A micro-grid power quality global optimization method

Abstract

The application discloses a micro-grid power quality global optimization method, comprising the following steps: collecting real-time data, dividing the real-time data into several segments according to the frequency, and calculating the harmonic compensation capacity of each frequency segment according to the real-time data; according to the calculated harmonic compensation capacity, priority allocation is performed on the compensation order of the contaminated nodes in the micro-grid; the virtual impedance of the inverter and the injected damping resistance are adjusted, and the harmonic current and resonance phenomenon in the micro-grid are suppressed in the frequency segment; according to the adjusted virtual impedance and damping resistance, the node admittance matrix is updated, the compensation capacity of the inverter is monitored in real time, the real-time monitoring data is compared with the threshold value, if the threshold value is exceeded, the inverter is corrected, otherwise, no change is made. Through the frequency segment control, the pertinence and effect of harmonic suppression are improved, the frequency segment suppression of the micro-grid harmonic and high-frequency resonance is realized, the residual capacity of the inverter is dynamically matched with the harmonic compensation demand, and the safe and stable operation of the system is ensured.

Description

Technical Field

[0001] This invention relates to the field of power supply technology, and in particular to a method for global optimization of power quality in microgrids. Background Technology

[0002] With the transformation of the energy structure and the rapid development of distributed generation technology, microgrids, as a local power supply network integrating distributed power sources, energy storage devices, loads, and related protection and monitoring devices, have shown great advantages in improving energy utilization efficiency and enhancing grid reliability and flexibility. However, the integration of a large number of power electronic devices into microgrids, such as frequency converters, rectifiers, switching power supplies, and LED lighting, has made harmonic problems increasingly prominent, seriously affecting the power quality of microgrids.

[0003] Traditional harmonic mitigation methods primarily target single voltage levels, employing centralized or distributed filtering devices such as passive filters and active power filters (APFs). Passive filters are simple in structure and low in cost, but can only filter harmonics of specific orders and are prone to resonance with the power grid. While active power filters can dynamically compensate for harmonics, they are more expensive and face technical bottlenecks in large-capacity harmonic compensation. Traditional single-voltage-level mitigation methods cannot effectively address the problem of harmonic propagation across regions, resulting in poor harmonic mitigation performance. Furthermore, the propagation paths of harmonics in microgrids are complex and diverse, with differences in harmonic characteristics (such as frequency, amplitude, and phase) along different paths. Traditional mitigation methods struggle to accurately address different types of harmonic paths. Summary of the Invention

[0004] This application provides a global optimization method for power quality in microgrids. By using frequency band control, it improves the targeting and effectiveness of harmonic suppression, achieves frequency band suppression of harmonics and high-frequency resonances in microgrids, dynamically matches the remaining capacity of the inverter with the harmonic compensation requirements, and ensures the safe and stable operation of the system.

[0005] This application provides a global optimization method for power quality in microgrids, including:

[0006] S101, collect real-time data, divide the real-time data into several segments according to frequency, and calculate the harmonic compensation capacity of each frequency band according to the real-time data; the frequency band refers to the low frequency band, the mid frequency band and the high frequency band.

[0007] S102, Based on the calculated harmonic compensation capacity, prioritize the compensation order of polluted nodes in the microgrid;

[0008] S103 suppresses low-frequency harmonics in priority nodes by adjusting the virtual impedance of the inverter, and passively dissipates high-frequency resonances in priority nodes by calculating and injecting damping resistors.

[0009] S104 Updates the node admittance matrix based on the adjusted virtual impedance and damping resistance, monitors the inverter's compensation capacity in real time, compares the real-time monitoring data with the threshold, and corrects the inverter if the threshold is exceeded; otherwise, no change is made.

[0010] S201. Based on the collected real-time data, a connection diagram is drawn. Based on the power electronic transformer in the connection diagram, the transformer ratio and leakage inductance are added to the updated node admittance matrix to form a coupling admittance matrix. The admittance components of the distributed capacitance at the harmonic frequency are superimposed on the coupling admittance matrix to form a corrected coupling admittance matrix. The harmonic voltage amplification factor is calculated based on the corrected coupling admittance matrix. The harmonic voltage amplification factor is compared with a preset threshold to determine whether the harmonic propagation phenomenon exists across regions. If the harmonic voltage amplification factor is greater than the preset threshold, it indicates that the harmonic propagation phenomenon exists across regions. Conversely, if the harmonic voltage amplification factor is less than or equal to the preset threshold, it indicates that the harmonic propagation phenomenon does not exist across regions.

