DC bus harmonic suppression method and system for industrial park photovoltaic grid connection

Abstract

The invention discloses a direct-current bus harmonic suppression method and system for photovoltaic grid connection in an industrial park, and relates to the technical field of harmonic suppression of a direct-current bus of a photovoltaic power supply and improvement of the power quality of a power distribution network, and the method comprises the steps: generating required direct-current output through series voltage boosting and parallel current increasing, constructing a photovoltaic power generation unit, and adding a DC-DC converter, based on MPPT, a three-layer control method is adopted to track the maximum power point and control a DC-DC converter switching device; for a DC-DC converter and a DC-AC inverter, system mathematical modeling and theoretical analysis are carried out, and a DC side current is deduced; and based on the collected DC side current, extracting a specific harmonic component and generating a reverse compensation signal, and injecting the signal into a corresponding DC bus control link for harmonic suppression. According to the method, the DC bus voltage ripple coefficient is reduced, harmonic waves generated by MPPT, phase-locked loop disturbance and switch modulation are suppressed, the total harmonic distortion rate of the output current of the inverter can be reduced, and the stability margin of the system under the weak power grid condition is improved.

Description

Technical Field

[0001] This invention relates to the field of harmonic suppression of DC buses in photovoltaic power sources and improvement of power quality in distribution networks, specifically a method and system for harmonic suppression of DC buses for photovoltaic grid connection in industrial parks. Background Technology

[0002] With the gradual advancement of global dual-carbon goals and the increasing installed capacity of new energy sources, wind and solar power installations have achieved a historic breakthrough and, based on current trends, are expected to surpass traditional generator installations in the future. Solar energy, as a core representative of green and low-carbon energy, saw an additional 59.71 million kilowatts of solar power generation added in the first quarter of 2025 alone, with a photovoltaic power generation utilization rate as high as 93.6%. Driven by the continuous market-oriented reforms of industrial and commercial electricity prices, the economic viability of industrial and commercial photovoltaic power has been significantly improved.

[0003] Unlike residential solar PV, industrial and commercial solar PV is typically deployed on factory rooftops, with relatively large-scale arrays and a wider usable area. Furthermore, industrial and commercial businesses generally consume more electricity during the day, enabling them to better achieve "self-consumption," with surplus power sold to the grid. Against this backdrop, supported by favorable policies and superior economics, industrial parks and some factory areas have gradually become key areas for industrial solar PV development. Many parks and enterprises are making full use of idle rooftops or factory roofs to install solar power systems, achieving both "self-consumption" and "surplus power sold to the grid." This not only fully utilizes idle resources within the parks but also effectively reduces energy costs for businesses and the parks themselves. Simultaneously, combining energy storage and demand response management can enhance the parks' ability to support regional load regulation and expand their adjustable capacity.

[0004] Distributed photovoltaic (PV) systems in industrial parks are connected to the power grid, prioritizing power supply for industries within the park. This allows them to meet their own load demands locally and participate in regional supply-demand balance by feeding surplus power into the grid, improving energy utilization efficiency and enhancing the stability of the power distribution network. However, some advanced manufacturing industries have high requirements for power quality. Due to the volatility and randomness of PV power generation, large-scale distributed PV systems can also lead to voltage fluctuations and harmonic pollution, making it difficult to meet industrial power demands, reducing product qualification rates, and seriously impacting the economic benefits of the industry.

[0005] Therefore, current harmonic suppression is necessary in the photovoltaic grid connection process to improve grid-connected power quality. For photovoltaic grid connection, common harmonic components mainly include high-frequency harmonics and low-frequency harmonics. High-frequency harmonics primarily originate from factors such as switching frequency sidebands generated during the modulation of high-frequency carrier waves by low-frequency signals and non-ideal switching conduction. Low-frequency harmonics are mainly caused by non-ideal grid conditions, power fluctuations due to MPPT control, and phase-locked loop (PLL) jitter. Without effective harmonic suppression and filtering measures, not only will current distortion increase and grid connection power quality deteriorate, but it may also adversely affect surrounding sensitive loads, power electronic equipment, and even the stable operation of the system.

[0006] The grid-connected inverter unit, as the core coupling environment between the photovoltaic power generation system and the distribution network, is closely related to the generation of harmonic components. Based on this analysis, the photovoltaic grid-connected topology and its supporting control components not only undertake energy conversion functions but also play a crucial role in the generation and suppression of harmonics. Traditional LCL-type grid-connected filters, as the core component for eliminating high-frequency harmonics, are an indispensable part of most photovoltaic grid-connected systems, and many studies have optimized the design of traditional LCL filters based on this. However, LCL filters mainly focus on filtering mid-to-high frequency harmonics, and their ability to suppress the coupling problem between low-frequency harmonics and background harmonics caused by factors such as inverter control strategies, modulation methods, and grid connection point voltage distortion is limited, especially under weak grid conditions.

[0007] Therefore, relying solely on passive filters is insufficient to meet the power quality requirements under high-proportion photovoltaic (PV) grid connection conditions. There is an urgent need to introduce active harmonic suppression mechanisms at the grid-connected inverter topology and its control level to achieve targeted compensation and suppression of key harmonic components. This paper, based on a typical PV grid-connected topology, introduces a harmonic suppression strategy into its control framework to actively manage grid-connected current harmonics at the control level, thereby improving the power quality, grid stability, and sustainable operation capability of the PV grid-connected system. Summary of the Invention

[0008] In view of the above-mentioned problems, the present invention is proposed.

