Ripple compensation method and device, computer equipment and storage medium

Abstract

The invention relates to a ripple compensation method and device, computer equipment and a storage medium. The method comprises the steps of determining a current reference value and a current compensation reference value according to a direct current side support capacitor voltage of the grid-connected converter under the condition that a ripple ratio of a direct current side actual current of the grid-connected converter meets a preset condition; and according to the current reference value and the current compensation reference value, ripple compensation is carried out on the actual current of the direct current side of the grid-connected converter. By adopting the method, the ripples in the direct current side output current can be effectively suppressed, and the ripple suppression cost is reduced.

Description

Technical Field

[0001] The present application relates to the field of power grid technology, and in particular to a ripple compensation method, device, computer equipment and storage medium. Background Art

[0002] DC current ripple is the fluctuation of the DC side output current of the grid-connected converter, which will have many adverse effects on the performance and reliability of the grid-connected converter.

[0003] In order to compensate for the DC current ripple, in the related art, a large-capacity filter capacitor is mainly provided on the DC side of the grid-connected converter to filter out the ripple in the DC side output current through the filter capacitor.

[0004] However, the ripple compensation method in the related art cannot effectively suppress the ripple in the DC side output current, and the ripple suppression cost is relatively high. Summary of the invention

[0005] Based on this, it is necessary to provide a ripple compensation method, device, computer equipment and storage medium to address the above technical problems, which can effectively suppress the ripple in the DC side output current and reduce the ripple suppression cost.

[0006] In a first aspect, the present application provides a ripple compensation method, comprising:

[0007] When the ripple ratio of the actual current on the DC side of the grid-connected converter meets the preset conditions, the current reference value and the current compensation reference value are determined according to the DC side support capacitor voltage of the grid-connected converter;

[0008] According to the current reference value and the current compensation reference value, ripple compensation is performed on the actual current at the DC side of the grid-connected converter.

[0009] In one embodiment, determining a current compensation reference value according to a DC side support capacitor voltage of a grid-connected converter includes:

[0010] Extracting a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter; and obtaining a virtual admittance value of the grid-connected converter;

[0011] A current compensation reference value is determined based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value.

[0012] In one of the embodiments, extracting a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter includes:

[0013] Obtain the voltage ripple frequency in the DC side support capacitor voltage;

[0014] The voltage ripple frequency is filtered using a bandpass filter to obtain a voltage ripple component corresponding to the DC side support capacitor voltage.

[0015] In one embodiment, determining a current compensation reference value based on a DC side support capacitor voltage, a voltage ripple component, and a virtual admittance value includes:

[0016] The product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value is used as a current compensation reference value.

[0017] In one embodiment, the method further comprises:

[0018] Obtaining the ripple ratio of the DC side support capacitor voltage of the grid-connected converter;

[0019] comparing the ripple ratio of the DC side support capacitor voltage with a preset threshold;

[0020] If the comparison result is that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than the preset threshold, it is determined that the ripple ratio of the actual current on the DC side meets the preset condition.

[0021] In one embodiment, obtaining the ripple ratio of the DC side support capacitor voltage of the grid-connected converter includes:

[0022] Preprocessing and decomposing the DC side support capacitor voltage of the grid-connected converter to obtain modal parameter information of the DC side support capacitor voltage;

[0023] Modal identification is performed on the modal parameter information to predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter.

[0024] In one embodiment, performing ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value includes:

[0025] The sum of the current reference value and the current compensation reference value is used as the target current reference value;

[0026] Determine control signals of multiple switch tubes in the grid-connected converter according to the difference between the target current reference value and the actual current on the DC side;

[0027] Based on the control signals of the multiple switch tubes, the multiple switch tubes in the grid-connected converter are controlled.

[0028] In a second aspect, the present application further provides a ripple compensation device, comprising:

[0029] A determination module, used to determine a current reference value and a current compensation reference value according to a DC side support capacitor voltage of the grid-connected converter when a ripple ratio of an actual current on the DC side of the grid-connected converter meets a preset condition;

[0030] The compensation module is used to perform ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value.

[0031] In a third aspect, the present application further provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the content of any one embodiment of the ripple compensation method in the first aspect is implemented.

[0032] In a fourth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the content of any one embodiment of the ripple compensation method in the first aspect above.

[0033] In a fifth aspect, the present application further provides a computer program product, including a computer program, which, when executed by a processor, implements the content of any one embodiment of the ripple compensation method in the first aspect above.

