A three-level T-type inverter grid-connected control method based on a sliding mode observer

Abstract

The application discloses a grid-connected control method of a three-level T-type inverter based on a sliding mode observer and relates to the technical field of grid-connected control. The application provides a preset time sliding mode control scheme based on a sliding mode observer for the grid-connected control of the three-level T-type inverter based on the sliding mode observer, introduces a continuous Sigmoid function to replace a nonlinear sign function to construct a sliding mode observation reaching law, can effectively and smoothly control a signal, significantly suppresses the high-frequency chattering phenomenon inherent to the sign function in the traditional sliding mode control, and simultaneously improves the convergence speed and tracking precision of the system. On the basis of observing the grid voltage as an external disturbance through the sliding mode observer, the external disturbance is feedforward compensated and applied in the preset time sliding mode control reaching law, so as to suppress the chattering, accelerate the convergence process of the output current and improve the timeliness and stability of the grid-connected control of the three-level T-type inverter based on the sliding mode observer.

Description

Technical Field

[0001] This invention relates to the field of grid-connected control technology, and in particular to a grid-connected control method for a three-level T-type inverter based on a sliding mode observer. Background Technology

[0002] Currently, the effective and sustainable operation of power systems heavily relies on the performance of the power grid. Therefore, uninterruptible power supplies (UPS) have become crucial for supporting and protecting critical loads that cannot withstand power outages, particularly in the medical, communications, and high-precision equipment sectors. In UPS applications, the inverter, as a key power conversion device connecting the DC power supply to the AC grid, directly determines the quality of the system's output power. Traditional two-level grid-connected inverters suffer from low output efficiency and high switching frequency losses, while three-level T-type inverters (3LT²I) offer advantages such as low total harmonic distortion (THD) and excellent transient response characteristics.

[0003] Stability and robustness are the most critical considerations for grid control schemes. Among numerous inverter topologies, the 3LT²I has attracted much attention due to its ability to improve system performance. These inverters can be divided into two categories: stand-alone and grid-connected. The goal of a grid-connected inverter is to convert the energy from DC power supply into AC output with the required frequency and inject it into the grid through a filter to minimize output voltage distortion.

[0004] Although existing control methods can achieve grid connection targets, grid voltage waveforms typically exhibit high THD. A 3LT²I grid connection may introduce instability issues caused by harmonic distortion, phase imbalance, and reactive power fluctuations, posing challenges to system performance and requiring close attention to the robustness of the closed-loop system. Furthermore, power system disturbances can exacerbate these problems, leading to system current instability.

[0005] In existing technologies, sliding mode control (SMC) is widely used in power electronics applications as an alternative to compensate for all disturbances in the power grid. Traditional 3LT²I sliding mode control technology achieves the desired switching frequency by modeling the inverter in the α-β or dq coordinate system, constructing the sliding surface, and determining the control law.

[0006] However, the discontinuous switching characteristics inherent in traditional SMCs can cause high-frequency chattering problems, which have an adverse effect on the steady-state accuracy of the power system and the lifespan of switching devices. Furthermore, the convergence time of traditional SMCs usually depends heavily on initial conditions and power system uncertainties, which is too slow for critical grid applications that require fast and stable operation, resulting in poor grid connection control stability. Summary of the Invention

[0007] Therefore, it is necessary to provide a grid-connected control method for a three-level T-type inverter based on a sliding mode observer to address the aforementioned technical problems.

[0008] The present invention adopts the following technical solution: This invention provides a grid-connected control method for a three-level T-type inverter based on a sliding mode observer. First, a reference current for the output current of the three-level T-type inverter is determined. Then, the grid voltage is used as an external disturbance to establish the state-space equation of the three-level T-type inverter. Next, based on the state-space equation of the three-level T-type inverter, a sliding mode observation reaching law is constructed by replacing the sign function with the sigmoid function. A sliding mode observer is then constructed based on the sliding mode observation reaching law to observe the output current of the three-level T-type inverter, so as to obtain the output current when the observation converges. The process involves: real-time estimation of the external disturbance; construction of the sliding surface of the sliding mode controller based on the tracking error of the reference current based on the output current; and construction of the sliding mode controller to track and control the output current of the three-level T-type inverter based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and a terminal attractor that causes the output current of the three-level T-type inverter to converge to the reference current within a preset time. The terminal attractor is constructed based on the preset convergence time, the sliding surface and norm of the sliding mode observer, and exponential and power functions based on the norm.

