A harmonic energy utilization method and system for multi-dc source input distribution network

Abstract

This application relates to the field of harmonic energy utilization technology in distribution networks, specifically to a method and system for harmonic energy utilization in distribution networks with multiple DC source inputs. The method includes: real-time acquisition of current signals using a current sensor installed on the main line of the distribution network and located before an LC filter circuit; presetting the adjustment period of the resonant frequency of the LC filter circuit; assessing whether to initiate resonant frequency adjustment; if initiated, determining whether to issue a fault warning and terminating subsequent processing; if not terminated, acquiring the harmonic fluctuation degree for each cycle; obtaining the harmonic deviation degree for each cycle for a single harmonic; acquiring the adjustment coefficient of the capacitor in the LC filter circuit, adjusting the capacitor in each cycle to adjust the resonant frequency of the LC filter circuit; and extracting harmonic current for use by low-voltage loads. This application aims to improve the harmonic energy utilization rate by adjusting the resonant frequency to enhance the ability to extract harmonic current.

Description

Technical Field

[0001] This application relates to the field of harmonic energy utilization technology in distribution networks, specifically to a method and system for harmonic energy utilization in distribution networks with multiple DC source inputs. Background Technology

[0002] DC power distribution has significant advantages such as low line loss and high transmission efficiency. However, with the connection of multiple DC sources such as new energy power generation, charging piles, and energy storage devices to the distribution network, the large number of harmonics generated by their grid-connected converters will not only accelerate the aging of grid equipment and shorten its service life, but also reduce power quality and cause waste of electrical resources.

[0003] LC filter circuits are currently the mainstream harmonic mitigation technology. By matching the resonant frequency with the target harmonic frequency, they can extract and utilize harmonic currents with minimal fundamental frequency loss. However, the resonant frequency of existing LC filter circuits is usually a fixed value and cannot be adjusted according to changes in the location of harmonic energy distribution. In multi-DC source input distribution networks, the random fluctuations in renewable energy output and operating conditions cause dynamic shifts in the location of harmonic energy distribution. Fixed resonant frequencies cannot match this shift, resulting in a significant increase in the impedance of the LC filter circuit to harmonics, reducing the harmonic current extraction rate, and causing a decrease in harmonic energy utilization. Summary of the Invention

[0004] In view of the above, it is necessary to provide a method and system for harmonic energy utilization in distribution networks with multiple DC input sources. Compared with traditional methods for harmonic energy utilization in distribution networks with multiple DC input sources, this method improves the ability to extract harmonic currents by adjusting the resonant frequency, thereby improving the utilization rate of harmonic energy.

[0005] In a first aspect, embodiments of this application provide a method for harmonic energy utilization in distribution networks with multiple DC source inputs, the method comprising the following steps: Current signals are collected in real time by a current sensor installed on the main line of the distribution network and located before the LC filter circuit. The system presets the adjustment period for the resonant frequency of the LC filter circuit. It assesses whether to initiate resonant frequency adjustment based on the fluctuation of the current signal within each period. If initiated, it determines whether to issue a fault warning and terminate subsequent processing based on the similarity of the current signal between each period and its adjacent preceding period. If not terminated, it obtains the harmonic fluctuation degree of the single harmonic within each period based on the similarity of the current signal between each period and its adjacent preceding period, as well as the difference in single harmonic energy. For single harmonics, it obtains the harmonic deviation degree of each period by monitoring the energy distribution offset of the single harmonic in the amplitude spectrum of the current signal between each period and its adjacent preceding period. This is then combined with the harmonic fluctuation degree to obtain the adjustment coefficient of the capacitor in the LC filter circuit. The capacitor is adjusted within each period to adjust the resonant frequency of the LC filter circuit. Finally, the harmonic current is extracted from the LC filter circuit after resonant frequency adjustment for use by low-voltage loads.

[0006] In one embodiment, the process of evaluating whether to initiate resonant frequency adjustment is as follows: The maximum and minimum values ​​of the current signal in the positive half-cycle of each period are statistically analyzed. The ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the positive half-cycle ripple. The maximum and minimum values ​​of the current signal in the negative half-cycle valley in each cycle are statistically analyzed. The absolute value of the ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the negative half-cycle fluctuation. The maximum value between the positive half-cycle fluctuation and the negative half-cycle fluctuation is denoted as the current fluctuation. If the current fluctuation exceeds a preset amplitude fluctuation threshold, the resonant frequency adjustment is initiated.

