Multi-rate hybrid simulation method for a hydroelectric power plant with a flexible high voltage direct current transmission system

Abstract

This application relates to a multi-rate hybrid simulation method for a single-pipe multi-unit hydropower group transmitted via flexible direct current (FDDC). The FDDC system is divided into a slow-variable subsystem and a fast-variable subsystem based on the speed of its dynamic response. The slow-variable subsystem is simulated using a large step size, while the fast-variable subsystem is simulated using a small step size. The unit speed and mechanical power are selected as interface variables for bidirectional interaction. Real values ​​are exchanged at synchronization points, and linear interpolation is used to construct the mechanical power input at asynchronous points, enabling continuous simulation of the fast subsystem. This process is repeated until the full-time-domain simulation is completed. Addressing the coexistence of slow hydraulic dynamics and fast electromagnetic transient dynamics, this method significantly improves computational efficiency while maintaining simulation accuracy. It is suitable for long-term simulation and multi-condition analysis of high-head single-pipe multi-unit hydropower groups transmitted via MMC-HVDC.

Description

Technical Field

[0001] This application relates to the field of hybrid simulation technology of hydropower generation systems and flexible DC transmission systems, and in particular to a multi-rate hybrid simulation method for a multi-unit hydropower generator group transmitted through a flexible DC transmission system. Background Technology

[0002] With the increasing proportion of power electronic equipment in power systems and the growing differences in time scales between different subsystems, multi-rate simulation has gradually become an important research direction for the efficient solution of complex power systems. The basic idea of ​​multi-rate simulation is to solve each subsystem independently using different time steps based on their varying dynamic response speeds, and to achieve coupled computation of the overall system through the exchange of interface variables and coordination of timing. Given the difficulty in simultaneously achieving both simulation accuracy and computational efficiency with a uniform time step, multi-rate simulation provides a new technical approach for the joint analysis of fast and slow dynamic processes in complex systems.

[0003] For scenarios involving high-head, multi-unit hydroelectric generator groups transmitting power via MMC-HVDC, the entire system can be considered a complex water-machine-electric-grid coupled system composed of a hydraulic subsystem, a mechanical subsystem, electrical equipment, and an AC / DC network. This system not only exhibits significant multi-timescale characteristics but also demonstrates pronounced multi-physics coupling characteristics between hydraulics, mechanics, electrical systems, and the power grid. The simulation challenges primarily lie in the strong heterogeneity of the models, complex interface coordination, and the difficulty in achieving both accuracy and efficiency with a unified step size.

[0004] Specifically, the hydraulic subsystem mainly includes the intake pipe, branch pipe, surge tank, turbine, and speed control system. The transient hydraulic processes in a high-head intake system are typically described by one-dimensional unsteady flow equations. For this type of hyperbolic partial differential equation system, the method of characteristics is the most commonly used numerical solution method, and its numerical stability must satisfy the Courant condition. In high-head long intake systems, the water hammer wave velocity is typically between 800 m / s and 1200 m / s. When the pipe segment length is taken as 100 m, the maximum allowable simulation step size is approximately 0.083 s to 0.125 s. In actual engineering simulations, to ensure calculation accuracy and accurately capture the propagation process of the water hammer wave, a step size of 0.01 s to 0.02 s is usually used. Therefore, the hydraulic subsystem is a typical slow-dynamic system.

[0005] The power subsystem mainly includes synchronous generators, AC networks, MMC converter stations, and their control systems. The electromechanical dynamics of synchronous generators are typically within a range of 10... -The timescale is from 1s to 10¹s, while the MMC converter station and its control loop have significantly faster dynamic characteristics. The switching behavior of power electronic devices in the MMC occurs on the order of microseconds, and the control cycles of the current inner loop, phase-locked loop, and modulation loop are typically 50μs to 200μs. Therefore, to accurately simulate electromagnetic transients, the power subsystem usually requires a microsecond-level step size.