[0011] S202 uses a dual-channel impedance adjustment to make the fundamental current present a low impedance and the harmonic current present a high impedance, and detects the harmonic spectrum in the microgrid in real time and adjusts the impedance value according to the detection results.

[0012] S203 uses a sensor to detect power flow and adjusts the impedance according to the direction of power flow.

[0013] Preferably, the compensation capacity for the low-frequency band, mid-frequency band, and high-frequency band is calculated based on the collected real-time data; the formula for calculating the compensation capacity for the low-frequency band is: ,in, For harmonic compensation capacity of low-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. The formula for calculating the mid-frequency compensation capacity is: ,in, For harmonic compensation capacity of mid-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. The formula for calculating the high-frequency compensation capacity is: ,in, For harmonic compensation capacity of high-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage.

[0014] Preferably, the apparent power is the product of the effective value of the fundamental voltage and the effective value of the harmonic current in the microgrid, reflecting the equivalent power demand generated by the harmonic current under the action of the fundamental voltage, which includes both active power and reactive power that are actually done.

[0015] Preferably, the node admittance matrix is ​​a square matrix representing the relationship between node voltage and current in a power system. Its elements reflect the admittance between nodes, and a power network model is constructed through diagonal and off-diagonal elements.

[0016] Preferably, the formula for identifying harmonic cross-regional propagation based on the coupling admittance matrix is ​​as follows: ,in, This is the harmonic voltage amplification factor. The admittance of the coupling term between the AC and DC sides. The corrected coupling admittance matrix is ​​denoted by m, which represents the transformer turns ratio. A threshold is set based on the calculated harmonic voltage amplification factor. If the harmonic voltage amplification factor is greater than the preset threshold, it indicates that the harmonics are crossing regions. Conversely, if the harmonic voltage amplification factor is less than or equal to the preset threshold, it indicates that the harmonics are not crossing regions.

[0017] Preferably, the dual channels include a fundamental wave channel and a harmonic channel. The fundamental wave channel is obtained by using an algorithm to synchronously track the fundamental wave signal to obtain a synchronization signal, and a low impedance that allows the fundamental wave current to pass through is set based on the synchronization signal. The harmonic channel is obtained by using a filter to screen the harmonic current, and a high impedance that can impede the propagation of the harmonic current is set according to the harmonic current.

[0018] Preferably, the active power on the AC side and the DC side is calculated based on the data measured by the sensor. If the active power is positive, the flow from the AC side to the DC side is the forward flow. If the active power is negative, the flow from the AC side to the DC side is the reverse flow.

[0019] Preferably, in step S301, multiple paths are identified based on the data collected in real time;

[0020] S302, Generate a blocking strategy based on the identified multipaths;

[0021] S303, constructs an energy monitoring network based on the identified multipaths.

[0022] Preferably, the identified multipaths are classified into high-frequency paths, low-frequency paths, and resonant paths. The high-frequency paths are blocked using active filters, the low-frequency paths are blocked using passive filters, and the resonant paths are blocked using active damping resistors.

[0023] One or more technical solutions provided in this application have at least the following technical effects or advantages: By using frequency band control, the targeting and effectiveness of harmonic suppression are improved, frequency band suppression of microgrid harmonics and high-frequency resonances is achieved, the remaining capacity of the inverter is dynamically matched with the harmonic compensation requirements, the safe and stable operation of the system is ensured, the governance priority of key nodes is improved, resource allocation is optimized, the pollution of the power grid by harmonics is reduced, and the power quality is improved.

[0024] By adjusting the impedance through the coupling admittance matrix and dual channels, the cross-regional propagation path of harmonics is successfully blocked, reducing the harmonic pollution level on both the AC and DC sides. While blocking harmonics, the normal transmission of fundamental power is ensured, improving the overall operating efficiency of the system. The blocking impedance value is dynamically adjusted according to the real-time detected harmonic spectrum and power flow direction to achieve more precise harmonic suppression.

[0025] By setting up dedicated monitoring points for different types of harmonic paths (high frequency, low frequency, resonance), power quality problems on each path can be captured more accurately. When power quality problems or faults occur in the power grid, appropriate blocking devices and parameters can be selected based on the harmonic characteristics and power quality problems on different paths to achieve precise management, effectively improve harmonic blocking efficiency, reduce equipment losses and the impact on power, thereby improving the power quality of the entire power grid. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a global optimization method for power quality in a microgrid according to the present invention.

