MMC virtual resistor regulation and control method, system and device and medium

Abstract

The invention discloses an MMC virtual resistance regulation and control method, system and device and a medium, and the method comprises the steps: setting an operation environment of a modular multilevel converter (MMC) in a mountain area power distribution network, carrying out the equivalent combination of the electrical parameters of an AC side and a bridge arm, and building an average simplified model suitable for large disturbance analysis; analyzing an energy relationship between non-energy storage and energy storage elements by applying a mixed potential function theory, and constructing a large interference stability criterion; a virtual resistance variable is introduced to a direct current side, equivalent power consumption is converted into a d-axis active current adjusting variable according to an alternating current and direct current side power balance relation, an adjusted current reference value is generated, and a stable control scheme is formed; the virtual resistance is incorporated into stability criteria, boundary constraints meeting stability conditions are deduced in combination with typical disturbance (such as voltage drop and load abrupt change) characteristics of a mountainous area, and the value range and the setting value of the virtual resistance are determined. According to the invention, the transient stability and the power supply reliability of the MMC in the weak mountainous area power distribution network are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of power distribution network control technology, and in particular to an MMC virtual resistance control method, system, device and medium. Background Technology

[0002] Due to the complex terrain and dispersed user base in mountainous power distribution networks, the need for flexible interconnection technology is particularly urgent. Connecting different distribution areas to achieve energy sharing is a key means of improving power supply reliability. Modular multilevel converters (MMCs), as the core equipment supporting this interconnection architecture, directly determine the reliability of the entire energy sharing system through their stable operation. However, the operating environment of mountainous power distribution networks is very unique—natural factors such as lightning strikes and icing frequently cause voltage drops, while load fluctuations from agricultural irrigation and small hydropower stations create strong impact loads. Furthermore, the lines are generally very long, making them prone to short circuits or grounding faults. These complex disturbances continuously threaten the stable operation of MMCs.

[0003] Existing technologies also have significant shortcomings in ensuring the stable operation of MMCs in mountainous areas. On the one hand, improving stability by optimizing the main circuit hardware parameters requires replacing equipment, which is not only extremely costly but also difficult to apply to existing mountainous projects. On the other hand, simply adjusting control parameters cannot resolve the contradiction between increased system damping and power loss—because the resistance in the system has a dual impact on MMC stability: increasing the equivalent resistance on the AC side and the bridge arm resistance can indeed enhance damping, but if the resistance is too large, the loss will increase significantly; more problematicly, increasing the equivalent resistance on the AC side will degrade the dynamic performance on the DC side, thus affecting overall stability. Most importantly, there is currently a lack of quantitative analysis methods based on large disturbance stability criteria, making it impossible to determine the appropriate range for resistance parameters, which naturally makes it difficult to meet the stable operation requirements of mountainous areas under various complex disturbances. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides an MMC virtual resistance control method, system, device, and medium to solve the problem that existing technologies cannot guarantee the stable operation of flexible interconnection in operational mountain power distribution networks.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for controlling the virtual resistance of an MMC, comprising: The topology and operating environment of the modular multilevel converter in the mountain power distribution network are set, and the electrical parameters of the AC side and the bridge arm are equivalently merged to establish an average simplified model. Based on the average simplified model, the energy relationship between non-energy storage components and energy storage components in the system is analyzed by applying the mixed potential function theory to obtain the large disturbance stability criterion. Based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model, a virtual resistance variable is introduced on the DC side of the modular multilevel converter. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, and an adjusted active current component reference value is generated to obtain the control scheme of the modular multilevel converter. Based on the virtual resistance variable and the large disturbance stability criterion introduced in the modular multilevel converter control scheme, the virtual resistance variable is incorporated into the analysis framework of the large disturbance stability criterion. Combined with the characteristics of typical disturbance scenarios in mountainous areas, the boundary constraints are solved to obtain the value range of the virtual resistance and determine the specific setting value of the virtual resistance.

[0007] As a preferred embodiment of the MMC virtual resistance control method described in this invention, the average simplified model includes: The equivalent AC resistance is obtained by combining the AC side resistance and the bridge arm resistance. The AC-side equivalent inductance is obtained by combining the AC-side inductance and the bridge arm inductance. The DC-side equivalent capacitance is obtained by adjusting the capacitance of each submodule in the bridge arm according to the number of submodules. As a preferred embodiment of the MMC virtual resistance control method described in this invention, the large disturbance stability criterion includes: A hybrid potential function is constructed based on the current potential function of non-energy storage components and the voltage potential function of capacitor voltage. By performing second-order partial derivative operations on the mixed potential function with respect to the current variable and the voltage variable respectively, the second-order derivative matrices of the current potential function and the voltage potential function are obtained. The sum of the minimum eigenvalues ​​of the two second-order derivative matrices is calculated and used as the basis for stability judgment.