[0006] In summary, a 10-type hydraulic system is suitable. - The simulation step size is on the order of 2s, while flexible DC electromagnetic transient processes in power systems typically require a step size of 10. -5 s to 10 -4 The simulation step size is on the order of s, with at least two orders of magnitude difference between the two. This significant separation of time scales constitutes the fundamental motivation for constructing multi-rate hybrid simulation methods.

[0007] To address the aforementioned timescale differences, there are generally two intuitive strategies for applying a uniform step size to the entire system. The first is to use a larger step size for uniform simulation. While this approach can adequately meet the numerical computation requirements of hydraulic systems, for flexible DC systems, the rapid dynamics of electromagnetic transient processes are difficult to accurately characterize. This is particularly true for fast control components such as the switching behavior of the MMC converter, the current inner loop, and the phase-locked loop. Excessive step size can lead to significant distortion and even numerical stability issues. The second strategy is to use a smaller step size for uniform simulation. While this approach can accurately describe the rapid dynamics of the power subsystem, it significantly increases the computational load on the hydraulic subsystem. For example, using the method of characteristics, if the hydraulic model originally used a 0.01s step size, and the uniform step size is changed to 50μs, the number of time steps will increase by approximately 200 times. With the total simulation time remaining constant, the calculations of flow rate, head, and boundary conditions at each discrete node in the hydraulic system need to be repeated hundreds of times, resulting in a significant increase in overall computation time. A comparison of the two strategies for uniform step size simulation is shown in Table 1.

[0008] Table 1 Comparison of Uniform Step Size Strategies

[0009] Therefore, the fundamental contradiction in uniform step size simulation lies in the fact that the hydraulic subsystem requires a larger step size to ensure computational efficiency, while the electric subsystem requires a smaller step size to ensure electromagnetic transient accuracy. The optimal step size requirements for the two are not the same.

[0010] Multi-rate simulation has provided a relatively mature methodological framework for the joint solution of complex power system processes at different time scales, and has made significant progress in areas such as hybrid simulation of electromagnetic transients and dynamic phasors, multi-rate electromagnetic transient simulation, asynchronous coordination, interface algorithms, and performance evaluation. However, existing research mainly focuses on general AC / DC power systems, new energy grid-connected systems, or scenarios requiring accelerated electromagnetic transient solutions. Research on the complex water-machine-electricity-grid coupled object of high-head single-pipe multi-machine hydropower groups transmitting power via MMC-HVDC is still relatively insufficient. The main difficulties are as follows: First, high-head single-pipe multi-machine systems typically employ complex hydraulic models based on the method of characteristics, while MMC-HVDC and AC / DC networks require microsecond-level electromagnetic transient models. The model forms among the hydraulic system, generating units, power electronic devices, and AC / DC networks differ greatly, exhibiting strong heterogeneity. Second, the coexistence of slow hydraulic dynamics, electromechanical transients, and AC / DC electromagnetic transients makes it difficult to simultaneously balance physical accuracy and computational efficiency in simulation with a unified step size. Third, the selection of interface variables, coordination of synchronous and asynchronous times, and implementation of cross-platform data interaction for this type of scenario are quite difficult, and existing methods are still insufficient in terms of engineering applicability.

[0011] Therefore, it is necessary to further study applicable multi-rate simulation methods for high-head, multi-unit water-machine-electricity-grid coupled systems, especially for the core fast and slow dynamic coupling problem between the hydraulic system, the units and the electrical side, it is necessary to carry out water-machine-electricity multi-rate hybrid simulation research. Summary of the Invention

[0012] Based on this, it is necessary to provide a multi-rate hybrid simulation method for a system with a single pipe and multiple generators in a flexible direct power transmission system, in order to address the above-mentioned technical problems.

