A general network configuration type converter electromechanical transient modeling method and system

Abstract

The application provides a general network-structured converter electromechanical transient modeling method and system, and relates to the technical field of electromechanical transient modeling, and comprises the following steps: simplifying electromagnetic transient models of network-structured converters with different topologies into grid-connected equivalent circuits in the electromechanical transient time scale, and uniformly representing by using the model of power outer loop control and internal potential series reactance to establish a general grid-connected interface model of network-structured converter electromechanical transient; combining active control mathematical transformation and reactive control mode to form a general power outer loop control model of network-structured converter; reconstructing a new internal potential meeting the current limiting constraint by using the method based on internal potential reconstruction to establish a general current limiting model suitable for network-structured electromechanical transient model; the application can simulate various topological structures, various power outer loop controls and various current limiting strategies, which is not only beneficial to the flexible use of models in large-scale power system simulation, but also beneficial to reducing the complexity of model development and maintenance.

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:

[0004] 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.

[0005] 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.

[0006] Finally, the complexity of current limiting protection strategy is a big difficulty in electromechanical transient modeling. Grid-forming devices are extremely sensitive to overload, and must be equipped with diversified current limiting strategies, such as ring current limiting that maintains phase, instantaneous current limiting that limits x / y-axis component, current limiting with specified priority, and switching to grid-following control strategy, etc. In electromechanical transient simulation that ignores fast dynamics, how to accurately simulate the influence of these current limiting logics on current amplitude and phase is a challenge. Existing models are often difficult to maintain simulation efficiency while being compatible with the above-mentioned multiple current limiting strategies.

[0007] In summary, the existing electromechanical transient modeling technology for grid-forming converters has deficiencies in adapting to various topological structures, being compatible with various power outer loop controls, and accurately simulating various current limiting strategies, which ultimately affects the flexibility and accuracy of large-scale power system simulation. SUMMARY

[0008] To solve the above problems, a general grid-forming converter electromechanical transient modeling method and system are proposed, which can simulate various topological structures, various power outer loop controls, and various current limiting strategies, and is not only conducive to the flexible use of models in large-scale power system simulation, but also conducive to reducing the complexity of model development and maintenance.

[0009] According to some embodiments, the present application adopts the following technical scheme:

[0010] A general grid-forming converter electromechanical transient modeling method, comprising:

[0011] By analyzing the response time scale of each topological structure of the converter, the electromagnetic transient model of the grid-forming converter of different topologies is simplified into a grid-connected equivalent circuit of the electromechanical transient time scale, and the model of the internal potential series reactance of the power outer loop control is used to uniformly represent, to establish a general grid-connected interface model of the grid-forming converter electromechanical transient;

[0012] By combining the mathematical transformation of active control with the mode of reactive control, a general active outer loop control model and a general reactive outer loop control model are respectively constructed to form a general power outer loop control model of the grid-forming converter;

[0013] By the method based on internal potential reconstruction, the new internal potential that satisfies the current limiting constraint is reconstructed according to the current instruction phasor after current limiting and the terminal voltage, and a general current limiting model suitable for the grid-forming electromechanical transient model is established.

[0014] According to some embodiments, the present application adopts the following technical scheme:

[0015] A general grid-forming converter electromechanical transient modeling system, comprising:

[0016] The grid connection interface modeling module is configured to: by analyzing the response time scale of each topology of the converter, simplify the electromagnetic transient state model of the grid-connection type converter of different topologies into a grid connection equivalent circuit of the electromechanical transient state time scale, and uniformly represent by a model of power outer loop control and internal potential series reactance to establish a general grid connection interface model of the grid-connection type converter of the electromechanical transient state.

[0017] The outer loop control modeling module is configured to: by combining the mathematical transformation of active control and the mode of reactive control, respectively build a general active outer loop control model and a general reactive outer loop control model to form a general power outer loop control model of the grid-connection type converter.

[0018] The current limiting modeling module is configured to: by the method based on internal potential reconstruction, reconstruct a new internal potential meeting the current limiting constraint according to the current instruction phasor after current limiting and the terminal voltage to establish a general current limiting model applicable to the electromechanical transient state model of the grid-connection type.

