A multi-port converter electromagnetic transient modeling and simulation method

Abstract

The application discloses a multi-port converter electromagnetic transient modeling and simulation method, and belongs to the field of multi-port converters. The method establishes a switch function discretization equivalent circuit of each single-phase converter, increases or decreases the number of corresponding sub-circuits according to the number of external ports in the converter, and determines a Norton equivalent model of a multi-port converter to be studied. Based on the discretization equivalent circuit, the values of elements in an external port equivalent node admittance matrix and the values of elements of a current matrix injected by internal historical current sources into external port nodes are directly updated according to the parameters of the switch function equivalent circuit in different working modes of the circuit, without the need of matrix operation. The application solves the problems of fast modeling and efficient solving of the multi-port Norton equivalent of the converter.

Description

Technical Field

[0001] This invention relates to the field of multi-port converters, and in particular to a method for electromagnetic transient modeling and simulation of multi-port converters. Background Technology

[0002] Profound changes are taking place in the power system field, and the electromagnetic transient characteristics of power systems are becoming increasingly complex. Accurate modeling and detailed, rapid electromagnetic transient simulation analysis of relevant power system components can provide a precise understanding of the dynamic characteristics of the power system, offering crucial assistance for its planning, design, construction, development, and operation.

[0003] With the continuous advancement of power system construction, the number of new energy power plants is increasing, resulting in a large number of voltage source converters, which brings new challenges to the electromagnetic transient simulation of power systems.

[0004] With the continuous expansion of AC and DC power grids, the requirements for the speed and accuracy of electromagnetic transient simulation are constantly increasing. Power system electromagnetic transient simulation faces the following challenges:

[0005] 1) Expanding Power Grid Scale. Existing numerical algorithms for electromagnetic transient simulation, whether employing the state-space method or the nodal voltage method, ultimately require solving a system of linear algebraic equations. The computational complexity is typically exponentially related to the order of the equations, causing the simulation speed to drop drastically and become unacceptable as the system size increases. Currently, AC / DC hybrid power grids are massive, with numerous devices and a total of nearly 30,000 simulation nodes. Directly applying existing numerical algorithms to such a large-scale system presents the challenge of solving extremely high-order linear algebraic equations. Therefore, it is necessary to research efficient computational methods that achieve a relationship between computational complexity and system size that is less than or approximately linear.

[0006] 2) Complex Equipment Characteristics. With the increasing research and in-depth analysis of various linear and nonlinear models of converters, new energy power plants, complex control systems, and cyber-physical systems, researchers using electromagnetic transient simulation as a tool face increasingly complex and diverse research objects and objectives. More complex power electronic devices have emerged, exhibiting varying performance, frequent switching operations, and time-varying and nonlinear characteristics. The computational efficiency of their models directly affects the speed of electromagnetic transient simulation across the entire power grid. Therefore, it is necessary to research computationally efficient modeling theories or methods for power electronic devices.

[0007] 3) More diverse topologies. With in-depth research into energy transfer, power electronic devices often need to adopt multi-stage and / or multi-port structures to meet multidirectional flow requirements. Series or parallel connections are often used to link ports and conversion stages, and the electro-magnetic coupling between ports and conversion stages is tight, resulting in more complex and diverse device topologies. Therefore, a universal modeling method is needed to unify different topologies.

[0008] Electromagnetic transient simulation needs to be both accurate and fast. However, the changes mentioned above have made the contradiction between accuracy and speed in voltage source converter simulation more prominent. Existing methods are no longer applicable, and there is an urgent need to improve or propose new methods.

[0009] Existing offline simulation acceleration models for electromagnetic transients of voltage source converters all strive to achieve a trade-off between the accuracy of detailed models and simulation efficiency. Existing voltage source converter models can be broadly classified into three categories:

[0010] (1) Detailed Model

[0011] It retains all control system and capacitor voltage calculation records of the converter, which can be used to analyze internal anomalies of the converter, such as harmonic analysis. However, because the detailed model retains the complete topology of the converter, the computational load is large, making it unsuitable for the analysis of large systems. It is often used as a reference model to test other improved models.

[0012] Detailed models, due to consideration of the transient behavior of semiconductor switches, require solving a large number of electrical nodes, as well as a fast algorithm for solving nonlinear switching events. Furthermore, the computational method must be capable of solving "rigid" differential equations, resulting in a long overall computation time. They are mainly used to verify other simplified equivalent models and are not suitable for simulation modeling of large-scale power systems.

[0013] (2) Dynamic phasor model

[0014] The dynamic phasor model uses phasor description, and its essence is to transform the high-frequency changing instantaneous value model represented by the switching function in electromagnetic transient simulation into a dynamic phasor model described by a slowly varying analytic signal through a certain transformation method. The dynamic phasor model can be solved using either the state-space method or the nodal analysis method.

[0015] In theory, when sufficient order is considered, the dynamic phasor method can approach the accuracy of a detailed model. However, in practical applications, as the system size increases, the computational speed decreases due to limitations in the hardware capabilities of the computing platform, leading to an increase in the order of the equations.

[0016] (3) Multi-port equivalent model

[0017] The multi-port equivalent model employs a nested approach to implement a two-layer simulation strategy for both the system and the equipment. At the system level, the converter is performed as a whole in the simulation of the entire system through multi-port equivalent modeling. After the system-level simulation is completed and the port characteristics are obtained, the equipment-level simulation is then performed to calculate the internal characteristics of the converter, update historical current sources, and determine the port admittance matrix for the next time step.

