A multi-inverter system distributed harmonic control method, device and multi-inverter system

Abstract

This invention relates to the field of microgrid control technology, and discloses a distributed harmonic control method, device, and multi-inverter system for multi-inverter systems. In this invention, adjacent inverter control units are connected to form a ring network. During harmonic control, the output voltage and output current of the inverter in the inverter control unit are used to separate the fundamental and harmonic components. Based on the obtained fundamental component, the fundamental component of the outer loop reference voltage is calculated. The harmonic power is calculated based on the harmonic current component. Combined with the harmonic power of other interconnected units, a harmonic power sharing controller is calculated to determine the harmonic voltage gain coefficient. Based on this coefficient and the harmonic current component, the harmonic component of the outer loop reference voltage is obtained. The outer loop reference voltage is then calculated, and the control voltage for the corresponding three-phase inverter bridge is obtained from this reference voltage. This invention is unaffected by grid interference and feeder impedance mismatch, compensates for voltage distortion caused by nonlinear loads, and achieves precise harmonic power distribution between the DG (Distributed Generator and Controller).

Description

Technical Field

[0001] This invention relates to the field of microgrid control technology, and in particular to a distributed harmonic control method, device and multi-inverter system for multi-inverter systems. Background Technology

[0002] With the increasing scarcity of traditional energy sources and the escalation of environmental problems, distributed generation (DG) units such as photovoltaic and wind turbines have experienced rapid development. To coordinate the regulation of multiple parallel DG units, microgrids, composed of distributed generation, energy storage, and local loads, are being increasingly widely used. Microgrids can operate flexibly in grid-connected or islanded mode. In islanded mode, microgrids need to provide high-quality power to critical loads. With the increasing penetration of nonlinear loads such as power electronic devices, the nonlinear loads contained in microgrids can cause significant voltage harmonic pollution, resulting in serious power quality problems, affecting equipment lifespan, and causing significant transmission line losses. Therefore, it is urgent to suppress the PCC (point of common) voltage harmonic components caused by nonlinear loads to ensure the power quality of microgrids.

[0003] Fundamental research on achieving comprehensive power quality control in microgrids mainly revolves around compensation and suppression. Traditional technologies employ active power filters for harmonic compensation in microgrid environments. To better adapt to the microgrid environment, active power filters are combined with distributed generation systems, satisfying the latter's normal grid connection requirements while also providing voltage and power factor compensation. However, this approach increases system complexity and cost.

[0004] Existing technologies suppress microgrid harmonics through the inverter itself, employing appropriate control strategies to reduce voltage harmonic distortion at the PCC (Power Control Center) and manage harmonic power between the DGs (Distributed Generation Generators). However, existing control strategies are susceptible to grid interference and feeder impedance mismatch, thus failing to effectively compensate for voltage distortion caused by nonlinear loads and making it difficult to achieve precise harmonic power distribution between the DGs. Summary of the Invention

[0005] This invention provides a distributed harmonic control method, device, and multi-inverter system for multi-inverter systems. It solves the technical problem that existing control strategies based on the inverter itself to achieve harmonic suppression in microgrids are easily affected by grid interference and feeder impedance mismatch, thus failing to effectively compensate for voltage distortion caused by nonlinear loads and making it difficult to achieve accurate harmonic power distribution between DGs.

[0006] The first aspect of this invention provides a distributed harmonic control method for a multi-inverter system, the multi-inverter system comprising multiple inverter control units, each inverter control unit connected to a three-phase inverter, and adjacent inverter control units communicatively connected to form a ring network, the method comprising:

[0007] The inverter control unit collects the output voltage and output current of the connected three-phase inverter;

[0008] The inverter control unit separates the fundamental and harmonic components of the collected output voltage and output current to obtain the corresponding fundamental and harmonic components.

[0009] The inverter control unit calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power.

[0010] The inverter control unit calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order.

[0011] The inverter control unit obtains the harmonic voltage gain coefficient through the PI controller according to the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order according to the harmonic current component and the harmonic voltage gain coefficient.

[0012] The inverter control unit calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

[0013] According to one achievable method of the first aspect of the present invention, the fundamental and harmonic separation of the acquired output voltage and output current includes:

[0014] The A-phase voltage of the collected output voltage is passed through a phase-locked loop to obtain the angular frequency. The collected output current is passed through Matrix transformation to In the coordinate system, the DC component is obtained. and Based on the real-time phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. Transform to obtain the corresponding fundamental current component;

[0015] Based on the real-time harmonic phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. The transformation yields the harmonic current components of the corresponding preset harmonic order, where... This indicates the preset harmonic order.

[0016] According to a method achievable according to a first aspect of the present invention, the calculation of the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component includes:

[0017] Calculate the fundamental active power and reactive power using the following formulas:

[0018]

[0019] In the formula, Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis.

