An electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid

Abstract

The present invention discloses an electromagnetic transient simulation power flow initialization method for an AC-DC hybrid power grid, including: obtaining model parameters according to the simulation example file of the AC-DC hybrid power grid and performing power flow calculation to obtain the power flow calculation results; performing electromagnetic transient simulation according to the simulation example file and the power flow calculation results to obtain the position information of each electrical component; traversing all electrical components of the simulation example file, generating AC steady-state equations and DC steady-state equations and solving them to obtain the steady-state node voltage vector; traversing all electrical components in the simulation example file to obtain the steady-state values of all electrical quantities in each electrical component except for the high-voltage DC converter component, and obtaining the circuit topology of each high-voltage DC converter component at the initial simulation moment; performing initialization settings on the control systems of each high-voltage DC converter component and adding power flow initialization auxiliary power supply components to stabilize the power supply voltage. The present invention takes into account the influence of complex control systems and can obtain more accurate steady-state initialization results.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and particularly to a method for initializing the electromagnetic transient simulation power flow of an AC-DC hybrid power grid. Background Art

[0002] With the rapid development and wide application of high-voltage direct current (HVDC) transmission technology and the large-scale deployment of flexible alternating current (FACTS) devices and static var compensators, contemporary power systems exhibit obvious characteristics of power electronics and AC-DC hybrid operation. The scale of AC-DC hybrid power grids is gradually expanding, and their operation and control logics are becoming increasingly complex.

[0003] Power system initialization, as the basis of electromagnetic transient simulation and a prerequisite for various dynamic analyses, is also a huge challenge for the electromagnetic transient research of AC-DC hybrid power grids. However, existing power system initialization methods rarely consider the influence of complex control systems, resulting in inaccurate initialization results for AC-DC hybrid power grids. Considering the influence of complex control systems in the electromagnetic transient initialization method of AC-DC hybrid power grids is an issue that must be addressed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for initializing the electromagnetic transient simulation power flow of an AC-DC hybrid power grid to solve the technical problem that the existing electromagnetic transient initialization method for AC-DC hybrid power grids does not consider the influence of complex control systems, resulting in inaccurate initialization results.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for initializing the electromagnetic transient simulation power flow of an AC-DC hybrid power grid includes:

[0007] Determine the model parameters of the AC-DC hybrid power grid according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid, perform power flow calculation based on the model parameters, and write the power flow calculation results at steady state into the power flow calculation result file;

[0008] Perform electromagnetic transient simulation according to the electromagnetic transient simulation example file and the power flow calculation result file to obtain the position information of each electrical component in the AC-DC hybrid power grid;

[0009] Traverse all electrical components in the electromagnetic transient simulation example file, generate AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information, and solve them to obtain the steady-state node voltage vector; the component types include capacitor components in the DC power grid, inductor components in the DC power grid, AC power source components, and high-voltage DC converter components;

[0010] Traverse all electrical components in the electromagnetic transient simulation case file, and obtain the steady-state values of all electrical quantities inside each of the electrical components except for the HVDC converter components according to the steady-state node voltage vector and the admittance values of each internal branch. Calculate the conduction states of the switches inside each HVDC converter component at the initial simulation moment to obtain the circuit topology at the initial simulation moment;

[0011] Initialize the control systems of each HVDC converter component according to the firing angles, extinction angles of each HVDC converter component and the steady-state values of the measuring components; Add power flow initialization auxiliary power supply components to each HVDC converter component to stabilize the power supply voltage.

[0012] Optionally, generating AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information includes:

[0013] Fill the steady-state admittance values of each electrical component into the corresponding positions of the steady-state node admittance matrix according to the component type and the position information to generate AC steady-state calculation equations and DC steady-state calculation equations.

[0014] Optionally, filling the steady-state admittance values of each electrical component into the corresponding positions of the steady-state node admittance matrix according to the component type and the position information to generate AC steady-state calculation equations and DC steady-state calculation equations includes:

[0015] For the capacitor components in the DC grid, fill the steady-state node admittance matrix in the open-circuit form;

[0016] For the inductor components in the DC grid, fill the steady-state node admittance matrix in the short-circuit form;

[0017] For the AC power source components, obtain their three-phase voltages according to the power flow calculation result file and fill them into the power source vector of the AC steady-state calculation equation;

[0018] For the HVDC converter components, obtain the three-phase voltage amplitudes and phases of their AC ports according to the power flow calculation result file and fill them into the power source vector of the AC steady-state calculation equation; Obtain the voltage of their DC ports according to the power flow calculation result file and fill it into the power source vector of the DC steady-state calculation equation.

[0019] Optionally, initializing the control systems of each HVDC converter component according to the firing angles, extinction angles of each HVDC converter component and the steady-state values of the measuring components includes:

[0020] Judge whether the HVDC converter component is an inverter-side converter. If not, skip the HVDC converter component and add it to the end of the element queue to be processed until all inverter-side converters are processed;

[0021] Construct a queue of input ports to be traversed, whose elements are all the input ports of the HVDC converter control system, and construct a queue of output ports to be traversed, whose elements are all the output ports of the HVDC converter control system;

[0022] According to the signal flow direction of the HVDC converter control system, traverse the control elements starting from the head of the queue of input ports to be traversed. For each control element, calculate the output signal of the control element according to its input-output relationship and use it as the input signal of the next control element until the queue of input ports to be traversed is empty;

[0023] If the queue of output ports to be traversed is not empty, traverse the control elements starting from the head of the queue of output ports to be traversed according to the reverse direction of the signal flow of the HVDC converter control system. For each control element, calculate the input signal of the control element according to its input-output relationship and use it as the output signal of the next control element until the queue of output ports to be traversed is empty.