[0009] This invention provides a grid-connected control device for a three-level T-type inverter based on a sliding mode observer, comprising: The power control module is used to determine the reference current for the output current of the three-level T-type inverter; The modeling module is used to treat the grid voltage as an external disturbance to the three-level T-type inverter and establish the state-space equation of the three-level T-type inverter. The sliding mode observation module is used to construct a sliding mode observation reaching law based on the state space equation of the three-level T-type inverter, using the Sigmoid function as the sign function replacement. Based on the sliding mode observation reaching law, a sliding mode observer is constructed to observe the output current of the three-level T-type inverter, so as to obtain a real-time estimate of the external disturbance when the observation converges. The sliding mode control module is used to construct the sliding surface of the sliding mode controller based on the tracking error of the reference current based on the output current; and to construct the sliding mode controller to track and control the output current of the three-level T-type inverter based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and the terminal attractor that makes the output current of the three-level T-type inverter converge to the reference current within a preset time. The terminal attractor is constructed based on a preset convergence time, the sliding surface and norm of the sliding mode observer, and an exponential and power functions based on the norm.

[0010] This invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described three-level T-type inverter grid-connected control method based on a sliding mode observer.

[0011] The present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the above-described three-level T-type inverter grid-connected control method based on a sliding mode observer.

[0012] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: This invention addresses grid-connected control of three-level T-type inverters based on sliding mode observers. It proposes a preset-time sliding mode control scheme using a sliding mode observer. By introducing a continuous sigmoid function to replace the nonlinear sign function in constructing the sliding mode observation reaching law, the control signal can be effectively and smoothly controlled. This significantly suppresses the high-frequency chattering inherent in traditional sliding mode control due to the sign function, while simultaneously improving the system's convergence speed and tracking accuracy. Based on the observation of the grid voltage as an external disturbance using a sliding mode observer, feedforward compensation for the external disturbance is applied to the preset-time sliding mode control reaching law to suppress chattering, accelerate the output current convergence process, and improve the timeliness and stability of grid-connected control of three-level T-type inverters based on sliding mode observers. Attached Figure Description

[0013] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0014] Figure 1 A schematic flowchart of a grid-connected control method for a three-level T-type inverter based on a sliding mode observer provided by the present invention; Figure 2 A grid-connected 3LT provided by the present invention 2 I. Circuit topology diagram; Figure 3 A schematic diagram of the overall architecture of a grid-connected control loop provided by the present invention; Figure 4 A schematic diagram of the grid-side output voltage waveform provided by the present invention; Figure 5 A schematic diagram of the grid-side output current waveform provided by the present invention; Figure 6 A schematic diagram of the output voltage and current signals of an inverter provided by the present invention; Figure 7 A schematic diagram of a grid-connected voltage estimation value provided by the present invention; Figure 8 A schematic diagram of the output voltage of a three-phase inverter provided by the present invention; Figure 9 A schematic diagram of a phase-a control switching signal provided by the present invention; Figure 10 A comparative schematic diagram of the output voltage signal of an inverter under PI control and its FFT analysis provided by the present invention; Figure 11 A comparative schematic diagram of the output current signal of an inverter under PI control and its FFT analysis provided by the present invention; Figure 12 This invention provides a schematic diagram of a three-level T-type inverter grid-connected control device based on a sliding mode observer. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0016] Currently, various control strategies have been proposed to regulate the output voltage of 3LT²I to achieve desired performance, such as proportional-integral control using pulse-width modulation (PWM), predictive control, multi-loop feedback, and repetitive composite control. Furthermore, sliding mode control is also widely used in power electronics applications.