[0020] According to a first aspect of the present invention, the step of calculating the fundamental component of the outer loop reference voltage based on the fundamental active power and reactive power includes:

[0021] Calculate the first Fundamental active power co-controller of each inverter control unit:

[0022]

[0023] In the formula, Indicates the first The fundamental active power coordinated controller of the inverter control unit. For coupling gain, It indicates the first The fundamental active power droop factor of each inverter control unit. It indicates the first The fundamental active power droop factor of each inverter control unit. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental active power calculated by each inverter control unit To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit;

[0024] The calculation is based on the fundamental active power co-controller. Reference frequency of each inverter control unit:

[0025]

[0026] In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit;

[0027] According to the first The reference frequency of each inverter control unit is calculated using the following formula to determine the fundamental component of the outer loop reference voltage:

[0028]

[0029] In the formula, This indicates the fundamental component of the outer loop reference voltage. For the first The reference voltage of each inverter control unit For the first Phase angle of each inverter control unit, Indicates time, This represents the initial phase angle of the three-phase inverter.

[0030] The obtained fundamental component of the outer loop reference voltage is obtained through... Matrix transformation to In the coordinate system, the fundamental component of the outer voltage loop reference voltage is obtained. Transformation values ​​in the coordinate system.

[0031] According to one achievable method of the first aspect of the present invention, the calculation of the harmonic power of the preset harmonic order based on the obtained harmonic current components includes:

[0032] The harmonic power of the preset harmonic order is calculated using the following formula:

[0033]

[0034] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power This represents the effective value of the output voltage of the three-phase inverter. To preset the harmonic order, This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis.

[0035] According to one embodiment of the first aspect of the present invention, the harmonic power sharing controller for calculating the harmonic power of a preset harmonic order in conjunction with the harmonic power of other inverter control units connected in communication includes:

[0036] The harmonic power distribution controller for preset harmonic orders is calculated using the following formula:

[0037]

[0038] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller For coupling gain, Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the relationship with the first A collection of inverter control units that are communicatively connected to each other. To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power.

[0039] According to a method achievable under a first aspect of the present invention, the step of obtaining a harmonic voltage gain coefficient via a PI controller based on the harmonic power sharing controller, and calculating a voltage outer loop reference voltage harmonic component of a preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient, includes:

[0040] The harmonic voltage gain coefficient is obtained using the following formula:

[0041]

[0042] In the formula, Represents the harmonic voltage gain coefficient. It is the first The proportional gain of each inverter control unit It is the first Integral gain of each inverter control unit, For complex frequencies, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller To preset the harmonic order;

[0043] The harmonic components of the outer loop reference voltage are calculated using the following formula:

[0044]

[0045] In the formula, This indicates that the harmonic components of the outer loop reference voltage are in Transformation values ​​in the coordinate system Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is Transformation values ​​in the coordinate system.

[0046] According to one achievable method of the first aspect of the present invention, for the outer voltage loop reference voltage, a dual-loop control of the outer voltage loop and inner current loop based on a PR controller is employed to obtain the corresponding control voltage of the three-phase inverter bridge, comprising:

[0047] The difference between the outer voltage loop reference voltage and the corresponding three-phase inverter output voltage is calculated. This calculated voltage difference is then passed through a first PR controller to obtain the inner current loop reference value. The first PR controller is:

[0048]

[0049] In the formula, This is the transfer function of the first PR controller. For proportional gain, The fundamental resonant coefficient, for Subharmonic resonance coefficient For the rated frequency, It is a complex frequency;

[0050] The difference between the reference value of the inner current loop and the corresponding output current of the three-phase inverter is calculated. This calculated current difference is then passed through a second PR controller to obtain the control voltage for the three-phase inverter bridge. The second PR controller is:

[0051]

[0052] In the formula, This is the transfer function for the second PR controller. It is proportional gain. It is the fundamental frequency resonance coefficient.

[0053] A second aspect of the present invention provides a multi-inverter system with a nonlinear load, the multi-inverter system comprising a plurality of inverter control units, each inverter control unit being connected to a three-phase inverter, and adjacent inverter control units being communicatively connected to form a ring network, the inverter control unit comprising:

[0054] A voltage sensor is used to collect the output voltage of the corresponding connected three-phase inverter.

[0055] A current sensor is used to collect the output current of the corresponding connected three-phase inverter;

[0056] The main controller is used to separate the fundamental and harmonic components of the acquired output voltage and output current to obtain the corresponding fundamental and harmonic components.

[0057] The main controller calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power.

[0058] The main controller calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order.

[0059] The main controller obtains the harmonic voltage gain coefficient through the PI controller based on the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient.

