General electromechanical transient modeling method and system for network-forming converter

Abstract

The invention provides a general electromechanical transient modeling method and system for a network-building converter, and relates to the technical field of electromechanical transient modeling, and the method comprises the steps: simplifying the electromagnetic transient models of network-building converters of different topologies into a grid-connected equivalent circuit of an electromechanical transient time scale; uniformly representing by using an internal potential series reactance model controlled by a power outer ring so as to establish an electromechanical transient general grid-connected interface model of the grid-forming converter; combining mathematical transformation of active power control with a reactive power control mode to form a general power outer loop control model of the network construction type converter; through a method based on internal potential reconstruction, reconstructing a new internal potential satisfying a current limiting constraint, and establishing a general current limiting model suitable for a network construction type electromechanical transient model; according to the method, various topological structures, various power outer loop control and various current limiting strategies can be simulated, flexible use of models in large-scale power system simulation is facilitated, and the complexity of model development and maintenance is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromechanical transient modeling, and in particular to a general grid-forming converter electromechanical transient modeling method and system. BACKGROUND

[0002] New energy power generation represented by wind energy and solar energy is increasing in the power system, and the power supply structure of the power system is undergoing profound changes. Traditional synchronous generators are gradually replaced by converter devices based on power electronics technology, making the power system exhibit low inertia and weak damping characteristics. In order to cope with the voltage and frequency stability challenges brought by high proportion of new energy access, grid-forming (GFM) control technology emerges as the times require. Grid-forming converters can simulate the voltage source characteristics of synchronous generators, autonomously establish voltage and frequency, and provide necessary support for the grid, which is a key equipment for building a new type of power system.

[0003] In the planning and operation analysis of large-scale power systems, electromechanical transient simulation is the core means to evaluate system angle stability and security. However, for the electromechanical transient modeling of grid-forming converters, the current technical status still faces significant problems such as poor model universality and heavy development and maintenance burden, mainly in three aspects of topology structure, control strategy and current limiting protection: Firstly, the hardware topology and control architecture of grid-forming converters are different, making it difficult to model the simulation interface. The current mainstream grid-forming converter electromagnetic transient model topology mainly falls into three categories: one is the "direct control + LCL filter" structure, which directly regulates the internal potential of the converter; the second is the "double-loop control + LCL filter" structure, which generates internal potential instructions through voltage and current double-loop control; the third is the "double-loop control + virtual impedance control + LC filter" structure, which introduces a virtual impedance. These three topologies differ in physical parameters and control loop response time scales. Existing electromechanical transient modeling methods usually develop models for specific topologies separately, lacking a general grid-connected interface model that can uniformly describe multiple topology structures based on response time scale analysis, making it extremely tedious to switch between different hardware schemes in simulation.

[0004] Secondly, there are many power outer loop control strategies, and there is a lack of a unified mathematical description framework. In order to achieve power distribution and synchronization, there are various control routes in the industry, including virtual synchronous machine control simulating rotor motion, droop control, droop control with filter, and power synchronization control, etc. Although these strategies are all adjusting the amplitude and phase of internal potential in physical essence, their transfer function structures and parameter definitions are different. Existing simulation models often use a "one strategy corresponds to one model" development mode, with low code reuse rate, lacking a general outer loop model that can cover mainstream control strategies through parameter configuration only.

[0005] Finally, the complexity of current-limiting protection strategies is a major challenge in electromechanical transient modeling. Networked devices are extremely sensitive to overload and must be equipped with diverse current-limiting strategies, such as ring current limiting to maintain phase, instantaneous current limiting to restrict x / y axis components, priority-based current limiting, and strategies that switch to network-based control. Accurately simulating the impact of these current-limiting logics on current amplitude and phase is a challenge in electromechanical transient simulations that neglect fast dynamics. Existing models often struggle to maintain simulation efficiency while being compatible with multiple current-limiting strategies.

[0006] In summary, existing electromechanical transient modeling techniques for grid-connected converters are insufficient in adapting to various topologies, being compatible with various power outer loop controls, and accurately simulating various current limiting strategies, ultimately affecting the flexibility and accuracy of large-scale power system simulation. Summary of the Invention

[0007] To address the aforementioned problems, this invention proposes a general electromechanical transient modeling method and system for grid-connected converters, capable of simulating various topologies, power outer loop control, and current limiting strategies. This not only facilitates the flexible use of models in large-scale power system simulations but also reduces the complexity of model development and maintenance.