[0008] As a preferred embodiment of the MMC virtual resistance control method described in this invention, the step of introducing a virtual resistance variable on the DC side of the modular multilevel converter includes: In the control logic, construct a power term that is proportional to the square of the DC voltage and inversely proportional to the virtual resistance value; Add the power item to the AC side active power command.

[0009] As a preferred embodiment of the MMC virtual resistance control method of the present invention, the step of converting the power consumption corresponding to the virtual resistance into an adjustment command for the active current component includes: Collect the DC side voltage and AC side active voltage components; The active current regulation is calculated based on the virtual resistance value, DC side voltage, and AC side active voltage component. The active current adjustment is superimposed on the active current reference value.

[0010] As a preferred embodiment of the MMC virtual resistance control method described in this invention, the typical disturbance scenario characteristics in mountainous areas include: The grid voltage dropped; A sudden change in load power is sufficient to cause a significant deviation of the DC-side voltage of the modular multilevel converter from its steady-state value. The duration of the disturbance exceeds the initial stage of the transient response of the control system.

[0011] The beneficial effect of this preferred technical solution is that, through the clear definition of the characteristics of typical disturbance scenarios in mountainous areas, the virtual resistance parameter tuning can cover the most severe large-interference conditions in actual operation, thereby ensuring the stability of the modular multilevel converter under voltage drops, severe load fluctuations and continuous disturbances.

[0012] As a preferred embodiment of the MMC virtual resistance control method described in this invention, the step of incorporating the virtual resistance variable into the analysis framework of the large disturbance stability criterion includes: The influence of a virtual resistance variable on the DC-side power balance is explicitly introduced into the hybrid potential function; Reconstruct the voltage potential function that includes the virtual resistance variable; Recalculate the minimum eigenvalue after introducing the virtual resistance.

[0013] The beneficial effect of this preferred technical solution is that by explicitly embedding the virtual resistance variable into the hybrid potential function and reconstructing the voltage potential function, the large disturbance stability criterion can accurately reflect the influence of the virtual resistance on the system energy balance, thereby providing a theoretical basis for the stability domain tuning of the virtual resistance parameter.

[0014] Secondly, the present invention provides an MMC virtual resistance control system, comprising: The large disturbance stability modeling and criterion generation module is used to set the topology and operating environment of modular multilevel converters in mountainous power distribution networks, and to equivalently merge the electrical parameters of the AC side and the bridge arm to establish an average simplified model. Based on the average simplified model, the mixed potential function theory is applied to analyze the energy relationship between non-energy storage components and energy storage components in the system to obtain the large disturbance stability criterion. The adjustment command generation module is used to introduce a virtual resistance variable on the DC side of the modular multilevel converter based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, generating an adjusted active current component reference value, and obtaining the control scheme of the modular multilevel converter. The virtual resistance parameter tuning module is used to incorporate the virtual resistance variable introduced in the modular multilevel converter control scheme and the large disturbance stability criterion. It integrates the virtual resistance variable into the analysis framework of the large disturbance stability criterion, combines the characteristics of typical disturbance scenarios in mountainous areas, solves the boundary constraints, obtains the value range of the virtual resistance, and determines the specific tuning value of the virtual resistance.

[0015] Thirdly, the present invention provides an electronic device, comprising: Memory, used to store programs; A processor for executing the computer-executable instructions, which, when executed by the processor, implement the steps of the MMC virtual resistance control method.

[0016] Fourthly, the present invention provides a computer-readable storage medium comprising: when the program is executed by a processor, the step of implementing the MMC virtual resistance control method.

[0017] The beneficial effects of this invention are as follows: By establishing a simplified average model of a modular multilevel converter that considers the actual topology and operating environment of a mountainous power distribution network, and by applying the hybrid potential function theory to construct a large disturbance stability criterion, a quantitative assessment of the nonlinear stability of the system under severe disturbances such as voltage dips and load step jumps can be achieved. By introducing a virtual resistance variable on the DC side and equating it to an adjustment command of the active current component based on the AC / DC power balance relationship, lossless control that can dynamically adjust the system damping without physical energy-consuming components can be achieved. By incorporating the virtual resistance variable into the stability criterion analysis framework and solving its stability domain boundary in combination with the characteristics of typical disturbance scenarios in mountainous areas, the theoretical tuning and engineering feasibility of the virtual resistance parameter can be unified, ensuring the robust stability of the control scheme under large disturbances. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the basic process of an MMC virtual resistance control method provided in one embodiment of the present invention.

[0019] Figure 2 The diagram shows an MMC system topology for an MMC virtual resistance control method provided in one embodiment of the present invention.

[0020] Figure 3 A simplified average model diagram of an MMC system for an MMC virtual resistance control method provided in an embodiment of the present invention.

