A method for model validation of a direct current transmission system

Abstract

The application discloses a kind of direct current transmission system model verification method, comprising the following steps: step 1) according to the given AC-DC hybrid power system model, establish the equivalent power grid model for direct current transmission system model verification;Step 2) according to power grid flow state information, initialize transient stability simulation to obtain state variable initial value;Step 3) numerical integration method is used to carry out hybrid simulation to the equivalent power grid model, step 4) using interpolation algorithm keeps the sampling period of online phasor measurement unit and simulation step length synchronous, periodically injects measured data to replace the corresponding value obtained by solving network equation in simulation process;Step 5) compare the AC side power curve with the measured power curve, to evaluate the accuracy of direct current transmission system model.The method supports the transient response after multiple disturbances under different power grid operating conditions, and comprehensively analyzes the dynamic characteristics of AC-DC interconnected system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrical engineering, and particularly relates to a DC power transmission system model verification method based on hybrid simulation and PMU signal injection. BACKGROUND

[0002] Under the background of new power system, high proportion of renewable energy and power electronic equipment show high time-varying, high nonlinearity and high uncertainty, under different types of large disturbances such as AC side fault and DC system blocking, the system transient and recovery characteristics after fault are complex, which easily leads to security and stability problems, and the instability characteristics are different, which brings great challenges to the security and stability operation of AC / DC hybrid new power system. In extreme cases, local faults will gradually turn into systemic cascading failures, and the systemic security (blackout) risk continues to increase. The growing random and dynamic behavior in the new power system poses an increasingly greater challenge to the safe and economic operation of the power grid. Too conservative models will lead to excessive investment and great waste of social resources; while too optimistic models will cause power grid security and stability problems, causing loss of life and property. In view of the high uncertainty and strong randomness of the "double high" new power system, the model quality used for power system planning and dispatch is crucial to the safe, stable and economic operation of the power grid, and the power industry currently lacks effective power grid model quality evaluation system and method.

[0003] Domestic and foreign research institutions have carried out preliminary research on the modeling quality of power system, but there are still serious challenges, which are embodied in: (1) there is no relevant standard for model quality evaluation for power grid simulation and online safety evaluation, and it is difficult to form a unified evaluation system; (2) online simulation analysis system mostly uses static model parameters (such as load model parameters), which is difficult to accurately evaluate the dynamic characteristics and real operation risk of the power grid; (3) the existing deterministic simulation analysis means and control logic are difficult to cope with complex and variable power grid conditions; (4) the existing online simulation program lacks comprehensive early warning capability. In view of the high uncertainty and strong randomness of the "double high" new power system, it is urgent to improve the overall quality of the power grid model to ensure the simulation accuracy, form the precise online safety risk evaluation and early warning capability, and realize the comprehensive evaluation system of the simulation model quality suitable for the new power system

[0004] In the past decades, North American agencies including NERC and WECC have established industry standards (MOD33, MOD26 and MOD27) to improve the overall quality of power grid models from both steady state and dynamic aspects, providing effective support for power grid planning and operation simulation analysis. To achieve this goal, a traditional method is to conduct a drag-net test on the generator to obtain electromechanical transient stability model parameters for planning and operation simulation calculation; however, this method is quite costly because the generator needs to be disconnected from the grid, restarted and tested, and affects the revenue of the generator owner. In recent years, using online phasor measurement units (PMU) or digital fault recorders (DFR) to conduct "event playback" measurements to verify model accuracy and calibrate parameters has become a low-cost and promising method. Once a power grid major disturbance event is captured, the measured voltage and bus frequency (or phase angle) curve is imported into the model of the generator, and the model response is checked from both active power and reactive power. If the curve matches well between the model response and the actual measurement, it indicates that the model has good accuracy. If there is a significant model problem, a curve fitting method based on a nonlinear least squares algorithm, a Kalman Filter-based algorithm, a genetic algorithm and a particle swarm optimization algorithm can be used to adjust the parameters.