[0024] Optionally, calculating the output signal of the control element according to its input-output relationship for each control element further includes:

[0025] For a transfer function element, calculate its state quantity based on the input and output signals and use it as the steady-state initial value;

[0026] For a multi-input control element, determine whether each input has been calculated. If so, calculate its output signal and move to the next control element; if not, add the multi-input control element to the tail of the queue of input ports to be traversed, and then continue searching from the head;

[0027] For an integrator element with a limit, make a judgment according to its input signal. If the absolute value of the input signal is less than the preset value, the integrator element is the end point of the traversal path, and the steady-state initial value of the integrator element cannot be determined. Remove the head element of the current queue of input ports to be traversed and continue searching from the next element; otherwise, if the input signal is positive, set the steady-state initial value and output signal of the integrator element to the upper limit of the limit, and if the input signal is negative, set the steady-state initial value and output signal of the integrator element to the lower limit of the limit, and move to the next control element;

[0028] If the output signal of the currently traversed control element is connected to the output port of the HVDC converter control system, the control element is the end point of the traversal path. Remove the output port from the queue of output ports to be traversed, remove the head element of the queue of input ports to be traversed, and continue searching from the next element.

[0029] Optionally, calculating the input signal of each control element according to its input-output relationship further includes:

[0030] For a transfer function element, calculating its state quantity based on the input and output signals and using it as the steady-state initial value;

[0031] For a multiplexer element, setting each input signal to be equal to the output signal, taking the multiplexer element as the end point of the current traversal path, and adding the control elements connected to each input signal to the queue of output ports to be traversed;

[0032] For an integrator element with a limiter, using the output signal as its steady-state initial value, taking the integrator element as the end point of the current traversal path, and continuing the next traversal from the head of the queue of output ports to be traversed.

[0033] Optionally, obtaining the steady-state values of all electrical quantities inside each of the electrical elements except the HVDC converter element according to the steady-state node voltage vector and the admittance values of each internal branch includes:

[0034] For each of the electrical elements except the HVDC converter element, obtaining the element port voltage according to the position of the element port voltage in the steady-state node voltage vector;

[0035] Calculating the steady-state values of all electrical quantities inside the electrical element according to the element port voltage and the admittance values of each internal branch of the electrical element.

[0036] Optionally, calculating the conduction states of the switches inside each of the HVDC converter elements at the initial simulation moment to obtain the circuit topology at the initial simulation moment includes:

[0037] For each of the HVDC converter elements, obtaining the corresponding firing angle and extinction angle from the power flow calculation result file;

[0038] Calculating the conduction states of the internal power electronic switches at the initial simulation moment according to the firing angle, the extinction angle and the steady-state value of the AC port voltage, and obtaining the circuit topology at the initial simulation moment according to the conduction states.

[0039] Optionally, adding a power flow initialization auxiliary power supply element to each of the HVDC converter elements to stabilize the power supply voltage includes:

[0040] Connecting a first three-phase voltage source to the AC port of the HVDC converter element, setting the amplitude and phase of the first three-phase voltage source according to the power flow calculation result file, setting the connection time to the initial simulation moment, and removing the first three-phase voltage source after a preset cut-off time;

[0041] Connect a second three-phase voltage source to the DC port of the HVDC converter element, set the voltage value of the second three-phase voltage source according to the power flow calculation result file, set the connection time to the initial simulation time, and remove the second three-phase voltage source after the preset cut-off time.

[0042] Optionally, obtaining the position information of each electrical component in the AC-DC hybrid power grid includes:

[0043] For each electrical component, obtain its subordination relationship with the AC power grid and the DC power grid, and obtain the position of its admittance element in the steady-state nodal admittance matrix, the position of the port voltage in the steady-state nodal voltage vector, and the position of the power source in the power source vector.

[0044] The present invention provides an electromagnetic transient simulation power flow initialization method for an AC-DC hybrid power grid, including: determining the model parameters of the AC-DC hybrid power grid according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid, performing a power flow calculation according to the model parameters, and writing the power flow calculation result at the steady state into the power flow calculation result file; performing an electromagnetic transient simulation according to the electromagnetic transient simulation example file and the power flow calculation result file to obtain the position information of each electrical component in the AC-DC hybrid power grid; traversing all electrical components in the electromagnetic transient simulation example file, generating AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information, and solving to obtain the steady-state nodal voltage vector; the component types include capacitor elements in the DC power grid, inductor elements in the DC power grid, AC power source elements, and HVDC converter elements; traversing all electrical components in the electromagnetic transient simulation example file, obtaining the steady-state values of all electrical quantities inside each of the electrical components except the HVDC converter element according to the steady-state nodal voltage vector and the internal branch admittance values, calculating the conduction states of the switches inside each of the HVDC converter elements at the initial simulation time to obtain the circuit topology at the initial simulation time; performing an initialization setting on the control system of each of the HVDC converter elements according to the trigger angle, arc extinction angle of each of the HVDC converter elements and the steady-state values of the measurement elements; adding a power flow initialization auxiliary power source element to each of the HVDC converter elements to stabilize the power supply voltage.