[0007] In one embodiment, the method for determining whether to issue a fault warning and terminate subsequent processing is as follows: If the correlation coefficient of the current signal between each cycle and its adjacent previous cycle in the time domain is negative, a fault warning is issued and subsequent processing is terminated.

[0008] In one embodiment, the process of obtaining the harmonic fluctuation degree is as follows: Calculate the difference in single harmonic energy of the current signal between each cycle and the previous cycle; the ratio of the difference to the single harmonic energy of the current signal in the previous cycle is denoted as the harmonic difference degree. The harmonic fluctuation degree is positively correlated with the harmonic difference degree and negatively correlated with the correlation coefficient.

[0009] In one embodiment, the method for calculating the harmonic fluctuation degree is as follows: The correlation coefficient is shifted to a first positive number; the harmonic difference is mapped to a second positive number. The harmonic fluctuation is the normalized value of the ratio of the second positive number to the first positive number.

[0010] In one embodiment, the process of obtaining the harmonic deviation is as follows: Extract the frequency of the peak value closest to the single harmonic from the amplitude spectrum of the current signal in each cycle; Calculate the difference between the frequency extracted from the previous adjacent period and the frequency extracted from each period; The harmonic deviation is the ratio of the difference to the frequency extracted from the adjacent previous cycle.

[0011] In one embodiment, the process of obtaining the adjustment coefficient is as follows: Calculate the product of the harmonic deviation and the harmonic fluctuation. The adjustment coefficient is positively correlated with the product.

[0012] In one embodiment, when adjusting the capacitor in each cycle, the product of the adjustment coefficient and the value of the capacitor in the adjacent previous cycle is used as the adjusted capacitor value in each cycle.

[0013] In one embodiment, when adjusting the resonant frequency of the LC filter circuit, the rounded result of the difference between the adjusted capacitance value in each cycle and the capacitance value in the adjacent previous cycle is used as the switching capacitance value in each cycle.

[0014] Secondly, embodiments of this application also provide a harmonic energy utilization system for a multi-DC-source input distribution network, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of the harmonic energy utilization method for a multi-DC-source input distribution network described above.

[0015] This application has at least the following beneficial effects: This application analyzes the fluctuation of the current signal and evaluates whether to initiate resonant frequency adjustment in each cycle. It can realize intelligent start control of resonant frequency adjustment of LC filter circuit, and only initiate the subsequent complex adjustment process when the current fluctuation is severe and the harmonic energy distribution may be deviated, thus avoiding unnecessary adjustment when the current is stable. Furthermore, by analyzing the similarity of current signals between two adjacent cycles for fault identification, extreme abnormal changes in the current waveform can be identified in a timely manner, avoiding the risk of secondary damage caused by capacitor adjustment under abnormal operating conditions. In the absence of faults, the similarity of current signals between two adjacent cycles quantifies the degree of change of the current signal in the time domain; the lower the current similarity, the more severe the current fluctuation and the more unstable the distribution of harmonic energy. The difference in single harmonic energy between two adjacent cycles accurately reflects the relative change of single harmonic energy between them. Furthermore, by combining current similarity and harmonic difference, the harmonic fluctuation degree is obtained, comprehensively characterizing the fluctuation features of the current signal from two dimensions: time-domain waveform similarity and frequency-domain harmonic content changes. This comprehensively quantifies the severity of harmonic fluctuations between each cycle and its preceding adjacent cycle, providing a crucial basis for subsequently determining the capacitor adjustment amplitude. Furthermore, by monitoring the degree of energy distribution shift of single harmonics in the amplitude spectrum, the harmonic energy shift caused by random fluctuations of multiple DC sources can be accurately reflected. This not only quantifies the magnitude of the positional shift of the harmonic energy distribution, but also clarifies the direction of the shift through the positive or negative sign of the harmonic deviation, providing key information for the subsequent adjustment of capacitor amplitude and direction. Furthermore, by obtaining adjustment coefficients through harmonic fluctuation and harmonic deviation, the adjustment amplitude of the capacitor can be dynamically adjusted according to the severity of harmonic fluctuations and the degree of displacement of the harmonic energy distribution position. This changes the resonant frequency of the LC filter circuit, enabling the resonant frequency of the LC filter circuit to dynamically track the actual distribution position of the harmonic energy. Thus, even when the random fluctuations of multiple DC sources cause the harmonic energy distribution position to shift, the circuit maintains a high efficiency in extracting harmonic current, significantly improving the utilization rate of harmonic energy. Attached Figure Description

