A microgrid harmonic current distribution method and electronic equipment

Abstract

This invention discloses a method and electronic device for harmonic current distribution in a microgrid. The method acquires the terminal voltage and grid-side current of each micro-source inverter in the microgrid, and calculates the actual power through conjugate operations. A second-order generalized integrator is used to extract the fundamental current component from the grid-side current to obtain the harmonic current and calculate its effective value. The remaining capacity of each inverter is calculated based on its rated capacity and actual power. Based on the remaining capacity, a consensus algorithm is used to calculate the weighting coefficient and global consensus control quantity, and then the harmonic virtual impedance is calculated. The harmonic virtual impedance is superimposed with the fundamental virtual impedance and applied to the voltage loop and current loop control to achieve harmonic current distribution proportional to the remaining capacity. This invention achieves reasonable distribution of harmonic current in microgrids with high penetration of new energy sources, avoids inverter overload, improves power quality, has a simple implementation scheme, requires no multi-harmonic resonant controller, has low computational complexity, is easy to deploy in engineering, and is suitable for both off-grid and grid-connected operation scenarios.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of energy storage converters, and in particular to a microgrid harmonic current distribution method and electronic equipment. Background Technology

[0002] With the rapid growth of installed capacity of new energy sources such as photovoltaics and wind power, requirements for local consumption of distributed energy have been put forward, and the construction of microgrids has also entered a stage of rapid development. Compared with traditional grid-connected inverters, grid-connected inverters have been increasingly widely used in microgrids due to their better voltage support and frequency regulation capabilities.

[0003] However, microgrids typically contain nonlinear loads that generate various harmonic currents. When a microgrid is in islanded operation, these harmonic currents can cause voltage distortion and degrade power quality. More seriously, if harmonic currents are not properly distributed among the micro-inverters, they can lead to overloads of some inverters, affecting the safe and stable operation of the system.

[0004] Currently, some technical solutions exist for the harmonic current distribution problem in microgrids. For example, harmonics and reactive current are distributed proportionally to remaining capacity. However, this solution is only suitable for grid-connected inverters, relying on grid voltage support and cannot be used in off-grid environments, limiting its application scenarios. Additionally, there are solutions based on consensus algorithms to achieve harmonic power sharing control based on the inverter's remaining capacity. However, in microgrids with high renewable energy penetration, the output of energy sources such as photovoltaics and wind turbines is significantly affected by weather, and the fundamental power may not be accurately distributed according to the droop factor. Under conditions of large fluctuations in wind and solar power output, this solution may cause microgrid system instability, affecting the safe operation of the grid.

[0005] In addition, particle swarm optimization (PSO) can be used to optimize the virtual impedance of inverters to improve the power quality of microgrids. However, PSO is a global optimization algorithm with a large computational load and long computation time. When wind and solar power output fluctuates significantly, the system state changes rapidly, making it difficult for this method to converge to the optimal solution within a finite time, thus failing to meet the requirements of real-time control. Summary of the Invention

[0006] The main technical problem solved by the embodiments of the present invention is to provide a microgrid harmonic current distribution method and electronic device, which can overcome at least some of the defects of existing microgrid harmonic current distribution schemes.

[0007] In a first aspect, an embodiment of the present application provides a micro-grid harmonic current distribution method, comprising the following steps: obtaining terminal voltages and grid-side currents of each micro-source inverter in the micro-grid, and calculating actual powers of the micro-sources; extracting a fundamental current component from the grid-side currents, and obtaining harmonic currents according to differences between the grid-side currents and the fundamental current component, and calculating effective values of the harmonic currents; calculating residual capacities of the micro-sources according to rated capacities and the actual powers of the micro-sources; calculating harmonic virtual impedances of the micro-sources by a consistency algorithm based on the residual capacities of the micro-sources; and applying the harmonic virtual impedances to voltage and current controls of the micro-sources, and distributing the harmonic currents according to the residual capacities of the micro-sources.

[0008] In a second aspect, an embodiment of the present application provides an electronic device, comprising: at least one processor; at least one network interface, which is in communication connection with the corresponding processor; and a memory in communication connection with the at least one processor; wherein the network interface is configured to establish a communication connection between the processor and other external devices; and the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the micro-grid harmonic current distribution method according to the first aspect.

[0009] In a third aspect, an embodiment of the present application provides a non-volatile computer storage medium, which stores computer executable instructions, and the computer executable instructions are executed by one or more processors to enable the one or more processors to perform the micro-grid harmonic current distribution method according to the first aspect.

[0010] The embodiment of the present application has the following beneficial effects: Different from the prior art, the embodiment of the present application calculates harmonic virtual impedances based on a consistency algorithm of residual capacities, realizes reasonable distribution of harmonic currents according to residual capacities in a network-type micro-grid, is applicable to island and grid-connected operation, overcomes the limitation that the prior art is only applicable to grid-connected inverters, avoids overloading of inverters by dynamically distributing harmonic currents, and still maintains stability when new energy fluctuates, realizes a simple scheme, only needs to extract a fundamental current and calculate a total effective value of harmonic currents, does not need a multi-harmonic sub-harmonic resonant controller, has small calculation amount, good real-time performance, and is easy to deploy in engineering, effectively reduces voltage harmonic distortion, and improves power quality. BRIEF DESCRIPTION OF DRAWINGS

[0011] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are schematic and not intended to be limiting of the embodiments, and in which like reference numerals refer to like elements in the various figures of the drawings in which: the figures are not to scale.

[0012] Figure 1 is a structural schematic diagram of a micro-grid harmonic current distribution system provided by an embodiment of the present application;

[0013] Figure 2 is a flowchart of a micro-grid harmonic current distribution method provided by an embodiment of the present application;

[0014] Figure 3 is a current waveform diagram of the micro-grid harmonic current distribution method shown in FIG. 4 when the power is the same; Figure 2

[0015] Figure 4 is a frequency spectrum analysis diagram of the micro-grid harmonic current distribution method shown in FIG. 4 when the power is the same; Figure 2

[0016] Figure 5 is a current waveform diagram of the micro-grid harmonic current distribution method shown in FIG. 5 when the power is different; Figure 2

[0017] Figure 6 is a frequency spectrum analysis diagram of the micro-grid harmonic current distribution method shown in FIG. 5 when the power is different; Figure 2

[0018] Figure 7 is a waveform diagram of the active power index when the micro-grid harmonic current distribution method shown in FIG. 6 is applied; Figure 2

[0019] Figure 8 is a waveform diagram of the harmonic current distribution ratio when the micro-grid harmonic current distribution method shown in FIG. 6 is applied; Figure 2

[0020] Figure 9 is a structural schematic diagram of an electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] ​​​​​​To facilitate understanding of this application, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected" to another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. The terms "upper," "lower," "inner," "outer," "bottom," etc., used in this specification indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0022] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0023] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0024] The technical solutions in this application will be described below with reference to the accompanying drawings.

[0025] In some embodiments of this application, please refer to Figure 1 , Figure 1 A schematic diagram of a microgrid harmonic current distribution system provided by an embodiment of the present invention is shown. Figure 1 As shown, the microgrid harmonic current distribution system includes multiple micro-source inverters, an AC bus, a microgrid controller, and a communication bus.

