Photovoltaic grid-connected system harmonic suppression method and system based on MPPT variable step size control strategy

Abstract

The invention discloses a photovoltaic grid-connected system harmonic suppression method and system based on an MPPT variable step size control strategy, and the method comprises the steps: obtaining a voltage value corresponding to the maximum power point of a photovoltaic array, and a preset first disturbance step size and a preset second disturbance step size; calculating a first critical voltage threshold value and a second critical voltage threshold value based on the voltage value corresponding to the maximum power point of the photovoltaic array and the first disturbance step length; dividing a power-voltage curve corresponding to the photovoltaic array into three intervals based on the first critical voltage threshold and the second critical voltage threshold; and aiming at each interval, finding the maximum power point as a target, combining the first disturbance step length and the second disturbance step length, adopting a tracking step length strategy corresponding to each interval, adjusting the output voltage of the photovoltaic array acquired in real time, and generating a final output voltage instruction value. According to the invention, the output voltage is more stable, the total harmonic distortion of the grid-connected current is obviously reduced, and low-frequency and high-frequency harmonics can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of harmonic suppression technology, specifically relating to a harmonic suppression method and system for photovoltaic grid-connected systems based on MPPT variable step size control strategy. Background Technology

[0002] Grid-connected photovoltaic (PV) power generation systems have become a global focus and necessity due to their cleanliness, efficiency, and sustainability. However, because the output characteristics of PV cells exhibit strong nonlinearity with changes in solar radiation intensity and temperature, a unique maximum power point (MPP) exists under specific operating conditions. The application of maximum power point tracking (MPPT) technology in PV systems is crucial to ensure that the system achieves maximum power output under various operating conditions.

[0003] Traditional MPPT control methods, such as the perturbation and observation (P&O) method and the incremental conductance (INC) method, while exhibiting good tracking capabilities in practical applications, may lead to steady-state oscillations, power losses, and even the introduction of high harmonic components due to their fixed step size design, thus affecting power quality. Studies have shown that traditional fixed-step MPPT is prone to power oscillations in the steady-state region, resulting in harmonic injection and impacting the quality of grid voltage and current.

[0004] Therefore, optimizing MPPT control strategies to reduce harmonic interference and improve power quality has become a key research focus. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a harmonic suppression method and system for photovoltaic grid-connected systems based on MPPT variable step size control strategy. This method can achieve a more stable output voltage, significantly reduce the total harmonic distortion (THD) of the grid-connected current, reduce low-frequency and high-frequency harmonics, make the grid-connected current waveform closer to a sine wave, improve the operating efficiency of the grid-connected inverter, and enhance both power quality and system stability.

[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a harmonic suppression method for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, comprising:

[0008] Obtain the voltage value corresponding to the maximum power point of the photovoltaic array, as well as the preset first perturbation step size and second perturbation step size;

[0009] Based on the voltage value corresponding to the maximum power point of the photovoltaic array and the first perturbation step size, the first critical voltage threshold and the second critical voltage threshold are calculated.

[0010] Based on the first critical voltage threshold and the second critical voltage threshold, the power-voltage curve corresponding to the photovoltaic array is divided into three intervals;

[0011] For each interval, with the goal of finding the maximum power point, the tracking step size strategy corresponding to each interval is adopted by combining the first perturbation step size and the second perturbation step size to adjust the output voltage of the photovoltaic array collected in real time and generate the final output voltage command value.

[0012] In conjunction with the first aspect, optionally, the first perturbation step size is 0.02V and the second perturbation step size is 0.005V.

[0013] In conjunction with the first aspect, optionally, the method for obtaining the maximum power point of the photovoltaic array includes:

[0014] Under constant light intensity and temperature conditions, record the output voltage V and corresponding output power P of the photovoltaic array;

[0015] Plot the power-voltage curve and find the voltage value corresponding to the maximum power point of the photovoltaic array. .

[0016] In conjunction with the first aspect, optionally, the formulas for calculating the first critical voltage threshold and the second critical voltage threshold are as follows:

[0017] ,

[0018] In the formula, This is the second critical voltage threshold. This is the first critical voltage threshold. The first perturbation step size, This represents the voltage value corresponding to the maximum power point of the photovoltaic array.

[0019] In conjunction with the first aspect, optionally, the method for dividing the three intervals includes:

[0020] Using the first and second critical voltage thresholds as boundaries, the power-voltage curve is divided into three distinct intervals, labeled as Interval 1, Interval 2, and Interval 3, respectively.

