Efficient electromagnetic transient modeling method for hybrid high-voltage direct-current power transmission system containing IGCT (integrated gate commutated thyristor)

Abstract

The invention relates to a high-efficiency electromagnetic transient modeling method for a hybrid high-voltage direct-current power transmission system containing an IGCT (integrated gate commutation current transformer), and belongs to the field of electric digital data processing. The IGCT high-voltage direct-current power transmission system comprises a power grid commutation current transformer at a sending end, an IGCT current transformer at a receiving end and a direct-current power transmission line between the power grid commutation current transformer and the IGCT current transformer; the efficient electromagnetic transient modeling method comprises the following steps: at a power grid commutation current converter at a sending end, simplifying the switching operation of a thyristor into a port voltage and current average value model by adopting an averaging modeling method, thereby improving the simulation efficiency of the current converter at the sending end; a Thevenin equivalent method is adopted at the IGCT current converter of the receiving end, and an IGCT switch is dynamically simplified into a Norton equivalent circuit model of a current source and impedance, so that the simulation efficiency of the current converter of the receiving end is improved; for a direct current transmission line between transmitting and receiving end converter stations, a Bergeron model is adopted to decouple the two ends of the whole line, so that the electrical response of the two ends can be processed independently, the complexity of mutual coupling of the two ends of the line is reduced, and the calculation process is simplified.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic transient simulation, and in particular relates to a high-efficiency electromagnetic transient modeling method for a hybrid high-voltage direct current power transmission system containing an IGCT. Background Art

[0002] High-voltage direct current (HVDC) transmission technology has become a key technology in modern power grid construction due to its significant advantages in long-distance and large-capacity power transmission. The high-voltage direct current transmission system is mainly composed of rectifier stations, inverter stations and DC transmission lines. In practical applications, the dynamic response and fault recovery capabilities of the HVDC system are crucial to the safe and stable operation of the system. Therefore, electromagnetic transient simulation, as a core means of evaluating the dynamic behavior of the system, plays an important role in the design and operation of power systems.

[0003] As the proportion of power electronic switchgear in the power grid continues to increase, its high-frequency switching operation, complex control strategies and diverse topological structures pose a huge challenge to improving the efficiency of electromagnetic transient simulation. How to effectively improve simulation efficiency while ensuring simulation accuracy has become a technical problem that needs to be solved urgently.

[0004] In the prior art, a variety of modeling methods have been proposed for different parts of the HVDC system, but the IGCT high-voltage direct current transmission system has not been considered, and most of these methods only consider the single link of rectification, transmission, and inversion. For example:

[0005] Grid-commutated converter (LCC) at the sending end: LCC is based on thyristor components (SCR) and relies on the grid for natural commutation. Its commutation process is relatively fixed, usually operates at a lower frequency, and generates fewer harmonic components. There are many options for fast modeling methods of LCC, including detailed switch modeling, dynamic phasor modeling, and average modeling. Detailed switch modeling can accurately capture the switching behavior of thyristors, but the simulation efficiency is low. The dynamic phasor model can track the dynamic response of the system at different frequencies. However, this method over-focuses on unnecessary high-frequency responses, which increases the complexity and calculation time of the simulation. Therefore, although the dynamic phasor method is accurate, it is not suitable for scenarios that require efficient calculation and simplified modeling. In contrast, average modeling does not consider specific switching actions, but greatly improves the simulation speed by equating the switching operation of the converter to a continuous signal of average voltage or current without accurately tracking the switching transient behavior of each thyristor. In large-scale AC and DC power grid simulations, in order to improve the simulation speed, the details of the power electronic switching action inside the converter are usually ignored, and the external characteristics of the converter are focused on. Considering that in a system like LCC where low-frequency dynamics dominate, the use of a dynamic phasor model will increase the simulation burden without significantly improving accuracy. Therefore, an averaging model is chosen that strikes a good balance between accuracy and efficiency.

[0006] IGCT converter at the receiving end: Some researchers have proposed that fully controlled integrated gate-commutated thyristors (IGCTs) can be used to replace the thyristors in the LCC bridge arms. This IGCT-based LCC-HVDC configuration can effectively reduce the probability of commutation failure, significantly improve the control flexibility and response speed of the system, and the transformation process is relatively simple, with significant advantages in terms of cost-effectiveness and efficiency. However, the switching dynamics of IGCT are complex. In the prior art, precise switch modeling is mostly used for modeling IGCT. Although the accuracy is high, the computational complexity is extremely high, which limits the efficiency improvement of the simulation. So far, no relevant research has proposed a fast modeling method for converters based on IGCT. Therefore, the present invention innovatively proposes to use the Thevenin equivalent method to quickly model the IGCT converter, by simplifying the complex IGCT switching operation into a combination of an equivalent current source and an impedance, while ensuring the simulation accuracy and improving the simulation speed.

[0007] DC transmission lines: Modeling methods for long-distance DC transmission lines include the π-type equivalent circuit model and the Berelon model. The π-type equivalent circuit model is suitable for steady-state analysis, but it is difficult to accurately describe the electromagnetic wave propagation phenomenon in the line. The Berelon model is based on the traveling wave theory and can effectively describe the propagation process of voltage and current waves, and is suitable for transient analysis. The Berelon model decouples the transient behavior of the two ends of the line through the transmission characteristics of electromagnetic waves, effectively reducing the complexity of the mutual coupling between the two ends of the line, simplifying the calculation process, and improving the simulation efficiency.

[0008] Although the existing technology has provided different efficient modeling options for various links of the HVDC system, there is no efficient modeling method that comprehensively considers the entire system for the IGCT high-voltage direct current transmission system.