[0026] Specifically, each micro-inverter is connected to the AC bus via a feeder. In this embodiment, the micro-inverter may include, but is not limited to, photovoltaic inverters, wind power inverters, and energy storage inverters. Figure 1 The example shows micro-inverters 1, 2, and so on up to n, where n is a positive integer representing the total number of micro-inverters. The AC output of each micro-inverter is connected in sequence to a filter inductor L1 and a filter capacitor C. fThen, it is connected to the AC bus via a corresponding feeder. The feeder refers to the transmission line connecting the micro-inverter and the AC bus, and has a certain line impedance. Figure 1 Z in Chinese line For example, the feeder impedance corresponding to micro-source inverter 1 is Z. line1 The feeder impedance corresponding to micro-source inverter 2 is Z. line2 The feeder impedance corresponding to the micro-source inverter n is Z. linen .

[0027] The terminal voltage refers to the voltage across the filter capacitors of each micro-inverter, expressed in U. c The grid-side current refers to the current output by each micro-source inverter to the AC bus through the feeder, denoted by i. o This is represented by, for example, the terminal voltage of micro-inverter 1 is U. c1 The grid-side current is i o1 .

[0028] By way of example and not limitation, the AC bus can be selectively connected to the external power grid via a circuit breaker. When the circuit breaker is closed, the microgrid is in grid-connected operation mode; when the circuit breaker is open, the microgrid is in islanded operation mode. The method of this invention is applicable to both islanded and grid-connected operation modes.

[0029] In some embodiments of this application, the microgrid controller communicates with each micro-inverter via a communication bus. The communication bus can employ CAN bus, Ethernet, or other industrial communication protocols. The microgrid controller coordinates the operation of each micro-inverter, including receiving local information reported by each micro-inverter and distributing global information to each micro-inverter.

[0030] Specifically, loads are connected to the AC bus. These loads can include linear and nonlinear loads. Nonlinear loads generate harmonic currents, which can cause bus voltage distortion and reduce power quality when the microgrid is in islanded operation. This invention aims to achieve a reasonable distribution of harmonic currents among the various micro-inverters, preventing individual inverters from affecting system stability due to harmonic overload.

[0031] In some embodiments of this application, based on Figure 1 The microgrid harmonic current distribution system shown in this embodiment provides a method for distributing harmonic currents in a microgrid. For example... Figure 2 As shown, the microgrid harmonic current distribution method includes the following steps.

[0032] Step S100: Obtain the terminal voltage and grid-side current of each micro-inverter in the microgrid, and calculate the actual power of each micro-inverter.

[0033] In some embodiments of this application, each micro-inverter collects its terminal voltage and grid-side current in real time using voltage and current sensors. Specifically, the actual power includes active power and reactive power. Each micro-inverter calculates its actual power based on the collected terminal voltage and grid-side current using a power calculation method. The actual power reflects the current operating status of each micro-inverter.

[0034] Step S200: Extract the fundamental current component from the grid-side current, and obtain the harmonic current based on the difference between the grid-side current and the fundamental current component, and calculate the effective value of the harmonic current.

[0035] In some embodiments of this application, the fundamental current component refers to the component of the grid-side current with the fundamental frequency, i.e., the current component with the same fundamental frequency as the grid. Each micro-source inverter uses signal processing methods to extract the fundamental current component from the grid-side current.

[0036] The difference between the grid-side current and the fundamental current component is the harmonic current. The harmonic current refers to the current component whose frequency is an integer multiple of the fundamental frequency, encompassing all harmonic components in the grid-side current except for the fundamental frequency, such as the 3rd, 5th, and 7th harmonics. Harmonic currents are generated by nonlinear loads (such as rectifiers and frequency converters) in the microgrid, causing voltage waveform distortion and affecting power quality. Furthermore, each micro-inverter calculates the effective value of the harmonic current based on the harmonic current.

[0037] Step S300: Calculate the remaining capacity of each micro-inverter based on its rated capacity and actual power.

[0038] In some embodiments of this application, the rated capacity refers to the maximum apparent power that the micro-inverter is designed to output, typically denoted by S. The remaining capacity refers to the available capacity of the micro-inverter after deducting the current actual output power from its rated capacity, indicating how much additional load the inverter can still handle. The remaining capacity reflects the current load status and availability margin of the micro-inverter.

[0039] Specifically, each micro-inverter calculates its current remaining capacity based on its rated capacity and the actual power calculated in step S100. The larger the remaining capacity, the lighter the current load of the micro-inverter, and the more harmonic current it can handle; the smaller the remaining capacity, the heavier the current load of the micro-inverter, and the proportion of harmonic current it should handle should be reduced.

[0040] Step S400: Based on the remaining capacity of each micro-source inverter, calculate the harmonic virtual impedance of each micro-source inverter using a consensus algorithm.

[0041] In some embodiments of this application, the consensus algorithm is a distributed cooperative control algorithm that achieves overall coordinated control by enabling consistency of state variables among multiple control units or allocating them according to a specific ratio through information interaction between multiple control units. In this invention, the consensus algorithm is used to realize information sharing and coordinated control among micro-inverters, ensuring that the harmonic current borne by each micro-inverter is proportional to its remaining capacity.

[0042] As an example, and not a limitation, each micro-inverter calculates its own harmonic virtual impedance using a consensus algorithm based on its own remaining capacity and the remaining capacity information of other micro-inverters. This harmonic virtual impedance is an equivalent impedance constructed through a control algorithm; it is not a physical, actual impedance, but rather a control strategy that makes the inverter exhibit specific impedance characteristics. This harmonic virtual impedance is used to adjust the equivalent output impedance characteristics of each micro-inverter to harmonic currents, i.e., to change the magnitude of the impedance presented by the inverter, thereby affecting the current distribution flowing through the inverter.

[0043] Step S500: Apply the harmonic virtual impedance to the voltage and current control of each micro-source inverter, and distribute the harmonic current according to the remaining capacity of each micro-source inverter.

[0044] In some embodiments of this application, each micro-source inverter applies the calculated harmonic virtual impedance to voltage and current control. This voltage and current control includes voltage loop control and current loop control, a commonly used dual-closed-loop control structure for inverters. The voltage loop control is used to control the inverter output voltage to track a voltage setpoint, and the current loop control is used to control the inverter output current to track a current setpoint.

[0045] By adjusting the harmonic virtual impedance, the equivalent output impedance characteristics of each micro-inverter can be altered, thereby affecting the proportion of harmonic current handled by each micro-inverter. The equivalent output impedance refers to the equivalent impedance viewed from the inverter's output terminal, which determines the magnitude of the current flowing through the inverter under the same voltage conditions. When an inverter has a large remaining capacity, the harmonic virtual impedance calculated by the consensus algorithm is relatively small, indicating a smaller impedance to harmonic currents, thus handling more harmonic currents. Conversely, when an inverter has a small remaining capacity, the harmonic virtual impedance calculated by the consensus algorithm is relatively large, indicating a larger impedance to harmonic currents, thus handling less harmonic currents.

[0046] The microgrid harmonic current distribution method provided in this embodiment is applicable to both islanded and grid-connected operation modes of microgrids. In islanded operation mode, the microgrid is disconnected from the external power grid, and each micro-inverter supports the microgrid voltage and frequency through grid control. In grid-connected operation mode, the microgrid is connected to the external power grid through circuit breakers, and each micro-inverter outputs power according to dispatch commands.

