A VSC converter electromagnetic transient simulation method, system, device and medium

Abstract

The application discloses a VSC converter electromagnetic transient simulation method, system, device and medium, relates to the electromagnetic transient simulation field, and the method comprises the steps of constructing a single-phase bridge arm decoupling circuit based on the circuit topological structure of each single-phase bridge arm of a converter in a power grid; superimposing all single-phase bridge arm decoupling circuits into a three-phase decoupling circuit based on the superposition principle; constructing an AC side and a DC side two decoupling subsystems based on the three-phase decoupling circuit; transferring the switching state change of the converter to a controlled source based on the three-phase decoupling circuit to obtain a controlled source expression of the converter; controlling the controlled source transfer of the state variables of the AC side and the DC side of the converter in the three-phase decoupling circuit to the opposite side, and performing parallel simulation calculation on the two decoupling subsystems based on the equivalent duty ratio of the converter switching signal and the controlled source expression to obtain simulation results. The application solves the problem of the contradiction between the electromagnetic transient simulation precision and efficiency of the power system containing the VSC converter.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic transient simulation, and in particular to a method, system, device and medium for electromagnetic transient simulation of VSC converters. Background Technology

[0002] Currently, the proportion of clean energy in China's energy supply continues to rise. To support the large-scale development and utilization of clean energy, technologies such as new energy power generation and DC transmission have developed rapidly in recent years, leading to a continuous increase in the penetration rate of power electronic equipment in power systems. Voltage source converters (VSCs) have advantages such as improved energy efficiency and operational control flexibility, and are therefore widely used in new energy power systems. However, they also bring significant challenges to electromagnetic transient simulation technology, mainly in the following aspects:

[0003] 1) The single-unit capacity of power supply with power electronics as the interface is usually much smaller than that of traditional synchronous generator sets. They are also often connected in the form of distributed generation. Therefore, there are a large number of devices and they are widely distributed. Due to the voltage withstand capability of individual power electronic devices, cascaded topologies are often used in high-voltage scenarios, which complicates the circuit model. Describing each component in detail will cause the "curse of dimensionality" problem in simulation.

[0004] 2) The large-scale integration of power electronic equipment has exacerbated the rigidity and nonlinearity of the power system model, and has also transformed the system model into a complex system containing both continuous and discrete variables and multiple time-scale dynamic processes coupled together. This has made it necessary to use a smaller simulation step size to meet the accuracy requirements for electromagnetic transient simulation, which has greatly increased the computational burden.

[0005] Therefore, studying the modeling and simulation methods of VSC converters, and improving the simulation efficiency of VSC converter models while ensuring simulation accuracy, is of great significance for the electromagnetic transient simulation of new power systems.

[0006] The existing methods for electromagnetic transient simulation of VSC converters mainly include the following:

[0007] 1) The VSC converter is modeled using a detailed model. The detailed model models each power electronic device separately, retaining all control system and capacitor voltage calculation records of the converter. It has high calculation accuracy, but the admittance matrix is ​​time-varying and requires the configuration of various switching event processing algorithms. For example, the double interpolation method (DIM) is used to process switching events within the step size. The DIM algorithm is complex and will bring a large computational burden when there are many power electronic devices in the system, resulting in low simulation efficiency.

[0008] 2) The VSC converter is modeled using a switching function model. The switching function model introduces switching functions that characterize the switching states. Then, based on the main circuit topology under different switching states, circuit equations containing the switching functions are listed to realize device modeling. The model does not contain components representing switches, which improves simulation efficiency. However, it cannot describe the voltage and current characteristics of the switches inside the model.

[0009] 3) The VSC converter is modeled using an average value model. Based on the switching function model, the average value of the variable during the switching cycle is used instead of its actual value. It only needs to describe the power frequency characteristics of the device's input / output ports and ignores the high-order harmonics generated by pulse width modulation (PWM). Therefore, a larger simulation step size is allowed, and a significant improvement in simulation efficiency is achieved by sacrificing some accuracy.

[0010] 4) A semi-implicit decoupling model is used to model the VSC converter. This model starts from the system state equations and uses matrix splitting technology to group the system state variables. Different integral forms are then applied to the grouped variables to achieve decoupling between the state variables and improve simulation efficiency. However, it does not consider the switching actions of power electronic devices within a simulation step. When a switching event occurs between two time points, since the voltage value can only be updated at the end of the simulation step, the integrated current has accumulated errors, affecting the simulation accuracy.

[0011] The existing methods for electromagnetic transient simulation of VSC converters have the following main problems:

[0012] 1) Detailed model: Since the admittance matrix is ​​time-varying, the admittance matrix needs to be recalculated and LU re-decomposed after each switching action. In order to handle switching events within the step size, various switching event processing algorithms, such as DIM, need to be configured. The algorithm process is complex and the amount of computation is large, which seriously affects the simulation efficiency.

[0013] 2) The switching function model only describes the input / output characteristics of the external ports of the power electronic equipment and cannot describe the voltage and current characteristics of the internal switches; the average value model only describes the power frequency characteristics of the input / output ports of the equipment, and the simulation accuracy is very limited.