[0021] Figure 4 The diagram shows a simplified average MMC model after adding a resistor, which is provided as an embodiment of the present invention for an MMC virtual resistance control method.

[0022] Figure 5 The image shows the MMC simulation waveforms before and after resistance regulation under voltage drop conditions in a mountainous power grid, as provided in an embodiment of the present invention, for an MMC virtual resistance regulation method.

[0023] Figure 6 The image shows the MMC simulation waveforms before and after resistance adjustment under mountainous impact load conditions, which is an embodiment of the present invention. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0025] Example 1, referring to Figure 1 As an embodiment of the present invention, an MMC virtual resistance control method is provided, comprising: S100: Set the topology and operating environment of the modular multilevel converter in the mountain power distribution network, and equivalently merge the electrical parameters of the AC side and the bridge arm to establish an average simplified model; based on the average simplified model, apply the mixed potential function theory to analyze the energy relationship between non-energy storage components and energy storage components in the system, and obtain the large disturbance stability criterion. S200: Based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model, a virtual resistance variable is introduced on the DC side of the modular multilevel converter. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, generating an adjusted active current component reference value, and thus obtaining the control scheme of the modular multilevel converter. S300: Based on the virtual resistance variable and large disturbance stability criterion introduced in the modular multilevel converter control scheme, the virtual resistance variable is incorporated into the analysis framework of the large disturbance stability criterion. Combined with the characteristics of typical disturbance scenarios in mountainous areas, the boundary constraints are solved to obtain the value range of the virtual resistance and determine the specific setting value of the virtual resistance.

[0026] It should be noted that existing technologies face multiple severe challenges during the operation of power distribution networks in mountainous areas. These include weak power grid structures and small short-circuit capacity, making them susceptible to natural factors such as lightning strikes and icing, leading to frequent deep voltage drops. Furthermore, the dispersed and highly seasonal and impulsive load distribution (such as the centralized start-up and shutdown of irrigation pump clusters and random disconnection of small hydropower stations) causes significant step changes in load power within a short period. Simultaneously, such disturbances often last for extended periods, exceeding the initial stage of the control system's transient response, rendering traditional stability analysis methods based on small-signal linearization ineffective. Existing MMC control strategies lack effective damping mechanisms for energy imbalances on the AC and DC sides under large disturbances, easily triggering severe DC voltage fluctuations, bridge arm circulating current divergence, and even converter blockage, seriously threatening the safe and stable operation of the system.

[0027] Therefore, to address the issue that existing technologies cannot guarantee the stable operation of flexible interconnection in operational mountain power distribution networks, the steps S100-S300 are implemented. By constructing a simplified average model of a modular multilevel converter suitable for large disturbance scenarios in mountainous areas and a large disturbance stability criterion, combined with lossless virtual resistance control and parameter design based on stability domain boundary tuning, robust and stable operation of the MMC system under severe conditions such as deep voltage drops and drastic load changes is achieved.

[0028] Example 2, this is an embodiment of the present invention, which provides an MMC virtual resistance control method based on the previous embodiment, including: In the embodiments of this application, such as Figure 2 The diagram shows a typical system topology for a Modular Multilevel Converter (MMC). This topology consists of three arms, each containing multiple sub-modules (SMs), connected in series to form a three-phase output circuit. Each sub-module is typically a half-bridge or full-bridge structure, used to achieve voltage step synthesis. A DC capacitor is connected to the DC side. And constant power load (CPL) is used to maintain DC voltage stability and simulate actual load characteristics. The AC side is connected via an inductor. and resistance Connected to the power grid, the PCC (point-to-point connection point) is connected to a three-phase power grid voltage source. , , An inductor and resistor are connected in series in each bridge arm to suppress circulating current and limit the rate of change of current. The dashed box in the lower right corner of the diagram shows the average value model of a single submodule, representing its equivalent as a simplified circuit of a controlled voltage source in parallel with a capacitor. Output voltage for the submodule. The current represents the submodule current; this model is used for subsequent dynamic analysis and control design. The overall topology demonstrates the high reliability and flexible control capability of the MMC in high-voltage, high-power applications.

[0029] In the embodiments of this application, such as Figure 3 The figure shows a simplified average value model of a modular multilevel converter (MMC) in a dq synchronous rotating coordinate system. This model, through equivalent parameter merging, abstracts the complex three-phase bridge arm structure into multiple independent equivalent circuit branches for analyzing the system's dynamic characteristics. The two branches on the left represent the equivalent circuits of the AC side d-axis and q-axis, respectively. , For the equivalent resistance and inductance on the AC side, , The grid voltage has d-axis and q-axis components. , The current difference between the bridge arms , For submodule voltage deviation, controlled voltage source and This represents the coupling effect in a rotating coordinate system. The two branches on the upper right represent the bridge arm circulation loop, among which... , This is the equivalent circulating impedance. For the submodule capacitor voltage and, Half the DC voltage This represents the DC-side current. The bottom branch is the DC-side equivalent circuit. This is the equivalent capacitance. The sum of the capacitor voltages, For constant power load, This represents the DC-side current. The entire model preserves the AC / DC power balance, making it suitable for large-disturbance stability analysis and virtual resistance control design.