[0016] Figure 1 A flowchart illustrating the steps of a method for utilizing harmonic energy in a multi-DC-source-input distribution network, as provided in one embodiment of this application; Figure 2 This is a schematic diagram of the capacitor adjustment process. Detailed Implementation

[0017] The following description, in conjunction with the accompanying drawings, details a specific scheme for a harmonic energy utilization method and system for multi-DC-source input distribution networks provided in this application.

[0018] Please see Figure 1 The diagram illustrates a flowchart of a method for harmonic energy utilization in a multi-DC-source input distribution network according to an embodiment of this application. The method includes the following steps: Step 1: Acquire current signals in real time using a current sensor installed on the main distribution line and located before the LC filter circuit.

[0019] Current signals are acquired in real time using a current sensor installed on the main distribution network line before the LC filter circuit. Furthermore, to avoid the influence of electromagnetic interference on the current signal, the acquired current signal is denoised.

[0020] In this embodiment, the sampling frequency of the current signal is 5kHz. The sampling frequency of the current signal is preset by the user and can be set by the implementer according to the actual situation. This application does not impose any special restrictions.

[0021] In this embodiment, a wavelet threshold denoising algorithm is used to denoise the acquired current signal. The wavelet threshold denoising algorithm is a well-known technology and will not be described in detail here. As other implementation methods, based on the ability to denoise the acquired current signal, implementers may use other existing feasible technologies. This application does not impose any special restrictions.

[0022] Step 2: Preset the adjustment period of the resonant frequency of the LC filter circuit; evaluate whether to start the resonant frequency adjustment by observing the fluctuation of the current signal in each period.

[0023] When multiple DC sources randomly fluctuate in the input distribution network main line, such as random switching of multiple DC sources or random power output from new energy sources, the current in the main line of the distribution network will typically fluctuate randomly. The greater the fluctuation, the more likely the position of the harmonic energy distribution in the current signal spectrum will shift. For example, the third harmonic energy is ideally concentrated at 150Hz, but when the current fluctuation is severe, the peak point of the amplitude spectrum may deviate from 150Hz to a nearby frequency, such as 149Hz. This causes the LC filter circuit to reduce the harmonic current extraction efficiency due to resonant frequency mismatch, thereby affecting the harmonic energy utilization rate. In this embodiment, the fundamental frequency is 50Hz.

[0024] The adjustment period for the resonant frequency of the preset LC filter circuit.

[0025] In this embodiment, the length of the period is 1 second. The length of the period is preset by the user and can be set by the implementer according to the actual situation. This application does not impose any special restrictions.

[0026] To analyze the fluctuation of the current signal, the peak value of the positive half-cycle and the valley value of the negative half-cycle of the current signal in the time domain are obtained within each cycle. The maximum and minimum values ​​of the peak values ​​of the current signal in the positive half-cycle of each cycle are statistically analyzed, and the ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the positive half-cycle fluctuation. The maximum and minimum values ​​of the valley values ​​of the current signal in the negative half-cycle of each cycle are statistically analyzed, and the absolute value of the ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the negative half-cycle fluctuation. The maximum value of the positive half-cycle fluctuation and the negative half-cycle fluctuation is recorded as the current fluctuation. The current fluctuation reflects the fluctuation of the current signal in each cycle. The larger the calculated current fluctuation, the greater the current fluctuation in each cycle, and the more likely it is to be affected by random switching of multiple DC sources or random power output of new energy sources. The position of the harmonic energy distribution in the spectrum of the current signal is more likely to shift.