[0018] The process of obtaining port characteristics by performing external port equivalence calculations and full system solutions for the converter at the system level, as well as the process of inversely solving its internal characteristics at the device level, both involve matrix operations. Extensive matrix operations can lead to low solution efficiency, especially when the system is complex, resulting in even lower simulation efficiency. Furthermore, this method also uses matrix operations to form the nodal admittance matrix, failing to utilize the physical nature of the circuit for process simplification and speed-up.

[0019] In summary, the main drawbacks of existing technologies are:

[0020] In the context of large-scale power grids, electromagnetic transient simulation of voltage source converters presents a dilemma between achieving both accuracy and computational efficiency. Summary of the Invention

[0021] The purpose of this invention is to provide a method for electromagnetic transient modeling and simulation of multi-port converters, which can solve the problems of rapid modeling and efficient solution of multi-port Norton equivalent converters.

[0022] To achieve the above objectives, the present invention provides the following solution:

[0023] A method for electromagnetic transient modeling and simulation of multi-port converters includes:

[0024] Construct the binary resistor equivalent circuit for each single-phase converter in the multi-port converter to be studied;

[0025] Based on the state equation in the form of conductance corresponding to the binary resistor equivalent circuit, the switching function equivalent circuit of each single-phase converter in the multi-port converter under study is obtained, and the parameters of the switching function equivalent circuit are defined.

[0026] Discretize the equivalent circuit of the switching function of each single-phase converter to obtain the discretized equivalent circuit of the switching function of each single-phase converter, and define the discretized parameters.

[0027] Based on the discretized equivalent circuit of the switching function of each single-phase converter, the Norton equivalent model of the multi-port converter under study is determined; wherein, the Norton equivalent model includes the external port equivalent node admittance matrix, the current matrix of the internal historical current source injected into the external port node, and the voltage matrix of the external port node; the elements in the external port equivalent node admittance matrix and the elements in the current matrix of the internal historical current source injected into the external port node are all represented by the parameters of the switching function equivalent circuit of the single-phase converter;

[0028] Simulations are performed on the multi-port converter under study to determine its current operating mode.

[0029] If the current operating mode is determined to be a normal state, a locked state under forward charging, or a locked state under reverse charging, then the parameter values ​​of the equivalent circuit of the switching function are updated according to the parameter switching state combination corresponding to the current operating mode in the switching state table of the multi-port converter under study.

[0030] Based on the updated parameter values ​​of the equivalent circuit of the switching function, update the values ​​of the elements in the admittance matrix of the external port equivalent node and the values ​​of the elements in the current matrix of the internal historical current source injected into the external port node to obtain the simplified Norton equivalent model.

[0031] Based on the simplified Norton equivalent model, solve for the voltage matrix of the external port node at the current moment;

[0032] Based on the voltage matrix of the external port nodes at the current moment, update the discretized parameter values ​​in the discretized equivalent circuit of the switching function of the multi-port converter under study;

[0033] If the current operating mode is determined to be a latched state under high impedance, the parameter values ​​of the equivalent circuit of the switching function are calculated and updated according to the calculated parameter values ​​of the equivalent circuit of the switching function. At the same time, the process returns to the step "update the values ​​of the elements in the admittance matrix of the external port equivalent node and the values ​​of the elements in the current matrix of the internal historical current source injected into the external port node according to the updated parameter values ​​of the equivalent circuit of the switching function, and obtain the simplified Norton equivalent model".

[0034] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0035] This invention discloses an electromagnetic transient modeling and simulation method for multi-port converters. Based on the principle that inductor branches in a converter cannot be short-circuited and capacitor branches cannot be open-circuited, the equivalent circuit corresponding to the original converter is obtained. This method is applicable not only to half-bridge, H-bridge, VSC, LCC, T-type, and NPC-type three-level converters, but also to any multi-port voltage source converter. When the number of external ports in the converter changes, only the corresponding sub-circuits need to be added or removed in the equivalent circuit, achieving rapid multi-port Norton equivalent modeling of the converter. Based on the discretized equivalent circuit, the parameters of the corresponding switching function equivalent circuit are obtained according to different operating modes of the circuit. The values ​​of elements in the external port equivalent node admittance matrix and the values ​​of elements in the current matrix injected into the external port nodes by internal historical current sources are directly updated without matrix operations, thus improving computational efficiency. Attached Figure Description

[0036] 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.

[0037] Figure 1 A flowchart illustrating an electromagnetic transient modeling and simulation method for a multi-port converter, provided in an embodiment of the present invention;

[0038] Figure 2 This is a circuit diagram of an arbitrary multi-port voltage source converter provided in an embodiment of the present invention;

[0039] Figure 3 Equivalent circuit diagram of a binary resistor bridge arm provided in an embodiment of the present invention;

[0040] Figure 4 Equivalent circuit diagram of the switching function provided in the embodiments of the present invention;

[0041] Figure 5 The discrete equivalent circuit diagram provided in the embodiments of the present invention;

[0042] Figure 6 The equivalent circuit diagram of the unit voltage source at node P provided in the embodiments of the present invention;

[0043] Figure 7 Historical current source I provided for embodiments of the present invention hisL Equivalent circuit diagram for single-function operation;

[0044] Figure 8 A simulation flowchart provided for embodiments of the present invention;

[0045] Figure 9A two-level half-bridge circuit diagram provided for an embodiment of the present invention;

[0046] Figure 10 This is a two-level LCC circuit diagram provided in an embodiment of the present invention;

[0047] Figure 11 A T-type three-level circuit diagram provided for an embodiment of the present invention;

[0048] Figure 12 The NPC three-level circuit diagram provided for embodiments of the present invention. Detailed Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] With the continuous advancement of power system construction, the number of new energy power plants is increasing, leading to a large number of voltage source converters, which poses new challenges to the electromagnetic transient simulation of power systems. Existing voltage source converter models, such as detailed models, while highly accurate, are computationally intensive, slow in simulation speed, and inefficient, making them unsuitable for the analysis of large-scale systems.