[0009] Therefore, the technical problem solved by this invention is that existing methods for connecting distributed photovoltaic power to the distribution network have limited harmonic suppression capabilities, poor system stability, and weak power quality control capabilities, as well as the problem of how to achieve active harmonic suppression from the DC side source.

[0010] To address the aforementioned technical problems, this invention provides the following technical solution: a DC bus harmonic suppression method for grid-connected photovoltaic systems in industrial parks, comprising constructing a photovoltaic power generation unit by generating the required DC output through series boosting and parallel current boosting, adding a DC-DC converter, and using a three-layer control method based on MPPT to track the maximum power point and control the switching devices of the DC-DC converter; performing system mathematical modeling and theoretical analysis for the DC-DC converter and DC-AC inverter, and deriving the DC-side current; based on the collected DC-side current, extracting specific harmonic components and generating a reverse compensation signal, and injecting the signal into the corresponding DC bus control loop for harmonic suppression.

[0011] As a preferred embodiment of the DC bus harmonic suppression method for grid-connected photovoltaic systems in industrial parks as described in this invention, the method of constructing a photovoltaic power generation unit by generating the required DC output through series voltage boosting and parallel current boosting includes generating a DC output with the required voltage and power level by connecting multiple photovoltaic units in series voltage boosting and parallel current boosting according to actual application needs. The IV nonlinear characteristic of the photovoltaic cell can be expressed as: ; in, The output current of the photovoltaic module. The current generated by light, This is the reverse saturation current of the diode. The amount of electron charge. For diode ideality factor, This refers to the terminal voltage of the photovoltaic module. This refers to the series resistance of a photovoltaic cell or module. This represents the number of battery cells connected in series / the number of battery nodes connected in series. Boltzmann's constant, Absolute temperature It is the parallel resistance of a photovoltaic cell or module.

[0012] As a preferred embodiment of the DC bus harmonic suppression method for grid-connected photovoltaic systems in industrial parks as described in this invention, the maximum power point tracking (MPPT) based three-layer control method includes: the upper layer uses MPPT to track the maximum power point and outputs a corresponding middle-layer voltage reference signal based on the real-time voltage and current characteristics of the photovoltaic sequence; the middle layer uses voltage PI regulation to output a reference current signal to the lower layer; the lower-layer control loop performs inner-loop regulation of the inductor current and generates a corresponding duty cycle modulation signal through a current PI controller to drive the switching devices of the DC-DC converter, thereby achieving high dynamic response and stable control of the boost-buck process.

[0013] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the method of using MPPT to track the maximum power point includes: adaptively adjusting the operating point using the incremental conductance method; utilizing the characteristic that the first derivative of the output power with respect to the terminal voltage is zero at the maximum power point; comparing the ratio of the current increment to the voltage increment, i.e., the incremental conductance, with the ratio of the current to the voltage, i.e., the instantaneous conductance; at the maximum power point, the two are equal in magnitude and opposite in sign; and adjusting the operating point accordingly to converge to the maximum power point.

[0014] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the system mathematical modeling and theoretical analysis includes, based on Fourier analysis, the DC-side current of the DC-DC converter is expressed as: ; in, This refers to the DC-side output current of the DC-to-buck converter module. for Phase / unit parallel connection, here , Let be the independent variable, representing the change of current or voltage over time. For the first The current of the phase converter, For the first The DC component of the phase current For the first The first phase current DC component of second harmonic amplitude The base frequency (carrier) angular frequency of the DC-DC switch. For the first Xiangdi Second harmonic phase angle.

[0015] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the system mathematical modeling and theoretical analysis includes, through Fourier analysis, the AC side current of the DC-AC inverter is expressed as: ; Therefore, the DC-side current of a DC-AC inverter is expressed as: ; Therefore, the DC side can be represented as: ; in, This refers to the AC side current of a two-level voltage source inverter. For the AC side current, the first Second harmonic amplitude ( (fundamental amplitude) For measuring AC current, the first First harmonic phase angle, This refers to the DC-side current of a two-level voltage source inverter. This represents the fundamental amplitude of the AC output current of the inverter. This is the phase difference (power factor angle) between the AC side voltage and current. The inverter carrier angular frequency, The fundamental angular frequency of the grid connection. For carrier harmonic group index, take a positive integer. , This is the fundamental band index, rounded to the nearest integer. , This represents the average component of the DC-side current (corresponding to the DC current component required for active power transmission), and the subsequent double summation term represents the carrier and sideband harmonic components. These are the coefficients of the corresponding frequency components in the Fourier expansion. This refers to the DC-side output current of the DC boost-buck module.

[0016] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the extraction of specific harmonic components includes: firstly, converting the acquired time-domain current signal into a frequency-domain signal using a Fourier transform method to analyze the harmonic components and amplitude characteristics in the current; and after obtaining the spectrum information, extracting the specific harmonic components that need to be compensated according to the preset harmonic frequency range.