[0045] Based on the above technical solutions, the beneficial effects brought by the present invention are:

[0046] The present invention performs a power flow calculation based on an electromagnetic transient simulation example file of an AC / DC hybrid power grid to obtain the power flow calculation results, and performs an electromagnetic transient simulation based on the electromagnetic transient simulation example file and the power flow calculation results to obtain the position information of each electrical component. Through the mutual cooperation of the power flow calculation program and the electromagnetic transient simulation program, the position information of each electrical component can be obtained quickly and accurately; by traversing all the electrical components in the electromagnetic transient simulation example file, the steady-state values of all the electrical quantities inside each electrical component except for the high-voltage DC converter component are obtained, and the circuit topology of each high-voltage DC converter component at the initial moment of the simulation is obtained, thereby realizing the steady-state initialization setting of the AC / DC hybrid power grid; at the same time, considering the influence of the complex control system, the present invention initializes the control system of the high-voltage DC converter component, and adds a power flow initialization auxiliary power supply component to each high-voltage DC converter component to stabilize the power supply voltage, and can obtain more accurate control system initialization values, and realizes the high-precision power flow initialization of the AC / DC hybrid power grid through the electromagnetic transient simulation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic flow chart of the method of the present invention;

[0048] Figure 2 It is a schematic diagram of CIGRE-HVDC in the embodiment of the method of the present invention;

[0049] Figure 3 It is a schematic diagram of the AC side and the DC side of the converter in the present invention;

[0050] Figure 4 It is a schematic diagram of the first-order system of the present invention;

[0051] Figure 5 It is a schematic diagram of the proportional-integral (PI) controller of the present invention;

[0052] Figure 6 It is a schematic diagram of the control system composed of the first-order system and the PI controller in the present invention;

[0053] Figure 7 It is a schematic diagram of the power flow initialization auxiliary power supply component in the embodiment of the present invention;

[0054] Figure 8 It is a schematic diagram of the simulation result of the embodiment of the present invention in TSDG Figure 1 ;

[0055] Figure 9 It is a schematic diagram of the simulation result of the embodiment of the present invention in TSDG Figure 2 ;

[0056] Figure 10 It is a schematic diagram of the simulation result of the embodiment of the present invention in TSDG Figure 3 ;

[0057] Figure 11 Schematic diagram of the simulation results of the embodiments of the present invention in TSDG Figure 4 ;

[0058] Figure 12 Schematic diagram of the simulation results of the embodiments of the present invention in TSDG Figure 5 ;

[0059] Figure 13 Schematic diagram of the simulation results of the embodiments of the present invention in TSDG Figure 6 。 Detailed implementation manners

[0060] The embodiments of the present invention provide an electromagnetic transient simulation power flow initialization method for an AC-DC hybrid power grid to solve the technical problem that the existing electromagnetic transient initialization method for an AC-DC hybrid power grid does not consider the influence of complex control systems, resulting in inaccurate initialization results.

[0061] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0062] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0063] As the contemporary power system gradually moves towards energy diversification, power electronics, and AC-DC hybridization, the mutual influence between AC and DC, multiple DCs, and sources, networks, and loads intensifies. The scale of DC transmission continues to expand and become increasingly complex, and the safe operation of the power grid faces severe challenges. On the other hand, as the backbone UHV grid in China is gradually completed, the number of UHV DC lines continues to increase, the landing points are more concentrated, the AC-DC hybrid characteristics are more prominent, and the stability characteristics of large power grids will be more complex.

[0064] Since the electromagnetic transient simulation algorithm was proposed in the 1960s, it has been proven in practice that it can accurately reproduce various phenomena such as fast transients, unbalanced operating conditions, higher harmonics, and low-frequency oscillations. The continuous expansion of the contemporary power system scale and the formation of AC-DC hybrid power grids have put forward new requirements for power system transient simulation technology. On the one hand, high-voltage DC transmission systems are equipped with power electronic devices, and their control systems have extremely fast response speeds, requiring more precise optimization of electromagnetic transient simulation models. On the other hand, for the simulation calculation of large-scale national power grids, due to the large number of DCs, the simulation scale of electromagnetic transients will increase rapidly, and at the same time, the node scale of the AC power grid will also increase to tens of thousands. At the same time, for AC-DC hybrid networks, physical processes on the electromagnetic transient time scale such as AC system harmonic distortion and DC rapid regulation changes will interact with each other on a larger scale, and the influence area of AC-DC chain reactions may affect the entire power grid. In this case, electromagnetic transient simulation is crucial for accurately reflecting the electromagnetic transient process of AC-DC hybrid networks. Therefore, improving electromagnetic transient simulation and its initialization method based on the new characteristics of AC-DC hybrid networks has become an irresistible trend.

[0065] Power system initialization, as the basis of electromagnetic transient simulation and a prerequisite for various dynamic analyses, is also a huge challenge for the electromagnetic transient research of AC-DC hybrid power grids. A relatively simple initialization method is to start the simulation from a zero state, but this method will fail under the conditions of complex control systems. On the other hand, a short simulation step size will also lead to an overly long simulation execution time. Another method is steady-state initialization, which requires the results of power flow calculations to calculate the initial states of electrical systems and control systems. The general method is that considering black-box components and nonlinear components, the simulation results can reach a steady state in a relatively short time. For a network containing a modular multilevel converter (MMC), the arm voltage and arm current of the MMC can be used to initialize the electrical and control systems of the AC-DC hybrid system. However, the existing initialization methods rarely consider the influence of complex control systems, which has become a problem that must be solved in the future initialization methods for AC-DC hybrid power grids.

