Modular multilevel converter adaptive sliding mode control system and method based on two-phase stationary coordinate system

Abstract

The application provides an MMC adaptive sliding mode control system and method based on a two-phase stationary coordinate system, and relates to the field of power transmission. The method comprises the following steps: obtaining the alpha-beta axis components of the grid voltage and current, and constructing a mathematical model of the modular multilevel converter in the two-phase stationary coordinate system; calculating the current error value on the alpha-beta axis of the two-phase stationary coordinate system model; and presetting a composite sliding surface comprising a linear term and an integral term, which is used for dynamic convergence control target; constructing an adaptive sliding mode approach rate function with the error value as the independent variable, which is used for dynamically adjusting the approach speed according to the error size; and generating the control voltage signal on the alpha-beta axis based on the sliding surface and the adaptive approach rate, and outputting the control voltage signal to the power devices of the MMC through carrier shift modulation. The method solves the problem of high overall processing calculation complexity and control delay caused by the need to use a large number of calculations in the PI control technology of the traditional dq coordinate system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electric power transmission, in particular to an MMC adaptive sliding mode control system and method based on two-phase stationary coordinate system. BACKGROUND

[0002] With the large-scale renewable energy such as photovoltaic and wind power being connected to the grid, and the AC / DC loads such as electric vehicles and fuel cells being connected to the grid, the medium-voltage direct current distribution network (MVDC) is attracting more and more attention. The existing MMC system has the characteristics of modularity, strong scalability, high efficiency, small voltage stress of power semiconductor devices, good output voltage quality, etc., and has been applied to many completed AC / DC HDN pilot projects as an interconnected converter. However, during its actual use, the controlled object needs to be Clark transformed, Park transformed and inverse Park transformed to realize coordinate conversion, and a phase-locked loop needs to be matched to ensure phase synchronization, so that the overall process needs to use a large number of mathematical operations, increasing the system calculation complexity, requiring high hardware computing power, and in the limited computing power scene, control delay is prone to occur. SUMMARY

[0003] The present application provides an MMC adaptive sliding mode control system and method based on two-phase stationary coordinate system, which solves the technical problem that the traditional dq coordinate system needs to use a large number of calculations in PI control technology, making the overall processing calculation complex and high, and causing control delay.

[0004] To achieve the above purpose, the present application adopts the following technical solutions:

[0005] In a first aspect, the MMC adaptive sliding mode control system based on two-phase stationary coordinate system comprises: a two-phase stationary coordinate system modeling module, which obtains the αβ-axis components of grid voltage and current, and constructs a mathematical model of the modular multilevel converter in the two-phase stationary coordinate system; an error calculation and sliding mode surface design module, which calculates the current error value on the αβ-axis of the two-phase stationary coordinate system model; and a preset composite sliding mode surface including a linear term and an integral term, which is used for dynamic convergence control target; an adaptive sliding mode reaching rate design module, which constructs an adaptive sliding mode reaching rate function with the error value as the independent variable, and is used for dynamically adjusting the reaching speed according to the error size; and a control signal generation module, which generates the control voltage signal on the αβ-axis based on the sliding mode surface and the adaptive reaching rate, and outputs to the power devices of the MMC through carrier shift modulation.

[0006] Based on the above technical solutions, in the MMC adaptive sliding mode control system based on a two-phase stationary coordinate system provided in this application, the two-phase stationary coordinate system modeling module effectively eliminates the phase-locked loop, Park transformation, and inverse Park transformation required by the traditional dq model, fundamentally reducing computational complexity and solving the problems of poor real-time performance and algorithm burden caused by coordinate transformation in PI control. Simultaneously, by using a sliding surface composite of linear and integral terms in the error calculation and sliding surface design module, combined with the nonlinear function of the adaptive sliding mode approach rate design module to dynamically adjust the approach speed, intelligent control of "fast approach for large errors and slow adjustment for small errors" is achieved, significantly improving transient response speed and suppressing overshoot, overcoming the dynamic sluggishness and oscillation problems caused by the linear characteristics and multi-loop series connection of PI controllers. The introduction of the external integral term continuously compensates for small errors, making the steady-state error approach zero, while Lyapunov stability verification ensures the robustness of the system under disturbances, solving the problem of insufficient steady-state accuracy of PI control in nonlinear multi-timescale systems. Finally, the control signal generation module softens the output through a saturation function and combines it with carrier phase-shift modulation to generate a smooth control voltage signal, thereby enhancing overall stability.

[0007] In conjunction with the first aspect mentioned above, in one possible implementation, the construction of the two-phase stationary coordinate system modeling module specifically includes: acquiring the instantaneous voltage and current signals of the three-phase power grid and recording them as three-phase voltage and current signals; converting the three-phase voltage and current signals into α-axis and β-axis components in the two-phase stationary coordinate system through the Clarke transform unit; and establishing a mathematical model of MMC in the two-phase stationary coordinate system.

[0008] In conjunction with the first aspect mentioned above, in one possible implementation, the error calculation and sliding surface design module includes an error calculation unit and a sliding surface design unit: the error calculation unit calculates the current error values ​​on the α-axis and β-axis based on the reference current value and the actual current value; the sliding surface design unit obtains the linear term and integral term through the current error value and presets the composite sliding surface.

[0009] In conjunction with the first aspect mentioned above, in one possible implementation, the process of the adaptive sliding mode approach rate design module outputting the adaptive approach rate value specifically includes: converting the current error value e... α e β and sliding mode surface value s α s β As the independent variable, a nonlinear adaptive approach rate function is constructed. ,in This is the error proportion term. For the sliding mode surface modulation term; the approach rate value is obtained by running the nonlinear adaptive approach rate function. and For the convergence rate value Lyapunov stability condition verification is performed.

[0010] With the first aspect, in a possible implementation, the process of Lyapunov stability condition verification specifically includes: presetting a Lyapunov function, and embedding a radial unboundedness requirement and a negative definiteness requirement; obtaining a convergence rate value When the radial unboundedness requirement and the negative definiteness requirement are both met, the convergence rate value is fed back to a control signal generation module.

[0011] With the first aspect, in a possible implementation, the process of the control signal generation module generating a final control signal specifically includes: obtaining current error values and , a sliding surface value and , and a convergence rate value ; calling a control voltage formula to calculate control voltage signals on the α-axis and the β-axis; and inputting the control voltage signals to a carrier phase-shift modulation module to generate a PWM modulation signal, which is fed back to the MMC power device to drive the MMC bridge arm switch to act.

