Current inter-harmonic control method and system for grid-connected photovoltaic system

Abstract

This invention discloses a method for controlling the interharmonic current of a grid-connected photovoltaic (PV) system. The method includes: acquiring data information of the target grid-connected PV system; constructing a continuous state-space model of a three-phase grid-connected PV inverter in a dq rotating coordinate system, considering the influence of interharmonic disturbances; designing an extended state observer for the interharmonic disturbances; constructing an objective function for controlling the interharmonic current of the grid-connected PV system, considering current tracking accuracy, control smoothness, and interharmonic suppression effect; constructing stability constraints based on Lyapunov theory; and solving the constructed objective function according to the established constraints to complete the interharmonic current control of the grid-connected PV system. This invention also discloses a system for implementing the aforementioned interharmonic current control method for the grid-connected PV system. This invention not only achieves the suppression and control of interharmonic current in the grid-connected PV system but also offers higher reliability and better accuracy.

Description

Technical Field

[0001] This invention belongs to the field of electrical automation, and specifically relates to a method and system for controlling inter-harmonic currents in a grid-connected photovoltaic system. Background Technology

[0002] With economic and technological development and the improvement of people's living standards, electricity has become an indispensable secondary energy source in people's production and daily life, bringing endless convenience. Therefore, ensuring a stable and reliable supply of electricity has become one of the most important tasks of the power system.

[0003] Currently, an increasing number of photovoltaic (PV) power generation systems are being connected to the power grid and generating electricity. In grid-connected PV systems, due to power coupling between the front-end DC / DC converter and the back-end DC / AC inverter, as well as the nonlinear characteristics of the inverter's own PWM modulation strategy, the system often generates interharmonic components of non-integer multiples of the fundamental frequency while feeding the fundamental current to the grid. These interharmonics not only cause distortion of the grid-connected current waveform and power fluctuations, but may also induce electrical resonance with nearby transmission lines or reactive power compensation devices, and in severe cases, even induce subsynchronous oscillations, threatening the safe and stable operation of the PV power plant and the main grid. Therefore, controlling the current interharmonics of grid-connected PV systems is of great significance to the power system.

[0004] Currently, traditional photovoltaic grid-connected inverter control mostly employs PI or PR regulators, supplemented by grid voltage feedforward compensation. While these methods have achieved some success in suppressing integer harmonics, their ability to suppress interharmonics, which are time-varying and complex in composition, is limited. This is mainly because: interharmonic frequencies are not integer multiples of the fundamental frequency, making accurate compensation difficult using traditional resonant controllers; and interharmonics possess randomness and uncertainty, rendering regulators with fixed parameters unable to adapt to their dynamic changes. Summary of the Invention

[0005] One of the objectives of this invention is to provide a highly reliable and accurate method for controlling the interharmonic current of a grid-connected photovoltaic system.

[0006] The second objective of this invention is to provide a system for implementing the current interharmonic control method of the grid-connected photovoltaic system.

[0007] The current interharmonic control method for a grid-connected photovoltaic system provided by this invention includes the following steps:

[0008] S1. Obtain data information of the target grid-connected photovoltaic system;

[0009] S2. Based on the data obtained in step S1, and considering the influence of interharmonic disturbances, construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system.

[0010] S3. For the model constructed in step S2, design an extended state observer for the interharmonic disturbance;

[0011] S4. Based on the data obtained in step S3, and taking into account current tracking accuracy, control smoothness and interharmonic suppression effect, construct the current interharmonic control objective function of the grid-connected photovoltaic system.

[0012] S5. Based on the objective function constructed in step S4, construct stability constraints based on Lyapunov theory;

[0013] S6. Based on the established constraints, solve the constructed objective function to complete the inter-harmonic current control of the grid-connected photovoltaic system.

[0014] Step S1, which involves obtaining data information of the target grid-connected photovoltaic system, specifically includes the following steps:

[0015] Obtain data information from the target grid-connected photovoltaic system;

[0016] The data information includes current information and grid control quantity information of the three-phase grid-connected photovoltaic inverter of the target grid-connected photovoltaic system, as well as voltage information, frequency information, filter resistor and filter inductor information of the power system.