[0051] This invention proposes a general and efficient method for electromagnetic transient modeling and simulation of voltage source converters, which mainly solves the problem of rapid modeling and efficient solution of multi-port Norton equivalent converters.

[0052] 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.

[0053] The converter topology modeled in this invention features three voltage levels on the DC side and a multi-phase AC side, with each phase branch connected to an inductor. For this type of converter, a suitable topology can be developed. Figure 2 Let L1~L2 represent the topology of any multi-port converter module. n T is the port inductance when the AC side of the converter is connected to an external system. n-1 ~T n-m This represents the m switch groups in the nth branch. The combination of these switch groups varies depending on the converter. For a two-level VSC, the switch group consists of an IGBT and a VD connected in anti-parallel. For an LCC, the switch group consists of a thyristor. C1 and C2 are the DC-side port capacitors of the converter. For an LCC, the DC side does not contain port capacitors C1 and C2, so they are represented by dashed lines.a1 ~u an i is the AC side node voltage of the converter. a1 ~i an For the AC side node current of the converter, u P u O u N i is the DC-side node voltage of the converter. P i O i N This represents the DC-side node current of the converter. Different values ​​of n in this converter can represent converters with different numbers of AC-side ports.

[0054] like Figure 1 As shown, this embodiment of the invention provides a method for electromagnetic transient modeling and simulation of a multi-port converter, including:

[0055] Step 1: Construct the binary resistor equivalent circuit for each single-phase converter in the multi-port converter to be studied.

[0056] Let's take phase a1 as an example first. Figure 2 The equivalent of any multiport converter shown is applied. Figure 2 Each switch group uses a binary resistor model (resistance value is R when on). on =0.01Ω, resistance is R when turned off off =1MΩ), we can get Figure 3 The equivalent circuit shown is shown.

[0057] Figure 3 a in 1in For the internal node of port module a1, R P R N R O These are the equivalent resistors for P, N, and O voltage levels, respectively, R. PO R NO These are the equivalent resistances between the PO and NO ports, respectively. Some simpler converters do not have this equivalent resistance R. O R PO R NO Therefore, a dashed line is used to illustrate the diagram. For example, a two-level VSC and LCC converter only contains R. P R N Similar LCC converters do not have port capacitors C1 and C2, and are also represented by dashed lines. The specific values ​​of these equivalent resistors can be obtained from the physical meaning of the mutual admittance in the nodal admittance matrix elements. Let R... P For example, first, all historical current sources are opened; second, node P in the network is connected to a unit voltage source, and all other nodes are short-circuited to ground. Then, based on the current flowing into node a... 1in The value of the current can be used to obtain a. 1in The mutual admittance between node Y and node PP The specific value.

[0058] Step 2: Based on the state equation in the conductance form corresponding to the binary resistor equivalent circuit, obtain the switching function equivalent circuit of each single-phase converter in the multi-port converter under study, and define the parameters of the switching function equivalent circuit.

[0059] Taking a single-phase example again, with inductor current and DC-side node voltage as state variables, for Figure 3 Write the state equations in conductance form for the equivalent circuit of the binary resistive bridge arm of the single-phase converter shown:

[0060]

[0061] In equation (1), L is the equivalent port inductance when the AC side is connected to an external system, and i L R is the current flowing through the inductor on the AC side. eq S is the equivalent resistance on the AC side. P S N S O These are the switching functions on the three bridge arms on the DC side, V P V N V O The voltages I at external port nodes P, N, and O are respectively. P I N I O The currents at external port nodes P, N, and O are represented by V. A Let G be the external port voltage of phase a, C1 and C2 be the two capacitors on the DC side, and G be the voltage of phase a. eqPN G eqPO G eqNO These are the admittances between nodes P and N, between nodes P and O, and between nodes N and O, respectively.

[0062] The equivalent circuit of the corresponding switching function can be obtained from the state equation, such as... Figure 4 The switching function model is shown below. Figure 4 The switching function model, for U in AC measurement eq Essentially, it is an equivalent voltage source where the node voltage on the DC side affects the AC side, and the J on the DC side... eq Essentially, they are equivalent current sources that affect the DC side from the AC measuring port current. Therefore, they are neither voltage sources nor current sources in the original equivalent circuit. eq and J eq The effects of these equivalent power sources cannot be ignored in calculations and cannot be treated as short-circuited or open-circuited.

[0063] Figure 4 The relevant parameters are defined as follows:

[0064]

[0065] In the parameter definition, S P S N S O These are the switching functions on the three bridge arms, respectively.

[0066] In equation (2), R P R N R O These are the equivalent resistances corresponding to the voltage levels at nodes P, N, and O, respectively. P For a in The mutual admittance between node P and node Y N For a in The mutual admittance between node N and node Y O For a in The mutual admittance between node O and node R PO R NO The equivalent resistances between ports PO and NO are respectively, Y PO Y NO Y represents the mutual admittance between nodes P, N, and O, respectively. eq For the equivalent admittance on the AC side, U eq V represents the equivalent voltage source matrix that represents the influence of the DC-side node voltage on the AC side. P V N V O These are the voltage matrices for external port nodes P, N, and O, respectively. eqP J eqN J eqO These are the equivalent current source matrices representing the influence of the AC-side port current on DC-side nodes P, N, and O, respectively. L This is the current matrix flowing through the inductor on the AC side.