[0013] Firstly, this application provides a multi-rate hybrid simulation method for a system with a single-pipe multi-generator hydropower group transmitted via flexible direct power. The method includes: The multi-unit hydroelectric generator group via a flexible direct current transmission system is divided into a slow-variable subsystem and a fast-variable subsystem based on the speed of its dynamic response. The slow-variable subsystem includes a governor, turbine, and water intake system, and adopts a large step size. Simulation-based advancement is employed; the fast-changing subsystem includes a synchronous generator, AC / DC power grid, and a modular multilevel converter control system, employing a small step size... Simulation is used for advancement, and the following conditions are met: ,in A positive integer represents the multiplier factor; Select the speed of each unit and the mechanical power of each unit The rotational speed is used as an interface variable. The mechanical power is transmitted from the fast-changing subsystem to the slow-changing subsystem. The change is transmitted from the slow-changing subsystem to the fast-changing subsystem; At the synchronization time The slow-varying subsystem receives the rotational speed at the current moment. And calculate mechanical power The fast-change subsystem receives the mechanical power. And update the status; Asynchronous moments between adjacent synchronization moments The fast-changing subsystem employs a linear interpolation method, based on the mechanical power at two adjacent synchronization moments. and The mechanical power input at the current moment is calculated; Repeat the above process of interaction between synchronous and asynchronous moments until the full-time domain simulation is completed.

[0014] Optionally, in one embodiment of this application, the large step size The value is 10 milliseconds, and the small step size is... The value is 50 microseconds, and the rate factor is... The value is 200.

[0015] Optionally, in one embodiment of this application, the synchronization time... Defined as ,in It is an integer greater than or equal to zero.

[0016] Optionally, in one embodiment of this application, the asynchronous time... Defined as ,in .

[0017] Optionally, in one embodiment of this application, the linear interpolation method calculates the mechanical power input according to the following formula:

[0018] in, .

[0019] Optionally, in one embodiment of this application, in each large step interval Within, the fast-changing subsystem operates according to the small step size. The process continues, and after obtaining the mechanical power input through the linear interpolation method at each asynchronous moment, the speed of each unit is updated. At the next synchronous moment, the updated speed is fed back to the slow variable subsystem.

[0020] Optionally, in one embodiment of this application, the slow-changing subsystem uses the method of characteristics to simulate the hydraulic transient process, while the fast-changing subsystem uses the electromagnetic transient simulation method to simulate the process.

[0021] Optionally, in one embodiment of this application, in each large step interval Within, the slowly varying subsystem synchronizes at specific times. rotational speed Using this as a constant input within the interval, a large-step integration is performed to obtain the right endpoint of the interval. mechanical power .

[0022] Optionally, in one embodiment of this application, an initialization step is further included before the simulation begins: Determine the initial head and initial flow rate of each turbine; set the initial mechanical power and initial speed of each unit; set the initial voltage and initial current of the sending-end power grid and the initial state of each modular multilevel converter station; calculate the initial power flow of the system to ensure that the electrical network and the hydraulic system are in equilibrium.

[0023] Optionally, in one embodiment of this application, within the first large step size interval, the slowly varying subsystem uses large step sizes. Perform an integration to complete the state update; the fast-change subsystem performs this update within the first large step interval. The process involves several small-step iterations, with interpolation performed using the initial mechanical power provided by the slowly varying subsystem.

[0024] The multi-rate hybrid simulation method for the above-mentioned multi-unit hydropower group via flexible direct transmission system has the following advantages compared with the existing technology: First, this invention addresses the situation where a multi-machine hydroelectric generator group in a single pipe is supplied by an MMC-HVDC system, where slow hydraulic dynamics and fast electromagnetic transient dynamics coexist. It provides a water-machine-electric multi-rate hybrid simulation method, which can significantly improve the simulation efficiency of complex water-machine-electric coupled systems while ensuring the accuracy of the system's key dynamic responses. It is especially suitable for long-term operation and multi-condition analysis.