[0027] In this embodiment, an automatic multi-scale peak lookup algorithm is used to obtain the peak value of the current signal in the time domain within each cycle. The automatic multi-scale peak lookup algorithm is a well-known technology and will not be described in detail in this application.

[0028] In this embodiment, when calculating the ratio, if there is a case where the denominator is 0, the denominator is first mapped to a positive number before subsequent calculations are performed. There are many methods to map data to a positive number, and the implementer can choose an existing feasible method according to the actual situation. In this embodiment, the purpose of mapping the data to a positive number is achieved by calculating the sum of the data and a preset value greater than 0. The value of the preset value greater than 0 is preset by the user, and the implementer can set it according to the actual situation. This application does not impose any special restrictions. In this embodiment, the value of the preset value greater than 0 is 0.01, and the unit of the preset value greater than 0 is the same as that of the data that needs to be mapped to a positive number.

[0029] If the current fluctuation in each cycle is greater than the preset amplitude fluctuation threshold, it indicates that the current fluctuation in each cycle is large, which is likely to cause the distribution position of harmonic energy in the spectrum of the current signal to shift, and it is determined that the resonant frequency adjustment is initiated; otherwise, it indicates that the current fluctuation in each cycle is not serious and will not cause the distribution position of harmonic energy in the spectrum of the current signal to shift, and it is determined that the resonant frequency adjustment is not initiated.

[0030] In this embodiment, the preset amplitude fluctuation threshold is set to 20%, and the preset amplitude fluctuation threshold is calculated based on experimental data.

[0031] Step 3: If started, determine whether to issue a fault warning and terminate subsequent processing. If not terminated, obtain the harmonic fluctuation degree of the single harmonic in each cycle; for the single harmonic, obtain the harmonic deviation degree of each cycle; obtain the adjustment coefficient of the capacitor in the LC filter circuit, and adjust the capacitor in each cycle.

[0032] Step 3.1: Based on the similarity of the current signals between each cycle and its adjacent previous cycle, determine whether to issue a fault warning and terminate subsequent processing. If not, obtain the harmonic fluctuation degree of the single harmonic in each cycle based on the similarity of the current signals between each cycle and its adjacent previous cycle and the difference in single harmonic energy.

[0033] If the similarity between the current signal in each cycle and the current signal in the adjacent previous cycle is too low, it indicates that the current phase has reversed, which is an extreme fault situation.

[0034] Based on the above analysis, the correlation coefficient of the current signal between each cycle and its adjacent previous cycle in the time domain is calculated and denoted as the current similarity. If the current similarity is negative, a fault warning is issued and subsequent processing is terminated. The distribution network harmonic energy utilization analysis is carried out again after the fault is inspected and repaired.

[0035] In this embodiment, the correlation coefficient is the Pearson correlation coefficient. The calculation of the Pearson correlation coefficient is a well-known technique and will not be described in detail here.

[0036] Furthermore, the harmonic currents in the distribution network are mainly concentrated in the 3rd, 5th, and 7th harmonics. If the fluctuation of the current signal in each cycle is large, the similarity between the current signal in each cycle and the current signal in the adjacent previous cycle will decrease, and the difference in single harmonic energy between the current signal in each cycle and the current signal in the adjacent previous cycle will increase. At this time, the degree of harmonic fluctuation between each cycle and the adjacent previous cycle will increase, and the distribution position of harmonic energy in each cycle is more likely to shift.

[0037] Based on the above analysis, for single harmonics, the harmonic fluctuation degree of single harmonics in each period is obtained by considering the similarity of current signals between each period and its adjacent previous period, as well as the energy difference of single harmonics. The specific process is as follows: Calculate the difference in single harmonic energy of the current signal between each cycle and the previous cycle; the ratio of the difference to the single harmonic energy of the current signal in the previous cycle is denoted as the harmonic difference degree. The harmonic fluctuation degree of a single harmonic within each period is positively correlated with the harmonic difference degree and negatively correlated with the current similarity degree. The acquisition of energy from a single harmonic is a known technique and will not be elaborated upon in this application.