[0027] Figure 2 This is a schematic diagram illustrating the process of constructing the coupling admittance matrix for this invention;

[0028] Figure 3 This is a schematic diagram illustrating the process of constructing an energy monitoring network according to the present invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more complete description of this application will be given below with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a more thorough and complete understanding of the disclosure of the present invention.

[0030] It should be noted that the terms "vertical," "horizontal," "up," "down," "left," "right," and similar expressions used in this article are for illustrative purposes only and do not represent the only possible implementation.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] Example 1: Figure 1 This is a flowchart illustrating a global power quality optimization method for microgrids according to an embodiment of the present invention, including:

[0033] S101, collect real-time data, divide the real-time data into several segments according to frequency, and calculate the harmonic compensation capacity of each frequency band according to the real-time data; the frequency band refers to the low frequency band, the mid frequency band and the high frequency band.

[0034] Furthermore, the frequency information of harmonic current and fundamental voltage in the microgrid, as well as the dynamic frequency change of inverter output power, are collected. Harmonic and fundamental frequencies are monitored using a Fluke 435 power quality analyzer. For harmonic frequencies, the current and voltage signals are decomposed in real time using a Fast Fourier Transform (FFT) to extract the frequency components of the 3rd to 25th harmonics. The sampling frequency and frequency resolution of the power quality analyzer, such as the Fluke 435, are set. For the fundamental frequency, the zero-crossing detection method is used to track the fundamental frequency in real time. This method captures the zero-crossing points of the fundamental voltage or current signal (the moment the waveform changes from positive to negative or vice versa) in real time. A timer records the time interval between adjacent zero-crossing points, and the fundamental frequency is calculated based on the time interval. Inverter output power is collected using a DC-side current sensor and an AC-side voltage transformer. Smart meters are installed next to the DC-side current sensor and AC-side voltage transformer. The collected data is converted by an analog-to-digital converter, and the instantaneous power is calculated. The collected data is transmitted to the central controller via a wireless communication device and stored in a database.

[0035] The total harmonic compensation capacity is calculated based on the received real-time data. The calculation formula is as follows: ,in, The total harmonic compensation capacity of the node is given by and the apparent power is given by . These are the three-phase system coefficients, derived from the geometric relationship between line voltage and phase voltage in a three-phase balanced circuit. This represents the effective value of the fundamental voltage of the microgrid. Let represent the amplitude of the i-th harmonic current at node , where i is the harmonic order (usually an odd number; even-order harmonics are generally smaller due to symmetry and can be ignored), and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. The apparent power generated by the harmonic current under the fundamental voltage, calculated by the above formula, reflects the total power that the harmonic mitigation device needs to output. The apparent power is the product of the effective value of the fundamental voltage and the effective value of the harmonic current in the microgrid, reflecting the equivalent power demand generated by the harmonic current under the action of the fundamental voltage. It includes both the active power that actually does work and the reactive power used to establish the electromagnetic field but does not consume energy. The apparent power is the total capacity that the harmonic mitigation device (such as APF) needs to output. Its value determines the ability of the compensation equipment to suppress voltage distortion and reduce line losses. The harmonics are divided into three segments according to frequency: low frequency, mid frequency, and high frequency. The compensation capacity of each frequency segment is calculated. The low frequency segment contains harmonic components (such as the 3rd, 5th, 7th, and 9th harmonics) generated by nonlinear loads (such as frequency converters and rectifiers). The formula for calculating the compensation capacity of the low frequency segment is: ,in, For harmonic compensation capacity of low-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. Low-frequency harmonics have high energy and significantly affect equipment such as transformers and motors, requiring priority compensation. The intermediate frequency band includes intermediate frequency harmonics (such as the 11th, 13th, 15th, 17th, and 19th harmonics), generated by equipment such as electric arc furnaces and intermediate frequency induction furnaces. The formula for calculating the compensation capacity of the intermediate frequency band is: ,in, For harmonic compensation capacity of mid-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. Mid-frequency harmonics have a significant impact on equipment such as cable insulation and capacitors, requiring targeted compensation. The high-frequency band includes high-frequency harmonics (such as the 21st, 23rd, and 25th harmonics), generated by equipment such as switching power supplies and LED lighting. The formula for calculating the high-frequency band compensation capacity is: ,in, For harmonic compensation capacity of high-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. High-frequency harmonics attenuate faster, but they significantly interfere with precision electronic equipment and require appropriate compensation.