[0034] The above-mentioned ripple compensation method, device, computer equipment and storage medium, when the ripple ratio of the actual current on the DC side of the grid-connected converter meets the preset conditions, determines the current reference value and the current compensation reference value according to the DC side support capacitor voltage of the grid-connected converter; and performs ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value. The method limits the ripple ratio of the actual current on the DC side by preset conditions, and only when the preset conditions are met, determines the current reference value and the current compensation reference value based on the DC side support capacitor voltage, and performs ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value, which can effectively suppress the DC voltage ripple, and there is no need to add hardware filtering equipment in the grid-connected converter, reduce the dependence on the filter capacitor, and thus reduce the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the drawings required for use in the embodiments of the present application or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0036] FIG1 is a diagram showing an application environment of a ripple compensation method in one embodiment;

[0037] FIG2 is a schematic flow chart of a ripple compensation method in one embodiment;

[0038] FIG3 is a circuit diagram of a grid-connected converter in one embodiment;

[0039] FIG4 is a schematic flow chart of a ripple compensation method in one embodiment;

[0040] FIG5 is a schematic flow chart of a ripple compensation method in one embodiment;

[0041] FIG6 is a schematic flow chart of a ripple compensation method in one embodiment;

[0042] FIG7 is a schematic flow chart of a ripple compensation method in one embodiment;

[0043] FIG8 is a schematic flow chart of a ripple compensation method in one embodiment;

[0044] FIG9 is a control flow chart of ripple suppression in one embodiment;

[0045] FIG10 is a schematic diagram of a curve of DC side output impedance in one embodiment;

[0046] FIG11 is a schematic diagram of verification results of DC side output impedance in one embodiment;

[0047] FIG12 is a schematic diagram of a curve showing a DC bus voltage changing with time in one embodiment;

[0048] FIG13 is a schematic diagram of a curve showing a DC bus voltage changing with time in one embodiment;

[0049] FIG14 is a schematic flow chart of a ripple compensation method in one embodiment;

[0050] FIG. 15 is a structural block diagram of a ripple compensation device in one embodiment. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0052] Before introducing the technical solution of the present application in detail, a brief introduction to the background technology of the present application is first given.

[0053] Grid-connected converters are important devices that convert DC power into AC power synchronized with the power grid. They are widely used in renewable energy power generation (such as photovoltaic power generation and wind power generation) and power quality improvement systems.

[0054] As the proportion of renewable energy connected to the grid increases, the demand and technological development of grid-connected converters have also received widespread attention. Traditional grid-connected converters usually require large-capacity filter capacitors on the DC side to suppress the ripple of the DC voltage. These filter capacitors not only increase the cost and volume of the system, but also bring reliability and life issues. At the same time, as the grid-connected system has higher requirements for power quality, traditional grid-connected converters are difficult to meet the requirements for high-frequency ripple suppression, which easily causes grid harmonics, thereby affecting the stability of the grid.

[0055] The technical development of traditional grid-connected converters is as follows:

[0056] 1) Development of filtering technology: Traditional grid-connected converters mainly rely on physical filters (e.g., capacitors, inductors, etc.) to suppress ripple. With the rapid development of power electronic devices, improving filtering methods has become an important means to improve the performance of grid-connected converters. For example, active filters based on control algorithms can adaptively suppress harmonics and ripples according to grid and load conditions.

[0057] 2) High-frequency switching technology: The application of high-frequency switching technology enables the converter to respond to changes in the power grid and the DC side more quickly, thereby more effectively suppressing the voltage ripple on the DC side. In addition, the introduction of high-frequency switching can also reduce the size of filter components and increase the power density of the equipment.

[0058] 3) Adaptive control algorithm: In recent years, the technology based on adaptive control has gradually matured. Adaptive control can monitor the DC voltage ripple in real time and dynamically adjust the control parameters of the converter to achieve the effect of fast response and ripple suppression. This intelligent control method allows the system to automatically adjust according to the actual working conditions, thereby achieving higher voltage stabilization accuracy and stronger anti-disturbance ability.

[0059] 4) Multifunctional grid-connected converter: In order to improve the comprehensive performance of grid-connected converters, modern converters are not only responsible for the conversion of DC to AC power, but also have power quality management functions, such as reactive power compensation, harmonic suppression, etc. The integration of these functions enables the converter to manage the flow of power more effectively and ensure the stable operation of the power grid.

[0060] Although the above technology solves the DC voltage ripple problem in the grid-connected converter to a certain extent, it still has the following technical defects and shortcomings:

[0061] 1) Disadvantages of large capacitor filtering technology

[0062] Large size and high cost: Large capacitors take up a large space in the system, increasing the system volume and weight, and are not suitable for application scenarios that require high power density. At the same time, the cost of capacitors is high, which increases the overall cost of the system.

[0063] Poor reliability: Large capacitors are susceptible to high-frequency ripple and are prone to aging under long-term operation, resulting in degradation of electrical performance or even failure, which seriously affects the reliability and life of the system.

[0064] Slow dynamic response: Capacitor filters mainly target low-frequency ripples and have poor suppression effects on high-frequency ripples, making it difficult for the converter to effectively suppress ripples under rapidly changing operating conditions.

[0065] Disadvantages of Active Power Filters

[0066] Complex design and high implementation cost: Active power filters rely on complex control algorithms and high-performance sensor systems, which increases the difficulty of system design and implementation. At the same time, this also means that its cost is high, especially for small and medium-sized systems, and the cost-effectiveness is not high.