[0017] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the reverse compensation signal includes, for the selected harmonic component, the system further generates a corresponding reverse current signal, and injects it into the DC side through a controller to generate a compensation current, expressed as: ; in, This is the active harmonic suppression current between the two parallel capacitors. For the set of harmonics that need to be compensated, For the first The angular frequency of each target frequency point for At amplitude, for In phase, It is an inverting phase, used to cancel out harmonic components at a specific frequency.

[0018] The compensation current is injected into the DC side using a current reference superposition method, so that the compensated bus capacitor current satisfies: ; For any target point Pick At that time, the frequency harmonic components are canceled out by equal amplitude and opposite phase, therefore In all The harmonic components are zero. DC-side harmonic suppression.

[0019] As a preferred embodiment of the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks described in this invention, the step of injecting a signal into the corresponding DC bus control loop for harmonic suppression includes converting the generated compensation current into a corresponding reference signal, injecting it into the boost / buck converter or inverter controller through a controller, so that the actual injected current is approximately the active harmonic suppression current between two parallel capacitors, and the compensated current signal is fed back to the corresponding control unit in real time for online monitoring and dynamic adjustment.

[0020] Another objective of this invention is to provide a DC bus harmonic suppression system for grid-connected photovoltaic systems in industrial parks. This system can extract specific harmonic components based on the collected DC side current and generate a reverse compensation signal, which is then injected into the corresponding control circuit for harmonic suppression. This solves the problem of limited harmonic suppression capability in current distributed photovoltaic grids.

[0021] As a preferred embodiment of the DC bus harmonic suppression system for grid-connected photovoltaic systems in industrial parks as described in this invention, the system includes: a photovoltaic power generation unit construction module, a three-layer control module based on MPPT, a mathematical modeling and theoretical analysis module, and an active harmonic suppression implementation module. The photovoltaic power generation unit construction module is used to construct photovoltaic power generation units by connecting multiple photovoltaic units in series to increase voltage and in parallel to increase current, thereby generating DC outputs of the required voltage and power levels. The three-layer control module based on MPPT incorporates a DC-DC converter into the photovoltaic unit and inverter structure, employing a three-level control method. The upper layer uses MPPT to track the maximum power point, the middle layer uses voltage PI control to output a reference current signal, and the lower layer control loop performs rapid inner-loop adjustment of the inductor current, generating a corresponding duty cycle through a current PI controller. The control signal drives the switching devices of the DC-DC converter; the mathematical modeling and theoretical analysis module is used to derive the DC-DC current of the DC-DC converter and the AC current of the DC-AC inverter based on Fourier transform for the DC-DC converter section and the DC-AC inverter section, and derive the DC-side current of the two-level inverter, and establish the DC-side current model of the entire topology system; the active harmonic suppression implementation module is used to convert the acquired time-domain current signal into a frequency-domain signal through Fourier transform, analyze the harmonic components and amplitude characteristics of the current, extract the specific harmonic components that need to be compensated according to the preset harmonic frequency range, further generate the corresponding reverse current signal for the selected harmonic components, and inject it into the DC side through the controller to generate a compensation current and convert it into a corresponding reference signal and inject it into the DC side.

[0022] The beneficial effects of this invention are: The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks provided by this invention performs Fourier analysis on the harmonic components of the DC current and generates a reverse compensation signal in real time based on the control program. This signal is superimposed on the DC current reference value to actively cancel the DC harmonics, thereby significantly reducing the DC bus voltage ripple, improving the dynamic stability of the inverter input and the power quality of the grid-connected output. By suppressing harmonics at the DC source, this method not only significantly reduces the DC bus voltage ripple coefficient and suppresses harmonics generated by MPPT, phase-locked loop disturbances, and switching modulation, but also reduces the total harmonic distortion (THD) of the inverter output current and improves the stability margin of the system under weak grid conditions. It can effectively reduce the grid-connected current THD and improve the grid power quality. At the same time, it does not require the addition of additional power devices and has the advantages of simple structure, low implementation cost, and strong engineering applicability. This invention achieves better results in DC side harmonic suppression, system stability under weak grid conditions, and control of the total harmonic distortion of the grid-connected current. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0024] Figure 1 This is an overall flowchart of a DC bus harmonic suppression method for photovoltaic grid connection in industrial parks, provided in Embodiment 1 of the present invention.

[0025] Figure 2 The photovoltaic grid-connected topology diagram is provided for a DC bus harmonic suppression method for photovoltaic grid connection in industrial parks, as shown in Embodiment 2 of the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail 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 skilled in the art without creative effort should fall within the protection scope of the present invention.

[0027] Example 1, referring to Figures 1-2 As an embodiment of the present invention, a method for suppressing harmonics on the DC bus for photovoltaic grid connection in industrial parks is provided, comprising: S1: A photovoltaic power generation unit is constructed by generating the required DC output through series boosting and parallel current boosting, and a DC-DC converter is added. A three-layer control method is used for MPPT tracking.

[0028] Specifically, based on the principles of photovoltaic power generation systems, multiple photovoltaic units 100 are connected in series to increase voltage and in parallel to increase current, according to actual application requirements, to generate DC output with the required voltage and power levels, thus constructing a photovoltaic power generation unit. The photovoltaic cell module, as the smallest power generation unit, is typically made of monocrystalline or polycrystalline silicon, and after encapsulation with materials such as EVA film and processes such as anti-oxidation and moisture-proofing, it forms the photovoltaic unit 100. Multiple photovoltaic units 100 are then connected in series to increase voltage and in parallel to increase current, according to actual application requirements, to generate DC output with the required voltage and power levels.