[0008] According to some embodiments, the present invention adopts the following technical solution: A general electromechanical transient modeling method for grid-type converters includes: By analyzing the response time scale of various converter topologies, the electromagnetic transient model of grid-connected converters with different topologies is simplified into a grid-connected equivalent circuit with electromechanical transient time scale. The model of internal potential series reactance controlled by the power outer loop is used to uniformly represent the model, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. By combining the mathematical transformation of active power control with the mode of reactive power control, a general active power outer loop control model and a general reactive power outer loop control model are constructed respectively, forming a general power outer loop control model for grid-type converters. By using an internal potential reconstruction method, a new internal potential that satisfies the current limiting constraint is reconstructed based on the current command phasor and terminal voltage after current limiting, thus establishing a general current limiting model applicable to network-type electromechanical transient models.

[0009] According to some embodiments, the present invention adopts the following technical solution: A general electromechanical transient modeling system for grid-type converters includes: The grid-connected interface modeling module is configured to: simplify the electromagnetic transient model of grid-connected converters with different topologies into grid-connected equivalent circuits with electromechanical transient time scales by analyzing the response time scale of each converter topology, and use the model of internal potential series reactance controlled by the power outer loop to uniformly represent it, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. The outer loop control modeling module is configured to: construct a general active outer loop control model and a general reactive outer loop control model by combining the mathematical transformation of active control with the mode of reactive control, thus forming a general power outer loop control model for grid-type converters. The current limiting modeling module is configured to: reconstruct a new internal potential that satisfies the current limiting constraint based on the current command phasor and terminal voltage after current limiting by using an internal potential reconstruction method, and establish a general current limiting model applicable to network electromechanical transient models.

[0010] According to some embodiments, the present invention adopts the following technical solution: A computer program product includes a computer program that, when executed by a processor, implements the general electromechanical transient modeling method for grid-type converters.

[0011] According to some embodiments, the present invention adopts the following technical solution: A non-transitory computer-readable storage medium is provided for storing computer instructions, which, when executed by a processor, implement the general electromechanical transient modeling method for grid-type converters.

[0012] According to some embodiments, the present invention adopts the following technical solution: An electronic device includes a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to implement a general electromechanical transient modeling method for grid-type converters.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes a general electromechanical transient modeling method and system for grid-connected converters. Through a unified equivalent interface of "internal potential series reactance", a parameterized general power outer loop control model, and a general current limiting strategy model based on internal potential reconstruction, it achieves high compatibility with various hardware topologies, control strategies, and current limiting methods, significantly reducing the complexity of model development and maintenance. While ensuring the accuracy of electromechanical transient simulation, this method significantly improves modeling efficiency and simulation flexibility, providing a standardized and configurable key tool for stability analysis, equipment development, and grid connection evaluation of high-proportion new energy power systems. It strongly supports the large-scale application of grid-connected converters in new power systems and the safe and stable operation of the systems. Attached Figure Description

[0014] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0015] Figure 1 This is a flowchart of a general electromechanical transient modeling method for a grid-type converter, as shown in Example 1.

[0016] Figure 2 This is an electromagnetic transient model diagram of a grid-type converter with a direct control + LCL filter topology in Example 1. Figure 3 This is an electromagnetic transient model diagram of a grid-type converter with a dual-loop control + LCL filter topology in Example 1. Figure 4 This is an electromagnetic transient model diagram of a grid-type converter with a dual-loop control + virtual impedance control + LC filter topology in Example 1. Figure 5 The above is the grid-connected equivalent circuit diagram of the grid-type converter with single-loop control + LCL filtering topology in Example 1. Figure 6 This is the grid-connected equivalent circuit diagram of the grid-type converter with dual-loop control + LCL filtering topology in Example 1. Figure 7 This is the grid-connected equivalent circuit diagram of the grid-type converter with dual-loop control + virtual impedance control + LC filtering topology in Example 1. Figure 8 This is a general grid-connected interface model diagram of a grid-type converter in the form of the Thevenin equivalent circuit in Example 1. Figure 9 This is a general grid-connected interface model diagram of a grid-type converter in the form of the Norton equivalent circuit in Example 1. Figure 10 is a block diagram of the power outer loop control transfer function of the grid-type converter in Example 1. In Figure 10(a), it is a power synchronization control diagram, Figure 10(b) is a droop control diagram, Figure 10(c) is a droop control diagram with a filter, and Figure 10(d) is a virtual synchronizer control diagram.

[0017] Figure 11 This is the general active power outer loop control diagram for the grid-type converter in Example 1. Figure 12 This is the general reactive power outer loop control diagram for the grid-type converter in Example 1.

[0018] Figure 13 is a phasor diagram of the current limiting strategy for the grid-type converter in Example 1. Figure 13(a) is a ring current limiting strategy diagram, Figure 13(b) is an instantaneous current limiting strategy diagram, Figure 13(c) is a specified priority current limiting strategy diagram, and Figure 13(d) is a current limiting strategy diagram converted to grid-type control.

