LCC converter electromagnetic transient simulation initialization method and system based on steady-state working condition

Abstract

The invention discloses an LCC converter electromagnetic transient simulation initialization method and system based on a steady-state working condition, and belongs to the technical field of power system simulation. The method comprises the following steps: establishing an electromagnetic transient model of the LCC; obtaining a power flow result of the power system, and determining a steady-state electrical angle of each thyristor valve in combination with a winding connection mode of a converter transformer; calculating an initial current of each branch by using a preset interpolation function based on the power flow result, the model topology and the valve electricity angle; and calculating the initial voltage of each branch based on the power flow result, the model topology, the valve electrical angle and a switching function representing the valve switching state. According to the method, the valve electrical angle in a steady state is accurately calculated, and correct initial current and voltage are directly given to the simulation model by using an interpolation function and a switching function, so that electromagnetic transient simulation can be directly started from a steady-state working condition without going through a long transition process from zero starting, the simulation time is greatly shortened, and the starting impact is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of power system simulation technology, specifically relating to an initialization method and system for electromagnetic transient simulation of LCC converters based on steady-state operating conditions. Background Technology

[0002] With the rapid growth of the global economy, the power industry has developed rapidly, with power generation and load increasing year by year, leading to an increase in grid scale and transmission capacity. Direct current (DC) transmission is becoming a rapidly developing power transmission method due to its advantages in long-distance and submarine transmission, ease of precise control and regulation, and ability to improve the stability of AC grids. Among these, DC transmission systems based on line-commutated converters (LCCs) are the most mature and widely used. While bringing numerous social and economic benefits, the huge reactive power demand of LCC converters, harmonic injection, and commutation failures during faults also profoundly affect the dynamic characteristics of power systems. Therefore, to correctly analyze these phenomena, electromagnetic transient simulation of LCC converters has become a research topic for many scholars.

[0003] Currently, when performing electromagnetic transient simulations of LCC converters, the entire DC system always starts from a non-start-up state, controlled by the rectifier and inverter converters to establish DC voltage and current, reaching steady state. This process takes about 1 second of simulation, after which faults are added. However, this approach is only suitable for simulating independent DC systems. For DC systems embedded in large power grids, starting from zero not only fails to correspond to power flow results but also causes a huge power surge to both the sending and receiving grids, potentially leading to system instability. Therefore, this method cannot be applied to electromagnetic transient simulations of large power grids. Thus, research is urgently needed on an initialization method for LCC converter electromagnetic transient simulations based on steady-state operating conditions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an initialization method and system for electromagnetic transient simulation of LCC converter based on steady-state operating conditions, which addresses the shortcomings of the prior art. This method solves the technical problems that existing electromagnetic transient simulation of LCC converters must start from zero and go through a long dynamic setup process, resulting in low simulation efficiency. Furthermore, when embedded in large power grid simulation, the startup shock may cause system instability and fail to correspond with power flow results, making it difficult to apply to electromagnetic transient analysis of large power grids.

[0005] The present invention adopts the following technical solution: The initialization method for electromagnetic transient simulation of LCC converter based on steady-state operating conditions includes the following steps: S1. Establish an electromagnetic transient model of the LCC converter. The electromagnetic transient model of the LCC converter includes a three-winding converter transformer, two six-pulse converter bridges, a set of AC filters and a smoothing reactor. Except for the thyristor valve, the other branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, taking a small resistance value when it is turned on and a large resistance value when it is turned off. S2. Obtain the power flow results of the power system, and determine the electrical angle corresponding to each thyristor valve in combination with the winding connection method of the three-winding converter transformer described in step S1. The electrical angle is used to characterize the triggering time of the valve relative to the phase voltage of the AC bus under ideal steady state. The electrical angles of the six thyristor valves in the same converter bridge are sequentially delayed by 60 degrees. S3. Based on the power flow results, the topology of the LCC converter electromagnetic transient model constructed in step S1, and the electrical angles of each thyristor valve determined in step S2, the initial current of each branch in the LCC converter is calculated using a preset interpolation function. The DC current path is determined by the series structure of the two six-pulse converter bridges, the current distribution of each phase winding is determined by the connection relationship between the y-winding and d-winding on the converter valve side, and the current transfer process is approximated by linear interpolation during commutation. S4. Based on the power flow results, the topology of the LCC converter electromagnetic transient model constructed in step S1, the electrical angles of each thyristor valve determined in step S2, and the switching functions used to characterize the thyristor on / off states, calculate the initial voltage of each branch in the LCC converter; according to the winding connection relationship and leakage impedance parameters of the three-winding converter transformer, combined with the on-state of the converter bridge arm reflected by the switching function, determine the terminal voltage of each winding of the converter transformer during the non-commutation period and the commutation period.

[0006] Preferably, in step S2, when the absolute phase of the AC bus phase A voltage is zero at the start of the simulation and the voltage rises above zero, the electrical angle of the thyristor valve V1 connected to the y winding of the converter valve side is the phase of the AC bus phase A voltage minus 30 degrees. When the phase voltage of phase A is at its positive peak at the start of the simulation, the electrical angle of the thyristor valve V1 connected to the d winding on the valve side is the phase of the phase voltage of phase A on the AC bus minus 60 degrees.