[0012] With the first aspect, in a possible implementation, the direct current side control module is further configured to balance the voltage of the MMC sub-modules, and the outer ring voltage stabilization unit compares a sub-module voltage reference value with an average value U a of the upper and lower bridge arm sub-module voltages of each phase to generate a circulating current reference value ; the inner ring circulating current control unit compares the circulating current reference value with an actual circulating current value to generate a circulating current control signal ; the signal synthesis unit obtains a final control signal based on the circulating current reference value and the circulating current control signal ; and the voltage balancing control unit calculates a voltage balancing coefficient K and outputs a voltage balancing compensation signal .

[0013] With the first aspect, in a possible implementation, the direct current side control module further includes a CPS-PWM modulation unit: based on the final control signal and the voltage balancing compensation signal, the CPS-PWM modulation unit generates multiple triangular carrier signals with the same frequency but with a phase offset in sequence; the CPS-PWM modulation unit compares the multiple triangular carrier signals with a modulation wave to generate a PWM driving signal, which is fed back to the sub-module power device of the MMC, to balance the voltage of the sub-modules and suppress the circulating current.

[0014] In a second aspect, the MMC adaptive sliding mode control system based on a two-phase stationary coordinate system is provided, comprising: an alternating current side and a direct current side; the direct current side obtains the αβ axis components of the grid voltage and current, and constructs a mathematical model of the modular multilevel converter in the two-phase stationary coordinate system; the current error value on the αβ axis of the two-phase stationary coordinate system model is calculated; and a composite sliding surface including a linear term and an integral term is preset for dynamic convergence control target; an adaptive sliding mode reaching rate function is constructed with the error value as the independent variable, for dynamically adjusting the reaching speed according to the error size; based on the sliding surface and the adaptive reaching rate, the control voltage signal on the αβ axis is generated, and is output to the power device of the MMC through carrier phase-shift modulation. The direct current side of the MMC comprises: a comparison submodule voltage reference value and the average value of the upper and lower bridge arm submodule voltages in each phase to generate a circulating current reference value ; the circulating current reference value is compared with the actual circulating current value to generate a circulating current control signal ; the final control signal is obtained based on the circulating current reference value and the circulating current control signal ; the voltage equalization coefficient K is calculated, and the voltage equalization compensation signal is output.

[0015] The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system is provided, which can effectively save the phase-locked loop, Park transformation and inverse Park transformation links required by the traditional dq model through the two-phase stationary coordinate system modeling module, thereby reducing the calculation complexity from the root cause, solving the real-time poor and algorithm burden problems caused by coordinate transformation in PI control. At the same time, through the error calculation and sliding surface design module, the sliding surface with linear term and integral term is adopted, and the nonlinear function dynamic adjustment reaching speed of the adaptive sliding mode reaching rate design module is combined, the intelligent control of “large error fast approaching, small error slow regulation” is realized, the transient response speed is significantly improved and the overshoot is suppressed, and the dynamic delay and oscillation problems caused by the linear characteristics and multi-loop series of the PI controller are overcome. The introduction of the integral term will continuously compensate the small error, so that the steady-state error tends to zero, and the Lyapunov stability verification ensures the robustness of the system under disturbance, solving the defect of insufficient steady-state accuracy of PI control in nonlinear multi-time scale system. The final control signal generation module softens the output through the saturation function and combines the carrier phase-shift modulation to generate a smooth control voltage signal, thereby enhancing the overall stability.

[0016] It should be understood that the description of technical features, technical solutions, advantages or similar language in this application does not imply that all features and advantages can be realized in any single embodiment. Instead, it can be understood that the description of a feature or advantage means that the specific technical feature, technical solution or advantage is included in at least one embodiment. Therefore, the description of technical features, technical solutions or advantages in this specification does not necessarily refer to the same embodiment. Further, the technical features, technical solutions and advantages described in this embodiment can be combined in any appropriate manner. Those skilled in the art will understand that the embodiments can be implemented without one or more specific technical features, technical solutions or advantages of a specific embodiment. In other embodiments, additional technical features and advantages can be identified in specific embodiments that do not embody all embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The architecture diagram of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0018] Figure 2 The AC side control diagram in the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0019] Figure 3 The flowchart of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0020] Figure 4 The flowchart of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0021] Figure 5 The phase plane diagram of the adaptive approach rate in the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0022] Figure 6 The flowchart of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0023] Figure 7 The control diagram of the DC side of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0024] Figure 8 The overall control diagram of the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system is provided for the embodiments of the application.

[0025] Figure 9A MMC circulating current equalization suppression diagram in the MMC adaptive sliding mode control system based on a two-phase stationary coordinate system provided by the embodiment of the present application;

[0026] Figure 10 A flowchart of the MMC adaptive sliding mode control system based on a two-phase stationary coordinate system provided by the embodiment of the present application;

[0027] Figure 11 A flowchart of the MMC adaptive sliding mode control system based on a two-phase stationary coordinate system provided by the embodiment of the present application;

[0028] Figure 12 A flowchart of the MMC adaptive sliding mode control method based on a two-phase stationary coordinate system provided by the embodiment of the present application.

[0029] In the figure: 100, MMC system; 101, AC side; 1011, two-phase stationary coordinate system modeling module; 1012, error calculation and sliding mode surface design module; 1013, adaptive sliding mode reaching rate design module; 1014, control signal generation module; 102 is DC side; 1021, outer ring voltage stabilization unit; 1022, inner ring circulating current control unit; 1023, signal synthesis unit; 1024, CPS-PWM modulation unit; 1025, equalization control unit. DETAILED DESCRIPTION

[0030] In the description of the present application, unless otherwise specified, " / " means "or", for example, A / B can mean A or B. "And / or" in this document is only a description of the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean: A alone, A and B together, and B alone. In addition, "at least one" means one or more, and "multiple" means two or more. "First", "second", and the like do not limit the quantity and execution order, and "first", "second", and the like do not necessarily mean different.

[0031] It should be noted that in the present application, "exemplary" or "for example" is used to mean example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the use of "exemplary" or "for example" is intended to present the relevant concept in a specific manner.