[0067] Step 3: Discretize the equivalent circuit of the switching function of each single-phase converter to obtain the discretized equivalent circuit of the switching function of each single-phase converter, and define the discretized parameters.

[0068] The specific process of discretization is as follows:

[0069] The trapezoidal method is used to discretize the inductance on the AC side of the equivalent circuit of the switching function of each single-phase converter into the form of a resistor connected in parallel with the historical current source. Similarly, the capacitor on the DC side is discretized into the form of a resistor connected in parallel with the historical current source, thus obtaining the discretized equivalent circuit of the switching function of each single-phase converter.

[0070] like Figure 5 As shown, the discretized parameters are defined as follows:

[0071]

[0072] In equation (3), R L I hisL These represent the discretized resistance and historical current source of the inductor on the AC side, R. C1 I hisC1 These represent the resistance and historical current source corresponding to the discretized DC-side capacitor C1, R. C2 I hisC2 These represent the discretized resistance and historical current source of the DC-side capacitor C2, respectively. Δt is the time step, and the superscript n indicates n branches. C1 i C2 These are the currents flowing into the DC-side capacitors C1 and C2, respectively, V a1 The voltage at external port node a1, u in This refers to the internal node voltage.

[0073] Step 4: Based on the discretized equivalent circuit of the switching function of each single-phase converter, determine the Norton equivalent model of the multi-port converter under study; wherein, the Norton equivalent model includes the external port equivalent node admittance matrix, the current matrix of the internal historical current source injected into the external port node, and the voltage matrix of the external port node; the elements in the external port equivalent node admittance matrix and the elements in the current matrix of the internal historical current source injected into the external port node are all represented by the parameters of the switching function equivalent circuit of the single-phase converter.

[0074] The modeling method used in this invention is essentially a holistic modeling method for converters. For a converter with n-phase branches on the AC side, if it is connected to the system as a holistic model, its equivalent model is shown in equation (3):

[0075]

[0076] Where I is the current matrix of the external port nodes of the converter, with dimension (n+3), U is the voltage matrix of the external port nodes of the converter, with dimension (n+3), and G is the equivalent node admittance matrix of the external port of the converter, with dimension (n+3)×(n+3). his The current matrix represents the historical current sources inside the converter injected into the external port nodes (in this invention, the outflow ports are positive), with a dimension of (n+3). The superscript t indicates time t, and the superscript t-1 indicates time t-1.

[0077] This invention first takes a single phase as an example to obtain the equivalent model of a single phase, and then further obtains the equivalent model of an n-phase phase. Equation (4) can be decomposed into the following form to form the element values ​​of the correlation matrix and column vector:

[0078]

[0079] Among them G C This represents the self-admittance and mutual admittance generated by the interaction of the DC-side capacitor branches. G i Indicates the AC side endpoint a i Self-admittance and mutual admittance in relation to the DC-side terminals P, N, and O. hisC This represents the current injected into each node from the historical current sources generated by all capacitor branches on the DC side. hisi This represents the current injected into each node from the historical current source generated by the AC-side inductor branch.

[0080] For example, the process of constructing the voltage matrix of the external port node is as follows:

[0081] By connecting any one node on the AC side of each single-phase converter to a unit voltage source, and short-circuiting and grounding the remaining nodes on the AC side while opening the historical current source, expressions for the AC side current and the DC side current flowing through each node in each single-phase converter are obtained. Based on the principle that in each single-phase converter, the mutual admittance between the node connected to the unit voltage source on the DC side and the AC side is taken as the value of the AC side current, the self-admittance of the node connected to the unit voltage source on the DC side is taken as the value of the current flowing through itself, and the mutual admittance between the node connected to the unit voltage source on the DC side and the other nodes is taken as the value of the current flowing through the other nodes, the expressions for the self-admittance of the node connected to the unit voltage source on the DC side, the mutual admittance between the node connected to the unit voltage source on the DC side and the other nodes, and the current expressions for the self-admittance and mutual admittance of the interaction between the AC side endpoint and the DC side node in all single-phase converters are added to the external port equivalent node admittance matrix.

[0082] The process of constructing the current matrix of internal historical current sources injected into external port nodes is as follows:

[0083] The historical current sources of each phase inductor are discretized and applied individually. The historical current sources are open-circuited and all AC-side nodes are short-circuited to ground. The current expressions for the historical current sources generated by all capacitor branches on the DC side of each single-phase converter and injected into each node, as well as the current expressions for the historical current sources generated by the inductor branches on the AC side, are obtained. These expressions are then added to the current matrix of the internal historical current sources injected into the external port nodes.

[0084] Depend on Figure 5 The equivalent model obtained by discretizing the switching function of a single-phase converter is as follows:

[0085]

[0086] For the nodal admittance matrix G:

[0087] by Figure 5 Taking node P connected to a unit voltage source as an example, all other nodes are short-circuited to ground and their historical current sources are open-circuited. eq and J eq Excluding the equivalent power source, we can obtain Figure 6 The equivalent circuit of the node unit voltage source is shown.