[0007] Preferably, in step S3, the calculation of the initial current of each branch in the LCC converter is specifically as follows: For DC current, during the non-commutation period, it is determined that all DC current flows through the switches that are conducting in the common anode group and the common cathode group; during the commutation period, the distribution of current in each bridge arm during the commutation process is approximately determined by linear interpolation. For the converter transformer valve-side winding current, based on the relationship between the current path of the valve-side y-winding and d-winding and the conducting valve, a periodic linear interpolation function with electrical angle as the independent variable is established to determine its current waveform. For the branch current of the AC filter, the phasor domain results in the power flow results are used directly to determine it.

[0008] Preferably, the interpolation function is a periodic function with a period of 360 degrees, used to linearly interpolate the current of the d winding on the commutator valve side within the commutation interval. The interpolation point is set according to the proportion of load current borne by each phase winding during the non-commutation period, wherein the load current bears 2 / 3 and 1 / 3 respectively in the two paths with an impedance ratio of 1:2.

[0009] Preferably, the Y winding current on the converter transformer side is calculated by superimposing the y winding current and the d winding current on the valve side, satisfying the steady-state condition that the three-phase currents are symmetrical and lag by 120 degrees in sequence.

[0010] Preferably, the internal state of the AC filter includes voltage and current, which are determined directly from the phasor domain data in the power flow results.

[0011] Preferably, in step S4, calculating the initial voltage of each branch specifically includes: For the voltage of the converter transformer valve-side winding, general expressions for the voltage of the valve-side y-winding and d-winding are established respectively. The expressions use switching functions to characterize the influence of the commutation process on the winding terminal voltage. For the converter bridge arm voltage, expressions for the bridge arm voltage connected to the y-winding and d-winding on the converter transformer valve side are established respectively. These expressions use switching functions to characterize the voltage in the on and off states of the bridge arm.

[0012] Preferably, for the y-winding on the valve side of the converter transformer, during the two-phase commutation period, the terminal voltages of the two commutated windings are forced to be equal, and the voltage difference is borne by the leakage inductance; for the d-winding on the valve side, during any phase commutation period, the voltages of all three windings are affected by the commutation, wherein the commutated winding is short-circuited, and the remaining two windings are connected in series in the forward direction to form a loop.

[0013] Preferably, the voltage of the commutator bridge arm is determined according to the switching function of the corresponding thyristor: When the switch is on, the voltage across the bridge arm is 0; when the switch is off, the voltage across the bridge arm is the line voltage of the converter transformer valve side winding.

[0014] Secondly, embodiments of the present invention provide an electromagnetic transient simulation initialization system for an LCC converter based on steady-state operating conditions, comprising: The module is used to build an electromagnetic transient model of the LCC converter. The model includes a three-winding converter transformer, two six-pulse converter bridges, a set of AC filters and a smoothing reactor. Except for the thyristor valve, the other branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, with a small resistance value when it is turned on and a large resistance value when it is turned off. The electrical angle module is used to obtain the power flow results of the power system and, in combination with the winding connection method of the three-winding converter transformer, determine the electrical angle corresponding to each thyristor valve. The electrical angles of the six thyristor valves in the same converter bridge are sequentially lagging by 60 degrees. The current module is used to calculate the initial current of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, and the electrical angle of each thyristor valve, combined with a preset interpolation function. The voltage module is used to calculate the initial voltage of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, the electrical angle of each thyristor valve, and the switching function used to characterize the thyristor on / off state.

[0015] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions.

[0016] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions.

[0017] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions.

[0018] Sixthly, embodiments of the present invention provide an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-described initialization method for electromagnetic transient simulation of LCC converter based on steady-state operating conditions.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects: An electromagnetic transient simulation initialization method for LCC converters based on steady-state operating conditions is proposed. This method comprehensively covers the key aspects of LCC converter simulation initialization, and the model composition closely matches the actual engineering topology, ensuring the realism of the simulation model. Using power flow results as the core input, and combining techniques such as winding connection methods, interpolation functions, and switching functions, it achieves precise matching between initialization and steady-state operating conditions. Compared to existing zero-initial-value start-up methods, this method avoids oscillations caused by power flow mismatch from the outset, obtains steady-state initial conditions at instantaneous time, significantly shortens the simulation's ineffective time, and improves the efficiency of large power grid simulation. Simultaneously, it adapts to the current source characteristics of LCC converters, ensuring stable convergence of the simulation process and providing a reliable foundation for subsequent transient characteristic analysis.

[0020] Furthermore, the calculation rules for the thyristor valve electrical angle under two typical operating conditions are clarified. For the two scenarios of the AC bus A-phase voltage rising to zero and reaching a positive peak, the calculation methods for the thyristor valve electrical angle corresponding to the valve-side y-winding and d-winding are specified respectively. This improves the accuracy and operability of the electrical angle calculation, solving the problems of neglecting the winding connection phase relationship and ambiguous calculation logic in the existing technology. This constraint is based on the inherent phase difference between the converter transformer valve-side winding and the AC bus, enabling the electrical angle to accurately characterize the desired triggering time of the thyristor, providing accurate parameter support for subsequent current and voltage calculations; avoiding current distribution imbalance during commutation due to electrical angle deviation, reducing waveform distortion in the early stages of simulation, further ensuring steady-state start-up at zero moment of simulation, and improving the reliability and engineering applicability of the entire initialization scheme.