[0025] Secondly, in this invention, the fast-changing subsystem adopts the same microsecond-level step size as the unified small-step electromagnetic transient simulation. The switching behavior of the MMC converter, the current inner loop, and the phase-locked loop, among other fast dynamic processes, are all fully characterized. The simulation accuracy of the power subsystem is completely consistent with that of traditional small-step electromagnetic transient simulation, and there is no accuracy loss due to the increased step size. The efficiency improvement of this invention comes entirely from the use of a large step size in the hydraulic subsystem, rather than sacrificing the simulation step size of the power subsystem.

[0026] Third, by designing a strategy for dividing the fast and slow subsystems, exchanging interface variables, and jointly solving synchronous and asynchronous time points, this invention can effectively analyze the risks of power linkage between units, local disturbance propagation, and low-frequency oscillations, providing reliable technical support for the planning, operation, and safety assessment of high-head units transmitted via flexible DC transmission systems.

[0027] Fourth, the method of the present invention has good engineering applicability and scalability, and can be applied to the simulation of other multi-timescale hydraulic-electric coupling systems, supporting system operation optimization and engineering design. Attached Figure Description

[0028] Figure 1 This is a timing diagram for a multi-rate simulation in one embodiment. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0030] As described in the background section, the high-head single-pipe multi-unit hydroelectric generator group, transmitted via MMC-HVDC, is composed of a hydraulic subsystem, a mechanical subsystem, electrical equipment, and an AC / DC network. The hydraulic system operates in a slow dynamic (10 - (on the order of 2s) and MMC electromagnetic transient fast dynamics (10 -5 s to 10 -4 There are at least two orders of magnitude time scale differences between simulations with uniform step sizes (on the order of seconds), making it difficult to balance accuracy and efficiency.

[0031] To address the aforementioned problems, this invention proposes a multi-rate hybrid simulation method for a single-pipe multi-turbine hydropower group system transmitted via flexible direct current. The overall architecture is as follows: the entire coupled system is divided into slow-variable subsystems and fast-variable subsystems based on the speed of its dynamic response. The slow-variable subsystem corresponds to the governor, turbine, and water intake system, and employs a large step size... Solve for the following: The fast-changing subsystem corresponds to the synchronous generator, AC / DC power grid, and MMC control system, using a small step size. Solve for the following:

[0032] in, This is the scaling factor. In a specific embodiment of the present invention, , , .

[0033] Based on this, by selecting appropriate interface variables, exchanging real values ​​at synchronous times and constructing slow variable inputs through interpolation at asynchronous times, the fast and slow subsystems can maintain closed-loop coupling under different time step conditions.

[0034] In this embodiment, within the multi-rate hybrid simulation architecture of the present invention, the fast-changing subsystem is still simulated using a small step size of 50 μs, the same step size used on the electrical side as the unified small-step simulation. The fast dynamic processes of power electronic devices in the MMC converter, such as switching behavior, current inner loop, phase-locked loop, and modulation circuitry, are all fully characterized at this step size. Therefore, the simulation accuracy of the power subsystem in this invention is completely consistent with that of the unified small-step all-electromagnetic transient simulation, and there are no fast dynamic distortions or numerical stability problems caused by increasing the step size.

[0035] The efficiency improvement of this invention comes entirely from the large step size of the hydraulic subsystem, rather than sacrificing the simulation step size of the power subsystem, as shown in Table 2.

[0036] Table 2 Comparison of Uniform Step Size Small Step Size Simulation and Multi-rate Simulation of the Present Invention (Table 2)

[0037] Therefore, the core advantage of this invention is that, without reducing the accuracy of electromagnetic transient simulation of the power system, it significantly improves the overall simulation efficiency by freeing the hydraulic subsystem from microsecond-level step size constraints.

[0038] In this embodiment, addressing issues such as time scale mismatch between the hydraulic and electrical subsystems, heterogeneous model implementations, and complex interface interactions, this invention constructs a multi-rate hybrid simulation interface for water-mechanical-electric coupled systems. This interface is based on the principles of large step sizes for hydraulic systems, small step sizes for electrical systems, and coordinated interface interpolation. The following sections describe the process from aspects such as the division of fast and slow subsystems, selection of interface variables, handling mechanisms for synchronous and asynchronous time points, and interface interpolation strategies.