[0017] Step S2, which involves constructing a continuous state-space model of a three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the data obtained in step S1 and considering the influence of interharmonic disturbances, specifically includes the following steps:

[0018] The following formula is used as the continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system:

[0019] In the formula This refers to the d-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the q-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the filter resistor value of the power system. This refers to the filter inductance value of the power system. The angular frequency of the power system; This refers to the d-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter. This is the q-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter; The voltage along the d-axis of the power system; This refers to the q-axis voltage of the power system. This is the d-axis equivalent perturbation term containing interharmonic components; This is the q-axis equivalent perturbation term containing interharmonic components;

[0020] Using sampling period Discretizing the constructed continuous state-space model yields the discrete prediction model:

[0021] In the formula Let be the measurement state in the k-th control cycle, and , This represents the d-axis current measurement value of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the k-th control cycle. The measured value of the q-axis current of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the kth control cycle; This is the control input for the kth control cycle, i.e., the d-axis and q-axis voltage control quantities output by the inverter; Let be the equivalent disturbance term for the k-th control cycle, and , This is the equivalent disturbance term containing interharmonic components on the d-axis during the k-th control cycle. This is the equivalent disturbance term containing interharmonic components on the q-axis during the k-th control cycle; This is the discretized system state matrix; This is the discretized control input matrix; This is the perturbation input matrix.

[0022] Step S3, which describes the design of an extended state observer for the interharmonic disturbance based on the model constructed in step S2, specifically includes the following steps:

[0023] Will Extend this to new state variables of the system and construct an augmented system, represented as:

[0024] In the formula It is the identity matrix, used to describe the transition relationship of the disturbance term from step k to step k+1; Original system state Process noise; For disturbance terms Process noise;

[0025] For the constructed augmented system, a Luneburg observer is constructed, represented as:

[0026] In the formula The original system state in the k-th control cycle The estimated value; The interharmonic estimate output by the observer in the k-th control cycle corresponds to the disturbance quantity. The estimate; The gain matrix of the observer; For measurement output, and ; This is the output matrix of the augmented system.

[0027] Step S4, based on the data obtained in step S3 and considering current tracking accuracy, control smoothness, and interharmonic suppression effect, constructs the current interharmonic control objective function for the grid-connected photovoltaic system. This specifically includes the following steps:

[0028] The following formula is used as the objective function for controlling the inter-harmonic current of the grid-connected photovoltaic system. :

[0029] In the formula This refers to the number of time steps used in model predictive control to predict the future behavior of the system. Predict the system state at time k+i for the kth control cycle; The system reference state at time k+i is typically the desired current command value. The number of control variables that need to be optimized; The change in control input at time k+i is predicted for the kth control cycle; The interharmonic disturbance estimate is predicted for time k+i during the kth control cycle. This is a weighted quadratic form of the state tracking error; A weighted quadratic form to control the changes in input; It is a weighted quadratic form of the disturbance estimate.

[0030] Step S5 involves constructing stability constraints based on the objective function built in step S4, specifically including the following steps:

[0031] The quadratic Lyapunov function is selected and represented as:

[0032] In the formula It is a quadratic Lyapunov function; It is a positive definite symmetric matrix;

[0033] According to Lyapunov's stability theorem, the stability condition is: if there exists a control law such that... If the condition holds true for all non-zero states, the system will eventually stabilize.

[0034] The stability condition is converted into a terminal constraint, expressed as:

[0035] In the formula It is the attenuation factor;

[0036] Thus, the terminal invariant set constraint is obtained:

[0037] In the formula The quadratic form of the interharmonic disturbance estimate after being weighted by the weight matrix W; The threshold value is set.

[0038] Step S6, which involves solving the constructed objective function based on the established constraints to achieve current harmonic control of the grid-connected photovoltaic system, specifically includes the following steps:

[0039] Based on the established constraints, in each control cycle k, based on the current measurement state... Interharmonic estimates from the observer output Solve the following optimization problem:

[0040] In the formula The control input quantity predicted at time k+i in the k-th control cycle; This is the minimum value of the voltage control quantity output by the inverter; This represents the maximum value of the voltage control quantity output by the inverter. This represents the minimum voltage change. This represents the maximum voltage change.

[0041] After solving, we get As a control quantity for the current cycle;

[0042] Will After coordinate inverse transformation and PWM modulation, control signals for the inverter switching transistors of the grid-connected photovoltaic system are generated to control the inverter of the grid-connected photovoltaic system, thereby completing the inter-harmonic current control of the grid-connected photovoltaic system.

