A current feedforward method and system for improving stability of grid-connected inverter system

Abstract

This invention discloses a current feedforward method and system for improving the stability of grid-connected inverter systems, relating to the field of power electronics control technology. Addressing the problem of broadband oscillations caused by phase angle errors in phase-locked loops (PLLs) under weak grid conditions, this invention extracts the PLL phase angle error in real time through an angle-oriented feedback loop without altering the original current closed-loop structure. This error is then used to construct a compensation signal with opposite polarity, which is directly fed forward and superimposed onto the modulation wave, thus canceling out disturbances caused by coordinate transformation coupling and grid impedance amplification at the source. This invention requires no additional hardware sensors or reconfiguration of controller parameters; deployment is achieved only through software upgrades, offering non-intrusive, low-cost, and highly compatible features. The method effectively suppresses broadband resonance under low short-circuit ratio conditions, decouples the constraint between PLL bandwidth and stability, and significantly improves the dynamic response capability, steady-state accuracy, and grid friendliness of grid-connected systems. It is applicable to scenarios such as new energy power generation and flexible DC interconnection.

Description

Technical Field

[0001] This invention belongs to the field of power quality improvement technology, specifically relating to a current feedforward method and system for improving the stability of grid-connected inverter systems. Background Technology

[0002] In the field of power quality improvement technology, grid-connected inverters, as the core interface between the power grid and renewable energy generation, have become key equipment for promoting the high proportion of new energy integration and supporting the implementation of the dual-carbon strategy due to their efficient power transfer and power conversion capabilities. Traditional grid-connected inverters generally adopt a grid-following control strategy, which uses a phase-locked loop to detect the phase and frequency of the voltage at the grid connection point, generates a reference signal to control the inverter output, and ensures that the inverter output power is in phase and frequency with the grid. This control method can achieve stable operation under scenarios with sufficient grid strength.

[0003] However, with the large-scale development of new energy power generation, the inverse distribution of energy resources and load centers in my country means that wind and solar power plants are mostly located far from load centers, resulting in long power transmission distances and significant high-impedance, weak grid characteristics on the grid side. In engineering, the short-circuit ratio (SCR) is used to characterize grid strength; the smaller the SCR value, the weaker the grid. Meanwhile, to improve the dynamic response speed of the phase-locked loop (PLL), the PLL bandwidth is often increased in engineering, but this can easily lead to an increase in the PLL output phase angle error.

[0004] Under the combined conditions of a weak power grid and a high-bandwidth phase-locked loop (PLL), traditional grid-connected control systems exhibit significant technical deficiencies: First, the reference current signal generated by the PLL-detected grid connection point information, after being transmitted through the large grid impedance, produces non-negligible voltage disturbances, severely impacting the power quality at the grid connection point. Second, the phase angle error output by the PLL generates disturbance current in the current loop, which acts on the grid impedance, creating unfavorable interactions with the weak grid and triggering system instability and oscillations. Third, traditional PLLs can only output a reference phase angle and cannot detect the phase angle deviation between the system coordinate axis and the control coordinate axis, lacking effective means to suppress phase angle errors. Fourth, to solve the oscillation problem, the existing control architecture requires significant modifications to the current closed-loop control structure or the addition of numerous hardware sensors, resulting in high modification costs and the need to readjust control parameters, leading to poor engineering operability. These problems cause a significant decrease in the stability of grid-connected inverter systems under weak power grid and high-bandwidth PLL conditions, limiting the grid connection and consumption of new energy in weak grid areas and becoming a pressing technical challenge in the field of new energy power generation.

[0005] Therefore, there is an urgent need for a method that can accurately extract the phase angle error of the phase-locked loop in real time and directly cancel the disturbance current caused by it through feedforward, so as to solve the stability problem of grid-connected inverter systems under weak power grids. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a current feedforward method and system for improving the stability of grid-connected inverter systems, in order to address the shortcomings of the prior art. This method is used to solve the technical problem that existing grid-connected inverter systems under grid control are prone to system oscillation when the grid is weak and the bandwidth of the phase-locked loop is too large.

[0007] The present invention adopts the following technical solution: A current feedforward system for improving the stability of a grid-connected inverter system is applied to a grid-connected inverter system under grid-following control. The grid-connected inverter system includes a main circuit module and a control module. The control module outputs the reference phase and frequency of the grid connection point through a phase-locked loop to control the coordinate transformation module output, and controls the current tracking current command through a current closed loop under the dq control axis. The system also includes: Angle-oriented feedback loop is used to acquire the three-phase symmetrical AC grid voltage and convert it into voltage components in a stationary coordinate system. and Receives the phase angle of the control coordinate axis output by the phase-locked loop. and according to The error voltage signal was calculated. When the phase angle difference is very small, the error voltage signal Approximately equal to the real-time phase angle error between the system coordinate axis and the control coordinate axis ; The current feedforward control loop, connected to the angle orientation feedback loop, is used to receive the error voltage signal. Or the real-time phase angle error The compensation amount generated based on this error is then superimposed onto the modulation signal of the current closed-loop control output. The compensation amount is used to offset the real-time phase angle error. The disturbance term generated in the current loop.