[0066] Currently, there are various types of power system simulation software platforms at home and abroad. Typical ones include EMTP jointly developed by multiple Western countries, PSCAD / EMTDC developed by Manitoba Hydro in Canada, SimPowersystems developed by MathWorks in the United States based on Matlab, etc. Domestically, there are ADPSS developed by China Electric Power Research Institute, PSModel, CloudPSS developed by Tsinghua University, DSIM, etc. However, with the contemporary power system gradually moving towards energy diversification, power electronics, and AC-DC hybridity, there are significant deviations between the design concepts of traditional simulation tools and the development trends of new power systems, and it is urgent to upgrade concepts, adjust strategies, and actively practice.

[0067] TSDG is an electromagnetic transient simulation software independently developed by Tianjin University, with complete independent intellectual property rights. The software supports electromagnetic transient simulations of various basic electrical components, distributed power sources, control systems, and HVDC transmission systems. It uses an interpolation algorithm to handle the simulation problems of large-scale power electronic circuits and adopts a multi-threaded parallel computing strategy to accelerate the calculation speed of the transient simulation program. The software adopts object-oriented design based on C++, with good maintainability and scalability.

[0068] DSP is a power system analysis software with international advanced level developed by China Southern Power Grid Company based on the BPA power system analysis program of the Bonneville Power Administration of the United States. It has the functions of steady-state power flow calculation and power system fault analysis, and supports electromagnetic transient simulations of basic electrical components and AC / DC transmission systems. It has been widely used in power system planning and design, dispatching operation, and teaching and research departments.

[0069] Please refer to Figure 1 , an embodiment of the electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid provided by the present invention, includes:

[0070] S100: Determine the model parameters of the AC / DC hybrid power grid according to the electromagnetic transient simulation example file of the AC / DC hybrid power grid, perform power flow calculation according to the model parameters, and write the power flow calculation results at steady state into the power flow calculation result file;

[0071] S200: Perform electromagnetic transient simulation according to the electromagnetic transient simulation example file and the power flow calculation result file to obtain the position information of each electrical component in the AC / DC hybrid power grid;

[0072] S300: Traverse all electrical components in the electromagnetic transient simulation example file, generate AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information, and solve them to obtain the steady-state node voltage vector; the component types include capacitor components in the DC power grid, inductor components in the DC power grid, AC power source components, and HVDC converter components;

[0073] S400: Traverse all electrical components in the electromagnetic transient simulation example file, obtain the steady-state values of all electrical quantities inside each of the electrical components except the HVDC converter component according to the steady-state node voltage vector and the internal branch admittance values, and calculate the conduction states of the switches inside each HVDC converter component at the simulation initial moment to obtain the circuit topology at the simulation initial moment;

[0074] S500: Initialize the control systems of each of the high-voltage DC converter components according to the firing angles, extinction angles of each of the high-voltage DC converter components, and the steady-state values of the measuring components; add a power flow initialization auxiliary power supply component to each of the high-voltage DC converter components to stabilize the power supply voltage.

[0075] In step S100, first, determine the model parameters of the AC-DC hybrid power grid according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid; then, perform a power flow calculation according to the model parameters, and write the power flow calculation results when reaching the steady state into the power flow calculation result file.

[0076] Specifically, determine the component parameters and structure of the AC-DC hybrid power grid according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid. Table 1 shows the parameter information of each component. The structure refers to the interconnection relationship between components. Figure 2 shows the connection relationship between components in the CIGRE-HVDC AC-DC hybrid power grid example; it should be noted that the CIGRE-HVDC AC-DC hybrid power grid example is a standard example familiar to those skilled in the art.

[0077] In an embodiment of the present invention, the steady-state initialization process of the CIGRE-HVDC AC-DC hybrid power grid example as Figure 2 shown is described. This example includes a rectifier-side generator set (RECGEN), an inverter-side generator set (INVGEN), a rectifier-side converter station (RECDC), an inverter-side converter station (INVDC), and a DC transmission line between the two. The converter stations RECDC and INVDC are connected to their respective rectifier-side and inverter-side AC buses RECAC and INVAC through two converter transformers.

[0078] The main parameters of this embodiment are shown in Table 1. Table 1 is the parameter of the CIGRE-HVDC AC-DC hybrid power grid example. In the example, the transmission power of the high-voltage DC transmission system is set to 1000 MW, and the reference voltage of the DC transmission line is set to 500 kV.

[0079] Table 1

[0080]

[0081]

[0082] Perform a power flow calculation based on the model parameters and write the power flow calculation results at steady state to the power flow calculation result file. Specifically, start the power flow calculation program according to the model parameters, and calculate the three-phase voltage amplitudes and phases of all AC power sources and the AC ports of HVDC converters, the voltages and currents of the DC ports of HVDC converters, and the firing angles and extinction angles of HVDC converters in the AC-DC hybrid power grid at steady state. Write the above information to the power flow calculation result file in the form of (component name, power flow result) key-value pairs.

[0083] In step S200, perform an electromagnetic transient simulation based on the electromagnetic transient simulation example file and the power flow calculation result file to obtain the position information of each electrical component in the AC-DC hybrid power grid.