[0019] According to some embodiments, the present application adopts the following technical solutions:

[0020] A computer program product comprising a computer program which, when executed by a processor, implements the general grid-connection type converter electromechanical transient state modeling method.

[0021] According to some embodiments, the present application adopts the following technical solutions:

[0022] A non-transitory computer readable storage medium for storing computer instructions, which, when executed by a processor, implement the general grid-connection type converter electromechanical transient state modeling method.

[0023] According to some embodiments, the present application adopts the following technical solutions:

[0024] An electronic device comprising a processor, a memory and a computer program; wherein the processor is connected with the memory, and the computer program is stored in the memory; when the electronic device is running, the processor executes the computer program stored in the memory to make the electronic device execute the general grid-connection type converter electromechanical transient state modeling method.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 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

[0027] 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.

[0028] Figure 1 This is a flowchart of a general electromechanical transient modeling method for a grid-type converter, as shown in Example 1.

[0029] Figure 2 This is an electromagnetic transient model diagram of a grid-type converter with a direct control + LCL filter topology in Example 1.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Figure 9Figure 1 is a general grid-forming converter universal grid-connection interface model diagram in the form of Norton equivalent circuit for the grid-forming converter in Example 1.

[0037] Figure 10 is a grid-forming converter power outer-loop control transfer function block diagram in Example 1, wherein Figure 10 (a) is a power synchronization control diagram, Figure 10 (b) is a droop control diagram, Figure 10 (c) is a droop control diagram with filter, and Figure 10 (d) is a virtual synchronous machine control diagram.

[0038] Figure 11 Figure 11 is a grid-forming converter universal active power outer-loop control diagram in Example 1.

[0039] Figure 12 Figure 12 is a grid-forming converter universal reactive power outer-loop control diagram in Example 1.

[0040] Figure 13 is a grid-forming converter current-limiting strategy phasor diagram in Example 1, wherein Figure 13 (a) is a ring-shaped 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 into grid-following control.

[0041] Figure 14 Figure 14 is a grid-forming converter inner-loop control structure diagram in Example 1.

[0042] Figure 15 Figure 15 is a grid-forming converter universal current-limiting model algorithm based on internal potential reconstruction in Example 1. DETAILED DESCRIPTION

[0043] The application will be further described below in conjunction with the drawings and examples.

[0044] Example 1

[0045] In an embodiment of the application, a general grid-forming converter electromechanical transient modeling method is provided, as shown in the following formula (1), which comprises the following steps: Figure 1

[0046] S1, by analyzing the response time scale of each topology of the converter, the grid-forming converter electromagnetic transient model of different topologies is simplified into a grid-connection equivalent circuit of electromechanical transient time scale, and a model of power outer-loop control internal potential series reactance is used to uniformly represent, so as to establish a general grid-connection interface model of grid-forming converter electromechanical transient;

[0047] Further, the topology structure comprises single-loop control+LCL filter, double-loop control+LCL filter, double-loop control+virtual impedance control+LC filter;

[0048] Single-loop control+LCL filter, represented as a control signal for generating the internal potential of the converter through power outer-loop control ​directly control the internal voltage of the converter ; this type of topology converter is simplified by ignoring the modulation link of the bridge arm level control time scale: the power outer loop control generates the internal voltage phasor of the converter, and the series filter reactance is connected to the grid;

[0049] Dual-loop control + LCL filter, represented as a control signal that generates a filter capacitor voltage through power outer loop control , and then generates a converter internal voltage control signal through voltage and current inner loop control , and finally controls the internal voltage of the converter ; this type of topology converter is simplified by ignoring the voltage and current inner loop control and the dynamic of the modulation link: the power outer loop control generates the capacitor drop point voltage phasor, and the series filter reactance is connected to the grid;

[0050] Dual-loop control + virtual impedance control + LC filter, simplified as a virtual internal voltage control signal generated by power outer loop control , then a control signal that generates a filter capacitor voltage through virtual impedance control , and then generates a converter internal voltage control signal through voltage and current inner loop control , and finally controls the internal voltage of the converter ; this type of topology converter is simplified in the same way as the dual-loop control + LCL filter topology type, and finally simplified as: the power outer loop control generates the virtual internal voltage phasor, and the series virtual reactance is connected to the grid.