[0038] It should be noted that: positive correlation means that the variables change in the same direction, that is, when one variable increases, the other variable also increases, and when one variable decreases, the other variable also decreases; negative correlation means that the variables change in opposite directions, that is, when one variable increases, the other variable decreases, and when one variable decreases, the other variable increases.

[0039] In this embodiment, the difference between single harmonic energies is the absolute value of the difference.

[0040] In this embodiment, the expression for the harmonic fluctuation degree of a single harmonic within each period is: In the formula, This represents the harmonic fluctuation degree of the t-th period; Indicates the normalization method; This represents the harmonic difference degree of a single harmonic within the t-th period; This represents the current similarity between the t-th cycle and its adjacent previous cycle. This represents a preset constant greater than 0, used in the numerator to avoid the harmonic difference being 0, and in the denominator to shift the current similarity to a positive number.

[0041] In this embodiment, The value is 0.01. The value is preset by the user, and the implementer can set it according to the actual situation. This application does not impose any special restrictions.

[0042] In this embodiment, the maximum value normalization method is used to... Normalization is performed, where the maximum value refers to the maximum value of the harmonic fluctuation of a single harmonic within each period and all its historical periods. The method for normalizing the maximum value is a well-known technique and will not be described in detail in this application.

[0043] It should be noted that in existing data analysis methods, if any fluctuation characteristic of the target is difficult to measure directly, features related to that fluctuation characteristic are usually used for joint representation. In this application, the features related to the harmonic fluctuation characteristics of the current signal are current similarity and harmonic difference. Therefore, by analyzing the current similarity and harmonic difference between each cycle and its adjacent previous cycle, the harmonic fluctuation situation between each cycle and its adjacent previous cycle is evaluated. Because the current fluctuations caused by distribution network harmonics are random, regardless of whether the distribution position of harmonic energy in the spectrum of the current signal in the adjacent previous cycle has shifted, the lower the similarity of the current signal between each cycle and its adjacent previous cycle, the greater the fluctuation of the current signal in each cycle, and the greater the harmonic fluctuation between each cycle and its adjacent previous cycle. The harmonic difference degree is used to reflect the degree of difference of single harmonic energy between each cycle and its adjacent previous cycle. The greater the calculated harmonic difference degree, the greater the difference of single harmonic energy between each cycle and its adjacent previous cycle, and the greater the harmonic fluctuation between each cycle and its adjacent previous cycle. Therefore, the greater the calculated harmonic fluctuation degree, the greater the harmonic fluctuation between each cycle and its adjacent previous cycle, and the more likely the distribution position of harmonic energy in the spectrum of the current signal in each cycle may shift compared to the adjacent previous cycle.

[0044] Step 3.2: For single harmonics, the harmonic deviation of each period is obtained by monitoring the degree of energy distribution shift of the single harmonic in the amplitude spectrum of the current signal between each period and its adjacent previous period.

[0045] To extract multiple harmonic currents simultaneously, multiple parallel LC filter circuits with different inductors and capacitors are typically used. However, the harmonic fluctuation cannot accurately determine whether the distribution position of harmonic energy has shifted compared to the adjacent preceding period. Therefore, further analysis of the energy distribution position shift of the 3rd, 5th, and 7th harmonics is required.

[0046] Based on the above analysis, for single harmonics, the harmonic deviation of each period is obtained by monitoring the degree of energy distribution shift of the single harmonic in the amplitude spectrum of the current signal between each period and its adjacent previous period. The specific process is as follows: Extract the frequency of the peak value closest to the single harmonic from the amplitude spectrum of the current signal in each cycle; Calculate the difference between the frequency extracted from the previous adjacent period and the frequency extracted from each period; The harmonic deviation of each cycle is the ratio of the difference to the frequency extracted from the adjacent previous cycle.

[0047] In this embodiment, the amplitude spectrum is first obtained by performing a Fourier transform on the time-domain current signal. Then, the peak value in the amplitude spectrum is obtained by using an automatic multi-scale peak search algorithm. Finally, the frequency of the peak value closest to the single harmonic is extracted from the amplitude spectrum. The Hilbert transform is a well-known technique and will not be described in detail in this application.

[0048] It should be added that the frequency of a single harmonic energy will not change drastically between two adjacent cycles, and the theoretical range of the harmonic deviation is (-1, 1).