[0008] Preferably, the angle orientation feedback loop is specifically configured as follows: Obtain the phase angle of the system coordinate axes The phase angle with the control coordinate axis The voltage amplitude of the power grid is Using relational expressions and Determine the voltage components in the stationary coordinate system; perform the calculation. The error voltage signal is obtained. Based on the principle of small angle approximation The error voltage signal As the real-time phase angle error The estimated value.

[0009] Preferably, the main circuit module includes: The three-phase two-level output unit consists of 6 IGBTs; DC-side voltage source unit, used to provide DC-side voltage ; LC filter unit, including filter inductor and filter capacitor It is connected to the output terminal of the three-phase two-level output unit; Equivalent grid impedance unit, including grid-side line resistance and line inductance It is connected between the LC filter unit and the three-phase symmetrical AC power grid; The bridge arm output voltage generated by the three-phase two-level output unit is described above. , Modulated signal generated by the control module , Control, and satisfy ,in .

[0010] Preferably, when the current feedforward control loop achieves compensation, it does not change the basic structure and control parameters of the original current closed-loop control; the current feedforward control loop only obtains the real-time phase angle error by collecting the three-phase voltage under the system coordinate axis and through the angle orientation feedback loop, and generates the compensation amount.

[0011] Preferably, the modulation signal output by the current closed-loop control and The formation process includes: Receive active current command and reactive current command and actual current feedback and ; via current controller The basic control quantity is calculated; the basic control quantity and the compensation quantity are linearly superimposed to obtain the final modulation signal; wherein, the polarity of the compensation quantity is related to the real-time phase angle error. The resulting disturbance terms have opposite polarities, causing the superimposed modulation signal to cancel out the disturbance terms when applied to the main circuit.

[0012] Preferably, the angle orientation feedback circuit is further configured as follows: It connects to the grid voltage sampling points in parallel and operates independently of the internal structure of the phase-locked loop; it calculates in real time through digital logic or software algorithms. The real-time phase angle error can be obtained without adding additional hardware sensors. .

[0013] Preferably, the system is suitable for weak power grid environments and high-bandwidth phase-locked loop scenarios; When the grid strength SCR decreases to the point that the grid impedance becomes non-negligible, or when the phase-locked loop bandwidth is too large to the point that the output phase angle error increases, the current feedforward control loop is configured to be active to suppress the resulting system oscillation.

[0014] Preferably, the propagation path of the disturbance term in the current loop is described as follows: The real-time phase angle error By introducing coordinate transformation relationships into the current control equations, a result is generated containing... The cross-coupling term; the cross-coupling term is controlled by a current controller. and PWM gain After amplification, a disturbance current is formed that acts on the grid impedance; the compensation amount directly cancels out the cross-coupling term and blocks the generation path of the disturbance current.

[0015] Secondly, embodiments of the present invention provide a current feedforward method for improving the stability of a grid-connected inverter system, comprising the following steps: S1. Obtain the reference phase and frequency of the grid connection point through a phase-locked loop, and output the phase angle of the control coordinate axis. ; S2. Acquire the voltage signal of the three-phase symmetrical AC power grid and convert it into voltage components in a stationary coordinate system. and ; S3. Utilizing the angle orientation feedback loop, based on the voltage component... , and the phase angle According to the formula The error voltage signal was calculated. And when the phase angle difference is very small, the error voltage signal will be... As real-time phase angle error ; S4. Based on the real-time phase angle error Generate compensation amount; S5. During the closed-loop current control process under the dq control axis, the compensation amount is superimposed on the modulation signal output by the current controller to offset the real-time phase angle error. The disturbance term generated in the current loop; S6. Control the inverter switching action according to the superimposed modulation signal to achieve stable operation of the grid-connected inverter system.

[0016] Preferably, the process of generating the modulated signal includes: Get Current Command , With actual current , The deviation; the deviation is input to the current controller. The basic modulation component is obtained; the compensation amount is added to the basic modulation component to obtain the final modulation signal under the control coordinate axis. and The introduction of the compensation amount makes the small-signal model of the system composed of... The resulting disturbance terms are canceled out; The applicability assessment is performed based on the superimposed modulation signal controlling the inverter's switching action, specifically including: Monitor the grid strength SCR value and phase-locked loop bandwidth; when the grid strength SCR is detected to be lower than the preset threshold and exhibiting weak grid characteristics, or when the phase-locked loop bandwidth is higher than the preset frequency value, automatically activate the feedforward compensation process of steps S3 to S5; when the system is in a strong grid state and the phase-locked loop bandwidth is appropriate, maintain or adjust the gain of the compensation amount. Monitor the output current waveform at the grid connection point; if the system oscillation is suppressed under the condition that the grid strength decreases from strong to weak and the PLL bandwidth increases, it is confirmed that the compensation amount effectively offsets the adverse effects caused by the PLL error and its interaction with the weak grid.