[0047] In some embodiments of this application, the following steps may be included before performing step S100:

[0048] Step S010: Each micro-inverter receives the power setpoint from the microgrid controller.

[0049] In some embodiments of this application, the microgrid controller allocates power setpoints to each micro-inverter based on the output of new energy sources and the load power. The power setpoints include active power setpoints and reactive power setpoints, used to guide the power output of each micro-inverter.

[0050] As an example, and not a limitation, the microgrid controller can determine the power setpoint for each micro-inverter by comprehensively considering information such as renewable energy forecast curves, actual renewable energy output, and actual power of each load, taking into account the operating status of each micro-inverter and system requirements. The power setpoint is then transmitted to each micro-inverter via the communication bus.

[0051] After receiving the power setpoint, each micro-inverter will perform power control according to the power setpoint, so that the actual output power tracks the power setpoint. The power setpoint is the scheduling instruction of the microgrid controller to each micro-inverter.

[0052] After the remaining capacity is calculated in step S300, a virtual synchronization control step may be included before step S400 or in step S500.

[0053] Step S350: Each micro-source inverter obtains the voltage amplitude setpoint and phase setpoint through virtual synchronization control based on the power setpoint and actual power, which are used for the control of the voltage loop and current loop.

[0054] In some embodiments of this application, the virtual synchronization control is a control method that enables a grid-connected inverter to simulate the external characteristics of a synchronous generator. By introducing virtual inertia and virtual damping into the control algorithm, the inverter exhibits dynamic response characteristics similar to those of a synchronous generator. Through virtual synchronization control, the grid-connected inverter can provide inertia support and damping characteristics, thereby improving the stability of the microgrid.

[0055] Specifically, the virtual synchronization control calculates the angular frequency and phase setpoints based on the deviation between the power setpoint and the actual power, and simultaneously calculates the voltage amplitude setpoint based on the reactive power deviation. The formula for the virtual synchronization control is:

[0056]

[0057]

[0058]

[0059] Where, ω i Let ω1 be the angular frequency setpoint of the i-th micro-inverter, where ω1 is the rated angular frequency, and P is the angular frequency setpoint. refi and Q refi J represents the active power setpoint and reactive power setpoint of the i-th micro-inverter, respectively. i and D i These are the inertia coefficient and damping coefficient of the i-th micro-inverter, respectively. , θ i E is the phase setpoint for the i-th micro-inverter. i Let U0 be the voltage amplitude setpoint for the i-th micro-inverter, and G be the rated voltage. qi (s) is the reactive power regulation transfer function.

[0060] Wherein, the reactive power regulation transfer function G qi (s) is used to adjust the voltage amplitude to achieve the droop characteristic of reactive power and voltage. The droop characteristic refers to the characteristic that the voltage decreases as reactive power increases and increases as reactive power decreases, similar to the excitation regulation characteristic of a synchronous generator, and is used to realize the automatic distribution of reactive power among multiple inverters.

[0061] As an example, and not a limitation, when the actual power P i Less than the power setpoint P refi At that time, the given value of angular frequency ω i It will be higher than the rated angular frequency ω1, driving the inverter to increase power output; when the actual power P i Greater than the power setpoint P refi When the angular frequency setpoint ωi is lower than the rated angular frequency ω1, the inverter will reduce its power output. The phase setpoint θ is obtained through integration. i .

[0062] Furthermore, when the actual reactive power Q i Less than the reactive power setpoint Q refi At that time, the voltage amplitude setpoint E i The voltage will be lower than the rated voltage U0, driving the inverter to increase reactive power output; when the actual reactive power Q i Greater than the reactive power setpoint Q refi At that time, the voltage amplitude setpoint E i It will be higher than the rated voltage U0, driving the inverter to reduce reactive power output.

[0063] Virtual synchronization control primarily regulates the fundamental power, while the harmonic virtual impedance of this invention primarily distributes harmonic currents. Working together, virtual synchronization control ensures that each micro-inverter outputs fundamental power according to its power setpoint, while the harmonic virtual impedance ensures that each micro-inverter shares the harmonic current according to its remaining capacity, jointly achieving stable operation of the microgrid and improved power quality.

[0064] In some embodiments of this application, step S100 specifically includes the following steps:

[0065] Step S110: Perform conjugate calculations on the terminal voltage and grid-side current of each micro-source inverter to obtain the corresponding instantaneous power value.

[0066] As an example, not a limitation, for the i-th micro-inverter, the terminal voltage U ci and grid-side current i oi All are complex phasors. The terminal voltage U... ci With grid-side current i oi The conjugate complex number i * oi Multiplying these gives the complex form of the power. The formula for the conjugate operation is:

[0067]

[0068] Among them, P i Let Q be the active power of the i-th micro-inverter. i U represents the reactive power of the i-th micro-inverter. ci Let i be the terminal voltage phasor of the i-th micro-inverter. oi Let be the grid-side current phasor of the i-th micro-inverter, where * denotes conjugate operation and i is the inverter number.

[0069] In the complex form of power, the real part represents the active power P. i The imaginary part represents the reactive power Q. i P obtained through conjugate operation i + jQ i Let P be the complex expression for power, where P is the power. i Q represents the power of the actual work done. i This represents the power used to establish the electromagnetic field.

[0070] Furthermore, the instantaneous power value refers to the power value calculated through conjugate operation at each sampling moment. Since voltage and current are alternating current quantities that change with time, a set of instantaneous voltage and current values ​​can be obtained at each sampling moment, and the corresponding instantaneous power value can be obtained through conjugate operation. The instantaneous power value includes both active power and reactive power instantaneous values.

[0071] Step S120: Calculate the average value of the instantaneous power within one power grid cycle to obtain the actual power.

[0072] In some embodiments of this application, a power grid cycle refers to the time required for the fundamental wave of the power grid to complete one full oscillation.

[0073] Specifically, within a power grid cycle, the controller samples the generator terminal voltage and grid-side current multiple times at a certain sampling frequency. Assuming there are N sampling points within a power grid cycle, N sets of instantaneous power values ​​can be obtained. The average power within that power grid cycle is obtained by arithmetically averaging these N instantaneous power values.

[0074] It is easy to understand that the actual power is the active and reactive power obtained after averaging. By averaging the instantaneous power value over a power grid cycle, high-frequency fluctuations in the power can be effectively filtered out, resulting in a stable power measurement value. The actual power reflects the average power output level of the micro-inverter at that moment.

[0075] In some embodiments of this application, step S200 specifically includes the following steps:

[0076] Step S210: Use the second-order generalized integrator SOGI algorithm to extract the fundamental current component from the grid-side current.

[0077] In some embodiments of this application, the second-order generalized integrator is an abbreviation for Second Order Generalized Integrator, or SOGI for short. The SOGI algorithm possesses excellent frequency selectivity and anti-interference capabilities. The frequency selectivity refers to the algorithm's ability to accurately lock onto and extract the target frequency component in a wideband signal while suppressing other frequency components. In this invention, the SOGI algorithm is used to extract the current component with the fundamental frequency from the grid-side current.

[0078] The SOGI algorithm is based on a mathematical model of a second-order system. A second-order system refers to a dynamic system whose mathematical description includes a second-order differential equation or a transfer function whose denominator is a second-order polynomial. Second-order systems possess natural frequencies and damping characteristics; when the excitation frequency approaches the natural frequency, a resonance phenomenon occurs. This characteristic can be used to selectively extract specific frequency components.