[0029] Constructing a photovoltaic power generation unit by series boosting and parallel current boosting to generate the required DC output includes, according to actual application requirements, generating a DC output with the required voltage and power level by series boosting and parallel current boosting of multiple photovoltaic units 100. The IV nonlinear characteristic of the photovoltaic cell can be expressed as: ; in, The output current of the photovoltaic module. The current generated by light, This is the reverse saturation current of the diode. The amount of electron charge. For diode ideality factor, This refers to the terminal voltage of the photovoltaic module. This refers to the series resistance of a photovoltaic cell or module. This represents the number of battery cells connected in series / the number of battery nodes connected in series. Boltzmann's constant, Absolute temperature The parallel resistance of a photovoltaic cell or module, and the constant of electron charge. Boltzmann constant .

[0030] It should be noted that, considering the intermittency and volatility of photovoltaic grid-connected systems under different environments, and in response to different needs and the strong demand for stable DC-side input of the inverter, a DC-DC converter 200 is added to the photovoltaic unit 100 and the inverter structure. It mainly includes a boost-buck conversion structure of two units and mainly adopts a three-level control method.

[0031] The MPPT600 tracking method using a three-layer control approach includes: the upper layer uses MPPT600 to track the maximum power point; the middle layer outputs a corresponding voltage reference signal based on the real-time voltage and current characteristics of the photovoltaic sequence; the output power of the photovoltaic module is expressed as: ; in, For the output power of photovoltaic modules, The voltage of the photovoltaic module. The current generated by light.

[0032] During the tracking of the maximum power point, the MPPT600 uses the incremental conductance method to achieve adaptive adjustment of the operating point. This method is based on the derivative characteristics of the output power of the photovoltaic array. C99 code is written based on the incremental conductance method, and the power change trend is indirectly inferred by implementing sampled values.

[0033] Voltage increment: ; Current increment: ; Power increment: ; in, For voltage increment, For the first The instantaneous value of the photovoltaic module terminal voltage collected in each sampling period. For the first The instantaneous value of the photovoltaic module terminal voltage collected in each sampling period. For current increment, For the first The instantaneous value of the output current of the photovoltaic module collected in each sampling period. For the first The instantaneous value of the output current of the photovoltaic module collected in each sampling period. For power increment, For the first The instantaneous output power of the photovoltaic module obtained from each sampling period. For the first The instantaneous output power of the photovoltaic module is obtained from each sampling period.

[0034] when The operating point is on the left side of the MPP, requiring a voltage boost; when The operating point is to the right of the MPP, requiring a voltage reduction; when the two are equal, the maximum power point is reached. Based on this, the output voltage signal is integrated and then a constant parameter is applied to the subsequent voltage control loop, expressed as: ; in, For voltage reference signal, In order to be in Voltage reference signal for each control cycle This is the integral gain coefficient. This is the system sampling period.

[0035] The middle layer uses voltage PI control to output a reference current signal to the lower layer; the lower layer control loop performs inner-loop regulation of the inductor current, and generates a corresponding duty cycle modulation signal through the current PI controller to drive the switching devices of the DC-DC converter 200, thereby achieving high dynamic response and stable control of the boost-buck process.

[0036] It should also be noted that a photovoltaic power generation system mainly consists of photovoltaic DC modules and a DC-AC inverter topology. The photovoltaic array converts light signals into electrical signals to output DC power, which cannot be directly connected to the power grid. Therefore, it needs to complete the inverter process through a DC-AC conversion topology, and then be connected to the power grid after high-frequency harmonics are filtered out by an LCL 400 filter. For example... Figure 2 The DC-AC inverter 300 refers to the six switching transistors of the bridge inverter. Through control methods such as maximum power point tracking, the photovoltaic panels are adjusted to their optimal operating state according to the continuous changes in solar intensity and temperature, thereby achieving more efficient photovoltaic power generation.

[0037] The MPPT600 method for tracking the maximum power point includes using the incremental conductance method to adaptively adjust the operating point. It utilizes the characteristic that the first derivative of the output power with respect to the terminal voltage is zero at the maximum power point to establish a corresponding criterion: at the maximum power point, the incremental conductance and the instantaneous conductance are equal in magnitude and opposite in sign, and the operating point is adjusted accordingly to converge to the maximum power point.

[0038] Satisfies at the point of maximum power Therefore, the criterion can be derived. Incremental conductance It equals the negative of the instantaneous conductance ( The algorithm collects the voltage and current changes in real time between two adjacent sampling periods. Calculate incremental conductance and Comparison: When When the operating point is to the left of the maximum power point, the operating voltage should be increased; when When the operating point is to the right of the maximum power point, the operating voltage should be reduced; when the two are equal, it indicates that the maximum power point has been reached, and the control quantity remains unchanged. Through the above judgment and iterative adjustment, the duty cycle is gradually corrected, so that the operating point of the photovoltaic module quickly approaches and stabilizes near the maximum power point, achieving efficient energy tracking.