[0021] Furthermore, separate calculation strategies were developed for DC current, converter transformer valve-side winding current, and AC filter current to achieve refined and differentiated current calculations, adapting to the current characteristics of different branches: DC current distinguishes between non-commutation and commutation periods, with linear interpolation during the commutation period ensuring smooth current transfer; converter transformer winding current is based on the relationship between the current path and the conduction valve, establishing a periodic interpolation function to match the periodic operation of the converter; AC filter current directly uses the power flow phasor domain results, simplifying calculations while ensuring accuracy. This solves the problem of initial current distortion caused by the general current calculations and neglect of branch characteristic differences in existing technologies, ensuring that the initial current values ​​of each branch are highly consistent with the steady-state operating conditions, effectively suppressing current surges and oscillations during commutation, improving the dynamic response accuracy of the simulation model, and reducing computational redundancy, thus balancing simulation efficiency and accuracy.

[0022] Furthermore, the periodic characteristics of the interpolation function and the load current distribution ratio are clearly defined, and the key parameters of the interpolation function are quantified, making the commutation current calculation more targeted and accurate. A 360-degree periodic adaptation is used to match the periodicity of the converter's power frequency operation, ensuring that the interpolation calculation can cyclically adapt to the converter's continuous operation. The load current distribution ratio is set based on the impedance characteristics of the converter transformer valve-side winding, conforming to the actual current shunting law and avoiding simulation deviations caused by unreasonable current distribution assumptions. This solves the problems of ambiguous parameters and poor adaptability in existing interpolation functions, making the linear approximation of the commutation current transfer process more closely resemble the actual physical process, improving the reliability of the initial current calculation, further ensuring the steady state of the DC current at zero time, eliminating oscillation risks, and providing reusable calculation logic for converters with different parameters.

[0023] Furthermore, the calculation method specifies that the Y-winding current on the converter transformer grid side is calculated by superimposing the currents of the valve-side Y-winding and d-winding, and satisfies the steady-state condition of three-phase current symmetry and sequential lag of 120 degrees. This follows the winding current coupling law of the converter transformer, ensuring topological consistency and physical rationality in the current calculation. The grid-side current is a key parameter for the interaction between the converter and the AC grid. This calculation method, based on the inherent relationship of the winding connections, avoids the three-phase imbalance problem caused by independently calculating the grid-side current. The three-phase symmetrical steady-state condition closely matches the operating characteristics of the AC grid, making the initial current more consistent with the actual system conditions. This solves the problems of neglecting the winding current coupling relationship and the disconnect between the calculation results and the actual topology in existing technologies, improving the overall consistency of the simulation model, ensuring power balance between the AC and DC sides, further enhancing the accuracy and reliability of the simulation, and providing reliable data for subsequent analysis of grid interaction characteristics.

[0024] Furthermore, the initial state calculation of the filter is simplified, balancing efficiency and accuracy. The core function of the AC filter is to filter harmonics, and its steady-state characteristics can be accurately characterized through power flow phasor domain results without complex time-domain calculations. Directly reusing power flow data avoids additional modeling errors, while reducing computational load and improving simulation initialization efficiency. This solves the problems of cumbersome initial state calculation and easy introduction of errors in existing technologies, ensuring that the filter's initial state is consistent with the system's steady-state condition, avoiding simulation distortion of harmonic suppression effects due to filter state deviations, and simplifying the initialization process.

[0025] Furthermore, the calculation logic for the converter transformer valve-side winding voltage and the converter bridge arm voltage both employ switching functions to characterize key influencing factors. This achieves modularization and precision in voltage calculation, adapting to the voltage characteristics of different components. The winding voltage expression incorporates the influence of the commutation process, and the bridge arm voltage expression is associated with the on / off state, enabling the voltage calculation to dynamically respond to thyristor switching actions. The introduction of switching functions simplifies the mapping relationship between voltage and switching states, avoiding complex time-domain equation solving and improving computational efficiency. This solves the problem of vague voltage calculations and neglect of the dynamic influence of switching states in existing technologies, ensuring that the initial values ​​of each branch voltage accurately reflect the switching characteristics under steady-state conditions, reducing voltage waveform distortion and low-frequency oscillations, further guaranteeing the steady-state at zero time of simulation, and enhancing the scientific rigor and soundness of the entire technical solution.

[0026] Furthermore, it accurately characterizes the dynamic characteristics of the commutation period voltage, improving the physical realism of voltage calculations. During the commutation period of the y-winding, the two-phase voltages are forced to be equal, with the voltage difference borne by the leakage inductance. During the commutation period of the d-winding, the phase being commutated is short-circuited, and the remaining two phases are connected in series. This closely matches the actual physical process of converter commutation, avoiding idealized assumptions in commutation period voltage calculations. It solves the problems of oversimplification in existing commutation period voltage models and large deviations between simulation results and reality. This ensures that the initial voltage value accurately reflects the dynamic influence of the commutation process, further suppresses low-frequency voltage oscillations, ensures the realism and reliability of the simulation waveform, and provides accurate initial conditions for analyzing transient characteristics such as commutation failure.