[0017] This invention will provide a grid-connected 3LT 2I apply a fast SMC based on a predefined time-reaching law and propose an improved SMO to enhance robustness. The proposed SMO is used to estimate disturbances and reduces chattering more effectively than the traditional SMO. Furthermore, the estimated disturbances are incorporated into the output of the predefined-time sliding mode control (PTSMC) through feedback compensation. Specifically:

[0018] (1) A novel SMO design with optimized nonlinear switching terms is proposed to achieve accurate disturbance estimation. Disturbance compensation is integrated into the control system to achieve robust performance. The accuracy of the observer is demonstrated by verifying the stability of the error system.

[0019] (2) First time targeting grid-connected 3LT 2 I. A PTSMC scheme with pre-defined performance is proposed to address the inherent limitations of traditional SMC. Reachability is proven using Lyapunov functions, and the effectiveness of the pre-defined performance is verified.

[0020] (3) Related grid-connected 3LTs were developed. 2 Simulation experiments on the inverter and the three-phase power simulation results demonstrate the superior performance of the proposed scheme in terms of convergence speed, disturbance rejection capability, and current tracking accuracy.

[0021] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of a grid-connected control method for a three-level T-type inverter based on a sliding mode observer according to the present invention, which specifically includes the following steps: S101: Reference current for determining the output current of a three-level T-type inverter.

[0023] S102: Using the grid voltage as an external disturbance to the three-level T-type inverter, establish the state-space equation of the three-level T-type inverter.

[0024] S103: Based on the state-space equation of the three-level T-type inverter, a sliding mode observation reaching law is constructed by replacing the sign function with the Sigmoid function. Based on the sliding mode observation reaching law, a sliding mode observer is constructed to observe the output current of the three-level T-type inverter so as to obtain a real-time estimate of the external disturbance when the observation converges.

[0025] S104: Construct the sliding surface of the sliding mode controller based on the tracking error of the reference current based on the output current; construct the sliding mode controller to track and control the output current of the three-level T-type inverter based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and the terminal attractor that makes the output current of the three-level T-type inverter converge to the reference current within a preset time.

[0026] Figure 2 A grid-connected 3LT in this invention 2 I. Circuit topology diagram, Figure 2 In the middle, 3LT 2 The inverter is connected to the grid via a smooth inductor L with parasitic resistance R. A 3LT will be built subsequently. 2 I. A mathematical model of the inverter system is presented, and its current and voltage variation characteristics under grid-connected conditions are analyzed.

[0027] In one or more embodiments of the present invention, a mathematical model of a three-level T-type inverter in the α-β two-phase stationary coordinate system can be established based on Kirchhoff's laws and circuit analysis; the grid voltage is taken as the external disturbance of the three-level T-type inverter, and the state-space equation of the three-level T-type inverter is established based on the mathematical model of the three-level T-type inverter in the α-β two-phase stationary coordinate system.

[0028] like Figure 1 As shown, according to Kirchhoff's laws and circuit analysis, under normal circumstances, 3LT 2 The mathematical model of the inverter system can be derived as follows: (1).

[0029] in, It is a three-phase current. and They represent 3LT respectively 2 I. Inverter output voltage and grid voltage The relationship between the output voltage and the switching state is shown in the following formula: (2).

[0030] In the formula, This indicates the switching status of different bridge arms.

[0031] To simplify the calculation, the system (1) is transformed to the following transformation matrix. Coordinate system: .

[0032] System (1) is represented as follows: (3).

[0033] 3LT 2 The inverter current is defined as the system state. The grid voltage is considered an unknown disturbance. Therefore, the state-space equation (3) can be further rewritten as:

[0034] (4).

[0035] Where C is the output matrix, and the state variable matrix A, input control matrix B, and disturbance matrix F are represented as follows: .

[0036] Control objective: The control objective of this invention is to ensure 3LT through precise current control. 2 The voltage and current output by the inverter meet grid connection requirements, thereby maintaining system stability. This effectively reduces the risk of system instability and ensures the safe and reliable operation of the power system. Specifically, in one or more embodiments of the present invention, a reference current for the output current of the three-level T-type inverter can be generated based on the active power-frequency droop and reactive power-voltage droop characteristics, according to the virtual synchronous generator control strategy of the outer loop control.

[0037] To achieve the above control effect, a grid-connected 3LT 2 The control objective of the inverter is defined as follows: 1. Current component and Their reference values ​​should be tracked separately. and Reference value and Calculated from power regulation: (5).