[0014] 3) The semi-implicit decoupling model is only an improvement on the model and does not take into account the switching events within a simulation step, which will lead to cumulative errors and affect the simulation accuracy.

[0015] In summary, how to improve simulation speed while ensuring simulation accuracy has become an urgent problem to be solved. Summary of the Invention

[0016] Based on this, embodiments of the present invention provide a method, system, device and medium for electromagnetic transient simulation of VSC converters, in order to solve the problem of the contradiction between the accuracy and efficiency of electromagnetic transient simulation of power systems containing VSC converters, and to improve the simulation speed while ensuring the simulation accuracy.

[0017] To achieve the above objectives, embodiments of the present invention provide the following solutions:

[0018] A method for electromagnetic transient simulation of a VSC converter includes:

[0019] Construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid;

[0020] Based on the superposition principle, all single-phase bridge arm decoupling circuits are superimposed into a three-phase decoupling circuit;

[0021] A first decoupling subsystem and a second decoupling subsystem are constructed based on the three-phase decoupling circuit. The first decoupling subsystem includes a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit. The second decoupling subsystem includes a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit.

[0022] Based on the three-phase decoupling circuit, the switching state changes of the converter are transferred to the controlled source, and the controlled source expression of the converter is obtained.

[0023] The AC and DC sides of the converter in the three-phase decoupling circuit are controlled to transmit their respective state variables to the controlled source on the opposite side. Based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source, the first decoupling subsystem and the second decoupling subsystem are simulated in parallel to obtain the simulation results.

[0024] The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

[0025] Optionally, parallel simulation calculations are performed on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the controlled source expression to obtain simulation results, specifically including:

[0026] For the current simulation time step, the switching signal for the current simulation time step is determined based on the modulation wave and the carrier wave;

[0027] If the switch signal of the current simulation time step is the same as the switch signal of the previous simulation time step, then the switch state of the current simulation time step is determined to be 0 or 1.

[0028] If the switching signal of the current simulation time step is different from the switching signal of the previous simulation time step, then the equivalent duty cycle of the switching signal in the current simulation time step is determined as the switching state of the current simulation time step.

[0029] Based on the switching state of the current simulation time step, the AC-side inductor current and the DC-side capacitor voltage of the previous simulation time step, calculate the controlled source parameters of the current simulation time step; the controlled source parameters include: the controlled voltage source on the AC side and the controlled current source on the DC side.

[0030] Kirchhoff's current law is used to calculate the node injection current of each node in the power grid based on the switching state and the controlled source parameters of the current simulation time step. Based on the node injection current, the electrical quantities of the first decoupled subsystem, the electrical quantities of the second decoupled subsystem, the AC side inductor current of the converter, and the DC side capacitor voltage of the converter are determined at the current simulation time step.

[0031] Determine whether the simulation end time of the current simulation time step has reached the set maximum simulation time.

[0032] If the target is not reached, proceed with the simulation calculation for the next simulation time step; otherwise, terminate the simulation calculation.

[0033] Optionally, the simulation results may also include the output-side voltage of the converter at each simulation time step.

[0034] Optionally, after employing Kirchhoff's current law to calculate the node injection current of each node in the power grid based on the switching state and controlled source parameters of the current simulation time step, and determining the electrical quantities of the first decoupled subsystem, the second decoupled subsystem, the AC-side inductor current of the converter, and the DC-side capacitor voltage of the converter at the current simulation time step based on the node injection current, the method further includes:

[0035] When the equivalent duty cycle of the switching signal in the current simulation time step is determined as the switching state of the current simulation time step, the controlled voltage source on the AC side of the current simulation time step is recalculated based on the new switching state of the current simulation time step and the DC side capacitor voltage of the previous simulation time step, so as to obtain the updated controlled voltage source; the new switching state is the value of the switching state being 0 or 1.

[0036] The output voltage of the converter at the current simulation time step is determined based on the updated controlled voltage source.

[0037] Optionally, the controlled source expression is:

[0038]

[0039] Among them, VeqA This indicates the controlled voltage source for phase A on the AC side; V eqB This indicates the controlled voltage source of phase B on the AC side; V eqC This indicates a controlled voltage source for phase C on the AC side; J eq1 J represents the controlled current source of the upper arm in the DC-side bridge arm; eq2 S represents the controlled current source of the lower arm in the DC-side bridge arm. ap This indicates the switching state of the upper arm in the A-phase bridge arm of the converter; S an Indicates the switching status of the lower arm in phase A of the converter; S bp This indicates the switching state of the upper arm in the B-phase bridge arm of the converter; S bn Indicates the switching status of the lower arm in phase B of the converter; S cp This indicates the switching state of the upper arm in the C-phase bridge arm of the converter; S cn Indicates the switching state of the lower arm in the C-phase bridge arm of the converter; i a Indicates the current of phase A on the AC side; i b Indicates the current in phase B of the AC side; i c Indicates the C-phase current on the AC side; u c1 The capacitor voltage of the upper arm in the DC-side bridge arm; u c2 This represents the capacitor voltage of the lower arm in the DC-side bridge arm.