[0027] Furthermore, the commutator arm voltage is zero when the thyristor is on and equal to the valve-side winding line voltage when it is off. This ensures a precise match between the voltage and switching states. Based on the characteristics of the thyristor switching resistor model, the small resistor approximates a short circuit when on and an large resistor approximates an open circuit when off, making the voltage calculation highly consistent with the device model. This solves the problems of unclear correlation between the arm voltage and switching state and complex calculations in existing technologies, ensuring the accuracy and reliability of the initial value of the arm voltage, further guaranteeing no low-frequency oscillations in the DC voltage, and improving the consistency and stability of the simulation model.

[0028] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0029] In summary, this invention, by integrating power flow data and physical models, accurately generates the initial electromagnetic transient state of an LCC converter, avoiding zero-start-up shocks and long-term transient processes, and realizing direct, accurate, and rapid initialization of the electromagnetic transient simulation of an LCC converter from steady-state conditions.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 Electromagnetic transient model of LCC converter; Figure 2 This is a schematic diagram of the voltage that valve V1 bears when it is about to be turned on, where (a) is the y winding side and (b) is the d winding side. Figure 3 The diagram shows the phasor diagram of the three sides of the converter transformer, where (a) is the grid-side Y winding, (b) is the valve-side y winding, and (c) is the valve-side d winding. Figure 4 The graph shows the relationship between valve current (top) and switching function (bottom) and electrical angle. Figure 5 This is a diagram showing the operating status of the d-winding on the converter transformer valve side during the non-commutation period. Figure 6 This is a schematic diagram of the converter transformer branch topology and voltage symbols; Figure 7 Comparison chart of DC current initialization effects; Figure 8 Comparison chart of DC voltage initialization effects; Figure 9 A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 10 This is a block diagram of a chip according to an embodiment of the present invention; Figure 11 This is a schematic diagram of the method flow of the present invention.

[0032] Among them, 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0035] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0036] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0037] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0038] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0039] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0040] This invention provides an initialization method for electromagnetic transient simulation of LCC converters based on steady-state operating conditions. It organically combines power flow results, converter winding connection methods, electrical angles, interpolation functions, and switching functions to construct a physically consistent initial state. The electrical angle is precisely defined through the y / d winding phase relationship, commutation current distribution is handled using linear interpolation, and the winding terminal voltages during commutation are accurately modeled based on the switching functions, such as equal voltage across two phases on the y side and three-phase coupling on the d side, thereby generating initial values ​​that perfectly match the actual steady state. Experiments show that after initialization, the DC current / voltage exhibits no oscillations and directly enters a steady state, verifying the high accuracy and practicality of this method in engineering simulation.

[0041] Please see Figure 11 This invention provides an electromagnetic transient simulation initialization method for an LCC converter based on steady-state operating conditions, comprising the following steps: S1. Establish the electromagnetic transient model of the LCC converter. Please see Figure 1 The electromagnetic transient model of the LCC converter includes one three-winding converter transformer, two converter bridges, one AC filter, and one smoothing reactor. Except for the thyristor valve, all branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, with a very small resistance when it is turned on and a very large resistance when it is turned off.

[0042] S2. Determine the electrical angle of each thyristor valve based on the power flow results. Based on the ideal steady-state assumption of the DC system, an "electrical angle" is defined for each thyristor valve, and the voltage, current and electrical angle of all thyristor valves satisfy the same functional relationship.

[0043] The ideal steady-state meaning of a DC system is that the AC bus voltage contains only the positive sequence component of the power frequency, all parameters of each phase are symmetrical, the switching action time is negligible, and the inductance of the smoothing reactor is infinite, so that the DC current contains only the DC component.

[0044] Under these conditions, all operating variables in the DC system have a period of 0.02s. For ease of analysis, electrical angle is used instead of time, and the relationship between the operating variables and electrical angle is denoted as: (1) in, It is a periodic function that satisfies All All results are obtained modulo 360.

[0045] Under steady state, the behavior of the six valves in the same converter bridge is similar, except that valves V1 to V6 lag by 60 electrical degrees in time. If an electrical degree is defined for each valve... If we lag them by 60 degrees in sequence, then the state of each valve branch can be represented by the same function to simplify the analysis.

[0046] Please see Figure 2 Determine the electrical angle of valve V1. ; Figure 2 This describes the operating state of the common cathode section of the converter bridge when valve V1 is about to open. At this time, V1 and V3 are off, V5 is on, and the positive voltage across V1 is the line voltage. , The moment of a positive zero crossing is theoretically the earliest triggerable moment for V1; definition The moment of positive zero crossing is Then the actual triggering time of V1 is .

[0047] Please see Figure 3 The diagram shows the potential phasor diagram of the three windings. For the y-winding side, the line voltage is the sum of the voltages of the two windings; for the d-winding side, the line voltage is the voltage of a single winding, and the positive voltage across V1. Examining their phase relationship, the valve voltage can be determined. Phase voltage of AC bus A The phase relationship is as follows: the y-side valve lags behind by 30 degrees, and the d-side valve lags behind by 60 degrees.

