A method and device for optimizing RTDS simulation for equivalent ac voltage source

Abstract

The application relates to the field of power system simulation, and discloses an RTDS simulation method and device for optimizing an equivalent AC voltage source, which comprises a steady-state discrimination module and an AC voltage control module; the steady-state discrimination module is used for discriminating whether the system reaches a steady state; the AC voltage module is used for controlling the equivalent AC voltage source; the AC voltage value of an actual project is calculated, and a voltage error is obtained by subtracting a target AC voltage value; the voltage error is closed-loop controlled through an integral link to eliminate the error, and the voltage signal after eliminating the error is transmitted to the equivalent AC voltage source; the size of the time constant of the integral link is selected according to the system state: when the system reaches the steady state, a larger time constant is selected; otherwise, a smaller time constant is selected. The method can avoid that the DC voltage cannot reach a reference value in a steady-state process, the steady-state parameter checking is inconsistent with the actual project, and oscillation caused in a fault recovery process.

Description

Technical Field

[0001] This invention belongs to the field of power system simulation, specifically relating to an RTDS simulation method and apparatus for optimizing equivalent AC voltage sources. Background Technology

[0002] Three-phase equivalent voltage sources play a crucial role in simulation modeling. Typically, they simulate the three-phase bus voltage using given system impedance and other parameters, based on engineering needs. For control and protection simulation tests before the construction of DC transmission projects, modeling and completion are usually performed using real-time digital simulation (RTDS) platforms. Regardless of whether it's domestically or internationally, or across different regions of China, the voltage levels and grid strength of construction projects vary, necessitating modeling based on the specific parameter requirements of each actual project. The three-phase equivalent voltage source is a critical component of DC transmission project modeling and research; its selection directly impacts the realism of AC grid simulation and the reliability of control and protection tests. An inappropriate equivalent voltage source can lead to commutation failures, voltage instability, or failure to reach reference values. More seriously, it can result in significant discrepancies between voltage and current parameters and actual engineering requirements. Therefore, a reliable and safe three-phase equivalent voltage source device is needed to accurately simulate the grid characteristics of actual projects, maximizing the realism of control and protection tests.

[0003] Currently, factory testing is required before DC power projects are put into operation. To maintain consistency with the field testing environment as much as possible, equivalent simulations of the AC voltage levels and grid strength of the two converter stations are necessary during factory testing. When modeling the actual project in RTDS, the AC voltage source is set as a constant voltage source, which leads to the DC voltage failing to reach the reference value when increasing power under weak grid conditions. Furthermore, the voltage and current parameters during steady-state parameter verification differ significantly from the requirements of the actual project. Even with optimization by introducing an integral feedback loop into the AC voltage source, the unreasonable setting of the time constant, and the use of the same time constant in both the steady-state process and after reaching steady state, causes oscillations in the voltage and current during the recovery process when simulating AC system faults.

[0004] The existing solution sets the AC voltage source to a constant voltage source, which can lead to the DC voltage failing to reach the reference value when increasing power in a weak power grid. Furthermore, the voltage and current parameters used in steady-state parameter verification differ significantly from the requirements of actual engineering projects. Summary of the Invention

[0005] This invention provides an RTDS simulation method and apparatus for optimizing equivalent AC voltage sources, in order to solve the problem that the voltage and current parameters caused by using a constant voltage source for equivalence differ significantly from the actual engineering requirements.

[0006] To solve the above-mentioned technical problems, the technical solutions included in this invention and their corresponding beneficial effects are as follows:

[0007] This invention provides a scheme for optimizing an equivalent AC voltage source using RTDS simulation. The method calculates the AC voltage value of the actual engineering project and subtracts it from the target AC voltage value to obtain the voltage error. The voltage error is then eliminated through closed-loop control using an integral element. The voltage signal after error elimination is then sent to the equivalent AC voltage source. The time constant of the integral element is selected based on the system state: a larger time constant is selected when the system reaches steady state; otherwise, a smaller time constant is selected.