[0038] 2. The output voltage must be synchronized with the mains voltage in amplitude, frequency, and phase: (6).

[0039] Power control: The proposed virtual synchronous generator control strategy aims to simulate the operating characteristics of a synchronous generator. This is achieved by controlling the 3LT... 2 The inverter's power conversion interface enables it to reproduce the inertial response and damping characteristics of a traditional synchronous generator. The power control loop consists of two main parts: active power-frequency regulation and reactive power-amplitude regulation. By implementing power regulation and providing sufficient inertia and damping to the system, the proposed virtual synchronous generator control strategy can achieve grid-connected voltage synchronization.

[0040] The active power analysis uses a second-order mathematical model, and its equations of motion are as follows: (7).

[0041] in, Represents the virtual inertia constant; and These represent the mechanical power reference value and the electromagnetic power, respectively. The rated angular frequency of the power grid; and 3LT respectively 2 I. Angular frequency and phase angle of the inverter output voltage; This represents the damping coefficient.

[0042] Based on the above model, the governing equations are as follows: (8).

[0043] in, and These represent the active power reference value and the active frequency droop coefficient, respectively. This adjustment process involves adjusting... , making 3LT 2 I. Inverter output frequency Adaptive approach to the rated frequency of the power grid This achieves frequency synchronization. Similar to active power control, the mathematical model for reactive power control is expressed as:

[0044] .

[0045] in, and These represent the output voltage amplitude reference value and the grid rated voltage amplitude, respectively. and These represent the reactive power reference value and the actual output reactive power, respectively. This is the reactive power-voltage droop coefficient. It can be adjusted... You can adjust 3LT 2 I. The output voltage amplitude of the inverter is adjusted to achieve amplitude synchronization.

[0046] Therefore, the system's equivalent work angle and equivalent electromotive force can be expressed as follows: and Therefore, the reference voltage can be obtained. , Based on these quantities, a reference current can be generated. Tracking control of the system can be achieved by tracking these reference signals.

[0047] Three-phase active power and reactive power exist The calculation formula in the coordinate system is as follows: (9).

[0048] Under ideal conditions where losses are negligible, the AC output power equals the DC input power. Typically, the reference current value can be obtained using the reference voltage generated by the aforementioned outer-loop power control. and .

[0049] By rotation matrix Transformation of stationary coordinate system to The transformation formula for rotating the coordinate system is as follows: .

[0050] To more clearly illustrate the control framework, this invention provides Figure 3 The overall architecture diagram of the control loop under grid connection can intuitively show the direction of the control loop.

[0051] Sliding mode observer: Based on system (4), a novel sliding mode observer is constructed as follows: (10).

[0052] in, Indicates in Estimated current in coordinate system The input signal of the sliding mode observer. This refers to the sliding surface-based control term used to drive the state convergence of the sliding mode observer. It is a nonlinear feedback signal generated internally by the sliding mode observer based on the observation error of the output current, through the sliding surface. Its physical meaning is a real-time estimate of an unknown disturbance in the power system (i.e., the grid voltage). The sliding surface is constructed as follows:

[0053] (11).

[0054] In the formula, For the sliding surface of the sliding mode observer, This represents the output current of a true three-level T-type inverter. The output current of the three-level T-type inverter is estimated for observation.

[0055] However, using the sign function as the switching function can lead to severe chattering. To improve convergence speed and tracking accuracy, the proposed novel reaching law can be expressed as follows:

[0056] (12).

[0057] Where the gain coefficient K >0 and power coefficient m >0 represents a positive constant parameter selected based on application requirements, and the traditional switching function is replaced by the sigmoid function: (13).

[0058] in, It is a natural constant. δ >0 is a constant used for smoothness adjustment. Therefore, the sliding mode observer can be transformed into the following form:

[0059] (14).

[0060] The observation error is defined as Then the error system can be derived as follows: (15).

[0061] The design goal of the sliding mode observer is to force the error It converges to zero within a finite time. When the system enters the sliding mode, it satisfies... and ,Right now and Equation (15) can be directly solved to obtain:

[0062] .

[0063] At this time, the nonlinear input signal of the sliding mode observer This can be equivalent to an unknown disturbance in the system. The estimated value .