[0009] Therefore, at this stage, it is necessary to design efficient electromagnetic transient modeling methods, systems and storage media for hybrid HVDC transmission systems containing IGCTs to solve the above problems. Summary of the invention

[0010] The present invention aims to provide an efficient electromagnetic transient modeling method, system and storage medium for a hybrid high-voltage direct current transmission system containing IGCT, comprehensively considering all parts of the high-voltage direct current transmission system, and reasonably selecting and integrating the modeling methods of the sending-end converter, the direct current transmission line and the receiving-end converter, thereby improving the simulation efficiency and accuracy of the entire system, and having a certain reference value in engineering applications.

[0011] To achieve the above object, the technical solution of the present invention is:

[0012] An efficient electromagnetic transient modeling method for a hybrid high-voltage direct current transmission system containing an IGCT, wherein the IGCT high-voltage direct current transmission system comprises a grid commutation converter at a sending end, an IGCT converter at a receiving end, and a direct current transmission line therebetween, and the efficient electromagnetic transient modeling method comprises the following steps:

[0013] S1. At the grid-commutated converter at the sending end, an average modeling method is used to simplify the switching operation of the thyristor into a port voltage and current average value model, thereby improving the simulation efficiency of the sending-end converter;

[0014] S2. At the IGCT converter at the receiving end, the Thevenin equivalent method is used to simplify the IGCT switch dynamics into a Norton equivalent circuit model of current source and impedance, thereby improving the simulation efficiency of the converter at the receiving end;

[0015] S3. For the DC transmission line between the sending and receiving converter stations, the Berelon model is used to decouple the two ends of the entire line so that the electrical responses at both ends can be processed independently, reducing the complexity of the mutual coupling between the two ends of the line and simplifying the calculation process.

[0016] Further, in step S1,

[0017] For a periodic fluctuating signal f(t), its instantaneous value always fluctuates around the DC component of the signal. The DC component of the signal can be obtained by averaging the instantaneous value of the signal within a period. This process is called "averaging". Specifically, for a variable or function f(t), its average value is:

[0018]

[0019] Where: t represents time; T s Represents the averaging period, and the variable values ​​after averaging are uniformly marked with an overline;

[0020] Averaging modeling uses a controlled source circuit to equate the converter and describe the relationship between AC and DC current and voltage under the current working conditions; on the AC and DC sides, there is a set of variables obtained through measurement and a set of variables output by the controlled source. During the simulation process, the averaging model calculates the controlled source output on the other side through the measured values ​​on one side. Specifically, it is determined that the rectifier converter is equivalent to a controlled AC voltage source on the AC side and a controlled DC current source on the DC side. The measured quantities include AC current and DC voltage. It is necessary to establish the relationship between the various components of the AC voltage and the DC voltage, as well as the averaging equations between the various components of the AC current and the DC current.

[0021] When an asymmetric fault occurs in the AC system, harmonic components will appear in the current and voltage on both sides of the AC and DC. Each harmonic component can be decomposed into positive and negative sequence symmetrical components. The voltage and current of the AC bus of the converter can be decomposed into components as shown in formula (2);

[0022]

[0023] Where: and Represent the DC components of the j-phase voltage and current respectively; and They represent the positive sequence components of the voltage and current of the j-phase n-order; and They represent the negative sequence components of the voltage and current of the j-phase nth order, respectively; j represents the a, b or c phase;

[0024] Assume ω e is the angular velocity of the fundamental synchronous rotating coordinate system, then the instantaneous value expressions of each voltage and current component are:

[0025]

[0026] Where: k represents voltage v or current i; and Respectively represent the amplitudes of the positive and negative sequence components of the nth harmonic; and Respectively represent the phase angles of the positive and negative sequence components of the nth harmonic;

[0027] The original three-phase AC signal components are converted into steady-state components of the dq axis in the synchronous coordinate system. The relationship between the AC voltage components and the DC voltage, and between the AC current components and the DC current of the controlled AC voltage source can be expressed as follows:

[0028] 1) Relationship between controlled AC voltage source and DC voltage

[0029] The parameter averaging equation between the positive sequence component of the AC voltage nth harmonic and the DC voltage is:

[0030]

[0031] Where: and They represent the d-axis and q-axis components of each positive sequence component of the AC voltage obtained by transforming the corresponding synchronous coordinate system; Represents the DC voltage on the rectifier side; for The angle with the d-axis;

[0032] Similarly, the parameter averaging equation corresponding to the negative sequence component of the AC voltage is as follows:

[0033]

[0034] The parameter averaging equation corresponding to the DC bias component is as follows:

[0035]

[0036] Where: Represents the DC voltage on the rectifier side; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC voltage obtained by corresponding synchronous coordinate system transformation;

[0037]

[0038] for The angle with the d-axis; and They respectively represent the magnitude of the resultant vector of the DC component of the three-phase voltage of the rectifier after being transformed through the stationary dq coordinate system and its angle with the d-axis;

[0039] In the formula, Unknown algebraic functions used to describe the average behavior of the rectifier switching unit to characterize its dynamic characteristics and electrical relationships under different operating conditions;

[0040] 2) Relationship between controlled DC current source and AC current

[0041] The parameter averaging equation between the positive sequence and negative sequence components of the AC current and the DC current is as follows:

[0042]

[0043] Where: Represents the DC current on the rectifier side; in and They respectively represent the d-axis and q-axis components of the positive-sequence components of the rectifier AC current obtained by the corresponding synchronous coordinate system transformation; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC current obtained by corresponding synchronous coordinate system transformation;

[0044] In the formula, is a parameter that changes with the inverter firing angle and load conditions;

[0045] By equivalently modeling the converter through averaging equations, electrical decoupling of the AC and DC sides can be achieved, and only secondary information such as voltage and current values ​​can be transmitted using controlled sources. The relationship between the current and voltage at the AC and DC ports of the converter is transformed from the original switching function representation to a set of parameterized algebraic equations.