[0079] After processing with the SOGI algorithm, the fundamental current component i can be accurately extracted from the grid-side current containing both fundamental and multiple harmonics. o1 The fundamental current component retains all information about the grid-side current at the fundamental frequency, including amplitude and phase, while filtering out harmonic components of other frequencies.

[0080] Step S220: Obtain the harmonic current based on the difference between the grid-side current and the fundamental current component.

[0081] In some embodiments of this application, the grid-side current i o Includes fundamental and harmonic components. Fundamental component i o1 The harmonic current is obtained by the SOGI algorithm in step S210. The difference between the grid-side current and the fundamental current component is the harmonic current.

[0082] Specifically, the formula for calculating the harmonic current is:

[0083]

[0084] Among them, i oh For harmonic current, i o For grid-side current, i o1 This is the fundamental current component.

[0085] The above formula is based on the principle of signal decomposition, which refers to decomposing a composite signal into a superposition of several simple signals. In this invention, the grid-side current i o It can be regarded as the fundamental current i o1 Harmonic current i oh The superposition of i o = i o1 +i oh The harmonic current is obtained by subtracting the fundamental current component from the grid-side current.

[0086] Harmonic current i oh It is a time-varying signal, and its waveform is the result of the superposition of various harmonic components. The superposition of harmonic components of different orders, amplitudes, and phases forms a complex harmonic current waveform. The waveform characteristics of the harmonic current depend on the type and operating state of the nonlinear load.

[0087] In some embodiments of this application, the extraction of harmonic current does not require the extraction and analysis of each harmonic separately. Instead, all components other than the fundamental frequency are treated as a whole, which simplifies the algorithm complexity and avoids the tedious process of designing resonant controllers for each harmonic order.

[0088] Step S230: Calculate the effective value of the harmonic current based on the harmonic current.

[0089] In some embodiments of this application, the effective value of harmonic current is an important parameter characterizing the magnitude of harmonic current. The effective value, also known as the root mean square (RMS) value, is a standard representation of the magnitude of alternating current.

[0090] Specifically, the formula for calculating the effective value of the harmonic current is as follows:

[0091]

[0092] Among them, i hi Let i be the effective value of the harmonic current of the i-th micro-inverter. oh j represents the instantaneous value of the harmonic current at the j-th sampling point, and N represents the number of sampling points within one power grid cycle.

[0093] In some embodiments of this application, the calculation of the RMS value of harmonic current needs to be performed in real time. The RMS value of harmonic current is recalculated after each power grid cycle. This real-time calculation refers to the controller continuously and cyclically performing the calculation to reflect changes in harmonic current in a timely manner. Since the load of the microgrid may change, the harmonic current generated by the nonlinear load will also change accordingly, thus requiring real-time updates to the RMS value of harmonic current.

[0094] For the same harmonic current waveform, if the fundamental current component is not extracted accurately, it will lead to harmonic current i oh The residual fundamental frequency component reduces the effective value of the harmonic current i hi Too large.

[0095] Furthermore, in a three-phase system, the effective values ​​of the three-phase harmonic currents need to be calculated separately, and then the total effective value of the three-phase harmonic currents can be calculated. The three-phase system refers to an AC power system containing three phases: A, B, and C. For a balanced three-phase system, the effective values ​​of the three-phase harmonic currents are essentially equal; for an unbalanced system, the effective values ​​of the three-phase harmonic currents may differ.

[0096] In some embodiments of this application, the remaining capacity of each micro-source inverter is obtained using the following calculation formula:

[0097]

[0098] S Ri S represents the remaining capacity of the i-th micro-inverter. Ni Let P be the rated capacity of the i-th micro-inverter. i and Q i These are the active power and reactive power of the i-th micro-inverter, respectively.

[0099] As an example and not a limitation, apparent power is a physical quantity characterizing the total power of an AC circuit in a power system, defined as the product of the effective value of voltage and the effective value of current, denoted by the letter S. Apparent power includes two components: active power and reactive power, which are related by the Pythagorean theorem: S² = P² + Q².

[0100] Furthermore, in the above formula for calculating remaining capacity, P i ² + Qi ² represents the square of the current actual output apparent power, i.e., the current apparent power. The current apparent power reflects the actual power output level of the inverter at the current moment, taking into account the contributions of active and reactive power.

[0101] Remaining capacity S Ri The calculation is based on geometric relationships. From the perspective of the power triangle, the rated capacity S... Ni This can be viewed as the upper limit of the hypotenuse length of the power triangle, representing the current apparent power. This is the actual hypotenuse length; the difference between the two is the remaining capacity. The remaining capacity indicates how much additional apparent power output the inverter can generate without exceeding the rated capacity limit.

[0102] Specifically, when the active power P of the micro-source inverter i and reactive power Q i When it is small, the current apparent power Smaller, remaining capacity S Ri A relatively large value indicates that the inverter load is relatively light, and there is still a large power output margin; when the active power P i and reactive power Q i When it is large, the current apparent power Approximately rated capacity S Ni Remaining capacity S Ri A smaller value indicates that the inverter is under heavy load and has limited power output margin.

[0103] In some embodiments of this application, it should be noted that the calculation of remaining capacity assumes P i ² + Q i ² ≤ S Ni ², meaning the current apparent power does not exceed the rated capacity. Under normal operating conditions, the microgrid controller ensures that the power setpoint of each micro-inverter does not exceed its rated capacity to prevent inverter overload. If an inverter's apparent power exceeds its rated capacity due to a fault or abnormal condition, the calculated remaining capacity will be an imaginary or negative number. In actual control, protection measures should be triggered to limit the power output of that inverter.

[0104] In some embodiments of this application, step S400 specifically includes the following steps:

[0105] Step S410: Calculate the weighting coefficient based on the remaining capacity of each micro-source inverter.

[0106] In some embodiments of this application, the weighting coefficient is a key parameter in the consensus algorithm, used to quantify the relative proportion that each micro-inverter should bear in harmonic current distribution. The magnitude of the weighting coefficient directly reflects the load-bearing capacity of each micro-inverter.

[0107] Specifically, the formula for calculating the weighting coefficient is as follows:

[0108]

[0109] Among them, K i S is the weighting coefficient for the i-th micro-inverter. Ri Let n be the remaining capacity of the i-th micro-inverter, and n be the total number of micro-inverters. This represents the summation of the remaining capacity of all micro-source inverters, i.e., the total remaining capacity of the system.

[0110] Weighting coefficient K i It is a dimensionless value between 0 and 1. The essence of the weighting coefficient is the share or proportion of the remaining capacity of each micro-source inverter in the total remaining capacity.

[0111] Furthermore, the weighting coefficient is directly proportional to the remaining capacity. When the remaining capacity S of a certain micro-inverter... Ri When it is large, its weighting coefficient K i A relatively large capacity indicates that the inverter has a strong ability to handle harmonic currents; when the remaining capacity S of a certain micro-inverter is relatively large... Ri When it is small, its weighting coefficient K i The value is also relatively small, indicating that the inverter has a limited ability to handle harmonic currents.