[0067] The effect of controlling DC side ripple is limited: Active power filters are mainly used for harmonic and reactive power compensation on the grid side. They have limited ability to suppress DC voltage ripple and cannot fundamentally solve the ripple problem on the DC side of the grid-connected converter.

[0068] Increased power losses: Active filter control requires additional power input, which can lead to a decrease in overall system efficiency, especially during long operation periods.

[0069] 3) Defects of high-frequency switching technology

[0070] Increased switching losses: Although increasing the switching frequency can reduce ripple, it will also increase the switching losses of power devices and reduce efficiency, which is particularly evident in high-power applications.

[0071] Complex heat dissipation design: The high losses caused by high-frequency switching technology require complex heat dissipation design, which increases the difficulty and cost of heat dissipation in the system.

[0072] Limited effect on high-frequency ripple control: Although high-frequency switching can reduce DC voltage ripple to a certain extent, it is still difficult to completely eliminate high-frequency ripple under complex grid conditions, and additional filtering devices are required.

[0073] Based on the above analysis, the most important technical issue is the effective suppression of DC voltage ripple and the optimal balance between system cost and reliability. The ripple suppression effect is often limited by high costs, system complexity and long-term operating reliability.

[0074] In this context, how to simplify the system structure, reduce costs, improve dynamic response speed and long-term reliability while effectively suppressing DC voltage ripple has become a problem to be solved urgently. Therefore, the present application provides a ripple compensation method, device, computer equipment and storage medium, which can effectively suppress DC voltage ripple and reduce dependence on filter capacitors, thereby improving system performance, reducing costs and extending the service life of the equipment. Of course, the technical solution provided in the embodiments of the present application is not limited to solving only the above-mentioned problems, and there are other technical effects, which can be specifically referred to in the following embodiments. Next, the technical solution of the present application is introduced in detail.

[0075] The ripple compensation method provided in the embodiment of the present application can be applied in the application environment as shown in Figure 1. The computer device in the application environment can be a server, a personal computer, a laptop computer, a smart phone, a tablet computer, a smart mobile phone, etc. The computer device may include a processor, a memory and a network interface connected via a system bus or wirelessly. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device may include a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store data in the ripple compensation process. The network interface of the computer device is used to communicate with an external terminal through a network connection, and the computer program is executed by the processor to implement a ripple compensation method.

[0076] In an exemplary embodiment, as shown in FIG2 , a ripple compensation method is provided, which is described by taking the method applied to the computer device in FIG1 as an example, and includes the following steps 201 to 202. Among them:

[0077] S201, when the ripple ratio of the actual current on the DC side of the grid-connected converter meets a preset condition, determine a current reference value and a current compensation reference value according to the DC side support capacitor voltage of the grid-connected converter.

[0078] FIG3 is a circuit diagram of a grid-connected converter, which includes a filter inductor L2, a filter capacitor Cf, a filter inductor L1, a DC side support capacitor Cdc, and 6 semiconductor metal oxide (MOS) tubes. The left side of the filter inductor L2 is connected to the output end of the three-phase AC power supply, and the right side of the DC side support capacitor Cdc is connected to the load. The filter inductor L2, the filter capacitor Cf, and the filter inductor L1 form an LCL filter structure, and the DC side support capacitor Cdc maintains the DC side voltage. The voltage of the three-phase AC power supply can be 311V, the DC side support capacitor voltage Udc of the grid-connected converter can be 700V, the AC voltage frequency can be 50Hz, and the switching frequency can be 10kHz.

[0079] The ripple ratio of the actual current on the DC side represents the ratio of the effective DC current to the AC current ripple.

[0080] In the embodiment of the present application, the computer device can detect the AC current and DC current in the grid-connected converter using the current detection device, and calculate the ripple ratio of the actual current on the DC side according to the detected DC current and AC current. And determine whether the ripple ratio of the actual current on the DC side meets the preset conditions. If it does, it means that the ripple fluctuation of the actual current on the DC side is large and ripple compensation is required. If it does not meet the conditions, it means that the ripple fluctuation of the actual current on the DC side is large and no ripple compensation is required.

[0081] When ripple compensation is required, the computer device can linearly control (PI control) the DC side support capacitor voltage of the grid-connected converter according to the capacitance reference value of the DC side support capacitor to obtain a current reference value. Also, according to the DC side support capacitor voltage, the DC side output impedance of the grid-connected converter is updated, and the current compensation reference value is determined based on the updated DC side output impedance.

[0082] Alternatively, the computer device may also input the DC side support capacitor voltage into a preset neural network model, analyze the DC side support capacitor voltage through the neural network model, and determine the current reference value and current compensation reference value of the grid-connected converter.

[0083] S202, performing ripple compensation on the actual current at the DC side of the grid-connected converter according to the current reference value and the current compensation reference value.