[0036] S102, Based on the calculated harmonic compensation capacity, prioritize the compensation order of polluted nodes in the microgrid;

[0037] Specifically, based on the calculated harmonic compensation capacity, and given the limited capacity, the priority for power quality management is allocated by analyzing the degree of harmonic pollution at nodes and the remaining capacity of the inverter. Simultaneously, it ensures that the inverter operates within a safe threshold (avoiding overload), achieving efficient utilization of compensation resources. The harmonics used for compensation are transmitted to the inverter, which generates a compensation current with the same amplitude but opposite phase to the harmonic current, thereby offsetting the harmonic pollution generated by the load. Constraints are set to ensure the inverter has a safety margin to cope with dynamic harmonic fluctuations or sudden load changes. The formula for the constraints is: ,in, The total harmonic compensation capacity of the node, This represents the remaining available capacity of the inverter at the node, which is the inverter's rated capacity minus the currently compensated capacity. For safety reasons, in this embodiment... =0.8, used to prevent inverter overload. If a node does not meet the constraints, the filter parameters need to be adjusted or phased compensation should be performed (compensate the low-frequency band first, then the high-frequency band). The relative severity of harmonic pollution at each node is reflected by calculating the ratio of the compensation requirement of each node to the remaining capacity of the inverter. The formula for calculating the ratio is: ,in, To compensate for the ratio of demand to the remaining capacity of the inverter, The larger the value, the more severe the harmonic pollution at node j relative to the inverter capacity, and the more priority it needs to be addressed. The total harmonic compensation capacity of the node, To determine the remaining available capacity of the inverter at each node, allocate all nodes... Normalization is performed to obtain dynamic weights. Based on the dynamic weights and load types, a threshold range is set, including a maximum threshold and a minimum threshold. Nodes are divided into three levels: high-priority nodes, medium-priority nodes, and low-priority nodes. High-priority nodes have dynamic weights greater than the maximum threshold, are severely polluted by harmonics, and are load-sensitive (such as hospital CT scanners). Sufficient compensation capacity must be allocated immediately, even at the expense of the treatment effect of some low-priority nodes. Medium-priority nodes have dynamic weights greater than the minimum threshold and less than or equal to the maximum threshold. After meeting the needs of high-priority nodes, the remaining capacity is allocated according to the weight ratio. Low-priority nodes have dynamic weights less than or equal to the minimum threshold. Compensation is only performed when the inverter capacity is sufficient, or through time-sharing compensation (such as during low-load periods at night).

[0038] S103 suppresses low-frequency harmonics in priority nodes by adjusting the virtual impedance of the inverter, and passively dissipates high-frequency resonances in priority nodes by calculating and injecting damping resistors.

[0039] Furthermore, for low-frequency harmonic suppression, low-frequency harmonics (such as the 3rd, 5th, 7th, and 11th harmonics) are the most common harmonic components in the power grid, mainly generated by nonlinear loads. By adjusting the virtual impedance of the inverter, the impedance characteristics of the inverter to specific frequency harmonics are changed, making it exhibit a high impedance state, thereby reducing harmonic current flowing into the power grid. Harmonic currents and voltages in the power grid are collected using current transformers and voltage transformers. A particle swarm optimization (PSO) algorithm is used to dynamically adjust the virtual impedance of the inverter. For nodes with severe harmonic pollution, their virtual impedance is increased to... Rapidly suppressing harmonics; for high-frequency resonant damping, high-frequency resonance is usually caused by the interaction of capacitive components (such as long cables, capacitor banks) and inductive components (such as transformer leakage inductance) in the power grid, forming an impedance peak at a specific frequency (such as 5.5kHz), leading to a sharp amplification of voltage or current, threatening equipment safety. By injecting damping resistors, the resonant energy can be consumed, the impedance peak can be reduced, and thus the resonance can be suppressed. The impedance characteristics of the power grid in the high-frequency band can be identified through a small-signal injection model. Based on the magnitude of the harmonic current at the resonant frequency, the formula for calculating the magnitude of the injected damping resistor is as follows: ,in, The value of the injected damping resistor is used to suppress high-frequency resonance in the power grid. This is a hard upper limit value for the damping resistor, set according to the system capacity and the equipment's withstand voltage capability. The adjustment factor is used to calibrate the calculated value of the damping resistance. The harmonic voltage spectrum To determine the rated capacity of the system at the resonant frequency, the damping resistor value is superimposed on the virtual impedance of the inverter, which is equivalent to adding a resistive load at the resonant frequency to consume resonant energy. In the low-frequency range, harmonic suppression is the main function, and active blocking is achieved by adjusting the virtual impedance. In the high-frequency range, resonant damping is the main function, and passive energy consumption is achieved by injecting damping resistors.