[0040] Optionally, the formula for calculating the equivalent duty cycle of the converter switching signal is:

[0041]

[0042] in, Indicates the equivalent duty cycle; sin represents the sine wave function, carr represents the triangular carrier wave function; ω is the angular velocity; t n-2 Indicates the start time of the simulation time step; t n-1 This indicates the end time of the simulation time step; min indicates taking the minimum value, and abs indicates taking the absolute value.

[0043] Optionally, a single-phase bridge arm decoupling circuit is constructed based on the circuit topology of each single-phase bridge arm of the converter in the power grid, specifically including:

[0044] Determine the circuit topology of each single-phase bridge arm of the converter in the power grid;

[0045] For any single-phase bridge arm circuit topology, the IGBT anti-parallel diode structure in the single-phase bridge arm circuit topology is equivalent to a switch, thus obtaining the equivalent circuit of the single-phase bridge arm.

[0046] The state equation of a single-phase bridge arm is determined based on its equivalent circuit.

[0047] The state equations are converted into matrix form and the switching functions are separated to obtain the state matrix of a single-phase bridge arm.

[0048] Based on the semi-implicit decoupling principle, the state matrix of a single-phase bridge arm is discretized to obtain the state discrete matrix of the single-phase bridge arm.

[0049] The decoupling circuit of a single-phase bridge arm is determined based on the state discrete matrix of the single-phase bridge arm.

[0050] This invention also provides an electromagnetic transient simulation system for a VSC converter, comprising:

[0051] A single-phase decoupling circuit determination module is used to construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid.

[0052] The three-phase decoupling circuit determination module is used to superimpose all single-phase bridge arm decoupling circuits into a three-phase decoupling circuit based on the superposition principle.

[0053] A decoupling subsystem construction module is used to construct a first decoupling subsystem and a second decoupling subsystem based on the three-phase decoupling circuit; the first decoupling subsystem includes: a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit; the second decoupling subsystem includes: a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit;

[0054] The controlled source construction module is used to transfer the switching state changes of the converter to the controlled source based on the three-phase decoupling circuit, so as to obtain the controlled source expression of the converter.

[0055] The converter simulation module is used to control the AC and DC sides of the converter in the three-phase decoupling circuit to transmit their own state variables to the controlled source on the opposite side, and to perform parallel simulation calculations on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source to obtain simulation results;

[0056] The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

[0057] The present invention also provides an electronic device, including a memory and a processor, wherein the memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to perform the above-described electromagnetic transient simulation method for VSC converters.

[0058] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described electromagnetic transient simulation method for VSC converters.

[0059] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0060] This invention constructs a single-phase bridge arm decoupling circuit to obtain a three-phase decoupling circuit. It controls the AC and DC sides of the converter in the three-phase decoupling circuit to transmit their respective state variables to the controlled source on the opposite side. Based on the equivalent duty cycle of the converter switching signals and the expression of the controlled source, parallel simulation calculations are performed on the two decoupling subsystems, achieving parallel calculations on the DC and AC sides of the converter and improving computational efficiency. Furthermore, by considering switching events within the simulation step size using the equivalent duty cycle of the converter switching signals, computational accuracy is improved. Therefore, this invention solves the problem of the contradiction between accuracy and efficiency in electromagnetic transient simulation of power systems with VSC converters, achieving the goal of improving simulation speed while ensuring simulation accuracy. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0062] Figure 1 A flowchart of the electromagnetic transient simulation method for VSC converters provided in this embodiment of the invention;

[0063] Figure 2 The circuit topology of a single-phase bridge arm and its equivalent circuit diagram are provided for embodiments of the present invention.

[0064] Figure 3 This is a structural diagram of a single-phase bridge arm decoupling circuit provided in an embodiment of the present invention;

[0065] Figure 4 This is a structural diagram of a three-phase decoupling circuit provided in an embodiment of the present invention;

[0066] Figure 5 This is a schematic diagram of the computation timing provided in an embodiment of the present invention;

[0067] Figure 6 A schematic diagram illustrating the interpolation method for determining the switching timing provided in an embodiment of the present invention;

[0068] Figure 7 This is a specific implementation process diagram of the electromagnetic transient simulation method for VSC converters provided in an embodiment of the present invention;

[0069] Figure 8 The diagram shows the structure of the VSC converter electromagnetic transient simulation system provided in this embodiment of the invention. Detailed Implementation

[0070] The technical solutions of the present invention will now be described with reference to the accompanying drawings in the embodiments of the present invention.

[0071] The purpose of this invention is to provide a method, system, device and medium for electromagnetic transient simulation of VSC converters. The VSC converter is modeled using a decoupled model, and the duty cycle of the switching function within the step size is equalized to replace DIM, thereby improving the simulation speed while ensuring simulation accuracy.

[0072] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0073] Example 1

[0074] See Figure 1 The electromagnetic transient simulation method for VSC converters in this embodiment is based on the equivalent duty cycle of the switching function. This method specifically includes:

[0075] Step 101: Construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid.

[0076] Step 101 specifically includes:

[0077] (11) Determine the circuit topology of each single-phase bridge arm of the converter in the power grid.