[0084] Specifically, start the electromagnetic transient simulation program according to the electromagnetic transient simulation example file and the power flow calculation result file of the AC-DC hybrid power grid, allocate memory for the matrices, vectors, and various component parameters required for the electromagnetic transient simulation according to the conventional startup process, and additionally allocate memory for the AC steady-state calculation equation and the DC steady-state calculation equation G(ω)U = I. Where G(ω) is the steady-state nodal admittance matrix, ω is the angular frequency. For the AC steady-state calculation equation, ω is the power frequency, and for the DC steady-state calculation equation, ω is 0; U is the steady-state nodal voltage vector, and I is the power vector. For each electrical component, determine its position information in the AC-DC hybrid power grid, specifically including: determining its subordination relationship with the AC power grid and the DC power grid, and determining the positions of its admittance elements in the steady-state nodal admittance matrix, the positions of its port voltages in the steady-state nodal voltage vector, and the positions of its power sources in the power vector.

[0085] In step S300, traverse all the electrical components in the electromagnetic transient simulation example file, generate the AC steady-state calculation equation and the DC steady-state calculation equation according to the component type and the position information, and solve to obtain the steady-state nodal voltage vector; the component types include capacitor components in the DC power grid, inductor components in the DC power grid, AC power source components, and HVDC converter components.

[0086] Specifically, traverse all the components in the electromagnetic transient simulation example file of the hybrid power grid, and fill the steady-state admittance values of the components into the corresponding positions of the steady-state nodal admittance matrix according to the component type and the position information of each electrical component in the AC-DC hybrid power grid:

[0087] (1) For capacitor components in the DC power grid, fill the steady-state nodal admittance matrix in the open-circuit form;

[0088] (2) For inductor components in the DC power grid, fill the steady-state nodal admittance matrix in the short-circuit form;

[0089] (3) For AC power source components, such asFigure 3 For the power supply AC in Figure 3 the magnitude and phase of V1 in

[0090] (4) For the conventional HVDC converter element, the three-phase voltage magnitude and phase of its AC port shall also be retrieved from the key-value pairs in the power flow calculation result file according to the element name and filled into the power supply vector of the AC steady-state calculation equation; and the voltage of its DC port shall be retrieved, for example Figure 3 the voltage V of DC in d shall be filled into the power supply vector of the DC steady-state calculation equation. V d is the voltage of the DC port of the conventional HVDC converter, k T is the turn ratio of the converter transformer, k T V1 is the voltage of the secondary side of the circulating current transformer, X e is the leakage reactance of the converter transformer, and V2 is the voltage of the AC side of the converter.

[0091] After generating the AC steady-state calculation equation and the DC steady-state calculation equation, solve the AC steady-state calculation equation and the DC steady-state calculation equation G(ω)U = I respectively to obtain the steady-state node voltage vector U.

[0092] In step S400, traverse all the electrical components in the electromagnetic transient simulation case file, and obtain the steady-state values of all the electrical quantities inside each of the electrical components except the HVDC converter element according to the steady-state node voltage vector and the admittance values of each internal branch, and calculate the conduction states of the switches inside each HVDC converter element at the simulation initial moment to obtain the circuit topology at the simulation initial moment.

[0093] In this embodiment, traverse all the components in the electromagnetic transient simulation case file of the AC-DC hybrid power grid. For all the components except the conventional HVDC converter, obtain the component port voltage according to the position of the component port voltage in the steady-state node voltage vector; then calculate the steady-state values of all the electrical quantities inside the component based on the component port voltage and the admittance of each internal branch of the component.

[0094] Due to the complexity of the HVDC converter control system and its pivotal role in coupling and connecting the AC and DC networks, and considering its particularity in determining the power flow distribution of the AC-DC network, for each conventional HVDC converter element encountered during the traversal in step S400, retrieve its firing angle and extinction angle from the key-value pairs in the power flow calculation result file according to the element name, and calculate the conduction states of the power electronic switches inside the conventional HVDC converter at the simulation initial moment, i.e., at t0 moment, based on its firing angle and extinction angle and the steady-state value of the AC port voltage of the conventional HVDC converter, and determine the circuit topology of the conventional HVDC converter at the simulation initial moment.

[0095] In step S500, the control systems of the high-voltage DC converter elements are initialized according to the trigger angles, extinction angles of the high-voltage DC converter elements and the steady-state values of the measuring elements; a power flow initialization auxiliary power supply element is added to each of the high-voltage DC converter elements to stabilize the power supply voltage.

[0096] For each conventional high-voltage DC converter element, the control system of the conventional high-voltage DC converter is initialized based on its trigger angle, extinction angle and the steady-state value of the electrical measuring element. The specific method is as follows:

[0097] (1) Determine whether the current conventional high-voltage DC converter element is an inverter-side converter. If not, skip the high-voltage DC converter element and add it to the end of the element queue to be processed until all inverter-side converters are processed.

[0098] (2) Construct a queue of input ports to be traversed, where the elements are all input ports of the control system of the conventional high-voltage DC converter; construct a queue of output ports to be traversed, where the elements are all output ports of the control system of the conventional high-voltage DC converter.

[0099] (3) Traverse the control elements starting from the head of the queue of input ports to be traversed in accordance with the signal flow direction of the control system of the conventional high-voltage DC converter. For each control element, calculate the output signal of the element according to its input-output relationship and use it as the input signal of the next control element until the queue of input ports to be traversed is empty. It should be noted that the following element types require additional calculations:

[0100] a) For transfer function elements, calculate their state quantities based on the input and output signals and use them as the steady-state initial values. Typical transfer function elements are as Figure 4 shown first-order inertia link, Figure 4 where T is the inertia time constant, and the box with the ∫ symbol is an integrator;

[0101] b) For multi-input control elements, determine whether each input has been calculated. If so, calculate its output signal and move to the next control element. If not, add the current element to the end of the queue of input ports to be traversed and then continue searching from the head.