[0039] In one embodiment of this application, the fast-change subsystem mainly corresponds to the synchronous generator, AC / DC power grid, MMC and its control system, and can be written as a set of differential-algebraic equations:

[0040] in, and These are the state variables (electromagnetic transient variables, such as generator voltage, current, and converter state) and algebraic variables (such as network node voltage and passive branch constraints) of the fast subsystem, respectively. The external input, in this invention, is mainly the mechanical power of each unit. .function , Specific calculations can be performed based on the system's physical characteristics and control strategies.

[0041] The slow-changing subsystem mainly corresponds to the governor, turbine, and water intake system, and can be denoted as:

[0042] in, These are the state variables of the slow subsystem (turbine speed, guide vane opening, surge tank water level, etc.). This is the unit speed feedback input at the synchronization time. This represents the mechanical power output of the hydraulic subsystem. (Function) , Specific calculations can be performed based on the system's physical characteristics and control strategy. The slow subsystem update occurs at the synchronization point. , No. Each synchronization moment is defined as: In each large step interval Within the system, the fast subsystem advances continuously in small steps, and the asynchronous moment is defined as:

[0043] In this embodiment, the hydraulic subsystem and the electrical subsystem are coupled through a mechanical power-speed closed loop. For a multi-unit system, the electrical subsystem feeds back the rotational speed of each unit to the hydraulic subsystem.

[0044] The governor, turbine, and water intake system calculate the mechanical power of each unit based on the current speed feedback and internal hydraulic state.

[0045] Subsequently, mechanical power The output is sent to the power subsystem as input to the generator rotor motion equations. After the power subsystem completes the solution, it generates the new rotational speed. The data is fed back to the hydraulic subsystem, thus forming a complete data loop.

[0046] Therefore, this invention employs two types of interface variables: the first type is the feedback variable transmitted from the power side to the hydraulic side, namely the rotational speed of each unit. The second category is the output variable transmitted from the hydraulic side to the electric side, namely the mechanical power of each unit. . It reflects the electromechanical operating status of the unit and is an important input for governor regulation and turbine power calculation; It is a key input in the generator rotor motion equation.

[0047] The water-mechanical-electric multi-rate hybrid simulation interface encapsulates a multi-machine high-head turbine unit model (governor and servo system, turbine and water intake system) within its inner code, receiving speed feedback. And output mechanical power The interface corresponds to the synchronous generator and AC / DC power grid models in the simulation platform. Input the generator model and obtain the solution. Returning to the inner side, this interface design enables the establishment of a stable data exchange channel between the code model and the platform model, providing a foundation for time coordination and interpolation in subsequent multi-rate coupling.

[0048] In this embodiment of the application, during multi-rate hybrid simulation, because the hydraulic subsystem and the power subsystem use different simulation step sizes, data exchange between the two cannot be directly performed at every small step. After each large hydraulic step, the two subsystems realign in time; this moment is called the synchronization moment. The remaining small step moments within the large step interval are called asynchronous moments.

[0049] At the synchronization time Both the hydraulic and electrical subsystems have completed their state updates at the corresponding time points, and the interface variable information is complete, allowing for direct exchange of real values. During asynchronous times... ( The fast subsystem needs to continue advancing in small steps, but the slow subsystem has not yet completed the next large step update, therefore there is no real mechanical power. This creates an information gap problem.

[0050] This invention employs an interpolation strategy to reconstruct the mechanical power at asynchronous moments. Since mechanical power is physically a slow variable, its change is relatively gradual within a single large step interval, and it can be estimated using the mechanical power at adjacent synchronous moments. The key to timing coordination in multi-rate hybrid simulation lies not in forcibly synchronizing the two subsystems, but in exchanging real information at synchronous moments and supplementing the slow variable input through interpolation at asynchronous moments.