[0078] Specifically, considering the mutually exclusive conduction characteristics of the upper and lower bridge arms of a bridge switching circuit, and the relatively stable DC voltage, with no interference between the three-phase bridge arms, the circuit can be decoupled into three single-phase circuits. The superposition theorem can then be used to obtain the complete three-phase circuit. The topology of a single-phase bridge arm is as follows: Figure 2 As shown in part (a).

[0079] (12) For any single-phase bridge arm circuit topology, the IGBT anti-parallel diode structure in the single-phase bridge arm circuit topology is equivalent to a switch to obtain the equivalent circuit of the single-phase bridge arm.

[0080] Specifically, will Figure 2 The IGBT anti-parallel diode structure in the circuit topology shown in part (a) is equivalent to a switch, resulting in... Figure 2 The equivalent circuit shown in part (b).

[0081] (13) Determine the state equation of a single-phase bridge arm based on the equivalent circuit of the single-phase bridge arm.

[0082] Specifically, root Figure 2Write the state equations for the equivalent circuit shown in part (b), and let S... ap and S an Represents the switching state of the upper and lower bridge arms of phase A. When S ap and S an When the value is 1, the on-resistance R on =0.005Ω; S ap and S an When the value is 0, the shut-off resistor R is turned off. off = 1e6Ω; Bridge arm equivalent resistance R on R off / (R on +R off It can be approximated as R on The state equations for a single-phase bridge arm, with inductor current and capacitor voltage as state variables, are as follows:

[0083]

[0084] t represents time, u a Where L is the AC side voltage of the converter, C1 and C2 are the AC side inductance, and i is the DC side capacitor. a For phase A AC side current, u c1 u c2 i is the DC-side capacitor voltage. d1 i d2 This is the DC side current.

[0085] (14) Convert the state equation into a matrix form and separate the switching function to obtain the state matrix of a single-phase bridge arm.

[0086] Specifically, it is approximately assumed that 1 / (R) on +R off If ) is 0, the above state equations are written in matrix form, and the switching function matrix is ​​separated. The expression for the state matrix of a single-phase bridge arm is as follows:

[0087]

[0088] (15) Based on the semi-implicit decoupling principle, the state matrix of a single-phase bridge arm is discretized to obtain the state discrete matrix of the single-phase bridge arm.

[0089] Specifically, observing the state matrix of a single-phase bridge arm reveals that its admittance matrix is ​​a definite admittance matrix, and the changes in the switching states are all reflected in the switching function matrix S. Based on the semi-implicit decoupling principle, the first half of the right-hand side of the expression for the state matrix of a single-phase bridge arm... Discretization is performed using the trapezoidal integral method, and the latter half... Discretization using the forward Euler method yields the following expression for the state discrete matrix of a single-phase bridge arm:

[0090]

[0091] In the formula, Δt is the simulation time step, n represents the nth step of the simulation, the superscript n indicates the value of the variable at time n*Δt, and L, C1, C2, R on All are constants.

[0092] (16) Determine the single-phase bridge arm decoupling circuit based on the state discrete matrix of the single-phase bridge arm. Finally, the three single-phase bridge arm decoupling circuits of phase A, phase B and phase C can be superimposed to form a three-phase decoupling circuit.

[0093] The decoupling circuit for a single-phase bridge arm of the VSC can be obtained from the state discrete matrix of the single-phase bridge arm, such as... Figure 3 As shown, where: V eq =-S ap u c1 -S an u c2 J eq1 =S ap i a J eq2 =S an i a V eq J represents the controlled voltage source on the AC side. eq1 J eq2 This represents the controlled current source on the DC side. Changes in the switching state are transferred to the controlled source. This decoupling circuit achieves parallel computation on both the AC and DC sides by mutually transmitting state variables to the controlled source on the other side, thus improving simulation efficiency.

[0094] Step 102: Based on the superposition principle, all single-phase bridge arm decoupling circuits are superimposed into a three-phase decoupling circuit. The structure of the three-phase decoupling circuit is as follows: Figure 4 As shown.

[0095] Step 103: Construct a first decoupling subsystem and a second decoupling subsystem based on the three-phase decoupling circuit.

[0096] The first decoupling subsystem includes a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit; the second decoupling subsystem includes a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit.

[0097] Step 104: Based on the three-phase decoupling circuit, the switching state changes of the converter are transferred to the controlled source, thus obtaining the controlled source expression of the converter. The controlled source expression is:

[0098]

[0099] Among them, V eqA This indicates the controlled voltage source for phase A on the AC side; V eqB This indicates the controlled voltage source of phase B on the AC side; V eqC This indicates a controlled voltage source for phase C on the AC side; J eq1 J represents the controlled current source of the upper arm in the DC-side bridge arm; eq2 S represents the controlled current source of the lower arm in the DC-side bridge arm. ap This indicates the switching state of the upper arm in the A-phase bridge arm of the converter; S an Indicates the switching status of the lower arm in phase A of the converter; S bp This indicates the switching state of the upper arm in the B-phase bridge arm of the converter; S bn Indicates the switching status of the lower arm in phase B of the converter; S cp This indicates the switching state of the upper arm in the C-phase bridge arm of the converter; S cn Indicates the switching state of the lower arm in the C-phase bridge arm of the converter; i a Indicates the current of phase A on the AC side; i b Indicates the current in phase B of the AC side; i c Indicates the C-phase current on the AC side; u c1 The capacitor voltage of the upper arm in the DC-side bridge arm; u c2 This represents the capacitor voltage of the lower arm in the DC-side bridge arm.