[0019] Figure 14 This is a diagram of the inner loop control structure of the grid-type converter in Example 1. Figure 15 This is a diagram of the general current limiting model algorithm for grid-type converters based on internal potential reconstruction in Example 1. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1 One embodiment of the present invention provides a general electromechanical transient modeling method for grid-type converters, such as... Figure 1 As shown, it includes: S1. By analyzing the response time scale of each converter topology, the electromagnetic transient model of grid-connected converters with different topologies is simplified into a grid-connected equivalent circuit with electromechanical transient time scale, and a unified representation is made using the model of internal potential series reactance controlled by the power outer loop, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. Furthermore, the topology includes single-loop control + LCL filtering, dual-loop control + LCL filtering, and dual-loop control + virtual impedance control + LC filtering; Single-loop control + LCL filtering means generating the converter's internal electromotive force through the power outer loop control. Directly control the electromotive force inside the converter This type of topology converter simplifies the process by ignoring the modulation stage of the bridge arm control time scale: the power outer loop control generates the potential phasor within the converter and connects it in series with the filter reactor and then into the power grid. Dual-loop control + LCL filtering means that the control signal that generates the filter capacitor voltage is controlled by the outer power loop. Then, the voltage and current inner loop control generates the converter's internal potential control signal. Finally, control the internal electromotive force of the converter. This type of topology converter simplifies the process by ignoring the voltage and current inner loop control and the dynamics of the modulation stage: the power outer loop control generates the capacitor landing point voltage phasor and connects it in series with the filter reactor and feeds it into the grid. Dual-loop control + virtual impedance control + LC filtering, simplified to generating a virtual internal potential control signal through power outer loop control. Then, a control signal for generating the filter capacitor voltage is generated through virtual impedance control. Then, the voltage and current inner loop control generates the converter's internal potential control signal. Finally, control the internal electromotive force of the converter. The simplification method of this type of topology converter is the same as that of the dual-loop control + LCL filter topology, which is finally simplified to: the power outer loop control generates a virtual internal potential phasor and connects it in series with the virtual reactance into the grid.

[0022] Furthermore, in the model of internal potential series reactance controlled by the power outer loop, the physical meanings of internal potential and reactance are respectively adapted to the internal potential of the strain gauge and the filter reactance, the capacitor landing voltage and the filter reactance, and the virtual internal potential and the virtual reactance according to the selected topology.

[0023] Specifically, for the problem of simulating the grid-connected external characteristics of grid-connected converters with different control structures and filter circuits, this embodiment establishes a general grid-connected interface model for electromechanical transients of grid-connected converters by analyzing the time scale of the response of each control structure of the converter. The steps are as follows: 1) Simplification of electromagnetic transient models for various topological network converters based on response time-scale analysis The electromagnetic transient model topologies of common grid-type converters are mainly divided into three categories: single-loop control + LCL filter, dual-loop control + LCL filter, and dual-loop control + virtual impedance control + LC filter. Their topologies are as follows: Figure 2 , 3 As shown in Figure 4, the core part is: A grid-type converter with a single-loop control + LCL filter topology, such as... Figure 2 As shown, the control signal for generating the internal potential of the converter is generated through the power outer loop control. The internal electromotive force of the converter can be directly controlled by modulation. .

[0024] A grid-type converter with dual-loop control and LCL filtering topology, such as... Figure 3 As shown, the control signal for generating the filter capacitor voltage is controlled through the power outer loop. Then, the voltage and current inner loop control generates the converter's internal potential control signal. Finally, the internal potential of the converter is controlled by modulation. .

[0025] A grid-type converter with a dual-loop control + virtual impedance control + LC filter topology, such as... Figure 4 As shown, a virtual internal potential control signal is generated through power outer loop control. Then, a control signal for generating the filter capacitor voltage is generated through virtual impedance control. Then, the voltage and current inner loop control generates the converter's internal potential control signal. Finally, the internal potential of the converter is controlled by modulation. .

[0026] For a single-loop control + LCL filter topology, since the converter modulation stage is at the bridge arm level, the typical time scale is 10. ~100 However, in electromechanical transient simulations studying the fundamental frequency characteristics (with a typical simulation step size of 0.01s), this modulation process can be ignored. Furthermore, the filter capacitor value at the fundamental frequency is very small. Therefore, the grid-connected equivalent circuit of the single-loop control + LCL filter topology for a grid-connected converter under electromechanical transient timescale can be expressed as follows: Figure 5 The equivalent circuit generates the internal potential phasor of the converter by controlling the power outer loop. And in series filter reactance It is connected to the power grid.