[0039] The operating state of a photovoltaic (PV) panel is primarily determined by its terminal voltage, output current, and corresponding power output. Its position on the I-V and P-V curves indicates whether it is currently operating at its maximum power point (MPP). The optimal operating state of a PV panel, i.e., its MPP, dynamically changes with external conditions: Light intensity primarily affects the output current and is approximately proportional to it; increased light intensity significantly increases both the short-circuit current and maximum output power. Temperature primarily affects the terminal voltage; rising temperatures lead to a significant decrease in open-circuit voltage and reduced efficiency, causing the MPP to shift towards lower voltage and lower power output. In engineering applications, the MPPT600 adjusts the equivalent input impedance seen on the PV side by controlling the duty cycle of the DC-DC converter 200. This actively changes the PV panel's terminal voltage and current operating point, allowing it to continuously track and stably operate near its MPP despite changes in light intensity and temperature, thus automatically maintaining maximum power output.

[0040] It should also be noted that the photovoltaic power generation unit increases the output voltage through series connection and increases the output current through parallel connection to obtain the required DC output. A DC-DC converter 200 is introduced on the photovoltaic side, and a three-layer control structure is adopted to achieve maximum power point tracking. Specifically, the outer loop of the MPPT600 generates voltage / current reference quantities based on the incremental conductance method; the middle loop of the DC bus voltage completes energy balance and bus stability regulation; and the inner loop of the inductor current achieves fast current tracking and outputs duty cycle / modulation commands. This method can enable the photovoltaic array's operating point to quickly converge and stabilize near the maximum power point under varying illumination and temperature conditions, reducing power fluctuations and efficiency degradation caused by deviations from the maximum power point. Furthermore, in grid-connected scenarios, it provides more stable DC-side conditions for downstream inverters, thereby improving power generation efficiency, system adaptability, and grid-connected operation stability.

[0041] S2: For DC-DC converters and DC-AC inverters, perform system mathematical modeling and theoretical analysis, and derive the DC side current.

[0042] Specifically, based on topology modeling and control architecture, systematic mathematical modeling and theoretical analysis are carried out for the two main topology components, namely the DC-DC converter 200 and the DC-AC inverter 300.

[0043] The system mathematical modeling and theoretical analysis include, based on Fourier analysis, expressing the DC-side current of the DC-DC converter 200 as: ; in, This refers to the DC-side output current of the DC-to-buck converter module. for Phase / unit parallel connection, here , Let be the independent variable, representing the change of current or voltage over time. For the first The current of the phase converter, For the first The DC component of the phase current For the first The first phase current DC component of second harmonic amplitude The base frequency (carrier) angular frequency of the DC-DC switch. For the first Xiangdi Second harmonic phase angle.

[0044] The system mathematical modeling and theoretical analysis include, through Fourier analysis, expressing the AC side current of the DC-AC inverter 300 as: ; Therefore, the DC-AC inverter 300's DC-side current is expressed as: ; Therefore, DC side 500 can be expressed as: ; in, This refers to the AC side current of a two-level voltage source inverter. For the AC side current, the first Second harmonic amplitude ( (fundamental amplitude) For measuring AC current, the first First harmonic phase angle, This refers to the DC-side current of a two-level voltage source inverter. This represents the fundamental amplitude of the AC output current of the inverter. This is the phase difference (power factor angle) between the AC side voltage and current. The inverter carrier angular frequency, The fundamental angular frequency of the grid connection. For carrier harmonic group index, take a positive integer. , This is the fundamental band index, rounded to the nearest integer. , This represents the average component of the DC-side current (corresponding to the DC current component required for active power transmission), and the subsequent double summation term represents the carrier and sideband harmonic components. These are the coefficients of the corresponding frequency components in the Fourier expansion. This refers to the DC-side output current of the DC boost-buck module.

[0045] It should be noted that the reverse compensation signal includes, for the selected harmonic component, the system further generates a corresponding reverse current signal, which is injected into the DC side through the controller to generate a compensation current, expressed as: ; in, This is the active harmonic suppression current between the two parallel capacitors. For the set of harmonics that need to be compensated, For the first The angular frequency of each target frequency point for At amplitude, for In phase, It is an inverting phase, used to cancel out harmonic components at a specific frequency.

[0046] The compensation current is injected into the DC side using a current reference superposition method, so that the compensated bus capacitor current satisfies: ; For any target point Pick At that time, the frequency harmonic components are canceled out by equal amplitude and opposite phase, therefore In all The harmonic components are zero, thus achieving DC-side harmonic suppression.

[0047] in, The overall topology system has a DC side current of 500. The DC-side current of the overall topology system after active harmonic suppression is 500. The DC-side output current of the DC-to-buck converter is 500 Ω. The DC side current is 500 for a two-level voltage source inverter.

[0048] It should also be noted that by performing mathematical modeling and theoretical analysis on the DC-DC converter 200 and the DC-AC inverter 300, the precise expression of the DC-side current 500 is derived, solving the problem of complex system-level current components and difficulty in precise analysis and control. This provides a key theoretical basis for the design of advanced control algorithms and improves the power quality and grid connection reliability of the entire photovoltaic power generation system.

[0049] S3: Based on the acquired DC-side current, extract specific harmonic components and generate a reverse compensation signal, then inject the signal into the corresponding control loop for harmonic suppression.