[0100] As can be seen from the above controlled source expression, the VSC decoupling model transfers the switching state changes in the circuit to the controlled sources. By mutually transferring the state variables of their respective sides to the controlled sources on the other side, parallel calculations on the AC and DC sides are achieved, improving simulation efficiency. Furthermore, since the controlled sources in the model are related to the switching state S... p,n The function can leverage this characteristic to further approximate the area of ​​the duty cycle of the switching function within a simulation step, thereby improving simulation accuracy. The subsequent circuit solution steps can be designed based on these advantages.

[0101] Step 105: Control the AC and DC sides of the converter in the three-phase decoupling circuit to transmit their respective state variables to the controlled source on the opposite side, and perform parallel simulation calculations on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source to obtain simulation results.

[0102] The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

[0103] The state variables include AC-side inductor current and DC-side capacitor voltage. The AC and DC sides of the converter in the three-phase decoupling circuit are controlled to transmit their respective state variables to the controlled source on the opposite side. That is, the AC side of the converter in the three-phase decoupling circuit is controlled to provide inductor current to the DC side and the DC side is controlled to provide capacitor voltage to the AC side.

[0104] Step 105 specifically includes:

[0105] (51) For the current simulation time step, determine the switching signal of the current simulation time step based on the modulation wave and the carrier wave.

[0106] (52) If the switch signal of the current simulation time step is the same as the switch signal of the previous simulation time step, then the switch state of the current simulation time step is determined to be 0 or 1.

[0107] If the switch signal of the current simulation time step is different from the switch signal of the previous simulation time step, then the equivalent duty cycle of the switch signal in the current simulation time step is determined as the switch state of the current simulation time step.

[0108] In addition, during the first simulation time step, the initial switch state is treated as off, i.e., the value is 0.

[0109] The following section describes the specific process for determining the equivalent duty cycle of the converter switching signal.

[0110] Based on the characteristics of the VSC decoupling circuit, this model can be used to divide the large system into subnets during large-scale simulations of new power systems. Each subnet can be solved separately, allowing for parallel computation and improving simulation efficiency. The state variables after grouping are decoupled in one step, with no separation of step sizes between subsystems. The calculation timing is as follows: Figure 5 As shown.

[0111] To obtain the average value of the switching signal within a step size, the precise timing of the switching action is needed. Based on the principle of triangle similarity, the specific moment of the switching event is located. This method approximates the modulation wave at time t. n-1 The value of time and t fall The values ​​at time t are equal. n+2 The value of time and t rise The values ​​at time points are equal, the principle is as follows: Figure 6 As shown. (t) fall For example, time Figure 6 In the middle, t fall The switching signal changes from 1 to 0 at any given moment, h is the difference between the two steps before and after the carrier wave, Δt is the simulation step size, and S ref As the reference value for the switching signal, according to the approximation condition, h1 = sin(ωt) n-1 )-carr(t n-2), sin represents the sine function, carr is the trigonometric carrier function, ω is the angular velocity, and Δt1 and t can be obtained from h1 / h=Δt1 / Δt. n+2 +Δt1 represents the specific moment of the switch action, while the ratio of Δt1 to Δt is the equivalent area of ​​the switch signal, i.e., the equivalent duty cycle of the switch function within the step size.

[0112] Among them, t n-2 ~t n-1 Taking this simulation time step as an example, when a switching event occurs within this step, the formula for calculating the equivalent duty cycle of the converter switching signal in this simulation time step is:

[0113]

[0114] in, Indicates the equivalent duty cycle; sin represents the sine wave function, carr represents the triangular carrier wave function; ω is the angular velocity; t n-2 Indicates the start time of the simulation time step; t n-1 This indicates the end time of the simulation time step; min indicates taking the minimum value, and abs indicates taking the absolute value.

[0115] (53) Calculate the controlled source parameters of the current simulation time step based on the switching state of the current simulation time step, the AC side inductor current and the DC side capacitor voltage of the previous simulation time step; the controlled source parameters include: the controlled voltage source on the AC side and the controlled current source on the DC side.

[0116] In addition, in the first simulation time step, the inductor current and capacitor voltage are both 0 at the initial moment, and the switch state is also 0.

[0117] (54) Using Kirchhoff's current law, calculate the node injection current of each node in the power grid based on the switching state and the controlled source parameters of the current simulation time step, and determine the electrical quantities of the first decoupled subsystem, the electrical quantities of the second decoupled subsystem, the AC side inductor current of the converter, and the DC side capacitor voltage of the converter under the current simulation time step based on the node injection current.

[0118] (55) Determine whether the simulation end time of the current simulation time step has reached the set maximum simulation time. If not, proceed with the simulation calculation for the next simulation time step; otherwise, end the simulation calculation.