[0027] For the dual-loop control + LCL filter topology and the dual-loop control + virtual impedance control + LC filter topology, the voltage loop and current loop typically employ high-bandwidth designs to achieve rapid adjustment of the filter capacitor voltage and enable rapid tracking of the reference value. Specifically, the current loop bandwidth is usually set to 1 / 10 of the PWM switching frequency, with a response time scale of approximately 1 ms; the voltage loop bandwidth is typically set to 1 / 10 of the current loop bandwidth, with a response time scale of approximately 10 ms. In contrast, the dynamics of the frequency and power angle of the active power outer loop control typically have a time scale of 1~10 s, while the internal voltage dynamics of the reactive power outer loop control typically have a time scale of approximately 0.1 s. Therefore, in electromechanical transient simulations studying fundamental frequency characteristics, the dynamic characteristics of the voltage and current inner loops can be ignored. In summary, the grid-connected equivalent circuit of the grid-connected converter with dual-loop control + LCL filter topology under electromechanical transient time scales can be expressed as follows: Figure 6 The equivalent circuit generates the capacitor landing point voltage phasor by controlling the power outer loop. And in series filter reactance Connected to the grid. The grid-connected equivalent circuit of a grid-type converter with a dual-loop control + virtual impedance control + LC filter topology under electromechanical transient time scale can be represented as follows: Figure 7 The equivalent circuit generates a virtual internal potential phasor by controlling the power outer loop. And in series virtual reactance It is connected to the power grid.

[0028] 2) General Representation Method for Grid-Connected Interface of Electromechanical Transient Model of Grid-Connected Converter Based on the simplification analysis using the response time scale, the grid-connected interface models of the three topology types of grid-connected converters are ultimately equivalent to models of internal potential series reactance controlled by the power outer loop. Therefore, a universal grid-connected interface model for grid-connected converters capable of simultaneously simulating the three topologies can be established, such as... Figure 8 As shown, the grid-connected interface model adopts the form of a Thevenin equivalent circuit, and generates the internal potential phasor through power outer loop control. And further series reactor Grid connection.

[0029] It is worth noting that when using this grid-connected interface to simulate the converter characteristics of the three topologies, the internal potential... With reactance The physical quantities described are different, and their specific physical meanings are shown in Table 1.

[0030] Table 1 Physical Meaning of General Grid-Connected Interface Model Parameters for Grid-Type Converters

[0031] 3) Grid-connected interface model conversion suitable for electromechanical transient simulation In practical electromechanical transient simulations, it is necessary to convert the grid-connected interface in the form of the Thevenin equivalent circuit into a form such as... Figure 9 The grid-connected interface shown is in the form of a Norton equivalent circuit. The internal potential phasor generated by the power outer loop control is also shown. (It can also be written as) ), calculate the injected current phasor and further parallel ampere Grid connection. The interface model conversion formula for transforming the Thevenin equivalent circuit into the Norton equivalent circuit is shown in (1), where and These are the injected current phasor and the shunt susceptance in the Norton equivalent circuit, respectively. and These are the internal potential phasor and series reactance under the Thevenin equivalent circuit, respectively.

[0032] (1) S2. By combining the mathematical transformation of active power control with the mode of reactive power control, a general active power outer loop control model and a general reactive power outer loop control model are constructed respectively, forming a general power outer loop control model for grid-type converters. Furthermore, the transfer function block diagram of the general active power outer loop control model includes a configurable first-order inertial element and its proportional coefficient and time constant parameters. By configuring the proportional coefficient and time constant of the inertial element, the model can characterize any of the active power regulation characteristics in power synchronization control, droop control, droop control with filter, and virtual synchronous machine control.

[0033] Furthermore, the transfer function block diagram of the general reactive power outer loop control model includes a configurable reactive power control flag. The model includes an inertial element and an integral element for simulating synchronous machine excitation regulation. By configuring the reactive power control flag, the proportional coefficient and time constant of the first-order inertial element, and the time constant of the integral element, the model can characterize any reactive power regulation characteristic among power synchronization control, droop control, droop control with a filter, and virtual synchronous machine control.

[0034] Specifically, addressing the modeling complexity of various power outer-loop control strategies, this embodiment establishes a general power outer-loop control model for grid-type converters through a combination of mathematical transformations and models. The steps are as follows: 1) Power outer loop control strategy for grid-type converters The outer-loop power control of a grid-type converter mainly includes: power synchronization control, droop control, droop control with a filter, and virtual synchronizer control. Its transfer function block diagram is shown in Figure 10. For power synchronization control, its active power control description is the active power deviation. The internal potential phase deviation is generated through the integration process, and then further superimposed with the phase at the rated speed. Generation of internal potential phase Its reactive power control is described as reactive power deviation multiplied by reactive power droop coefficient. The internal potential deviation is obtained, and then the initial internal potential value is superimposed. The internal potential amplitude is obtained. For droop control, its active power control simulates the active-frequency droop characteristic of a synchronous machine, which can be described as the active power deviation generating an angular frequency deviation through an active power droop coefficient, further superimposed with the rated angular frequency and integrated to obtain the internal potential phase. Its reactive power control is consistent with the power synchronization control. For droop control with a filter, its active and reactive power control are based on droop control with the addition of an inertial element to simulate the measurement delay of electrical quantities. For virtual synchronous machine control, its active power control simulates the rotor motion equation of a synchronous machine, and its reactive power control simulates the excitation characteristics of a synchronous machine.