[0048] In the power flow results, the phase of the node voltage only represents the phase difference between that node and the reference node. At the start of the simulation, the absolute phase of the reference node can be arbitrarily chosen. However, the electrical angle of the valve is determined by the time-domain state and must satisfy certain conditions. hour Therefore, only when the phasors in the system are specified... Only when the correspondence between time-domain quantities is established can the electrical angle of the valve have a definite relationship with the phase of the AC bus in the power flow results.

[0049] If stipulated Then the electrical angle of V1 is (2) If stipulated Then the electrical angle of V1 is (3) Among them, the electrical angles of V1 to V6 lag by 60 degrees respectively, that is... (4) S3. Determine the current of each branch based on the power flow results, the electrical angles of each valve, and the interpolation function. The current in each branch is determined based on the power flow results, the electrical angles of each valve, and the interpolation function. For DC current, the two six-pulse commutator bridges are connected in series, and the current flowing through them is... During the non-commutation period, only one of the three switches in both the common anode and common cathode groups is conducting, carrying the entire DC current. During the commutation period, two of the three switches in one group are conducting, and the current transfers from one bridge arm to another. The rate of transfer is limited by the inductance of the converter transformer valve winding. This process can be viewed as a decay process of circulating current in the resistive-inductive circuit. If the current change during commutation is approximated as linear, the distribution of DC current among them can be determined by linear interpolation.

[0050] Please see Figure 4 , which represents the functional relationship between valve current and electrical angle, and also defines the switching function. The function value is a logical value, taking the value 1 when the switch is on and 0 when it is off, representing the time period during which the switch is on. The product of two switching functions in the same group represents the time period during which the two valves commutate. Using the switching function as a window function simplifies the expression and avoids writing it in piecewise function form, which will be used in subsequent analysis.

[0051] The buffer branch connected in parallel with the switch only has current flowing during commutation in steady-state operation. The peak value is less than 3% of the load current and decays rapidly. Therefore, its current is considered to be 0 during initialization.

[0052] The current in the y-winding on the converter transformer valve side is the sum of the currents in the upper and lower bridge arms of each phase (in fact, at least one of these two currents is always 0), and only during non-commutation periods is the current in the y-winding. The three values ​​correspond to handling forward current, reverse current, or open circuit.

[0053] (5) The d-winding on the converter transformer valve side is not in an open-circuit state; each winding carries current during each non-commutation period, such as... Figure 5 As shown. The load current has two paths with an impedance ratio of 1:2, carrying 2 / 3 and 1 / 3 of the load current respectively. Therefore, the winding current during the non-commutation period has Four possible values.

[0054] Table 1. Relationship between phase currents of the d-winding on the commutator valve side and the conduction valve during the non-commutation period.

[0055] The relationship between the phase currents of each phase in the d-winding of the commutator transformer on the non-commutation period and the conduction valve is shown in Table 1. The phase currents of phases A, B, and C lag by 120 degrees respectively, indicating that as long as a functional relationship is established... That is, .

[0056] Assuming the current in the d-winding on the commutator valve side is linear during commutation, a linear interpolation function is constructed. The interpolation points are listed in Table 2.

[0057] Table 2. Interpolation Point Table of Phase A Current Interpolation Function for Valve-Side D Winding of Converter Transformer

[0058] It should be noted that this interpolation function has a period of 360 degrees, which may affect the x-axis if it is not within the range of 360 degrees. Interpolation points within the interval need to be shifted to the interval itself.

[0059] The grid-side Y-winding current can be calculated by analyzing the currents in the two windings on the converter valve side. (6) For an AC filter, it can be assumed that it operates in an ideal AC system, and all its internal states (voltage, current) can be directly determined using the results of the phasor domain.

[0060] S4. Determine the voltage of each branch based on the power flow results, the electrical angles of each valve, and the switching function. Please see Figure 6 The voltage of each branch is determined based on the power flow results, the electrical angles of each valve, and the switching function. The converter transformer topology and symbol used for branch voltage analysis are as follows: Figure 6 As shown, each side consists of an ideal winding and a leakage impedance; This represents the sum of the voltages of the ideal winding and the leakage impedance, i.e., the voltage of the entire actual winding. This represents the sum of the voltages across the ideal winding and the leakage resistance. The valve-side y-winding is not shown in the diagram, but its notation is the same as the y-side.

[0061] Let's analyze the converter transformer branch voltage using only phase A as an example. Equation (7) holds true at any time, and the differential term in the first equation... It can be obtained from the interpolation function of current and electrical angle, but for the sake of simplifying the analysis, considering... Since the term is relatively small, it can be ignored, and the equation is simplified to a purely algebraic relation.

[0062] (7) During the non-commutation period, direct current flows through the valve-side winding, and no voltage drop is generated across the inductor. During the commutation period, when two phase switches in the same group are turned on, a phase-to-phase short circuit occurs between the two phases, forcing the terminal voltages to be equal, and the voltage difference is borne by the leakage inductance.

[0063] For the y-side, when switching from C to A (valves 5 and 1 or valves 2 and 4 are simultaneously turned on). When switching from A to B (valves 1 and 3 or valves 4 and 6 are simultaneously turned on). When commutating from B to C, phase A is unaffected. Represent the commutation process using switching functions, and write the general expression for the voltage on the y-side winding. (8) For the d-side, during the commutation from C to A, the C-phase winding is directly short-circuited. , They are connected in series in the forward direction to form a loop, which is easy to obtain The same situation applies when commutating from A to B and from B to C. It can be seen that when the valve-side d winding is commutated, the voltages of all three windings are affected, while when the y-side winding is commutated, only the voltages of two windings are affected.

