine include the runner diameter, moment of inertia and characteristic curve; the doubly fed asynchronous motor and its machine-side converter parameters include the doubly fed asynchronous motor parameters and its converter control parameters.

[0007] In the preferred solution, in step 2, the use of NURBS surface to express the full characteristics of the pump-turbine is based on the measured data points of the full characteristics of the pump-turbine, and the cubic non-uniform B-spline space curves of each opening line are constructed.

[0008] In a preferred solution, in step 2, the calculation process of the stator and rotor voltage, current and output active power of the doubly-fed motor is: The partial differential equation of the doubly fed machine is as follows: 1) The basic equation of the doubly-fed machine is: (1); in: ; ; ; In the formula, For stator and rotor Shaft voltage; For stator and rotor Shaft current; They are the stator self-inductance, rotor self-inductance and the mutual inductance between the stator and rotor; are the stator and rotor resistances respectively; are the rotor angular frequency and the grid angular frequency; 2) The expression of electromagnetic torque is: (2); 3) The active power and reactive power equations are: (3); Where: is the stator reactive power; is the stator active power; is the rotor reactive power; is the rotor active power; 4) The rotation equation of the doubly-fed motor is as follows: (4); Where: is the rotational inertia time constant, is the electromagnetic torque, is the initial torque of the turbine; In steady state, the partial differential term in the basic equation of the doubly fed machine is 0, so the following equation is obtained: (5); From the rotation equation and electromagnetic torque equation of the doubly-fed motor, we can get: (6); At this time, the stator voltage and reactive power are known, and the Newton-Raphson iteration method can be used to solve the rotation equation, electromagnetic torque equation, doubly fed machine basic equation and active power equation to obtain the stator and rotor current, stator and rotor voltage, stator and rotor active power and rotor reactive power in steady state.

[0009] In a preferred solution, in step 4, the short-time step transition process of the electrical system is calculated by using the fourth-order Runge-Kutta method to solve the partial differential equations of the doubly-fed motor and its converter, thereby obtaining the transition process parameters at each moment.

[0010] In a preferred solution, the partial differential equation of the doubly-fed motor converter is: The rotor voltage is calculated according to the following formula under speed priority: (7); The rotor voltage under power priority is calculated according to the following formula: (8); Where: is the gain coefficient of the PI controller in different links, is the integral coefficient of the PI controller in different links; are the intermediate parameters of different links, For the rotor Shaft voltage reference value; To regulate the target stator reactive power, is the stator reactive power; is the target stator active power to be regulated, is the stator active power; To adjust the target speed, is the rotor speed, is the grid angular frequency.

[0011] In the preferred solution, in step 5, the long-time step transition process calculation of the pump-turbine adopts NURBS surface to express the full characteristics of the pump-turbine, and obtains the characteristic curve under the current opening by linear interpolation method. Substitute the electromagnetic torque of the doubly-fed machine at the moment into the turbine solution process to solve The unit speed, flow rate, volute end pressure and tailwater pipe inlet pressure at the moment.

[0012] In the preferred solution, the expression for expressing the overall characteristics of the pump-turbine using the NURBS surface is: ; Where: , , It is the unit speed, unit flow, and unit torque curve; , Represent the opening line and the points on the opening line respectively. , are the number of opening lines and the number of control points on the opening lines respectively; are the control vertices of the desired spatial surface; and is the B-spline basis.

[0013] In a preferred solution, in step 6, the long-time step transition process of the water pipeline system is calculated by using a characteristic line method to solve the pipeline system and solve the transition process parameters of each calculation node at the next moment.

[0014] In a preferred solution, the characteristic line method obtains the following formula after discretizing the basic equation of unsteady flow of the hydraulic system: ; ; ; ; ; ; ; ; ; ; ; in: It is the angle between the line connecting the centroids of each section of the pipeline and the horizontal plane; is the cross-sectional area; is the wave speed; is the acceleration due to gravity; is the water head of the piezometer based on a certain elevation; is the cross-sectional flow velocity; S is the cross-sectional wetted perimeter; is the Darcy–Weisbach friction coefficient; is the time step; the subscript R of each symbol represents the calculation point R, the subscript S represents the calculation point S, and the subscript P represents the calculation point P; , is the equation code, , ~ is the intermediate calculation parameter.