[0051] In this embodiment, during asynchronous moments, the mechanical power input required by the fast subsystem cannot be directly provided in real time by the slow subsystem; an approximate value within the interval must be constructed using interpolation methods. Zero-order hold is simple to implement but introduces a significant step at synchronization moments; higher-order interpolation requires more historical data points and may introduce additional oscillations. Mechanical power originates from the coupling process of the governor, turbine, and diversion system, and typically exhibits gradual changes, no significant high-frequency components, and bounded second derivatives within the interval. Therefore, linear interpolation offers a good balance between accuracy, stability, and implementation complexity.

[0052] Let the current large step size interval be ,in The mechanical power output of the slow subsystem at two synchronization moments is known to be... and Then at asynchronous times ( The interpolated mechanical power supplied to the power system is:

[0053] Equivalent land, expressed using a multiplier factor, is as follows:

[0054] For the For a tandem unit, the above formula can be written as:

[0055] This formula shows that the mechanical power at any small step size within the interval is linearly constructed from the mechanical power at two adjacent synchronous moments. Since the linear interpolation matches the true value at the interval endpoints, and the interpolated value always lies between the two endpoints, it does not introduce additional overshoot, which helps maintain the continuity and numerical stability of the input signal. For the slow variable of mechanical power used in this invention, this treatment conforms to its physical variation law and meets the efficiency requirements of engineering simulation.

[0056] From an error perspective, the local error of linear interpolation is mainly related to the second derivative of the interpolated object within the interval and the size of the large step size. When the mechanical power changes gradually within the interval and the second derivative is bounded, reducing the large step size is beneficial. This will help reduce interpolation errors. Since the hydraulic subsystem step size is 10ms in this invention, and the mechanical power changes relatively smoothly within a single large step size interval, linear interpolation can provide an approximate input that meets engineering accuracy requirements with lower computational overhead.

[0057] To illustrate the implementation process of multi-rate hybrid simulation, Figure 1 The time axis relationship and data interaction process between the hydraulic subsystem and the power subsystem are presented. The slow subsystem advances in large steps of 10ms, calculating and buffering mechanical power at each synchronization moment; the fast subsystem advances in small steps of 50μs, constructing the mechanical power input by calling the linear interpolation formula at each asynchronous moment; the unit speed obtained by the fast subsystem is used as the input for the slow subsystem calculation in the next large step, thus achieving continuous coupling.

[0058] In one embodiment of this application, the initialization steps before the simulation begins include: determining the initial head and flow rate of each turbine; setting the initial mechanical power and speed of each unit; setting the initial voltage and current of the sending-end power grid and the status of each MMC-HVDC converter station; calculating the initial power flow of the system to ensure that the electrical network and the hydraulic system are in a balanced state; and determining the slow subsystem step size. and fast subsystem step size And construct the interpolation input for the first large step interval.

[0059] In the first large step interval, the slow subsystem first adopts a large step size. Performing an integration completes one state update; the fast subsystem operates within this interval. The system uses small step iterations and utilizes the initial values ​​provided by the slow subsystem to interpolate mechanical power, ensuring the continuity of interface variables and the dynamic consistency of the system.

[0060] Based on the above process, the complete implementation steps of the multi-rate hybrid simulation of the present invention are as follows: Step 1, at the synchronization time Obtain the unit speed feedback from the fast subsystem .

[0061] Step two, the slow subsystem based on Proceed in large steps to In each large step interval Synchronization time rotational speed Perform large-step integration as a constant input to obtain and buffer the mechanical power at the interval endpoints. and .

[0062] Step 3, in the interval Inside, the tachyon system advances in small steps of 50 μs.

[0063] Step four, when When the time is asynchronous, the mechanical power input is calculated using the linear interpolation formula. Then input it into the generator model.