[0051] Further, in the model of the internal voltage series reactance controlled by the power outer loop, the physical meanings of the internal voltage and the reactance correspond to the converter internal voltage and the filter reactance, the capacitor drop point voltage and the filter reactance, and the virtual internal voltage and the virtual reactance, respectively, according to the selected topology structure.

[0052] Specifically, for the grid-connected external characteristic simulation problem of grid-connected converters with different control structures and filter circuit network types, the embodiment establishes a general grid-connected interface model of grid-connected converters by analyzing the response time scale of each control structure of the converter, and the steps are as follows:

[0053] 1) Simplification of electromagnetic transient model of multiple topology grid-connected converters based on response time scale analysis

[0054] The electromagnetic transient model topology structures of common grid-connected 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, whose topology structures are shown in Figure 2 、 3 , 4, wherein the core part is:

[0055] The grid-connected converter of the single-loop control + LCL filter topology type, such asFigure 2 The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control .

[0056] The grid-connected converter of the double-loop control + LCL filter topology type, as shown in FIG. 6, generates the control signal of the filter capacitor voltage by the power outer loop control Figure 3 The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control .

[0057] The grid-connected converter of the double-loop control + virtual impedance control + LC filter topology type, as shown in FIG. 7, generates the control signal of the virtual inner potential by the power outer loop control Figure 4 The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control .

[0058] For the single-loop control + LCL filter topology type, since the converter modulation link belongs to the control of the bridge arm level, the typical time scale is 10 ~100 However, in the study of the base frequency characteristics of the electromechanical transient simulation (the simulation step length is typically 0.01s), the modulation process can be ignored, and at the same time, the filter capacitor value is very small in the base frequency, so that the grid-connected converter of the single-loop control + LCL filter topology type, in the electromechanical transient time scale, the equivalent circuit of the grid-connected can be represented as Figure 5 The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control The control signal of the filter capacitor voltage is generated by the power outer loop control

[0059] For the double-loop control + LCL filter topology type and the double-loop control + virtual impedance control + LC filter topology type, the voltage loop and the current loop are usually designed with high bandwidth to achieve fast regulation of the filter capacitor voltage and fast tracking of the reference value of the filter capacitor voltage; wherein, the current loop bandwidth is usually set to 1 / 10 of the switching frequency of the PWM, and the response time scale is about 1ms; the voltage loop bandwidth is usually set to 1 / 10 of the current loop bandwidth, and the response time scale is about 10ms; in comparison, the frequency and power angle dynamics of the active power outer loop control are usually in the time scale of 1-10s, and the internal voltage dynamics of the reactive power outer loop control are usually in the time scale of about 0.1s; therefore, in the study of the base frequency characteristics of the electromechanical transient simulation, the dynamic characteristics of the voltage and current inner loops can be ignored. In summary, the grid-connected equivalent circuit of the grid-forming converter in the electromechanical transient time scale of the double-loop control + LCL filter topology type can be represented as Figure 6 , the equivalent circuit is generated by the power outer loop control to generate the capacitor landing point voltage phase , and the filter reactance is connected in series and connected to the grid. The grid-connected equivalent circuit of the grid-forming converter in the electromechanical transient time scale of the double-loop control + virtual impedance control + LC filter topology type can be represented as Figure 7 , the equivalent circuit is generated by the power outer loop control to generate the virtual internal potential phase , and the virtual reactance is connected in series and connected to the grid.

[0060] 2) General representation method of grid-connected interface of electromechanical transient model of grid-forming converter

[0061] According to the analysis and simplification based on the response time scale, the grid-connected interface model of the grid-forming converter of the three topology types is finally equivalent to a model of the internal potential of the power outer loop control in series with the reactance, so that a general grid-connected interface model of the grid-forming converter capable of simulating the three topologies at the same time can be established, as shown in Figure 8 , the grid-connected interface model adopts the form of Thevenin equivalent circuit, generates the internal potential phase through the power outer loop control, and further connects the reactance to the grid.

[0062] It is worth noting that when simulating the characteristics of the converter of the three topologies using the grid-connected interface, the internal potential and the reactance described are different, and the specific physical meanings are shown in Table 1.