[0084] In an embodiment of the present application, the current compensation reference value is a value used to suppress the ripple in the current reference value. Therefore, after obtaining the current reference value and the current compensation reference value, the computer device can fuse the current reference value with the current compensation reference value, and use the fusion result as a new current reference value, and perform ripple compensation on the actual current on the DC side of the grid-connected converter based on the new current reference value.

[0085] In the above ripple compensation method, when the ripple ratio of the actual current on the DC side of the grid-connected converter meets the preset conditions, the current reference value and the current compensation reference value are determined according to the DC side support capacitor voltage of the grid-connected converter; and the ripple compensation is performed on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value. This method limits the ripple ratio of the actual current on the DC side by preset conditions. Only when the preset conditions are met, the current reference value and the current compensation reference value are determined based on the DC side support capacitor voltage, and the ripple compensation is performed on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value. This method can effectively suppress the DC voltage ripple, and there is no need to add hardware filtering equipment in the grid-connected converter, reduce the dependence on the filter capacitor, and thus reduce the cost.

[0086] In one embodiment, as shown in FIG4 , the specific content of determining the current compensation reference value according to the DC side support capacitor voltage of the grid-connected converter is introduced in detail, and the content includes the following steps:

[0087] S301, extracting a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter; and obtaining a virtual admittance value of the grid-connected converter;

[0088] In the embodiment of the present application, the computer device can analyze the DC side support capacitor voltage of the grid-connected converter by a ripple component extraction algorithm to extract the voltage ripple component corresponding to the DC side support capacitor voltage. The virtual admittance value of the grid-connected converter can be expressed as:

[0089]

[0090] Among them, Y h * is the virtual admittance reference value; Y h,max is the maximum value of virtual admittance; I re is the deliverable current; I re,max is the maximum deliverable current; I dc is the DC side current; I h,rms is the effective value of the ripple current; v is the power consumption coefficient; P n is the active power on the DC side; k is the maximum possible ripple ratio of the DC side voltage.

[0091] S302, determining a current compensation reference value based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value.

[0092] In an embodiment of the present application, the computer device can input the DC side support capacitor voltage, voltage ripple component and virtual admittance value into a preset neural network model, and obtain the current compensation reference value by calculating the DC side support capacitor voltage, voltage ripple component and virtual admittance value through the neural network model. Alternatively, the computer device can also substitute the DC side support capacitor voltage, voltage ripple component and virtual admittance value into the calculation formula of the current compensation reference value, and calculate through the calculation formula to obtain the current compensation reference value.

[0093] In one embodiment, the specific content of determining the current compensation reference value based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value includes:

[0094] The product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value is used as a current compensation reference value.

[0095] The current compensation reference value iref can be expressed as:

[0096]

[0097] Among them, G BPF Represents the voltage ripple component; Y h Indicates the virtual admittance value; U dc Indicates the DC side support capacitor voltage.

[0098] In the above ripple compensation method, according to the DC side support capacitor voltage of the grid-connected converter, the voltage ripple component corresponding to the DC side support capacitor voltage is extracted; and the virtual admittance value of the grid-connected converter is obtained; the product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value is used as the current compensation reference value. The DC side support capacitor voltage of this method can accurately obtain the voltage ripple component, and the product of the voltage ripple component, the virtual admittance value and the DC side support capacitor voltage is used as the ripple compensation current reference, which is added to the current inner loop of the double closed-loop control of the grid-connected converter, which is equivalent to reducing the impedance of the converter at the ripple frequency, absorbing the ripple current, and achieving the effect of suppressing the DC bus voltage ripple.

[0099] Next, the specific process of obtaining the voltage ripple component is described. In one embodiment, as shown in FIG5 , the specific content of extracting the voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter includes:

[0100] S401, obtaining a voltage ripple frequency in a DC side support capacitor voltage.

[0101] In the embodiment of the present application, the computer device can use Stein's Unbiased Risk Estimate (SURE) wavelet threshold denoising method to preprocess the DC side support capacitor voltage, and then decompose the preprocessed signal through empirical mode decomposition (EMD). After that, the modal identification method of LS-Prony is used to perform modal identification on the decomposed modal parameter information to determine the voltage ripple frequency of the DC side support capacitor voltage.

[0102] S402, filtering the voltage ripple frequency by using a bandpass filter to obtain a voltage ripple component corresponding to the DC side support capacitor voltage.

[0103] In the embodiment of the present application, the computer device can filter the voltage ripple frequency through a band-pass filter (BPF) to determine the voltage ripple component corresponding to the DC side support capacitor voltage. The voltage ripple component can be expressed as:

[0104]

[0105] Among them, fh is the ripple frequency, ωh=2πfh; Q is the quality factor, which determines the bandwidth fbw.

[0106] In the above ripple compensation method, the voltage ripple frequency in the DC side support capacitor voltage is obtained; the voltage ripple frequency is filtered using a bandpass filter to obtain the voltage ripple component corresponding to the DC side support capacitor voltage. This method uses a bandpass filter to accurately filter the voltage ripple frequency in the DC side support capacitor voltage, making the obtained voltage ripple component more accurate.