[0032] To solve the technical problems that in the prior art, the controlled object needs to be subjected to Clark transformation, Park transformation and inverse Park transformation to realize coordinate conversion, and a phase-locked loop needs to be matched to ensure phase synchronization, a large number of mathematical operations increase the system calculation complexity, the hardware computing power requirement is high, and in a computing power limited scene, control delay is prone to occur; meanwhile, the linear characteristic of the PI controller, the multi-loop series structure and the nonlinear, multi-time scale and strong coupling characteristics of the MMC are not matched, so that the system response speed is limited by the lowest bandwidth of the outer loop control, and to ensure robust stability, conservative low-bandwidth parameters need to be selected, which will cause the system to experience slow transient response when a disturbance or a control instruction is changed, and it takes a long time to recover to a stable state; under the working conditions of MMC pre-starting and grid voltage fluctuation, the PI controller bandwidth has an inherent upper limit, the output thereof cannot follow the dramatic changes in system state in time, the grid-connected current is prone to overshoot, and the integral term is prone to entering a saturation state in a dynamic process, and it takes a certain time for the integrator to exit the saturation when the instruction is reversed or the system recovers, further exacerbating the transient overshoot problem. In addition, the MMC is a nonlinear and strongly coupled system, and the operating parameters will fluctuate significantly with the power level, DC voltage and AC system strength, and the linear and constant PI controller parameter design is based on a specific working condition, and cannot maintain optimal performance in the whole operating range, and the control rings with different bandwidths are prone to adverse interaction, leading to difficulty in eliminating steady-state error, and the control accuracy is prone to decrease and the robustness is insufficient under complex working conditions, and it is difficult to adapt to the dynamic load changes caused by renewable energy grid connection, the embodiments of the present application provide an MMC adaptive sliding mode control system based on a two-phase stationary coordinate system, the method can effectively save the phase-locked loop, Park transformation and inverse Park transformation links required by the traditional dq model through a two-phase stationary coordinate system modeling module 1011, and reduces the calculation complexity from the root cause, and solves the real-time poor and algorithm burden problems caused by coordinate transformation in PI control. Meanwhile, through error calculation and sliding mode surface design module 1012, a sliding mode surface with a linear term and an integral term is adopted, a nonlinear function dynamic adjustment approach speed of the adaptive sliding mode approach rate design module 1013 is combined, intelligent control of “fast approach to large error and slow adjustment to small error” is realized, transient response speed is significantly improved, and overshoot is suppressed, and the dynamic delay and oscillation problems caused by the linear characteristic and multi-loop series connection of the PI controller are overcome. The introduction of the outer integral term will continuously compensate for small errors, so that the steady-state error approaches zero, and Lyapunov stability verification ensures the robustness of the system under disturbance, and solves the defect of insufficient steady-state accuracy of the PI control in a nonlinear multi-time scale system. Finally, the control signal generation module 1014 softens the output through a saturation function and combines carrier phase-shifted modulation to generate a smooth control voltage signal, and the overall stability is enhanced.

[0033] As Figure 1As shown, the MMC adaptive sliding mode control system based on the two-phase stationary coordinate system provided by the embodiments of the present application comprises:

[0034] The two-phase stationary coordinate system modeling module 1011 acquires the αβ-axis components of the grid voltage and current, and constructs a mathematical model of the modular multilevel converter under the two-phase stationary coordinate system.

[0035] The two-phase stationary coordinate system modeling module 1011 refers to a component responsible for signal conversion and model construction, which can effectively eliminate the need for a phase-locked loop (PLL), Park transformation, and inverse Park transformation, thereby reducing the computational burden. Moreover, it can ensure that the model accurately describes the dynamic behavior of the MMC under the αβ coordinate system, especially in terms of robustness during grid frequency fluctuations.

[0036] In laboratory simulation or actual grid applications, LEM LV25-P type voltage sensors and LEM LA55-P type current sensors are used to collect three-phase voltage and current signals, with a sampling frequency set to 10 kHz. Then, a digital signal processor such as TI TMS320F28379D performs Clarke transformation to convert the three-phase signals into αβ-axis components, and finally, a mathematical model is established based on the MMC submodule parameters.

[0037] In some implementations, the three-phase grid voltage and current signals of the MMC are first converted into components under the two-phase stationary coordinate system (αβ coordinate system) through Clarke transformation, mainly including voltage components (such as 、 ) and current components (such as 、 ). The mathematical model of the MMC can be directly constructed based on the known components (i.e., the current differential equation), and the reference current value under the αβ axis (such as 、 ) is output. This can effectively avoid the cross-coupling terms in the rotating coordinate system. However, a digital signal processor (DSP) or FPGA hardware platform is required for real-time transformation calculation during actual operation.

[0038] The error calculation and sliding mode surface design module 1012 calculates the current error value on the αβ axis of the two-phase stationary coordinate system model, and presets a composite sliding mode surface including linear and integral terms for dynamic convergence control targets.

[0039] The error calculation and sliding mode surface design module 1012 allows the composite sliding mode surface to provide rapid transient response through the linear term, and combines the linear and integral terms to eliminate steady-state errors and improve tracking accuracy.

[0040] In some implementations, the error value can be directly calculated based on the reference current and actual current values on the αβ axis from the two-phase stationary coordinate system modeling module 1011. Meanwhile, a composite sliding mode surface is designed by combining the linear term and integral term, so as to eliminate the steady-state error and improve the dynamic convergence performance.

[0041] It should be noted that the sliding mode surface design is mainly based on the Lyapunov stability theory, and a dynamic convergence law is formed by combining the linear term and the integral term.

[0042] The adaptive sliding mode reaching rate design module 1013 constructs an adaptive sliding mode reaching rate function with the error value as the independent variable, which is used to dynamically adjust the reaching speed according to the error size.

[0043] The adaptive sliding mode reaching rate design module 1013 can dynamically adjust the reaching speed with the error as the independent variable, so as to achieve a balance between fast response and low chattering. Meanwhile, the internal adaptive mechanism can effectively enable the system to quickly track under disturbance and smoothly adjust in the steady state, thereby solving the contradiction between fast response and low chattering in traditional sliding mode control.

[0044] In some implementations, the adaptive reaching rate function is constructed based on the error value and the sliding mode surface value from the error calculation and sliding mode surface design module 1012, so that the adaptive reaching rate function can achieve the effect of "fast reaching for large error and slow adjustment for small error". After verifying the stability by the Lyapunov function, the adaptive reaching rate value is output for control signal generation.