[0063] Table 1 Physical meaning of parameters of general grid-connected interface model of grid-forming converter

[0064]

[0065] 3) Grid-connected interface model conversion suitable for electromechanical transient simulation

[0066] In actual electromechanical transient simulation, the grid-connected interface in the form of Thevenin equivalent circuit needs to be converted into the grid-connected interface in the form of Norton equivalent circuit as shown in Figure 9 The grid-connected interface in the form of Norton equivalent circuit generates an injected current phasor (also can be written as ) according to the internal electromotive force phasor generated by the power outer loop control, and further calculates the shunt admittance The interface model conversion formula from Thevenin equivalent circuit to Norton equivalent circuit is shown in (1), wherein and are the injected current phasor and the shunt admittance in the Norton equivalent circuit, respectively, and are the internal electromotive force phasor and the series reactance in the Thevenin equivalent circuit, respectively.

[0067] (1)

[0068] S2, by combining the mathematical transformation of active control and the mode of reactive control, a general active outer loop control model and a general reactive outer loop control model are respectively constructed, to form a general power outer loop control model of grid-connected converter;

[0069] Further, the transfer function block diagram of the general active outer loop control model comprises a configurable first-order inertia link and its proportional coefficient and time constant parameters, and by configuring the inertia link proportional coefficient and time constant, the model can represent any one of the active regulation characteristics in power synchronization control, droop control, droop control with filter and virtual synchronous machine control.

[0070] Further, the transfer function block diagram of the general reactive outer loop control model comprises a configurable reactive control flag , a first-order inertia link and an integral link simulating synchronous machine excitation regulation; by configuring the reactive control flag, the proportional coefficient and time constant of the first-order inertia link and the time constant of the integral link, the model can represent any one of the reactive regulation characteristics in power synchronization control, droop control, droop control with filter and virtual synchronous machine control.

[0071] Specifically, in view of the modeling complexity problem of various power outer loop control strategies, the embodiment establishes a general power outer loop control model of grid-connected converter by means of mathematical transformation and model combination, and the steps are as follows:

[0072] 1) Power outer loop control strategy of grid-connected converter

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 2) General active power outer loop control model

[0077] 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 are equivalent, so the power synchronization control and the droop control are equivalent in active power control, although the control objects are different (the power synchronization control adjusts the internal voltage phase deviation, and the droop control adjusts the angular frequency deviation), but the active power control transfer functions of the two are completely equivalent.

[0078] (2)

[0079] (3)

[0080] According to the transfer function block diagrams of the droop control with filter and the virtual synchronous machine control in Figs. 10(c) and 10(d), the active power control transfer functions of the two can be written as (4) and (5) respectively:

[0081] (4)

[0082] (5)

[0083] wherein, is the internal voltage phase of the active power control output, is the rated angular frequency, is the active power reference value, is the active power output value, is the active droop coefficient, represents the filter bandwidth angular frequency of the droop control with filter, represents the deviation between the angular frequency of the virtual synchronous machine control and the rated angular frequency, represents the inertia coefficient, is the damping coefficient.

[0084] The active power control transfer functions of the droop control with filter and the virtual synchronous machine control are arranged respectively to obtain formulas (6) and (7), so it can be seen that the active power control of the two is: the active power deviation generates an angular frequency deviation signal through a first-order inertia link, and the rated angular frequency is added to obtain the internal voltage phase , so the active power control of the two is similar in the transfer function structure.

[0085] (6)

[0086] (7)

[0087] wherein, is the internal voltage phase of the active power control output, is the rated angular frequency, is the active power reference value, is the active power output value, is the active droop coefficient, ωf represents the filter bandwidth angular frequency of the filter-based droop control, ωi represents the inertia coefficient, ωd represents the damping coefficient.

[0088] The active control transfer function of the power synchronization control and the droop control can be expressed by formula (8), wherein ωf represents the filter bandwidth angular frequency of the filter-based droop control and the virtual synchronous machine control, ωf represents the filter bandwidth angular frequency of the filter-based droop control and the virtual synchronous machine control, ωi represents the first-order inertia link time constant, when the parameter in formula (9) is 0, formula (8) and formula (9) are completely equivalent, so in terms of active control, the filter-based droop control and the virtual synchronous machine control only increase inertia compared with the power synchronization control and the droop control, and still have the characteristics of the droop control.