[0088] Depend on Figure 6 The following relationships can be identified:

[0089]

[0090] The mutual admittance between the DC-side node P and the AC-side phase a1 is the current i L The values ​​can be directly obtained from the AC-side equivalent circuit. The self-admittance of the P-node and the mutual admittance of the N and O nodes on the DC side are the current i. P i N i O The value can be obtained directly from the DC-side equivalent circuit. When the converter is n-phase, the node admittance matrix G can be expanded to (n+3)×(n+3) dimensions, where the elements of the i-phase AC side are added to the i-row and i-column of the matrix, and the elements of the DC side (the 3×3 matrix in the lower right corner) are directly added together, as shown in the above formula (5).

[0091] For historical item I his :

[0092] Taking the discrete historical current source of phase a1 inductor as an example, its open-circuit treatment (U) eq and J eq (excluding the equivalent power source) and short-circuiting all nodes to ground, we can obtain: Figure 7 The historical current source I shown hisL Equivalent circuit for standalone operation.

[0093] Depend on Figure 7 The following relationships can be identified:

[0094]

[0095] Therefore, the current i flowing through nodes a1, P, N, and O L i P i N i O (The current in this invention is positive at the outflow port). When the converter is n-phase, historical item I can be used. his The vector is expanded to (n+3) dimensions, where the elements of the i-th phase of the AC side are added to the i-th row of the vector, and the elements of the DC side (the last 3 rows) are directly added together, as shown in the above formula (5).

[0096] Internal node voltage u in :

[0097] The corresponding formulas for calculating internal nodes are as follows.

[0098] u in =u ain +u Pin +u Nin +u Oin +u Lhisin +u C1hisin +u C2hisin (8)

[0099] in:

[0100]

[0101]

[0102] In the formula, u in Let u be the internal node voltage. Different voltages on the right side of the equation are indicated by subscripts when different power sources act alone. a1 I is the external port voltage of phase a1. Lhist This represents the historical current flowing through the inductor.

[0103] The equivalent model of the switching function is defined because the switching function S is defined. P S N S O Its essence is a physical expression composed of the binary resistor model of the bridge arm switch. Therefore, it can more accurately and universally describe the operating state of the switching device and reflect all operating conditions of the converter (normal operation, lockout or internal fault).

[0104] Step 5: Simulate the multi-port converter under study to determine its current operating mode.

[0105] If we consider R off →∞, and apply it to the analytical expression of the switching function model parameters. The parameters R of the equivalent model can be obtained according to the switching state combinations. eq G eq S, U eq J eq Simplification is performed to further improve computational efficiency. Converters can be divided into normal (unlocked) and locked states according to their operating conditions. The parameter simplification of the equivalent models for both states is described below.

[0106] Under normal conditions:

[0107] When the converter is operating in normal condition (unlocked), according to the principle that the inductor branch cannot be open-circuited and the capacitor branch cannot be short-circuited, there must be a path from the AC side to the DC side. Therefore, the parameter G can be simplified. eq R is 0 eq For R on or R on The multiples (depending on the switching conduction status of the converter under normal conditions) are such that only one of the switching functions S is 1, and the rest are 0. Therefore, when updating the topology due to switching actions, it is not necessary to recalculate the equivalent resistance R of all resistors in the binary resistor equivalent circuit; the parameters of the corresponding equivalent model can be quickly updated according to the switching state combination. The multiples are integer multiples.

[0108] In the locked state:

[0109] When the converter is in the latch-up state, all IGBTs are turned off. Based on the current direction, the states are divided into forward charging, reverse charging, and high resistance. The parameter values ​​in the forward charging and reverse charging states are the same as those in the normal operating state. Only the parameters of the corresponding equivalent model need to be updated according to the switching state combination.

[0110] This invention lists simplified parameters of the equivalent circuits of the switching functions of single-phase modules with two-level VSC, LCC, T-type three-level, and NPC-type three-level switching functions in normal and locked states. See Tables 1-4 below for circuit examples, where "1" represents switch group T. k Conduction.

[0111] Figure 8 The simulation process is as follows:

[0112] Step 6: If the current operating mode is determined to be a normal state, a latched state under forward charging, or a latched state under reverse charging, then update the parameter values ​​of the equivalent circuit of the switching function according to the parameter switching state combination corresponding to the current operating mode in the switching state table of the multi-port converter under study.

[0113] The switch status table includes: the status of each switch group, and the equivalent resistance R on the AC side. eq The value of G, the admittance eq The values ​​of , the weights of the switching function S, and the equivalent voltage source U that affects the DC-side node voltage on the AC side. eq The value of J and the equivalent current source J that affects the AC measuring port current on the DC side. eq The value of i and L The value of .

[0114] Step 7: Based on the updated parameter values ​​of the equivalent circuit of the switching function, update the values ​​of the elements in the admittance matrix of the external port equivalent nodes and the values ​​of the elements in the current matrix of the internal historical current sources injected into the external port nodes to obtain the simplified Norton equivalent model.

[0115] Step 8: Solve for the voltage matrix of the external port node at the current moment based on the simplified Norton equivalent model.

[0116] Step 9: Update the discretized parameter values ​​in the discretized equivalent circuit of the switching function of the multi-port converter under study based on the voltage matrix of the external port node at the current moment.

[0117] The specific process is as follows:

[0118] Based on the voltage matrix of the external port nodes at the current moment, the voltage of the internal nodes at the current moment is calculated using the formula for calculating the voltage of the internal nodes; based on the voltage matrix of the external port nodes at the current moment and the voltage of the internal nodes at the current moment, the formula is used to calculate the voltage of the internal nodes at the current moment. Update the parameter values ​​of the discretized equivalent circuit of the switching function of the multi-port converter under study.