[0045] It should be noted that the adaptive reaching rate is based on the nonlinear control theory and dynamically adjusts the gain through error feedback.

[0046] The control signal generation module 1014 generates the control voltage signal on the αβ axis based on the sliding mode surface and the adaptive reaching rate, and outputs the control voltage signal to the power devices of the MMC through carrier shift modulation.

[0047] The control signal generation module 1014 refers to a component responsible for generating the final control signal based on the sliding mode surface and the adaptive reaching rate. The control signal generation is mainly based on the sliding mode control theory, and the system state is driven to slide along the sliding mode surface through the reaching rate. The setting of the internal saturation function is derived from the boundary layer method, which is used to soften the control signal. Combined with the modulation principle, efficient energy conversion is ensured, which not only effectively suppresses chattering, but also ensures accurate driving of the power devices in the modulation link, so that the control signal generation module 1014 can achieve smooth output of the control signal and overall stability of the system.

[0048] The process of generating the final control signal by the control signal generation module 1014 specifically includes:

[0049] Obtaining the current error value , sliding surface value and reaching rate value ;

[0050] Call control voltage formula to calculate the control voltage signal on the α-axis and β-axis ;

[0051] The control voltage signal is input to the carrier phase shift modulation module to generate a PWM modulation signal feedback to the MMC power device to drive the MMC bridge arm switch action.

[0052] In some implementations, the received real-time current error value and and the sliding surface value and are obtained, and the adaptive reaching rate value and are obtained. The embedded processor (such as TI TMS320F28379D) reads the inductance parameter L and resistance parameter R of the MMC AC side 101 in the system storage unit, combines the grid voltage α-axis and β-axis components and input by the grid voltage sensor, and obtains the actual current value and The current differential value and is obtained by current signal difference calculation (sampling time Ts=100μs), that is, all its data are substituted into the control voltage formula for real-time calculation to obtain the control voltage signal on the α-axis and β-axis , and transmitted to the carrier phase shift modulation submodule through the data bus, and the CPS-PWM signal (carrier frequency 2kHz) is generated by the submodule, and finally the power device switch (such as IGBT module, model optional Infineon FF450R17ME4) is output to drive the MMC bridge arm switch action, thereby completing the whole process from signal acquisition, calculation to modulation, and ensuring that the system response time is less than 1ms.

[0053] It should be noted that during its operation, the control voltage formula is mainly designed based on system parameters such as inductance L and resistance R, and the chattering is suppressed by the saturation function, so that the carrier shift modulation ensures the voltage balance of the submodule and the circulation suppression, and the whole generation process depends on real-time data input and stability verification.

[0054] Based on the above technical scheme, taking the two-phase stationary coordinate system (αβ coordinate system) as the modeling basis, combining the adaptive sliding mode strategy, realizing intelligent control through data processing, algorithm optimization and real-time feedback adjustment, a complete closed-loop control system can be effectively formed, thereby effectively saving the conversion link, simplifying data processing, and solving the problems of high calculation complexity, structural limitations, dynamic performance bottlenecks and insufficient robustness of traditional dq-PI control, and realizing efficient calculation, rapid response, high precision and strong robustness control effect.

[0055] In a possible implementation manner of the embodiment of the present application, the two-phase stationary coordinate system modeling module 1011 can be implemented through the following steps 201 to 203, which are described in detail below. Figures 1-3 As shown in the figure, the two-phase stationary coordinate system modeling module 1011 can be implemented through the following steps 201 to 203, which are described in detail below.

[0056] Step 201, obtaining the voltage and current instantaneous value signals of the three-phase power grid, denoted as three-phase voltage and current signals.

[0057] The acquisition device configuration is that high-precision sensors such as a voltage transformer (for example, LEM LV 25-P type) and a current transformer (for example, LEM LA 55-P type) are directly connected to the line of the three-phase power grid and integrated in the control cabinet of the MMC system 100, and the instantaneous values are obtained in a non-invasive or invasive manner through a sampling frequency greater than 10 kHz.

[0058] The acquisition environment condition is that the acquisition environment is set to an actual power grid operation site (such as a renewable energy grid connection point or a city distribution network) or a laboratory simulation platform, the environmental temperature range is generally -40°C to +85°C to adapt to the industrial standard, the humidity needs to be controlled within a certain range to prevent condensation from affecting; at the same time, the power grid may have non-ideal conditions such as frequency fluctuation, voltage sag or harmonic interference, and the acquisition unit must have anti-interference ability to ensure signal purity.

[0059] The acquisition signal type is that the acquisition object is the voltage and current instantaneous value signals from the three-phase power grid AC side 101, which are usually high voltage and large current environments of power frequency (such as 50Hz or 60Hz), such as medium voltage distribution network (MVDC) scenarios, the voltage level can reach more than 10kV, and the current can reach hundreds of amperes.

[0060] Step 202, converting the voltage and current instantaneous value signals of the three-phase power grid into α-axis and β-axis components in the two-phase stationary coordinate system through a Clarke transformation unit;

[0061] In some implementation manners, the voltage and current instantaneous value signals of the three-phase power grid are collected in real time through sensors and input into the Clarke transformation unit, and the transformation formula is 、 and ​This allows the three-phase signal to be converted into αβ axis components. and The coefficients of the transformation matrix ensure power conservation.

[0062] Step 203: Establish the mathematical model of MMC in a two-phase stationary coordinate system;

[0063] In some implementations, MMC circuit parameters (such as bridge arm resistance R and inductance L) are obtained through electromagnetic shielding laboratory or field shielding cabinet experiments or by design specifications (MMC electrical design specifications or submodule datasheets), combined with αβ axis current components. and αβ axis grid voltage components and and control voltage component Establish a differential equation model and This method describes the current dynamics, allowing the model to be built directly in a two-phase stationary coordinate system, eliminating the need for phase-locked loops, Park transformations, and inverse Park transformations, thereby reducing computational complexity and achieving essential decoupling of the control system.

[0064] Based on the above technical solution, by eliminating the complex transformation steps in the traditional rotating coordinate system (dq coordinate system), the control system can be directly constructed in the two-phase stationary coordinate system (αβ coordinate system), which can significantly reduce the computational complexity, thereby simplifying the system structure and improving its robustness.