[0040] S104 Updates the node admittance matrix based on the adjusted virtual impedance and damping resistance, monitors the inverter's compensation capacity in real time, compares the real-time monitoring data with the threshold, and corrects the inverter if the threshold is exceeded; otherwise, no change is made.

[0041] Specifically, the node admittance matrix is ​​a square matrix representing the relationship between node voltage and current in a power system. Its elements reflect the admittance between nodes (i.e., the reciprocal of the impedance). A power network model is constructed using diagonal elements (self-admittance, including equivalent virtual impedances of lines, loads, and inverters) and off-diagonal elements (mutual admittance, reflecting coupling between nodes). The calculated virtual impedance and damping resistance are input into the node admittance matrix to update it, using the following formula: = ,in, This represents the nodal admittance matrix after the virtual impedances are superimposed. This is the original nodal admittance matrix. The inverter equivalent virtual resistance at node k is used to regulate the active power distribution. The inverter equivalent virtual reactance at node k is used to regulate reactive power distribution. = ,in, This is the nodal admittance matrix updated using virtual impedance and damping resistance. This represents the nodal admittance matrix after the virtual impedances are superimposed. To determine the required damping resistor value, the global admittance matrix is ​​updated using sparse matrix storage technology based on the above formula to ensure computational efficiency. An overload threshold is set according to the inverter parameters. By monitoring the inverter's compensation capacity, the compensation capacity is compared with the overload threshold. If the compensation capacity exceeds the overload threshold, the inverter is dynamically corrected by transferring 20% ​​of the overload inverter's compensation task (decomposed by harmonic order) to a redundant inverter.

[0042] The technical solutions described in the above embodiments of this application have at least the following technical effects or advantages: By using frequency band control, the targeting and effectiveness of harmonic suppression are improved, frequency band suppression of microgrid harmonics and high-frequency resonances is achieved, the remaining capacity of the inverter is dynamically matched with the harmonic compensation requirements, the safe and stable operation of the system is ensured, the governance priority of key nodes is increased, resource allocation is optimized, the pollution of the power grid by harmonics is reduced, and the power quality is improved.

[0043] Example 2: Based on Example 1 above, in a microgrid, harmonics propagate between different voltage levels through transformers. Example 1 only addresses single-voltage-level mitigation, leading to a harmonic amplification effect across regions, such as... Figure 2 As shown.

[0044] S201. Based on the collected real-time data, a connection diagram is drawn. Based on the power electronic transformer in the connection diagram, the transformer ratio and leakage inductance are added to the updated node admittance matrix to form a coupling admittance matrix. The admittance components of the distributed capacitance at the harmonic frequency are superimposed on the coupling admittance matrix to form a corrected coupling admittance matrix. The harmonic voltage amplification factor is calculated based on the corrected coupling admittance matrix. The harmonic voltage amplification factor is compared with a preset threshold to determine whether the harmonic propagation phenomenon exists across regions. If the harmonic voltage amplification factor is greater than the preset threshold, it indicates that the harmonic propagation phenomenon exists across regions. Conversely, if the harmonic voltage amplification factor is less than or equal to the preset threshold, it indicates that the harmonic propagation phenomenon does not exist across regions.

[0045] Based on the collected data, Visio was used to draw the connection diagram between the AC and DC sides of the microgrid. On the AC side, connection points for both 10kV and 400V voltage levels were marked, while on the DC side, connection points for ±750V and 380V were marked. The diagram also clearly marked the locations of power electronic transformers (PETs), distributed power sources (including photovoltaic power generation equipment and energy storage devices), and loads (distinguishing between critical and non-critical loads), making the connection relationships between each device readily apparent. In the microgrid, the AC and DC sides are connected through power electronic transformers (PETs). The transformer turns ratio and leakage inductance affect the propagation of harmonics. The transformer turns ratio determines the voltage conversion relationship between the AC and DC sides, while the leakage inductance generates inductive reactance when harmonic currents pass through, hindering current flow. To reflect the coupling relationship between the AC and DC sides in the admittance matrix, the updated node admittance matrix was used as the basis... Based on this, the transformer turns ratio and leakage inductance are increased to form a coupling admittance matrix. This matrix connects the inductive reactance of the leakage inductance in parallel with the DC-side admittance calculated by the turns ratio, and then takes the reciprocal to obtain the coupling admittance value. Through this value, the coupling admittance matrix can quantify the influence of transformer physical parameters on harmonic propagation across regions. The degree of obstruction to harmonic propagation from the AC side to the DC side increases, thus providing a theoretical basis for formulating harmonic blocking strategies. A modified coupling admittance matrix is ​​formed by superimposing the admittance component of the distributed capacitance at the harmonic frequency onto the coupling admittance matrix. This admittance component is the imaginary unit multiplied by the harmonic angular frequency and then by the distributed capacitance value. The cross-regional propagation of harmonics is identified based on the coupling admittance matrix, using the following formula: ,in, Harmonic voltage amplification factor measures the degree to which the voltage amplitude is amplified when a harmonic of a specific order h propagates from the AC side to the DC side. The admittance of the coupling term between the AC and DC sides. The corrected coupling admittance matrix is ​​denoted by m, which represents the transformer turns ratio. A threshold is set based on the calculated harmonic voltage amplification factor. If the harmonic voltage amplification factor is greater than the preset threshold, it indicates that the harmonics are crossing regions. Conversely, if the harmonic voltage amplification factor is less than or equal to the preset threshold, it indicates that the harmonics are not crossing regions.