[0008] The beneficial effects of the above technical solution are as follows: By introducing an integral element into the externally controlled AC source, and using DC flow to determine whether the system is in a steady state, and considering that the time constant determines the strength of the integral element, two scenarios are set up: one during the steady state process and the other after the steady state is reached. This allows for the control of the AC voltage value in actual engineering projects, avoiding situations where the DC voltage cannot reach the reference value during the steady state process, inconsistencies between the steady state parameter verification and the actual engineering process, and oscillations caused during fault recovery.

[0009] Furthermore, the system state is determined based on whether the comparison results of DC voltage and DC power with their respective target values ​​are within the allowable error range; if the comparison results are within the allowable error range, the system has reached a steady state; otherwise, the system has not reached a steady state.

[0010] The system can directly use the voltage and power in the DC system to determine whether the system has reached steady state. The DC voltage and DC power are easy to obtain, and there is no need to use other methods to calculate the criteria to determine whether the system has reached steady state, which improves efficiency.

[0011] Furthermore, the time constant after the system reaches steady state is fixed to the larger time constant mentioned above.

[0012] Since the system is in steady state after the voltage and power reach the target values ​​in a DC system, and to avoid oscillation problems caused by faults, the time constant after the system reaches steady state is fixed to the larger time constant and no longer changes.

[0013] Furthermore, the AC voltage of the actual project is calculated from the three-phase bus voltage.

[0014] Furthermore, the three-phase voltage of the bus is obtained by real-time monitoring by a monitoring device.

[0015] This invention also provides a scheme for an RTDS simulation device optimized for an equivalent AC voltage source, including a steady-state discrimination module and an AC voltage control module; the AC voltage control module is used to calculate the AC voltage value of the actual engineering project and obtain the voltage error by subtracting it from the target AC voltage value; the voltage error is eliminated by closed-loop control through an integral element, and the voltage signal after error elimination is sent to the equivalent AC voltage source; the time constant of the integral element is selected according to the system state determined by the steady-state discrimination module: a larger time constant is selected when the system reaches a steady state; otherwise, a smaller time constant is selected.

[0016] The beneficial effects of the above technical solution are as follows: By introducing an integral element into the externally controlled AC source, and using DC flow to determine whether the system is in a steady state, and considering that the time constant determines the strength of the integral element, two scenarios are set up: one during the steady state process and the other after the steady state is reached. This allows for the control of the AC voltage value in actual engineering projects, avoiding situations where the DC voltage cannot reach the reference value during the steady state process, inconsistencies between the steady state parameter verification and the actual engineering process, and oscillations caused during fault recovery.

[0017] Furthermore, the system state is determined based on whether the comparison results of DC voltage and DC power with their respective target values ​​are within the allowable error range; if the comparison results are within the allowable error range, the system has reached a steady state; otherwise, the system has not reached a steady state.

[0018] The system can directly use the voltage and power in the DC system to determine whether the system has reached steady state. The DC voltage and DC power are easy to obtain, and there is no need to use other methods to calculate the criteria to determine whether the system has reached steady state, which improves efficiency.

[0019] Furthermore, the time constant after the system reaches steady state is fixed to the larger time constant mentioned above.

[0020] Since the system is in steady state after the voltage and power reach the target values ​​in a DC system, and to avoid oscillation problems caused by faults, the time constant after the system reaches steady state is fixed to the larger time constant mentioned above.

[0021] Furthermore, the AC voltage of the actual project is calculated from the three-phase bus voltage.