[0119] Step 10: If the current operating mode is determined to be a latch-up state under high impedance, calculate the parameter values ​​of the equivalent circuit of the switching function, update the parameter values ​​of the equivalent circuit of the switching function according to the calculated parameter values, and return to step "update the values ​​of the elements in the admittance matrix of the external port equivalent node and the values ​​of the elements in the current matrix of the internal historical current source injected into the external port node according to the updated parameter values ​​of the equivalent circuit of the switching function to obtain the simplified Norton equivalent model".

[0120] Figure 8 The condition for the simulation to end is that the simulation time reaches the preset simulation duration.

[0121] Examples of applications of the above methods:

[0122] ① Half-bridge circuit

[0123] Figure 9 Part (a) in the diagram represents the topology of a half-bridge circuit. Figure 9 Part (b) in the diagram represents the binary resistor equivalent circuit of the half-bridge circuit. Figure 9 Part (c) in the diagram represents the equivalent circuit of the switching function of the half-bridge circuit.

[0124] T1 and T2 represent the switching groups consisting of IGBTs and diodes in the upper and lower bridge arms, respectively, and R1 and R2 represent the binary resistors of switching groups T1 and T2, respectively. For a half-bridge two-level circuit, R... P =R1,R N =R². Because R O RPO and R NO The branch is essentially an open circuit, so G is ignored. eq13 G eq23 and J eq3 .

[0125] Table 1 Half-bridge circuit switching status table

[0126]

[0127] ②LCC two-level circuit

[0128] Figure 10 Part (a) in the diagram represents the topology of a two-level LCC circuit. Figure 10 Part (b) in the diagram represents the binary resistor equivalent circuit of the LCC two-level circuit. Figure 10 Part (c) in the diagram represents the equivalent circuit of the switching function of the two-level LCC circuit.

[0129] T1 and T2 represent the thyristors of the upper and lower bridge arms, respectively, and R1 and R2 represent the binary resistors of the switching groups T1 and T2, respectively. For the LCC two-level circuit, R... P =R1,R N =R². Because R O R PO and R NO The branch is essentially an open circuit, so G is ignored. eq13 G eq23 and J eq3 .

[0130] Table 2 LCC Circuit Switch Status Table

[0131]

[0132] ③ T-type three-level circuit

[0133] Figure 11 Part (a) in the diagram represents the topology of a T-type three-level circuit. Figure 11 Part (b) in the diagram represents the binary resistor equivalent circuit of the T-type three-level circuit. Figure 11 Part (c) in the diagram represents the equivalent circuit of the switching function of a T-type three-level circuit.

[0134] T1, T2, T3, and T4 represent the switching groups consisting of three bridge arms IGBTs and diodes, respectively, and R1, R2, R3, and R4 represent the binary resistors of the corresponding switching groups. PO and R NO The branch is essentially an open circuit, so R is ignored. PO and R NO .

[0135] Table 3. Switch Status Table for Type T Three-Level Circuit

[0136]

[0137] ④NPC three-level circuit

[0138] Figure 12 Part (a) in the diagram represents the topology of the NPC three-level circuit. Figure 12 Part (b) in the diagram represents the binary resistor equivalent circuit of the NPC three-level circuit. Figure 12 Part (c) in the diagram represents the equivalent circuit of the switching function of the NPC three-level circuit.

[0139] T1, T2, T3, and T4 represent the IGBTs of the three bridge arms, D1, D2, D3, D4, D5, and D6 represent the diodes of the three bridge arms, and R1, R2, R3, R4, R5, and R6 represent the binary resistors of the corresponding switch groups.

[0140] Table 4. Switch Status Table for NPC Three-Level Circuit

[0141]

[0142]

[0143] The key points and areas to be protected in this invention are:

[0144] 1. Equivalent circuit of the converter

[0145] The original converter circuit is equivalently transformed to obtain the switching function equivalent circuit, forming several equivalent sub-circuits with separate AC and DC sides. When the number of external ports in the converter changes, only the number of corresponding sub-circuits needs to be added or removed. The switching function S is defined, which is essentially a physical expression composed of the binary resistor model of the bridge arm switches. Therefore, it can more accurately and universally describe the operating state of the switching devices and reflect all operating conditions of the converter (normal operation, lockout, or internal fault), providing a theoretical basis for the efficient calculation of related elements in the subsequent equivalent model.

[0146] 2. Obtain the nodal admittance matrix G and the history term I from the physical meaning of the equivalent circuit. his Method

[0147] Based on the discretized equivalent circuit, the parameters of the corresponding switching function equivalent circuit are obtained according to different operating modes of the circuit. By substituting the parameters of the equivalent circuit into the formula, the values ​​of the corresponding elements are updated. This allows direct acquisition of the nodal admittance matrix G and the history term I. his The corresponding element value can be obtained without matrix operations.

[0148] 3. Simplify parameters using the converter switching table.

[0149] By using the switch combinations of the converter under different operating conditions and the selected trapezoidal integration method, the corresponding switch state table is obtained. Under different operating conditions, the relevant elements of the equivalent model can be directly modified based on the switch state table, without the need for matrix internal node elimination operations, resulting in high computational efficiency.