[0030] In the embodiments of this application, based on Figure 2 Based on the MMC system topology shown, and considering the dynamic characteristics of the MMC interconnection system in mountainous distribution networks, a simplified average MMC model adapted to complex disturbance scenarios in mountainous areas is constructed (e.g., Figure 3 As shown in the figure, the stability criterion for large disturbances is derived, and the influence mechanism of resistance parameters on the stability of MMC in mountainous areas is clarified.

[0031] In this embodiment of the application, the average simplified model in step S100 includes: The equivalent AC resistance is obtained by combining the AC side resistance and the bridge arm resistance. The AC-side equivalent inductance is obtained by combining the AC-side inductance and the bridge arm inductance. The DC-side equivalent capacitance is obtained by adjusting the capacitance of each submodule in the bridge arm according to the number of submodules. In this embodiment, the AC side resistance, inductance, and bridge arm parameters are combined into an equivalent parameter as follows: N represents the number of submodules per bridge arm.

[0032] In this embodiment of the application, the large disturbance stability criterion in step S100 includes: A hybrid potential function is constructed based on the current potential function of non-energy storage components and the voltage potential function of capacitor voltage. By performing second-order partial derivative operations on the mixed potential function with respect to the current variable and the voltage variable respectively, the second-order derivative matrices of the current potential function and the voltage potential function are obtained. The sum of the smallest eigenvalues ​​of the two second-order derivative matrices is used as a criterion for stability judgment.

[0033] In this embodiment of the application, the large disturbance stability criterion and verification system in step S100 constructs an average simplified model of MMC, decouples the energy relationship between non-energy storage components and energy storage components based on the hybrid potential function theory, explicitly introduces the influence of virtual resistance on DC side power balance, reconstructs the voltage potential function and calculates the sum of the minimum eigenvalues ​​of the second derivative matrix of the current and voltage potential functions, and uses the sum being greater than zero as the criterion for the system to remain stable under typical large disturbances in mountainous areas.

[0034] In an optional implementation, the large disturbance stability criterion and verification system in step S100 can also be based on the MMC average simplified model to construct a Lyapunov energy function that includes the DC side equivalent capacitance energy storage and the AC side inductance magnetic energy. The power dissipation term corresponding to the virtual resistance is introduced to characterize its damping effect. By proving that the derivative of the energy function along the system trajectory is negative definite or semi-negative definite under typical mountain disturbances, the large disturbance stability of the system can be determined.

[0035] In an optional implementation, the large disturbance stability criterion and verification system in step S100 can also be based on the MMC average simplified model to carry out time-domain simulation under typical disturbance scenarios in mountainous areas (such as voltage drop and load step), obtain the dynamic response trajectory of key state variables such as DC voltage and bridge arm current, and calculate the trajectory sensitivity of the virtual resistance parameter output by the calculation system, and invert the range of virtual resistance values ​​that meet the stability requirements by combining stability boundary indicators (such as voltage fluctuation amplitude and convergence time).

[0036] In this embodiment of the application, the dynamic equivalent characterization method of MMC in step S100 models the MMC system in a synchronous rotating coordinate system, and equivalently merges the electrical parameters of the AC side line and the bridge arm to form a simplified AC side impedance; the energy storage characteristics of each sub-module are concentrated and characterized as an equivalent DC side capacitor; finally, an averaged dynamic model that can reflect the AC and DC side power coupling relationship and is suitable for large disturbance stability analysis is constructed.

[0037] In an optional implementation, the MMC dynamic equivalent characterization method in step S100 can also establish a high-frequency switching function based on the switching state of the sub-module, perform time averaging of the bridge arm voltage and current within the power frequency cycle, retain the fundamental wave and the main dynamic components, thereby directly obtaining a continuous average model containing the characteristics of circulating current and DC voltage coupling without relying on dq transformation.

[0038] In an optional implementation, the dynamic equivalent characterization method of MMC in step S100 can also identify its dynamic characteristics by applying excitation signals to the AC and DC ports of MMC and collecting input and output response data, thereby establishing an equivalent external model composed of controlled voltage sources or current sources to characterize the AC and DC power interaction behavior of the system under mountain disturbances.

[0039] In this embodiment, the virtual resistance stable feasible region is generated in step S100 by explicitly embedding the virtual resistance variable into the large disturbance stability criterion constructed based on the mixed potential function, reconstructing the voltage potential function containing its influence, and deriving an analytical inequality constrained by the sum of the minimum eigenvalues ​​being greater than zero, thereby directly solving for the upper limit of the virtual resistance value that satisfies the system stability under typical mountain disturbances.