[0119] In one example, due to the use of an equivalent duty cycle calculation circuit for the switching signal, the converter outlet voltage is calculated to be between -U at the step tail of the switching event. dc / 2 to U dc A number between / 2, U dcThis is the DC side voltage of the converter, which does not match the actual situation. Since the switching event occurs within the step size, the switch is already in the on or off state at the end of the step size. Therefore, after calculating the state variables using the equivalent duty cycle of the switching function, the converter output voltage should be updated with the new switching state while keeping the state variables unchanged, so that its value is always -U. dc / 2 or U dc / 2.

[0120] Therefore, the simulation results also include the output-side voltage of the converter at each simulation time step.

[0121] In this example, after step (55) above, the following is also included:

[0122] (56) When the equivalent duty cycle of the switch signal in the current simulation time step is determined as the switch state of the current simulation time step, the controlled voltage source of the AC side of the current simulation time step is recalculated based on the new switch state of the current simulation time step and the DC side capacitor voltage of the previous simulation time step to obtain the updated controlled voltage source; the new switch state is the value of the switch state being 0 or 1.

[0123] (57) Determine the output voltage of the converter at the current simulation time step based on the updated controlled voltage source.

[0124] The VSC electromagnetic transient simulation method in this embodiment firstly derives the VSC decoupling model from the VSC state equation, enabling parallel computation of the DC and AC sides of the converter and improving computational efficiency. Secondly, by equivalencing the duty cycle of the switching function within a simulation step, the switching events within the simulation step are considered, avoiding the interpolation backoff operation of the DIM algorithm, thus ensuring simulation accuracy while improving simulation efficiency.

[0125] Specifically, based on the VSC decoupling model, the switching function is further area-equivalent to obtain its equivalent duty cycle within the step size, ensuring simulation accuracy while avoiding interpolation backoff and other operations, thus improving simulation speed.

[0126] The equivalent duty cycle of the switching function within the step size is calculated using the interpolation method, which is simple, effective, and easy to implement. Furthermore, the equivalent duty cycle of the switching function can be obtained before the first system solution, making the proposed method theoretically applicable to real-time simulation of converters.

[0127] After calculating the state variables using the equivalent duty cycle of the switching function, the converter output voltage was updated with new switching states while keeping the state variables unchanged, making the calculation results closer to the actual situation.

[0128] The following section presents a more detailed implementation process of the electromagnetic transient simulation method for VSC converters, aiming to simulate electrical quantities, AC-side inductor current, DC-side capacitor voltage, and converter outlet voltage.

[0129] Based on the characteristics of the VSC decoupling circuit, the power grid can be divided into subgrids; based on the principle of triangle similarity, the equivalent duty cycle of the switching function within the step size can be obtained; by updating the converter output voltage with a new switching state while keeping the state variables unchanged, a result that is more consistent with the actual situation can be obtained.

[0130] See Figure 7 The steps of the electromagnetic transient simulation method for the VSC converter designed in this way are as follows:

[0131] Step 1: Locate the position of the VSC converter in the power grid, and treat the VSC converter as equivalent to... Figure 4 The decoupling circuit shown has subsystems A and B connected to the AC and DC sides of the VSC, respectively. Based on the characteristics of the VSC decoupling circuit, the original power grid can be divided into two decoupled subsystems: a decoupled subsystem containing A and the AC side of the VSC, and a decoupled subsystem containing B and the DC side of the VSC. The electrical quantities of the two subsystems can be calculated in parallel without separating the step size, thus improving simulation efficiency.

[0132] Step 2: Obtain the switching signal by comparing the modulated wave and the carrier wave. Compare the switching signal of the current step with the switching signal of the previous step. If they are the same, no switching event has occurred within the step size. Taking phase A as an example, when the sine wave sin is greater than the triangular carrier wave carr, the switching function S... ap Take 1, otherwise S ap Set S to 0 an =1-S ap Similarly, B and C are used for the calculation of the controlled source in step three.

[0133] If they are different, it indicates that a switching event has occurred within this step. The equivalent duty cycle of the switching signal within the step is calculated using the formula for calculating the equivalent duty cycle of the converter switching signal. Taking phase A as an example again This is a number between 0 and 1 calculated using the formula for the equivalent duty cycle of the converter switching signal. Similarly, B and C are equivalent, and the equivalent switching function is used for the calculation of the controlled source in step three.

[0134] Step 3: Transfer the AC-side inductor current and DC-side capacitor voltage calculated in the previous step to the other side, and calculate the current time-step controlled source (V) according to the controlled source expression. eq J eq The value of ).

[0135] Step 4: Calculate the KCL equation YU=I, where Y is the admittance matrix of each subsystem, U is the node voltage of each node in the system, and I is the node injection current of each node. This will give you the branch electrical quantities of subsystems A and B, as well as the AC side inductor current and DC side capacitor voltage of the VSC converter.

[0136] Step 5: If S = 0 to 1, update the converter output voltage with the new switching state while keeping the state variables unchanged, and then advance the time grid forward by Δt; otherwise, advance the time grid forward by Δt directly.

[0137] Step 6: Determine if the current simulation time is less than the simulation duration. If so, return to Step 2 and perform the next round of calculations until the simulation ends.