[0089] (8)

[0090] (9)

[0091] Based on the above, a general active control can be established, and a transfer function block diagram thereof is shown in formula (10), wherein the active power deviation Figure 11 is generated into an angular frequency deviation value through a first-order inertia link, and further superimposed after the rated angular frequency and integrated to obtain the internal potential phase. By configuring the parameters of the general active outer loop control, different active outer loop control strategies can be simulated, and the specific configuration method is shown in Table 2. By configuring the parameters in Table 2, the model can realize the switching of the active control strategy by changing the input parameters without changing the code structure, wherein

[0092] ωd represents the active droop coefficient, ωf represents the filter bandwidth angular frequency of the filter-based droop control, ωi represents the inertia coefficient, ωd represents the damping coefficient.

[0093] Table 2 Configuration table of general active outer loop control parameters of grid-connected type converter

[0094]

[0095] 3) General reactive outer loop control model

[0096] ​It can be seen from FIG. 10(a) and FIG. 10(b) that the reactive power control of the power synchronization control is consistent with that of the droop control; the transfer function of the reactive power control of the droop control with filter in FIG. 10(c) can be written as formula (10), wherein represents the initial value of the internal potential amplitude, represents the droop coefficient of the reactive power, represents the bandwidth angular frequency of the filter, represents the initial value of the internal potential amplitude, represents the reference value of the reactive power, represents the output value of the reactive power, and the difference between the former two lies in that the reactive power deviation is multiplied by the droop coefficient after passing through a first-order inertia link (i.e. ); therefore, the reactive power control of the three can be represented as formula (11), wherein represents the proportional coefficient related to the reactive power deviation, represents the time constant of the first-order inertia link. When is 0, it can be used to represent the reactive power control of the power synchronization control and the droop control, and when it is not 0, it can be used to represent the reactive power control of the droop control with filter.

[0097] (10)

[0098] (11)

[0099] The reactive power control of the virtual synchronous machine control is different from other control modes, simulates the excitation characteristics of the synchronous machine, first generates a voltage control signal by using the droop control, as shown in formula (12), and then adjusts the internal potential by using an integrator, so that the terminal voltage is equal to the reference value, as shown in formula (13), wherein, represents the command value of the terminal voltage, represents the reference value of the terminal voltage, represents the droop coefficient of the reactive power, represents the time constant of the integral link.

[0100] (12)

[0101] (13)

[0102] By comprehensively considering formula (11), (12) and (13), a general reactive power control can be established, and the transfer function block diagram thereof is shown in FIG. 10(d); when the reactive power control flag Figure 12 , the model generates an internal potential deviation value by passing the reactive power deviation through an inertia link, and further superimposes the initial value of the internal potential to generate the internal potential amplitude; when the reactive power control flag , the model generates an internal potential deviation value by passing the reactive power deviation At this time, the model will generate a reactive power deviation The droop control deviation is generated by the inertia link, and the terminal voltage deviation is further superimposed And the internal potential deviation is generated by the integral link, and the initial value of the internal potential is further superimposed The internal potential amplitude is generated.

[0103] By configuring the parameters of the general reactive power outer loop control, different reactive power outer loop control strategies are simulated, and the specific configuration method is shown in Table 3. By configuring the parameters in Table 3, the model can realize the switching of the reactive power control strategy by changing the input parameters without changing the code structure, wherein represents the reactive droop coefficient, represents the filter bandwidth angular frequency of the droop control with filter, represents the integral link time constant.

[0104] Table 3 Configuration table of general reactive power outer loop control parameters of grid-connected converter

[0105]

[0106] S3, by the method based on internal potential reconstruction, the internal potential phase sequence output by the power outer loop is calculated according to the output current instruction phase sequence without current limiting, and then the current limiting strategy is selected to generate the current instruction phase sequence after current limiting. Then, the new internal potential satisfying the current limiting constraint is reconstructed by using the current instruction phase sequence after current limiting and the terminal voltage, and the new internal potential phase sequence satisfying the current limiting constraint is reconstructed according to the current phase sequence after current limiting and the terminal voltage, and the output current of the grid-connected converter is calculated by using the internal potential, and a general current limiting model suitable for grid-connected electromechanical transient model is established.