[0035] Due to the reactance of high-voltage transmission networks Much greater than resistance Therefore, the flow of active power can be controlled by controlling the phase of the node voltage, and the flow of reactive power can be controlled by controlling the amplitude of the node voltage. Based on this characteristic, regardless of the grid type, the power outer loop control includes both active and reactive power control. However, different control strategies have different applicable scenarios and structures, and the program development burden of developing a separate model for each control strategy is severe.

[0036] Therefore, this embodiment proposes a general power outer loop control model by combining the mathematical transformation of active power control with the mode of reactive power control. Different power outer loop controls can be simulated simply by filling in different parameters. 2) General active power outer loop control model Based on the transfer function block diagrams of power synchronization control and droop control in Figures 10(a) and 10(b), the transfer functions of their active power control can be written as shown in (2) and (3), respectively. It is the phase of the internal electromotive force of the active power control output. It is the rated angular frequency. This is a reference value for active power. This is the active power output value. This is the active power droop coefficient. Because... and They are equivalent. Therefore, although power synchronization control and droop control control have different controlled objects (power synchronization control regulates the phase deviation of the internal potential, while droop control regulates the angular frequency deviation), their active power control transfer functions are completely equivalent.

[0037] (2) (3) Based on the transfer function block diagrams of the droop control with filter and the virtual synchronous machine control in Figures 10(c) and 10(d), the transfer functions of their active power control can be written as shown in (4) and (5): (4) (5) in, It is the phase of the internal electromotive force of the active power control output. It is the rated angular frequency. This is a reference value for active power. This is the active power output value. This is the active power droop coefficient. This represents the angular frequency of the filter bandwidth with droop control. This indicates the deviation between the control angular frequency and the rated angular frequency of the virtual synchronizer. Indicates the coefficient of inertia. is the damping coefficient.

[0038] By rearranging the active power control transfer functions of the droop control with filter and the virtual synchronous machine control, we can obtain formulas (6) and (7) respectively. It can be seen that the active power control of both is as follows: the active power deviation generates an angular frequency deviation signal through a first-order inertial element, which is superimposed with the rated angular frequency. The phase of the internal potential is obtained by integration. Therefore, the active power control of the two is similar in terms of transfer function structure.

[0039] (6) (7) in, It is the phase of the internal electromotive force of the active power control output. It is the rated angular frequency. This is a reference value for active power. This is the active power output value. This is the active power droop coefficient. This represents the angular frequency of the filter bandwidth with droop control. Indicates the coefficient of inertia. is the damping coefficient.

[0040] The active power control transfer function for power synchronization control and droop control can be expressed by formula (8), where The proportional coefficient related to the active power deviation is given; the active power control transfer function of the droop control with filter and the virtual synchronous machine control can be expressed by formula (9), where, This represents the proportionality coefficient related to the active power deviation. The time constant of a first-order inertial element is given by the parameter in formula (9). When the value is 0, formula (8) and formula (9) are completely equivalent. Therefore, in terms of active power control, the droop control with filter and the virtual synchronous machine control only add inertia compared to power synchronization control and droop control, and still have the characteristics of droop control.

[0041] (8) (9) In summary, a general active power control system can be established, and its transfer function block diagram is shown below. Figure 11 As shown, this model will include active power deviation. The angular frequency deviation value is generated by a first-order inertial element, and then superimposed with the rated angular frequency. The internal potential phase is then obtained by integration.

[0042] By configuring the parameters of the general active power outer loop control, different active power outer loop control strategies can be simulated. The specific configuration method is shown in Table 2. By configuring the parameters in Table 2, this model can switch active power control strategies by changing the input parameters without altering the code structure. Both represent the active power droop coefficient. This represents the angular frequency of the filter bandwidth with droop control. Indicates the coefficient of inertia. is the damping coefficient.

[0043] Table 2. General Active Power Outer Loop Control Parameter Configuration Table for Network-Type Converters

[0044] 3) General reactive power outer loop control model As shown in Figures 10(a) and 10(b), the reactive power control of power synchronization control and droop control is consistent; the reactive power control transfer function of the droop control with filter in Figure 10(c) can be written as formula (10), where The internal electromotive force amplitude of the reactive power control output. This represents the reactive power droop coefficient. Indicates the filter bandwidth angular frequency. This represents the initial value of the internal potential amplitude. This represents the reference value for reactive power. The difference between reactive power output and the previous two lies in the fact that reactive power deviation passes through a first-order inertial element (i.e., Then multiply by the droop coefficient; therefore, the reactive power control of the three can be expressed as formula (11), where This represents the proportionality coefficient related to reactive power deviation. This is expressed as the time constant of a first-order inertial element. When A value of 0 can be used to represent reactive power control with power synchronization control and droop control. A value that is not 0 can be used to represent reactive power control with droop control and filter.