[0015] The present invention provides a method for simulating a transient process of a hydro-mechanical long-short time step coupling for a variable-speed pumped-storage power station, which has the following beneficial effects: 1. This method can reduce the computational resources required while establishing a sophisticated variable-speed pumped storage system transient process simulation model.

[0016] 2. This method can be applied to any water transmission and power generation system, and is not restricted by the water transmission and power generation system of the variable-speed pumped storage power station, and has a wide range of application prospects; 3. This method has good scalability and is suitable for simulations in scenarios with different time scales, such as the layout of the coupling between the open channel and the pressurized pipeline in the pipeline system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 A schematic diagram of a model test bench for verifying the method of the present invention; Figure 3 This is a simulation comparison chart of increasing or decreasing the speed and power of the unit under power generation conditions; Figure 4 This is a simulation comparison chart of increasing or decreasing power by increasing or decreasing the speed of a pumping unit. DETAILED DESCRIPTION

[0019] Combination Figure 1 The specific embodiments of the present invention are described in further detail.

[0020] It is clear and complete that the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] At present, the transition process of variable-speed pumped-storage power stations is mainly studied by numerical simulation methods at home and abroad, lacking the necessary real machine verification or physical model test verification. In order to verify the simulation strategy of long and short time step coupling proposed by this method, this embodiment relies on the domestically invested double-fed variable-speed pumped-storage test bench to carry out experimental research. The test bench consists of ten subsystems, including model pipelines, circulating waterways, double-fed reversible pump-turbine units, speed regulators, AC excitation systems, cooperative controllers, and monitoring systems. It can be considered as a small variable-speed pumped-storage power station. The schematic diagram of the model test bench is shown in the figure. Figure 2 shown.

[0022] Relying on the variable speed pumped storage test bench, the corresponding simulation model is established to carry out numerical simulation of power generation and pumping conditions, and the simulation conditions are guaranteed to be consistent with the model test. The hydraulic machinery side uses a time step of 10ms, and the doubly fed generator uses a time step of 1ms for calculation.

[0023] Based on the above conditions, verification of power generation conditions and pumping conditions is carried out according to the method of the present invention.

[0024] Given two working conditions, the power instructions are as follows: Power generation conditions: The unit speed is 920r / min, the initial unit output is 40kW, the guide vane opening is about 42%, and the flow rate is about 172L / s. About 20s, the co-coupler issues a command to increase the speed from 920r / min to 954r / min, and the power from 40kW to 50kW; about 200s, the co-coupler issues a command to reduce the speed from 954r / min to 920r / min, and the power from 50kW to 40kW. The active current of the machine-side converter is in the speed outer loop control mode, and the speed regulator controls the active power of the unit.

[0025] Pumping condition: At the initial moment, the speed is -1004r / min, and the unit input is about -77kW; the guide vane opening determines the speed command and the opening command according to the target power, and the speed and opening act in tandem. Set the active reference value to decrease by 10kW around 30s, increase by 10kW around 270s, decrease by 10kW again around 320s, and increase by 10kW again around 450s. Similarly, the active current of the machine-side converter under the pumping condition is in the speed outer loop control mode.

[0026] A transient process simulation method for the coupling of long and short time steps of hydro-mechanical and electrical systems in variable-speed pumped storage power stations, such as Figure 1 As shown, the following steps are included: Step 1: Establish a simulation model: Input the basic parameters of the variable-speed pumped-storage power station according to the actual power station parameters, including the pipeline parameters of the water transmission and power generation system, the basic parameters of the pump-turbine, the doubly-fed generator and its machine-side converter parameters.

[0027] The pipeline parameters of the water transmission and power generation system include the length and diameter of each pipeline and the topological relationship of the water transmission pipeline; the basic parameters of the pump turbine include the runner diameter, moment of inertia and characteristic curve; the doubly fed asynchronous motor and its machine-side converter parameters include the doubly fed motor parameters and its converter control parameters.

[0028] Specifically, the pipeline system data is extracted from the water pipeline system of the variable-speed pumped storage power station, the unit parameters are extracted from the pump-turbine, and the doubly-fed motor parameters are extracted from the doubly-fed motor.