[0050] Specifically, based on theoretical analysis, we assume... Figure 2 The active harmonic cancellation angles of the two core topologies are respectively and The equation for the current between the two parallel capacitors is then expressed as: ; ; ; ; in, The overall topology system has a DC side current of 500. The DC-side current of the overall topology system after active harmonic suppression is 500. To suppress harmonic current between the two parallel capacitors, 700 AHM current is required. and For active harmonic cancellation angle, The DC-side current of the two-level voltage source inverter 300 has harmonic suppression. This refers to the DC-side output current of the DC-DC boost-buck module with harmonic suppression. N represents the N phases / units connected in parallel, where N=2. Let be the independent variable, representing the change of current or voltage over time. For the first The current of the phase converter, For the first The DC component of the phase current For the first The first phase current Second harmonic amplitude The base frequency (carrier) angular frequency of the DC-DC switch. For the first Xiangdi Second harmonic phase angle and This represents the equivalent amplitude and phase of the parallel current at that frequency.

[0051] ; Among them, let Therefore, it can be represented as: ; Therefore, we can conclude that: ; ; in, This represents the fundamental amplitude of the AC output current of the inverter 300. This is the phase difference (power factor angle) between the AC side voltage and current. The inverter carrier angular frequency, The fundamental angular frequency of the grid connection. For carrier harmonic group index, take a positive integer. , This is the fundamental band index, rounded to the nearest integer. , This represents the average component of the DC-side current (corresponding to the DC current component required for active power transmission), and the subsequent double summation term represents the carrier wave and its sideband harmonic components. , These are the coefficients of the corresponding frequency components in the Fourier expansion. This is expressed as the DC-AC inverter's 300 DC-side current. The middle belongs to the double Fourier expansion Each frequency component introduces a phase shift. The subsequent time-domain representation, and This represents the equivalent amplitude and phase angle at that frequency.

[0052] when At that frequency point: ; in, To add separately and This is the DC-side current for the active harmonic cancellation angle.

[0053] Based on Fourier analysis, most signals can be expressed as such an expression; therefore, we assume: ; in, The DC-side current of the overall topology system after active harmonic suppression, 500 Ω, can also be represented by a time-domain expression of the constructed (or observed) current signal. For the first The amplitude of the subharmonic. For the first Phase angle of the subharmonic.

[0054] Based on this, it can be deduced that when the reverse harmonic suppression 700 signal generated by the analysis is infinitely close to satisfying the following three formulas, it can effectively cancel the DC side 500 harmonic component: ; ; ; in, for No. Second harmonic components For the parallel DC-DC converter, the current of each phase is in the first... The equivalent amplitude and phase obtained by superposition at the second harmonic. For this frequency point phase, The base frequency (carrier) angular frequency of the DC-DC switch. It is a type of division operation.

[0055] It should be noted that, based on the above theoretical analysis, the present invention uses the C-script module in the PLECS simulation environment to collect and process the DC side 500 current in real time in the system design.

[0056] Extracting specific harmonic components involves first converting the acquired time-domain current signal into a frequency-domain signal using a Fourier transform method to analyze the harmonic components and amplitude characteristics in the current. After obtaining the spectral information, specific harmonic components that need to be compensated are extracted according to a pre-set harmonic frequency range.

[0057] The Frequency-Frequency Transform (FFT) performs a Discrete Fourier Transform on the acquired discrete-time signals, mapping the originally time-sequential signal samples to a set of complex spectral coefficients arranged by frequency, thus achieving a conversion from the time domain to the frequency domain. Specifically, the algorithm treats the time-domain sampling sequence as a superposition of sine waves of different frequencies, separating the amplitude and phase of each frequency component through correlation operations. The horizontal axis of the transformation result corresponds to frequency, and the vertical axis corresponds to amplitude or power, with the peak value representing the main frequency components contained in the signal. In this way, features such as periodicity, harmonics, or noise, which are difficult to perceive intuitively in the time domain, can be clearly presented and quantitatively analyzed in the frequency domain.

[0058] Frequency domain analysis can clarify the contribution of each order of harmonics in the system, providing a precise basis for subsequent harmonic compensation. After obtaining the spectrum information, this invention selectively extracts the specific harmonic components that need to be compensated according to the pre-set harmonic frequency range, while ignoring non-target frequency components, that is, temporarily ignoring those outside this range, thereby avoiding interference from irrelevant signals and improving the accuracy of compensation control.

[0059] It should also be noted that the reverse compensation signal includes, for the selected harmonic component, the system further generates a corresponding reverse current signal, which is injected into the DC side through the controller to generate a compensation current, expressed as: ; in, This is the active harmonic suppression current between the two parallel capacitors. For the set of harmonics that need to be compensated, For the first The angular frequency of each target frequency point for At amplitude, for In phase, It is an inverting phase, used to cancel out harmonic components at a specific frequency.

[0060] Injecting a signal into the corresponding control loop for harmonic suppression 700 includes converting the generated compensation current into a corresponding reference signal, which is then injected into the DC side through the controller, so that the actual injected current is approximately the active harmonic suppression current between two parallel capacitors 700. At the same time, the compensated current signal is fed back to the corresponding control unit in real time for online monitoring and dynamic adjustment.