[0045] (10) (11) The reactive power control of the virtual synchronous machine control differs from other control methods. It simulates the excitation characteristics of a synchronous machine. First, a voltage control signal is generated using droop control, as shown in formula (12). Then, an integrator is used to adjust the internal potential, thereby making the terminal voltage equal to the reference value, as shown in formula (13). Indicates the terminal voltage command value. Indicates the terminal voltage reference value. This represents the reactive power droop coefficient. This represents the time constant of the integration process.

[0046] (12) (13) Combining formulas (11), (12), and (13), a general reactive power control can be established, and its transfer function block diagram is shown below. Figure 12 As shown, when the reactive power control flag... At that time, the model will include reactive power deviation. An internal potential deviation is generated through an inertial element, which is then superimposed with the initial internal potential value. Generate internal potential amplitude; when reactive power control flag At that time, the model will include reactive power deviation. The droop control deviation is generated through an inertial element, and then further superimposed with the terminal voltage deviation. The internal potential deviation is generated through integration, and then the initial internal potential value is added to it. Generate the internal potential amplitude.

[0047] By configuring the parameters of the general reactive power outer loop control, different reactive power outer loop control strategies can be simulated. The specific configuration method is shown in Table 3. By configuring the parameters in Table 3, this model can switch reactive power control strategies by changing the input parameters without altering the code structure. This represents the reactive power droop coefficient. This represents the angular frequency of the filter bandwidth with droop control. This represents the time constant of the integral element.

[0048] Table 3. General Reactive Power Outer Loop Control Parameter Configuration Table for Network Converters

[0049] S3. Using the internal potential reconstruction method, the output current command phasor without current limiting is calculated based on the internal potential phasor and terminal voltage of the power outer loop output. Then, a current limiting strategy is selected to generate the current-limited output current command phasor. Then, using the current-limited current command phasor and terminal voltage, a new internal potential that meets the current limiting constraint is reconstructed. Based on the current-limited current phasor and terminal voltage, a new internal potential phasor that meets the current limiting constraint is reconstructed. The output current of the grid-type converter is calculated using this internal potential, and a general current limiting model applicable to the grid-type electromechanical transient model is established.

[0050] Furthermore, the specific method for reconstructing the new internal potential that satisfies the current-limiting constraint is as follows: The current command phasor after current limiting is calculated based on the selected current limiting strategy. Then use the formula The calculation yielded that, For terminal voltage phasors, It is the equivalent series reactance.

[0051] Specifically, addressing the modeling complexity of various grid-connected converter current limiting strategies, this embodiment proposes a method based on internal potential reconstruction. This method recalculates an internal potential using the current command value after current limiting. This internal potential is no longer the same as the internal potential output by the power outer loop control. The reconstructed internal potential is used as part of the grid-connected interface model to calculate the Norton equivalent injection current, thereby establishing a general current limiting model applicable to grid-connected electromechanical transient models. The steps are as follows: 1) Mathematical description method of current limiting strategies for various grid-type converters The current limiting strategies for grid-type converters mainly include ring current limiting strategy, instantaneous current limiting strategy, specified priority current limiting strategy, and current limiting strategy converted to grid-type control. The phasor diagrams of the current before and after current limiting are shown in Figure 13. In Figures 13(a), 13(c), and 13(d), the dashed circles represent current limiting circles, and their radius is the maximum allowable output current. In Figure 13(b), the current limiting region is represented by a square dashed line, with its four vertices located at a radius of [missing information]. On the circle. Among them, The current before current limiting. The xy axis represents the current after current limiting; the xy axis is the grid synchronization reference coordinate axis, which rotates at the rated frequency; the dq axis has different meanings in the specified priority current limiting strategy and the current limiting strategy converted to grid-based control. In the specified priority current limiting strategy, the d-axis phase is equal to the phase of the internal potential output of the active power outer loop control. In the current limiting strategy converted to grid-based control, the d-axis phase is equal to the phase of the voltage output of the phase-locked loop.

[0052] The following provides mathematical descriptions of four types of current limiting strategies for grid-type converters, which can be embedded in the subsequently developed general current limiting model for grid-type converters: As shown in Figure 13(a), the characteristic of the ring current limiting strategy is that the phase of the current remains unchanged before and after current limiting, and the amplitude is limited to... When the current amplitude exceeds After current limiting, the current can be expressed by formula (14), where , These represent the x and y axis components of the output current after current limiting, respectively. , These represent the x and y components of the output current before current limiting, respectively. This represents the maximum allowable output current.