[0049] It should be noted that the positive or negative value of the harmonic deviation only indicates the direction of the harmonic energy deviation. When the harmonic deviation is positive, it means that the frequency of the single harmonic energy in each cycle is lower than that of the previous cycle. Conversely, it means that the frequency of the single harmonic energy in each cycle is higher than that of the previous cycle.

[0050] Step 3.3: Combine the harmonic fluctuation degree and the harmonic deviation degree to obtain the adjustment coefficient of the capacitor in the LC filter circuit, so as to adjust the capacitor in each cycle.

[0051] The greater the harmonic fluctuation and the greater the harmonic deviation, the greater the degree of harmonic fluctuation between each cycle and its adjacent preceding cycle. Furthermore, the greater the deviation of the harmonic energy distribution within each cycle from its adjacent preceding cycle, the more difficult it is for the LC filter circuit to accurately extract single harmonic currents using the resonant frequency within the adjacent preceding cycle. This leads to a decrease in the harmonic current extraction rate and utilization rate. Therefore, dynamic adjustment of the resonant frequency within the adjacent preceding cycle is necessary. The relationship between the resonant frequency and the capacitance satisfies the following formula: In the formula, The resonant frequency of the LC filter is represented by L and C, which represent the inductance and capacitance of the LC filter circuit, respectively, and are both inversely proportional to the square of the resonant frequency. Since the resonant frequency of the LC filter circuit is determined by the inductance and capacitance, it cannot be directly adjusted. Therefore, this application achieves dynamic adjustment of the resonant frequency by adjusting the capacitance.

[0052] Based on the above analysis, for single harmonics, the adjustment coefficient of the capacitor in the LC filter circuit is obtained by combining the harmonic fluctuation and harmonic deviation of each cycle, so as to adjust the capacitor in each cycle. The specific process is as follows: Calculate the product of harmonic deviation and harmonic fluctuation for each period; The adjustment coefficient of the capacitor in the LC filter circuit is positively correlated with the product. The product of the adjustment coefficient of the capacitor in the LC filter circuit and the value of the capacitor in the previous cycle is used as the adjusted capacitor value in each cycle.

[0053] In this embodiment, the square of the sum of the product and 1 is used as the adjustment coefficient for the capacitor in the LC filter circuit. Since the square of the resonant frequency of the LC filter circuit is negatively correlated with the capacitance, the adjustment coefficient is calculated in a squared form to adjust the capacitor.

[0054] It should be noted that: if the adjusted capacitance value in each cycle is greater than the upper limit of the capacitance adjustment range, the adjusted capacitance value in each cycle will be assigned the upper limit of the capacitance adjustment range; conversely, if the adjusted capacitance value in each cycle is less than the lower limit of the capacitance adjustment range, the adjusted capacitance value in each cycle will be assigned the lower limit of the capacitance adjustment range. The capacitance adjustment range is determined based on the capacitor's model.

[0055] It should be noted that: when the harmonic deviation of each cycle is negative, it indicates that the frequency of the single harmonic energy in each cycle is higher than that in the adjacent previous cycle. In this case, the resonant frequency needs to be increased, and the capacitor should be decreased. Conversely, when the harmonic deviation of each cycle is positive, it indicates that the frequency of the single harmonic energy in each cycle is lower than that in the adjacent previous cycle. In this case, the resonant frequency needs to be decreased, and the capacitor should be increased. The larger the absolute value of the product, the greater the adjustment of the capacitor. If the harmonic deviation is 0, it means that the distribution position of the harmonic energy in each cycle has not shifted compared to the adjacent previous cycle, so no adjustment of the capacitor is required.

[0056] It should be noted that if a parameter is too large or too small, it is usually corrected by subtracting or adding an adjustment factor from the original coefficient 1. In this application, due to the shift in the distribution position of harmonic energy, the resonant frequency of the LC filter circuit may no longer be applicable. Therefore, the capacitor needs to be adjusted appropriately. The product is used as an adjustment factor to calculate the adjustment coefficient, which is then used to adjust the capacitor to meet the capacitance requirements in each cycle, thereby improving the harmonic current extraction rate. A schematic diagram of the capacitor adjustment process is shown below. Figure 2 As shown.