[0065] In one possible implementation of the embodiments of this application, combined with Figures 1-4 As shown, the error calculation and sliding surface design module 1012 can be implemented through the following steps 301 to 302, which are explained in detail below:

[0066] Step 301: The error calculation unit calculates the current error values ​​on the α-axis and β-axis based on the reference current value and the actual current value.

[0067] In some implementations, the actual current value is obtained by measuring it in real time using a current sensor. and And from the two-phase stationary coordinate system modeling module 1011, through active power command P, reactive power command Q, and grid voltage... and You can pass and The reference current value was calculated. and At this point, the error calculation unit can be directly activated, through... and Calculate the current error values ​​on the α-axis and β-axis. and .

[0068] Among them, the current sensor can be a Hall effect sensor such as LEM LAH 100-P.

[0069] Step 302: The sliding surface design unit obtains the linear term and integral term through the current error value and presets the composite sliding surface.

[0070] In some implementations, the coefficients of the linear terms are set by the time constant τ. and (Usually chosen from 1 to 1000) and coefficient of the integral term (according to Time selection ), and make it satisfy By using the coefficients of the linear terms Multiplying the result by the error value yields the linear part. Simultaneously, the error value is integrated using an integrator, and the result is compared with the coefficient of the integral term. Multiplying yields the integral, which is obtained by... and The final superimposed output sliding surface value The signal is then transmitted to the adaptive sliding mode approach rate design module 1013 to generate a control voltage signal.

[0071] The digital signal processor can be implemented using the TI TMS320F28379D to ensure continuous data flow and logical progression.

[0072] Based on the above technical solution, a composite sliding surface structure integrates linear and integral terms. This ensures a fast transient response for the linear term while eliminating steady-state error for the integral term, thus solving the technical problems of large overshoot, slow response, and large steady-state error in traditional PI control. Simultaneously, the structure where the error calculation unit directly processes signals from two stationary coordinate systems effectively avoids the step of coordinate transformation, reducing computational complexity. This allows the sliding surface design unit to achieve dynamic optimization through adaptive parameter configuration, improving system robustness and control accuracy.

[0073] In one possible implementation of the embodiments of this application, combined with Figures 1-6 As shown, the adaptive sliding mode approach rate design module 1013 can be implemented through the following steps 401 to 404, which are explained in detail below:

[0074] Step 401: Set the current error value and sliding surface value As the independent variable, a nonlinear adaptive approach rate function is constructed. ,in This is the error proportion term. This is a sliding surface modulation term.

[0075] wherein the sliding surface modulation term can directly reflect the size of the system tracking error, the larger the error, the larger the gain, to ensure fast response. The adaptive reaching rate coefficient is calculated based on the system sampling period Ts or time constant τ (such as or ), and depends on the system scale (such as the motor control , which is usually 10-50), and satisfies . The amplitude adjustment parameter λ is used to control the non-negative range of the function value, and satisfies , when the dependence adjustment, the amplitude adjustment parameter λ decreases, when the dependence adjustment, the amplitude adjustment parameter λ increases. The switching smoothness parameter η is used to affect the transition characteristics of the function with the sliding surface, and satisfies , when fast switching is performed, η is increased, when smooth switching is performed, η is decreased.

[0076] Step 402, running a nonlinear adaptive reaching rate function to obtain a reaching rate value .

[0077] In some implementations, the current error values on the α-axis and the β-axis and the sliding surface values are received in real time through an internal data bus, and the received data is taken as input to call the stored nonlinear function program. The absolute value of the error is calculated first, and then the modulation term can be calculated in combination with the adaptive reaching rate coefficient , the amplitude adjustment parameter λ, and the switching smoothness parameter η, and finally the reaching rate value is obtained.

[0078] Step 403, Lyapunov stability condition verification is performed on the reaching rate value .

[0079] A Lyapunov function is preset, and the radial unboundedness requirement and the negative definiteness requirement are embedded;

[0080] wherein the Lyapunov function is a positive definite scalar function used to measure the energy or distance deviation from the equilibrium point of the system state.

[0081] The radial unboundedness requirement is , which is used to ensure that the function is unbounded at infinity, preventing the system state from diverging.

[0082] The negative definiteness requirement is that the time derivative of the Lyapunov function is less than 0 and all , which is used to indicate that the system energy decreases over time and the state approaches the equilibrium point.

[0083] In some implementations, the received sliding surface value s defines a Lyapunov function and satisfies V ≥ 0, and V = 0 when s = 0. Analyzing the nonlinear adaptive reaching rate function yields an expression for the derivative of the sliding surface adjusted by an adaptive function , so that the time derivative of the Lyapunov function can be directly calculated as .

[0084] It is noted that sign(s) is a sign function. is the derivative of the sliding surface s. sat(s) is a saturation function used to replace the sign function to reduce chattering, and is defined as where Δ is a boundary layer thickness (typically between 0.01 and 0.5) determined by simulation optimization, and is calculated as .

[0085] When the reaching rate value satisfies both the radial unboundedness requirement and the negative definiteness, the reaching rate value is fed back to the control signal generation module 1014;

[0086] In some implementations, the non-negativity of f(e, s) and the positivity of are checked in real time, and when , it is verified that < 0, i.e., a stability confirmation signal can be output to the control signal generation module 1014 to ensure that the system state approaches the sliding surface, and the entire process is continuously executed in each control period to form a closed-loop verification.

[0087] For example, assuming that the system starts with a current error e = 0.1 A, a sliding surface value s = 0.5, and parameters = 10, λ = 0.7, and η = 7, then is calculated, and substituted into = -0.243 * 0.5 = -0.1215 < 0, satisfying the stability condition; when the system approaches a steady state with e = 0.001 A and s = 0.01, then f(e, s) ≈ 0.0001, ≈ 0, verifying the smooth transition.

[0088] ​Based on the above technical solution, by constructing a nonlinear approach rate function to dynamically adjust the approach speed, the error and sliding surface feedback can be effectively utilized to achieve the effect of "fast approach for large errors and slow adjustment for small errors," thus resolving the contradiction between speed and low chattering in traditional sliding mode control. This allows for the effective use of parameter adaptive mechanisms to improve the system's transient response speed, suppress steady-state errors and overshoot, reduce computational complexity, and avoid the multi-loop coupling problem of traditional PI control. Consequently, the robustness and dynamic performance of the MMC system 100 can be effectively enhanced, making it more suitable for computationally limited scenarios.