[0029] Step 2: Calculation of hydro-mechanical steady-state of variable-speed pumped-storage power station system: NURBS surface is used to express the full characteristics of the pump-turbine. According to the actual opening of the pump-turbine, the unit flow, working head and turbine torque at the corresponding opening are interpolated.

[0030] Substitute the obtained turbine unit flow and working head into the finite element method to calculate the flow of each pipeline and the pressure of each node in the variable speed pumped storage power station pipeline system, as follows: The process of the finite element method is as follows: The finite element method divides the pipe network water supply system into several pipe units and node units. The pipe unit has a certain length and is called a line unit; the node unit is regarded as a unit with a length of 0 and is called a point unit. The front and back nodes are nodes With Node , the water flow direction of the line unit is specified as Then the total energy at nodes i and j is For Node With Node The energy equation of the pipeline is as follows: ; Where: For pipeline k The resistance coefficient includes the along-the-way and local resistance coefficients.

[0031] Linearize the above equation, express it in incremental form, and ignore the square term of the incremental term, and we get: ; Where: is the number of iterations; For the At iteration The increment of and They are and Iteration The increment of time. Among them: ; For continuous point units, their energy is generally unique, and their equation is the flow continuity equation. The unit equation of node i is shown as follows: ; Where: Representation and point unit There are connected line units, External input point unit of traffic.

[0032] Linearizing the unit equation of node i also yields: ; Combine and organize the energy equations of all pipes and nodes in the piping system with the unit equations: ; Solving the above equation can obtain the flow rate and node head of the pipe.

[0033] Substitute the obtained turbine torque value into the basic motor equation, and use the Newton-Raphson iteration method to obtain the stator and rotor voltage, current and output active power of the doubly fed motor, as follows: The basic equation of the doubly-fed machine is shown below: ; ; ; ; In the formula, For stator and rotor Shaft voltage; For stator and rotor Shaft current; They are the stator self-inductance, rotor self-inductance and the mutual inductance between the stator and rotor; is the stator and rotor resistance; are the rotor angular frequency and the grid angular frequency.

[0034] The expression of electromagnetic torque is: ; The rotation equation of the doubly-fed machine is as follows: ; Where: is the rotational inertia time constant, is the electromagnetic torque, is the initial torque of the turbine.

[0035] In steady state, the partial differential term in the basic equation of the doubly fed machine is 0, so the following equation can be obtained: ; From the speed motion equation and electromagnetic torque equation, we can get: ; At this time, the stator voltage and reactive power are known, and the stator and rotor currents and rotor voltage can be obtained by solving the above equations using the Newton-Raphson iteration method.

[0036] The general form of the Newton-Raphson iterative scheme is: ; Where: For the equation to be solved, The equation to be solved is The first derivative of , is the result of the nth and n-1th iterations, is the deviation of the solution for the nth iteration, when If the error is less than the allowed accuracy, the iteration is stopped.

[0037] The NURBS surface is used to express the full characteristics of the pump-turbine. It is based on the measured data points of the full characteristics of the pump-turbine, and the cubic non-uniform B-spline space curves of each opening line are constructed.

[0038] The expression for expressing the overall characteristics of the pump turbine using the NURBS surface is: ; Where: , , It is the unit speed, unit flow, and unit torque curve; , Represent the opening line and the points on the opening line respectively. , are the number of opening lines and the number of control points on the opening lines respectively; are the control vertices of the desired spatial surface; and is the B-spline basis.

[0039] Step 3: Initialization of hydraulic system transient process calculation: assign the flow rate of each pipeline and the pressure of each node obtained by steady-state calculation to each node in the pipeline through interpolation; set the regulation target of the pump turbine and converter, that is, the target speed and target output; set the calculation step size of the doubly fed generator and converter , about 0.1ms~1ms; set the calculation step length of the water pipeline system and the pump turbine , about 10ms; set the total calculation length T , about .

[0040] Step 4: Calculation of electrical system short time step transient process: Calculation , , …, , The transition process parameters of the doubly fed machine and the converter at the moment, the transition process parameters of the doubly fed machine and the converter, the parameters are mainly the stator and rotor voltage, the stator and rotor current and the converter intermediate parameters, the stator and rotor active and reactive power and the electromagnetic torque can be calculated through the stator and rotor voltage and current; the number of calculation steps is Step 1, in calculating During the process of adjusting the electrical parameters, the speed of the pump turbine is constant. The value of the moment.