[0040] In an optional implementation, the virtual resistance stable feasible region generation method in step S100 can also be based on the MMC average simplified model, with the virtual resistance as a variable parameter. By scanning its value and analyzing the pole distribution of the closed-loop system or the phase / gain margin of the open-loop frequency response, the feasible range of the virtual resistance that meets the stability requirements (such as all poles being located in the left half-plane or the margin being greater than a preset threshold) can be screened out.

[0041] In an optional implementation, the method for generating the virtual resistance stable feasible region in step S100 can also be based on typical disturbance scenarios in mountainous areas (such as voltage drop, load step) to generate a large amount of MMC operation simulation data. With disturbance type, amplitude and system state as input, and stability / instability label or performance index as output, a machine learning model (such as neural network or support vector machine) is trained, and then the range of virtual resistance values ​​that meet the stability requirements is predicted online or offline.

[0042] In this embodiment of the application, in addition to constructing the average simplified model and the large disturbance stability criterion, step S100 also includes the following specific operations: Based on the dq synchronous rotating coordinate system, the three-phase AC quantities are converted into dq-axis components through Park transformation. Combined with a dual-closed-loop control strategy (outer loop DC voltage control adapts to the voltage stability requirements of energy sharing in mountainous areas, and inner loop current control quickly responds to load fluctuations), an equivalent circuit model including controlled voltage and current sources is established. The dual-closed-loop control structure is employed: the outer loop is for DC voltage control, used to maintain the stability of the DC bus in multi-terminal interconnections in mountainous areas; the inner loop is for current control, used to quickly suppress current disturbances caused by impulsive loads. This accurately reflects the external characteristics of the MMC AC side during voltage dips in mountainous areas and the dynamic behavior of the DC side during load surges.

[0043] Based on the hybrid potential function theory, a stability criterion for MMC systems adapted to large disturbance scenarios in mountainous areas is constructed. The hybrid potential function is obtained based on the current potential function A(i) and the capacitor voltage potential function B(v) of the non-energy storage components, and its expression is: γ and α are determined by the topology and interconnection method of the MMC in the mountainous area.

[0044] The matrices Aii(i) and Bvv(v) are obtained through second-order partial differential operations, and their minimum eigenvalues ​​μ1 and μ2 are calculated. The system tends to be stable when μ1 + μ2 > 0.

[0045] In this embodiment of the application, step S200, which introduces a virtual resistance variable on the DC side of the modular multilevel converter, includes: In the control logic, construct a power term that is proportional to the square of the DC voltage and inversely proportional to the virtual resistance value; Add the power item to the AC side active power command.

[0046] like Figure 4 As shown, a virtual resistor is connected in parallel in the DC-side equivalent circuit. This forms a structure containing the equivalent capacitance. Constant power load and controlled current source A simplified model is used to characterize the effect of virtual resistance on DC-side energy balance.

[0047] In this embodiment of the application, step S200, which converts the power consumption corresponding to the virtual resistor into an adjustment command for the active current component, includes: Collect the DC side voltage and AC side active voltage components; The active current regulation is calculated based on the virtual resistance value, DC side voltage, and AC side active voltage component. The active current adjustment is superimposed on the active current reference value.

[0048] In this embodiment of the application, the virtual resistor is introduced in step S200 by constructing an equivalent power term in the DC side control logic that is proportional to the square of the DC voltage and inversely proportional to the virtual resistance value. This term is then converted into a d-axis active current adjustment based on the AC / DC power balance relationship and superimposed on the current inner loop reference value. This achieves lossless damping control of the virtual resistor without increasing the physical energy-consuming components.

[0049] In an alternative implementation, the virtual resistor introduced in step S200 can also be a braking resistor controlled by a power electronic switch connected in parallel across the MMC DC bus. When a disturbance in the mountainous area (such as a voltage drop or a sudden increase in load) causes the DC voltage to exceed the limit, the switch is triggered to close and connect the resistor. The surplus energy is dissipated in real time to suppress DC voltage fluctuations, thereby improving the transient stability of the system.

[0050] In an alternative implementation, the virtual resistor introduced in step S200 can also be superimposed on a virtual impedance voltage drop term proportional to the d-axis current in the MMC AC side current inner loop control, which effectively increases the system output impedance to enhance damping, thereby improving the ability to suppress large disturbances such as voltage drops and load changes in mountainous areas without modifying the DC side structure.

[0051] In this embodiment of the application, in step S200, in addition to introducing a virtual resistance variable and converting it into an active current regulation command, a specific power conservation equation is also included, the expression of which is: in, For AC side power, For DC-side power transmission, V dc DC voltage This is a virtual resistance value, and the design is adapted to the power dynamic balance requirements in mountain energy exchange.