[0064] Using switching functions to represent the commutation process, the general expression for the voltage of the d-side winding is as follows: (9) For each converter bridge arm, the voltage across it is 0 when the switch is on; when the switch is off, the voltage across it is the line voltage of the converter transformer valve-side winding. The expression for the voltage of the converter bridge arm connected to the y-side of the converter transformer is: (10) Let's take the first equation as an example for explanation: When the switch is on, the voltage it withstands is 0. At that time, the voltage it withstands is , At that time, the voltage it withstands is ; when At that time, the voltage it withstands is .

[0065] Replacing the line voltage, the expression for the voltage of the converter bridge arm connected to the d side of the converter transformer is: (11) in, These are the thyristor valve switching functions corresponding to the 3rd and 5th arms of the d-side converter bridge, respectively. These are the thyristor valve switching functions corresponding to the 5th and 1st arms of the d-side converter bridge, respectively. These are the thyristor valve switching functions corresponding to the 1st and 3rd arms of the d-side converter bridge, respectively. For the switching function of the thyristor valve in the 6th bridge arm, This is the switching function for the thyristor valve in the second bridge arm. This is the switching function for the thyristor valve in the fourth bridge arm.

[0066] In another embodiment of the present invention, an electromagnetic transient simulation initialization system for an LCC converter based on steady-state operating conditions is provided. This system can be used to implement the above-mentioned electromagnetic transient simulation initialization method for an LCC converter based on steady-state operating conditions. Specifically, the electromagnetic transient simulation initialization system for an LCC converter based on steady-state operating conditions includes a construction module, an electrical angle module, a current module, and a voltage module.

[0067] The construction module is used to establish an electromagnetic transient model of the LCC converter. The model includes a three-winding converter transformer, two six-pulse converter bridges, a set of AC filters, and a smoothing reactor. Except for the thyristor valve, the other branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, with a small resistance value when it is turned on and a large resistance value when it is turned off. The electrical angle module is used to obtain the power flow results of the power system and, in combination with the winding connection method of the three-winding converter transformer, determine the electrical angle corresponding to each thyristor valve. The electrical angles of the six thyristor valves in the same converter bridge are sequentially lagging by 60 degrees. The current module is used to calculate the initial current of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, and the electrical angle of each thyristor valve, combined with a preset interpolation function. The voltage module is used to calculate the initial voltage of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, the electrical angle of each thyristor valve, and the switching function used to characterize the thyristor on / off state.

[0068] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or function. The processor described in this embodiment can be used for the operation of an LCC converter electromagnetic transient simulation initialization method based on steady-state operating conditions, including: An electromagnetic transient model of an LCC converter is established, comprising a three-winding converter transformer, two six-pulse converter bridges, an AC filter, and a smoothing reactor. Except for the thyristor valves, all other branches are time-invariant linear components. The thyristor valves employ a switching resistor model, using a small resistance value when on and a large resistance value when off. Power flow results are obtained, and the electrical angles of each thyristor valve are determined based on the winding connection method of the three-winding converter transformer. These electrical angles characterize the triggering time of the valve relative to the AC bus phase voltage under ideal steady-state conditions. The electrical angles of the six thyristor valves in the same converter bridge lag by 60 degrees sequentially. Based on the power flow results, the topology of the constructed LCC converter electromagnetic transient model, and the determined electrical angles of each thyristor valve... The initial current of each branch in the LCC converter is calculated using electrical angles and a preset interpolation function. Specifically, the DC current path is determined by the series structure of the two six-pulse converter bridges, and the current distribution of each phase winding is determined by the connection relationship between the y-winding and d-winding on the converter transformer valve side. During commutation, the current transfer process is approximated by linear interpolation. Based on the power flow results, the topology of the constructed LCC converter electromagnetic transient model, the determined electrical angles of each thyristor valve, and the switching function used to characterize the thyristor on / off state, the initial voltage of each branch in the LCC converter is calculated. According to the winding connection relationship and leakage impedance parameters of the three-winding converter transformer, combined with the on-state of the converter bridge arm reflected by the switching function, the terminal voltages of each winding side of the converter transformer during the non-commutation period and the commutation period are determined.

[0069] Please see Figure 9 The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When the processor 61 executes the computer program 63, it implements the LCC converter electromagnetic transient simulation initialization method based on steady-state operating conditions as described in this embodiment. To avoid repetition, these details are not elaborated here. Alternatively, when the processor 61 executes the computer program 63, it implements the functions of each model / unit in the LCC converter electromagnetic transient simulation initialization system based on steady-state operating conditions as described in this embodiment. To avoid repetition, these details are not elaborated here.

[0070] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 9 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0071] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0072] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0073] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0074] Please see Figure 10 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0075] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 11 The steps are shown in the figure.