[0089] In one possible implementation of the embodiments of this application, combined with Figures 1-10 As shown, the DC side 102 control module can be implemented through the following steps 701 to 704, which are explained in detail below:

[0090] Step 701: The outer loop voltage regulator unit 1021 compares the voltage reference value of the submodule. The average voltage U of each phase upper and lower bridge arm submodule a Generate circulation reference values .

[0091] Submodule voltage stabilization refers to maintaining the capacitor voltage of each submodule near its rated value through control, avoiding overvoltage or undervoltage. The voltage sensor can be an LV 25-P type voltage sensor, the current sensor can be an LA 55-P type current sensor, and the controller can be a TI TMS320F28379D digital signal processor.

[0092] In some implementations, after the DC side 102 control module is started, the sub-module voltage acquisition unit obtains the capacitor voltage value U of each sub-module in real time through voltage sensors. cj [The subscript j represents the submodule index (j=1,2,n, where n is the total number of submodules)], and is transmitted to the voltage outer loop regulator unit 1021 and the voltage equalization control unit 1025. The voltage outer loop regulator unit 1021 can then calculate the average voltage U of each phase's upper and lower bridge arm submodules. a and the average value U a Compared with the system-set submodule voltage reference value The comparison is performed to generate a circulating current reference value via the PI controller. As an input to the inner loop circulation control unit 1022.

[0093] Step 702: The inner loop flow control unit 1022 transmits the circulation reference value. Compared with actual circulation value Compare and generate circulating control signals .

[0094] The digital signal processor can be a TI TMS320F28379D, and the overall sampling period is T. s It is typically set to the microsecond level (e.g., 100μs) to ensure a fast dynamic response.

[0095] In some implementations, the actual circulating current value is measured using a current sensor. Calculate the actual circulation value Compared with circulation reference value The circulating error e between circ =i circ,re f−i circ This allows the circulation error to be directly calculated. As input to the PI controller, it activates the proportional-integral control unit, obtains the proportional coefficient Kp (ranging from 0.1 to 10) which determines the system response speed, and then modulates the proportional coefficient Kp with the error... Multiplying them yields the proportional term P, and simultaneously the integral coefficient Ki (ranging from 0.01 to 1) and the error integral are calculated. Multiplying the terms gives the integral term I. Then, adding the proportional and integral terms together yields the circulating control signal. This signal serves as a voltage-type output modulated PWM pulse.

[0096] It should be noted that the proportional term provides fast tracking capability and reduces response delay during transient processes. The integral term, on the other hand, accumulates small errors and eliminates deviations in steady state, thereby improving the overall robustness and accuracy of the system. However, the design of a PI controller must consider the nonlinear characteristics of the system, thus requiring a synergistic approach combined with anti-saturation mechanisms (such as integral separation).

[0097] Step 703: Signal synthesis unit 1023 based on circulating reference value and circulating control signal Obtain the final control signal .

[0098] Step 704: The equalization control unit 1025 calculates the equalization coefficient K and outputs the equalization compensation signal. .

[0099] In some implementations, through Calculate the absolute deviation ΔU between the voltage and average value of each submodule, and obtain the reference coefficient kbase (usually set to 0.5), adjustment gain θ (range 0.5-1.0), and normalization factor δ (value 5-10V). Then, you can... Calculate the voltage equalization factor K. This allows direct access to the system's maximum permissible voltage deviation rating, Umax, thus enabling... Calculate the compensation signal The system can reduce the modulation amplitude and the on-time by the compensation signal when the voltage of a certain submodule is too high, so as to reduce the voltage.

[0100] The tanh function is used for smoothing the nonlinear transition, which can ensure that the coefficient K can quickly respond to large deviations and maintain smooth control when the deviation is small.

[0101] Based on the above technical solutions, a layered control structure is formed by outer ring voltage stabilization, inner ring circulating current and voltage equalization control, and the processing direction of each layer is also the same. The outer ring voltage stabilization unit 1021 adjusts the circulating current reference through voltage comparison to solve the problem of voltage fluctuation; the inner ring circulating current control unit 1022 realizes fast tracking and suppresses transient oscillation; and the voltage equalization control unit 1025 solves the problem of uneven voltage of submodules through dynamic compensation of voltage deviation. Thus, the rapid stabilization and efficient voltage equalization of the submodule voltage are realized through data progressive connection (such as voltage acquisition, outer ring, inner ring and synthesis), and the defects of slow response and poor voltage equalization effect of the traditional single control are overcome.

[0102] In a possible implementation of the embodiment of the application, as shown in Figures 1-11 The CPS-PWM modulation unit 1024 in the DC side 102 control module can be implemented through the following steps 801 to 802, which are described in detail below.

[0103] Step 801: Based on the final control signal and the voltage equalization compensation signal, a plurality of triangular carrier signals with the same frequency but sequentially offset phases are generated.

[0104] In some implementations, a basic triangular carrier signal is generated through an internal oscillation circuit or a digital signal processor (such as TI TMS320F28379D), and the frequency of the basic triangular carrier signal is set to a fixed value (for example, 2 kHz) according to system requirements. The basic triangular carrier signal can be copied and processed in multiple ways through a phase offset circuit or algorithm, so that the phase of each carrier signal is uniformly offset by 360 / n degrees (for example, for n submodules, the phase is sequentially offset by 360 / n degrees).

[0105] Step 802: Compare the plurality of triangular carrier signals with the modulation wave to generate a PWM driving signal and feed it back to the submodule power device of the MMC, which is used for voltage equalization and circulating current suppression of the submodule.

[0106] The submodule power device refers to an insulated gate bipolar transistor (IGBT) used for switching control in the MMC, such as an IGBT module with the type FF450R12KE4.

[0107] In some implementations, a plurality of triangular carrier signals with the same frequency but sequentially phase offset are compared with the modulation wave in real time, a high level PWM pulse is generated when the modulation wave amplitude is higher than the carrier, otherwise a low level, thereby generating a PWM driving signal, the PWM driving signal can be fed back to the sub-module power device of the MMC through the driving circuit, the switching action of the sub-module power device is controlled, voltage balancing is achieved by adjusting the input and cut-out of the sub-module, and the bridge arm circulating current is suppressed.