[0052] In this embodiment, the virtual resistance current regulation loop adapted to mountainous disturbance response is added to the MMC voltage outer loop control structure, including the DC side voltage. V dc Real-time sampling (accurately capturing voltage fluctuations caused by disturbances in mountainous areas), based on virtual resistance power demand, calculates the d-axis current change as follows: in, V sd The AC side d-axis voltage; By superimposing the current on the d-axis reference current and controlling the current through the inner current loop, the d-axis current can be dynamically adjusted, effectively constructing the damping characteristics of a virtual resistor and enhancing the system's ability to resist large interferences.

[0053] It should be noted that increasing the equivalent resistance R0 on the AC side will simultaneously affect both the system damping and the dynamic performance on the DC side: on the one hand, it increases the damping of the current loop, suppressing current surges caused by voltage dips; on the other hand, it weakens the DC voltage regulation capability, making it prone to voltage oscillations during energy exchange. Therefore, a quantitative balance must be struck using stability criteria to avoid blindly increasing the damping.

[0054] In this embodiment of the application, the characteristics of a typical disturbance scenario in a mountainous area in step S300 include: The grid voltage dropped; A sudden change in load power is sufficient to cause a significant deviation of the DC-side voltage of the modular multilevel converter from its steady-state value. The duration of the disturbance exceeds the initial stage of the transient response of the control system.

[0055] In this embodiment of the application, the characteristics of the typical disturbance scenario in the mountainous area in step S300 specifically include: the grid voltage drops sharply due to natural factors such as lightning strikes and icing, with the drop range being 40% to 80% of the rated value; the load power experiences a sudden increase or decrease of more than 500 MW within 0.1 seconds due to reasons such as the centralized start-up and shutdown of irrigation pump groups or the random disconnection of small hydropower from the grid; and the duration of the above disturbances exceeds 0.5 seconds, which is beyond the initial stage of the transient response of the control system and belongs to a large disturbance condition that requires energy balance and damping mechanisms to maintain stability.

[0056] In this embodiment of the application, step S300 incorporates the virtual resistance variable into the analysis framework of the large disturbance stability criterion, including: The influence of a virtual resistance variable on the DC-side power balance is explicitly introduced into the hybrid potential function; Reconstruct the voltage potential function that includes the virtual resistance variable; Recalculate the minimum eigenvalue after introducing the virtual resistance.

[0057] In this embodiment of the application, the stability criterion is expressed as: in, , These are the minimum eigenvalues ​​of the mixed potential function with respect to current and voltage, respectively. , The equivalent resistance and inductance on the AC side; , For the equivalent resistance and inductance of the bridge arm; This is the proportional gain of the inner current loop; The proportional gain of the circulating current controller; This is the voltage outer loop proportional gain; This is a reference value for DC voltage. The difference in d-axis current between bridge arms; This is the equivalent capacitance on the DC side; This is the sum of the capacitor voltages of all submodules; The active power consumed by a constant power load; This is a virtual resistance value.

[0058] The maximum constraint condition for virtual resistance is derived from the above stability criterion, namely: Example 3, referring to Figures 5-6 This is one embodiment of the present invention, which provides an MMC virtual resistance control method. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through specific implementation methods and implementation effects.

[0059] The specific details of this embodiment are as follows: To verify the feasibility of this patent, a simulation model was built based on the MMC system, using an average value model topology. The control strategy is a dual closed-loop control (outer loop DC voltage control and inner loop current control). The inverter side is equivalent to a constant power load (CPL). The simulation parameters are shown in Table 1.

[0060] Table 1 Simulation System Parameter Table

[0061] Experiment 1: The simulation of voltage drops in the power grid caused by natural factors such as lightning strikes and icing in mountainous areas verifies the ability of virtual resistance to suppress typical disturbances in mountainous areas.

[0062] The system initially operates stably under normal conditions in a mountainous power distribution network: the AC grid rated voltage is 200kV, the load power is 400MW (including residential and basic industrial loads in the mountainous area), and the energy balance architecture is in stable operation. At 1.5s, a lightning strike is simulated on the mountainous line, causing the AC grid voltage to drop to 60% of its rated value (120kV). The system response is compared with and without a virtual resistor (simulation waveforms are shown below). Figure 5 (As shown).

[0063] Without a virtual resistor: the system's stability criterion for large disturbances is less than 0; voltage drops in mountainous areas disrupt the MMC energy balance; the AC side d-axis current (id) surges and then exhibits periodic fluctuations that cannot converge (e.g. Figure 5 As shown in (a), the system shut down due to transient instability, directly causing an interruption in energy exchange within the mountainous power distribution network and affecting power supply reliability.