[0057] Step 4: Adjust the resonant frequency of the LC filter circuit; then, extract the harmonic current through the LC filter circuit with the adjusted resonant frequency for use by the low-voltage load.

[0058] For single harmonics, after obtaining the adjusted capacitance values ​​for each period, the capacitors need to be switched. Specifically, the difference between the adjusted capacitance value for each period and the capacitance value in the preceding period is rounded to the nearest integer and used as the switched capacitance value for each period. The unit of the switched capacitance value is μF.

[0059] By controlling the thyristor switch to quickly switch the required capacitance, the capacitor in the LC filter circuit is adjusted, thereby adjusting the resonant frequency of the LC filter circuit. The capacitor switching technique is well-known and will not be described in detail here.

[0060] When the resonant frequency of the LC filter circuit is matched with the single harmonic, the impedance to the single harmonic is basically 0, allowing the single harmonic current to pass through. However, it presents a high impedance to the fundamental wave and other harmonics, preventing the fundamental wave and other harmonics from passing through, thereby achieving efficient extraction of the single harmonic current.

[0061] The extracted harmonic currents are converted into stable low-voltage DC power by a DC-DC voltage regulator module and then connected to low-voltage loads such as lighting, heating, and monitoring. This completes the conversion of harmonic energy into usable electrical energy, improves the utilization rate of harmonic current in the distribution network, and achieves efficient utilization of harmonic energy in distribution networks with multiple DC source inputs. The DC-DC voltage regulator module is a known technology and will not be described further in this application.

[0062] In this embodiment, the 3rd, 5th, and 7th harmonic currents are extracted.

[0063] Based on the same inventive concept as the above method, this application embodiment also provides a harmonic energy utilization system for a multi-DC-source input distribution network, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above-described harmonic energy utilization methods for a multi-DC-source input distribution network.

[0064] In summary, this application, by analyzing the fluctuation of the current signal and evaluating whether to initiate resonant frequency adjustment in each cycle, can achieve intelligent initiation control of resonant frequency adjustment of the LC filter circuit. The subsequent complex adjustment process is only initiated when the current fluctuation is severe and the harmonic energy distribution may be shifted, thus avoiding unnecessary adjustments when the current is stable. Furthermore, by analyzing the similarity of current signals between two adjacent cycles for fault identification, extreme abnormal changes in the current waveform can be identified in a timely manner, avoiding the risk of secondary damage caused by capacitor adjustment under abnormal operating conditions. In the absence of faults, the similarity of current signals between two adjacent cycles quantifies the degree of change of the current signal in the time domain; the lower the current similarity, the more severe the current fluctuation and the more unstable the distribution of harmonic energy. The difference in single harmonic energy between two adjacent cycles accurately reflects the relative change of single harmonic energy between them. Furthermore, by combining current similarity and harmonic difference, the harmonic fluctuation degree is obtained, comprehensively characterizing the fluctuation features of the current signal from two dimensions: time-domain waveform similarity and frequency-domain harmonic content changes. This comprehensively quantifies the severity of harmonic fluctuations between each cycle and its preceding adjacent cycle, providing a crucial basis for subsequently determining the capacitor adjustment amplitude. Furthermore, by monitoring the degree of energy distribution shift of single harmonics in the amplitude spectrum, the harmonic energy shift caused by random fluctuations of multiple DC sources can be accurately reflected. This not only quantifies the magnitude of the positional shift of the harmonic energy distribution, but also clarifies the direction of the shift through the positive or negative sign of the harmonic deviation, providing key information for the subsequent adjustment of capacitor amplitude and direction. Furthermore, by obtaining adjustment coefficients through harmonic fluctuation and harmonic deviation, the adjustment amplitude of the capacitor can be dynamically adjusted according to the severity of harmonic fluctuations and the degree of displacement of the harmonic energy distribution position. This changes the resonant frequency of the LC filter circuit, enabling the resonant frequency of the LC filter circuit to dynamically track the actual distribution position of the harmonic energy. Thus, even when the random fluctuations of multiple DC sources cause the harmonic energy distribution position to shift, the circuit maintains a high efficiency in extracting harmonic current, significantly improving the utilization rate of harmonic energy.