[0046] The parameters in these equations are usually described by unknown algebraic functions, which depend on the operating state of the system, including the trigger angle of the converter and the load condition. In order to accurately identify these algebraic functions, the present invention uses a multi-gate hybrid expert model (MMOE) to handle the nonlinear relationship in complex systems. MMOE is used to fit the voltage and current relationship under complex system states through multiple expert models, and the most suitable expert is dynamically selected through the gating network to handle the current state, so that the unknown algebraic function can be accurately obtained.

[0047] Further, in step S2,

[0048] In the structure of the receiving-end IGCT converter, the bridge arm is composed of multiple IGCT devices connected in series and protected by a buffer circuit. A single IGCT and its buffer circuit are regarded as a submodule.

[0049] In electromagnetic transient simulation, the IGCT gate trigger is processed into a control signal. The switch-on condition is that the switch-on forward voltage is greater than or equal to 0, and the switch-off condition is that the switch-on forward current is less than or equal to 0. The IGCT is equivalent to a variable resistor R0, and the switch element is equivalent.

[0050] The dynamic element capacitance is discretized using the trapezoidal method as follows:

[0051] The differential dynamic equation of capacitance can be expressed as:

[0052]

[0053] Where C0 is the submodule capacitance, v C0 (t) is the voltage across the capacitor, i C0 (t) is the current flowing through the capacitor; the capacitor C0 is discretized, and a single IGC is equivalent, and the trapezoidal method is used to arrange equation (15) to obtain:

[0054] v C0 (t) = R ceq0 i C0 (t)+v ceq0 (t-Δt) (16)

[0055] Where Δt is the simulation step length, R ceq0 is the equivalent resistance of the discretized capacitor C0, vceq0 (t-Δt) is the equivalent historical voltage source after the capacitor C0 is discretized, That is, after the capacitor is discretized, it can be equivalent to a resistor series voltage source; R smeq is the Thevenin equivalent resistance of the submodule, v smeq (t) is the Thevenin equivalent voltage source of the submodule, v SM (t) represents the voltage of each submodule port at the current moment, i SM (t) represents the current flowing through the submodule at the current moment;

[0056] The six-pulse bridge of the converter has six bridge arms, each of which is obtained by connecting n submodules in series. The equivalent model of the bridge arm can be obtained by algebraic summation.

[0057] is the Thevenin equivalent resistance of the bridge arm, is the Thevenin equivalent voltage source of the bridge arm;

[0058] Convert Norton format, is the equivalent conductance of the bridge arm, is the Norton equivalent historical current source, v arm (t) represents the terminal voltage of the bridge arm at the current moment, i arm (t) represents the current flowing through the bridge arm at the current moment;

[0059] Thus, the original multi-node network of the bridge arm is transformed into a two-node branch in which a resistor and a historical current source are connected in parallel.

[0060] Further, in step S3,

[0061] The line parameters of the Berelon model are calculated based on the power frequency of 50Hz. In the case of a single-phase lossless line, assume the inductance L1 and capacitance C1 of unit length; the voltage and current at point f on the transmission line at a distance x from the end m are functions of both distance and time; the voltage at time t is u(x,t) and the current is i(x,t); when ignoring the changes in line parameters with frequency and the conductance per unit length, the following wave equation can be established:

[0062]

[0063] Rewritten as a second-order wave equation:

[0064]

[0065] The D'Alembert solution is:

[0066]

[0067] In the formula, u f(tx / v) is the forward voltage wave propagating in the positive direction, u b (t+x / v) is the reverse voltage wave propagating in the reverse direction, i f (tx / v) is the forward current wave propagating in the positive direction, i b (t+x / v) is the reverse current wave propagating in the reverse direction; is the propagation speed of the traveling wave along the line, and the wave impedance is

[0068] Combining (19) and (20) and transforming them, we get (21)

[0069]

[0070] At the m and n ends of the line, x = 0 and x = l respectively, and let Substituting it into equation (21), we can get the relationship between the voltage and current at both ends of the line;

[0071] u m (t-τ)+Z c i m (t-τ) = u n (t)-Z c i n (t) (22)

[0072] By rearranging formula (22), we can obtain the port current expressed by wave impedance and equivalent current source:

[0073]

[0074] Among them, the corresponding equivalent current sources are:

[0075]

[0076] That is, the wave process in the distributed line parameter model can be represented by a lumped parameter model of wave impedance and equivalent current source, thereby constructing a two-port model of the transmission line; in this model, there is no direct physical connection between the two ports, but through the action of the current source, which is determined by the voltage and current at a previous moment. This method realizes the natural decoupling of the line.

[0077] For actual transmission lines, the line resistance can be treated as a concentrated resistance and introduced in series in sections. The line with a length of l is divided into two sections, each section is l / 2 long, and a concentrated resistance R / 4 is connected in series at both ends, and a concentrated resistance R / 2 is connected in the middle section, where R is the resistance of the entire line length; an equivalent two-port network considering resistance loss is obtained; two half-split line models are obtained along the dotted line; where

[0078] Port current:

[0079]

[0080] The corresponding equivalent current sources are:

[0081]

[0082] The two half-split lines are cascaded and simplified to obtain the Berelon transmission line model taking into account resistance losses.

[0083] The corresponding equivalent current sources are:

[0084]

[0085] A high-efficiency electromagnetic transient modeling system for a hybrid high-voltage direct current power transmission system containing IGCT, wherein the high-efficiency electromagnetic transient modeling system applies the high-efficiency electromagnetic transient modeling method for a hybrid high-voltage direct current power transmission system containing IGCT as described above to perform high-efficiency electromagnetic transient modeling.