[0107] Next, an embodiment is used to introduce the specific content of how to determine whether the ripple ratio of the actual current on the DC side meets the preset condition. As shown in FIG6 , the method further includes:

[0108] S501, obtaining a ripple ratio of a DC side supporting capacitor voltage of a grid-connected converter.

[0109] In an embodiment of the present application, the computer device can use Stein's Unbiased Risk Estimate (SURE) wavelet threshold denoising method to preprocess the DC side support capacitor voltage, and then decompose the preprocessed signal through empirical mode decomposition (EMD). After that, the modal identification method of LS-Prony is used to perform modal identification on the decomposed modal parameter information to determine the amplitude, frequency, phase and attenuation factor of the DC side support capacitor voltage. Based on the amplitude, frequency, phase and attenuation factor of the DC side support capacitor voltage, the ripple ratio of the DC side support capacitor voltage of the grid-connected converter is predicted.

[0110] S502: Compare the ripple ratio of the DC side support capacitor voltage with a preset threshold.

[0111] In an embodiment of the present application, the computer device can compare the ripple ratio of the DC side support capacitor voltage with a preset threshold value to determine whether the ripple ratio of the DC side support capacitor voltage is greater than or equal to the preset threshold value to obtain a comparison result.

[0112] S503: If the comparison result shows that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than the preset threshold, it is determined that the ripple ratio of the actual current on the DC side meets the preset condition.

[0113] In an embodiment of the present application, when the comparison result is determined to be that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than a preset threshold, it means that the ripple of the actual current on the DC side is large and ripple suppression is required. At this time, the computer device can determine that the ripple ratio of the actual current on the DC side meets the preset conditions.

[0114] In the above ripple compensation method, the ripple ratio of the DC side support capacitor voltage of the grid-connected converter is obtained; the ripple ratio of the DC side support capacitor voltage is compared with a preset threshold; if the comparison result is that the ripple ratio of the actual DC side current of the grid-connected converter is greater than the preset threshold, it is determined that the ripple ratio of the actual DC side current meets the preset condition. This method compares the ripple ratio of the DC side support capacitor voltage with the preset threshold, and based on the comparison result, it can accurately determine whether the ripple ratio of the actual DC side current meets the preset condition, thereby accurately determining whether the actual DC side current needs ripple suppression.

[0115] In one embodiment, as shown in FIG7 , the specific content of obtaining the ripple ratio of the DC side support capacitor voltage of the grid-connected converter includes the following steps:

[0116] S601, preprocessing and decomposing the DC side support capacitor voltage of the grid-connected converter to obtain modal parameter information of the DC side support capacitor voltage.

[0117] The preprocessing method may be a SURE wavelet threshold denoising method, and the decomposition method is to decompose the preprocessed signal through EMD.

[0118] In the embodiment of the present application, the key to wavelet threshold denoising is the setting of the threshold and the selection of the threshold function. In order to meet the adaptive requirements of different noise conditions, a variable threshold is usually used. At the same time, in order to compensate for the existence of the "over-elimination" phenomenon, an adaptive threshold selection based on SURE is adopted. The risk value of each limit is calculated separately, and the limit with the smallest risk value is the threshold. Specifically, the computer device can use the risk algorithm (where l=1,2,...,L), sort the squares of the wavelet coefficients from small to large to obtain a new vector w=[w1,w2,···,wL]. Assuming that when l=D, the risk value r(l) is the minimum risk value, thus determining the corresponding wavelet coefficient wD. Then the threshold is:

[0119]

[0120]

[0121] in, is the estimated value of the standard deviation of the noise; Mf is the median of the magnitude of the wavelet coefficients.

[0122] The parameters that reflect the signal denoising effect are the signal noise ratio (SNR) and the mean square error (MSE), which are calculated as follows:

[0123]

[0124]

[0125] Where N is the signal sample length; is the original signal; is the denoised signal. In order to achieve a better denoising effect, the denoised signal is usually required to have a larger SNR and a smaller MSE.

[0126] After preprocessing, EMD is used to decompose the preprocessed signal. EMD can linearize and stabilize the preprocessed signal. The basic idea is to iteratively process the signal and decompose it into intrinsic mode functions (IMFs) and residuals with different characteristics. The specific process includes the following steps:

[0127] 1) Take the maximum and minimum points of the signal x(t), perform cubic spline interpolation to obtain the upper and lower envelopes, and then take the mean, recorded as m;

[0128] 2) Subtract x(t) from m, denoted as h(t), and repeat step 1). When the stopping criterion is met, it can be considered as an IMF component; the stopping criterion depends on the standard deviation (SD):

[0129]

[0130] When the SD value is less than the given threshold, the system will shut down;

[0131] 3) After shutdown, the first IMF component c(t) can be obtained, and then the difference between x(t) and c(t) is recorded as the residual component r(t), and it is regarded as the new x(t), and the above steps are repeated to obtain its IMF component;

[0132] 4) Until r(t) is a monotonic function that cannot be decomposed, multiple IMF components and a residual component are finally obtained. At this time, the EMD decomposition of the signal x(t) is completed:

[0133]

[0134] The IMF components obtained after EMD decomposition still retain the important features of the preprocessed signal and can be subsequently analyzed through the fitting process. The IMF components represent the modal parameter information of the DC side support capacitor voltage.