[0064] After adding a 260Ω virtual resistor: Based on the virtual resistance control strategy proposed in this invention, the voltage fluctuation of the DC side in mountainous areas is sampled in real time through the outer voltage loop, and the change in d-axis current is calculated. This is then superimposed on the reference current, effectively achieving damping regulation. At this point, the system's large disturbance stability criterion μ1+μ2>0, the AC side current rapidly converges to a stable value, and the DC voltage fluctuation amplitude is controlled within 5% (e.g., Figure 5 As shown in (b), the system maintained stable operation, effectively ensuring the continuous energy exchange under the voltage drop condition in mountainous areas, and verifying the suppression effect of virtual resistance on voltage disturbance in mountainous areas.

[0065] Experiment 2: The simulation of typical impact load scenarios, such as the concentrated start-up of agricultural irrigation equipment in mountainous areas and the output fluctuation of small hydropower stations, verifies the tolerance of virtual resistance to sudden load changes in mountainous areas.

[0066] The system initially operates stably at the normal load level in the mountainous area: the AC grid voltage is maintained at the rated value of 200kV, and the initial load power is 400MW. At 1.5s, a simulated concentrated pump start-up during the mountainous irrigation season causes a sudden increase in load power to 1400MW. The system response is compared with that without a virtual resistor and with a 600Ω virtual resistor (simulation waveforms are shown below). Figure 6 (As shown).

[0067] Without virtual resistance: the system's stability criterion for large disturbances is μ1+μ2<0. A sudden increase in load in mountainous areas causes power imbalance, resulting in drastic fluctuations in AC current and an inability to maintain power balance (e.g., Figure 6 (a) As shown, the MMC stopped operating due to transient instability, which caused the power supply of the mountain power grid to be interrupted, seriously affecting agricultural production and residential electricity consumption.

[0068] After adding a 600Ω virtual resistor: the virtual resistor control strategy based on the power conservation principle starts quickly, achieving power balance by dynamically adjusting the d-axis current. At this point, the system's large disturbance stability criterion μ1+μ2>0, and both the AC current and DC voltage quickly stabilize (e.g., Figure 6 (b) shows that the system maintains stable operation, proving that virtual resistance can effectively improve the MMC's tolerance to mountainous impact loads and provide stable support for the energy mutual assistance architecture of mountainous power distribution networks.

[0069] The results of Experiments 1 and 2 show that the MMC average simplified model, large disturbance stability criterion, and virtual resistance control method proposed in this invention can accurately reflect the dynamic characteristics of mountain power distribution networks. The virtual resistance can effectively enhance the ability of the MMC system to resist complex disturbances such as voltage drops and impulsive loads in mountainous areas. This provides strong technical support for building an energy mutual assistance architecture for mountain power distribution networks and improving power supply reliability, and verifies the correctness of the method and its applicability to mountainous scenarios.

[0070] Example 4 is an embodiment of the present invention. This embodiment differs from the first embodiment in that it provides an MMC virtual resistance control system.

[0071] It should be noted that the technical solution of the MMC virtual resistance control system and the technical solution of the MMC virtual resistance control method described above belong to the same concept. For details of the technical solution of the MMC virtual resistance control system not described in detail in this embodiment, please refer to the description of the technical solution of the MMC virtual resistance control method described above.

[0072] This embodiment provides an MMC virtual resistance control system, comprising: The large disturbance stability modeling and criterion generation module is used to set the topology and operating environment of modular multilevel converters in mountainous power distribution networks, and to equivalently merge the electrical parameters of the AC side and the bridge arm to establish an average simplified model. Based on the average simplified model, the mixed potential function theory is applied to analyze the energy relationship between non-energy storage components and energy storage components in the system to obtain the large disturbance stability criterion. The adjustment command generation module is used to introduce a virtual resistance variable on the DC side of the modular multilevel converter based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, generating an adjusted active current component reference value, and obtaining the control scheme of the modular multilevel converter. The virtual resistance parameter tuning module is used to incorporate the virtual resistance variable introduced in the modular multilevel converter control scheme and the large disturbance stability criterion. It integrates the virtual resistance variable into the analysis framework of the large disturbance stability criterion, combines the characteristics of typical disturbance scenarios in mountainous areas, solves the boundary constraints, obtains the value range of the virtual resistance, and determines the specific tuning value of the virtual resistance.

[0073] This embodiment also provides an electronic device applicable to an MMC virtual resistance control method, including: The memory and processor are used to store computer-executable instructions and execute the computer-executable instructions to implement an MMC virtual resistance control method as proposed in the above embodiments.

[0074] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements an MMC virtual resistance control method as proposed in the above embodiments.