[0041] The present invention calculates the voltage of the doubly-fed motor rotor according to the vector control strategy, and realizes the control of the doubly-fed motor through two control modes: speed priority and power priority. Therefore, the rotor voltage under speed priority can be calculated according to the following formula: ; The rotor voltage under power priority can be calculated according to the following formula: ; Where: is the gain coefficient of the PI controller in different links, is the integral coefficient of the PI controller in different links; are the intermediate parameters of different links, For the rotor Shaft voltage reference value; To regulate the target stator reactive power, is the stator reactive power; is the target stator active power to be regulated, is the stator active power; To adjust the target speed, is the rotor speed.

[0042] The fourth-order Runge-Kutta method is used to solve the partial differential equations of vector control and doubly fed motor, and we can get , , …, , The transient process parameters of the doubly-fed machine and converter at the moment, namely the stator-rotor voltage, stator-rotor current and converter intermediate parameters, can be used to calculate the stator-rotor active and reactive power and electromagnetic torque through the stator-rotor voltage and current; the number of calculation steps is Step 1, in calculating During the process of adjusting the electrical parameters, the speed of the pump turbine is constant. Substitute the stator and rotor voltage and current into the electromagnetic torque equation to calculate the electromagnetic torque at the corresponding moment.

[0043] Step 5: Calculation of long-time step transition process of pump-turbine: Substitute the electromagnetic torque into the solution process of pump-turbine and solve The transient process parameters of the pump-turbine at each moment include the unit speed, flow rate, volute end pressure and draft tube inlet pressure; The long-time step transition process calculation of the pump-turbine uses NURBS surface to express the full characteristics of the pump-turbine, and the characteristic curve under the current opening is obtained by linear interpolation method. Substitute the electromagnetic torque of the doubly-fed machine at the moment into the turbine solution process to solve The unit speed, flow rate, volute end pressure and tailwater pipe inlet pressure at the moment.

[0044] Step 6: Calculation of long-time step transition process of water pipeline system: Substitute the flow rate through the machine, the pressure at the end of the volute and the pressure at the inlet of the draft tube into the solution process of the pipeline system transition process to solve Transition process parameters of each node of the pipeline system at each moment; The long-time step transition process calculation of the water pipeline system is to solve the pipeline system using the characteristic line method and solve the transition process parameters of each calculation node at the next moment.

[0045] The characteristic line method obtains the following formula after discretizing the basic equation of unsteady flow of hydraulic system: ; Where: , It is an equation code and has no actual physical meaning. , ~ is the intermediate calculation parameter.

[0046] ; ; ; ; ; ; ; ; ; ; in: It is the angle between the line connecting the centroids of each section of the pipeline and the horizontal plane; is the cross-sectional area; is the wave speed; is the acceleration due to gravity; is the water head of the piezometer based on a certain elevation; is the cross-sectional flow velocity; S is the cross-sectional wetted perimeter; is the Darcy–Weisbach friction coefficient; is the time step; the subscript R of each symbol represents the calculation point R, the subscript S represents the calculation point S, and the subscript P represents the calculation point P.

[0047] Step 7: Update the calculation results: The transient process parameters of the doubly-fed machine and converter, the transient process parameters of the pump-turbine, and the transient process parameters of each node of the pipeline system at the moment are used as Solving for known values ​​at time; Step 8: Iterative calculation: Repeat steps 4 to 7 until the calculation is completely completed.

[0048] In order to verify the simulation efficiency and simulation accuracy of the proposed simulation strategy of long and short time step coupling, the simulation time required for the two simulation strategies under the same working conditions is compared, as shown in Table 1.

[0049]

[0050] The mean absolute percentage error is used to compare the simulation accuracy. The mean absolute percentage error calculation formula is: ; Where: is the total number of test samples, is the sampled measurement value, It is the simulated measured value.

[0051] The higher the simulation accuracy, the lower the mean absolute percentage error. The absolute percentage errors of different parameters under power generation and pumping conditions are shown in Table 2.