[0017] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described current feedforward method for improving the stability of a grid-connected inverter system.

[0018] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described current feedforward method for improving the stability of a grid-connected inverter system.

[0019] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described current feedforward method for improving the stability of a grid-connected inverter system.

[0020] In a sixth aspect, embodiments of the present invention provide an electronic device including a computer program, which, when executed by the electronic device, implements the steps of the above-described current feedforward method for improving the stability of a grid-connected inverter system.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects: A current feedforward method for improving the stability of grid-connected inverter systems is proposed. This method acquires the grid voltage components and the control shaft phase angle, and uses trigonometric functions to accurately estimate the real-time phase angle error. This method converts the error into a feedforward compensation amount, which is directly added to the modulation signal, thus canceling the disturbance current caused by the phase-locked loop error in a weak grid with high impedance. Without relying on complex impedance reshaping or additional hardware sensors, it achieves a closed loop of error detection-feedforward cancellation at extremely low computational cost, significantly improving the system's stability in weak grid and high-bandwidth PLL conditions, and solving the problem of oscillation in traditional grid-connected inverters.

[0022] Furthermore, by utilizing the small-angle approximation principle, the complex phase difference detection is transformed into simple algebraic operations, greatly reducing the computational burden on the digital controller. This implementation not only ensures the real-time performance and accuracy of phase angle error extraction in both steady-state and dynamic processes, but also avoids the tracking lag problem that may occur in traditional phase-locked loops when there is grid voltage distortion or frequency fluctuation. It provides a high-precision input signal for feedforward control and ensures timely compensation.

[0023] Furthermore, it was clarified that The coupling terms in gain and coordinate transformation provide a clear physical basis for the design of feedforward compensation. This is achieved by quantifying the grid impedance (…). Despite the impact of the grid impedance, this solution can be used to adjust parameters for specific weak grid scenarios (such as high impedance caused by long-distance power transmission), ensuring that the feedforward quantity can accurately offset the disturbance voltage amplified by the grid impedance, thus improving the feasibility and reliability of engineering applications.

[0024] Furthermore, without altering the original current closed-loop control structure and parameters, compensation is generated solely by acquiring phase angle errors from three-phase voltage data. This significantly reduces the engineering application cost and debugging difficulty of the system. The mature parameters and structure of the original current closed-loop control can be directly reused without the need for complex retuning of control parameters, greatly shortening the system modification and debugging cycle. Simultaneously, compensation can be achieved solely by acquiring three-phase voltage, eliminating the need for additional current, frequency, or other sensors, reducing hardware investment and lowering the risk of failure due to added sensors. This makes on-site deployment and subsequent maintenance of the system more convenient and suitable for upgrading existing grid-connected inverter systems.

[0025] Furthermore, the implementation logic of current feedforward compensation is made more specific. The compensation amount is linearly superimposed with the basic control amount output by the current controller, ensuring the real-time performance and effectiveness of the compensation. The design with opposite polarities enables precise cancellation of disturbance terms, completely blocking the transmission of disturbance terms to the main circuit from the control signal generation level. At the same time, the explicit modulation signal formation process provides a clear path for the design and adjustment of the compensation amount. The compensation amount can be flexibly adjusted according to the actual current deviation and phase angle error, adapting to different grid strengths and PLL bandwidth conditions, thus improving the system's adaptability.

[0026] Furthermore, fault isolation is achieved. Even if an anomaly occurs within the phase-locked loop, the feedforward circuit can still operate independently based on the grid voltage sampling value, improving the system's fault tolerance. The absence of additional hardware sensors means zero-cost incremental improvement, requiring only the use of existing voltage sampling channels.

[0027] Furthermore, the feedforward is only activated when the system faces instability risks (weak power grid, high bandwidth), while remaining silent or with low gain during normal operation of a strong power grid, thus avoiding noise introduction caused by unnecessary control actions. This ensures stability under extreme conditions while maintaining the system's simplicity and efficiency under normal conditions, extending equipment lifespan and improving overall operating efficiency.

[0028] Furthermore, by using feedforward to neutralize disturbances directly before they enter the current loop, rather than suppressing them after they occur, the oscillation sources caused by weak grid interactions can be fundamentally eliminated, significantly improving the system's stability margin and providing solid theoretical support for high-proportion renewable energy integration.