[0086] A storage medium having a computer program stored thereon, wherein the computer program, when executed, executes the above-mentioned efficient electromagnetic transient modeling method for a hybrid high-voltage direct current power transmission system containing IGCT.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] The present invention simplifies the complex switch operation by selecting the modeling method for each part of the system, especially innovatively adopting the Thevenin equivalent model for the IGCT-based converter at the receiving end. Compared with the traditional precise switch modeling method, the present invention can significantly improve the simulation speed while ensuring a certain simulation accuracy.

[0089] Although the present invention focuses on improving simulation efficiency, the modeling methods of each part still maintain a high degree of accuracy. By averaging the modeling of the sending-end LCC converter, the low-frequency dynamic characteristics in the system are effectively captured, the high-frequency switching behavior is simplified, and the simulation accuracy is ensured.

[0090] Although the prior art has proposed a technical solution to replace the thyristor in the grid commutation converter with IGCT, an efficient modeling solution for it has not yet been proposed. The present invention speeds up the modeling of the IGCT converter by Thevenin equivalent modeling, solving the problem of low modeling efficiency.

[0091] The present invention comprehensively considers the collaborative modeling of the sending-end converter, the DC transmission line and the receiving-end converter. By organically combining the various parts of the system, a system electromagnetic transient simulation method is formed, which significantly improves the overall simulation efficiency of the HVDC system and meets the real-time simulation requirements of large-scale power systems under complex operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 Schematic diagram of the process of LCC averaging modeling of the present invention.

[0093] Figure 2 It is a schematic diagram of the framework of the MMOE of the present invention.

[0094] Figure 3 It is a schematic diagram of the structure of the IGCT converter of the present invention.

[0095] Figure 4 It is an equivalent schematic diagram of the switch tube of the present invention.

[0096] Figure 5 It is a schematic diagram of a single IGCT equivalent model of the present invention.

[0097] Figure 6 It is a schematic diagram of the bridge arm equivalent model of the present invention.

[0098] Figure 7 It is a schematic diagram of the Berelon equivalent model of the single-phase lossless line of the present invention.

[0099] Figure 8 This is a schematic diagram of an equivalent two-port network considering resistance loss of the present invention.

[0100] Fig. 9 It is a schematic diagram of a half-split circuit model of the present invention.

[0101] Fig.10 It is a schematic diagram of the Berelon transmission line model considering resistance loss of the present invention.

[0102] Fig.11 It is a schematic flow chart of a method for efficient electromagnetic transient modeling of an IGCT high-voltage direct current transmission system of the present invention. DETAILED DESCRIPTION

[0103] like Fig.11 As shown, an efficient electromagnetic transient modeling method for an IGCT high-voltage direct current transmission system, the IGCT high-voltage direct current transmission system includes a grid commutation converter at a sending end, an IGCT converter at a receiving end, and a direct current transmission line therebetween, the efficient electromagnetic transient modeling method is implemented by the following steps:

[0104] (1) At the grid-commutated converter at the sending end, an average modeling method is used to simplify the switching operation of the thyristor into a port voltage and current average value model, thereby improving the simulation efficiency of the sending-end converter;

[0105] (2) At the IGCT converter at the receiving end, the Thevenin equivalent method is used to simplify the complex IGCT switching dynamics into a Norton equivalent circuit model of current source and impedance, thereby improving the simulation efficiency of the converter at the receiving end;

[0106] (3) For the DC transmission line between the sending and receiving converter stations, the Berelon model is used to decouple the two ends of the entire line so that the electrical responses at both ends can be processed independently, reducing the complexity of the mutual coupling between the two ends of the line, simplifying the calculation process, and improving the simulation efficiency.

[0107] The averaged modeling of the sending-end grid-commutated converter simplifies the high-frequency switching behavior in the sending-end converter into continuous voltage and current signals by integrating and averaging the switching cycles of the thyristors, thereby reducing the computational complexity and ensuring the simulation accuracy.

[0108] The Thevenin equivalent modeling of the receiving-end IGCT converter simplifies the switching behavior of multiple IGCT devices into an equivalent circuit composed of current sources and impedances, making it possible to accurately simulate the system voltage and current waveforms in a fast simulation.

[0109] The Berelon model is used for modeling DC transmission lines. It can improve the computational efficiency of system-level simulation by decoupling the transient behaviors of the converter stations at both ends.

[0110] By combining a variety of efficient modeling methods, including averaging modeling of the sending-end grid commutation converter, Thevenin equivalent modeling of the receiving-end IGCT converter, and DC transmission line decoupling based on the Berelon model, the computational efficiency of large-scale electromagnetic transient simulation can be significantly improved, which is especially suitable for real-time simulation and dynamic response analysis of complex high-voltage DC transmission systems.

[0111] 1. Average modeling of the sending-end converter station

[0112] In order to improve the simulation speed, in large-scale AC and DC power grid simulations, the specific details of the power electronic switch action inside the converter are usually omitted, and the focus is placed on the external characteristics of the converter.

[0113] The core method of averaging modeling is to ignore the transient details within each switching cycle and simplify the output description of the system by taking the average value of rapidly changing variables (such as voltage and current) within a cycle.

[0114] For a periodic fluctuating signal f(t), its instantaneous value always fluctuates around the DC component of the signal. The DC component of the signal can be obtained by averaging the instantaneous value of the signal within a period. This process is called "averaging". Specifically, for a variable or function f(t), its average value is:

[0115]

[0116] Where: t represents time; T s Represents the averaging period, and the variable values ​​after averaging are uniformly marked with an overline;

[0117] The process of LCC averaging modeling is as follows Figure 1 As shown:

[0118] Average modeling uses a controlled source circuit to equate the converter to describe the relationship between AC and DC current and voltage under the current working conditions; on the AC and DC sides, there are a set of variables obtained through measurement and a set of variables output by the controlled source. During the simulation process, the average model calculates the controlled source output on the other side through the measured values ​​on one side. Specifically, it is determined that the rectifier converter is equivalent to a controlled AC voltage source on the AC side and a controlled DC current source on the DC side. The measured quantities include AC current and DC voltage. It is necessary to establish the relationship between the AC voltage components and the DC voltage, as well as the average equation between the AC current components and the DC current.