[0052]

[0053] The simulation results in the two cases are as follows Figure 3~Figure 4As shown. Compared with the strategy of simulating the entire system with the same time step, the simulation strategy of coupling long and short time steps can greatly improve the simulation efficiency. The time required for power generation simulation is reduced from 298.744s to 24.624s, and the time required for pumping simulation is reduced from 284.573s to 23.435s. As shown in Table 2, the maximum average absolute percentage error of power generation and pumping conditions is 4.858%, which occurs in the guide vane opening of power generation conditions. The average absolute percentage errors of other parameters of power generation conditions are all less than 3.437%, and the average absolute percentage errors of all parameters of pumping conditions are less than 1.909%.

[0054] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here, that is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems of a variable speed pumped storage power station, characterized in that: The following steps are involved: Step 1: Establish a simulation model: Establish a simulation model including the water transmission and power generation system pipeline, pump-turbine, doubly-fed generator and its converter. According to the actual power station parameters, input the basic parameters of the variable-speed pumped storage power station into the simulation model, including the water transmission and power generation system pipeline parameters, pump-turbine basic parameters, doubly-fed generator and its machine-side converter parameters; Step 2: Calculation of hydro-mechanical steady-state of variable-speed pumped-storage power station system: Use NURBS surface to express the full characteristics of the pump-turbine, and interpolate the unit flow, working head and turbine torque at the corresponding opening according to the actual opening of the pump-turbine; Substitute the obtained turbine unit flow and working head into the finite element method to calculate the flow of each pipeline and the pressure of each node in the pipeline system of the variable-speed pumped-storage power station; Substitute the obtained turbine torque value into the basic equation of the doubly-fed generator, and use the Newton-Raphson iteration method to obtain the stator and rotor voltage, current and output active power of the doubly-fed generator; Step 3: Initialization of hydraulic system transient process calculation: assign the flow rate of each pipeline and the pressure of each node obtained by steady-state calculation to each node in the pipeline through interpolation; set the regulation target of the pump turbine and converter, that is, the target speed and target output; set the calculation step size of the doubly fed generator and converter ; Set the calculation step size of the water pipeline system and the pump turbine ; Set the total calculation length T ; Step 4: Calculation of electrical system short time step transient process: Calculation , , …, , The transient process parameters of the doubly fed machine and the converter at the moment include the stator and rotor voltage, the stator and rotor current and the intermediate parameters of the converter. The stator and rotor active and reactive power and the electromagnetic torque are calculated through the stator and rotor voltage and current. The number of calculation steps is Step 1, in calculating During the process of adjusting the electrical parameters, the speed of the pump turbine is constant. The value of the moment; Step 5: Calculation of long-time step transition process of pump-turbine: Substitute the electromagnetic torque into the solution process of pump-turbine and solve The transient process parameters of the pump-turbine at each moment include the unit speed, flow rate, volute end pressure and draft tube inlet pressure; Step 6: Calculation of long-time step transition process of water pipeline system: Substitute the flow rate through the machine, the pressure at the end of the volute and the pressure at the inlet of the draft tube into the solution process of the pipeline system transition process to solve Transition process parameters of each node of the pipeline system at each moment; Step 7: Update the calculation results: The transient process parameters of the doubly-fed machine and converter, the transient process parameters of the pump-turbine, and the transient process parameters of each node of the pipeline system at the moment are used as Solving for known values ​​at time; Step 8: Iterative calculation: Repeat steps 4 to 7 until the calculation is completely completed.

2. A method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems of a variable speed pumped storage power station according to claim 1, characterized in that: In step 1, the pipeline parameters of the water transmission and power generation system include the length and diameter of each pipeline and the topological relationship of the water transmission pipeline; the basic parameters of the pump turbine include the runner diameter, moment of inertia and characteristic curve; the doubly fed asynchronous motor and its machine-side converter parameters include the doubly fed asynchronous motor parameters and its converter control parameters.

3. The method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems for a variable speed pumped storage power station according to claim 1 is characterized in that: In step 2, the use of NURBS surface to express the full characteristics of the pump-turbine is based on the measured data points of the full characteristics of the pump-turbine, and the cubic non-uniform B-spline space curves of each opening line are constructed.