[0064] When the error system (15) converges, we can obtain The following theorem provides a sufficient condition for the robustness of this error system.

[0065] Theorem 1: Consider system (10) that satisfies the reaching law (12). If the sliding mode observer gain is chosen to satisfy:

[0066] (16).

[0067] The state estimate of the sliding mode observer based on this convergence law will converge to the state of the dynamic system (4).

[0068] Proof: Construct the Lyapunov candidate function as follows: (17).

[0069] but The derivative can be derived from equations (12) and (14). Let Based on the system dynamics equations:

[0070] .

[0071] Under the condition (16) being satisfied, it can be guaranteed that Therefore, according to Lyapunov's stability theory, when the estimated error trajectory reaches the sliding surface... At this point, the observed value of the output current will converge to the actual output current value. Proof complete.

[0072] The Sigmoid function is used in the proposed reaching law (12), which effectively improves the chattering phenomenon inherent in traditional sliding mode observers that use sign functions, while ensuring the Lyapunov stability proved by Theorem 1.

[0073] Slip mode controller: The goal of the controller is to minimize tracking error. At the preset time The neighborhood that converges to zero. Error The derivative can be expressed as:

[0074] .

[0075] For system (4), design feedback control input. This allows the trajectory of the tracking error to be determined at any chosen time. Reaching the neighborhood of the sliding surface: (18).

[0076] And thereafter all It remains on the sliding surface for a certain period of time. This refers to the sliding surface of the sliding mode controller.

[0077] The derivative with respect to time is: in Assuming the construction satisfy If the rank is full, then for all and The controller is designed as follows:

[0078] (19).

[0079] in v ∈R 2 For virtual control input. v It controls the output current to within a user-preset time. A terminal attractor that converges to zero within a preset time period guarantees that the system state converges. Therefore:

[0080] (20).

[0081] in And assume that it is bounded, that is, it satisfies Based on sliding mode dynamics (18) and controller design (19), a theorem for sliding mode control with a preset time is subsequently proposed.

[0082] Theorem 2: Consider system (4), let , , , and Given a constant. If the virtual control input v Selected as:

[0083] (twenty one).

[0084] in For sliding surface The abbreviated representation of indicates that the trajectory of the closed-loop system (4) is eventually consistent with the preset time. Furthermore, for any initial conditions... The solutions to equations (20) and (21) satisfy:

[0085] (twenty two).

[0086] Furthermore, tracking error It is ultimately uniformly bounded.

[0087] Proof: Consider the Lyapunov candidate function The time derivative is derived as follows: .

[0088] right Applying the Cauchy-Schwarz inequality, we get: .

[0089] Therefore, when At that time, there were: .

[0090] make Integrating the above equation, we obtain the inequality:

[0091] .

[0092] Right now: .

[0093] because The system (4) at the preset time .

[0094] Internally reached ,in This is to reach the upper bound of the time. Next, we will prove that the solution is within the preset time. Ultimately, it is constrained within the preset performance bounds. At time... ,condition It is established. Therefore, it can be deduced that… ,Right now:

[0095] .

[0096] Assume the system is The control input is entered into the neighborhood of the sliding surface at any time. Satisfying sliding mode At the preset time Then, the system enters the neighborhood of the sliding surface, satisfying... Error dynamics become The solution to this linear system satisfies the following inequality:

[0097] .

[0098] Then, the Lyapunov function is constructed. Its derivative is: .

[0099] If control gain Choosing the right one can guarantee... The eventual boundedness of . Proof complete.

[0100] The time is selected based on the desired convergence time, regardless of the initial state. In any case, the sliding surface will be within the preset time. Convergence, by ensuring exist Convergence is used to indirectly control tracking error. Rapid convergence.

[0101] parameter Used to adjust the convergence rate, larger ones It offers faster terminal convergence speed, while having a smaller... This makes the convergence process smoother. The exponential term in the virtual control law. This ensures fast convergence when far from the origin, while This ensures finite-time convergence near the origin.

[0102] The size of the final bounded set can be adjusted by selecting parameters. Increasing... It can reduce the radius of the bounded set and decrease This can improve the ability to suppress disturbances.