[0119] Harmonics will affect the triggering signals of the thyristors of the phase-commutating converters in the power grid, so the effects of the main harmonic components must be fully considered when constructing their models.

[0120] When an asymmetric fault occurs in the AC system, harmonic components will appear in the current and voltage on both sides of the AC and DC. Each harmonic component can be decomposed into positive and negative sequence symmetrical components. The voltage and current of the AC bus of the converter can be decomposed into components as shown in formula (2);

[0121]

[0122] Where: and Represent the DC components of the j-phase voltage and current respectively; and They represent the positive sequence components of the voltage and current of the j-phase n-order; and They represent the negative sequence components of the voltage and current of the j-phase nth order, respectively; j represents the a, b or c phase;

[0123] Assume ω e is the angular velocity of the fundamental synchronous rotating coordinate system, then the instantaneous value expressions of each voltage and current component are:

[0124]

[0125] Where: k represents voltage v or current i; and Respectively represent the amplitudes of the positive and negative sequence components of the nth harmonic; and Respectively represent the phase angles of the positive and negative sequence components of the nth harmonic;

[0126] The original three-phase AC signal components are converted into steady-state components of the dq axis in the synchronous coordinate system. The relationship between the AC voltage components and the DC voltage, and between the AC current components and the DC current of the controlled AC voltage source can be expressed as follows:

[0127] 1) Relationship between controlled AC voltage source and DC voltage

[0128] The parameter averaging equation between the positive sequence component of the AC voltage nth harmonic and the DC voltage is:

[0129]

[0130] Where: and They represent the d-axis and q-axis components of each positive sequence component of the AC voltage obtained by transforming the corresponding synchronous coordinate system; Represents the DC voltage on the rectifier side; for The angle with the d-axis;

[0131] Similarly, the parameter averaging equation corresponding to the negative sequence component of the AC voltage is as follows:

[0132]

[0133] The parameter averaging equation corresponding to the DC bias component is as follows:

[0134]

[0135] Where: Represents the DC voltage on the rectifier side; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC voltage obtained by corresponding synchronous coordinate system transformation;

[0136]

[0137] for The angle with the d-axis; and They respectively represent the magnitude of the resultant vector of the DC component of the three-phase voltage of the rectifier after being transformed through the stationary dq coordinate system and its angle with the d-axis;

[0138] In the formula, Unknown algebraic functions used to describe the average behavior of the rectifier switching unit to characterize its dynamic characteristics and electrical relationships under different operating conditions;

[0139] 2) Relationship between controlled DC current source and AC current

[0140] The parameter averaging equation between the positive sequence and negative sequence components of the AC current and the DC current is as follows:

[0141]

[0142] Where: Represents the DC current on the rectifier side; in and They respectively represent the d-axis and q-axis components of the positive-sequence components of the rectifier AC current obtained by the corresponding synchronous coordinate system transformation; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC current obtained by corresponding synchronous coordinate system transformation;

[0143] In the formula, is a parameter that changes with the inverter firing angle and load conditions;

[0144] By equivalently modeling the converter through averaging equations, electrical decoupling of the AC and DC sides can be achieved, and only secondary information such as voltage and current values ​​can be transmitted using controlled sources. The relationship between the current and voltage at the AC and DC ports of the converter is transformed from the original switching function representation to a set of parameterized algebraic equations.

[0145] The parameters in these equations are usually described by unknown algebraic functions, which depend on the operating state of the system, including the trigger angle of the converter and the load condition. In order to accurately identify these algebraic functions, the present invention uses a multi-gate hybrid expert model (MMOE) to handle the nonlinear relationship in complex systems. MMOE is used to fit the voltage and current relationship under complex system states through multiple expert models, and the most suitable expert is dynamically selected through the gating network to handle the current state, so that the unknown algebraic function can be accurately obtained.

[0146] The basic principles are as follows:

[0147] The framework of MMOE is as follows Figure 2 As shown in Figure 2, multi-task learning enables a single model to process current and voltage simultaneously, without designing an independent architecture for each subtask, avoiding the repeated construction of the same type of neuron configuration, while ensuring the flexibility and adaptability of the model.

[0148] The problem of identifying unknown algebraic functions is divided into multiple tasks. In this study, Task 1 is to fit the relationship between AC voltage and DC voltage, and Task 2 is to fit the relationship between AC current and DC current.

[0149] To accurately describe the system behavior under different load conditions and firing angles, multiple expert models are trained to handle different state spaces. Each expert model excels at handling nonlinear relationships under specific conditions, such as low load, high load, or a specific firing angle range.

[0150] The gating network is used to dynamically assign the weight of each expert model according to the current system status (such as trigger angle, load condition, etc.). The output of the gating network is the combined weight of each expert model, so that the model can adaptively select the optimal expert under different working conditions.

[0151] The weights of the gating network are used to combine the outputs of the expert models to obtain the final algebraic functions. These functions can accurately predict the relationship between AC and DC voltages and currents based on the measured values ​​under different operating conditions. The expert models and gating networks are trained with a large amount of measurement data, and the accuracy and adaptability of the models are verified through simulation. The final model can quickly calculate the output of the other side using the measured values ​​in a real-time system, achieving accurate modeling of the converter system.