[0060] The main controller calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

[0061] According to one embodiment of the second aspect of the present invention, the main controller includes a fundamental harmonic separation module for separating the fundamental frequency and harmonic frequencies of the acquired output voltage and output current, the fundamental harmonic separation module comprising:

[0062] The fundamental current separation submodule is used to obtain the angular frequency of the A-phase voltage of the acquired output voltage through a phase-locked loop. The collected output current is passed through Matrix transformation to In the coordinate system, the DC component is obtained. and Based on the real-time phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. Transform to obtain the corresponding fundamental current component;

[0063] The harmonic current separation submodule is used to determine the real-time harmonic phase of the phase-locked loop. By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. The transformation yields the harmonic current components of the corresponding preset harmonic order, where... This indicates the preset harmonic order.

[0064] According to one embodiment of the second aspect of the invention, the main controller further includes a first calculation module for calculating corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, the first calculation module comprising:

[0065] The first calculation submodule is used to calculate the fundamental active power and reactive power according to the following formula:

[0066]

[0067] In the formula, Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis.

[0068] According to one embodiment of the second aspect of the invention, the main controller further includes a second calculation module for calculating the fundamental component of the outer loop reference voltage based on the fundamental active power and reactive power, the second calculation module comprising:

[0069] The second calculation submodule is used to calculate the first... Fundamental active power co-controller of each inverter control unit:

[0070]

[0071] In the formula, Indicates the first The fundamental active power coordinated controller of the inverter control unit. For coupling gain, It indicates the first The fundamental active power droop factor of each inverter control unit. It indicates the first The fundamental active power droop factor of each inverter control unit. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental active power calculated by each inverter control unit To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit;

[0072] The third calculation submodule is used to calculate the first based on the fundamental active power co-controller. Reference frequency of each inverter control unit:

[0073]

[0074] In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit;

[0075] The fourth calculation submodule is used to calculate based on the first... The reference frequency of each inverter control unit is calculated using the following formula to determine the fundamental component of the outer loop reference voltage:

[0076]

[0077] In the formula, This indicates the fundamental component of the outer loop reference voltage. For the first The reference voltage of each inverter control unit For the first Phase angle of each inverter control unit, Indicates time, This represents the initial phase angle of the three-phase inverter.

[0078] The transformation submodule is used to transform the obtained outer loop reference voltage fundamental component through... Matrix transformation to In the coordinate system, the fundamental component of the outer voltage loop reference voltage is obtained. Transformation values ​​in the coordinate system.

[0079] According to one embodiment of the second aspect of the invention, the main controller includes a third calculation module for calculating the harmonic power of a preset harmonic order based on the obtained harmonic current components, the third calculation module comprising:

[0080] The fifth calculation submodule is used to calculate the harmonic power of a preset harmonic order according to the following formula:

[0081]

[0082] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power This represents the effective value of the output voltage of the three-phase inverter. To preset the harmonic order, This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis.

[0083] According to one embodiment of the second aspect of the invention, the main controller further includes a fourth calculation module for calculating the harmonic power of a preset harmonic order by combining the harmonic power of other inverter control units in communication, the fourth calculation module comprising:

[0084] The sixth calculation submodule is used to calculate the harmonic power sharing controller for the preset harmonic order according to the following formula:

[0085]

[0086] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller For coupling gain, Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the relationship with the first A collection of inverter control units that are communicatively connected to each other. To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power.

[0087] According to one embodiment of the second aspect of the present invention, the main controller includes a fifth calculation module, which is configured to obtain a harmonic voltage gain coefficient through a PI controller based on the harmonic power sharing controller, and calculate a voltage outer loop reference voltage harmonic component of a preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient; the fifth calculation module includes:

[0088] The seventh calculation submodule is used to obtain the harmonic voltage gain coefficient according to the following formula:

[0089]

[0090] In the formula, Represents the harmonic voltage gain coefficient. It is the first The proportional gain of each inverter control unit It is the first Integral gain of each inverter control unit, For complex frequencies, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller To preset the harmonic order;

[0091] The eighth calculation submodule is used to calculate the harmonic components of the outer loop reference voltage according to the following formula:

[0092]

[0093] In the formula, This indicates that the harmonic components of the outer loop reference voltage are in Transformation values ​​in the coordinate system Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is Transformation values ​​in the coordinate system.