[0005] Existing methods focus more on large generator set model verification, and there are fewer model quality evaluation methods for DC transmission systems. The present invention will draw on international advanced power grid modeling and evaluation methods and innovatively propose a comprehensive evaluation method for DC transmission system model quality in AC / DC hybrid power grids. The DC system AC side PMU measurement is used to comprehensively verify the DC system model, thereby improving the overall model quality. SUMMARY

[0006] To solve the problems in the prior art, the present invention provides a DC transmission system model verification method based on hybrid simulation and PMU signal injection to solve the above technical problems, which is specifically implemented by the following technical solutions:

[0007] The DC transmission system model verification method comprises the following steps:

[0008] Step 1) According to a given AC-DC hybrid power system model, an equivalent power grid model for DC power transmission system model verification is established, the equivalent power grid model includes two DC buses, rectifier side converter stations, inverter side converter stations, two generator units and two online phasor measurement units, the two DC buses at the outermost side are connected to the two AC buses of the AC power transmission system through the rectifier side converter stations and the inverter side converter stations respectively, the two generator units are connected to the two AC buses respectively, and the two online phasor measurement units are installed at the AC buses where the two generator units are located respectively to collect measurement data including bus voltage amplitude, voltage phase angle, line current, line power and frequency signal;

[0009] Step 2) According to power flow state information, the initial value of the state variable is obtained by transient stability simulation;

[0010] Step 3) The equivalent power grid model is hybrid simulated by using a hybrid electromechanical-electromagnetic transient simulation platform and a numerical integration method, wherein the AC system part is simulated by using an electromechanical transient model, and the DC power transmission system part is simulated by using an electromagnetic transient model;

[0011] Step 4) For the measurement data, an interpolation algorithm is used to keep the sampling period of the online phasor measurement unit and the simulation step length synchronous; during the hybrid simulation process, the voltage amplitude and frequency signal measured by the online phasor measurement unit are periodically injected to replace the corresponding values obtained by solving the network equation in the simulation process, and the AC side power curve obtained in the simulation process is saved;

[0012] Step 5) The AC side power curve is compared with the online phasor measurement unit measured power curve, the root mean square error between the two is calculated to evaluate the accuracy of the DC power transmission system model.

[0013] The DC power transmission system model verification method is further designed that in the step 5), when the root mean square error is less than a set threshold, it is determined that the quality of the DC power transmission system model meets the standard; when the root mean square error is greater than the set threshold, it is determined that the quality of the DC power transmission system model does not meet the standard.

[0014] The DC power transmission system model verification method is further designed that the range of the set threshold is set to (4%, 6%).

[0015] The DC power transmission system model verification method is further designed that in the step 4), the time interval of the periodic injection is set to 4 to 6 milliseconds.

[0016] The application also provides an electronic device including a memory, a processor and a computer program, wherein the computer program is stored in the memory and is configured to be executed by the processor to realize the DC power transmission system model verification method.

[0017] The application further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the DC power transmission system model verification method.

[0018] The application has the following beneficial effects:

[0019] The DC power transmission system model verification method of the application adopts a high-precision electromechanical-electromagnetic hybrid modeling and simulation platform, can use electromechanical transient simulation for the AC power grid and electromagnetic transient simulation for the DC power transmission system, and takes into account the scale of the AC power grid and the fine modeling of the DC system. The method supports the transient response after various disturbances under different power grid operating conditions, and comprehensively analyzes the dynamic characteristics of the AC-DC interconnected system.

[0020] The DC power transmission system model verification method of the application establishes an equivalent model of the AC system in the vicinity of the DC power transmission system, and collects PMU measurement information after a large disturbance of the system. The voltage amplitude and frequency information collected by the PMU is periodically injected into the simulation process according to the electromechanical transient simulation step, the electromechanical-electromagnetic transient hybrid simulation curve is obtained, and is compared with the measured PMU signal, so as to effectively evaluate the response of the DC power transmission system model. The application can effectively identify the deviation of the DC power transmission system model, improve the simulation accuracy, and support power system planning and dispatching decisions. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a flowchart of the DC power transmission system model verification method.

[0022] Figure 2 It is a single-line diagram of the AC-DC hybrid power system.

[0023] Figure 3 It is a schematic diagram of the equivalent model for DC power transmission system model verification.

[0024] Figure 4 It is a schematic diagram of the DC power transmission system model of the electromechanical-electromagnetic transient hybrid simulation platform. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings.