Claims

1. A method for harmonic energy utilization in distribution networks with multiple DC source inputs, characterized in that, The method includes the following steps: Current signals are collected in real time by a current sensor installed on the main line of the distribution network and located before the LC filter circuit. The system presets the adjustment period for the resonant frequency of the LC filter circuit. It assesses whether to initiate resonant frequency adjustment based on the fluctuation of the current signal within each period. If initiated, it determines whether to issue a fault warning and terminate subsequent processing based on the similarity of the current signal between each period and its adjacent preceding period. If not terminated, it obtains the harmonic fluctuation degree of the single harmonic within each period based on the similarity of the current signal between each period and its adjacent preceding period, as well as the difference in single harmonic energy. For single harmonics, it obtains the harmonic deviation degree of each period by monitoring the energy distribution offset of the single harmonic in the amplitude spectrum of the current signal between each period and its adjacent preceding period. This is then combined with the harmonic fluctuation degree to obtain the adjustment coefficient of the capacitor in the LC filter circuit. The capacitor is adjusted within each period to adjust the resonant frequency of the LC filter circuit. Finally, the harmonic current is extracted from the LC filter circuit after resonant frequency adjustment for use by low-voltage loads.

2. The method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 1, characterized in that, The process for assessing whether to initiate resonant frequency adjustment is as follows: The maximum and minimum values ​​of the current signal in the positive half-cycle of each period are statistically analyzed. The ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the positive half-cycle ripple. The maximum and minimum values ​​of the current signal in the negative half-cycle valley in each cycle are statistically analyzed. The absolute value of the ratio of the difference between the maximum and minimum values ​​to the maximum value is recorded as the negative half-cycle fluctuation. The maximum value between the positive half-cycle fluctuation and the negative half-cycle fluctuation is denoted as the current fluctuation. If the current fluctuation exceeds a preset amplitude fluctuation threshold, the resonant frequency adjustment is initiated.

3. The method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 1, characterized in that, The method for determining whether to issue a fault warning and terminate subsequent processing is as follows: If the correlation coefficient of the current signal between each cycle and its adjacent previous cycle in the time domain is negative, a fault warning is issued and subsequent processing is terminated.

4. The method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 3, characterized in that, The process of obtaining the harmonic fluctuation degree is as follows: Calculate the difference in single harmonic energy of the current signal between each cycle and the previous cycle; the ratio of the difference to the single harmonic energy of the current signal in the previous cycle is denoted as the harmonic difference degree. The harmonic fluctuation degree is positively correlated with the harmonic difference degree and negatively correlated with the correlation coefficient.

5. A method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 4, characterized in that, The method for calculating the harmonic fluctuation degree is as follows: The correlation coefficient is shifted to a first positive number; the harmonic difference is mapped to a second positive number. The harmonic fluctuation is the normalized value of the ratio of the second positive number to the first positive number.

6. A method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 1, characterized in that, The process for obtaining the harmonic deviation is as follows: Extract the frequency of the peak value closest to the single harmonic from the amplitude spectrum of the current signal in each cycle; Calculate the difference between the frequency extracted from the previous adjacent period and the frequency extracted from each period; The harmonic deviation is the ratio of the difference to the frequency extracted from the adjacent previous cycle.

7. A method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 1, characterized in that, The process of obtaining the adjustment coefficient is as follows: Calculate the product of the harmonic deviation and the harmonic fluctuation. The adjustment coefficient is positively correlated with the product.

8. A method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 1, characterized in that, When adjusting the capacitor in each cycle, the product of the adjustment coefficient and the value of the capacitor in the adjacent previous cycle is used as the adjusted capacitor value in each cycle.

9. A method for harmonic energy utilization in a multi-DC-source input distribution network as described in claim 8, characterized in that, When adjusting the resonant frequency of the LC filter circuit, the rounded result of the difference between the adjusted capacitance value in each cycle and the capacitance value in the adjacent previous cycle is used as the switching capacitance value in each cycle.

10. A harmonic energy utilization system for a multi-DC-source input distribution network, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the harmonic energy utilization method for a multi-DC source input distribution network as described in any one of claims 1-9.

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