[0022] Furthermore, the three-phase voltage of the bus is monitored in real time by a monitoring device. Attached Figure Description

[0023] Figure 1 This is a diagram of an RTDS simulation device for modeling an equivalent AC voltage source;

[0024] Figure 2This is a flowchart of the RTDS simulation method for modeling an equivalent AC voltage source. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] The basic concept of this invention is as follows: By monitoring the line voltage of the bus in real time and calculating the difference with the target AC voltage, the difference is eliminated through closed-loop control of the integral circuit. The resulting voltage signal is then sent to an externally controlled equivalent AC voltage source to improve accuracy. By controlling the time constant of the integral circuit through external logic, different time constants are selected during the steady-state process and after reaching steady state. This satisfies the requirement for rapid and accurate voltage boosting during steady-state operation while reducing oscillations caused by fault recovery during steady-state operation.

[0027] Method Implementation Examples:

[0028] like Figure 1 The simulation apparatus shown, applicable to the RTDS simulation method for optimizing an equivalent AC voltage source according to the present invention, includes a steady-state discrimination module and an AC voltage control module. Specifically, the steady-state discrimination module is used to determine whether the system has reached a steady state; the AC voltage module is used to control the equivalent AC voltage source.

[0029] like Figure 2 The RTDS simulation method for optimizing an equivalent AC voltage source, as shown, is implemented using the following steps:

[0030] (1) Set the target AC power supply voltage value Us according to the actual engineering modeling requirements;

[0031] (2) Calculate the actual AC voltage value Urms based on the three-phase bus voltage obtained from monitoring;

[0032] (3) Calculate the voltage error value ΔU, which is obtained by subtracting Urms from Us;

[0033] (4) ΔU is controlled in a closed loop through an integral element to eliminate errors, and its time constant Ti is controlled externally.

[0034] (5) The voltage value output by the integral element is sent to the equivalent AC voltage source, and the equivalent AC voltage source also selects the external control mode at this time.

[0035] (6) The strength of the integral effect depends on the value of Ti. The smaller Ti is, the stronger the integral effect; the larger Ti is, the weaker the integral effect. The time constant of the integral effect is set according to engineering requirements. Theoretically, Ti should be set small during steady-state process, denoted as Ts; after reaching steady state, Ti should be set large, denoted as Tb.

[0036] (7) Determine whether the system is in a steady-state process or has already reached a steady state, using DC voltage Udl and DC power Pdc as the judgment criteria;

[0037] (8) If the comparison results of Udl and Pdc with their respective target values ​​are within the allowable error, the system state is determined to be in steady state, and Tb is sent to the integrator; otherwise, Ts is sent to the integrator. Since the voltage and power are in steady state after reaching the reference value in the DC system, to avoid oscillation problems caused by faults, the time constant after steady state is fixed at Tb and no longer changes;

[0038] (9) The output of the integrator is used as the input of the equivalent AC voltage source.

[0039] Device Example:

[0040] The hardware structure and specific implementation method of the RTDS simulation device optimized for equivalent AC voltage sources of the present invention have been described sufficiently in the embodiments of the RTDS simulation method optimized for equivalent AC voltage sources, and will not be repeated here.

[0041] The beneficial effects of this invention are as follows: For situations where constant voltage sources cannot meet the needs of actual engineering, a clear method is proposed to use external control and introduce an integral element for the AC voltage source; considering the characteristic that the time constant determines the strength of the integral element, a criterion for identifying whether the DC system is in a steady state is set, and a clear method for selecting different time constants is proposed to simulate the AC voltage source used in modeling and simulation. This can avoid the DC voltage failing to reach the reference value during the steady-state process, inconsistencies between steady-state parameter verification and actual engineering, and oscillations caused during fault recovery.

[0042] The time constant of the integral element in this invention can be set to two or more according to actual needs; only the corresponding selection criteria need to be added.

[0043] The specific embodiments of the present invention have been given above, but the present invention is not limited to the described embodiments. Under the concept given by the present invention, the technical means in the above embodiments can be changed, replaced, or modified in a way that is easy for those skilled in the art to conceive of, and the effect is basically the same as the corresponding technical means in the present invention, and the purpose of the invention is also basically the same. The technical solution formed in this way is a fine-tuning of the above embodiments, and such technical solution still falls within the protection scope of the present invention.