[0135] S602, performing modal identification on the modal parameter information to predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter.

[0136] In the embodiment of the present application, the computer device can use the LS-Prony modal identification method to perform modal identification on the modal parameter information to determine the amplitude, frequency, phase, and attenuation factor of the DC side support capacitor voltage. And based on the amplitude, frequency, phase, and attenuation factor of the DC side support capacitor voltage, the ripple ratio of the DC side support capacitor voltage of the grid-connected converter is predicted.

[0137] Specifically, it is assumed that the DC side support capacitor voltage is a linear combination of a series of exponential functions:

[0138]

[0139]

[0140] The key to fitting the DC side support capacitor voltage using the Prony algorithm is to find the homogeneous solution of the linear difference equation with constant coefficients. The specific method is to construct the difference equation:

[0141]

[0142] In order to minimize the error, the least squares method is used and expanded into a set of linear matrix equations:

[0143]

[0144] Solving the problem yields the approximate values ​​of the parameters a0~ap, and then we can find the root z of the characteristic polynomial:

[0145]

[0146] The amplitude, frequency, phase and attenuation factor of the DC side support capacitor voltage are:

[0147]

[0148] The ripple ratio of the DC side support capacitor voltage can be expressed as:

[0149]

[0150] Among them, Udc,amp is the ripple voltage on the DC side, and Unom is the standard voltage on the DC side.

[0151] In the above ripple compensation method, the DC side support capacitor voltage of the grid-connected converter is preprocessed and decomposed to obtain the modal parameter information of the DC side support capacitor voltage; the modal parameter information is modally identified to predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter. This method can accurately obtain the modal parameter information of the DC side support capacitor voltage by preprocessing and decomposing, and can accurately estimate the ripple ratio of the DC side support capacitor voltage by modal identification.

[0152] The above embodiments are all detailed introductions to the calculation method of the current compensation reference value. Next, the details of performing ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value are described through an embodiment, as shown in FIG8 , which includes:

[0153] S701, taking the sum of the current reference value and the current compensation reference value as the target current reference value.

[0154] In an embodiment of the present application, after obtaining the current reference value and the current compensation reference value, the computer device can add the current reference value and the current compensation reference value, the result of the addition represents a current reference value that is not affected by the ripple or is less affected by the ripple, and the addition result is used as the target current reference value.

[0155] S702, determining control signals of multiple switch tubes in the grid-connected converter according to the difference between the target current reference value and the actual current on the DC side.

[0156] In an embodiment of the present application, the computer device may subtract the target current reference value from the actual current on the DC side to obtain the difference between the target current reference value and the actual current on the DC side. Then, the control signal of multiple switch tubes in the grid-connected converter is determined by using the model predictive current control (MPCC). For example, the control signal may be a three-phase modulated wave.

[0157] S703, based on the control signals of the multiple switch tubes, control the multiple switch tubes in the grid-connected converter.

[0158] In the embodiment of the present application, after obtaining the control signals of multiple switch tubes, for any switch tube, the computer device can use the control signal of the switch tube to control the conduction frequency of the switch tube to achieve control of the switch tube. In the above manner, all switch tubes can be controlled to adjust the actual current on the DC side to the target current reference value.

[0159] The process of adjusting the actual DC side current of the grid-connected converter to the target current reference value is equivalent to reshaping the DC side output impedance of the grid-connected converter at the ripple frequency, which is equivalent to realizing the DC-APF function at the DC bus.

[0160] Figure 9 is a control flow chart of ripple suppression. According to the voltage ripple component G BPF , DC side support capacitor voltage U dc and virtual admittance value Y h , output current compensation reference value iref. Based on the sum of current compensation reference value iref and current reference value ire as target current reference value i d * , and calculate the target current reference value i d * The difference between the actual current id on the DC side determines the control signals of multiple switching tubes in the grid-connected converter.

[0161] Combined with the content in Figure 9, the DC side output impedance of the grid-connected converter is modeled and obtained:

[0162]

[0163]

[0164] The DC side output impedance can be expressed as:

[0165]

[0166] Among them, G pll It is a phase-locked loop regulator. v and H i They are DC voltage loop and current loop regulators respectively; I 1d ,I 1q is the steady-state value of the inductor L1 current d and q axes; U d , U q is the filter capacitor C f Voltage d, q axis steady-state value; E d 、E q is the steady-state value of the voltage on the d and q axes at the three-phase bridge arm ports; u dref 、u qref are the d-axis and q-axis voltage reference values ​​output by the control system respectively; U * dc and U dc are the outer loop DC voltage command value and steady-state value respectively; I dc is the steady-state value of the DC side current; D is the modulation duty cycle; ω is the angular frequency output by the control system phase-locked loop; ω0 is the output angular frequency of the vehicle stability control system (VSC) during steady-state operation; Δ represents the small signal disturbance.