[0150] 4. When the number of ports changes, quickly generate a new node admittance matrix G. t and historical items Method

[0151] When the number of external port branches in the converter changes, the dimension of the matrix is ​​directly increased or decreased, and the elements at the corresponding positions in the matrix are changed. The new node admittance matrix G is then quickly obtained by accumulation. t and historical items

[0152] The advantages of this invention are:

[0153] 1. The equivalent circuit is simple, and the model has good versatility and scalability.

[0154] This invention, based on the principle that inductor branches in a converter cannot be short-circuited and capacitor branches cannot be open-circuited, derives an equivalent circuit corresponding to the original converter. This circuit is applicable not only to half-bridge, H-bridge, VSC, LCC, T-type, and NPC-type three-level converters, but also to any multi-port voltage source converter. Because it is based on the working principle of the converter, the resulting equivalent circuit is both simple in form and versatile. When the number of external ports in the converter changes, only the corresponding sub-circuits need to be added or removed in the equivalent circuit, and the node admittance matrix G... t and historical items In this method, you only need to change the dimension and add the corresponding variables at the appropriate positions, which has good scalability.

[0155] 2. Nodal admittance matrix G t and historical items The physical meaning is clear, concise and efficient.

[0156] According to the present invention, the nodal admittance matrix G can be directly obtained from the physical meaning of the equivalent circuit diagram. t and historical items The corresponding element values ​​are then simplified using switch combinations and corresponding discretization methods, resulting in the node admittance matrix G. t and historical items The solution process is concise and efficient, and the physical meaning is clear.

[0157] 3. Fast calculation speed

[0158] This invention simplifies the modeling method, eliminating the need for matrix operations, and allows for the rapid deriving of the nodal admittance matrix G using a general formula. tand historical items The values ​​of can be directly obtained from the physical meaning of the equivalent circuit diagram in each simulation calculation step, including the nodal admittance matrix G and the historical term I. his The corresponding element values ​​are obtained directly without matrix operations, thus achieving a speed-up effect. Then, simplification is achieved through switch state combinations and corresponding discretization methods, making the node admittance matrix G and the historical term I... his The solution process is concise and efficient, and the physical meaning is clear.

[0159] Terminology Explanation:

[0160] Half-bridge (HB)

[0161] H-bridge

[0162] Voltage source converter (VSC)

[0163] LCC Two-Level Model (Line-commuted Converter, LCC)

[0164] NPC Three-Level Inverter (VSC) Model

[0165] T-type three-level inverter (VSC) model

[0166] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0167] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this 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 this invention.

Claims

1. A method for electromagnetic transient modeling and simulation of a multi-port converter, characterized in that, include: Construct the binary resistor equivalent circuit for each single-phase converter in the multi-port converter to be studied; Based on the state equation in the form of conductance corresponding to the binary resistor equivalent circuit, the switching function equivalent circuit of each single-phase converter in the multi-port converter under study is obtained, and the parameters of the switching function equivalent circuit are defined. Discretize the equivalent circuit of the switching function of each single-phase converter to obtain the discretized equivalent circuit of the switching function of each single-phase converter, and define the discretized parameters. Based on the discretized equivalent circuit of the switching function of each single-phase converter, the Norton equivalent model of the multi-port converter under study is determined; wherein, the Norton equivalent model includes the external port equivalent node admittance matrix, the current matrix of the internal historical current source injected into the external port node, and the voltage matrix of the external port node; the elements in the external port equivalent node admittance matrix and the elements in the current matrix of the internal historical current source injected into the external port node are all represented by the parameters of the switching function equivalent circuit of the single-phase converter; Simulations are performed on the multi-port converter under study to determine its current operating mode. If the current operating mode is determined to be a normal state, a locked state under forward charging, or a locked state under reverse charging, then the parameter values ​​of the equivalent circuit of the switching function are updated according to the parameter switching state combination corresponding to the current operating mode in the switching state table of the multi-port converter under study. Based on the updated parameter values ​​of the equivalent circuit of the switching function, update the values ​​of the elements in the admittance matrix of the external port equivalent node and the values ​​of the elements in the current matrix of the internal historical current source injected into the external port node to obtain the simplified Norton equivalent model. Based on the simplified Norton equivalent model, solve for the voltage matrix of the external port node at the current moment; Based on the voltage matrix of the external port nodes at the current moment, update the discretized parameter values ​​in the discretized equivalent circuit of the switching function of the multi-port converter under study; If the current operating mode is determined to be a latch-up state under high impedance, the parameter values ​​of the equivalent circuit of the switching function are calculated and updated according to the calculated parameter values ​​of the equivalent circuit of the switching function. At the same time, the process returns to the step "Update the values ​​of the elements in the admittance matrix of the external port equivalent node and the values ​​of the elements in the current matrix of the internal historical current source injected into the external port node according to the updated parameter values ​​of the equivalent circuit of the switching function, and obtain the simplified Norton equivalent model".

2. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 1, characterized in that, The state equation in the form of conductivity is: ； In the formula, L This is the equivalent port inductance when the AC side is connected to an external system. i L For the current flowing through the inductor on the AC side, R eq This is the equivalent resistance on the AC side. S P , S N , S O These are the switching functions on the three bridge arms on the DC side. V P , V N , V O These represent the voltages at external port nodes P, N, and O, respectively. I P , I N , I O Let P be the current at external port nodes P, N, and O, respectively. V A Let be the external port voltage of phase a. C 1. C 2 are two capacitors on the DC side, G eqPN , G eqPO , G eqNO These are the admittances between node P and node N, between node P and node O, and between node N and node O, respectively.

3. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 2, characterized in that, The parameters of the equivalent circuit of the defined switching function are: ； In the formula, R P , R N , R O These are the equivalent resistances corresponding to the voltage levels at nodes P, N, and O, respectively. Y P For a in Mutual admittance between node P and node P Y N For a in The mutual admittance between node N and node N Y O For a in Mutual admittance between node O and node O R PO , R NO Equivalent resistors between ports PO and NO, respectively. ，Y PO , Y NO Let P, N, and O be the mutual admittances between nodes P, N, and O, respectively. Y eq For the equivalent admittance on the exchange side, This represents the equivalent voltage source matrix that shows the influence of the node voltage on the DC side on the AC side. , , These are the voltage matrices for external port nodes P, N, and O, respectively. , , These are the equivalent current source matrices representing the effects of the AC-side port current on DC-side nodes P, N, and O. This is the current matrix flowing through the inductor on the AC side.

4. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 3, characterized in that, Discretize the equivalent circuit of the switching function of each single-phase converter to obtain the discretized equivalent circuit of the switching function of each single-phase converter, and define the discretized parameters, specifically including: The trapezoidal method is used to discretize the inductance on the AC side of the equivalent circuit of the switching function of each single-phase converter into the form of a resistor connected in parallel with the historical current source. Similarly, the capacitor on the DC side is discretized into the form of a resistor connected in parallel with the historical current source, thus obtaining the discretized equivalent circuit of the switching function of each single-phase converter. Define the discretized parameters as follows In the formula, R L , I hisL These represent the discretized resistance of the inductor on the AC side and the historical current source, respectively. R C1 , I hisC1 These represent the resistance and historical current source corresponding to the discretized DC-side capacitor C1. R C2 , I hisC2 These represent the resistance and historical current source corresponding to the discretized DC-side capacitor C2, respectively. Δt is the time step, and the superscript n indicates the nth branch. i C1 , i C2 These are the currents flowing into the DC-side capacitors C1 and C2, respectively. V a1 external port node a 1 voltage, u in This refers to the internal node voltage.

5. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 4, characterized in that, The Norton equivalent model of the multi-port converter under study is: ； In the formula, I is the current matrix of the external port node, U is the voltage matrix of the external port node, G is the equivalent node admittance matrix of the external port, and I his This is the current matrix injected from the internal historical current source into the external port node. The superscript t indicates time t, and the superscript t-1 indicates time t-1.

6. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 5, characterized in that, The process of constructing the equivalent nodal admittance matrix of the external ports is as follows: Connect any one node on the AC side of each single-phase converter to a unit voltage source, short-circuit and ground the remaining nodes on the AC side, and open-circuit the historical current source to obtain the expressions for the AC side current and the DC side current flowing through each node in each single-phase converter. Based on the principle that in each single-phase converter, the mutual admittance between the node connected to the unit voltage source on the DC side and the AC side is taken as the value of the AC side current, the self-admittance of the node connected to the unit voltage source on the DC side is taken as the value of the current flowing through itself, and the mutual admittance between the node connected to the unit voltage source on the DC side and other nodes is taken as the value of the current flowing through the other nodes, the current expressions corresponding to the self-admittance of the node connected to the unit voltage source on the DC side, the mutual admittance between the node connected to the unit voltage source on the DC side and other nodes, and the self-admittance and mutual admittance between the AC side endpoint and the DC side node are all added to the external port equivalent node admittance matrix.

7. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 5, characterized in that, The process of constructing the current matrix of internal historical current sources injected into external port nodes is as follows: The historical current sources of each phase inductor are discretized and acted individually. The historical current sources are open-circuited and all AC side nodes are short-circuited and grounded. The current expressions of the historical current sources generated by all capacitor branches on the DC side of each single-phase converter and injected into each node, as well as the current expressions of the historical current sources generated by the inductor branches on the AC side and injected into each node, are obtained. The current expressions for injecting historical current sources generated by all capacitor branches on the DC side of all single-phase converters into each node, as well as the current expressions for injecting historical current sources generated by inductor branches on the AC side into each node, are added to the internal current matrix for injecting historical current sources into external port nodes.

8. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 5, characterized in that, Based on the discretized equivalent circuit of the switching function of each single-phase converter, the Norton equivalent model of the multi-port converter under study is determined, followed by: The formula for calculating the internal node voltage is as follows: ; in, Let u be the internal node voltage. Different voltages on the right side of the equation are indicated by subscripts when different power sources act alone. The internal node voltage u is calculated when different power sources act alone. In the formula, u a1 This is the external port voltage of phase a1. I Lhist This represents the historical current flowing through the inductor.

9. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 8, characterized in that, Based on the voltage matrix of the external port nodes at the current moment, update the discretized parameter values ​​in the discretized equivalent circuit of the switching function of the multi-port converter under study, specifically including: Based on the voltage matrix of the external port nodes at the current moment, the voltage of the internal nodes at the current moment is calculated using the formula for calculating the voltage of the internal nodes. Based on the voltage matrix of the external port nodes at the current moment and the voltage of the internal nodes at the current moment, according to the formula... Update the parameter values ​​of the discretized equivalent circuit of the switching function of the multi-port converter to be studied.

10. The electromagnetic transient modeling and simulation method for multi-port converters according to claim 8, characterized in that, The switch status table includes: the status of each switch group, and the equivalent resistance on the AC side. R eq The value of , admittance G eq Values ​​and switching functions S The equivalent voltage source that influences the weights of the DC-side node voltage on the AC side. U eq The value of and the equivalent current source that affects the AC measuring port current on the DC side. J eq The values ​​and i L The value of .

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