Claims

1. An RTDS simulation method for optimizing an equivalent AC voltage source, characterized in that... It includes the following steps: 1) Set the target AC power supply voltage value according to the actual engineering modeling requirements; calculate the actual AC voltage value based on the bus three-phase voltage obtained from monitoring the actual engineering; and obtain the voltage error by subtracting the actual AC voltage value from the target AC voltage value. 2) The voltage error is controlled in a closed loop through an integral element. The output of the integral element is used as the input of an equivalent AC voltage source to simulate the AC voltage source used in RTDS simulation modeling. In the integral element: a larger time constant is selected when the DC system reaches steady state; a smaller time constant is selected when the DC system has not reached steady state. The steady state of the DC system is determined by comparing the DC voltage and DC power in the DC system with their respective target values. If the comparison results are within the allowable error, the DC system has reached steady state; otherwise, the DC system has not reached steady state. The larger time constant selected during the process of the DC system reaching steady state and the smaller time constant selected during the process of the DC system not reaching steady state are used to control the AC voltage value in the actual project.

2. The RTDS simulation method for optimizing an equivalent AC voltage source according to claim 1, characterized in that... Set time constants for two or more of the integral stages.

3. The RTDS simulation method for optimizing an equivalent AC voltage source according to claim 2, characterized in that... Once the DC system reaches steady state, the time constant is fixed at the aforementioned large time constant and no longer changes.

4. The RTDS simulation method for optimizing an equivalent AC voltage source according to claim 1, characterized in that... When the DC system reaches steady state, choosing a larger time constant results in a weaker integral effect; when the DC system has not reached steady state, choosing a smaller time constant results in a stronger integral effect.

5. The RTDS simulation method for optimizing an equivalent AC voltage source according to claim 4, characterized in that... Add corresponding selection criteria for each set time constant.

6. An RTDS simulation device optimized for equivalent AC voltage sources, characterized in that... The system includes a steady-state discrimination module and an AC voltage control module. The AC voltage control module is used to obtain the voltage error by subtracting the actual AC voltage value from the target AC voltage value. Specifically, the target AC power supply voltage value is set according to the actual engineering modeling requirements; the actual AC voltage value is calculated based on the three-phase bus voltage obtained from monitoring the actual engineering; the voltage error is controlled in a closed loop through an integral element, and the output of the integral element is used as the input of an equivalent AC voltage source to simulate the AC voltage source used in RTDS simulation modeling. In the integral element: a larger time constant is selected when the DC system reaches steady state; a smaller time constant is selected when the DC system has not reached steady state; the DC system's steady state is determined by comparing the DC voltage and DC power in the DC system with their respective target values ​​to see if they are within the allowable error range. If the comparison results are within the allowable error range, the DC system has reached steady state; otherwise, the DC system has not reached steady state. The larger time constant selected during the process of the DC system reaching steady state and the smaller time constant selected during the process of the DC system not reaching steady state are used to control the AC voltage value of the actual engineering.

7. The RTDS simulation device for optimizing an equivalent AC voltage source according to claim 6, characterized in that... Set time constants for two or more of the integral stages.

8. The RTDS simulation device for optimizing an equivalent AC voltage source according to claim 7, characterized in that... Once the DC system reaches steady state, the time constant is fixed at the aforementioned large time constant and no longer changes.

9. The RTDS simulation device for optimizing an equivalent AC voltage source according to claim 6, characterized in that... When the DC system reaches steady state, choosing a larger time constant results in a weaker integral effect; when the DC system has not reached steady state, choosing a smaller time constant results in a stronger integral effect.

10. The RTDS simulation device for optimizing an equivalent AC voltage source according to claim 9, characterized in that... Add a corresponding selection criterion for each time constant set.

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