[0152] 2. Thevenin equivalent modeling of the receiving converter station

[0153] The structure of the receiving end IGCT converter is as follows: Figure 3 As shown in the left figure, the bridge arm is composed of multiple IGCT devices connected in series and protected by a buffer circuit. A single IGCT and its buffer circuit are regarded as a submodule. Figure 3 As shown in the picture on the right.

[0154] IGCT can combine the advantages of IGBT and GTO, with the conduction characteristics of GTO and the switching characteristics of IGBT, with strong current carrying capacity and low on-state voltage drop. In electromagnetic transient simulation, the IGCT gate trigger is processed into a control signal, and it is considered that IGCT uses a smaller resistor to replace it in the on state and a larger resistor to replace it in the off state. The switch on condition is that the switch forward voltage is greater than or equal to 0, and the switch off condition is that the switch forward current is less than or equal to 0. The IGCT is equivalent to a variable resistor R0. After the switch element is equivalent, the equivalent model of a single IGCT and its buffer circuit switch is as follows: Figure 4 shown.

[0155] The dynamic element capacitance is discretized using the trapezoidal method as follows:

[0156] The differential dynamic equation of capacitance can be expressed as:

[0157]

[0158] Where C0 is the submodule capacitance, v C0 (t) is the voltage across the capacitor, i C0(t) is the current flowing through the capacitor. Discretizing the capacitor C0 and performing an equivalent calculation on a single IGC yields Figure 5 , using the trapezoidal method to rearrange equation (15) we can get:

[0159] v C0 (t) = R ceq0 i C0 (t)+v ceq0 (t-Δt) (16)

[0160] Where Δt is the simulation step length, R ceq0 is the equivalent resistance of the discretized capacitor C0, v ceq0 (t-Δt) is the equivalent historical voltage source after the capacitor C0 is discretized, That is, after the capacitor is discretized, it can be equivalent to a resistor series voltage source. smeq is the Thevenin equivalent resistance of the submodule, v smeq (t) is the Thevenin equivalent voltage source of the submodule, v SM (t) represents the voltage of each submodule port at the current moment, i SM (t) represents the current flowing through the submodule at the current moment.

[0161] The six-pulse bridge of the converter has six bridge arms, each of which is obtained by connecting n submodules (including IGCT and snubber circuit) in series. The equivalent model of the bridge arm can be obtained by algebraic summation, such as Figure 6 shown.

[0162] In the left picture, is the Thevenin equivalent resistance of the bridge arm, is the Thevenin equivalent voltage source of the bridge arm. The right figure is the transformed Norton form. is the equivalent conductance of the bridge arm, is the Norton equivalent historical current source, v arm (t) represents the terminal voltage of the bridge arm at the current moment, i arm (t) represents the current flowing through the bridge arm at the current moment.

[0163] Thus, the original multi-node network of the bridge arm is transformed into a two-node branch in which a resistor and a historical current source are connected in parallel, thereby improving the computational efficiency.

[0164] 3. Decoupling model of DC transmission line

[0165] The line parameters of the Berelon model are calculated based on the power frequency of 50Hz. In the case of a single-phase lossless line, assume the inductance L1 and capacitance C1 of unit length; the voltage and current at point f on the transmission line at a distance x from the end m are functions of both distance and time; the voltage at time t is u(x,t) and the current is i(x,t); when ignoring the changes in line parameters with frequency and the conductance per unit length, the following wave equation can be established:

[0166]

[0167] Further rewritten as the second-order wave equation:

[0168]

[0169] The D'Alembert solution is:

[0170]

[0171] In the formula, u f (tx / v) is the forward voltage wave propagating in the positive direction, u b (t+x / v) is the reverse voltage wave propagating in the reverse direction, i f (tx / v) is the forward current wave propagating in the positive direction, i b (t+x / v) is the reverse current wave propagating in the reverse direction. is the propagation speed of the traveling wave along the line, and the wave impedance is

[0172] Combining (19) and (20) and transforming them, we get (21)

[0173]

[0174] At the m and n ends of the line, x = 0 and x = l respectively, and let Substituting it into equation (21) we can get the relationship between the voltage and current at both ends of the line.

[0175] u m (t-τ)+Z c i m (t-τ) = u n (t)-Z c i n (t) (22)

[0176] By rearranging formula (22), we can obtain the port current expressed by wave impedance and equivalent current source:

[0177]

[0178] Among them, the corresponding equivalent current sources are:

[0179]

[0180] That is, the distributed line parameter model containing the wave process can be expressed as a lumped parameter model of wave impedance and equivalent current source, and the obtained transmission line two-port model is as follows: Figure 7 As shown in Figure 1. In this model, there is no direct physical connection between the two ports. Instead, the two ports are connected through the action of a current source, which is determined by the voltage and current at a previous moment. This method achieves natural decoupling of the line.

[0181] For actual transmission lines, the line resistance can be treated as a concentrated resistance and connected in series in sections. A line with a length of l is divided into two sections, each with a length of l / 2. A concentrated resistance R / 4 is connected in series at both ends, and a concentrated resistance R / 2 is connected in the middle section. R is the resistance of the entire line. Figure 7 You can draw as Figure 8 The equivalent two-port network considering resistance loss is shown in Figure 2. Separating along the dotted line, we get two half-circuit models as shown in Figure 2. Fig. 9 shown.

[0182] Port current:

[0183]

[0184] The corresponding equivalent current sources are:

[0185]

[0186] Cascading the two half-circuits and simplifying them gives Fig.10 The Berelon transmission line model considering resistive losses is shown.

[0187] contrast, Fig. 9 Because the calculation conditions at both ends of the line including the time (t-τ / 2) are taken into account, only the current source term representing the history term changes.