[0026] As Figure 1 The DC power transmission system model verification method of the application includes the following steps:

[0027] Step 1) According to a given AC-DC hybrid power system model, an equivalent power grid model for DC power transmission system model verification is established. Figure 2 Figure 3 Figure 2 ​​In the embodiment, the DC power transmission system is composed of DC buses 01HVDC11, 01HVDC12, 01HVDC13, 01HVDC14, rectifier-side converter stations (connecting AC buses BUS11 and DC buses 01HVDC11) and inverter-side converter stations (connecting AC buses BUS8 and DC buses 01HVDC14). The electrical parts other than the DC system are AC power transmission systems. The equivalent power grid model includes DC buses, rectifier-side converter stations, inverter-side converter stations, two generator units and two online phasor measurement units. The two DC buses at the outermost side are respectively connected to the two AC buses of the AC power transmission system through the rectifier-side converter stations and the inverter-side converter stations. The two generator units are respectively connected to the two AC buses. The two online phasor measurement units are respectively installed at the AC buses where the two generator units are located to collect measurement data including bus voltage amplitude, voltage phase angle, line current and line power.

[0028] Step 2) According to the power flow state information of the power grid, the initial values of the state variables are obtained by initializing the transient stability simulation.

[0029] Step 3) The equivalent power grid model is hybrid simulated by using a numerical integration method on an electromechanical-electromagnetic hybrid simulation platform. The AC system part is simulated by using an electromechanical transient model, and the DC power transmission system part is simulated by using an electromagnetic transient model.

[0030] Step 4) For the measurement data, an interpolation algorithm is used to keep the sampling period of the online phasor measurement unit and the simulation step length synchronized. In the hybrid simulation process, the voltage amplitude and frequency signals measured by the online phasor measurement unit are periodically injected to replace the corresponding values obtained by solving the network equations in the simulation process. The AC side power curve obtained in the simulation process is saved, which includes the active power curve and the reactive power curve. The time interval of the periodic injection in this step is set to 4 to 6 milliseconds. In this embodiment, the time interval is preferably set to 5 milliseconds. Step 5) The AC side power curve is compared with the online phasor measurement unit measured power curve, and the root mean square error between the two is calculated to evaluate the accuracy of the DC power transmission system model. In this step, when the root mean square error is less than the set threshold, it is determined that the quality of the DC power transmission system model meets the standard; when the root mean square error is greater than the set threshold, it is determined that the quality of the DC power transmission system model does not meet the standard. The range of the set threshold is set to (4%, 6%). In this embodiment, the threshold is preferably set to 5%.

[0031] In this embodiment, the generator model uses the differential equations of the GENTPF model, as shown in formula (1).

[0032]

[0033] In formula (1), six state variables are defined, including E' q , E'd , E" q , E" d , δ, ω, I dg is the d-axis current in MVA base; I qg is the q-axis current in MVA base; E fd is the input voltage to the exciter model; P m is the mechanical power (input to the governor model); T e is the electrical torque; and the remaining unknowns are constant mechanical parameters.

[0034] The governor in this example is the IEEE Turbine / Governor Model (Type G1) which regulates the rotational frequency of the machine by providing a mechanical power signal P m to the generator model. The derivatives of the state variables for the IEEE Turbine / Governor Model (Type G1) are given by equation (2),

[0035]

[0036] When K2, K4, K6, and K8 are all zero, the mechanical power output to the machine model is given by: P m = K1s 2g1 + K3s 3g1 + K5s 4g1 + K7s 5g1 .

[0037] The exciter in the electromagnetic transient model in this example is used to provide transient voltage support after a voltage disturbance by restoring the bus voltage by providing a field voltage signal Efd to the generator. There are a variety of excitation system models that represent physical control systems with varying degrees of complexity. As a result, the number of state variables and actual control logic can vary depending on their parameter settings. In this example, the IEEE Type ac2 excitation system is used as described in equation (3),

[0038]

[0039] where

[0040] V fe = I fd K d + (Ke+ SE) s 3e

[0041]

[0042]

[0043]

[0044] E fd=ωs 3e F ex

[0045] The DC transmission system model in this embodiment is shown below. Figure 4 and equations (4) to (10)

[0046] P = -V d I d (4)

[0047]

[0048]

[0049]

[0050] μ=π-α-γ (8)

[0051]

[0052]

[0053] Among them, V d It is the DC voltage of the converter, I d It is the DC current of the converter, α is the ignition angle of the converter, γ is the arc suppression angle of the converter, and X is the DC current of the converter. c It is a bridge circuit for the commutator reactor, V d0 It is the open-circuit DC voltage, V LL It is the AC line voltage on the converter side, N b n is the number of bridges connected in series on the DC side. t It is the nominal voltage ratio of the transformer on the DC side of the rectifier, a t This is the nominal tap ratio of the transformer, and kc=1 is the nominal tap ratio of the converter. The angle by which the line current lags the neutral line voltage, and μ is the commutation voltage. To obtain the time-domain trajectory, the differential equations and network coupling equations can be solved alternately or simultaneously. For alternatives, explicit integration methods are commonly used in today's commercial tools. Examples include modified Euler, Runge-Kutta (second or fourth order), and Adams-Bashforth, all of which require smaller time steps (1 / 4 or 1 / 2 cycle) to obtain accurate dynamic behavior after perturbations and avoid numerical instabilities.