[0102] c) For integrator elements with limits, judge according to their input signals. If the absolute value of the input signal is less than the set value, the element is the end point of the traversal path and the steady-state initial value of the integrator element cannot be determined. Remove the head element of the current queue of input ports to be traversed and continue searching from the next element.

[0103] Otherwise, if the input signal is positive, the steady-state initial value and the output signal are set to the upper limit of the amplitude limit. If the input signal is negative, the steady-state initial value and the output signal are set to the lower limit of the amplitude limit, and move to the next control element.

[0104] As Figure 5 shown, the PI controller is a control link containing an integrator element with amplitude limit used in multiple places in this embodiment. Figure 5 The meanings of the symbols in it are: Kp is the gain of the proportional link, Ki is the gain of the integral link, Oint max and Oint min are respectively the upper and lower limits of the amplitude limit of the integrator, and O max and O min are the upper and lower limits of the amplitude limit link.

[0105] d) If the output signal of the currently traversed control element is connected to the output port of the conventional HVDC converter control system, then this element is the end point of this traversal path. Remove this output port from the queue of output ports to be traversed, remove the head element of the current queue of input ports to be traversed, and continue searching from the next element.

[0106] (4) If the queue of output ports to be traversed is not empty, traverse the control elements starting from the head of the queue of output ports to be traversed in the reverse direction of the signal flow of the conventional HVDC converter control system. For each control element, calculate the input signal of the element according to its input-output relationship and use it as the output signal of the next control element until the queue of output ports to be traversed is empty; it should be noted that the following element types need to be calculated additionally:

[0107] a) For the transfer function element, calculate its state quantity based on the input and output signals and use it as the steady-state initial value.

[0108] b) For the multiplexer element, set each input signal to be equal to the output signal, take this element as the end point of the current traversal path, and add the control elements connected to each input signal to the queue of output ports to be traversed.

[0109] c) For the integrator element with amplitude limit, use the output signal as its steady-state initial value, take this element as the end point of the current traversal path, and continue the next traversal from the head of the queue of output ports to be traversed.

[0110] For this embodiment, Figure 6The control system block diagram of the rectifier-side converter is shown. It consists of a first-order transfer function system and a PI controller, which is the core of the control system of the commutation equipment in the LCC-HVDC system. The parameters of the control module are shown in Table 2. The input quantities of this system are the direct current measured at the rectifier (CMR) and the current command at the inverter (CORDER). The steady-state initialization value (CMRS) output after the CMR passes through the first-order inertial system is equal to the CMR. The difference between the CORDER and the CMRS is the current deviation CERRR, which is the input quantity of the PI controller. The output quantity of the PI controller is its steady-state initialization value BETAR. The output quantity obtained by subtracting π from the BETAR is the rectifier angle (AOR). According to the initialization data of the electrical system, the steady-state values of all the above signals can be obtained, and then the parameter values on the other side can be calculated from the input / output side.

[0111] Table 2

[0112]

[0113] Among them,

[0114]

[0115] CERRR = CORDER - CMRS = 0

[0116] The steady-state initialization value of the first-order system is CMRS, and the steady-state input quantity of the PI controller is CERRR; to obtain the steady-state initial value of the PI controller, the derivation starts from its output side at this time:

[0117]

[0118] Since MinLimit < BETAR < MaxLimit, the integrator constraint condition is satisfied, so the PI controller can perform steady-state initialization, and the initial value is BETAR = 2.7925.

[0119] In summary, the initial values of the integral link and the first-order system required for the steady-state initialization of the control system can be obtained.

[0120] In step S500, the control systems of the high-voltage DC converter elements are initialized according to the trigger angles, extinction angles of the high-voltage DC converter elements and the steady-state values of the measuring elements; a power flow initialization auxiliary power supply element is added to each of the high-voltage DC converter elements to stabilize the power supply voltage.

[0121] In this embodiment, adding a power flow initialization auxiliary power supply element to each of the high-voltage DC converter elements to stabilize the power supply voltage includes:

[0122] Connect a first three-phase voltage source to the AC port of the HVDC converter element. Set the amplitude and phase of the first three-phase voltage source according to the power flow calculation result file. Set the connection time to the initial simulation time, and remove the first three-phase voltage source after a preset cut-off time.

[0123] Connect a second three-phase voltage source to the DC port of the HVDC converter element. Set the voltage value of the second three-phase voltage source according to the power flow calculation result file. Set the connection time to the initial simulation time, and remove the second three-phase voltage source after a preset cut-off time.

[0124] Specifically, for each conventional HVDC converter element, add a power flow initialization auxiliary power source element as shown in Figure 7 . The specific setting method is as follows:

[0125] (1) Connect an ideal three-phase voltage source to the AC port of each conventional HVDC converter element, that is, the converter AC port auxiliary power source shown in Figure 7 . Set its amplitude and phase according to the three-phase voltage amplitude and phase retrieved by component name from the key-value pairs in the power flow calculation result file. Set the connection time to be connected at the initial simulation time, and remove the three-phase voltage source after the set cut-off time.