[0188]

[0189] Actual transmission lines are usually three-phase systems. In order to more effectively apply the Berelon model to actual situations, the derivation process of the Berelon model for single-phase transmission lines can be used as a reference and extended to the Berelon model for three-phase transmission lines. Unlike the single-phase model, in the three-phase model, voltage and current are represented by vectors, while capacitance and inductance are described by matrices containing non-diagonal elements. Since the Berelon model is only valid under modal components, it is necessary to completely diagonalize the parameter matrix through matrix transformation to eliminate the coupling relationship between phases. Specifically, the matrix transformation converts the coupled equations in the phase domain into the decoupled equations in the modal domain, so that each modal component can be calculated independently. After such a transformation, each modal circuit can be calculated separately using the Berelon model, thereby achieving efficient analysis and simulation of the three-phase system.

Claims

1. An efficient electromagnetic transient modeling method for a hybrid high-voltage direct current transmission system containing IGCT, wherein the IGCT high-voltage direct current transmission system comprises a grid-commutated converter at a sending end, an IGCT converter at a receiving end, and a direct current transmission line therebetween, characterized in that: The efficient electromagnetic transient modeling method comprises the following steps: S1. At the grid-commutated converter at the sending end, an average modeling method is used to simplify the switching operation of the thyristor into a port voltage and current average value model, thereby improving the simulation efficiency of the sending-end converter; S2. At the IGCT converter at the receiving end, the Thevenin equivalent method is used to simplify the IGCT switch dynamics into a Norton equivalent circuit model of current source and impedance, thereby improving the simulation efficiency of the converter at the receiving end; S3. For the DC transmission line between the sending and receiving converter stations, the Berelon model is used to decouple the two ends of the entire line so that the electrical responses at both ends can be processed independently, reducing the complexity of the mutual coupling between the two ends of the line and simplifying the calculation process.

2. The efficient electromagnetic transient modeling method of a hybrid high voltage direct current transmission system containing IGCT according to claim 1 is characterized in that: In step S1, For a periodic fluctuating signal f(t), its instantaneous value always fluctuates around the DC component of the signal. The DC component of the signal can be obtained by averaging the instantaneous value of the signal within a period. This process is called "averaging". Specifically, for a variable or function f(t), its average value is: Where: t represents time; T s Represents the averaging period, and the variable values ​​after averaging are uniformly marked with an overline; Averaging modeling uses a controlled source circuit to equate the converter and describe the relationship between AC and DC current and voltage under the current working conditions; on the AC and DC sides, there is a set of variables obtained through measurement and a set of variables output by the controlled source. During the simulation process, the averaging model calculates the controlled source output on the other side through the measured values ​​on one side. Specifically, it is determined that the rectifier converter is equivalent to a controlled AC voltage source on the AC side and a controlled DC current source on the DC side. The measured quantities include AC current and DC voltage. It is necessary to establish the relationship between the various components of the AC voltage and the DC voltage, as well as the averaging equations between the various components of the AC current and the DC current. When an asymmetric fault occurs in the AC system, harmonic components will appear in the current and voltage on both sides of the AC and DC. Each harmonic component can be decomposed into positive and negative sequence symmetrical components. The voltage and current of the AC bus of the converter can be decomposed into components as shown in formula (2); Where: and Represent the DC components of the j-phase voltage and current respectively; and They represent the positive sequence components of the voltage and current of the j-phase n-order; and They represent the negative sequence components of the voltage and current of the j-phase nth order, respectively; j represents the a, b or c phase; Assume ω e is the angular velocity of the fundamental synchronous rotating coordinate system, then the instantaneous value expressions of each voltage and current component are: Where: k represents voltage v or current i; and Respectively represent the amplitudes of the positive and negative sequence components of the nth harmonic; and Respectively represent the phase angles of the positive and negative sequence components of the nth harmonic; The original three-phase AC signal components are converted into steady-state components of the dq axis in the synchronous coordinate system. The relationship between the AC voltage components and the DC voltage, and between the AC current components and the DC current of the controlled AC voltage source can be expressed as follows: 1) Relationship between controlled AC voltage source and DC voltage The parameter averaging equation between the positive sequence component of the AC voltage nth harmonic and the DC voltage is: Where: and They represent the d-axis and q-axis components of each positive sequence component of the AC voltage obtained by transforming the corresponding synchronous coordinate system; Represents the DC voltage on the rectifier side; for The angle with the d-axis; Similarly, the parameter averaging equation corresponding to the negative sequence component of the AC voltage is as follows: The parameter averaging equation corresponding to the DC bias component is as follows: Where: Represents the DC voltage on the rectifier side; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC voltage obtained by corresponding synchronous coordinate system transformation; for The angle with the d-axis; and They respectively represent the magnitude of the resultant vector of the DC component of the rectifier three-phase voltage after transformation through the stationary dq coordinate system and its angle with the d-axis; In the formula, Unknown algebraic functions used to describe the average behavior of the rectifier switching unit to characterize its dynamic characteristics and electrical relationships under different operating conditions; 2) Relationship between controlled DC current source and AC current The parameter averaging equation between the positive sequence and negative sequence components of the AC current and the DC current is as follows: Where: Represents the DC current on the rectifier side; in and They respectively represent the d-axis and q-axis components of the positive-sequence components of the rectifier AC current obtained by the corresponding synchronous coordinate system transformation; and They respectively represent the d-axis and q-axis components of the negative-sequence components of the rectifier AC current obtained by corresponding synchronous coordinate system transformation; In the formula, is a parameter that changes with the inverter firing angle and load conditions; By equivalently modeling the converter through averaging equations, electrical decoupling of the AC and DC sides can be achieved, and only secondary information such as voltage and current values ​​can be transmitted using controlled sources. The relationship between the current and voltage at the AC and DC ports of the converter is transformed from the original switching function representation to a set of parameterized algebraic equations. The parameters in these equations are usually described by unknown algebraic functions, which depend on the operating state of the system, including the trigger angle of the converter and the load condition. In order to accurately identify these algebraic functions, the present invention uses a multi-gate hybrid expert model (MMOE) to handle the nonlinear relationship in complex systems. MMOE is used to fit the voltage and current relationship under complex system states through multiple expert models, and the most suitable expert is dynamically selected through the gating network to handle the current state, so that the unknown algebraic function can be accurately obtained.