[0021] The voltages corresponding to the first interval are all less than the first critical voltage threshold.

[0022] The voltage corresponding to the second interval is located between the first critical voltage threshold and the second critical voltage threshold.

[0023] The voltages corresponding to interval three are all greater than the second critical voltage threshold.

[0024] In conjunction with the first aspect, optionally, for interval one, the final output voltage command value is obtained according to the following calculation formula:

[0025] ,

[0026] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

[0027] In conjunction with the first aspect, optionally, for interval two, if the real-time acquired output voltage of the photovoltaic array is greater than the first critical voltage threshold and less than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula:

[0028] ,

[0029] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

[0030] In conjunction with the first aspect, optionally, if the output voltage of the photovoltaic array acquired in real time is greater than the first critical voltage threshold and greater than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula:

[0031] ,

[0032] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

[0033] In conjunction with the first aspect, optionally, for interval three, the final output voltage command is obtained according to the following calculation formula:

[0034] ,

[0035] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

[0036] In a second aspect, the present invention provides a harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, including a storage medium and a processor;

[0037] The storage medium is used to store instructions;

[0038] The processor is configured to operate according to the instructions to perform the method according to any one of the first aspects.

[0039] Thirdly, the present invention provides a harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, comprising a photovoltaic array, an MPPT controller, a boost converter, a filter, and a grid-connected inverter connected in sequence.

[0040] The MPPT controller is configured to perform the method described in any one of the first aspects.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] This invention proposes a harmonic suppression method and system for photovoltaic grid-connected systems based on MPPT variable step size control strategy. It can achieve more stable output voltage, significantly reduce the total harmonic distortion (THD) of grid-connected current, reduce low-frequency and high-frequency harmonics, make the grid-connected current waveform closer to a sine wave, improve the operating efficiency of grid-connected inverters, and enhance power quality and system stability.

[0043] Furthermore, this invention employs a variable-step MPPT control strategy, using large perturbation step sizes for tracking on the low-voltage and high-voltage sides, which are far from the maximum power point, while using small perturbation step sizes for tracking near the operating point. This combines the advantages of fast tracking speed with large step sizes, mitigating the disadvantage of large voltage fluctuations that can lead to increased system power oscillations and thus increased harmonic content. It also combines the advantages of reduced power oscillations with small step sizes, mitigating the disadvantage of slower tracking speed. This results in a grid-connected current waveform closer to a sine wave, improving the operating efficiency of the grid-connected inverter, and enhancing both power quality and system stability. Therefore, the photovoltaic distribution network harmonic suppression method proposed in this invention can significantly improve the accuracy and reliability of harmonic suppression. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0045] Figure 1 This is a flowchart illustrating a harmonic suppression method for a photovoltaic grid-connected system based on an MPPT variable step size control strategy according to an embodiment of the present invention.

[0046] Figure 2This is a flowchart illustrating a tracking step size strategy according to an embodiment of the present invention.

[0047] Figure 3 This is a structural block diagram of a photovoltaic grid-connected system harmonic suppression system based on MPPT variable step size control strategy, according to an embodiment of the present invention. Detailed Implementation

[0048] 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 a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0049] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0050] Example 1

[0051] This invention provides a harmonic suppression method for photovoltaic grid-connected systems based on an MPPT variable step size control strategy, such as... Figure 1 As shown, it includes the following steps:

[0052] (1) Obtain the voltage value corresponding to the maximum power point of the photovoltaic array, as well as the preset first perturbation step size and second perturbation step size; the first perturbation step size is larger than the second perturbation step size. In the specific implementation process, the first perturbation step size can be called the large perturbation step size, and the second perturbation step size can be called the small perturbation step size.

[0053] (2) Based on the voltage value corresponding to the maximum power point of the photovoltaic array and the first perturbation step size, calculate the first critical voltage threshold and the second critical voltage threshold;

[0054] (3) Based on the first critical voltage threshold and the second critical voltage threshold, the power-voltage curve corresponding to the photovoltaic array is divided into three intervals;

[0055] (4) For each interval, with the goal of finding the maximum power point, the tracking step size strategy corresponding to each interval is adopted in combination with the first perturbation step size and the second perturbation step size to adjust the output voltage of the photovoltaic array collected in real time and generate the final output voltage command value.