[0112] In some embodiments of this application, since the remaining capacity of each micro-inverter changes in real time with the changes in renewable energy output and load demand, the weighting coefficients are also dynamically adjusted accordingly. This dynamic adjustment means that the weighting coefficients are not fixed, but are adaptively calculated based on the real-time remaining capacity to ensure that the harmonic current distribution is always proportional to the current remaining capacity.

[0113] To calculate the weighting coefficients, each micro-inverter needs to know the remaining capacity information of all inverters. Therefore, each micro-inverter will use its own remaining capacity S. Ri The remaining capacity is reported to the microgrid controller via the communication bus. After receiving the remaining capacity reported by each micro-inverter, the microgrid controller calculates the total remaining capacity and sends the total remaining capacity and the remaining capacity of each inverter as global information to each micro-inverter. Upon receiving the global information, each micro-inverter calculates its own weighting coefficient K according to the formula described above. i .

[0114] Step S420: Calculate the global consistency control quantity based on the weighting coefficients and the effective value of the harmonic current.

[0115] Specifically, the formula for calculating the global consistency control quantity is as follows:

[0116]

[0117] Where, ξ i Let i be the global consistency control quantity for the i-th micro-inverter. hi Let K be the effective value of the harmonic current of the i-th micro-inverter. i Let i be the weighting coefficient of the i-th micro-inverter. hj Let be the effective value of the harmonic current of the j-th micro-inverter, and n be the total number of micro-inverters.

[0118] In the above formula, i hi The effective value of the harmonic current currently actually borne by the i-th inverter is the actual measured value calculated from step S200. This represents the effective value of the harmonic current that the i-th inverter is expected to handle, based on the weighting coefficient K. i The ideal target value is calculated from the effective values ​​of all inverter harmonic currents.

[0119] Furthermore, the globally consistent control variable ξ i The sign and magnitude of ξ have explicit physical meaning. i When it is greater than zero, it indicates that the harmonic current i currently borne by the i-th inverter is... hi Greater than expected The inverter handles too much harmonic current, so its harmonic virtual impedance should be increased to reduce the harmonic current; when ξ i When it is less than zero, it indicates that the harmonic current i currently borne by the i-th inverter is... hi The value is less than expected, indicating that the inverter is handling too little harmonic current. Therefore, its virtual harmonic impedance should be reduced to increase the harmonic current. When ξ... i When the value is zero, it means that the harmonic current currently borne by the i-th inverter is exactly equal to the expected value, and the ideal distribution state has been achieved.

[0120] In some embodiments of this application, in order to calculate the global consistency control quantity, each micro-inverter also needs to know the effective value information of the harmonic current of all inverters. Therefore, each micro-inverter will use its own effective value of harmonic current i hi The harmonic current RMS values ​​are reported to the microgrid controller via the communication bus. After receiving the RMS values ​​of the harmonic currents reported by each micro-inverter, the microgrid controller sends the RMS values ​​of the harmonic currents of all inverters as global information to each micro-inverter. Upon receiving the global information, each micro-inverter combines it with its own weighting coefficient K. i Calculate its own global consistency control quantity ξ according to the above formula. i .

[0121] Step S430: Calculate the harmonic virtual impedance based on the global consistency control quantity.

[0122] The formula for calculating the harmonic virtual impedance is as follows:

[0123]

[0124] Among them, R hvi Let ξ be the harmonic virtual impedance of the i-th micro-inverter, D(s) be the transfer function of proportional-integral control or integral control, and ξ be the harmonic virtual impedance of the i-th micro-inverter. i Let be the global consistency control quantity for the i-th micro-inverter.

[0125] By way of example and not limitation, the transfer function is a mathematical expression describing the relationship between input and output in a control system, usually represented by a Laplace transform and denoted as D(s), where s is a complex frequency variable. The transfer function fully describes the dynamic characteristics and frequency response characteristics of the controller.

[0126] Furthermore, the proportional-integral (PI) control is one of the most commonly used control methods in classical control theory. The transfer function of PI control can be expressed as: D(s) = K p + K i / s, where K p K is the proportionality coefficient. i The integral coefficient is used. The proportional control section enables the output to respond quickly to changes in the input, while the integral control section can eliminate steady-state errors, ensuring that the control quantity tends to zero in steady state.

[0127] Through integral control or proportional-integral control, the harmonic virtual impedance can be automatically adjusted according to the globally consistent control value. When ξ i When R is greater than zero (harmonic current is excessive), hvi The harmonic virtual impedance will gradually increase, and the increased harmonic virtual impedance will increase the equivalent impedance of the inverter to the harmonic current, thereby reducing the harmonic current flowing through the inverter; when ξ i When R is less than zero (harmonic current is low), hvi The harmonic virtual impedance will gradually decrease, and the decreased harmonic virtual impedance reduces the inverter's equivalent impedance to harmonic currents, thereby increasing the harmonic current flowing through the inverter; when ξ i When R equals zero, hvi It remains unchanged, reaching a steady-state equilibrium.

[0128] In some embodiments of this application, under steady-state conditions, due to the effect of integral control, the globally consistent control quantity ξ i It tends towards zero. At this point, we have:

[0129]

[0130] Dividing both sides of the above equation by the effective value of the total harmonic current, we get:

[0131]

[0132] It's easy to understand that the above formula shows that the proportion of the effective value of the harmonic current borne by each micro-source inverter to the total effective value of the harmonic current is equal to its weighting coefficient. Because the weighting coefficient... Therefore:

[0133]

[0134] That is, the proportion of harmonic current borne by each micro-source inverter is equal to the proportion of its remaining capacity, thus achieving the goal of harmonic current allocation and control according to the remaining capacity as described in this invention.

[0135] By way of example and not limitation, the unit of the resistive virtual impedance is ohms (Ω). Harmonic virtual impedance R hvi The value is usually between a few ohms and tens of ohms, depending on the system parameters, controller parameters and the magnitude of harmonic current.

[0136] In some embodiments of this application, step S500 specifically includes the following steps:

[0137] Step S510: Superimpose the preset fundamental virtual impedance and harmonic virtual impedance to obtain the corresponding comprehensive virtual impedance.

[0138] In some embodiments of this application, the fundamental virtual impedance is a pre-set virtual impedance parameter, mainly used to adjust the fundamental current distribution characteristics of each micro-source inverter. The fundamental virtual impedance differs from the harmonic virtual impedance; the fundamental virtual impedance is a fixed parameter pre-designed and determined, while the harmonic virtual impedance is a variable parameter dynamically calculated based on the remaining capacity.

[0139] The setting of the fundamental virtual impedance affects the fundamental power distribution characteristics among the micro-source inverters. By properly designing the fundamental virtual impedance, droop control or power sharing control can be achieved. Droop control refers to the droop characteristic between the inverter output power and voltage or frequency; the higher the power, the lower the voltage or frequency. This droop characteristic enables automatic power distribution among multiple inverters.

[0140] As an example and not a limitation, the composite virtual impedance can be expressed as a combination of the virtual impedances of each frequency component. For the fundamental component, the composite virtual impedance is mainly determined by the fundamental virtual impedance; for the harmonic components, the composite virtual impedance is mainly determined by the harmonic virtual impedance. Since the harmonic virtual impedance is resistive, it has the same impedance value for each harmonic, while if the fundamental virtual impedance is inductive, its impedance to higher harmonics will increase with increasing frequency.