[0138] Based on the VSC decoupling model, the above method uses a counter to find the switching action time and calculates the equivalent duty cycle of the switching function within a simulation step, thus taking into account the action of the power electronic device within the step and avoiding interpolation backoff processing. This greatly simplifies the calculation process and improves the simulation speed while maintaining good accuracy.

[0139] Example 2

[0140] In order to implement the method corresponding to Embodiment 1 above and achieve the corresponding functions and technical effects, a VSC converter electromagnetic transient simulation system is provided below.

[0141] See Figure 8 The system includes:

[0142] The single-phase decoupling circuit determination module 201 is used to construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid.

[0143] The three-phase decoupling circuit determination module 202 is used to superimpose all single-phase bridge arm decoupling circuits into a three-phase decoupling circuit based on the superposition principle.

[0144] The decoupling subsystem construction module 203 is used to construct a first decoupling subsystem and a second decoupling subsystem based on the three-phase decoupling circuit; the first decoupling subsystem includes: a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit; the second decoupling subsystem includes: a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit.

[0145] The controlled source construction module 204 is used to transfer the switching state changes of the converter to the controlled source based on the three-phase decoupling circuit, so as to obtain the controlled source expression of the converter.

[0146] The converter simulation module 205 is used to control the AC and DC sides of the converter in the three-phase decoupling circuit to transmit their respective state variables to the controlled source on the opposite side, and to perform parallel simulation calculations on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source, so as to obtain the simulation results.

[0147] The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

[0148] Example 3

[0149] This embodiment provides an electronic device, including a memory and a processor. The memory is used to store computer programs, and the processor runs the computer programs to enable the electronic device to execute the VSC converter electromagnetic transient simulation method of Embodiment 1.

[0150] Alternatively, the aforementioned electronic device may be a server.

[0151] In addition, this embodiment of the invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the electromagnetic transient simulation method for VSC converters in Embodiment 1.

[0152] All of the above embodiments have the following advantages:

[0153] (1) Equivalent duty cycle of the switching function avoids the steps of backtracking to the exact action time after the switching action, interpolating back to the original time grid after calculating the state variables, thus greatly simplifying the calculation process and improving simulation efficiency. Furthermore, the equivalent duty cycle of the switching function can be obtained before the first system solution, making the proposed method theoretically applicable to real-time simulation of converters.

[0154] (2) Generally, the switching period is 10 times the simulation step size. The above embodiment considers the equivalent duty cycle of the switching function within one simulation step size and uses its equivalent area within the step size for calculation. Therefore, compared with the average value model based on the switching period, the proposed model of this invention has a 10-fold wider bandwidth, which allows harmonics close to the switching frequency to appear in the spectrum analysis, greatly improving the simulation accuracy.

[0155] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0156] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for electromagnetic transient simulation of a VSC converter, characterized in that, include: Construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid; Based on the superposition principle, all single-phase bridge arm decoupling circuits are superimposed into a three-phase decoupling circuit; A first decoupling subsystem and a second decoupling subsystem are constructed based on the three-phase decoupling circuit. The first decoupling subsystem includes: a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit; the second decoupling subsystem includes: a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit; Based on the three-phase decoupling circuit, the switching state changes of the converter are transferred to the controlled source, and the controlled source expression of the converter is obtained. The AC and DC sides of the converter in the three-phase decoupling circuit are controlled to transmit their respective state variables to the controlled source on the opposite side. Based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source, the first decoupling subsystem and the second decoupling subsystem are simulated in parallel to obtain the simulation results. The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

2. The electromagnetic transient simulation method for VSC converters according to claim 1, characterized in that, Parallel simulation calculations are performed on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source, and the simulation results are obtained, specifically including: For the current simulation time step, the switching signal for the current simulation time step is determined based on the modulation wave and the carrier wave; If the switch signal of the current simulation time step is the same as the switch signal of the previous simulation time step, then the switch state of the current simulation time step is determined to be 0 or 1. If the switching signal of the current simulation time step is different from the switching signal of the previous simulation time step, then the equivalent duty cycle of the switching signal in the current simulation time step is determined as the switching state of the current simulation time step. Based on the switching state of the current simulation time step, the AC-side inductor current and the DC-side capacitor voltage of the previous simulation time step, calculate the controlled source parameters of the current simulation time step; the controlled source parameters include: the controlled voltage source on the AC side and the controlled current source on the DC side. Kirchhoff's current law is used to calculate the node injection current of each node in the power grid based on the switching state and the controlled source parameters of the current simulation time step. Based on the node injection current, the electrical quantities of the first decoupled subsystem, the electrical quantities of the second decoupled subsystem, the AC side inductor current of the converter, and the DC side capacitor voltage of the converter are determined at the current simulation time step. Determine whether the simulation end time of the current simulation time step has reached the set maximum simulation time. If the target is not reached, proceed with the simulation calculation for the next simulation time step; otherwise, terminate the simulation calculation.

3. The electromagnetic transient simulation method for VSC converters according to claim 2, characterized in that, The simulation results also include the output-side voltage of the converter at each simulation time step.