[0094] According to one achievable embodiment of the second aspect of the present invention, the main controller includes a control module, the control module being configured to obtain the corresponding control voltage for the three-phase inverter bridge by employing a dual-loop control of the voltage outer loop and current inner loop based on a PR controller for the voltage outer loop reference voltage; the control module includes:

[0095] The first control submodule is used to calculate the difference between the outer voltage loop reference voltage and the corresponding three-phase inverter output voltage, and then uses the calculated voltage difference to obtain the inner current loop reference value through the first PR controller. The first PR controller is:

[0096]

[0097] In the formula, This is the transfer function of the first PR controller. For proportional gain, The fundamental resonant coefficient, for Subharmonic resonance coefficient For the rated frequency, It is a complex frequency;

[0098] The second control submodule is used to calculate the difference between the reference value of the inner current loop and the output current of the corresponding three-phase inverter, and to pass the calculated current difference through the second PR controller to obtain the control voltage of the three-phase inverter bridge. The second PR controller is:

[0099]

[0100] In the formula, This is the transfer function for the second PR controller. It is proportional gain. It is the fundamental frequency resonance coefficient.

[0101] A third aspect of this invention provides a distributed harmonic control method for a multi-inverter system, characterized in that the multi-inverter system includes multiple inverter control units, each inverter control unit is connected to a three-phase inverter, adjacent inverter control units are communicatively connected to form a ring network, each inverter control unit includes a voltage sensor, a current sensor, and a main controller, the voltage sensor is used to collect the output voltage of the corresponding connected three-phase inverter, the current sensor is used to collect the output current of the corresponding connected three-phase inverter, and the method is executed by the main controller, the method comprising:

[0102] The output voltage collected by the voltage sensor and the output current collected by the current sensor are acquired, and the fundamental and harmonic components of the output voltage and the output current are separated to obtain the corresponding fundamental and harmonic components.

[0103] The corresponding fundamental active power and reactive power are calculated based on the obtained fundamental voltage component and fundamental current component, and the fundamental component of the voltage outer loop reference voltage is calculated based on the fundamental active power and reactive power.

[0104] The harmonic power of the preset harmonic order is calculated based on the obtained harmonic current components. Combined with the harmonic power of the preset harmonic order of other inverter control units connected in communication, the harmonic power distribution controller of the preset harmonic order is calculated.

[0105] According to the harmonic power equalization controller, the harmonic voltage gain coefficient is obtained through the PI controller, and the harmonic current component and the harmonic voltage gain coefficient are used to calculate the voltage outer loop reference voltage harmonic component of the preset harmonic order.

[0106] The outer loop reference voltage is calculated based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

[0107] A fourth aspect of the present invention provides a distributed harmonic control device for a multi-inverter system, comprising:

[0108] A memory for storing instructions; wherein the instructions are used to implement the distributed harmonic control method for multi-inverter systems as described in the third aspect embodiment of the present invention;

[0109] A processor for executing instructions in the memory.

[0110] The fifth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the distributed harmonic control method for multi-inverter systems as described in the third aspect of the present invention.

[0111] As can be seen from the above technical solutions, the present invention has the following advantages:

[0112] The multi-inverter system of this invention includes multiple inverter control units connected to three-phase inverters. Adjacent inverter control units are communicatively connected to form a ring network. During harmonic control, the inverter control units separate the fundamental and harmonic components of the output voltage and output current of the three-phase inverters. Based on the obtained fundamental component, they calculate the fundamental component of the outer-loop reference voltage, calculate the harmonic power based on the harmonic current component, and combine the harmonic power of other communicatively connected inverter control units to calculate the harmonic power sharing controller, thereby obtaining the corresponding harmonic voltage gain coefficient. Based on the harmonic voltage gain coefficient and the harmonic current component, they calculate the harmonic component of the outer-loop reference voltage of a preset harmonic order. Finally, they obtain the outer-loop reference voltage based on the fundamental and harmonic components of the outer-loop reference voltage. Finally, based on the reference voltage, a dual-loop control of the voltage outer loop and current inner loop is performed to obtain the corresponding control voltage of the three-phase inverter bridge. In this invention, adjacent inverter control units communicate to form a ring network, which is unaffected by grid interference and feeder impedance mismatch. By combining the harmonic power of other inverter control units connected in communication, a harmonic power sharing controller is calculated, thereby realizing the sharing of harmonic power. The voltage outer loop reference voltage is then calculated, and based on the calculated voltage outer loop reference voltage, a dual-loop control of the voltage outer loop and current inner loop is performed to determine the control voltage of the three-phase inverter bridge. This can compensate for voltage distortion caused by nonlinear loads, achieve accurate harmonic power distribution between DGs, improve the voltage quality at the PCC, and also ensure the safe and stable operation of the microgrid. Attached Figure Description

[0113] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0114] Figure 1 A flowchart of a distributed harmonic control method for a multi-inverter system is provided as an optional embodiment of the present invention;

[0115] Figure 2 This is a schematic diagram of the physical network and communication topology of a multi-inverter test system provided in an optional embodiment of the present invention;

[0116] Figure 3(a) is a schematic diagram of the fundamental active power simulation results for controller performance testing provided by an optional embodiment of the present invention;

[0117] Figure 3(b) is a schematic diagram of the simulation results of the fifth harmonic power for controller performance testing provided by an optional embodiment of the present invention;

[0118] Figure 3(c) is a schematic diagram of the simulation results of the 7th harmonic power for controller performance testing provided by an optional embodiment of the present invention;

[0119] Figure 4(a) is a schematic diagram of the fundamental active power simulation results for a robustness evaluation test of nonlinear load variation provided by an optional embodiment of the present invention.