[0103] Finally, the three-level T-type inverter can be controlled by generating corresponding switching signals using space vector modulation (SVM) based on the control input of the sliding diaphragm controller, which will not be elaborated further in this invention.

[0104] based on Figure 1 The invention presents a grid-connected control method for a three-level T-type inverter based on a sliding mode observer. Specifically, it proposes a preset-time sliding mode control scheme based on a sliding mode observer. By introducing a continuous sigmoid function to replace the nonlinear sign function in constructing the sliding mode observation reaching law, it avoids chattering caused by the nonlinear sign function, improving convergence speed and tracking accuracy. Based on the observation of the grid voltage (an external disturbance) through a sliding mode observer, a preset-time sliding mode control reaching law is applied to suppress chattering and accelerate the convergence process of the output current, thereby improving the stability of the grid-connected control of the three-level T-type inverter based on the sliding mode observer.

[0105] When applying the grid-connected control method for a three-level T-type inverter based on a sliding mode observer provided by this invention, it is not necessary to... Figure 1 The steps shown are executed in sequence. The specific execution order of each step can be determined as needed, and this invention does not impose any restrictions on it.

[0106] Furthermore, application examples of the method of this invention are provided. To verify the effectiveness of sliding mode control based on the sliding mode observer, simulations were performed in Matlab / Simulink. It should be noted that no grid voltage was measured in any of the grid-connected simulations. The parameters of the three-level T-type inverter used in the simulations are shown in Table 1 below.

[0107] Table 1 System Parameters Figure 4 This is a schematic diagram of a grid-side output voltage waveform according to the present invention, such as... Figure 4 As shown, the total harmonic distortion (THD) of the grid-side voltage remains at a low level of 1.65%. The voltage stability performance indicates that the system can maintain normal operation under 50Hz grid synchronization. Furthermore, the voltage meets the preset time, achieving balance within 0.5 seconds.

[0108] Figure 5 This is a schematic diagram of a grid-side output current waveform according to the present invention. Figure 5 The total harmonic distortion (THD) of the grid-side current remained at 6.16%, indicating that the sliding mode control method based on the sliding mode observer exhibits excellent robustness against grid frequency drift in a three-level T-type inverter system. Furthermore, it can be seen that the current meets the control requirements and achieves balance before the preset time of 0.5 seconds.

[0109] Simulation results collectively demonstrate the effectiveness of the proposed sliding mode control strategy based on a sliding mode observer in maintaining power quality and system stability during grid connection. In actual grid operation, frequency fluctuations inherently possess uncertainty. Nevertheless, the proposed system exhibits the ability to quickly and accurately track the grid fundamental frequency while maintaining operational safety, and can effectively regulate the grid-connected current frequency.

[0110] Figure 6 This is a schematic diagram of the output voltage and current signals of an inverter according to the present invention, as shown below. Figure 6 As shown, voltage and current exhibit the same frequency and direction. The designed sliding mode control method based on a sliding mode observer effectively achieves current balance and voltage regulation in the grid-connected system.

[0111] Figure 7 This is a schematic diagram of an estimated grid-connected voltage value according to the present invention. Figure 7 The results of the sliding mode observer's estimation of the grid voltage are presented. Figure 8 This is a schematic diagram of the output voltage of the grid-connected three-phase inverter in this invention. Figure 8 The control effect of the sliding mode controller on a three-level T-type inverter system is shown, indicating that the sliding mode control has strong robustness and excellent performance in harmonic suppression.

[0112] Figure 9 This is a schematic diagram of a switching signal controlled by phase a in this invention. Figure 9 The control switch signal applied to phase a of the system is shown, where 0 represents closed and 1 represents open. For simplicity, the phase b and phase c signals are omitted. Ta1, Ta2, Ta3, and Ta4 correspond to... Figure 2 The power semiconductor switching device of phase a in the middle.

[0113] Figure 10 This diagram illustrates a comparison of the inverter output voltage signal under PI control and its FFT analysis according to the present invention. The simulation comparison was performed under the same conditions using PI control. Figure 10 As shown, PI control achieves voltage regulation. However, as... Figure 11 As shown, Figure 11 This is a comparative schematic diagram of the output current signal of an inverter under PI control and its FFT analysis in this invention. The current balance effect still needs improvement. Figure 6 The comparison shows that the sliding mode control method based on the sliding mode observer is superior. Experimental results verify the effectiveness of the proposed method under grid-connected operating conditions.