[0029] A current feedforward method to improve the stability of grid-connected inverter systems realizes a closed-loop control process from phase angle error detection, compensation quantity generation, control signal optimization to hardware execution. This provides clear operational steps for the engineering implementation of feedforward compensation, significantly reducing the application threshold of the method. At the same time, the closed-loop design of the entire process ensures the real-time performance and effectiveness of the compensation, and can quickly suppress system oscillations.

[0030] Furthermore, the modulation signal generation process and the system's applicability judgment logic were refined, and operating condition monitoring and compensation effect verification were added. The refined design of the modulation signal allows for more precise superposition of the compensation amount. By obtaining the basic modulation component through current deviation and then adding it to the compensation amount, the rationality of the control signal is ensured. The applicability judgment logic enables intelligent system adjustment, automatically starting and stopping the compensation process based on the grid strength SCR value and phase-locked loop bandwidth, improving the system's automation level. The compensation effect verification stage monitors the output current waveform at the grid connection point, allowing for real-time assessment of the compensation amount's effectiveness. This facilitates timely adjustment of compensation parameters, ensuring stable system operation under changing operating conditions. It also provides an intuitive basis for system debugging and maintenance, enhancing the system's practicality.

[0031] In summary, the method of the present invention can effectively improve the power quality and stability of the grid connection point in weak grid conditions, and can also effectively suppress system oscillations caused by improper design of the phase-locked loop bandwidth, providing a solution for improving the stability of grid-connected inverter systems based on grid-following control.

[0032] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0033] Figure 1 This is a control block diagram of a grid-connected inverter system under grid-connected control to which this invention applies; Figure 2 This is a schematic diagram of the phase-locked loop error obtained from the analysis of this invention; Figure 3 This is a small-signal description block diagram of the phase-locked loop error propagation path obtained from the analysis of this invention; Figure 4 This is a structural block diagram of the angle orientation feedback loop used in this invention to calculate the real-time phase angle error; Figure 5 This is a block diagram describing the small-signal current feedforward control obtained from the analysis of this invention; Figure 6 This is a block diagram of the current closed-loop control of the current feedforward control used in this invention. Figure 7 This is a diagram illustrating the implementation effect of the current feedforward control used in this invention. Figure 8 A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 9 This is a block diagram of a chip provided according to an embodiment of the present invention.

[0034] Among them, 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0039] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0040] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0041] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0042] This invention provides a current feedforward method to improve the stability of grid-connected inverter systems. It adds an angle-oriented feedback loop that operates independently of the phase-locked loop (PLL). By acquiring grid voltage and converting it into αβ-axis components, combined with the phase angle of the control coordinate axis output from the PLL, an error voltage signal is calculated using a formula and then approximated as a real-time phase angle error based on a small angle, overcoming the technical bottleneck of traditional PLLs in being unable to obtain phase angle errors. A current feedforward control loop is added, connected to the angle-oriented feedback loop. It generates a compensation amount based on the phase angle error and superimposes it onto the modulation signal output of the current closed-loop control. The polarity of the compensation amount is opposite to the disturbance term caused by the phase angle error. The compensation process does not change the original structure and parameters of the current closed-loop control; phase angle error detection is achieved solely by acquiring three-phase voltages, without requiring additional hardware. The sensor and angle orientation feedback loop enable accurate and uninterrupted detection of phase angle errors, providing a core basis for disturbance suppression. The digital algorithm implementation reduces hardware costs and interference risks. The current feedforward compensation loop precisely offsets the cross-coupling terms generated by phase angle errors in the current loop, blocking the generation of disturbance currents at the source and completely solving the oscillation problem caused by the interaction between phase-locked loop errors and weak grid conditions. It is compatible with existing control architectures and main circuits, requiring no parameter retuning, significantly reducing engineering modification costs and debugging difficulty, and can be directly applied to the upgrade and transformation of existing grid-connected inverter systems. The compensation loop can adaptively activate based on the grid strength SCR value and phase-locked loop bandwidth, ensuring stability under weak grid and high-bandwidth phase-locked loop conditions while improving operating efficiency under normal conditions.

[0043] Please see Figure 1 The present invention provides a current feedforward system for improving the stability of a grid-connected inverter system, comprising a main circuit module and a control module; The main circuit module consists of a three-phase two-level output unit composed of six IGBTs, a DC-side voltage source unit, an LC filter unit, an equivalent grid impedance unit, and a three-phase symmetrical AC grid. U dc This is the DC side voltage; L f and C f These are the filter inductor and the filter capacitor, respectively. R g and L g These are the line resistance and line inductance on the power grid side, respectively. u ga , u gb , u gcThe voltage is the grid voltage. The control module adopts a grid-following control method, using a phase-locked loop to output the reference phase and frequency of the grid connection point, controlling the coordinate transformation module output. Under the dq control axis, current tracking commands are achieved through a current closed-loop control, and the inverter switching is controlled through a PWM modulation stage to ensure that its output power meets both grid-side and power output requirements. i dref and i qref These are active and reactive current commands, respectively. θ It is the phase angle output by the PLL.