[0046] S202 uses a dual-channel impedance adjustment to make the fundamental current present a low impedance and the harmonic current present a high impedance, and detects the harmonic spectrum in the microgrid in real time and adjusts the impedance value according to the detection results.

[0047] Furthermore, a dual-channel adjustment is used, comprising a fundamental frequency channel and a harmonic channel. For the fundamental frequency channel, a phase-locked loop (PLL) is used to synchronously track the input fundamental frequency signal. The PLL can track the phase and frequency of the input signal in real time, ensuring that the output signal remains synchronized with the fundamental frequency signal. A low impedance is set based on the obtained synchronization signal. This low impedance allows the fundamental frequency current to pass smoothly, reducing energy loss during transmission and improving the fundamental frequency power transmission efficiency. For the harmonic channel, a bandpass filter is used to filter out harmonic signals within a specified frequency range, thereby eliminating the fundamental frequency and other harmonic signals. Interference from unrelated frequency signals is eliminated. Based on the detected harmonic current, a high impedance is output, which hinders the propagation of the harmonic current. A threshold for the harmonic current amplitude is set. When the detected harmonic current amplitude exceeds the threshold, an impedance switching mechanism is triggered. A proportional-integral (PI) control algorithm is used to switch the equivalent impedance from the fundamental channel to the harmonic channel. After the equivalent impedance is switched to the high impedance value of the harmonic channel, according to Ohm's law, under a constant harmonic voltage, the high impedance will limit the passage of the harmonic current, thereby effectively suppressing the further propagation of the harmonic current and preventing the harmonic current from causing greater damage to the equipment in the system.

[0048] The system uses a Fast Fourier Transform (FFT) algorithm to detect harmonic spectra in real time, identify the dominant harmonic order, and obtain its amplitude information. If a harmonic of a specific order is detected during system operation and its amplitude exceeds a preset threshold, it indicates that the harmonic poses a significant threat to the system. In this case, the system will increase the blocking impedance for this specific harmonic order to a higher level to further enhance its suppression effect, prevent damage to system equipment, and ensure stable system operation. When a harmonic of a different order is detected and its amplitude exceeds its preset threshold, the system will increase the blocking impedance for this harmonic order to a specific high impedance value to specifically suppress the harmonic and reduce its propagation and impact in the system. For other harmonic orders that do not exceed the preset threshold, the system will maintain its blocking impedance at a basic and fixed value.

[0049] S203 uses a sensor to detect power flow and adjusts the impedance according to the direction of power flow;

[0050] Specifically, current sensors and voltage sensors are installed on the AC and DC sides of the power electronic transformer (PET), respectively. The current and voltage sensors are used to acquire the current and voltage data of the AC and DC sides in real time. The active power on the AC and DC sides is calculated according to the active power calculation formula. The direction of power flow is determined by the sign of the active power. Flow from the AC side to the DC side is considered positive flow, and vice versa. When the power flow direction is detected to be positive, the system issues an impedance adjustment command to increase the blocking impedance on the DC side while keeping the blocking impedance on the AC side unchanged. When the power flow direction is detected to be reverse, the blocking impedance on the AC side is increased while the blocking impedance on the DC side remains unchanged.