[0053] (14) As shown in Figure 13(b), the instantaneous current limiting strategy is characterized by specifying the maximum components of the current along the x and y axes, as shown in formula (15), where This is the setting value for the maximum allowable x-axis component of the current. , These are the maximum x and y axis components of the output current, respectively. When the x-axis component of the current is greater than the maximum x-axis component, it is limited to that maximum value; when the y-axis component of the current is greater than the maximum y-axis component, it is limited to that maximum value. In summary, the current after current limiting can be expressed by formula (16).

[0054] (15) (16) As shown in Figure 13(c), the characteristic of the specified priority current limiting strategy is that the current phase after current limiting leads the phase of the active power outer loop control output internal potential. Angle Therefore, the current phase after current limiting is When the current amplitude exceeds After current limiting, the current can be expressed by formula (17), where This indicates the phase of the internal electromotive force output of the active outer loop control. This indicates that the current phase leads after current limiting. The angle is specified.

[0055] (17) As shown in Figure 13(d), the characteristic of the current limiting strategy converted to a grid-type control is that the current phase after current limiting is specified to lead the phase-locked loop output phase. Angle Therefore, the current phase after current limiting is When the current amplitude exceeds After current limiting, the current can be expressed by formula (18), where This indicates the angle of the phase-locked loop output. This indicates that the current phase leads after current limiting. The angle is specified.

[0056] (18) 2) Modeling a general current-limiting model based on internal potential reconstruction like Figure 14 As shown, the actual current limiting process of the electromagnetic transient model of the grid converter is as follows: the voltage loop determines the voltage reference value generated by the power outer loop. , Command value for generating current , The command value is obtained by using a current limiter with different current limiting strategies, such as formulas (14), (16), (17), and (18), to obtain the current command value after current limiting. , The current loop generates the converter internal potential command value based on the current command value. , Finally, the internal potential phasor is obtained through modulation. In the electromagnetic transient model, the current limiter is located between the voltage loop and the current loop control. Since the dynamic processes of the current loop, voltage loop, and modulation can be neglected on the electromechanical transient time scale, the current limiting can be considered to be completed instantaneously on this time scale. Therefore, this implementation model example proposes an algorithm-level general current limiting model based on internal potential reconstruction, according to the above actual current limiting process. The model algorithm flowchart is as follows... Figure 15 As shown.

[0057] First, the general power outer loop control model is initialized based on the power flow calculation results, which is reflected in the initialization of the power flow calculation results. Figure 11 , Figure 12 The inertial and integral modules in the active and reactive power control models set the initial values ​​for electromechanical transient simulation.

[0058] Secondly, according to Figure 11 , Figure 12 The internal potential phasor output by the general power outer loop control model With terminal voltage phasor Using the formula Calculate the unlimited output current command phase value And output it.

[0059] Then, determine the magnitude of the unlimited output current command phasor. Does it exceed the maximum current limit? When not exceeding When this happens, the output current command phasor after current limiting will be equal to the current command phasor without current limiting, that is... If it exceeds Then, according to the current limiting strategy set, the current command phasor after current limiting is calculated and output using the current limiting strategy formulas (14)(16)(17)(18). At this time, the current command phasors before and after current limiting are not equal.

[0060] Then, based on the current command phasor after current limiting, the formula is used. The internal potential is recalculated, and this internal potential phasor is used as a calculation parameter for the electromechanical transient model and the grid-connected interface model, using the formula... The current source interface model is further transformed into a Norton equivalent circuit to participate in the solution network.

[0061] It is worth noting that when the current is not limited, the reconstructed internal potential phasor Equal to the internal potential phasor generated by the power outer loop When current limiting occurs, the reconstructed internal potential phasor is not equal to the internal potential phasor generated by the power outer loop.

[0062] The proposed current limiting strategy based on internal potential reconstruction does not contain any dynamic integration module and is an algorithmic model, thus enabling instantaneous current limiting. In addition, the model can simulate various current limiting strategies, making it more versatile.

[0063] Example 2 One embodiment of the present invention provides a general electromechanical transient modeling system for grid-type converters, comprising: The grid-connected interface modeling module is configured to: simplify the electromagnetic transient model of grid-connected converters with different topologies into grid-connected equivalent circuits with electromechanical transient time scales by analyzing the response time scale of each converter topology, and use the model of internal potential series reactance controlled by the power outer loop to uniformly represent it, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. The outer loop control modeling module is configured to: construct a general active outer loop control model and a general reactive outer loop control model by combining the mathematical transformation of active control with the mode of reactive control, thus forming a general power outer loop control model for grid-type converters. The current limiting modeling module is configured to: reconstruct a new internal potential that satisfies the current limiting constraint based on the current command phasor and terminal voltage after current limiting by using an internal potential reconstruction method, and establish a general current limiting model applicable to network electromechanical transient models.