[0044] Please see Figure 2 The output error of the phase-locked loop causes the system coordinate axis (dq axis) to deviate from the control coordinate axis (dq axis). c q c (Axis) has a deviation Δ θ PLL Then, variables such as voltage and current x i The following relationship exists: (1) in, The electrical variable components along the d-axis are the system coordinate axes dq-axis. The q-axis electrical variable component is the system coordinate system axis dq-axis. , To control the electrical variables under the coordinate axes.

[0045] From the main circuit model, we know that the mathematical model of the system in coordinate axes is: (2) in, e d The inverter bridge arm output voltage can be controlled by modulation signals under the control coordinate axis. c d c and c q c Represented as: (3) in, K pwm = U dc / 2.

[0046] According to the control model, the modulation signal under the system coordinate axes satisfies the following relationship: (4) By combining (2), (3), and (4), the variables are... x = x 0+Δx Substituting and eliminating steady-state quantities, the current loop output expression under the influence of the phase-locked loop is obtained as follows: (5) From formula (5), it can be seen that the Δ generated by the phase-locked loop θ PLL This will generate a disturbance current in the current loop, which will ultimately act on the grid impedance. Its description block diagram is as follows: Figure 3 As shown, when the grid strength is sufficiently high, the grid impedance can be ignored, resulting in a small disturbance voltage and minimal impact on the grid connection point. Conversely, when the grid is in a weak grid state, the interaction between the disturbance caused by the phase-locked loop and the grid impedance will cause the grid-connected system to oscillate under weak grid conditions.

[0047] The key to implementing the current feedforward method is obtaining the real-time phase angle deviation Δ of the system. θ PLL Traditional phase-locked loops obtain the real-time phase angle by controlling the q-axis voltage to 0, but cannot obtain the phase angle deviation through their structure. This paper uses an angle-oriented feedback loop to obtain the real-time phase angle difference Δ between the system coordinate axis and the control coordinate axis. θ PLL Its control structure is as follows Figure 4 As shown, where V α = V m cos θ , V β = V m sin θ , θ and θ c Let be the phase angles of the system and control coordinate axes, respectively. Therefore, we can obtain: (6) When the phase angle difference is very small, sin( θ c - θ )≈Δ θ PLL .

[0048] Please see Figure 5 The diagram shows the small-signal description of the system after adopting current feedforward control. It can be seen that the addition of the feedforward link cancels out the disturbance term caused by the phase angle error, and to a certain extent suppresses the adverse effects caused by the phase-locked loop error and its interaction with the weak power grid.

[0049] Please see Figure 6The diagram shows the current closed-loop control block diagram after adopting current feedforward control. It can be seen that the feedforward link does not change the basic control structure and control parameters. Only the three-phase voltage under the system coordinate axis needs to be collected to obtain the real-time phase angle error.

[0050] Please see Figure 7 , is the output current at the grid connection point. The specific operating conditions are as follows: the system operating stably under traditional grid control adjusts the grid strength from strong grid (SCR=12) to weak grid (SCR=4) at 1 second and adjusts the phase-locked loop bandwidth from 50Hz to 350Hz; and the current feedforward link proposed in this invention is activated at 1.1 seconds.

[0051] The output results show that the addition of the current feedforward circuit effectively suppressed the system oscillations caused by excessive phase-locked loop bandwidth and weak grid strength.

[0052] This invention provides a current feedforward method for improving the stability of a grid-connected inverter system, comprising the following steps: S1. Obtain the reference phase and frequency of the grid connection point through a phase-locked loop, and output the phase angle of the control coordinate axis. ; S2. Acquire the voltage signal of the three-phase symmetrical AC power grid and convert it into voltage components in a stationary coordinate system. and ; S3. Utilizing the angle orientation feedback loop, based on the voltage component... , and the phase angle According to the formula The error voltage signal was calculated. And when the phase angle difference is very small, the error voltage signal will be... As real-time phase angle error ; The specific calculation process of the angle orientation feedback stage includes: Utilizing grid voltage amplitude Phase angle with system coordinate axes ,get and ;calculate The error voltage signal is obtained. Applying the principle of small-angle approximation, it is determined that... .

[0053] S4. Based on the real-time phase angle error Generate compensation amount; S5. During the closed-loop current control process under the dq control axis, the compensation amount is superimposed on the modulation signal output by the current controller to offset the real-time phase angle error. The disturbance term generated in the current loop; The process of generating a modulated signal includes: Get Current Command , With actual current , The deviation; the deviation is input to the current controller. The basic modulation component is obtained; the compensation amount is added to the basic modulation component to obtain the final modulation signal under the control coordinate axis. and The introduction of the compensation amount makes the small-signal model of the system composed of... The resulting disturbance term is canceled out.