[0141] Step S520: Based on the comprehensive virtual impedance, voltage loop and current loop control are performed to generate PWM signals to drive each micro-source inverter, so that the harmonic current borne by each micro-source inverter is distributed according to its remaining capacity.

[0142] The application of virtual impedance in voltage and current loop control is as follows: the grid-side current is decomposed into fundamental current components and harmonic current components. The fundamental current component generates a virtual voltage drop through the fundamental virtual impedance, and the harmonic current component generates a virtual voltage drop through the harmonic virtual impedance. The virtual voltage drop refers to the voltage value calculated by multiplying the virtual impedance and the current. Although it is called "virtual," it participates in the calculation as a real feedback signal in the control algorithm.

[0143] Furthermore, the fundamental and harmonic virtual voltage drops are superimposed, and then subtracted from the voltage setpoint to obtain the corrected voltage setpoint. The corrected voltage setpoint is compared with the actual terminal voltage to obtain the voltage error. The voltage error is input to the voltage loop controller, which outputs the current setpoint. The current setpoint is compared with the actual output current to obtain the current error. The current error is input to the current loop controller, which outputs a modulation signal.

[0144] Specifically, the modulation signal output by the current loop controller is compared with the triangular carrier signal to generate a PWM signal. The triangular carrier signal is a periodic triangular wave signal that serves as the reference signal for PWM generation. When the modulation signal is greater than the triangular carrier signal, the PWM signal is high; when the modulation signal is less than the triangular carrier signal, the PWM signal is low. By adjusting the amplitude of the modulation signal, the duty cycle of the PWM signal can be changed, thereby controlling the magnitude of the inverter's output voltage.

[0145] Furthermore, by adjusting the harmonic virtual impedance, the equivalent output impedance characteristics of each micro-source inverter to harmonic current can be changed, thereby achieving a reasonable distribution of harmonic current. When the harmonic virtual impedance of an inverter increases, the virtual voltage drop generated by that inverter through the harmonic virtual impedance increases, the corrected voltage setpoint decreases, and ultimately, the equivalent impedance of that inverter to harmonic current increases, resulting in a decrease in the harmonic current flowing through that inverter. Conversely, when the harmonic virtual impedance of an inverter decreases, the situation is reversed, and the harmonic current flowing through that inverter increases.

[0146] In some embodiments of this application, under steady-state conditions, due to the effect of integral control in step S430, the globally consistent control quantity ξ i As the harmonic virtual impedance approaches zero and reaches a stable value, the harmonic current borne by each micro-source inverter is proportional to its remaining capacity, thus achieving the goal of controlling the distribution of harmonic current according to the remaining capacity.

[0147] In some embodiments of this application, decoupled control of fundamental power control and harmonic current distribution is achieved based on voltage loop and current loop control using integrated virtual impedance. This decoupling control refers to separating multiple mutually coupled control objectives and controlling them independently to avoid mutual interference. The fundamental virtual impedance mainly affects the fundamental power distribution, while the harmonic virtual impedance mainly affects the harmonic current distribution. The two are relatively independent in control and do not interfere with each other, thus improving the performance and stability of the control system.

[0148] Please see Figures 3 to 8 , Figures 3 to 8 The simulation results of the method of the present invention under different working conditions are shown.

[0149] In some embodiments of this application, the simulation system is based on Figure 1 The microgrid structure shown is illustrated. The simulation system includes three micro-inverters, an AC bus, linear loads, and nonlinear loads.

[0150] Specifically, the rated capacity of each of the three micro-inverters is 20kVA. The rated capacity represents the maximum power handling capability of each inverter. The preset fundamental virtual impedance of each inverter is 2mH. This fundamental virtual impedance is used to adjust the fundamental power distribution characteristics.

[0151] Furthermore, the line impedance between each inverter and the AC bus is set as follows: the line impedance of the first inverter is 0.15 + 0.017 J ohms, the line impedance of the second inverter is 0.2 + 0.022 J ohms, and the line impedance of the third inverter is 0.18 + 0.02 J ohms.

[0152] As an example, and not a limitation, the capacity of the linear load is 26.6 kW. A linear load refers to a load where current and voltage have a linear relationship, such as a resistive load, which does not generate harmonic currents. The fundamental frequency capacity of the nonlinear load is 7.3 kW, and the harmonic capacity is approximately 7.5 kVA. A nonlinear load refers to a load where current and voltage do not have a linear relationship, such as rectifiers and frequency converters, which generate a large amount of harmonic currents. The fundamental frequency capacity refers to the fundamental power consumed by the nonlinear load, and the harmonic capacity refers to the harmonic power generated by the nonlinear load.

[0153] In some embodiments of this application, the harmonic current distribution is first verified when the active power of the three inverters is the same.

[0154] Specifically, under this operating condition, the per-unit active power of each inverter is 0.565 pu. The per-unit value is a commonly used relative value representation method in power system analysis, obtained by dividing the actual value by a reference value to obtain a dimensionless per-unit value. pu is an abbreviation for per unit. In this simulation, using the inverter's rated capacity of 20 kVA as the reference value, 0.565 pu represents an actual power of 0.565 × 20 kVA = 11.3 kVA.

[0155] It's easy to understand that when the active power of the three inverters is the same, assuming the reactive power is also basically the same, the actual power of each inverter is similar. According to the remaining capacity calculation formula in step S300, the remaining capacity of each inverter is also basically the same. According to the weighting coefficient calculation formula in step S410, the weighting coefficient of each inverter is approximately 1 / 3, meaning that each inverter should share the harmonic current equally.

[0156] Please see Figure 3 , Figure 3 The current waveforms of three inverters with the same power are shown. Figure 3 It contains three curves, representing the grid-side current waveforms of inverters 1, 2, and 3, respectively. From... Figure 3 As can be seen, the current waveforms of the three inverters almost completely overlap, making them difficult to distinguish. This overlap indicates that the magnitude and phase of the current output by the three inverters are basically the same.

[0157] Furthermore, from Figure 3 As can be seen from the waveform, the current waveform is not a perfect sine wave, but exhibits significant distortion. This distortion refers to the degree to which the waveform deviates from an ideal sine wave, and it is caused by harmonic components. The peak value of the current waveform is approximately 27A, and high-frequency oscillation components are superimposed on the waveform, indicating that the current contains harmonic components.

[0158] Please see Figure 4 , Figure 4 The spectrum analysis diagrams of three inverters with the same power are shown. Figure 4 It can be seen that:

[0159] First harmonic (fundamental frequency): The fundamental current amplitude of all three inverters is approximately 23A, and the three columns completely overlap, indicating that the fundamental current is the same. The fundamental current refers to the fundamental component with a frequency of 50Hz, which is the main component of the current and is used to transmit active and reactive power.

[0160] 5th harmonic: The amplitude of the 5th harmonic current of all three inverters is approximately 3A, and the three pillars overlap, indicating that the 5th harmonic current is evenly distributed. The 5th harmonic frequency is 250Hz, which is a typical harmonic order generated by nonlinear loads such as three-phase rectifiers.

[0161] 7th harmonic: The amplitude of the 7th harmonic current of all three inverters is approximately 2A, and the three pillars overlap, indicating that the 7th harmonic current is evenly distributed. The frequency of the 7th harmonic is 350Hz, which is also a typical harmonic of nonlinear loads.

[0162] The 11th and 13th harmonics have very small amplitudes, around 0.5A, and are basically the same in all three inverters.