[0051] The technical solutions in the above embodiments of this application have at least the following technical effects or advantages: by adjusting the impedance through the coupling admittance matrix and dual channels, the cross-regional propagation path of harmonics is successfully blocked, the harmonic pollution level on the AC side and DC side is reduced, and while blocking harmonics, the normal transmission of fundamental power is ensured, thereby improving the overall operating efficiency of the system. The blocking impedance value is dynamically adjusted according to the real-time detected harmonic spectrum and power flow direction to achieve more precise harmonic suppression.

[0052] Example 3: Based on Examples 1 and 2 above, this example identifies multipath harmonic pollution and blocks it through multiple paths. Based on the multipath blocking and global power quality optimization framework, a power monitoring network is constructed, such as... Figure 3 As shown.

[0053] S301 identifies multiple paths based on real-time collected data;

[0054] Furthermore, the real-time acquired data includes harmonics, voltage, frequency, three-phase imbalance, and reactive power. For three-phase imbalance monitoring, a three-phase imbalance monitoring device is deployed at the feeder outlet. The acquired data is preprocessed to remove noise and abnormal data. The acquired data is then input into the intelligent quality analysis software Fluke 435. Fluke 435 calculates the Poynting energy flow density of each branch. For each branch, its Poynting energy flow density is calculated as a percentage of the total energy in the microgrid, using the following formula: ,in, Let i be the energy percentage of the i-th branch. Let be the Poynting energy flux density of the i-th branch. To calculate the total energy flow density, a percentage threshold is set for each term when summing the Poynting energy flow density of all branches (from branch 1 to branch n) in the microgrid. The calculated energy percentage is compared with the percentage threshold, and paths with energy percentages greater than the threshold are marked as critical paths. The impedance matching degree is obtained using the node admittance matrix based on the marked critical paths. The coherence between different paths is calculated using a cross-correlation function, which describes the similarity of harmonic signals between different paths. The cross-correlation function is existing technology and will not be elaborated here. The formula for calculating the path weight based on energy percentage, coherence, and impedance matching degree is as follows: + + ,in, For path weights, Let i be the energy percentage of the i-th branch. Let the coherence between the i-th branch and the j-th branch be denoted as . For impedance matching, , and These are the energy proportion coefficient, the average coherence coefficient, and the impedance matching coefficient, respectively. =1.

[0055] S302, Generate a blocking strategy based on the identified multipaths;

[0056] Specifically, the identified paths are classified into high-frequency paths, low-frequency paths, and resonant paths. High-frequency paths are characterized by high frequency and rapid changes, and their electrical parameters are also more complex, requiring high response speed and filtering performance from the blocking devices. Active filters are used as blocking devices for high-frequency paths. Low-frequency paths are relatively stable with smaller frequency changes, but their energy is larger, so passive filters are used as blocking devices for low-frequency paths. Resonant paths are paths in the power grid where resonance occurs. When the harmonic frequency is close to the natural frequency of the power grid, resonance will occur, leading to amplification of harmonic currents and causing serious damage to power grid equipment. Active damping resistors are used to block resonant paths. The parameters of the selected blocking devices are optimized to improve the blocking effect, reduce equipment losses, and minimize the impact on power.

[0057] S303, Construct an energy monitoring network based on the identified multipaths;

[0058] Furthermore, based on the identified path type, monitoring points are set up at key nodes of each path. Monitoring points are also set up at the beginning, middle, and end of high-frequency paths to comprehensively monitor the propagation and changes of high-frequency harmonics in the path. For resonant paths, monitoring points are added at the nodes where resonance occurs and in the surrounding areas to detect resonance phenomena in a timely manner. In combination with the microgrid topology, monitoring points are set up at locations such as buses, feeders, and transformer output terminals to comprehensively understand the power quality status of various parts of the power grid. At the same time, monitoring points are avoided from being too concentrated or too dispersed to improve the coverage efficiency and data representativeness of the monitoring network. Monitoring equipment is installed at the monitoring points, and the system is integrated with the installed monitoring equipment to form a power monitoring network.