[0126] (2) Connect an ideal DC voltage source to the DC port of each conventional HVDC converter element, that is, the converter DC port auxiliary power source shown in Figure 7 . Set its voltage value according to the voltage of the DC port retrieved by component name from the key-value pairs in the power flow calculation result file. Set the connection time to be connected at the initial simulation time, and remove it after the set cut-off time. The cut-off operation does not consider current zero-crossing detection.

[0127] After the initialization settings are completed, based on the above AC-DC power grid initialization settings (such as the steady-state values of all electrical quantities inside each electrical component except the HVDC converter element, the circuit topology of each HVDC converter element at the initial simulation time, etc.), the initialization settings of the control system, and the auxiliary power source, start a time-step loop from the initial simulation time, that is, time t0.

[0128] The electromagnetic transient simulation power flow initialization method for the AC-DC hybrid power grid provided in this embodiment performs power flow calculation according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid to obtain the power flow calculation results, and performs electromagnetic transient simulation according to the electromagnetic transient simulation example file and the power flow calculation results to obtain the position information of each electrical component. Through the mutual cooperation of the power flow calculation program and the electromagnetic transient simulation program, the position information of each electrical component can be obtained quickly and accurately; by traversing all the electrical components in the electromagnetic transient simulation example file, the steady-state values of all the electrical quantities inside each electrical component except the high-voltage DC converter component are obtained, and the circuit topology of each high-voltage DC converter component at the initial moment of the simulation is obtained, so as to realize the steady-state initialization setting of the AC-DC hybrid power grid; at the same time, considering the influence of the complex control system, the present invention initializes the control system of the high-voltage DC converter component, and adds a power flow initialization auxiliary power supply component to each high-voltage DC converter component to stabilize the power supply voltage, and more accurate initialization values of the control system can be obtained, and high-precision power flow initialization of the AC-DC hybrid power grid is realized through the electromagnetic transient simulation method.

[0129] For this embodiment, as Figures 8 to 13 shown, when the time in the simulation reaches 0.1 s, the operation will tend to be stable. By comparing Tables 3 and 4, Table 3 is the comparison between the DSP power flow calculation results and the TSDG steady-state values, and Table 4 is the comparison between the DSP and TSDG control system initializations. It can be seen that the difference between the steady-state parameters of the electrical system obtained by the DSP power flow calculation and the steady-state parameters obtained by the TSDG operation is very small, and there is no obvious difference between the initial value and the steady-state value of the control system, indicating the accuracy of the initialization.

[0130] Table 3

[0131]

[0132] Table 4

[0133]

[0134] It can also be known from Figures 8 to 13 that after the simulation starts, the power of the auxiliary power supply after initialization is set as a part of the power flow calculation results. In the subsequent 0.04 s of simulation, the auxiliary power supply is always connected to the network to maintain the constant grid voltage.

[0135] Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the above-described system, device, and unit can refer to the corresponding processes in the foregoing method embodiments and will not be repeated here.

[0136] In the embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling, direct coupling, or electrical connection to each other can be through some interfaces, and the indirect coupling or electrical connection of devices or units can be in electrical, mechanical, or other forms.

[0137] The units described as separate components may or may not be physically separated. The components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0138] In addition, in each embodiment of the present invention, the functional units can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0139] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in each embodiment of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0140] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present invention.

Claims

1. An electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid, characterized in that Including: Determine the model parameters of the AC-DC hybrid power grid according to the electromagnetic transient simulation example file of the AC-DC hybrid power grid, perform power flow calculation according to the model parameters, and write the power flow calculation results at steady state into the power flow calculation result file; Perform electromagnetic transient simulation according to the electromagnetic transient simulation example file and the power flow calculation result file to obtain the position information of each electrical component in the AC-DC hybrid power grid; Traverse all electrical components in the electromagnetic transient simulation example file, generate AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information, and solve to obtain the steady-state node voltage vector; the component types include capacitor components in the DC power grid, inductor components in the DC power grid, AC power source components, and HVDC converter components; Traverse all electrical components in the electromagnetic transient simulation example file, obtain the steady-state values of all electrical quantities inside each of the electrical components except the HVDC converter components according to the steady-state node voltage vector and the internal branch admittance values, and calculate the conduction states of the switches inside each of the HVDC converter components at the initial moment of simulation to obtain the circuit topology at the initial moment of simulation; Perform initialization settings on the control systems of each of the HVDC converter components according to the trigger angles, extinction angles of each of the HVDC converter components and the steady-state values of the measurement components; add power flow initialization auxiliary power source components to each of the HVDC converter components to stabilize the power supply voltage.

2. The electromagnetic transient simulation power flow initialization method for the AC / DC hybrid power grid according to claim 1, wherein Generating AC steady-state calculation equations and DC steady-state calculation equations according to the component type and the position information includes: Fill the steady-state admittance values of each of the electrical components into the corresponding positions of the steady-state node admittance matrix according to the component type and the position information to generate AC steady-state calculation equations and DC steady-state calculation equations.

3. The electromagnetic transient simulation power flow initialization method for the AC / DC hybrid power grid according to claim 2, characterized in that, Filling the steady-state admittance values of each of the electrical components into the corresponding positions of the steady-state node admittance matrix according to the component type and the position information includes: For capacitor components in the DC power grid, fill the steady-state node admittance matrix in an open-circuit form; For inductor components in the DC power grid, fill the steady-state node admittance matrix in a short-circuit form; For AC power source components, obtain its three-phase voltage according to the power flow calculation result file and fill it into the power source vector of the AC steady-state calculation equation; For HVDC converter components, obtain the three-phase voltage amplitude and phase of its AC port according to the power flow calculation result file and fill it into the power source vector of the AC steady-state calculation equation; obtain the voltage of its DC port according to the power flow calculation result file and fill it into the power source vector of the DC steady-state calculation equation.