4. The method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems for a variable speed pumped storage power station according to claim 1 is characterized in that: In step 2, the calculation process of the stator and rotor voltage, current and output active power of the doubly-fed motor is as follows: The partial differential equation of the doubly fed machine is as follows: 1) The basic equation of the doubly-fed machine is: （1）； in: ； ； ； In the formula, For stator and rotor Shaft voltage; For stator and rotor Shaft current; They are the stator self-inductance, rotor self-inductance and the mutual inductance between the stator and rotor; are the stator and rotor resistances respectively; are the rotor angular frequency and the grid angular frequency; 2) The expression of electromagnetic torque is: （2）； 3) The active power and reactive power equations are: （3）； Where: is the stator reactive power; is the stator active power; is the rotor reactive power; is the rotor active power; 4) The rotation equation of the doubly-fed motor is as follows: （4）； Where: is the rotational inertia time constant, is the electromagnetic torque, is the initial torque of the turbine; In steady state, the partial differential term in the basic equation of the doubly fed machine is 0, so the following equation is obtained: （5）； From the rotation equation and electromagnetic torque equation of the doubly-fed motor, we can get: （6）； At this time, the stator voltage and reactive power are known, and the Newton-Raphson iteration method can be used to solve the rotation equation, electromagnetic torque equation, doubly fed machine basic equation and active power equation to obtain the stator and rotor current, stator and rotor voltage, stator and rotor active power and rotor reactive power in steady state.

5. A method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems of a variable speed pumped storage power station according to claim 4, characterized in that: In step 4, the short-time step transition process of the electrical system is calculated by using the fourth-order Runge-Kutta method to solve the partial differential equations of the doubly-fed machine and its converter, thereby obtaining the transition process parameters at each moment.

6. A method for simulating a transient process of coupling long and short time steps of hydro-mechanical and electrical systems for a variable-speed pumped-storage power station according to claim 5, characterized in that: The partial differential equation of the doubly-fed machine converter is: The rotor voltage is calculated according to the following formula under speed priority: （7）； The rotor voltage under power priority is calculated according to the following formula: （8）； Where: is the gain coefficient of the PI controller in different links, is the integral coefficient of the PI controller in different links; are the intermediate parameters of different links, For the rotor Shaft voltage reference value; To regulate the target stator reactive power, is the stator reactive power; To regulate the target stator active power, is the stator active power; To adjust the target speed, is the rotor speed, is the grid angular frequency.

7. A method for simulating a transient process of coupling long and short time steps of hydro-mechanical and electrical systems for a variable-speed pumped-storage power station according to claim 1, characterized in that: In step 5, the long-time step transition process calculation of the pump-turbine adopts NURBS surface to express the full characteristics of the pump-turbine, and obtains the characteristic curve under the current opening by linear interpolation method. Substitute the electromagnetic torque of the doubly-fed machine at the moment into the turbine solution process to solve The unit speed, flow rate, volute end pressure and tailwater pipe inlet pressure at the moment.

8. A method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems of a variable speed pumped storage power station according to claim 3 or 7, characterized in that: The expression for expressing the overall characteristics of the pump turbine using the NURBS surface is: ； Where: , , It is the unit speed, unit flow, and unit torque curve; , Represent the opening line and the points on the opening line respectively. , are the number of opening lines and the number of control points on the opening lines respectively; are the control vertices of the desired spatial surface; and is the B-spline basis.

9. The method for simulating the transient process of the long and short time step coupling of the hydro-mechanical and electrical systems for a variable speed pumped storage power station according to claim 1 is characterized in that: In step 6, the long-time step transition process calculation of the water pipeline system is to solve the pipeline system using the characteristic line method to solve the transition process parameters of each calculation node at the next moment.

10. A method for simulating a transient process of coupling long and short time steps of hydro-mechanical and electrical systems for a variable-speed pumped-storage power station according to claim 9, characterized in that: The characteristic line method obtains the following formula after discretizing the basic equation of unsteady flow of hydraulic system: ； ； ； ； ； ； ； ； ； ； ； in: It is the angle between the line connecting the centroids of each section of the pipeline and the horizontal plane; is the cross-sectional area; is the wave speed; is the acceleration due to gravity; is the water head of the piezometer based on a certain elevation; is the cross-sectional flow velocity; S is the cross-sectional wetted perimeter; is the Darcy–Weisbach friction coefficient; is the time step; the subscript R of each symbol represents the calculation point R, the subscript S represents the calculation point S, and the subscript P represents the calculation point P; , is the equation code, , ~ is the intermediate calculation parameter.

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