[0059] The technical solutions described in the above embodiments of this application have at least the following technical effects or advantages: setting up dedicated monitoring points for different types of harmonic paths (high frequency, low frequency, resonance) can more accurately capture power quality problems on each path. When power quality problems or faults occur in the power grid, appropriate blocking devices and parameters can be selected according to the harmonic characteristics and power quality problems on different paths to achieve precise management, effectively improve harmonic blocking efficiency, reduce equipment losses and the impact on power, thereby improving the power quality of the entire power grid.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for global optimization of power quality in microgrids, characterized in that, include: S101: Collect real-time data, divide the real-time data into several segments according to frequency, and calculate the harmonic compensation capacity of each frequency segment based on the real-time data. The frequency bands referred to are low frequency band, mid frequency band, and high frequency band; S102, Based on the calculated harmonic compensation capacity, prioritize the compensation order of polluted nodes in the microgrid; S103 suppresses low-frequency harmonics in priority nodes by adjusting the virtual impedance of the inverter, and passively dissipates high-frequency resonances in priority nodes by calculating and injecting damping resistors. S104 Updates the node admittance matrix based on the adjusted virtual impedance and damping resistance, monitors the inverter's compensation capacity in real time, compares the real-time monitoring data with the threshold, and corrects the inverter if the threshold is exceeded; otherwise, no change is made. S201. Based on the collected real-time data, draw a connection diagram. Based on the power electronic transformer in the connection diagram, add the transformer ratio and leakage inductance to the updated node admittance matrix to form a coupling admittance matrix. Superimpose the admittance components of the distributed capacitance at the harmonic frequency on the coupling admittance matrix to form a corrected coupling admittance matrix. Calculate the harmonic voltage amplification factor based on the corrected coupling admittance matrix. Compare the harmonic voltage amplification factor with a preset threshold to determine whether the harmonic propagation phenomenon exists across regions. If the harmonic voltage amplification factor is greater than the preset threshold, it indicates that the harmonics have a cross-region phenomenon; conversely, if the harmonic voltage amplification factor is less than or equal to the preset threshold, it indicates that the harmonics do not have a cross-region phenomenon. S202 If harmonics exhibit cross-regional phenomena, dual channels are used to adjust the impedance, resulting in low impedance for the fundamental current and high impedance for the harmonic current. The harmonic spectrum in the microgrid is detected in real time, and the impedance value is adjusted based on the detection results. S203 uses a sensor to detect power flow and adjusts the impedance according to the direction of power flow.

2. The microgrid power quality global optimization method as described in claim 1, characterized in that, The compensation capacity for the low-frequency band, mid-frequency band, and high-frequency band is calculated based on the collected real-time data. The formula for calculating the compensation capacity for the low-frequency band is as follows: ,in, For harmonic compensation capacity of low-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. The formula for calculating the mid-frequency compensation capacity is: ,in, For harmonic compensation capacity of mid-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage. The formula for calculating the high-frequency compensation capacity is: ,in, For harmonic compensation capacity of high-frequency nodes, For the three-phase system coefficients, This represents the effective value of the fundamental voltage of the microgrid. Let be the amplitude of the i-th harmonic current at node , where i is the harmonic order and n is the highest harmonic order involved in the calculation. Let be the phase angle of the i-th harmonic current relative to the fundamental voltage.

3. The global power quality optimization method for microgrids as described in claim 1, characterized in that, The node admittance matrix is ​​a square matrix in a power system that represents the relationship between node voltage and current. Its elements reflect the admittance between nodes, and a power network model is constructed through diagonal and off-diagonal elements.

4. The microgrid power quality global optimization method as described in claim 1, characterized in that, The formula for harmonic voltage amplification factor is: ,in, This is the harmonic voltage amplification factor. The admittance of the coupling term between the AC and DC sides. is the corrected coupling admittance matrix, and m is the transformer turns ratio.

5. The microgrid power quality global optimization method as described in claim 1, characterized in that, The dual channels include a fundamental wave channel and a harmonic channel. The fundamental wave channel uses an algorithm to synchronously track the fundamental wave signal to obtain a synchronization signal, and sets a low impedance that allows the fundamental wave current to pass through based on the synchronization signal. The harmonic channel uses a filter to screen the harmonic current, and sets a high impedance that can impede the propagation of the harmonic current based on the harmonic current.

6. The microgrid power quality global optimization method as described in claim 1, characterized in that, The active power on the AC and DC sides is calculated based on the data measured by the sensor. If the active power is positive, the flow from the AC side to the DC side is called positive flow. If the active power is negative, the flow from the AC side to the DC side is called reverse flow.

7. The microgrid power quality global optimization method as described in claim 1, characterized in that, S301 identifies multiple paths based on real-time collected data; S302, Generate a blocking strategy based on the identified multipaths; S303, constructs an energy monitoring network based on the identified multipaths.

8. The microgrid power quality global optimization method as described in claim 7, characterized in that, The identified multipaths are classified into high-frequency paths, low-frequency paths, and resonant paths. The high-frequency paths are blocked using active filters, the low-frequency paths are blocked using passive filters, and the resonant paths are blocked using active damping resistors.

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