[0056] Based on the above scheme, a more stable output voltage can be achieved, the total harmonic distortion (THD) of the grid-connected current can be significantly reduced, low-frequency and high-frequency harmonics can be reduced, the grid-connected current waveform can be made closer to a sine wave, the operating efficiency of the grid-connected inverter can be improved, and the power quality and system stability can be enhanced.

[0057] In one specific embodiment of the present invention, the first perturbation step size is 0.02V and the second perturbation step size is 0.005V.

[0058] The above scheme specifies the first and second perturbation step sizes, which can improve the accuracy of harmonic suppression.

[0059] In one specific embodiment of the present invention, the method for obtaining the maximum power point of the photovoltaic array includes:

[0060] Under constant light intensity and temperature conditions, record the output voltage V and corresponding output power P of the photovoltaic array;

[0061] Plot the power-voltage curve (i.e., the PV curve) to find the voltage value corresponding to the maximum power point of the photovoltaic array. The PV curve visually illustrates how the output power of a photovoltaic array changes with its output voltage under specific light intensity and temperature conditions. In the initial segment of the curve, as the voltage gradually increases, the power grows approximately linearly; during this stage, the photovoltaic array operates in a low-voltage, high-current state. When the voltage continues to climb to a certain value, the power reaches its peak, which is the maximum power point. At this point, the photovoltaic array converts solar energy into electrical energy with the highest efficiency. Afterward, if the voltage continues to increase, the power exhibits a rapid downward trend until the voltage reaches the open-circuit voltage, at which point the power drops to zero. The shape of the PV curve is not static. As light intensity increases, the curve shifts upward overall, and both the power and voltage corresponding to the maximum power point increase. When the temperature rises, the curve shifts downward, the power corresponding to the maximum power point decreases, and the voltage also decreases slightly. Therefore, light intensity and temperature are two important factors affecting the PV curve.

[0062] The above scheme proposes to find the voltage value corresponding to the maximum power point of the photovoltaic array based on the power-voltage curve (the vertical axis of the curve is power and the horizontal axis is voltage), which can improve the calculation accuracy of the voltage value corresponding to the maximum power point of the photovoltaic array.

[0063] In one specific embodiment of the present invention, the calculation formulas for the first critical voltage threshold and the second critical voltage threshold are as follows:

[0064] ,

[0065] In the formula, This is the second critical voltage threshold. This is the first critical voltage threshold. The first perturbation step size, This represents the voltage value corresponding to the maximum power point of the photovoltaic array.

[0066] The above scheme provides specific calculation formulas for the first critical voltage threshold and the second critical voltage threshold. The first critical voltage threshold... Less than the second critical voltage threshold Therefore, based on these two factors, the power-voltage curve can be divided into three intervals. In a specific embodiment of the present invention, the method for dividing the three intervals includes:

[0067] Using the first and second critical voltage thresholds as boundaries, the power-voltage curve is divided into three distinct intervals, labeled as Interval 1, Interval 2, and Interval 3, respectively.

[0068] The voltages corresponding to the first interval are all less than the first critical voltage threshold.

[0069] The voltage corresponding to the second interval is located between the first critical voltage threshold and the second critical voltage threshold.

[0070] The voltages corresponding to interval three are all greater than the second critical voltage threshold.

[0071] Based on the above scheme, the partitioning is based on the following: in the low-voltage region, lower power and larger step size are used to accelerate tracking; in the high-voltage region, lower power and larger step size are used to prevent lag tracking; ±2%P max The region is in a steady state, where power oscillation amplitude is small and has little impact on the overall tracking path. Therefore, a minimum step size is used to reduce power fluctuations and harmonics. Specifically,

[0072] Derivative analysis was performed based on the IV characteristic equation and PV curve of the photovoltaic array.