[0075] The storage medium proposed in this embodiment and the method for implementing MMC virtual resistance control proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0076] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0077] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for controlling the virtual resistance of an MMC (Multi-Mechanical Controlled Controller), characterized in that, include: The topology and operating environment of the modular multilevel converter in the mountain power distribution network are set, and the electrical parameters of the AC side and the bridge arm are equivalently merged to establish an average simplified model. Based on the average simplified model, the mixed potential function theory is applied to analyze the energy relationship between non-energy storage elements and energy storage elements in the system, and a large disturbance stability criterion is obtained. Based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model, a virtual resistance variable is introduced on the DC side of the modular multilevel converter. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, and an adjusted active current component reference value is generated to obtain the control scheme of the modular multilevel converter. Based on the virtual resistance variable and the large disturbance stability criterion introduced in the modular multilevel converter control scheme, the virtual resistance variable is incorporated into the analysis framework of the large disturbance stability criterion. Combined with the characteristics of typical disturbance scenarios in mountainous areas, the boundary constraints are solved to obtain the value range of the virtual resistance and determine the specific setting value of the virtual resistance.

2. The MMC virtual resistance control method as described in claim 1, characterized in that: The average simplified model includes: The equivalent AC resistance is obtained by combining the AC side resistance and the bridge arm resistance. The AC-side equivalent inductance is obtained by combining the AC-side inductance and the bridge arm inductance. The DC-side equivalent capacitance is obtained by adjusting the capacitance of each submodule in the bridge arm according to the number of submodules.

3. The MMC virtual resistance control method as described in claim 1 or 2, characterized in that: The stability criterion for large disturbances includes: A hybrid potential function is constructed based on the current potential function of non-energy storage components and the voltage potential function of capacitor voltage. By performing second-order partial derivative operations on the mixed potential function with respect to the current variable and the voltage variable respectively, the second-order derivative matrices of the current potential function and the voltage potential function are obtained. The sum of the minimum eigenvalues ​​of the two second-order derivative matrices is calculated and used as the basis for stability judgment.

4. The MMC virtual resistance control method as described in claim 3, characterized in that: The introduction of a virtual resistance variable on the DC side of the modular multilevel converter includes: Construct a power term in the control logic that is proportional to the square of the DC voltage and inversely proportional to the virtual resistance value; Add the power item to the AC side active power command.

5. The MMC virtual resistance control method as described in claim 4, characterized in that: The step of converting the power consumption corresponding to the virtual resistor into an adjustment command for the active current component includes: Collect the DC side voltage and AC side active voltage components; The active current regulation is calculated based on the virtual resistance value, DC side voltage, and AC side active voltage component. The active current adjustment is superimposed on the active current reference value.

6. The MMC virtual resistance control method as described in claim 5, characterized in that: The characteristics of typical disturbance scenarios in mountainous areas include: The grid voltage dropped; A sudden change in load power is sufficient to cause a significant deviation of the DC-side voltage of the modular multilevel converter from its steady-state value. The duration of the disturbance exceeds the initial stage of the transient response of the control system.

7. The MMC virtual resistance control method as described in claim 6, characterized in that: The analytical framework that incorporates virtual resistance variables into the large disturbance stability criterion includes: The influence of a virtual resistance variable on the DC-side power balance is explicitly introduced into the hybrid potential function; Reconstruct the voltage potential function that includes the virtual resistance variable; Recalculate the minimum eigenvalue after introducing the virtual resistance.

8. An MMC virtual resistance control system, using the method described in any one of claims 1-7, characterized in that, include: The large disturbance stability modeling and criterion generation module is used to set the topology and operating environment of modular multilevel converters in mountainous power distribution networks, and to equivalently merge the electrical parameters of the AC side and the bridge arm to establish an average simplified model. Based on the average simplified model, the mixed potential function theory is applied to analyze the energy relationship between non-energy storage components and energy storage components in the system to obtain the large disturbance stability criterion. The adjustment command generation module is used to introduce a virtual resistance variable on the DC side of the modular multilevel converter based on the average simplified model and the AC / DC power balance relationship reflected by the average simplified model. According to the AC / DC power balance relationship, the power consumption corresponding to the virtual resistance is converted into an adjustment command for the active current component, generating an adjusted active current component reference value, and obtaining the control scheme of the modular multilevel converter. The virtual resistance parameter tuning module is used to incorporate the virtual resistance variable introduced in the modular multilevel converter control scheme and the large disturbance stability criterion. It integrates the virtual resistance variable into the analysis framework of the large disturbance stability criterion, combines the characteristics of typical disturbance scenarios in mountainous areas, solves the boundary constraints, obtains the value range of the virtual resistance, and determines the specific tuning value of the virtual resistance.

9. An electronic device, characterized in that, include: Memory, used to store programs; A processor for loading the program to perform the steps of the method as claimed in any one of claims 1-7.

10. A computer-readable storage medium storing a program, characterized in that, When the program is executed by a processor, it implements the steps of the method as described in any one of claims 1-7.

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