[0054] S6. Control the inverter switching action according to the superimposed modulation signal to achieve stable operation of the grid-connected inverter system.

[0055] The applicability assessment is performed based on the superimposed modulation signal controlling the inverter's switching action, specifically including: Monitor the grid strength SCR value and phase-locked loop bandwidth; when the grid strength SCR is detected to be lower than the preset threshold and exhibiting weak grid characteristics, or when the phase-locked loop bandwidth is higher than the preset frequency value, automatically activate the feedforward compensation process of steps S3 to S5; when the system is in a strong grid state and the phase-locked loop bandwidth is appropriate, maintain or adjust the gain of the compensation amount. Effect verification: Monitor the output current waveform at the grid connection point; if the system oscillation is suppressed under the condition that the grid strength decreases from strong to weak and the PLL bandwidth increases, it is confirmed that the compensation amount effectively offsets the adverse effects caused by the PLL error and its interaction with the weak grid.

[0056] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or function. The processor described in this embodiment can be used in the operation of a current feedforward method to improve the stability of a grid-connected inverter system, including: The reference phase and frequency of the grid connection point are obtained through a phase-locked loop, and the phase angle of the control coordinate axis is output. The voltage signal of a three-phase symmetrical AC power grid is acquired and converted into voltage components in a stationary coordinate system. and ;Utilizing an angle-oriented feedback loop, based on the voltage component , and the phase angle According to the formula The error voltage signal was calculated. And when the phase angle difference is very small, the error voltage signal will be... As real-time phase angle error According to the real-time phase angle error A compensation amount is generated; during the current closed-loop control process under the dq control axis, the compensation amount is superimposed on the modulation signal output by the current controller to offset the real-time phase angle error. The disturbance term generated in the current loop is used to control the inverter switching action based on the superimposed modulation signal, thereby achieving stable operation of the grid-connected inverter system.

[0057] Please see Figure 8The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the current feedforward method for improving the stability of the grid-connected inverter system in this embodiment. To avoid repetition, these details are not elaborated here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the current feedforward system for improving the stability of the grid-connected inverter system in this embodiment. To avoid repetition, these details are not elaborated here.

[0058] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 8 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0059] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0060] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0061] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0062] Please see Figure 9 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0063] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 1 The steps are shown in the figure.

[0064] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0065] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0066] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0067] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0068] Example 4 This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0069] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0070] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0071] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the current feedforward method for improving the stability of the grid-connected inverter system in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps: The reference phase and frequency of the grid connection point are obtained through a phase-locked loop, and the phase angle of the control coordinate axis is output. The voltage signal of a three-phase symmetrical AC power grid is acquired and converted into voltage components in a stationary coordinate system. and ;Utilizing an angle-oriented feedback loop, based on the voltage component , and the phase angle According to the formula The error voltage signal was calculated. And when the phase angle difference is very small, the error voltage signal will be... As real-time phase angle error According to the real-time phase angle error A compensation amount is generated; during the current closed-loop control process under the dq control axis, the compensation amount is superimposed on the modulation signal output by the current controller to offset the real-time phase angle error. The disturbance term generated in the current loop is used to control the inverter switching action based on the superimposed modulation signal, thereby achieving stable operation of the grid-connected inverter system.

[0072] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0073] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0074] To verify the effectiveness of the invention, a MATLAB / Simulink simulation model was built to simulate the operation of a 50kW three-phase two-level grid-connected inverter under different grid intensities.

[0075] Experimental operating conditions settings: Initial state (0s-1.0s): Strong power grid environment, short-circuit ratio (SCR) = 12, phase-locked loop bandwidth set to 50Hz. The system adopts traditional grid-connected control and operates stably.

[0076] Disturbance introduction (at 1.0s): Simulating a grid fault or line switching, the grid strength drops sharply to a weak grid (SCR=4), and the PLL bandwidth is increased to 350Hz to test dynamic performance. At this time, the system under the traditional control strategy begins to exhibit violent oscillations.

[0077] The invention is activated (at 1.1s): the current feedforward control loop proposed in this invention is activated.

[0078] Analysis of experimental data results: Comparison of grid-connected current waveforms (for reference) Figure 7 ): During the period from 1.0s to 1.1s (without feedforward), the current of phase A at the grid connection point... Significant low-frequency oscillations appeared, and the total harmonic distortion (THD) rose sharply from the initial 1.5% to 18.6%, with amplitude fluctuations exceeding 20% ​​of the rated value, indicating that the system was in a critical unstable state.

[0079] After the method of this invention is applied for 1.1 seconds, the current oscillation decays rapidly within about 2 fundamental cycles (<40ms). After 1.2 seconds, the current waveform returns to a smooth sine wave, the THD drops to below 2.1%, and the amplitude stabilizes near the commanded value.