[0167] After adding the virtual admittance value, the target current reference value can be expressed as:

[0168]

[0169] The new DC side output impedance can be expressed as:

[0170]

[0171] FIG10 is a schematic diagram of the curve of the DC side output impedance. The upper figure is a curve diagram of the frequency and the amplitude of the DC side output impedance, and the lower figure is a curve diagram of the frequency and the phase of the DC side output impedance. It can be seen from the figure that when the frequency is 120Hz, the amplitude and phase will change. The bandpass filter only passes the signal near 120Hz and will not affect the signals of other frequencies.

[0172] FIG11 is a schematic diagram showing the verification result of the DC side output impedance, wherein the continuous curve in the figure represents the estimated value of the DC side output impedance, and the multiple circles represent the actual sampled values. The upper figure represents the verification result curve diagram of the frequency and the amplitude of the DC side output impedance, and the lower figure represents the verification result curve diagram of the frequency and the phase of the DC side output impedance.

[0173] FIG12 is a schematic diagram of a curve showing a change of the DC bus voltage over time. It can be seen from the figure that there is no ripple in the DC bus voltage. FIG13 is a schematic diagram showing a curve showing a change of the DC bus voltage over time. It can be seen from the figure that, from left to right, the leftmost part shows a schematic diagram of the DC bus voltage when the ripple is large, the middle part is the DC bus voltage during the ripple suppression process, and the rightmost part is the DC bus voltage after the ripple suppression. By comparison, the ripple suppression process can effectively suppress the ripple on the DC bus voltage.

[0174] In the above ripple compensation method, the sum of the current reference value and the current compensation reference value is used as the target current reference value; the control signals of multiple switch tubes in the grid-connected converter are determined according to the difference between the target current reference value and the actual current on the DC side; and the multiple switch tubes in the grid-connected converter are controlled based on the control signals of the multiple switch tubes. This method can determine the target current reference value on the DC side by calculating the sum of the current reference value and the current compensation reference value, and accurately generate the control signals of the multiple switch tubes based on the difference between the reference value and the actual current value, so that the ripple can be accurately suppressed based on the control signal.

[0175] As a specific embodiment of the present application, the ripple compensation process is described in detail below. In one embodiment, as shown in FIG14 , the ripple compensation method includes:

[0176] S801: preprocessing and decomposing the DC side support capacitor voltage of the grid-connected converter to obtain modal parameter information of the DC side support capacitor voltage;

[0177] S802: performing modal identification on the modal parameter information to predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter;

[0178] S803: Compare the ripple ratio of the DC side support capacitor voltage with a preset threshold;

[0179] S804: If the comparison result is that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than the preset threshold, determine that the ripple ratio of the actual current on the DC side meets the preset condition;

[0180] S805: Obtaining a voltage ripple frequency in the DC side support capacitor voltage; and obtaining a virtual admittance value of the grid-connected converter;

[0181] S806: Filter the voltage ripple frequency using a bandpass filter to obtain a voltage ripple component corresponding to the DC side support capacitor voltage;

[0182] S807: taking the product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value as a current compensation reference value;

[0183] S808: taking the sum of the current reference value and the current compensation reference value as the target current reference value;

[0184] S809: Determine control signals of multiple switch tubes in the grid-connected converter according to the difference between the target current reference value and the actual current on the DC side;

[0185] S810: Control multiple switch tubes in the grid-connected converter based on control signals of the multiple switch tubes.

[0186] It should be understood that, although the steps in the flowcharts involved in the above embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above embodiments may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0187] Based on the same inventive concept, the embodiment of the present application also provides a ripple compensation device for implementing the ripple compensation method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations of one or more ripple compensation device embodiments provided below can refer to the limitations of the ripple compensation method above, and will not be repeated here.

[0188] In an exemplary embodiment, as shown in FIG15 , a ripple compensation device is provided, comprising: a determination module 11 and a compensation module 12, wherein:

[0189] A determination module 11, configured to determine a current reference value and a current compensation reference value according to a DC side support capacitor voltage of the grid-connected converter when a ripple ratio of an actual current on the DC side of the grid-connected converter meets a preset condition;

[0190] The compensation module 12 is used to perform ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value.

[0191] In an exemplary embodiment, the determination module includes: an acquisition unit and a reference value determination unit, wherein:

[0192] An acquisition unit, configured to extract a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter; and to acquire a virtual admittance value of the grid-connected converter;

[0193] The reference value determination unit is used to determine the current compensation reference value based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value.

[0194] In an exemplary embodiment, the acquisition unit is further used to acquire the voltage ripple frequency in the DC side support capacitor voltage; and filter the voltage ripple frequency using a bandpass filter to obtain a voltage ripple component corresponding to the DC side support capacitor voltage.