[0043] This invention also provides a system for implementing the current interharmonic control method of the grid-connected photovoltaic system, comprising a data acquisition module, a model building module, an observation design module, a function construction module, a constraint construction module, and a harmonic control module; the data acquisition module, model building module, observation design module, function construction module, constraint construction module, and harmonic control module are connected in series; the data acquisition module is used to acquire data information of the target grid-connected photovoltaic system and upload the data information to the model building module; the model building module is used to construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the received data information and the acquired data information, considering the influence of interharmonic disturbances, and upload the data information to the observation design module; the observation design ...; the observation design module is used to construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the received data information and the acquired data information; the observation design module is used to construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the received data information and the acquired data information; the observation design module is used to construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the acquired data information and the acquired data information, considering the influence of interharmonic disturbances, and upload the data information According to the information, for the constructed model, an extended state observer is designed for interharmonic disturbances, and the data information is uploaded to the function construction module. The function construction module is used to construct the current interharmonic control objective function of the grid-connected photovoltaic system based on the received data information, considering current tracking accuracy, control action smoothness, and interharmonic suppression effect, and uploads the data information to the constraint construction module. The constraint construction module is used to construct stability constraints based on Lyapunov theory based on the constructed objective function, and upload the data information to the harmonic control module. The harmonic control module is used to solve the constructed objective function based on the received data information and the constructed conventional constraints to complete the current interharmonic control of the grid-connected photovoltaic system.

[0044] The current interharmonic control method and system for grid-connected photovoltaic systems provided by this invention introduces a dedicated interharmonic penalty term into the optimization objective function and uses an extended state observer to estimate unmeasurable interharmonics in real time. This not only achieves the suppression and control of current interharmonics in grid-connected photovoltaic systems, but also has higher reliability and better accuracy. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the method flow of the present invention.

[0046] Figure 2 This is a schematic diagram of the functional modules of the system of the present invention. Detailed Implementation

[0047] like Figure 1 The diagram shown is a flowchart of the method of the present invention: The current interharmonic control method for grid-connected photovoltaic systems disclosed in this invention includes the following steps:

[0048] S1. Obtain data information of the target grid-connected photovoltaic system; specifically including the following steps:

[0049] Obtain data information from the target grid-connected photovoltaic system;

[0050] The data information includes the current information and grid control quantity information of the three-phase grid-connected photovoltaic inverter of the target grid-connected photovoltaic system, as well as the voltage information, frequency information, filter resistor and filter inductor information of the power system;

[0051] S2. Based on the data obtained in step S1, and considering the influence of interharmonic disturbances, construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system; specifically including the following steps:

[0052] The following formula is used as the continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system:

[0053] In the formula This refers to the d-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the q-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the filter resistor value of the power system. This refers to the filter inductance value of the power system. The angular frequency of the power system; This refers to the d-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter. This is the q-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter; The voltage along the d-axis of the power system; This refers to the q-axis voltage of the power system. This is the d-axis equivalent perturbation term containing interharmonic components; This is the q-axis equivalent perturbation term containing interharmonic components;

[0054] Using sampling period Discretizing the constructed continuous state-space model yields the discrete prediction model:

[0055] In the formula Let be the measurement state in the k-th control cycle, and , This represents the d-axis current measurement value of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the k-th control cycle. The measured value of the q-axis current of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the kth control cycle; This is the control input for the kth control cycle, i.e., the d-axis and q-axis voltage control quantities output by the inverter; Let be the equivalent disturbance term for the k-th control cycle, and , This is the equivalent disturbance term containing interharmonic components on the d-axis during the k-th control cycle. This is the equivalent disturbance term containing interharmonic components on the q-axis during the k-th control cycle; This is the discretized system state matrix; This is the discretized control input matrix; The perturbation input matrix;

[0056] S3. For the model constructed in step S2, design an extended state observer for the interharmonic disturbance; specifically including the following steps:

[0057] Due to interharmonic disturbances Typically, it cannot be directly measured, therefore an extended state observer is designed to estimate it in real time; Extend this to new state variables of the system and construct an augmented system, represented as:

[0058] In the formula It is the identity matrix, used to describe the transition relationship of the disturbance term from step k to step k+1; Original system state Process noise; For disturbance terms Process noise;

[0059] For the constructed augmented system, a Luneburg observer is constructed, represented as:

[0060] In the formula The original system state in the k-th control cycle The estimated value; The interharmonic estimate output by the observer in the k-th control cycle corresponds to the disturbance quantity. The estimate; The gain matrix of the observer; For measurement output, and ; To augment the output matrix of the system;

[0061] S4. Based on the data obtained in step S3, and considering current tracking accuracy, control smoothness, and interharmonic suppression effect, construct the current interharmonic control objective function for the grid-connected photovoltaic system; specifically including the following steps:

[0062] The following formula is used as the objective function for controlling the inter-harmonic current of the grid-connected photovoltaic system. :

[0063] In the formula This refers to the number of time steps used in model predictive control to predict the future behavior of the system. Predict the system state at time k+i for the kth control cycle; The system reference state at time k+i is typically the desired current command value. The number of control variables that need to be optimized; The change in control input at time k+i is predicted for the kth control cycle; The interharmonic disturbance estimate is predicted for time k+i during the kth control cycle. This is a weighted quadratic form of the state tracking error; A weighted quadratic form to control the changes in input; The objective function is a weighted quadratic form of the disturbance estimate. The first term is used to reduce the current tracking error to ensure that the system tracks the reference command quickly. The second term is used to penalize large changes in the control quantity to reduce switching losses. The third term is an interharmonic suppression term, which is used to directly penalize the interharmonic disturbance estimate in the prediction time domain to make it tend to zero.

[0064] To enhance the suppression effect on interharmonics of different frequencies, the weight matrix W is designed in a frequency-dependent form: for specific interharmonic frequency bands with greater harm, a higher suppression weight is assigned.

[0065] S5. Based on the objective function constructed in step S4, construct stability constraints based on Lyapunov theory; specifically including the following steps:

[0066] To ensure the stability of the MPC closed-loop system, stability constraints based on Lyapunov theory are introduced; a quadratic Lyapunov function is selected, expressed as:

[0067] In the formula It is a quadratic Lyapunov function; It is a positive definite symmetric matrix;

[0068] According to Lyapunov's stability theorem, the stability condition is: if there exists a control law such that... If the condition holds true for all non-zero states, the system will eventually stabilize.

[0069] The stability condition is converted into a terminal constraint, expressed as:

[0070] In the formula The attenuation factor is preferably in the range of 0 to 1;

[0071] Thus, the terminal invariant set constraint is obtained:

[0072] In the formula The quadratic form of the interharmonic disturbance estimate after being weighted by the weight matrix W; The threshold is set; by ensuring that the terminal state enters an invariant set around the origin, the stability of the system is ensured throughout the entire prediction time domain;

[0073] In practice, matrix P can be obtained by solving the discrete Lyapunov equation or the LMI inequality.

[0074] S6. Based on the established constraints, solve the constructed objective function to complete the inter-harmonic current control of the grid-connected photovoltaic system; specifically including the following steps:

[0075] Based on the established constraints, in each control cycle k, based on the current measurement state... Interharmonic estimates from the observer output Solve the following optimization problem:

[0076] In the formula The control input quantity predicted at time k+i in the k-th control cycle; This is the minimum value of the voltage control quantity output by the inverter; This represents the maximum value of the voltage control quantity output by the inverter. This represents the minimum voltage change. This represents the maximum voltage change.

[0077] When solving, a quadratic programming (QP) solver can be used for efficient solution; after the solution is completed, the result is obtained. As a control quantity for the current cycle;

[0078] Will After coordinate inverse transformation and PWM modulation, control signals for the inverter switching transistors of the grid-connected photovoltaic system are generated to control the inverter of the grid-connected photovoltaic system, thereby completing the inter-harmonic current control of the grid-connected photovoltaic system.

[0079] In its specific implementation, the method of the present invention repeats the above steps to achieve continuous control of the inter-harmonic current of the grid-connected photovoltaic system.

[0080] The method of this invention achieves efficient suppression of interharmonics: by introducing a dedicated interharmonic penalty term into the MPC optimization objective function and using an extended state observer to estimate unmeasurable interharmonics in real time, this invention can actively predict and suppress interharmonic components, significantly reduce the total interharmonic distortion rate of grid-connected current, and meet the increasingly stringent power quality standards.

[0081] Meanwhile, the method of this invention guarantees the closed-loop stability of the control system: by integrating Lyapunov stability theory into the MPC framework and explicitly embedding stability conditions into the optimization solution process through the design of terminal cost constraints, the inherent defect of standard MPC in lacking stability guarantee in finite time domain rolling optimization is fundamentally overcome, so that the system can still maintain asymptotic stability under large disturbances and model mismatch.

[0082] Furthermore, the method of this invention achieves a balance between dynamic response and steady-state accuracy: the inherent rolling optimization mechanism of model predictive control endows the system with rapid dynamic response capability, enabling it to track changes in the current reference in a timely manner; while the introduction of interharmonic suppression terms and stability constraints significantly improves the output current quality of the system during steady-state operation, solving the problem that traditional control methods struggle to balance these two aspects.