3. The efficient electromagnetic transient modeling method of a hybrid high voltage direct current transmission system containing IGCT according to claim 1, characterized in that: In step S2, In the structure of the receiving-end IGCT converter, the bridge arm is composed of multiple IGCT devices connected in series and protected by a buffer circuit. A single IGCT and its buffer circuit are regarded as a submodule. In electromagnetic transient simulation, the IGCT gate trigger is processed into a control signal. The switch-on condition is that the switch-on forward voltage is greater than or equal to 0, and the switch-off condition is that the switch-on forward current is less than or equal to 0. The IGCT is equivalent to a variable resistor R0, and the switch element is equivalent. The dynamic element capacitance is discretized using the trapezoidal method as follows: The differential dynamic equation of capacitance can be expressed as: Where C0 is the submodule capacitance, v C0 (t) is the voltage across the capacitor, i C0 (t) is the current flowing through the capacitor; the capacitor C0 is discretized, and a single IGC is equivalent, and the trapezoidal method is used to arrange equation (15) to obtain: v C0 (t)=R ceq0 i C0 (t)+v ceq0 (t-Δt) (16) Where Δt is the simulation step length, R ceq0 is the equivalent resistance of the discretized capacitor C0, v ceq0 (t-Δt) is the equivalent historical voltage source after the capacitor C0 is discretized, That is, after the capacitor is discretized, it can be equivalent to a resistor series voltage source; R smeq is the Thevenin equivalent resistance of the submodule, v smeq (t) is the Thevenin equivalent voltage source of the submodule, v SM (t) represents the voltage of each submodule port at the current moment, i SM (t) represents the current flowing through the submodule at the current moment; The six-pulse bridge of the converter has six bridge arms, each of which is obtained by connecting n submodules in series. The equivalent model of the bridge arm can be obtained by algebraic summation. is the Thevenin equivalent resistance of the bridge arm, is the Thevenin equivalent voltage source of the bridge arm; Convert Norton format, is the equivalent conductance of the bridge arm, is the Norton equivalent historical current source, v arm (t) represents the terminal voltage of the bridge arm at the current moment, i arm (t) represents the current flowing through the bridge arm at the current moment; Thus, the original multi-node network of the bridge arm is transformed into a two-node branch in which a resistor and a historical current source are connected in parallel.

4. The efficient electromagnetic transient modeling method of a hybrid high voltage direct current transmission system containing IGCT according to claim 1, characterized in that: In step S3, The line parameters of the Berelon model are calculated based on the power frequency of 50Hz. In the case of a single-phase lossless line, the inductance L1 and the capacitance C1 are set to be unit length; the voltage and current at point f on the transmission line at a distance x from the end m are functions of both distance and time; Assume that the voltage at time t is u(x, t) and the current is i(x, t); when the change of line parameters with frequency and the conductance per unit length are ignored, the following wave equation can be established: Rewritten as a second-order wave equation: The D'Alembert solution is: In the formula, u f (tx / v) is the forward voltage wave propagating in the positive direction, u b (t+x / v) is the reverse voltage wave propagating in the reverse direction, i f (tx / v) is the forward current wave propagating in the positive direction, i b (t+x / v) is the reverse current wave propagating in the reverse direction; is the propagation speed of the traveling wave along the line, and the wave impedance is Combining (19) and (20) and transforming them, we get (21) At the m and n ends of the line, x = 0 and x = l respectively, and let Substituting it into equation (21), we can get the relationship between the voltage and current at both ends of the line; u m (t-τ)+Z c i m (t-τ)=u n (t)-Z c i n (t) (22) By rearranging formula (22), we can obtain the port current expressed by wave impedance and equivalent current source: Among them, the corresponding equivalent current sources are: That is, the wave process in the distributed line parameter model can be represented by a lumped parameter model of wave impedance and equivalent current source, thereby constructing a two-port model of the transmission line; in this model, there is no direct physical connection between the two ports, but through the action of the current source, which is determined by the voltage and current at a previous moment. This method realizes the natural decoupling of the line. For actual transmission lines, the line resistance can be treated as a concentrated resistance and introduced in series in sections. The line with a length of l is divided into two sections, each section is l / 2 long, and a concentrated resistance R / 4 is connected in series at both ends, and a concentrated resistance R / 2 is connected in the middle section, where R is the resistance of the entire line length; an equivalent two-port network considering resistance loss is obtained; two half-split line models are obtained along the dotted line; where Port current: The corresponding equivalent current sources are: The two half-split lines are cascaded and simplified to obtain the Berelon transmission line model taking into account resistance losses.

5. An efficient electromagnetic transient modeling system for a hybrid high voltage direct current transmission system containing IGCT, characterized in that: The efficient electromagnetic transient modeling system applies the efficient electromagnetic transient modeling method of a hybrid high-voltage direct current power transmission system containing IGCT described in any one of claims 1 to 4 to perform efficient electromagnetic transient modeling.

6. A storage medium, characterized in that: The storage medium stores a computer program, which, when executed, executes the efficient electromagnetic transient modeling method for a hybrid high-voltage direct current power transmission system containing an IGCT according to any one of claims 1 to 4.

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