[0064] Step 5: The fast subsystem is updated to obtain the new unit speed. And then feed back to the slow subsystem at the next synchronization moment.

[0065] Step 6: Repeat the above process until the full-time domain simulation is completed.

[0066] Therefore, the multi-rate hybrid simulation of this invention does not update the two subsystems simultaneously at each small step. Instead, it exchanges real information at synchronous moments and uses interpolation to supplement the slow variable input at asynchronous moments, thereby achieving coordinated advancement of the fast and slow subsystems. The linear interpolation strategy not only conforms to the physical variation law of mechanical power but also takes into account the computational efficiency and numerical stability of the multi-rate hybrid simulation.

[0067] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0068] In one embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above-described method embodiments.

[0069] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the steps in the above method embodiments.

[0070] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0071] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0072] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0073] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0074] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A multi-rate hybrid simulation method for a system of multiple hydropower generators connected to a single pipe via a flexible direct power transmission line, characterized in that: The method includes: The multi-unit hydroelectric generator group via a flexible direct current transmission system is divided into a slow-variable subsystem and a fast-variable subsystem based on the speed of dynamic response. The slow-variable subsystem includes a governor, turbine, and water intake system, and adopts a large step size... Simulation-based advancement is employed; the fast-changing subsystem includes a synchronous generator, AC / DC power grid, and a modular multilevel converter control system, employing a small step size... Simulation is used for advancement, and the following conditions are met: ,in A positive integer represents the multiplier factor; Select the speed of each unit and the mechanical power of each unit The rotational speed is used as an interface variable. The mechanical power is transmitted from the fast-changing subsystem to the slow-changing subsystem. The change is transmitted from the slow-changing subsystem to the fast-changing subsystem; At the synchronization time The slow-varying subsystem receives the rotational speed at the current moment. And calculate mechanical power The fast-change subsystem receives the mechanical power. And update the status; Asynchronous moments between adjacent synchronization moments The fast-changing subsystem employs a linear interpolation method, based on the mechanical power at two adjacent synchronization moments. and The mechanical power input at the current moment is calculated; Repeat the above process of interaction between synchronous and asynchronous moments until the full-time domain simulation is completed.

2. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, The large step size The value is 10 milliseconds, and the small step size is... The value is 50 microseconds, and the rate factor is... The value is 200.

3. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, The synchronization time Defined as ,in It is an integer greater than or equal to zero.

4. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, The asynchronous time Defined as ,in .

5. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, The linear interpolation method calculates the mechanical power input according to the following formula: in, .

6. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, In each large step interval Within, the fast-change subsystem operates according to the small step size. The process continues, and after obtaining the mechanical power input through the linear interpolation method at each asynchronous moment, the speed of each unit is updated. At the next synchronous moment, the updated speed is fed back to the slow variable subsystem.

7. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, The slow-changing subsystem is simulated using the method of characteristics to advance the hydraulic transient process, while the fast-changing subsystem is simulated using the electromagnetic transient simulation method.

8. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, In each large step interval Within, the slow-changing subsystem synchronizes at specific times. rotational speed Using this as a constant input within the interval, a large-step integration is performed to obtain the right endpoint of the interval. mechanical power .

9. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, Before the simulation begins, an initialization step is also included: Determine the initial head and initial flow rate of each turbine; set the initial mechanical power and initial speed of each unit; set the initial voltage and initial current of the sending-end power grid and the initial state of each modular multilevel converter station; The initial power flow of the calculation system ensures that the electrical network and hydraulic system are in equilibrium.

10. The multi-rate hybrid simulation method for a single-pipe multi-machine hydropower group via a flexible direct power transmission system according to claim 1, characterized in that, Within the first large step interval, the slowly varying subsystem uses large steps. Perform an integration to complete the state update; the fast-change subsystem performs this update within the first large step interval. The process involves several small-step iterations, with interpolation performed using the initial mechanical power provided by the slowly varying subsystem.

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