[0083] Finally, through real-time estimation by the interharmonic observer and adaptive adjustment of the MPC weight, this invention can adapt to complex operating conditions such as changes in grid impedance and background harmonic fluctuations, maintain excellent control performance under different grid environments, and improve the grid-connected adaptability of photovoltaic systems.

[0084] The algorithm of this invention can be transformed into a standard quadratic programming problem. Existing digital signal processors or field-programmable gate arrays can fully meet the real-time computing requirements and have good engineering practical value.

[0085] like Figure 2The diagram shows the functional modules of the system of the present invention: The system for implementing the current interharmonic control method of the grid-connected photovoltaic system disclosed in this invention includes a data acquisition module, a model building module, an observation design module, a function building module, a constraint building module, and a harmonic control module; the data acquisition module, model building module, observation design module, function building module, constraint building module, and harmonic control module are connected in series; the data acquisition module is used to acquire data information of the target grid-connected photovoltaic system and upload the data information to the model building module; the model building module is used to construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the received data information and the acquired data information, considering the influence of interharmonic disturbances, and upload the data information to the observation design module; the observation design module uses... Based on the received data, an extended state observer is designed for the interharmonic disturbances in the constructed model, and the data is uploaded to the function construction module. The function construction module, based on the received data and considering current tracking accuracy, control smoothness, and interharmonic suppression effect, constructs the current interharmonic control objective function for the grid-connected photovoltaic system and uploads the data to the constraint construction module. The constraint construction module, based on the received data and the constructed objective function, constructs stability constraints based on Lyapunov theory and uploads the data to the harmonic control module. The harmonic control module, based on the received data and the constructed constraints, solves the constructed objective function to complete the current interharmonic control of the grid-connected photovoltaic system.

Claims

1. A method for controlling inter-harmonic current in a grid-connected photovoltaic system, comprising the following steps: S1. Obtain data information of the target grid-connected photovoltaic system; S2. Based on the data obtained in step S1, and considering the influence of interharmonic disturbances, construct a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system. S3. For the model constructed in step S2, design an extended state observer for the interharmonic disturbance; S4. Based on the data obtained in step S3, and taking into account current tracking accuracy, control smoothness and interharmonic suppression effect, construct the current interharmonic control objective function of the grid-connected photovoltaic system. S5. Based on the objective function constructed in step S4, construct stability constraints based on Lyapunov theory; S6. Based on the established constraints, solve the constructed objective function to complete the inter-harmonic current control of the grid-connected photovoltaic system.

2. The current interharmonic control method of a grid-connected photovoltaic system according to claim 1, characterized in that Step S1, which involves obtaining data information of the target grid-connected photovoltaic system, specifically includes the following steps: Obtain data information from the target grid-connected photovoltaic system; The data information includes current information and grid control quantity information of the three-phase grid-connected photovoltaic inverter of the target grid-connected photovoltaic system, as well as voltage information, frequency information, filter resistor and filter inductor information of the power system.

3. The current interharmonic control method of a grid-connected photovoltaic system according to claim 2, characterized in that Step S2, which involves constructing a continuous state-space model of a three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the data obtained in step S1 and considering the influence of interharmonic disturbances, specifically includes the following steps: The following formula is used as the continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system: In the formula This refers to the d-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the q-axis current of a three-phase grid-connected photovoltaic inverter. This refers to the filter resistor value of the power system. This refers to the filter inductance value of the power system. The angular frequency of the power system; This refers to the d-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter. This is the q-axis voltage control quantity output by the three-phase grid-connected photovoltaic inverter; The voltage along the d-axis of the power system; This refers to the q-axis voltage of the power system. This is the d-axis equivalent perturbation term containing interharmonic components; This is the q-axis equivalent perturbation term containing interharmonic components; Using sampling period Discretizing the constructed continuous state-space model yields the discrete prediction model: In the formula Let be the measurement state in the k-th control cycle, and , This represents the d-axis current measurement value of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the k-th control cycle. The measured value of the q-axis current of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system during the kth control cycle; This is the control input for the k-th control cycle; Let be the equivalent disturbance term for the k-th control cycle, and , This is the equivalent disturbance term containing interharmonic components on the d-axis during the k-th control cycle. This is the equivalent disturbance term containing interharmonic components on the q-axis during the k-th control cycle; This is the discretized system state matrix; This is the discretized control input matrix; This is the perturbation input matrix.