[0073]

[0074] The above equation is the IV characteristic equation of the photovoltaic module, where V is the output voltage on the photovoltaic side, I is the output current on the photovoltaic side, A is the diode factor; q = 1.68 × 10¹⁹ C; K is the Boltzmann constant, with a value of 1.38 × 10¹⁹ C. -23 JK; T is the absolute temperature, since Rsh The resistance is generally large, R s The resistance is generally small, I ph with I sc They are very close, so they can be simplified to:

[0075] ,

[0076] The PV characteristic curve of a photovoltaic cell is a continuously differentiable curve with a unique extremum. On the power-voltage (PV) characteristic curve of a photovoltaic array, the maximum power point satisfies the following condition:

[0077] ,

[0078] According to the power formula P=VI, differentiating with respect to voltage V, we get:

[0079] ,

[0080] When the system is in MPP mode, the following conditions must be met:

[0081] ,

[0082] Further transformation yields:

[0083] ,

[0084] Therefore, the derivative can be calculated. To determine the position of the current operating point relative to the MPP, this is the core idea of ​​the incremental conductance method. In fact, the core idea is the same in the variable step size MPPT control strategy, which requires determining the disturbance step size by judging the position of the operating point.

[0085] When the output voltage of the photovoltaic array collected in real time is less than the first critical voltage threshold (Interval 1) is the low-voltage interval, which is far from the maximum power point. Theoretically, the step size should be larger, and the step size should move in the direction of increasing voltage. When the real-time acquired output voltage of the photovoltaic array is between and The interval between these points (interval two) is the medium voltage range. Since this is very close to the maximum power point, the theoretical step size should be small. Furthermore, it's necessary to determine the voltage at this point relative to the voltage at the maximum power point. The relationship is used to determine the direction of the step size; when the output voltage of the photovoltaic array acquired in real time is greater than... (Interval 3) is a high voltage interval. At this time, it is far from the maximum power point, so theoretically the step size should be larger, and the step size should move in the direction of decreasing voltage.

[0086] In one specific embodiment of the present invention, for interval one, based on the characteristic that the output power changes relatively quickly and fluctuates greatly in this interval, a large perturbation step size strategy is selected. The output power is tracked using a first perturbation step size to quickly search for the power change trend, such as... Figure 2 As shown, the final output voltage command value is obtained according to the following calculation formula:

[0087] ,

[0088] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

[0089] In one specific embodiment of the present invention, for interval two, considering that the output power change gradually tends to stabilize and approaches the maximum power point region, a small perturbation step size strategy is switched to more finely adjust the power to gradually approach the maximum power point. For example... Figure 2 As shown, specifically:

[0090] If the output voltage of the photovoltaic array acquired in real time is greater than the first critical voltage threshold but less than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula:

[0091] ,

[0092] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

[0093] If the output voltage of the photovoltaic array acquired in real time is greater than the first critical voltage threshold and greater than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula:

[0094] ,

[0095] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

[0096] In one specific embodiment of the present invention, for interval three, based on the characteristic that the output power changes relatively quickly and fluctuates greatly in this interval, a large perturbation step size strategy is selected. The output power is tracked using a first perturbation step size to quickly search for the power change trend and gradually approach the maximum power point. For example... Figure 2 As shown, the final output voltage command is obtained according to the following calculation formula:

[0097] ,

[0098] In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

[0099] Based on the above scheme, it can be seen that when the output voltage of the photovoltaic array is collected in real time... Within the critical voltage range , Within this timeframe, the system bases its decisions on the voltage at the current operating point relative to the maximum power point. The position is adjusted by perturbation, if Less than This indicates that the operating point is located to the left of the MPP, so a small perturbation step size is added. To gradually approach MPP; conversely, if Greater than This indicates that the operating point is located to the right of the MPP, so a small perturbation step size should be reduced. This reduces steady-state oscillations. And when When the voltage exceeds the critical voltage range, it indicates that the system deviates significantly from the MPP (Maximum Per Second) range. At this point, if... Less than This reduces the step size of a large perturbation. To speed up the tracking process; if Greater than Then, a large perturbation step size is added. To quickly pull back to the vicinity of MPP.

[0100] Based on the above analysis, it can be seen that the embodiments of the present invention employ a variable step size tracking step size strategy (MPPT control strategy). Large perturbation step sizes are used for tracking on the low-voltage and high-voltage sides, which are far from the maximum power point, while small perturbation step sizes are used for tracking at the operating point near the maximum power point. This combines the advantages of fast tracking speed with large step sizes, mitigating the disadvantage of large voltage fluctuations caused by large step sizes, which exacerbate system power oscillations and increase harmonic content. It also combines the advantages of reduced power oscillations with small step sizes, mitigating the disadvantage of slower tracking speed with small step sizes. This makes the grid-connected current waveform closer to a sine wave, improving the operating efficiency of the grid-connected inverter, and enhancing both power quality and system stability. Therefore, the photovoltaic distribution network harmonic suppression method proposed in this invention can significantly improve the accuracy and reliability of harmonic suppression.