[0108] Based on the above technical solution, through the carrier generation, comparison and signal distribution subunit, the comparison of the carrier signals with the same frequency but sequentially phase offset and the modulation wave is effectively realized, the technical problems of sub-module voltage imbalance and circulating current oscillation in the traditional PWM modulation are solved, the fine modulation based on carrier phase shift is realized, thereby the effects of improving voltage balance and reducing switching loss are achieved, and the robustness and dynamic response capability of the system are enhanced through the integrated voltage balancing compensation signal.

[0109] The above mainly introduces the scheme of the embodiments of the application from the perspective of device implementation. It can be understood that, in order to realize the above functions, each device, for example, the MMC adaptive sliding mode control system based on two-phase stationary coordinate system, contains at least one of the corresponding hardware structure and software module for executing each function. Those skilled in the art should easily realize that, in combination with the units and algorithm steps of each example described in the embodiments disclosed in the present text, the application can be realized in the form of hardware or the combination of hardware and computer software. Whether a certain function is executed in the form of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. The professional technicians can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the application.

[0110] The embodiments of the application provide an MMC adaptive sliding mode control method based on two-phase stationary coordinate system, which combines Figures 1-12 As shown in the figure, it comprises an alternating current side 101 and a direct current side 102: the alternating current side 101 comprises:

[0111] Step 901, obtaining the αβ axis components of the grid voltage and current, and constructing the mathematical model of the modular multilevel converter in the two-phase stationary coordinate system;

[0112] Step 902, calculating the current error value on the αβ axis of the two-phase stationary coordinate system model; and presetting a composite sliding mode surface comprising a linear term and an integral term, which is used for dynamic convergence control target; constructing an adaptive sliding mode approach rate function with the error value as the independent variable, which is used for dynamically adjusting the approach speed according to the error size;

[0113] Step 903, based on the sliding surface and the adaptive approach rate, a control voltage signal on the αβ axis is generated and output to the power device of the MMC through carrier shift modulation; the AC side 101 compares the voltage reference value U aref with the average value of the upper and lower bridge arm submodule voltages of each phase a to generate a circulating current reference value ;

[0114] Step 904, compare the circulating current reference value with the actual circulating current value to generate a circulating current control signal ; based on the circulating current reference value and the circulating current control signal , a final control signal is obtained; calculate the voltage equalization coefficient K and output the voltage equalization compensation signal .

[0115] In a possible implementation, the AC side 101 is also used for the construction of the two-phase stationary coordinate system modeling module 1011, specifically including: obtaining the voltage and current instantaneous value signals of the three-phase power grid; converting the three-phase voltage and current signals into α axis and β axis components in the two-phase stationary coordinate system through the Clarke transformation unit; establishing a mathematical model of the MMC in the two-phase stationary coordinate system.

[0116] In a possible implementation, the AC side 101 is also used for the error calculation and sliding surface design module 1012, which includes an error calculation unit and a sliding surface design unit: the error calculation unit calculates the current error value on the α axis and the β axis based on the reference current value and the actual current value; the sliding surface design unit obtains the linear term and the integral term through the current error value, and presets a composite sliding surface.

[0117] In a possible implementation, the AC side 101 is also used for the process of the adaptive sliding mode approach rate design module 1013 outputting the adaptive approach rate value, specifically including: taking the current error value and the sliding surface value as independent variables to construct a nonlinear adaptive approach rate function , where is the error proportional term, is the sliding surface modulation term; obtaining the approach rate value and by running the nonlinear adaptive approach rate function; and verifying the Lyapunov stability condition for the approach rate value .

[0118] In one possible implementation, the communication side 101 is also used for the process of verifying Lyapunov stability conditions, specifically including: presetting the Lyapunov function and embedding radial unboundedness requirements and negative definiteness requirements; and considering the convergence rate value... When both radial unboundedness and negative definiteness are satisfied, the approach rate value will be... Feedback is sent to the control signal generation module 1014.

[0119] In one possible implementation, the AC side 101 is also used to control the process of the signal generation module 1014 generating the final control signal, specifically including: acquiring the current error value. and Slip mode surface value and and the rate of convergence ; Calculate the control voltage signals on the α and β axes using the control voltage formula. ; control voltage signal The signal is input to the carrier phase-shift modulation module, which generates a PWM modulation signal that is fed back to the MMC power device to drive the MMC bridge arm switch.

[0120] In one possible implementation, a DC-side 102 control module is also included for MMC submodule voltage balancing: the outer-loop voltage regulator 1021 compares the submodule voltage reference value... The average voltage U of each phase upper and lower bridge arm submodule a Generate circulation reference values The inner loop flow control unit 1022 will display the loop reference value. Compared with actual circulation value Compare and generate circulating control signals The signal synthesis unit 1023 is based on the circulating reference value. and circulating control signal Obtain the final control signal The equalization control unit 1025 calculates the equalization coefficient K and outputs the equalization compensation signal. .

[0121] In one possible implementation, the DC side 102 control module also includes a CPS-PWM modulation unit 1024: based on the final control signal and the voltage equalization compensation signal, it generates multiple triangular carrier signals with the same frequency but sequentially offset phases; it compares the multiple triangular carrier signals with the modulation wave, generates a PWM drive signal, and feeds it back to the sub-module power device of the MMC for sub-module voltage equalization and circulating current suppression.

[0122] In the implementation process, each step in the method provided by the embodiment can be completed by the integrated logic circuit of hardware in the processor or the instruction in the form of software. The steps of the method disclosed by the embodiment of the present application can be directly embodied as hardware processor execution completion, or execution completion by hardware and software module combination in the processor.

[0123] The processor in the present application can include but is not limited to at least one of the following: a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a microcontroller unit (MCU), or various types of computing devices running software, such as artificial intelligence processors, each of which can include one or more cores for executing software instructions to perform operations or processing. The processor can be a separate semiconductor chip, or can be integrated with other circuits as a semiconductor chip, for example, it can form a SoC (system on chip) with other circuits (such as coding and decoding circuits, hardware acceleration circuits, or various bus and interface circuits), or it can be integrated as a built-in processor in an ASIC. The integrated processor ASIC can be packaged separately or packaged together with other circuits. In addition to including cores for executing software instructions to perform operations or processing, the processor can further include necessary hardware accelerators, such as field programmable gate arrays (FPGAs), PLDs (programmable logic devices), or logic circuits that implement special logic operations.