[0114] The above describes a three-level T-type inverter grid-connected control method based on a sliding mode observer, provided by one or more embodiments of the present invention. Based on the same idea, the present invention also provides a corresponding three-level T-type inverter grid-connected control device based on a sliding mode observer, such as... Figure 12As shown.

[0115] Figure 12 A schematic diagram of a three-level T-type inverter grid-connected control device based on a sliding mode observer provided by the present invention includes: The power control module 201 is used to determine the reference current for the output current of the three-level T-type inverter; Modeling module 202 is used to treat grid voltage as an external disturbance of the three-level T-type inverter and establish the state-space equation of the three-level T-type inverter. The sliding mode observation module 203 is used to construct a sliding mode observation reaching law based on the state space equation of the three-level T-type inverter, using the Sigmoid function as the sign function replacement, and construct a sliding mode observer based on the sliding mode observation reaching law to observe the output current of the three-level T-type inverter, so as to obtain a real-time estimate of the external disturbance when the observation converges. The sliding mode control module 204 is used to construct the sliding surface of the sliding mode controller based on the tracking error of the reference current based on the output current; and to construct the sliding mode controller to track and control the output current of the three-level T-type inverter based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and the terminal attractor that causes the output current of the three-level T-type inverter to converge to the reference current within a preset time. The terminal attractor is constructed based on a preset convergence time, the sliding surface and norm of the sliding mode observer, and an exponential and power functions based on the norm.

[0116] Specific limitations regarding the three-level T-type inverter grid-connected control device based on sliding mode observers can be found in the above-mentioned limitations on the three-level T-type inverter grid-connected control method based on sliding mode observers, and will not be repeated here. Each module in the aforementioned three-level T-type inverter grid-connected control device based on sliding mode observers can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in hardware or independently of the processor in a computer device, or stored in software in the memory of a computer device, so that the processor can call and execute the operations corresponding to each module.

[0117] The present invention also provides a computer-readable storage medium storing a computer program that can be used to execute the above-described... Figure 1 A grid-connected control method for a three-level T-type inverter based on a sliding mode observer is provided.

[0118] This invention also provides a computer device. At the hardware level, the computer device includes a processor, an internal bus, a network interface, memory, and non-volatile memory, and may also include other hardware required for various operations. The processor reads the corresponding computer program from the non-volatile memory into memory and then executes it to achieve the above-mentioned functions. Figure 1 A grid-connected control method for a three-level T-type inverter based on a sliding mode observer is provided.

[0119] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. Any references to memory, storage, databases, or other media used in the embodiments provided by this invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0120] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this invention.

Claims

1. A grid-connected control method for a three-level T-type inverter based on a sliding mode observer, characterized in that, include: Determine the reference current for the output current of the three-level T-type inverter; The grid voltage is used as an external disturbance to the three-level T-type inverter, and the state-space equation of the three-level T-type inverter is established. Based on the state-space equation of the three-level T-type inverter, a sliding mode observation reaching law is constructed by replacing the sign function with the Sigmoid function. A sliding mode observer is constructed based on the sliding mode observation reaching law to observe the output current of the three-level T-type inverter, so as to obtain a real-time estimate of the external disturbance when the observation converges. The sliding surface of the sliding mode controller is constructed based on the tracking error of the reference current based on the output current. Based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and the terminal attractor that makes the output current of the three-level T-type inverter converge to the reference current within a preset time, a sliding mode controller is constructed to track and control the output current of the three-level T-type inverter. The terminal attractor is constructed based on a preset convergence time, the sliding surface and norm of the sliding mode observer, and an exponential function and a power function based on the norm. The sliding mode controller is constructed based on the real-time estimation of the external disturbance and the terminal attractor that causes the output current of the three-level T-type inverter to converge to the reference current within a preset time. Specifically, this includes: A sliding mode controller is constructed based on the real-time estimation of the external disturbance and a terminal attractor that causes the output current of the three-level T-type inverter to converge to the reference current within a preset time, using the following formula: ， ， ， ， ， ， ， ， ； in, To control the input, This refers to the output current of a three-level T-type inverter. For time, For the input control matrix, For the state variable matrix, For the interference matrix, For real-time estimation of external disturbances, For the sliding surface of the sliding mode controller, For sliding surface The abbreviation of , For the tracking error of output current control, For terminal attractors, , , and As a preset constant, To preset the convergence time, As a preset lower bound constant, It is a natural constant.