[0101] The following describes in detail the harmonic suppression method for photovoltaic grid-connected systems based on MPPT variable step size control strategy in an embodiment of the present invention, with reference to a specific implementation method.

[0102] (1) Simulation of harmonic suppression based on fixed step size control strategy

[0103] The system operates under the preset initial illumination conditions within a 0-0.5s time period. During this process, the output voltage of the photovoltaic array and the three-phase voltage and current of the photovoltaic grid are monitored in real time and the data is stored in real time. Specifically, this step sets the initial illumination condition to 800 W / m² and performs simulation at a constant temperature.

[0104] At 0.5s, the light intensity is increased to simulate the changes in light intensity in the actual environment. The output voltage of the photovoltaic array and the three-phase voltage and current of the photovoltaic grid connection are collected in real time to ensure the continuity of data acquisition. Specifically, this step is set to increase the light intensity to 200 W / m² under the initial light conditions, that is, to simulate at a constant temperature with a light intensity of 1000 W / m².

[0105] Simulations were performed on the fixed-step MPPT control strategy under varying light intensity to obtain its output voltage V. dc-PV And the three-phase voltage V obtained after passing through the inverter and filter circuit. abc-PV The fixed step size is chosen between the large and small perturbation step sizes, and its value is 0.01V.

[0106] The collected data were comprehensively analyzed, and the total harmonic distortion (THD) of the photovoltaic grid-connected system was calculated using FFT transformation to analyze its stability. Finally, the harmonic status analysis results were obtained and presented in a combination of charts and text to obtain the evaluation results of the system's harmonic status.

[0107] The system operates under the preset initial illumination conditions within a 0-0.5s time period. During this process, it monitors the output voltage of the photovoltaic array and the three-phase voltage and current of the photovoltaic grid connection in real time and stores the data in real time.

[0108] (2) Harmonic suppression simulation based on the variable step size control strategy in the embodiments of the present invention.

[0109] During the 0-0.5s time period, the system operates under pre-set initial illumination conditions. Throughout this process, the output voltage of the photovoltaic array, as well as the three-phase voltage and current of the grid-connected photovoltaic system, are monitored in real time and the data is stored. Specifically, this step sets the initial illumination condition to 800 W / m² and simulates the process at a constant temperature.

[0110] At 0.5s, the light intensity is increased to simulate the changes in light intensity in the actual environment. The output voltage of the photovoltaic array and the three-phase voltage and current of the photovoltaic grid connection are collected in real time to ensure the continuity of data acquisition. Specifically, this step is set to increase the light intensity to 200 W / m² under the initial light conditions, that is, to simulate at a constant temperature with a light intensity of 1000 W / m².

[0111] Based on the method in this embodiment of the invention, simulations were performed under varying light intensity to obtain its output voltage V. dc-PV And the three-phase voltage V obtained after passing through the inverter and filter circuit. abc-PV ;

[0112] The collected data were comprehensively analyzed, and the total harmonic distortion (THD) of the photovoltaic grid-connected system was calculated using FFT transformation to analyze its stability. Finally, the harmonic status analysis results were obtained and presented in a combination of charts and text to obtain the evaluation results of the system's harmonic status.

[0113] By comparing the system harmonic state assessment results under the fixed step size MPPT control strategy and the system harmonic state assessment results under the variable step size MPPT control strategy, the effectiveness of the harmonic suppression strategy is demonstrated.

[0114] Example 2

[0115] Based on the same inventive concept as Embodiment 1, the present invention provides a harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, including a storage medium and a processor;

[0116] The storage medium is used to store instructions;

[0117] The processor is configured to operate according to the instructions to execute the method according to any one of Embodiment 1.

[0118] Example 3

[0119] This invention provides a harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, such as... Figure 3 As shown, it includes a photovoltaic array, an MPPT controller, a boost converter, a filter, and a grid-connected inverter connected in sequence.

[0120] The MPPT controller is configured to perform the method described in any one of Embodiment 1 to improve the conversion efficiency of solar energy and increase the power generation of the photovoltaic grid-connected system by quickly and accurately tracking the maximum power point.