4. The electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid according to claim 1, wherein Performing initialization settings on the control systems of each of the HVDC converter components according to the trigger angles, extinction angles of each of the HVDC converter components and the steady-state values of the measurement components includes: Judge whether the HVDC converter component is an inverter-side converter. If not, skip the HVDC converter component and add it to the end of the element queue to be processed until all inverter-side converters are processed; Construct a queue of input ports to be traversed, whose elements are all input ports of the HVDC converter control system, and construct a queue of output ports to be traversed, whose elements are all output ports of the HVDC converter control system; According to the signal flow direction of the HVDC converter control system, traverse the control elements starting from the head of the queue of input ports to be traversed. For each control element, calculate the output signal of the control element according to its input-output relationship and use it as the input signal of the next control element until the queue of input ports to be traversed is empty; If the queue of output ports to be traversed is not empty, traverse the control elements starting from the head of the queue of output ports to be traversed according to the reverse direction of the signal flow of the HVDC converter control system. For each control element, calculate the input signal of the control element according to its input-output relationship and use it as the output signal of the next control element until the queue of output ports to be traversed is empty.

5. The electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid according to claim 4, characterized in that, Calculating the output signal of each control element according to its input-output relationship further includes: For a transfer function element, calculate its state quantity based on the input and output signals and use it as the steady-state initial value; For a multi-input control element, determine whether each input has been calculated. If so, calculate its output signal and move to the next control element; if not, add the multi-input control element to the tail of the queue of input ports to be traversed, and then continue searching from the head; For an integrator element with a limit, make a judgment based on its input signal. If the absolute value of the input signal is less than the preset value, the integrator element is the end point of the traversal path and the steady-state initial value of the integrator element cannot be determined. Remove the head element of the current queue of input ports to be traversed and continue searching from the next element; otherwise, if the input signal is positive, set the steady-state initial value and output signal of the integrator element to the upper limit of the limit, and if the input signal is negative, set the steady-state initial value and output signal of the integrator element to the lower limit of the limit, and move to the next control element; If the output signal of the currently traversed control element is connected to the output port of the HVDC converter control system, the control element is the end point of the traversal path. Remove the output port from the queue of output ports to be traversed, remove the head element of the queue of input ports to be traversed, and continue searching from the next element.

6. The electromagnetic transient simulation power flow initialization method for the AC / DC hybrid power grid according to claim 4, wherein Calculating the input signal of each control element according to its input-output relationship further includes: For a transfer function element, calculate its state quantity based on the input and output signals and use it as the steady-state initial value; For a multiplexer element, set each input signal to be equal to the output signal, take the multiplexer element as the end point of the current traversal path, and add the control elements connected to each input signal to the queue of output ports to be traversed; For an integrator element with a limit, use the output signal as its steady-state initial value, take the integrator element as the end point of the current traversal path, and continue the next traversal from the head of the queue of output ports to be traversed.

7. The electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid according to claim 1, wherein Obtaining the steady-state values of all electrical quantities inside each of the electrical components except for the HVDC converter components based on the steady-state node voltage vector and the admittance values of each internal branch includes: For each of the electrical components except for the HVDC converter components, obtaining the component port voltage according to the position of the electrical component port voltage in the steady-state node voltage vector; Calculating the steady-state values of all electrical quantities inside the electrical component based on the component port voltage and the admittance values of each internal branch of the electrical component.

8. The electromagnetic transient simulation power flow initialization method for an AC / DC hybrid power grid according to claim 1, wherein Calculating the conduction states of the switches inside each of the HVDC converter components at the initial simulation moment to obtain the circuit topology at the initial simulation moment includes: For each of the HVDC converter components, obtaining the corresponding firing angle and extinction angle from the power flow calculation result file; Calculating the conduction states of the internal power electronic switches at the initial simulation moment according to the firing angle, the extinction angle, and the steady-state value of the AC port voltage, and obtaining the circuit topology at the initial simulation moment according to the conduction states.

9. The electromagnetic transient simulation power flow initialization method for the AC / DC hybrid power grid according to claim 1, wherein, Adding a power flow initialization auxiliary power supply component to each of the HVDC converter components to stabilize the power supply voltage includes: Connecting a first three-phase voltage source to the AC port of the HVDC converter component, setting the amplitude and phase of the first three-phase voltage source according to the power flow calculation result file, setting the connection time to the initial simulation moment, and removing the first three-phase voltage source after a preset cut-off time; Connecting a second three-phase voltage source to the DC port of the HVDC converter component, setting the voltage value of the second three-phase voltage source according to the power flow calculation result file, setting the connection time to the initial simulation moment, and removing the second three-phase voltage source after a preset cut-off time.

10. The electromagnetic transient simulation power flow initialization method for the AC / DC hybrid power grid according to claim 1, wherein Obtaining the position information of each electrical component in the AC-DC hybrid power grid includes: For each electrical component, obtaining its subordination relationship with the AC power grid and the DC power grid, and obtaining the position of its admittance element in the steady-state node admittance matrix, the position of its port voltage in the steady-state node voltage vector, and the position of its power supply in the power supply vector.

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