[0120] Figure 4(b) is a schematic diagram of the simulation results of the fifth harmonic power for the robustness evaluation test of nonlinear load variation provided by an optional embodiment of the present invention;

[0121] Figure 4(c) is a schematic diagram of the simulation results of the 7th harmonic power for the robustness evaluation test of nonlinear load variation provided by an optional embodiment of the present invention.

[0122] Figure 5(a) is a schematic diagram of the simulation results of the harmonic power equalization controller before activation for the voltage total distortion rate comparison test provided by an optional embodiment of the present invention;

[0123] Figure 5(b) is a schematic diagram of the simulation results of the harmonic power equalization controller after activation for the voltage total distortion rate comparison test provided by an optional embodiment of the present invention;

[0124] Figure 6 This is a structural connection block diagram of an inverter control unit in a multi-inverter system, provided as an optional embodiment of the present invention.

[0125] Figure 7 This is a structural connection block diagram of the main controller provided in an optional embodiment of the present invention;

[0126] Figure 8 The flowchart illustrates a distributed harmonic control method for a multi-inverter system executed by a main controller, as provided in an optional embodiment of the present invention.

[0127] Figure label:

[0128] Figure 6 In the diagram, 1-voltage sensor; 2-current sensor; 3-main controller;

[0129] Figure 7 In the middle, 31-fundamental harmonic separation module; 32-first calculation module; 33-second calculation module; 34-third calculation module; 35-fourth calculation module; 36-fifth calculation module; 37-control module. Detailed Implementation

[0130] This invention provides a distributed harmonic control method, device, and multi-inverter system for multi-inverter systems. It addresses the technical problem that existing control strategies based on the inverter itself to suppress harmonics in microgrids are easily affected by grid interference and feeder impedance mismatch, thus failing to effectively compensate for voltage distortion caused by nonlinear loads and making it difficult to achieve accurate harmonic power distribution between the inverters and generators.

[0131] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0132] This invention provides a distributed harmonic control method for a multi-inverter system. The multi-inverter system includes multiple inverter control units, each connected to a three-phase inverter, and adjacent inverter control units are communicatively connected to form a ring network.

[0133] As one specific implementation method, a multi-inverter system includes The inverter control unit, of which the first... Inverter control unit and the first Inverter control unit communication connection, number The inverter control unit is communicatively connected to the first inverter control unit, thus forming a ring network. Specifically, the two inverter control units are connected via a wired connection. Each inverter control unit can be equipped with a corresponding communication module, thereby enabling the second inverter control unit to communicate with the first inverter control unit. The communication module of the inverter control unit and the first The communication module of the inverter control unit is connected via a wired connection. The communication module of the inverter control unit is connected to the communication module of the first inverter control unit via a wired connection. Specifically, adjacent inverter control units communicate based on a distributed sparse communication network.

[0134] By configuring the inverter control unit according to the above-described communication scheme, the control strategy of the following embodiments of the present invention can be made unaffected by grid interference and feeder impedance mismatch.

[0135] As one specific implementation method, .

[0136] Please see Figure 1 , Figure 1 A flowchart of a distributed harmonic control method for a multi-inverter system provided by an embodiment of the present invention is shown.

[0137] The present invention provides a distributed harmonic control method for a multi-inverter system, comprising steps S1-S6.

[0138] Step S1: The inverter control unit collects the output voltage and output current of the connected three-phase inverter.

[0139] In step S2, the inverter control unit separates the fundamental and harmonic components of the collected output voltage and output current to obtain the corresponding fundamental and harmonic components.

[0140] In one feasible manner, the fundamental and harmonic separation of the acquired output voltage and output current includes:

[0141] The A-phase voltage of the collected output voltage is passed through a phase-locked loop to obtain the angular frequency. The collected output current is passed through Matrix transformation to In the coordinate system, the DC component is obtained. and Based on the real-time phase of the phase-locked loop (PLL) By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter (LPF). The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. Transform to obtain the corresponding fundamental current component;

[0142] Based on the real-time harmonic phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. The transformation yields the harmonic current components of the corresponding preset harmonic order, where... This indicates the preset harmonic order.

[0143] As one specific implementation method, Preferably, .

[0144] In this embodiment of the invention, the separation of the fundamental current component and the harmonic current component is achieved. Wherein, The matrix is ​​as follows:

[0145] .