[0107] Further, the specific method for reconstructing the new internal potential satisfying the current limiting constraint is:

[0108] According to the selected current limiting strategy, the current instruction phase sequence after current limiting is calculated , and the formula is used to calculate, wherein, is the terminal voltage phase sequence, is the equivalent series reactance.

[0109] Specifically, in view of the modeling complexity problem of various grid-connected converter current limiting strategies, the embodiment proposes a method based on internal potential reconstruction, which recalculates an internal potential by using the current instruction 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 injected current, thereby establishing a general current limiting model suitable for grid-connected electromechanical transient model. The steps are:

[0110] 1) Mathematical description of current limiting strategy of grid-forming converter

[0111] The current limiting strategy of grid-forming converter mainly includes the ring current limiting strategy, the instantaneous current limiting strategy, the specified priority current limiting strategy and the current limiting strategy converted into grid-following control. The phasor diagram of the current before and after current limiting is shown in FIG. 13. The circular dotted line in FIG. 13(a), FIG. 13(c) and FIG. 13(d) represents the current limiting circle, and the radius is the maximum value of the allowed output current . The current limiting area in FIG. 13(b) is represented as a square dotted line, and the four vertices are located on the circle with a radius of . Among them, is the current before current limiting, is the current after current limiting; the xy axis is the synchronous reference coordinate axis of the grid, which rotates at the rated frequency; the dq coordinate axis has different meanings in the specified priority current limiting strategy and the current limiting strategy converted into grid-following control. In the specified priority current limiting strategy, the phase of the d-axis is equal to the phase of the internal potential output of the active outer loop control. In the current limiting strategy converted into grid-following control, the phase of the d-axis is equal to the phase of the voltage output of the phase-locked loop.

[0112] The mathematical description methods of the four types of current limiting strategies of grid-forming converters are given below to embed the subsequent developed general current limiting model of grid-forming converters:

[0113] As shown in FIG. 13(a), the ring current limiting strategy has the characteristics that the phase of the current before and after current limiting remains unchanged, and the amplitude is limited to . When the amplitude of the current exceeds , the current after current limiting can be represented by formula (14), wherein , represent the x and y axis components of the output current after current limiting, , represent the x and y components of the output current before current limiting, is the maximum value of the allowed output current.

[0114] (14)

[0115] As shown in FIG. 13(b), the instantaneous current limiting strategy has the characteristics that the maximum components of the x and y axes of the current are specified, as shown in formula (15), wherein is the set value of the maximum x-axis component of the current, , are the maximum x and y axis components of the output current allowed. When the x-axis component of the current is greater than the maximum x-axis component, it is limited to the maximum value; when the y-axis component of the current is greater than the maximum y-axis component, it is limited to the maximum value. The current after current limiting can be represented by formula (16).

[0116] (15)

[0117] (16)

[0118] As shown in FIG. 13 (c), the feature of the specified priority current limiting strategy is that the phase of the current after current limiting leads the phase of the inner potential of the active outer loop control output by an angle , so the phase of the current after current limiting is , and when the current amplitude exceeds , the current after current limiting can be expressed by formula (17), wherein represents the phase of the inner potential of the active outer loop control output, represents the angle specified value by which the phase of the current after current limiting leads .

[0119] (17)

[0120] As shown in FIG. 13 (d), the feature of the current limiting strategy converted into grid-type control is that the phase of the current after current limiting leads the phase of the phase-locked loop output by an angle , so the phase of the current after current limiting is , and when the current amplitude exceeds , the current after current limiting can be expressed by formula (18), wherein represents the angle of the phase-locked loop output, represents the angle specified value by which the phase of the current after current limiting leads .