[0054] This embodiment also provides an electronic device, including a memory, a processor, and a computer program, wherein the computer program is stored in the memory and configured to be executed by the processor to implement a DC transmission system model verification method.

[0055] The embodiment also provides a computer readable storage medium, the storage medium stores a computer program, and the computer program is executed by a processor to implement the DC power transmission system model verification method.

[0056] The DC power transmission system model verification method of the embodiment adopts a high-precision electromechanical-electromagnetic hybrid modeling and simulation platform, can use electromechanical transient simulation for the AC power grid and electromagnetic transient simulation for the DC power transmission system, and takes into account the scale of the AC power grid and the fine modeling of the DC system. The method supports the transient response after various disturbances under different power grid operating conditions, and comprehensively analyzes the dynamic characteristics of the AC-DC interconnected system. The DC power transmission system model verification method establishes an equivalent model of the near-zone AC system of the DC power transmission system, and collects PMU measurement information after a large disturbance of the system. The voltage amplitude and frequency information collected by the PMU is periodically injected into the simulation process according to the electromechanical transient simulation step, the electromechanical-electromagnetic transient hybrid simulation curve is obtained, and is compared with the measured PMU signal, so as to effectively evaluate the response of the DC power transmission system model. The application can effectively identify the deviation of the DC power transmission system model, improve the simulation accuracy, and support power system planning and dispatching decision-making.

[0057] The technical means disclosed in the application scheme is not limited to the technical means disclosed in the above-mentioned embodiments, and also includes technical solutions composed of any combination of the above technical features. It should be noted that for those skilled in the art, without departing from the principles of the application, a number of improvements and refinements can be made, and these improvements and refinements are also considered within the protection scope of the application.

Claims

1. A method of model validation for a high voltage direct current power transmission system, characterized by The method comprises the following steps: Step 1) According to a given AC-DC hybrid power system model, an equivalent power grid model for checking a DC power transmission system model is established, the equivalent power grid model comprising two DC buses, a rectifier-side converter station, an inverter-side converter station, two generator units and two online phasor measurement units, the two DC buses at the outermost sides being connected to two AC buses of an AC power transmission system through the rectifier-side converter station and the inverter-side converter station respectively, the two generator units being connected to the two AC buses respectively, and the two online phasor measurement units being installed at the two AC buses respectively to collect measurement data including bus voltage amplitude, voltage phase angle, line current, line power and frequency signals; Step 2) According to power flow state information, state variable initial values are obtained through transient stability simulation; Step 3) A hybrid simulation platform of electromechanical-electromagnetic transient is used to perform hybrid simulation on the equivalent power grid model by using a numerical integration method, wherein the AC system part is simulated by using an electromechanical transient model, and the DC power transmission system part is simulated by using an electromagnetic transient model; Step 4) For the measurement data, an interpolation algorithm is used to keep the sampling period of the online phasor measurement unit and the simulation step length in synchronization; during the hybrid simulation, voltage amplitude and frequency signals measured by the online phasor measurement unit are periodically injected to replace corresponding values obtained by solving network equations during the simulation process, and an AC side power curve obtained during the simulation process is saved; Step 5) The AC side power curve is compared with an online phasor measurement unit measured power curve, and a root mean square error between the two is calculated to evaluate the accuracy of the DC power transmission system model; When the root mean square error is less than a set threshold value in the step 5), it is determined that the quality of the DC power transmission system model meets the standard; when the root mean square error is greater than the set threshold value, it is determined that the quality of the DC power transmission system model does not meet the standard; The set threshold value is set to be in the range of 4% to 6%; The time interval of the periodic injection in the step 4) is set to be 4 to 6 milliseconds.

2. An electronic device, comprising: A storage medium storing a computer program, the computer program being executed by a processor to implement the DC power transmission system model checking method of claim 1.

3. A computer-readable storage medium, characterized in that The storage medium stores a computer program, the computer program being executed by a processor to implement the DC power transmission system model checking method of claim 1.

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