[0080] Phase angle error observation data: Data shows that with SCR=4 and high bandwidth, the output phase angle of the phase-locked loop using the traditional method is... θ c Phase angle with real power grid There is an oscillation deviation with a frequency of approximately 15 Hz, with a peak value of 0.15 rad.

[0081] The present invention calculates through the angle orientation feedback circuit This is highly consistent with the deviation (correlation coefficient > 0.98). After implementing feedforward, the equivalent phase angle error disturbance is canceled out, and the amplitude of the cross-coupling component in the current loop is reduced by 92%.

[0082] Spectrum analysis: Without feedforward, the current spectrum exhibits significant sideband harmonic peaks at 15 Hz and 85 Hz.

[0083] After implementing feedforward, the harmonic amplitude at the aforementioned characteristic frequencies decreased by more than 35 dB, demonstrating the method's ability to accurately suppress oscillations at specific frequencies.

[0084] This invention has been applied to a research project on broadband resonance risk assessment and grid connection detection technology for a medium- and low-voltage distribution network flexible DC interconnection system. Addressing the technical challenge of broadband resonance easily occurring in the medium- and low-voltage distribution network flexible DC interconnection system under weak grid conditions, the current feedforward control strategy proposed in this invention was integrated into the control system of the flexible DC interconnection device. The invention was fully validated through demonstration applications in hardware-in-the-loop (HIL) and cross-voltage-level flexible DC interconnection scenarios. Test results show that: Under simulated extremely weak power grid conditions (low short-circuit ratio SCR) and high-bandwidth phase-locked loop conditions, this invention can effectively identify and counteract disturbance terms caused by phase angle errors of the phase-locked loop, significantly suppressing the risk of broadband resonance in the low-frequency and mid-to-high-frequency bands, and solving the problem of insufficient stability of traditional grid-following control strategies in complex distribution network environments.

[0085] In the demonstration scenario of cross-voltage level flexible DC interconnection, the device with the algorithm embedded in it maintained stable tracking of the grid current under dynamic disturbances such as load changes and grid fault ride-through, and no grid disconnection or protection malfunction occurred due to broadband interaction, which verified the effectiveness of the method of the present invention in improving the safe and stable operation of the distribution network flexible DC interconnection system.

[0086] This invention has successfully verified and strongly supported the project objectives, helping the broadband resonant evaluation and grid connection detection technology of distribution network flexible DC interconnection system to advance from level three maturity to level six, and laying a solid theoretical and experimental foundation for its large-scale promotion in subsequent large-scale new energy grid connection and flexible interconnection projects.

[0087] In summary, this invention presents a current feedforward method and system for improving the stability of grid-connected inverter systems. It pioneers a real-time error extraction and direct feedforward cancellation mechanism, cutting off the positive feedback oscillation chain caused by phase angle errors at the source, significantly improving system stability under extremely low short-circuit ratios and high bandwidth conditions. Employing a non-intrusive external architecture, it requires no modification to existing hardware or current loop parameters, achieving zero-cost deployment through software upgrades alone, demonstrating strong engineering compatibility. It successfully resolves the contradiction between phase-locked loop bandwidth and stability, significantly reducing current harmonics while ensuring high dynamic response and optimizing power quality. This invention has been verified through a flexible DC-DC interconnection project, demonstrating excellent performance in hardware-in-the-loop and demonstration applications. It effectively solves the pain point of grid-connected instability in new energy sources, possessing both theoretical innovation and engineering application value, providing key technical support for building highly resilient new power systems.

[0088] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0089] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0090] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0091] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0092] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0093] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0094] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random-access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0095] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0096] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0097] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0098] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A current feedforward system for improving the stability of a grid-connected inverter system, applied to a grid-connected inverter system under grid-following control, the grid-connected inverter system comprising a main circuit module and a control module, the control module being used to output the reference phase and frequency of the grid connection point through a phase-locked loop to control the coordinate transformation module output, and to control the current tracking current command through a current closed loop under the dq control axis, characterized in that, The system also includes: Angle-oriented feedback loop is used to acquire the three-phase symmetrical AC grid voltage and convert it into voltage components in a stationary coordinate system. and Receives the phase angle of the control coordinate axis output by the phase-locked loop. and according to The error voltage signal was calculated. When the phase angle difference is very small, the error voltage signal Approximately equal to the real-time phase angle error between the system coordinate axis and the control coordinate axis ; The current feedforward control loop, connected to the angle orientation feedback loop, is used to receive the error voltage signal. Or the real-time phase angle error The compensation amount generated based on this error is then superimposed onto the modulation signal of the current closed-loop control output. The compensation amount is used to offset the real-time phase angle error. The disturbance term generated in the current loop.

2. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 1, characterized in that, The angle orientation feedback process is specifically configured as follows: Obtain the phase angle of the system coordinate axes The phase angle with the control coordinate axis The voltage amplitude of the power grid is Using relational expressions and Determine the voltage components in the stationary coordinate system; perform the calculation. The error voltage signal is obtained. ; Based on the principle of small angle approximation The error voltage signal As the real-time phase angle error The estimated value.

3. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 1, characterized in that, The main circuit module includes: The three-phase two-level output unit consists of 6 IGBTs; DC-side voltage source unit, used to provide DC-side voltage ; LC filter unit, including filter inductor and filter capacitor It is connected to the output terminal of the three-phase two-level output unit; Equivalent grid impedance unit, including grid-side line resistance and line inductance It is connected between the LC filter unit and the three-phase symmetrical AC power grid; The bridge arm output voltage generated by the three-phase two-level output unit is described above. , Modulated signal generated by the control module , Control, and satisfy ,in .

4. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 1, characterized in that, When the current feedforward control loop achieves compensation, it does not change the basic structure and control parameters of the original current closed-loop control. The current feedforward control loop only collects the three-phase voltage under the system coordinate axis and obtains the real-time phase angle error through the angle orientation feedback loop to generate the compensation amount.

5. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 1, characterized in that, The modulation signal output by the current closed-loop control and The formation process includes: Receive active current command and reactive current command and actual current feedback and ; via current controller The basic control quantity is calculated; the basic control quantity and the compensation quantity are linearly superimposed to obtain the final modulation signal; wherein, the polarity of the compensation quantity is related to the real-time phase angle error. The resulting disturbance terms have opposite polarities, causing the superimposed modulation signal to cancel out the disturbance terms when applied to the main circuit.

6. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 2, characterized in that, The angle orientation feedback circuit is also configured to: It connects to the grid voltage sampling points in parallel and operates independently of the internal structure of the phase-locked loop; it calculates in real time through digital logic or software algorithms. The real-time phase angle error can be obtained without adding additional hardware sensors. .

7. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 1, characterized in that, The system is suitable for weak power grid environments and high-bandwidth phase-locked loop scenarios. When the grid strength SCR decreases to the point that the grid impedance becomes non-negligible, or when the phase-locked loop bandwidth is too large to the point that the output phase angle error increases, the current feedforward control loop is configured to be active to suppress the resulting system oscillation.

8. The current feedforward system for improving the stability of a grid-connected inverter system according to claim 3, characterized in that, The propagation path of the disturbance term in the current loop is described as follows: The real-time phase angle error By introducing coordinate transformation relationships into the current control equations, a result is generated containing... The cross-coupling term; the cross-coupling term is controlled by a current controller. and PWM gain After amplification, a disturbance current is formed that acts on the grid impedance; the compensation amount directly cancels out the cross-coupling term and blocks the generation path of the disturbance current.

9. A current feedforward method for improving the stability of a grid-connected inverter system, applied to the system as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Obtain the reference phase and frequency of the grid connection point through a phase-locked loop, and output the phase angle of the control coordinate axis. ; S2. Acquire the voltage signal of the three-phase symmetrical AC power grid and convert it into voltage components in a stationary coordinate system. and ; S3. Utilizing the angle orientation feedback loop, based on the voltage component... , and the phase angle According to the formula The error voltage signal was calculated. And when the phase angle difference is very small, the error voltage signal will be... As real-time phase angle error ; S4. Based on the real-time phase angle error Generate compensation amount; S5. During the closed-loop current control process under the dq control axis, the compensation amount is superimposed on the modulation signal output by the current controller to offset the real-time phase angle error. The disturbance term generated in the current loop; S6. Control the inverter switching action according to the superimposed modulation signal to achieve stable operation of the grid-connected inverter system.

10. The current feedforward method for improving the stability of a grid-connected inverter system according to claim 9, characterized in that, The process of generating a modulated signal includes: Get Current Command , With actual current , The deviation; the deviation is input to the current controller. The basic modulation component is obtained; the compensation amount is added to the basic modulation component to obtain the final modulation signal under the control coordinate axis. and The introduction of the compensation amount makes the small-signal model of the system composed of... The resulting disturbance terms are canceled out; The applicability assessment is performed based on the superimposed modulation signal controlling the inverter's switching action, specifically including: Monitor the grid strength SCR value and phase-locked loop bandwidth; when the grid strength SCR is detected to be lower than the preset threshold and exhibiting weak grid characteristics, or when the phase-locked loop bandwidth is higher than the preset frequency value, automatically activate the feedforward compensation process of steps S3 to S5; when the system is in a strong grid state and the phase-locked loop bandwidth is appropriate, maintain or adjust the gain of the compensation amount. Monitor the output current waveform at the grid connection point; if the system oscillation is suppressed under the condition that the grid strength decreases from strong to weak and the PLL bandwidth increases, it is confirmed that the compensation amount effectively offsets the adverse effects caused by the PLL error and its interaction with the weak grid.

Images