[0195] In an exemplary embodiment, the reference value determination unit is further configured to use the product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value as the current compensation reference value.

[0196] In an exemplary embodiment, the ripple compensation device further includes: an acquisition module, a comparison module and a condition determination module, wherein:

[0197] An acquisition module, used for acquiring a ripple ratio of a DC side support capacitor voltage of a grid-connected converter;

[0198] A comparison module, used for comparing the ripple ratio of the DC side support capacitor voltage with a preset threshold;

[0199] The condition determination module is used to determine whether the ripple ratio of the actual current on the DC side meets the preset condition when the comparison result shows that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than the preset threshold.

[0200] In one embodiment, the acquisition module includes: a processing unit and a prediction unit, wherein:

[0201] A processing unit, used for preprocessing and decomposing the DC side support capacitor voltage of the grid-connected converter to obtain modal parameter information of the DC side support capacitor voltage;

[0202] The prediction unit is used to perform modal identification on the modal parameter information and predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter.

[0203] In one embodiment, the compensation module comprises: a summing unit, a signal determining unit and a control unit, wherein:

[0204] A summing unit, used for taking the sum of the current reference value and the current compensation reference value as the target current reference value;

[0205] A signal determination unit, used to determine control signals of multiple switch tubes in the grid-connected converter according to the difference between the target current reference value and the actual current on the DC side;

[0206] The control unit is used to control multiple switch tubes in the grid-connected converter based on control signals of the multiple switch tubes.

[0207] Each module in the above ripple compensation device can be implemented in whole or in part by software, hardware, or a combination thereof. Each module can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to each module.

[0208] In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the content of any one embodiment of the ripple compensation method when executing the computer program.

[0209] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the content of any one embodiment of the ripple compensation method described above is implemented.

[0210] In one embodiment, a computer program product is provided, comprising a computer program, which implements the content of any one embodiment of the ripple compensation method when executed by a processor.

[0211] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0212] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, an artificial intelligence (AI) processor, etc., but are not limited to this.

[0213] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0214] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A ripple compensation method, characterized in that: The method comprises: When the ripple ratio of the actual current on the DC side of the grid-connected converter meets a preset condition, determining a current reference value and a current compensation reference value according to the DC side support capacitor voltage of the grid-connected converter; According to the current reference value and the current compensation reference value, ripple compensation is performed on the actual current at the DC side of the grid-connected converter.

2. The method according to claim 1, characterized in that Determining a current compensation reference value according to a DC side support capacitor voltage of the grid-connected converter includes: Extracting a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter; and obtaining a virtual admittance value of the grid-connected converter; The current compensation reference value is determined based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value.

3. The method according to claim 2, characterized in that The step of extracting a voltage ripple component corresponding to the DC side support capacitor voltage according to the DC side support capacitor voltage of the grid-connected converter includes: Obtaining a voltage ripple frequency in the DC side support capacitor voltage; The voltage ripple frequency is filtered by using a bandpass filter to obtain a voltage ripple component corresponding to the DC side support capacitor voltage.

4. The method according to claim 2, characterized in that: The determining the current compensation reference value based on the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value comprises: The product of the DC side support capacitor voltage, the voltage ripple component and the virtual admittance value is used as the current compensation reference value.

5. The method according to any one of claims 1 to 4, characterized in that: The method further comprises: Obtaining a ripple ratio of a DC side support capacitor voltage of the grid-connected converter; Comparing the ripple ratio of the DC side support capacitor voltage with the preset threshold; If the comparison result is that the ripple ratio of the actual current on the DC side of the grid-connected converter is greater than the preset threshold, it is determined that the ripple ratio of the actual current on the DC side meets the preset condition.

6. The method according to claim 5, characterized in that The obtaining of the ripple ratio of the DC side support capacitor voltage of the grid-connected converter comprises: Preprocessing and decomposing the DC side support capacitor voltage of the grid-connected converter to obtain modal parameter information of the DC side support capacitor voltage; Performing modal identification on the modal parameter information to predict the ripple ratio of the DC side support capacitor voltage of the grid-connected converter.

7. The method according to any one of claims 1 to 4, characterized in that: The performing ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value comprises: Taking the sum of the current reference value and the current compensation reference value as a target current reference value; Determining control signals of multiple switch tubes in the grid-connected converter according to the difference between the target current reference value and the actual current on the DC side; Based on the control signals of the multiple switch tubes, the multiple switch tubes in the grid-connected converter are controlled.

8. A ripple compensation device, characterized in that: The device comprises: A determination module, used to determine a current reference value and a current compensation reference value according to a DC side support capacitor voltage of the grid-connected converter when a ripple ratio of an actual current on the DC side of the grid-connected converter meets a preset condition; The compensation module is used to perform ripple compensation on the actual current on the DC side of the grid-connected converter according to the current reference value and the current compensation reference value.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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