2. The grid-connected control method for a three-level T-type inverter based on a sliding mode observer as described in claim 1, characterized in that, The process involves constructing a sliding mode observation reaching law based on the state-space equations of a three-level T-type inverter, using the Sigmoid function as a replacement for the sign function. A sliding mode observer is then constructed based on this law to observe the output current of the three-level T-type inverter. Specifically, this includes: The sliding surface of the sliding observer is constructed based on the observation error of the output current using the following formula: ， The sliding mode observation convergence law is constructed by replacing the sigmoid function with the sign function using the following formula: ， ， Based on the state-space equations of a three-level T-type inverter, a sliding mode observer is constructed using the sliding mode observation reaching law to observe the output current of the three-level T-type inverter: ， in, For the sliding surface of the sliding mode observer, This represents the output current of a true three-level T-type inverter. To observe and estimate the output current of the three-level T-type inverter, For the sliding mode observation reaching law, This is the gain coefficient. The power coefficient is... It is a natural constant. As a preset constant, Parasitic resistance, This is the output voltage of a three-level T-type inverter.

3. The grid-connected control method for a three-level T-type inverter based on a sliding mode observer as described in claim 1, characterized in that, The reference current for determining the output current of the three-level T-type inverter specifically includes: Based on the virtual synchronous generator control strategy of the outer loop control, and according to the active-frequency droop and reactive-voltage droop characteristics, a reference current for the output current of the three-level T-type inverter is generated.

4. The grid-connected control method for a three-level T-type inverter based on a sliding mode observer as described in claim 1, characterized in that, The process of using the grid voltage as an external disturbance to the three-level T-type inverter and establishing the state-space equations of the three-level T-type inverter specifically includes: Based on Kirchhoff's laws and circuit analysis, a mathematical model of a three-level T-type inverter in the α-β two-phase stationary coordinate system is established. The grid voltage is taken as the external disturbance of the three-level T-type inverter. The state-space equation of the three-level T-type inverter is established based on the mathematical model of the three-level T-type inverter in the α-β two-phase stationary coordinate system.

5. A grid-connected control device for a three-level T-type inverter grid-connected control method based on a sliding mode observer as described in any one of claims 1 to 4, characterized in that, include: The power control module is used to determine the reference current for the output current of the three-level T-type inverter; The modeling module is used to treat the grid voltage as an external disturbance to the three-level T-type inverter and establish the state-space equation of the three-level T-type inverter. The sliding mode observation module is used to construct a sliding mode observation reaching law based on the state space equation of the three-level T-type inverter, using the Sigmoid function as the sign function replacement. Based on the sliding mode observation reaching law, a sliding mode observer is constructed to observe the output current of the three-level T-type inverter, so as to obtain a real-time estimate of the external disturbance when the observation converges. The sliding mode control module is used to construct the sliding surface of the sliding mode controller based on the tracking error of the reference current based on the output current. Based on the sliding surface of the sliding mode controller, the real-time estimation of the external disturbance, and the terminal attractor that makes the output current of the three-level T-type inverter converge to the reference current within a preset time, a sliding mode controller is constructed to track and control the output current of the three-level T-type inverter. The terminal attractor is constructed based on a preset convergence time, the sliding surface and norm of the sliding mode observer, and an exponential and power functions based on the norm.

6. A computer-readable storage medium, characterized in that, The storage medium stores a computer program, which, when executed by a processor, implements the grid-connected control method for a three-level T-type inverter based on a sliding mode observer as described in any one of claims 1 to 4.

7. A computer device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the grid-connected control method for a three-level T-type inverter based on a sliding mode observer as described in any one of claims 1 to 4.

Images