[0064] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A general electromechanical transient modeling method for grid-type converters, characterized in that, include: By analyzing the response time scale of various converter topologies, the electromagnetic transient model of grid-connected converters with different topologies is simplified into a grid-connected equivalent circuit with electromechanical transient time scale. The model of internal potential series reactance controlled by the power outer loop is used to uniformly represent the model, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. By combining the mathematical transformation of active power control with the mode of reactive power control, a general active power outer loop control model and a general reactive power outer loop control model are constructed respectively, forming a general power outer loop control model for grid-type converters. By using an internal potential reconstruction method, a new internal potential that satisfies the current limiting constraint is reconstructed based on the current command phasor and terminal voltage after current limiting, thus establishing a general current limiting model applicable to network-type electromechanical transient models.

2. The general electromechanical transient modeling method for grid-type converters as described in claim 1, characterized in that, The topology includes single-loop control + LCL filtering, dual-loop control + LCL filtering, and dual-loop control + virtual impedance control + LC filtering. The topology converter with single-loop control + LCL filter topology is simplified to power outer loop control generating the internal potential phasor of the converter by ignoring the modulation link of the bridge arm level control time scale, and then connecting the filter reactance in series with the grid. The topology converter with dual-loop control + LCL filter topology is simplified to power outer-loop control by ignoring the voltage and current inner loop control and the dynamics of the modulation link, generating the capacitor landing voltage phasor and connecting it in series with the filter reactor and then into the grid. The topology converter with dual-loop control + virtual impedance control + LC filter topology is simplified to power outer loop control generating virtual internal potential phasors by ignoring the modulation link of the bridge arm level control time scale, and then connected in series with virtual reactance into the grid.

3. The general electromechanical transient modeling method for grid-type converters as described in claim 1, characterized in that, In the model of internal potential series reactance controlled by the power outer loop, the physical meanings of internal potential and reactance are respectively adapted to the internal potential of the strain gauge and the filter reactance, the capacitor landing voltage and the filter reactance, and the virtual internal potential and the virtual reactance according to the selected topology.

4. The general electromechanical transient modeling method for grid-type converters as described in claim 1, characterized in that, The transfer function block diagram of the general active power outer loop control model includes a configurable first-order inertial element and its proportional coefficient and time constant parameters. By configuring the proportional coefficient and time constant of the inertial element, the model can characterize any of the active power regulation characteristics in power synchronization control, droop control, droop control with filter, and virtual synchronous machine control.

5. The general electromechanical transient modeling method for grid-type converters as described in claim 1, characterized in that, The transfer function block diagram of the general reactive power outer loop control model includes a configurable reactive power control flag, a first-order inertial element, and an integral element for simulated synchronous machine excitation regulation. By configuring the reactive power control flag, the proportional coefficient and time constant of the first-order inertial element, and the time constant of the integral element, the model can characterize any reactive power regulation characteristic among power synchronization control, droop control, droop control with a filter, and virtual synchronous machine control.

6. The general electromechanical transient modeling method for grid-type converters as described in claim 1, characterized in that, The specific method for reconstructing a new internal potential that satisfies the current-limiting constraint is as follows: The current command phasor after current limiting is calculated based on the selected current limiting strategy. Then use the formula The calculation yielded that, For terminal voltage phasors, It is the equivalent series reactance.

7. A general electromechanical transient modeling system for grid-type converters, characterized in that, include: The grid-connected interface modeling module is configured to: simplify the electromagnetic transient model of grid-connected converters with different topologies into grid-connected equivalent circuits with electromechanical transient time scales by analyzing the response time scale of each converter topology, and use the model of internal potential series reactance controlled by the power outer loop to uniformly represent it, so as to establish a general grid-connected interface model for electromechanical transients of grid-connected converters. The outer loop control modeling module is configured to: construct a general active outer loop control model and a general reactive outer loop control model by combining the mathematical transformation of active control with the mode of reactive control, thus forming a general power outer loop control model for grid-type converters. The current limiting modeling module is configured to: reconstruct a new internal potential that satisfies the current limiting constraint based on the current command phasor and terminal voltage after current limiting by using an internal potential reconstruction method, and establish a general current limiting model applicable to network electromechanical transient models.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements a general electromechanical transient modeling method for grid-type converters as described in any one of claims 1-6.

9. A non-transitory computer-readable storage medium, characterized in that, The non-transitory computer-readable storage medium is used to store computer instructions, which, when executed by a processor, implement a general electromechanical transient modeling method for grid-type converters as described in any one of claims 1-6.

10. An electronic device, characterized in that, include: The device includes a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory to enable the electronic device to implement a general electromechanical transient modeling method for grid-type converters as described in any one of claims 1-6.

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