[0121] In practical implementation, the core function of the photovoltaic array is to directly convert solar energy into direct current using the photovoltaic effect. It consists of multiple photovoltaic cell units connected in series and parallel to meet different voltage and current output requirements, essentially constituting the power generation end.

[0122] The boost converter can be a Boost DC / DC boost converter. It raises the relatively low DC voltage output by the photovoltaic array to a voltage level suitable for the grid-connected inverter input. Since the output voltage of the photovoltaic array varies with factors such as light intensity and temperature, and is usually low, it cannot directly meet the grid connection requirements. The boost converter achieves voltage boosting through a circuit topology composed of inductors, capacitors, and other components.

[0123] The filter module can use LCL filtering to appropriately filter the voltage and current of the input power grid.

[0124] The grid-connected inverter module converts the DC power output from the boost converter into AC power that matches the grid frequency, phase, and voltage, thereby enabling the grid connection of photovoltaic power.

[0125] The grid-connected inverter is used to connect to the distribution network, which can be an IEEE 33-node distribution network system. It is responsible for efficiently and stably transmitting the electrical energy generated by the photovoltaic array and processed by subsequent modules to various electrical devices to meet the power needs of different users.

[0126] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0127] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), 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.

[0128] 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.

[0129] 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.

[0130] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

[0131] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy, characterized in that, include: Obtain the voltage value corresponding to the maximum power point of the photovoltaic array, as well as the preset first perturbation step size and second perturbation step size; Based on the voltage value corresponding to the maximum power point of the photovoltaic array and the first perturbation step size, the first critical voltage threshold and the second critical voltage threshold are calculated. Based on the first critical voltage threshold and the second critical voltage threshold, the power-voltage curve corresponding to the photovoltaic array is divided into three intervals; For each interval, with the goal of finding the maximum power point, the tracking step size strategy corresponding to each interval is adopted by combining the first perturbation step size and the second perturbation step size to adjust the output voltage of the photovoltaic array collected in real time and generate the final output voltage command value.

2. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 1, characterized in that, The first perturbation step size is 0.02V, and the second perturbation step size is 0.005V.

3. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 1, characterized in that, The method for obtaining the maximum power point of the photovoltaic array includes: Under constant light intensity and temperature conditions, record the output voltage V and corresponding output power P of the photovoltaic array; Plot the power-voltage curve and find the voltage value corresponding to the maximum power point of the photovoltaic array. .

4. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 1, characterized in that: The formulas for calculating the first critical voltage threshold and the second critical voltage threshold are as follows: ， In the formula, This is the second critical voltage threshold. This is the first critical voltage threshold. The first perturbation step size, This represents the voltage value corresponding to the maximum power point of the photovoltaic array.

5. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 1, characterized in that: The methods for dividing the three intervals include: Using the first and second critical voltage thresholds as boundaries, the power-voltage curve is divided into three distinct intervals, labeled as Interval 1, Interval 2, and Interval 3, respectively. The voltages corresponding to the first interval are all less than the first critical voltage threshold. The voltage corresponding to the second interval is located between the first critical voltage threshold and the second critical voltage threshold. The voltages corresponding to interval three are all greater than the second critical voltage threshold.

6. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 5, characterized in that: For interval one, the final output voltage command value is obtained according to the following calculation formula: ， In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

7. A harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 5, characterized in that: For interval two, if the real-time acquired output voltage of the photovoltaic array is greater than the first critical voltage threshold but less than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula: ， In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

8. The harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 7, characterized in that, If the output voltage of the photovoltaic array acquired in real time is greater than the first critical voltage threshold and greater than the voltage value corresponding to the maximum power point of the photovoltaic array, then the final output voltage command is obtained according to the following calculation formula: ， In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the second perturbation step size.

9. A harmonic suppression method for a photovoltaic grid-connected system based on MPPT variable step size control strategy according to claim 5, characterized in that: For interval three, the final output voltage command is obtained according to the following calculation formula: ， In the formula, This is the final output voltage command value. The output voltage of the photovoltaic array is collected in real time. This is the first perturbation step size.

10. A harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, characterized in that, Including storage media and processor; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the method according to any one of claims 1-9.

11. A harmonic suppression system for a photovoltaic grid-connected system based on an MPPT variable step size control strategy, characterized in that, It includes a photovoltaic array, an MPPT controller, a boost converter, a filter, and a grid-connected inverter connected in sequence; The MPPT controller is configured to perform the method of any one of claims 1-9.

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