[0076] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0077] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0078] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0079] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0080] Example 4 This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0081] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0082] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0083] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the electromagnetic transient simulation initialization method for LCC converters based on steady-state operating conditions in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor in the following steps: An electromagnetic transient model of an LCC converter is established, comprising a three-winding converter transformer, two six-pulse converter bridges, an AC filter, and a smoothing reactor. Except for the thyristor valves, all other branches are time-invariant linear components. The thyristor valves employ a switching resistor model, using a small resistance value when on and a large resistance value when off. Power flow results are obtained, and the electrical angles of each thyristor valve are determined based on the winding connection method of the three-winding converter transformer. These electrical angles characterize the triggering time of the valve relative to the AC bus phase voltage under ideal steady-state conditions. The electrical angles of the six thyristor valves in the same converter bridge lag by 60 degrees sequentially. Based on the power flow results, the topology of the constructed LCC converter electromagnetic transient model, and the determined electrical angles of each thyristor valve... The initial current of each branch in the LCC converter is calculated using electrical angles and a preset interpolation function. Specifically, the DC current path is determined by the series structure of the two six-pulse converter bridges, and the current distribution of each phase winding is determined by the connection relationship between the y-winding and d-winding on the converter transformer valve side. During commutation, the current transfer process is approximated by linear interpolation. Based on the power flow results, the topology of the constructed LCC converter electromagnetic transient model, the determined electrical angles of each thyristor valve, and the switching function used to characterize the thyristor on / off state, the initial voltage of each branch in the LCC converter is calculated. According to the winding connection relationship and leakage impedance parameters of the three-winding converter transformer, combined with the on-state of the converter bridge arm reflected by the switching function, the terminal voltages of each winding side of the converter transformer during the non-commutation period and the commutation period are determined.

[0084] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0085] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0086] For smoothing reactors, it is assumed that there is no voltage drop across the inductor, only the voltage drop across the resistor caused by the direct current.

[0087] The effectiveness of the above initialization method was verified using a two-terminal DC system, with the AC grid on both the rectifier and inverter sides using an equivalent infinite power supply.

[0088] Table 3 Test Case Parameters

[0089] The power flow results used for initialization are listed in Table 3. Transient simulations were run for 0.5 seconds with and without initialization, in steps of 50 µs. The results are as follows: Figure 7 and Figure 8 As shown.

[0090] Figure 7 These are the results of transient DC current simulation. Before initialization, the DC current gradually builds up from 0, accompanied by violent oscillations, and only reaches a steady-state value near 0.5s. After initialization, the DC current is at a steady-state value from 0s and does not oscillate.

[0091] Figure 8 This is the transient simulation result of the DC voltage of the rectifier, including a magnified view. Since the LCC converter is a current-source converter, it lacks a voltage buffer; therefore, the steady-state waveform contains a component equal to the switching frequency. Before initialization, the DC voltage waveform is the result of the superposition of the switching waveform and low-frequency oscillations, with the low-frequency oscillations decaying completely after approximately 0.3 seconds. After initialization, the DC voltage waveform only contains the steady-state switching waveform, without the low-frequency oscillations. Furthermore, in the 0.4–0.5 s range, the uninitialized and initialized waveforms overlap, proving that the initialization method only saves the process of establishing a steady state from a zero initial state and has no impact on the final steady state.

[0092] In summary, this invention provides an electromagnetic transient simulation initialization method and system for LCC converters based on steady-state operating conditions. It establishes an electromagnetic transient model of the LCC converter, including components such as a three-winding converter transformer and two six-pulse converter bridges, and uses a switched-resistor model for the thyristors. Combining power flow results and winding connection methods, the valve angle of each thyristor is determined. The initial current of each branch is calculated using interpolation functions, and current transfer is handled by linear interpolation during the commutation period. The initial voltage is calculated using switching functions, and the terminal voltage under different operating conditions is determined by combining the converter transformer parameters. This method achieves steady-state simulation at instantaneous time, eliminates low-frequency oscillations in DC current and voltage, eliminates the need to wait for the steady-state establishment process, significantly improves simulation efficiency, ensures the accuracy of simulation results, and does not affect the final steady-state characteristics.

[0093] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0094] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0095] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0096] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0097] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0098] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0099] If the integrated module / unit is implemented as 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, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random-access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0100] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0101] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0102] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0103] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An initialization method for electromagnetic transient simulation of LCC converter based on steady-state operating conditions, characterized in that, Includes the following steps: S1. Establish an electromagnetic transient model of the LCC converter. The electromagnetic transient model of the LCC converter includes a three-winding converter transformer, two six-pulse converter bridges, a set of AC filters and a smoothing reactor. Except for the thyristor valve, the other branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, taking a small resistance value when it is turned on and a large resistance value when it is turned off. S2. Obtain the power flow results of the power system, and determine the electrical angle corresponding to each thyristor valve in combination with the winding connection method of the three-winding converter transformer described in step S1. The electrical angle is used to characterize the triggering time of the valve relative to the phase voltage of the AC bus under ideal steady state. The electrical angles of the six thyristor valves in the same converter bridge are sequentially delayed by 60 degrees. S3. Based on the power flow results, the topology of the LCC converter electromagnetic transient model constructed in step S1, and the electrical angles of each thyristor valve determined in step S2, the initial current of each branch in the LCC converter is calculated using a preset interpolation function. The DC current path is determined by the series structure of the two six-pulse converter bridges, the current distribution of each phase winding is determined by the connection relationship between the y-winding and d-winding on the converter valve side, and the current transfer process is approximated by linear interpolation during commutation. S4. Based on the power flow results, the topology of the LCC converter electromagnetic transient model constructed in step S1, the electrical angles of each thyristor valve determined in step S2, and the switching functions used to characterize the thyristor on / off states, calculate the initial voltage of each branch in the LCC converter; according to the winding connection relationship and leakage impedance parameters of the three-winding converter transformer, combined with the on-state of the converter bridge arm reflected by the switching function, determine the terminal voltage of each winding of the converter transformer during the non-commutation period and the commutation period.