[0163] Furthermore, Figure 4 The results verify that when the three inverters have the same power and remaining capacity, the harmonic current is evenly distributed among them. Each inverter bears approximately one-third of the harmonic current, which meets the expected value of the weighting coefficient. This result demonstrates that the harmonic current distribution method of this invention can operate correctly under the same power conditions.

[0164] In some embodiments of this application, in order to verify the allocation effect of the method of the present invention under different remaining capacities, the power setpoint of each inverter is changed during the simulation process to simulate the change in the output of new energy.

[0165] Please see Figure 7 , Figure 7 The curve showing the change of the per-unit value of active power over time is presented. From Figure 7 It can be seen that during the time period t < 6 seconds, the per-unit value of the active power of the three inverters is 0.565 pu, which remains the same and corresponds to operating condition one.

[0166] As an example, and not a limitation, a power surge occurred at t=6 seconds. This power surge simulates changes in the output of new energy sources, such as a decrease in photovoltaic power generation due to cloud cover, or power fluctuations in wind power generation due to changes in wind speed. During the time period t>6 seconds, the active power of the three inverters diverged:

[0167] The per-unit active power of inverter 1 dropped to 0.4 pu, and stabilized at this value after a brief dynamic process. The reduction in power means that the load on inverter 1 is reduced, and the remaining capacity is increased.

[0168] The active power per unit of inverter 2 increased to 0.6 pu and stabilized after a dynamic process. The increase in power means that the load on inverter 2 increased, and the remaining capacity decreased relatively.

[0169] Inverter 3's active power per unit value rose to 0.68 pu, and also stabilized after a dynamic process. Inverter 3 has the highest power, the heaviest load, and the smallest remaining capacity.

[0170] It is easy to understand that, according to the remaining capacity calculation formula in step S300, the remaining capacity of each inverter when t>6 seconds can be calculated. Assuming that the reactive power is relatively small and the active power is the main factor, the order of remaining capacity is: Inverter 1>Inverter 2>Inverter 3.

[0171] Furthermore, based on the weighting coefficients calculated in step S410, the weighting coefficients for the three inverters are approximately 0.45, 0.31, and 0.24, respectively. These weighting coefficients reflect the proportion of harmonic current each inverter should bear. Inverter 1 has the largest remaining capacity and the largest weighting coefficient, and should bear 45% of the harmonic current; Inverter 3 has the smallest remaining capacity and the smallest weighting coefficient, and should bear 24% of the harmonic current.

[0172] Please see Figure 5 , Figure 5 The diagram shows the current waveforms of three inverters operating at different power levels. Figure 5 It can be seen that:

[0173] The peak current waveform of inverter 1 is approximately 20A, which is the smallest among the three inverters. The relatively small peak current is due to the low fundamental power of inverter 1 (0.4 pu).

[0174] The peak current waveform of inverter 2 is about 25A, which is at an intermediate level.

[0175] The peak current waveform of inverter 3 is approximately 30A, which is the largest among the three inverters. The relatively large peak current is due to the higher fundamental power of inverter 3 (0.68pu).

[0176] Figure 5 The differences in current waveforms are mainly reflected in the fundamental component, because the fundamental power of each inverter is different. However, in terms of waveform distortion, the waveform distortion of inverter 1 is relatively obvious, while the waveform of inverter 3 is relatively smooth. This phenomenon suggests that the proportion of harmonic current carried by each inverter is different.

[0177] Please see Figure 6 , Figure 6 The spectrum analysis diagrams of three inverters with different power outputs are shown. Figure 6 It can be seen that:

[0178] First harmonic (fundamental frequency): Inverter 1 approximately 16A, Inverter 2 approximately 25A, and Inverter 3 approximately 28A. The magnitude of the fundamental frequency current is proportional to the power of each inverter, verifying that each inverter outputs fundamental frequency power according to the power setpoint. The difference in fundamental frequency current reflects the fundamental frequency power distribution of each inverter.

[0179] The 5th harmonic current is approximately 5.5A for inverter 1, approximately 3A for inverter 2, and approximately 2.5A for inverter 3. The distribution of the 5th harmonic current exhibits an inverse characteristic; that is, the inverter with the smaller fundamental current bears the larger harmonic current.

[0180] The 7th harmonic current is approximately 3.5A for inverter 1, approximately 2.5A for inverter 2, and approximately 2A for inverter 3. The 7th harmonic current also exhibits a reverse distribution characteristic.

[0181] The 11th and 13th harmonics have smaller amplitudes, but they also follow the rule that the fundamental current is small and the harmonic current is large.

[0182] Figure 6 The results verified that inverters with lower fundamental power (larger remaining capacity) carry more harmonic currents, while inverters with higher fundamental power (smaller remaining capacity) carry less harmonic currents.

[0183] Please see Figure 8 , Figure 8 The curve showing the change in the harmonic current distribution ratio over time is illustrated. Figure 8 It can be seen that:

[0184] During the time period t < 6 seconds (condition 1), the harmonic current distribution ratio of the three inverters is approximately 0.33, meaning each inverter bears about 1 / 3 of the harmonic current. The three curves coincide on a horizontal line near 0.33, verifying the average distribution of harmonic current when the power is the same.

[0185] At t=6 seconds, a power surge occurs. As the power changes, the harmonic current distribution ratio also begins to adjust. The three curves diverge, indicating the start of a dynamic adjustment process.

[0186] During the time period t>6 seconds (condition 2), after a brief dynamic process, the harmonic current distribution ratio of the three inverters reaches a new stable state:

[0187] Inverter 1's allocation ratio is stable at approximately 0.45, meaning it handles 45% of the harmonic current.

[0188] Inverter 2's allocation ratio is stable at approximately 0.31, meaning it handles 31% of the harmonic current.

[0189] Inverter 3's allocation ratio is stable at approximately 0.24, meaning it handles 24% of the harmonic current.

[0190] Furthermore, Figure 8 The results perfectly match the theoretically calculated weighting coefficients. Based on the per-unit active power values ​​of 0.4 pu, 0.6 pu, and 0.68 pu, the theoretical allocation ratios obtained through remaining capacity calculation and weighting coefficient calculation are 0.45, 0.31, and 0.24, respectively. Figure 8The displayed actual allocation ratio is consistent with the actual ratio, with minimal error. This result fully verifies the accuracy and effectiveness of the method of the present invention.

[0191] Figure 8 The dynamic response characteristics of the method of this invention are also demonstrated. From the power surge at t=6 seconds to the distribution ratio reaching a new steady state, the entire adjustment process lasts approximately 0.5 seconds.

[0192] Unlike existing technologies, this invention calculates harmonic virtual impedance using a consensus algorithm based on remaining capacity, enabling reasonable allocation of harmonic currents according to remaining capacity in grid-connected microgrids. It is applicable to both islanded and grid-connected operation, overcoming the limitation of existing technologies that only apply to grid-connected inverters. Dynamic allocation of harmonic currents prevents inverter overload and maintains stability even during renewable energy fluctuations. The implementation is simple, requiring only the extraction of the fundamental current and calculation of the total effective value of harmonics, eliminating the need for a multi-harmonic resonance controller. It features low computational load, good real-time performance, and ease of engineering deployment. It effectively reduces voltage harmonic distortion and improves power quality.