4. The current interharmonic control method of a grid-connected photovoltaic system according to claim 3, characterized in that Step S3, which describes the design of an extended state observer for the interharmonic disturbance based on the model constructed in step S2, specifically includes the following steps: Will Extend this to new state variables of the system and construct an augmented system, represented as: wherein is the identity matrix; is the original system state is the process noise of the state is the process noise of the disturbance term is the process noise of the disturbance term For the constructed augmented system, a Luneburg observer is constructed, represented as: In the formula The original system state in the k-th control cycle The estimated value; This is the estimated interharmonic value output by the observer during the k-th control cycle; The gain matrix of the observer; For measurement output, and ; This is the output matrix of the augmented system.

5. The current interharmonic control method of a grid-connected photovoltaic system according to claim 4, characterized in that Step S4, based on the data obtained in step S3 and considering current tracking accuracy, control smoothness, and interharmonic suppression effect, constructs the current interharmonic control objective function for the grid-connected photovoltaic system. This specifically includes the following steps: The following equation is used as the current inter-harmonic control objective function for the grid-connected photovoltaic system : In the formula This refers to the number of time steps used in model predictive control to predict the future behavior of the system. Predict the system state at time k+i for the kth control cycle; The system reference state at time k+i is typically the desired current command value. The number of control variables that need to be optimized; The change in control input at time k+i is predicted for the kth control cycle; The interharmonic disturbance estimate is predicted for time k+i during the kth control cycle. It is a weighted quadratic form of the state tracking error; A weighted quadratic form to control the changes in input; It is a weighted quadratic form of the disturbance estimate.

6. The current interharmonic control method for a grid-connected photovoltaic system according to claim 5, characterized in that... Step S5 involves constructing stability constraints based on the objective function built in step S4, specifically including the following steps: The quadratic Lyapunov function is selected and represented as: In the formula It is a quadratic Lyapunov function; It is a positive definite symmetric matrix; According to Lyapunov stability theorem, the stability condition is: if there exists a control law such that holds for all nonzero states, then the system is ultimately stable; The stability condition is converted into a terminal constraint, expressed as: In the formula is an attenuation factor; Thus, the terminal invariant set constraint is obtained: In the formula The quadratic form of the interharmonic disturbance estimate after being weighted by the weight matrix W; The threshold value is set.

7. The current interharmonic control method for a grid-connected photovoltaic system according to claim 6, characterized in that... Step S6, which involves solving the constructed objective function based on the established constraints to achieve current harmonic control of the grid-connected photovoltaic system, specifically includes the following steps: Based on the established constraints, in each control cycle k, based on the current measurement state... Interharmonic estimates from the observer output Solve the following optimization problem: In the formula The control input quantity predicted at time k+i in the k-th control cycle; This is the minimum value of the voltage control quantity output by the inverter; This represents the maximum value of the voltage control quantity output by the inverter. This represents the minimum voltage change. This represents the maximum voltage change. After solving, we get As a control quantity for the current cycle; Will After coordinate inverse transformation and PWM modulation, control signals for the inverter switching transistors of the grid-connected photovoltaic system are generated to control the inverter of the grid-connected photovoltaic system, thereby completing the inter-harmonic current control of the grid-connected photovoltaic system.

8. A system for implementing the current interharmonic control method of a grid-connected photovoltaic system according to any one of claims 1 to 7, characterized in that... It includes a data acquisition module, a model building module, an observation design module, a function building module, a constraint building module, and a harmonic control module; these modules are connected in series. The data acquisition module acquires data information of the target grid-connected photovoltaic system and uploads it to the model building module. The model building module constructs a continuous state-space model of the three-phase grid-connected photovoltaic inverter in the dq rotating coordinate system based on the received and acquired data information, considering the influence of interharmonic disturbances, and uploads the data information to the observation design module. The observation design module is used to design an extended state observer for interharmonic disturbances based on the received data and the constructed model, and upload the data to the function construction module. The function construction module is used to construct the current interharmonic control objective function of the grid-connected photovoltaic system based on the received data information, taking into account current tracking accuracy, control smoothness, and interharmonic suppression effect, and upload the data information to the constraint construction module; the constraint construction module is used to construct stability constraints based on Lyapunov theory based on the constructed objective function and upload the data information to the harmonic control module. The harmonic control module is used to solve the constructed objective function based on the received data and the established constraints, thereby completing the inter-current harmonic control of the grid-connected photovoltaic system.

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