[0061] During the compensation process, the compensated current signal is fed back to the corresponding control unit in real time for online monitoring and dynamic adjustment, ensuring stable compensation results and preventing system oscillations or other instabilities. This method not only provides high-precision suppression of harmonics at specific frequencies but also guarantees stable system operation under different load conditions, fully demonstrating the practicality and innovation of this invention in active harmonic compensation and power system stability maintenance.

[0062] It should also be noted that by acquiring the DC-side 500V current in real time and using FFT to estimate the amplitude and phase of the target harmonic component, a compensation signal with the same amplitude and opposite phase as the harmonic component is generated and injected into the DC-side control loop to implement active current ripple compensation. This suppresses the specific frequency band ripple / harmonic components introduced by the converter switching action and its modulation effect within the control bandwidth, reduces the ripple current (RMS) of the DC-side 500V capacitor and its ESR loss and temperature rise, thereby reducing capacitor current stress and related device losses, and improving the power quality and operational stability of the photovoltaic grid-connected system.

[0063] Example 2, an embodiment of the present invention, provides a DC bus harmonic suppression system for photovoltaic grid connection in industrial parks, including a photovoltaic power generation unit construction module, a three-layer control module based on MPPT, a mathematical modeling and theoretical analysis module, and an active harmonic suppression implementation module.

[0064] The photovoltaic power generation unit building module is used to construct a photovoltaic power generation unit by connecting multiple photovoltaic units in series to increase voltage and in parallel to increase current, thereby generating DC output with the required voltage and power level according to actual application needs.

[0065] The MPPT-based three-layer control module is used to add a DC-DC converter to the photovoltaic unit and inverter structure. It adopts a three-level control method: the upper layer uses MPPT to track the maximum power point, the middle layer uses voltage PI to control the output reference current signal, and the lower layer control loop performs fast inner loop adjustment of the inductor current. The corresponding duty cycle modulation signal is generated by the current PI controller to drive the switching devices of the DC-DC converter.

[0066] The mathematical modeling and theoretical analysis module is used to derive the DC-DC current of the DC-DC converter and the AC current of the DC-AC inverter based on Fourier transform for the DC-DC converter and DC-AC inverter sections, and to derive the DC-DC current of the two-level inverter, and to establish the DC-DC current model of the entire topology system.

[0067] The active harmonic suppression implementation module is used to convert the acquired time-domain current signal into a frequency-domain signal using the Fourier transform method, analyze the harmonic components and amplitude characteristics in the current, extract the specific harmonic components that need to be compensated according to the preset harmonic frequency range, further generate the corresponding reverse current signal for the selected harmonic components, and inject it into the DC side through the controller to generate a compensation current and convert it into a corresponding reference signal to be injected into the DC side.

[0068] This embodiment also provides a computer device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as proposed in the above embodiment.

[0069] This embodiment also provides a computer-readable storage medium storing a computer program thereon. When the computer program is executed by a processor, it implements the DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as proposed in the above embodiment.

[0070] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0071] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-including system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0072] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0073] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0074] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for suppressing harmonics on the DC bus of a photovoltaic grid-connected industrial park, characterized in that, include: A photovoltaic power generation unit is constructed by generating the required DC output through series boosting and parallel current boosting, and a DC-DC converter is added. Based on MPPT, a three-layer control method is adopted to track the maximum power point and control the switching devices of the DC-DC converter. For DC-DC converters and DC-AC inverters, system mathematical modeling and theoretical analysis are performed, and the DC side current is derived. Based on the collected DC-side current, specific harmonic components are extracted and a reverse compensation signal is generated. The signal is then injected into the corresponding DC bus control circuit for harmonic suppression.

2. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 1, characterized in that: The method of constructing a photovoltaic power generation unit by generating the required DC output through series boosting and parallel current boosting includes... Based on practical application requirements, multiple photovoltaic units are connected in series to boost voltage and in parallel to increase current to generate DC output with the required voltage and power levels. The IV nonlinear characteristic of the photovoltaic cell can be expressed as: ； in, The output current of the photovoltaic module. The current generated by light, This is the reverse saturation current of the diode. The amount of electron charge. For diode ideality factor, This refers to the terminal voltage of the photovoltaic module. This refers to the series resistance of a photovoltaic cell or module. This represents the number of battery cells connected in series / the number of battery nodes connected in series. Boltzmann's constant, Absolute temperature It is the parallel resistance of a photovoltaic cell or module.

3. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 1 or 2, characterized in that: The maximum power point tracking based on MPPT using a three-layer control method includes... The upper layer uses MPPT to track the maximum power point and outputs the corresponding middle layer voltage reference signal based on the real-time voltage and current characteristics of the photovoltaic sequence. The middle layer uses voltage PI control to output a reference current signal to the lower layer; The lower-level control loop performs inner-loop regulation of the inductor current and generates a corresponding duty cycle modulation signal through the current PI controller to drive the switching devices of the DC-DC converter, thereby achieving high dynamic response and stable control of the boost-buck process.

4. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 3, characterized in that: The method of using MPPT to track the maximum power point includes, The incremental conductance method is used to adaptively adjust the operating point. Taking advantage of the fact that the first derivative of the output power with respect to the terminal voltage is zero at the maximum power point, the ratio of the current increment to the voltage increment, i.e., the incremental conductance, is compared with the ratio of the current to the voltage, i.e., the instantaneous conductance. At the maximum power point, the two are equal in magnitude and opposite in sign. Based on this, the operating point is adjusted to converge to the maximum power point.

5. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 1, 2, or 4, characterized in that: The aforementioned system mathematical modeling and theoretical analysis includes, Based on Fourier analysis, the DC-side current of a DC-DC converter is expressed as: ； in, This refers to the DC-side output current of the DC-to-buck converter module. for Phase / unit parallel connection, here , Let be the independent variable, representing the change of current or voltage over time. For the first The current of the phase converter, For the first The DC component of the phase current For the first The first phase current DC component of second harmonic amplitude The base frequency (carrier) angular frequency of the DC-DC switch. For the first Xiangdi Second harmonic phase angle.

6. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 5, characterized in that: The aforementioned system mathematical modeling and theoretical analysis includes, Based on Fourier analysis, the AC side current of the DC-AC inverter can be expressed as: ； Therefore, the DC-side current of a DC-AC inverter is expressed as: ； Therefore, the DC side can be represented as: ； in, This refers to the AC side current of a two-level voltage source inverter. For the AC side current, the first Second harmonic amplitude ( (fundamental amplitude) For measuring AC current, the first First harmonic phase angle, This refers to the DC-side current of a two-level voltage source inverter. This represents the fundamental amplitude of the AC output current of the inverter. This is the phase difference (power factor angle) between the AC side voltage and current. The inverter carrier angular frequency, The fundamental angular frequency of the grid connection. For carrier harmonic group index, take a positive integer. , This is the fundamental band index, rounded to the nearest integer. , This represents the average component of the DC-side current (corresponding to the DC current component required for active power transmission), and the subsequent double summation term represents the carrier and sideband harmonic components. These are the coefficients of the corresponding frequency components in the Fourier expansion. This refers to the DC-side output current of the DC boost-buck module.

7. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claims 1, 2, 4, or 6, characterized in that: The extraction of specific harmonic components includes, First, the acquired time-domain current signal is converted into a frequency-domain signal using the Fourier transform method to analyze the harmonic components and amplitude characteristics in the current. After obtaining the spectrum information, the specific harmonic components that need to be compensated are extracted according to the pre-set harmonic frequency range.

8. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claim 7, characterized in that: The reverse compensation signal includes, For the selected harmonic components, the system further generates the corresponding reverse current signal and injects it into the DC side through the controller to generate a compensation current, expressed as: ； in, This is the active harmonic suppression current between the two parallel capacitors. For the set of harmonics that need to be compensated, For the first The angular frequency of each target frequency point for At amplitude, for In phase, It is an inverting phase, used to cancel out harmonic components at a specific frequency point; The compensation current is injected into the DC side using a current reference superposition method, so that the compensated bus capacitor current satisfies: ； For any target point Pick At that time, the frequency harmonic components are canceled out by equal amplitude and opposite phase, therefore In all The harmonic components are zero. DC-side harmonic suppression.

9. The DC bus harmonic suppression method for photovoltaic grid connection in industrial parks as described in claims 1, 2, 4, 6, or 7, characterized in that: The step of injecting the signal into the corresponding DC bus control circuit for harmonic suppression includes... The generated compensation current is converted into a corresponding reference signal and injected into the boost / buck converter or inverter controller through the controller, so that the actual injected current is approximately the active harmonic suppression current between two parallel capacitors. At the same time, the compensated current signal is fed back to the corresponding control unit in real time for online monitoring and dynamic adjustment.

10. A DC bus harmonic suppression system for grid-connected photovoltaic systems in industrial parks, employing the DC bus harmonic suppression method for grid-connected photovoltaic systems in industrial parks as described in any one of claims 1 to 9, characterized in that: It includes a photovoltaic power generation unit construction module, a three-layer control module based on MPPT, a mathematical modeling and theoretical analysis module, and an active harmonic suppression implementation module; The photovoltaic power generation unit building module is used to construct a photovoltaic power generation unit by connecting multiple photovoltaic units in series to increase voltage and in parallel to increase current, thereby generating DC output with the required voltage and power level according to actual application needs. The MPPT-based three-layer control module is used to add a DC-DC converter to the photovoltaic unit and inverter structure. It adopts a three-level control method: the upper layer uses MPPT to track the maximum power point, the middle layer uses voltage PI to control the output reference current signal, and the lower layer control loop performs fast inner loop adjustment of the inductor current. The corresponding duty cycle modulation signal is generated by the current PI controller to drive the switching devices of the DC-DC converter. The mathematical modeling and theoretical analysis module is used to derive the DC-DC current of the DC-DC converter and the AC current of the DC-AC inverter based on Fourier transform for the DC-DC converter and DC-AC inverter sections, and to derive the DC-DC current of the two-level inverter, and to establish the DC-DC current model of the entire topology system. The active harmonic suppression implementation module is used to convert the acquired time-domain current signal into a frequency-domain signal using the Fourier transform method, analyze the harmonic components and amplitude characteristics in the current, extract the specific harmonic components that need to be compensated according to the preset harmonic frequency range, further generate the corresponding reverse current signal for the selected harmonic components, and inject it into the DC side through the controller to generate a compensation current and convert it into a corresponding reference signal to be injected into the DC side.

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