[0193] The present invention also provides an electronic device based on the above-described microgrid harmonic current distribution method, the schematic diagram of which is shown below. Figure 9 As shown, the electronic device 100 includes:

[0194] One or more processors 101, a network interface 102, and a memory 103, Figure 9 The example consists of a processor 101, a network interface 102, and a memory 103.

[0195] The network interface 102 is communicatively connected to the corresponding processor 101, and the processor 101 and the memory 103 can be connected via a bus or other means. Figure 9 Taking the example of a connection between China and Israel via a bus.

[0196] The network interface 102 is used to establish communication connections between the processor 101 and other external devices, including the following types: RJ-45 interface, SC fiber optic interface, AUI interface, FDDI interface and Console interface.

[0197] The memory 103, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. The processor 101 executes various functional applications and data processing of the electronic device by running the non-volatile software programs, instructions, and units stored in the memory 103, thereby implementing the microgrid harmonic current distribution method of the above method embodiment.

[0198] The memory 103 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the electronic device. Furthermore, the memory 103 may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 103 may optionally include memory remotely located relative to the processor 101, and these remote memories can be connected to the electronic device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0199] The one or more units are stored in the memory 103 and, when executed by one or more processors 101, execute the microgrid harmonic current distribution method in any of the above method embodiments.

[0200] The aforementioned electronic device can execute the microgrid harmonic current distribution method provided in the embodiments of the present invention, and has the corresponding program modules and beneficial effects for executing the method. Technical details not described in detail in the electronic device embodiments can be found in the microgrid harmonic current distribution method provided in the embodiments of the present invention.

[0201] This invention also provides a non-volatile computer-readable storage medium, which may be included in the device described in the above embodiments; or it may exist independently and not assembled into the device. The non-volatile computer-readable storage medium carries one or more programs, which, when executed, implement the microgrid harmonic current distribution method of this disclosure.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above. For the sake of brevity, they are not provided in detail; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for microgrid harmonic current sharing, the method comprising: The method comprises the following steps: obtaining the terminal voltage and the grid-side current of each micro-source inverter in the micro-grid, and calculating the actual power of each micro-source inverter; extracting the fundamental current component from the grid-side current, obtaining the harmonic current according to the difference between the grid-side current and the fundamental current component, and calculating the effective value of the harmonic current; calculating the residual capacity of each micro-source inverter according to the rated capacity and the actual power of each micro-source inverter; calculating the harmonic virtual impedance of each micro-source inverter through a consistency algorithm based on the residual capacity of each micro-source inverter, comprising: calculating a weight coefficient according to the residual capacity of each micro-source inverter; calculating a global consistency control quantity according to the weight coefficient and the effective value of the harmonic current; and calculating the harmonic virtual impedance according to the global consistency control quantity; wherein the harmonic virtual impedance is a resistance type virtual impedance; applying the harmonic virtual impedance to the voltage and current control of each micro-source inverter, and distributing the harmonic current according to the residual capacity of each micro-source inverter; the calculation formula of the weight coefficient is: wherein K i is the weight coefficient of the ith micro-source inverter, S Ri is the remaining capacity of the ith micro-source inverter, and n is the total number of micro-source inverters. the calculation formula of the global consistency control quantity is: wherein, ξ i is the global consistency control quantity of the ith micro-source inverter, i hi is the harmonic current effective value of the ith micro-source inverter, i hj is the harmonic current effective value of the jth micro-source inverter; the calculation formula of the harmonic virtual impedance is: wherein R hvi is the harmonic virtual impedance of the i-th micro-source inverter, and D(s) is the transfer function of proportional-integral control or integral control.

2. The method of claim 1, wherein, the obtaining of the terminal voltage and the grid-side current of each micro-source inverter in the micro-grid, and the calculation of the actual power of each micro-source inverter, comprises: performing conjugate operation on the terminal voltage and the grid-side current of each micro-source inverter to obtain corresponding power instantaneous values; performing average value operation on the power instantaneous values in one grid cycle to obtain the actual power; the formula of the conjugate operation is: where P i is the active power of the i-th micro-source inverter, Q i is the reactive power of the i-th micro-source inverter, U ci is the terminal voltage of the i-th micro-source inverter, i oi is the grid-side current of the i-th micro-source inverter, * denotes the conjugate operation, and i is the inverter number.

3. The method of claim 1, wherein, the calculation of the residual capacity of each micro-source inverter according to the rated capacity and the actual power of each micro-source inverter, comprises: calculating the residual capacity according to the following formula: where S Ri is the remaining capacity of the ith micro-source inverter, S Ni is the rated capacity of the ith micro-source inverter, P i and Q i are the active power and reactive power of the ith micro-source inverter, respectively.

4. The method of claim 1, wherein, the application of the harmonic virtual impedance to the voltage and current control of each micro-source inverter, and the distribution of the harmonic current according to the residual capacity of each micro-source inverter, comprises: superimposing a preset fundamental virtual impedance and the harmonic virtual impedance to obtain a corresponding comprehensive virtual impedance; performing voltage loop and current loop control based on the comprehensive virtual impedance to generate PWM signals to drive each micro-source inverter, so that the harmonic current borne by each micro-source inverter is distributed according to the residual capacity of each micro-source inverter.

5. The method of claim 1, wherein, the extraction of the fundamental current component from the grid-side current, the obtaining of the harmonic current according to the difference between the grid-side current and the fundamental current component, and the calculation of the effective value of the harmonic current, comprises: extracting the fundamental current component from the grid-side current by using a second-order generalized integrator (SOGI) algorithm; obtaining the harmonic current according to the difference between the grid-side current and the fundamental current component; calculating the effective value of the harmonic current according to the harmonic current; wherein the transfer function of the SOGI algorithm is: wherein ω1 is the rated angular frequency, and k is the gain coefficient; the calculation formula of the effective value of the harmonic current is: Wherein, i hi is the effective value of the harmonic current of the ith micro-source inverter, i ohj is the instantaneous value of the harmonic current at the sampling point, and N is the number of sampling points in one grid cycle.

6. The method according to any one of claims 1 to 5, characterized in that, further comprising: each micro-source inverter obtains a voltage amplitude given value and a phase given value through a virtual synchronous control according to a power given value and the actual power, which is used for voltage loop and current loop control; the formula of the virtual synchronous control is: where ωi i is the angular frequency of the ith micro-source inverter, ω1is the rated angular frequency, P refi and Q refi are the active power reference and the reactive power reference of the ith micro-source inverter, respectively, J i and D i are the inertia coefficient and the damping coefficient of the ith micro-source inverter, respectively, θ i is the phase reference of the ith micro-source inverter ，E i is the voltage amplitude reference of the ith micro-source inverter, U 0i is the rated voltage of the ith micro-source inverter, G qi (s) is the reactive power regulation transfer function.

7. An electronic device, comprising: comprising: at least one processor; at least one network interface, which is in communication connection with the respective processor; and, a memory in communication connection with the at least one processor; wherein the network interface is configured to establish a communication connection between the processor and other external devices; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the micro-grid harmonic current distribution method according to any one of claims 1-6.

8. A non-transitory computer storage medium, comprising, The computer storage medium stores computer executable instructions, and the computer executable instructions are executed by one or more processors to enable the one or more processors to perform the micro-grid harmonic current distribution method according to any one of claims 1-6.

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