[0121] (18)

[0122] 2) Modeling of general current limiting model based on inner potential reconstruction

[0123] As shown in FIG. 13 (e), the actual current limiting process of the grid-type converter electromagnetic transient model is: the voltage loop generates the instruction value of the current according to the voltage reference value generated by the power outer loop Figure 14 , , , the instruction value is obtained after the current limiting of the current limiting device by adopting different current limiting strategies such as formula (14), (16), (17), (18) , , , , and the current loop generates the instruction value of the inner potential of the converter according to the instruction value of the current , , and the internal potential phasor is obtained by modulation. The current limiter is located between the voltage loop and the current loop control in the electromagnetic transient model. Since the dynamic process of the current loop, the voltage loop and the modulation can be ignored in the electromechanical transient time scale, the current limiting is considered to be completed instantaneously in this time scale. Therefore, the general current limiting model based on the reconstructed internal potential is proposed according to the actual current limiting process in the above embodiment model example, and the model algorithm flow chart is shown in Figure 15 .

[0124] Firstly, the general power outer loop control model is initialized according to the power flow calculation results, which is embodied in setting the initial values of the inertia module and the integral module in the active power control and the reactive power control models for the electromechanical transient simulation. Figure 11 、 Figure 12 .

[0125] Secondly, the internal potential phasor Figure 11 and the terminal voltage phasor Figure 12 output by the general power outer loop control model composed of are used to calculate the output current instruction phase value without current limiting by using formula and output.

[0126] Then, it is judged whether the amplitude of the output current instruction phasor without current limiting exceeds the maximum current limit value . When it does not exceed , the output current instruction phasor after current limiting is equal to the current instruction phasor without current limiting, i.e. . If it exceeds , the current instruction phasor after current limiting is calculated and output according to the set current limiting strategy by using current limiting strategy formulas (14), (16), (17) and (18), and the current instruction phasor before and after current limiting is not equal.

[0127] Then, the internal potential is recalculated according to the current instruction phasor after current limiting by using formula , and the internal potential phasor is taken as the calculation parameter of the electromechanical transient model and the grid connection interface model, and is further converted into the current source interface model of the Norton equivalent circuit by using formula to participate in the network solution.

[0128] It is worth noting that when the current is not limited, the reconstructed internal potential phasor is equal to the internal potential phasor generated by the power outer loop . When the current is limited, the reconstructed internal potential phasor is not equal to the internal potential phasor generated by the power outer loop.

[0129] ​The proposed current limiting strategy based on internal potential reconstruction does not contain any dynamic integral module, is an algorithm model, and thus can realize instantaneous current limiting, and in addition, the model can simulate various current limiting strategies, so that the model has better universality.

[0130] Embodiment 2

[0131] In an embodiment of the present application, a general network configuration type converter electromechanical transient modeling system is provided, comprising:

[0132] The grid-connected interface modeling module is configured to: by analyzing the response time scale of each topology of the converter, simplify the electromagnetic transient model of the network configuration type converter of different topologies into a grid-connected equivalent circuit of the electromechanical transient time scale, and uniformly represent by using a model of internal potential series reactance of power outer loop control, to establish a general grid-connected interface model of the network configuration type converter electromechanical transient;

[0133] The outer loop control modeling module is configured to: by combining the mathematical transformation of active control and the mode of reactive control, respectively construct a general active outer loop control model and a general reactive outer loop control model, to constitute a general power outer loop control model of the network configuration type converter;

[0134] The current limiting modeling module is configured to: by a method based on internal potential reconstruction, according to the current instruction phasor after current limiting and the terminal voltage, reconstruct a new internal potential satisfying the current limiting constraint, to establish a general current limiting model applicable to the network configuration type electromechanical transient model.

[0135] The above describes the specific embodiments of the present application in combination with the drawings, but is not a limitation on the protection scope of the present application, and those skilled in the art should understand that various modifications or deformations made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

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. 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 to generate 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 to the grid. 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. The transfer function block diagram of the general active 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. 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 filter, and virtual synchronous machine control. By using the 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, and a general current limiting model applicable to network electromechanical transient models is established. 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.

2. 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.

3. 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 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 to generate 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 to the grid. 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 transfer function block diagram of the general active 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. 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 filter, and virtual synchronous machine control. 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; 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.

4. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the general electromechanical transient modeling method for grid-type converters as described in any one of claims 1-2.

5. 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 1-2.

6. 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 grid-type converter electromechanical transient modeling method as described in any one of claims 1-2.

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