[0146] It should be noted that when performing fundamental and harmonic separation on the output voltage, the output voltage can also be... Matrix transformation to The coordinate system is used, and the transformed values ​​are processed sequentially through the corresponding transformation matrix, low-pass filter, and corresponding inverse transformation matrix to obtain the fundamental voltage component. ,in Indicates the first The fundamental voltage component of the three-phase inverter output in the inverter control unit is coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output in the inverter control unit is coordinate system Transformation values ​​on the axis, This indicates the number of inverter control units.

[0147] Step S3: The inverter control unit calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the outer voltage loop reference voltage based on the fundamental active power and reactive power.

[0148] In one feasible manner, the calculation of the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component includes:

[0149] Calculate the fundamental active power and reactive power using the following formulas:

[0150]

[0151] In the formula, Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis.

[0152] In one feasible manner, the calculation of the fundamental component of the outer loop reference voltage based on the fundamental active power and reactive power includes:

[0153] Calculate the first Fundamental active power co-controller of each inverter control unit:

[0154]

[0155] In the formula, Indicates the first The fundamental active power coordinated controller of the inverter control unit. For coupling gain, It indicates the first The fundamental active power droop factor of each inverter control unit. It indicates the first The fundamental active power droop factor of each inverter control unit. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental active power calculated by each inverter control unit To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit;

[0156] The calculation is based on the fundamental active power co-controller. Reference frequency of each inverter control unit:

[0157]

[0158] In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit;

[0159] According to the first The reference frequency of each inverter control unit is calculated using the following formula to determine the fundamental component of the outer loop reference voltage:

[0160]

[0161] In the formula, This indicates the fundamental component of the outer loop reference voltage. For the first The reference voltage of each inverter control unit For the first Phase angle of each inverter control unit, Indicates time, This represents the initial phase angle of the three-phase inverter.

[0162] The obtained fundamental component of the outer loop reference voltage is obtained through... Matrix transformation to In the coordinate system, the fundamental component of the outer voltage loop reference voltage is obtained. Transformation values ​​in the coordinate system.

[0163] In existing technologies, the droop control equation of the fundamental wave is used to calculate the first... The reference voltage of the inverter control unit, and the droop control equation is:

[0164]

[0165] In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit Indicates the first The reference voltage of each inverter control unit Indicates the first The nominal voltage of each inverter control unit This is the active power droop coefficient. This is the reactive power droop factor. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit.

[0166] This embodiment introduces a harmonic power sharing controller to calculate the first harmonic power distribution equation based on the existing droop control equation. The reference frequency of each inverter control unit enables precise sharing of fundamental active power.

[0167] Step S4: The inverter control unit calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order.

[0168] In one feasible manner, the calculation of the harmonic power of the preset harmonic order based on the obtained harmonic current components includes:

[0169] The harmonic power of the preset harmonic order is calculated using the following formula:

[0170]

[0171] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power This represents the effective value of the output voltage of the three-phase inverter. To preset the harmonic order, This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis.

[0172] In one feasible approach, the calculation of the harmonic power sharing controller for the preset harmonic order, in conjunction with the harmonic power of other inverter control units in the communication connection, includes:

[0173] The harmonic power distribution controller for preset harmonic orders is calculated using the following formula:

[0174]

[0175] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller For coupling gain, Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the relationship with the first A collection of inverter control units that are communicatively connected to each other. To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power.

[0176] In the above embodiments of the present invention, by combining the harmonic power of the preset harmonic order of other inverter control units connected in communication, a harmonic power sharing controller of the preset harmonic order is calculated, thereby realizing the sharing of harmonic power.

[0177] Step S5: The inverter control unit obtains the harmonic voltage gain coefficient through the PI controller according to the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order according to the harmonic current component and the harmonic voltage gain coefficient.

[0178] In one feasible approach, the step of obtaining the harmonic voltage gain coefficient via a PI controller based on the harmonic power sharing controller, and calculating the harmonic components of the outer loop reference voltage of a preset harmonic order based on the harmonic current components and the harmonic voltage gain coefficient, includes:

[0179] The harmonic voltage gain coefficient is obtained using the following formula:

[0180]

[0181] In the formula, Represents the harmonic voltage gain coefficient. It is the first The proportional gain of each inverter control unit It is the first Integral gain of each inverter control unit, For complex frequencies, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller To preset the harmonic order;

[0182] The harmonic components of the outer loop reference voltage are calculated using the following formula:

[0183]

[0184] In the formula, This indicates that the harmonic components of the outer loop reference voltage are in Transformation values ​​in the coordinate system Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is Transformation values ​​in the coordinate system.

[0185] Step S6: The inverter control unit calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control based on the PR controller is used to obtain the corresponding control voltage of the three-phase inverter bridge.