2. The method for initializing electromagnetic transient simulation of LCC converter based on steady-state operating conditions according to claim 1, characterized in that, In step S2, when the absolute phase of the AC bus phase A voltage is zero at the start of the simulation and the voltage rises to zero, the electrical angle of the thyristor valve V1 connected to the y winding of the converter transformer is the phase of the AC bus phase A voltage minus 30 degrees. When the phase voltage of phase A is at its positive peak at the start of the simulation, the electrical angle of the thyristor valve V1 connected to the d winding on the valve side is the phase of the phase voltage of phase A on the AC bus minus 60 degrees.

3. The method for initializing electromagnetic transient simulation of LCC converter based on steady-state operating conditions according to claim 1, characterized in that, In step S3, the initial current of each branch in the LCC converter is calculated as follows: For DC current, during the non-commutation period, it is determined that all DC current flows through the switches that are conducting in the common anode group and the common cathode group; during the commutation period, the distribution of current in each bridge arm during the commutation process is approximately determined by linear interpolation. For the converter transformer valve-side winding current, based on the relationship between the current path of the valve-side y-winding and d-winding and the conducting valve, a periodic linear interpolation function with electrical angle as the independent variable is established to determine its current waveform. For the branch current of the AC filter, the phasor domain results in the power flow results are used directly to determine it.

4. The method for initializing electromagnetic transient simulation of LCC converter based on steady-state operating conditions according to claim 3, characterized in that, The interpolation function is a periodic function with a period of 360 degrees, used to linearly interpolate the current of the d winding on the commutator valve side within the commutation interval. The interpolation point is set according to the proportion of load current borne by each phase winding during the non-commutation period, wherein the load current bears 2 / 3 and 1 / 3 respectively in the two paths with an impedance ratio of 1:

2.

5. The method for initializing electromagnetic transient simulation of LCC converter based on steady-state operating conditions according to claim 3, characterized in that, The current of the Y winding on the converter transformer side is calculated by superimposing the current of the Y winding and the current of the d winding on the valve side, which satisfies the steady-state condition that the three-phase currents are symmetrical and lag by 120 degrees in sequence.

6. The method for initializing electromagnetic transient simulation of LCC converter based on steady-state operating conditions according to claim 3, characterized in that, The internal states of the AC filter, including voltage and current, are determined directly from the phasor domain data in the power flow results.

7. The method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions according to claim 1, characterized in that, In step S4, calculating the initial voltage of each branch specifically includes: For the voltage of the converter transformer valve-side winding, general expressions for the voltage of the valve-side y-winding and d-winding are established respectively. The expressions use switching functions to characterize the influence of the commutation process on the winding terminal voltage. For the converter bridge arm voltage, expressions for the bridge arm voltage connected to the y-winding and d-winding on the converter transformer valve side are established respectively. These expressions use switching functions to characterize the voltage in the on and off states of the bridge arm.

8. The method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions according to claim 7, characterized in that, For the y-winding on the valve side of the converter transformer, during the two-phase commutation period, the terminal voltages of the two commutated windings are forced to be equal, and the voltage difference is borne by the leakage inductance; for the d-winding on the valve side, during any phase commutation period, the voltages of all three windings are affected by the commutation, with the commutated winding being short-circuited and the remaining two windings connected in series in the forward direction to form a loop.

9. The method for initializing electromagnetic transient simulation of an LCC converter based on steady-state operating conditions according to claim 8, characterized in that, The voltage of the commutator bridge arm is determined based on the switching function of the corresponding thyristor: When the switch is on, the voltage across the bridge arm is 0; when the switch is off, the voltage across the bridge arm is the line voltage of the converter transformer valve side winding.

10. An electromagnetic transient simulation initialization system for an LCC converter based on steady-state operating conditions, characterized in that, include: The module is used to build an electromagnetic transient model of the LCC converter. The model includes a three-winding converter transformer, two six-pulse converter bridges, a set of AC filters and a smoothing reactor. Except for the thyristor valve, the other branches are time-invariant linear components. The thyristor valve adopts a switching resistor model, with a small resistance value when it is turned on and a large resistance value when it is turned off. The electrical angle module is used to obtain the power flow results of the power system and, in combination with the winding connection method of the three-winding converter transformer, determine the electrical angle corresponding to each thyristor valve. The electrical angles of the six thyristor valves in the same converter bridge are sequentially lagging by 60 degrees. The current module is used to calculate the initial current of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, and the electrical angle of each thyristor valve, combined with a preset interpolation function. The voltage module is used to calculate the initial voltage of each branch in the LCC converter based on the power flow results, the topology of the electromagnetic transient model of the LCC converter, the electrical angle of each thyristor valve, and the switching function used to characterize the thyristor on / off state.

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