4. The electromagnetic transient simulation method for VSC converters according to claim 3, characterized in that, After applying Kirchhoff's current law, calculating the node injection current at each node in the power grid based on the switching states and controlled source parameters at the current simulation time step, and determining the electrical quantities of the first decoupled subsystem, the second decoupled subsystem, the AC-side inductor current of the converter, and the DC-side capacitor voltage of the converter at the current simulation time step based on the node injection current, the following steps are also included: When the equivalent duty cycle of the switching signal in the current simulation time step is determined as the switching state of the current simulation time step, the controlled voltage source on the AC side of the current simulation time step is recalculated based on the new switching state of the current simulation time step and the DC side capacitor voltage of the previous simulation time step, so as to obtain the updated controlled voltage source; the new switching state is the value of the switching state being 0 or 1. The output voltage of the converter at the current simulation time step is determined based on the updated controlled voltage source.

5. The electromagnetic transient simulation method for VSC converters according to claim 1, characterized in that, The controlled source expression is: Among them, V eqA This indicates the controlled voltage source for phase A on the AC side; V eqB This indicates the controlled voltage source of phase B on the AC side; V eqC This indicates a controlled voltage source for phase C on the AC side; J eq1 J represents the controlled current source in the upper arm of the DC-side bridge arm; eq2 S represents the controlled current source of the lower arm in the DC-side bridge arm. ap This indicates the switching state of the upper arm in the A-phase bridge arm of the converter; S an Indicates the switching status of the lower arm in phase A of the converter; S bp This indicates the switching state of the upper arm in the B-phase bridge arm of the converter; S bn Indicates the switching status of the lower arm in phase B of the converter; S cp This indicates the switching state of the upper arm in the C-phase bridge arm of the converter; S cn Indicates the switching state of the lower arm in the C-phase bridge arm of the converter; i a Indicates the current of phase A on the AC side; i b Indicates the current in phase B of the AC side; i c Indicates the C-phase current on the AC side; u c1 The capacitor voltage of the upper arm in the DC-side bridge arm; u c2 This represents the capacitor voltage of the lower arm in the DC-side bridge arm.

6. The electromagnetic transient simulation method for VSC converters according to claim 1, characterized in that, The formula for calculating the equivalent duty cycle of the converter switching signal is: in, Indicates the equivalent duty cycle; sin represents the sine wave function, carr represents the triangular carrier wave function; ω is the angular velocity; t n-2 Indicates the start time of the simulation time step; t n-1 This indicates the end time of the simulation time step; min indicates taking the minimum value, and abs indicates taking the absolute value.

7. The electromagnetic transient simulation method for VSC converters according to claim 1, characterized in that, Based on the circuit topology of each single-phase bridge arm of the converter in the power grid, a single-phase bridge arm decoupling circuit is constructed, specifically including: Determine the circuit topology of each single-phase bridge arm of the converter in the power grid; For any single-phase bridge arm circuit topology, the IGBT anti-parallel diode structure in the single-phase bridge arm circuit topology is equivalent to a switch, thus obtaining the equivalent circuit of the single-phase bridge arm. The state equation of a single-phase bridge arm is determined based on its equivalent circuit. The state equations are converted into matrix form and the switching functions are separated to obtain the state matrix of a single-phase bridge arm. Based on the semi-implicit decoupling principle, the state matrix of a single-phase bridge arm is discretized to obtain the state discrete matrix of the single-phase bridge arm. The decoupling circuit of a single-phase bridge arm is determined based on the state discrete matrix of the single-phase bridge arm.

8. An electromagnetic transient simulation system for a VSC converter, characterized in that, include: A single-phase decoupling circuit determination module is used to construct a single-phase bridge arm decoupling circuit based on the circuit topology of each single-phase bridge arm of the converter in the power grid. The three-phase decoupling circuit determination module is used to superimpose all single-phase bridge arm decoupling circuits into a three-phase decoupling circuit based on the superposition principle. A decoupling subsystem construction module is used to construct a first decoupling subsystem and a second decoupling subsystem based on the three-phase decoupling circuit. The first decoupling subsystem includes: a subsystem connected to the AC side of the converter and the AC side portion of the converter in the three-phase decoupling circuit; the second decoupling subsystem includes: a subsystem connected to the DC side of the converter and the DC side portion of the converter in the three-phase decoupling circuit; The controlled source construction module is used to transfer the switching state changes of the converter to the controlled source based on the three-phase decoupling circuit, so as to obtain the controlled source expression of the converter. The converter simulation module is used to control the AC and DC sides of the converter in the three-phase decoupling circuit to transmit their own state variables to the controlled source on the opposite side, and to perform parallel simulation calculations on the first decoupling subsystem and the second decoupling subsystem based on the equivalent duty cycle of the converter switching signal and the expression of the controlled source to obtain simulation results; The simulation results include: simulation data of the converter at each simulation time step; the simulation data includes: electrical quantities, AC side inductor current and DC side capacitor voltage.

9. An electronic device, characterized in that, The device includes a memory and a processor, the memory being used to store a computer program, and the processor running the computer program to cause the electronic device to perform the VSC converter electromagnetic transient simulation method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed by a processor, implements the VSC converter electromagnetic transient simulation method as described in any one of claims 1 to 7.

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