[0186] In one feasible approach, for the outer voltage loop reference voltage, a dual-loop control based on a PR controller (outer voltage loop and inner current loop) is employed to obtain the corresponding control voltage for the three-phase inverter bridge, including:

[0187] The difference between the outer voltage loop reference voltage and the corresponding three-phase inverter output voltage is calculated. This calculated voltage difference is then passed through a first PR controller to obtain the inner current loop reference value. The first PR controller is:

[0188]

[0189] In the formula, This is the transfer function of the first PR controller. For proportional gain, The fundamental resonant coefficient, for Subharmonic resonance coefficient For the rated frequency, It is a complex frequency;

[0190] The difference between the reference value of the inner current loop and the corresponding output current of the three-phase inverter is calculated. This calculated current difference is then passed through a second PR controller to obtain the control voltage for the three-phase inverter bridge. The second PR controller is:

[0191]

[0192] In the formula, This is the transfer function for the second PR controller. It is proportional gain. It is the fundamental frequency resonance coefficient.

[0193] The embodiments of the present invention described above are unaffected by grid interference and feeder impedance mismatch. By compensating for voltage distortion caused by nonlinear loads through harmonic droop control, precise harmonic power sharing between DGs can be achieved, improving voltage quality at the PCC and ensuring the safe and stable operation of the microgrid.

[0194] To evaluate the effectiveness and innovation of the proposed control strategy, this invention conducted several comparative tests, attempting to compare aspects such as controller performance, robustness to nonlinear load changes, and total voltage distortion rate. Specifically, this invention uses a multi-inverter system composed of three inverter control units as an example.

[0195] First, define the following parameters:

[0196] DC side voltage of the first inverter control unit, the second inverter control unit, and the third inverter control unit:

[0197]

[0198] The rated voltage output by the first inverter control unit, the second inverter control unit, and the third inverter control unit:

[0199]

[0200] Feeder impedance of the first inverter control unit:

[0201]

[0202] Feeder impedance of the second inverter control unit:

[0203]

[0204] Feeder impedance of the third inverter control unit:

[0205]

[0206] The three-phase filter inductors of the first inverter control unit, the second inverter control unit, and the third inverter communication control unit:

[0207]

[0208] The three-phase filter capacitors of the first inverter control unit, the second inverter control unit, and the third inverter control unit:

[0209]

[0210] Linear load at PCC:

[0211]

[0212] Nonlinear load at PCC:

[0213]

[0214] Configure the relevant parameters in the method as follows:

[0215] , , , , , , , , , , , , , , , , , , , , .

[0216] An islanded microgrid with three three-phase inverters was simulated using MATLAB / SimPowerSystems, with linear and nonlinear loads (including rectifier bridges) connected at the PCC. The system comprises filters and resistors, forming a multi-inverter test system to verify the effectiveness of the invention's strategy. It is assumed that each three-phase inverter can access the necessary information from its neighbors via a sparse communication network. The physical network and communication topology of the multi-inverter test system are as follows: Figure 2 As shown, this invention focuses on the 5th and 7th harmonics. Figure 2 middle, The three-phase filter inductor of the inverter control unit. These are the three-phase filter capacitors for the inverter control unit. Indicates direct current. Both refer to three-phase inverters. These are the inductance and resistance of the feed line impedance 1, respectively. These are the inductance and resistance of the feed line impedance 2, respectively. These are the inductance and resistance of the feed line impedance 3, respectively. These are the inductance and resistance of a linear load, respectively. These are the inductance, capacitance, and resistance of a nonlinear load, respectively.

[0217] In Figures 3(a)-5(b), " "Indicates the fundamental active power," "Indicates the 5th harmonic power," "This indicates the 7th harmonic power," "Indicates time," "Indicates the harmonic order, " "(% of Fundamental)" indicates the harmonic amplitude.

[0218] Test Example 1: Performance test of the controller.

[0219] In this test embodiment, each three-phase inverter initially used only local droop control. At that time, the fundamental active power co-controller is activated, and fundamental active power sharing regulation begins. Simultaneously, the 5th and 7th harmonic power sharing controllers are activated. Simulation results are shown in Figures 3(a)-3(c). In Figure 3(a), when the fundamental active power co-controller is not activated, precise sharing of the fundamental active power is not achieved. At any given time, once the fundamental active power co-controller is activated, active power sharing can be quickly achieved. Similarly, as shown in Figures 3(b) and 3(c), in At that time, under the consensus mechanism of the 5th and 7th harmonics, harmonic power was also instantly shared. Therefore, the power sharing performance of the proposed harmonic sharing controller was well verified.

[0220] Test Example 2: Robustness assessment of nonlinear load variations.