[0124] The memory in the embodiment of the present application can include at least one of the following types: read-only memory (ROM) or other types of static storage devices that can store static information and instructions, random access memory (RAM) or other types of dynamic storage devices that can store information and instructions, and electrically erasable programmable read-only memory (EEPROM). In some scenarios, the memory can also be a compact disc read-only memory (CD-ROM) or other optical disk storage, optical disc storage (including compact discs, laser discs, optical discs, digital versatile discs, Blu-ray discs, etc.), magnetic disk storage medium or other magnetic storage device, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited to this.

[0125] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented using software programs, implementation can be, in whole or in part, in the form of a computer program product. This computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device containing one or more servers, data centers, etc., that can be integrated with the medium. The available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state disks (SSDs)).

[0126] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, the disclosure, and the appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple components. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0127] Although this application has been described in conjunction with specific features and embodiments, it is apparent that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely illustrative examples of the application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from the spirit and scope of this application. Thus, if such modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is also intended to include such modifications and variations.

Claims

1. An MMC adaptive sliding mode control system based on a two-phase stationary coordinate system, characterized in that, include: The two-phase stationary coordinate system modeling module obtains the αβ axis components of the grid voltage and current, and constructs a mathematical model of the modular multilevel converter in the two-phase stationary coordinate system. The error calculation and sliding surface design module calculates the current error value on the αβ axis of the two-phase stationary coordinate system model. It also pre-defines a composite sliding surface including linear and integral terms for dynamic convergence control objectives; The adaptive sliding mode approach rate design module will use the current error value e α e β and sliding mode surface value s α s β As the independent variable, a nonlinear adaptive approach rate function is constructed. It is used to dynamically adjust the approach speed according to the magnitude of the error, wherein For adaptive approach rate coefficient, For amplitude adjustment parameters, To switch the smoothness parameter, This is the error proportion term. For sliding surface modulation terms; The control signal generation module generates a control voltage signal on the αβ axis based on the composite sliding surface and the nonlinear adaptive approach rate function, and outputs it to the power device of the MMC through carrier shift modulation.

2. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 1, characterized in that, The construction of the two-phase stationary coordinate system modeling module specifically includes: The instantaneous voltage and current signals of the three-phase power grid are recorded as three-phase voltage and current signals; The three-phase voltage and current signals are converted into α-axis and β-axis components in a two-phase stationary coordinate system using a Clarke transform unit. A mathematical model of MMC in a two-phase stationary coordinate system is established.

3. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 2, characterized in that, The error calculation and sliding surface design module includes an error calculation unit and a sliding surface design unit: The error calculation unit calculates the current error values ​​on the α-axis and β-axis based on the reference current value and the actual current value. The sliding surface design unit obtains linear and integral terms through the current error value and presets a composite sliding surface.

4. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 3, characterized in that, The process by which the adaptive sliding mode approach rate design module outputs the adaptive approach rate value specifically includes: The approach rate value is obtained by running a nonlinear adaptive approach rate function. and ; For the convergence rate value Perform Lyapunov stability condition verification.

5. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 4, characterized in that, The process of verifying the Lyapunov stability conditions specifically includes: Pre-defined Lyapunov functions, with embedded radial unboundedness and negative definiteness requirements; The rate of convergence When both radial unboundedness and negative definiteness are satisfied, the approach rate value is... Feedback is sent to the control signal generation module.

6. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 5, characterized in that, The process by which the control signal generation module generates the final control signal specifically includes: Obtain the current error value and Slip mode surface value and and the rate of convergence ; Calculate the control voltage signals on the α and β axes using the control voltage formula. ; The control voltage signal The signal is input to the carrier phase-shift modulation module, which generates a PWM modulation signal that is fed back to the MMC power device to drive the MMC bridge arm switch.

7. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 6, characterized in that, It also includes a DC-side control module for voltage balancing of the MMC submodules: The outer loop voltage regulator unit compares the voltage reference value of the submodule. The average voltage U of each phase upper and lower bridge arm submodule a Generate circulation reference values ; The inner loop flow control unit will use the circulating reference value Compared with actual circulation value Compare and generate circulating control signals ; The signal synthesis unit is based on the circulating reference value. and circulating control signal Obtain the final control signal ; The pressure equalization control unit calculates the pressure equalization coefficient K and outputs a pressure equalization compensation signal. .

8. The MMC adaptive sliding mode control system based on a two-phase stationary coordinate system according to claim 7, characterized in that, The DC-side control module also includes a CPS-PWM modulation unit: Based on the final control signal and the voltage equalization compensation signal, a multi-channel triangular carrier signal with the same frequency but with sequentially shifted phase is generated. The multi-channel triangular carrier signal is compared with the modulated wave to generate a PWM drive signal, which is then fed back to the sub-module power device of the MMC for sub-module voltage equalization and circulating current suppression.

9. An MMC adaptive sliding mode control method based on a two-phase stationary coordinate system, characterized in that, The communication side of the MMC includes: Obtain the αβ axis components of the grid voltage and current, and construct a mathematical model of the modular multilevel converter in a two-phase stationary coordinate system; Calculate the current error value on the αβ axis of the two-phase stationary coordinate system model; and preset a composite sliding surface including linear and integral terms for dynamic convergence control target; The current error value e α e β and sliding mode surface value s α s β As the independent variable, a nonlinear adaptive approach rate function is constructed. It is used to dynamically adjust the approach speed according to the magnitude of the error, wherein For adaptive approach rate coefficient, For amplitude adjustment parameters, To switch the smoothness parameter, This is the error proportion term. For sliding surface modulation terms; Based on the composite sliding surface and the nonlinear adaptive approach rate function, a control voltage signal on the αβ axis is generated and output to the power device of the MMC through carrier shift modulation.

10. The MMC adaptive sliding mode control method based on a two-phase stationary coordinate system according to claim 9, characterized in that, The DC side of the MMC includes; By comparing the submodule voltage reference value Average voltage of each phase upper and lower bridge arm submodule Generate circulation reference values ; The circulation reference value Compared with actual circulation value Compare and generate circulating control signals ; Based on the circulation reference value and circulating control signal Obtain the final control signal ; Calculate the equalization coefficient K and output the equalization compensation signal. e .

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