[0221] To evaluate the robustness of the proposed scheme to nonlinear load variations, the nonlinear load resistance at PCC is... From 50 Become 25 The simulation results are shown in Figures 4(a)-4(c). In Figure 4(a), under the action of the fundamental active power co-controller, the fundamental power gradually converges at the beginning of the simulation, eventually achieving power sharing. At that time, the 5th and 7th harmonic power sharing controller is activated. Under the action of the controller, as shown in Figures 4(b) and 4(c), the 5th and 7th harmonics achieve equal distribution of load harmonic power. At that time, the nonlinear load resistance is 50 Become 25 The fundamental and harmonic power still maintain good balance characteristics. Simulation results show that the scheme has strong robustness to nonlinear load changes.

[0222] Test Example 3: Comparison of total voltage distortion rate.

[0223] Under the same simulation conditions as the robustness assessment of nonlinear load changes, the total harmonic distortion (THD) at the PCC was compared before and after the activation of the harmonic power sharing controller. As shown in Figures 5(a) and (b), the THD was 8.37% before activation and 6.35% after activation. Note that this application only controlled the 5th and 7th harmonic frequencies; higher harmonic frequencies can be considered if needed. Simulation results show that the PCC voltage quality is improved to a certain extent.

[0224] The present invention also provides a multi-inverter system with a nonlinear load.

[0225] The present invention provides a multi-inverter system with nonlinear load, which includes multiple inverter control units. Each inverter control unit is connected to a three-phase inverter, and adjacent inverter control units are communicatively connected to form a ring network.

[0226] like Figure 6 As shown, the inverter control unit includes:

[0227] Voltage sensor 1 is used to collect the output voltage of the corresponding connected three-phase inverter;

[0228] Current sensor 2 is used to collect the output current of the corresponding connected three-phase inverter;

[0229] The main controller 3 is used to separate the fundamental and harmonic components of the acquired output voltage and output current to obtain the corresponding fundamental and harmonic components.

[0230] The main controller 3 calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power.

[0231] The main controller 3 calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order.

[0232] The main controller 3 obtains the harmonic voltage gain coefficient through the PI controller according to the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order according to the harmonic current component and the harmonic voltage gain coefficient.

[0233] The main controller 3 calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

[0234] In one feasible way, such as Figure 7 As shown, the main controller 3 includes a fundamental harmonic separation module 31 for separating the fundamental frequency and harmonics of the acquired output voltage and output current. The fundamental harmonic separation module 31 includes:

[0235] The fundamental current separation submodule is used to obtain the angular frequency of the A-phase voltage of the acquired output voltage through a phase-locked loop. The collected output current is passed through Matrix transformation to In the coordinate system, the DC component is obtained. and Based on the real-time phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. Transform to obtain the corresponding fundamental current component;

[0236] The harmonic current separation submodule is used to determine the real-time harmonic phase of the phase-locked loop. By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. The transformation yields the harmonic current components of the corresponding preset harmonic order, where... This indicates the preset harmonic order.

[0237] In one feasible implementation, the main controller 3 further includes a first calculation module 32 for calculating the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, the first calculation module 32 including:

[0238] The first calculation submodule is used to calculate the fundamental active power and reactive power according to the following formula:

[0239]

[0240] In the formula, Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis.

[0241] In one feasible implementation, the main controller 3 further includes a second calculation module 33 for calculating the fundamental component of the outer loop reference voltage based on the fundamental active power and reactive power, the second calculation module 33 comprising:

[0242] The second calculation submodule is used to calculate the first... Fundamental active power co-controller of each inverter control unit:

[0243]

[0244] In the formula, Indicates the first The fundamental active power coordinated controller of the inverter control unit. For coupling gain, It indicates the first The fundamental active power droop factor of each inverter control unit. It indicates the first The fundamental active power droop factor of each inverter control unit. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental active power calculated by each inverter control unit To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit;

[0245] The third calculation submodule is used to calculate the first based on the fundamental active power co-controller. Reference frequency of each inverter control unit:

[0246]

[0247] In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit;

[0248] The fourth calculation submodule is used to calculate based on the first... The reference frequency of each inverter control unit is calculated using the following formula to determine the fundamental component of the outer loop reference voltage:

[0249]

[0250] In the formula, This indicates the fundamental component of the outer loop reference voltage. For the first The reference voltage of each inverter control unit For the first Phase angle of each inverter control unit, Indicates time, This represents the initial phase angle of the three-phase inverter.

[0251] The transformation submodule is used to transform the obtained outer loop reference voltage fundamental component through... Matrix transformation to In the coordinate system, the fundamental component of the outer voltage loop reference voltage is obtained. Transformation values ​​in the coordinate system. In one feasible implementation, the main controller 3 includes a third calculation module 34 for calculating the harmonic power of a preset harmonic order based on the obtained harmonic current components, the third calculation module 34 including:

[0252] The fifth calculation submodule is used to calculate the harmonic power of a preset harmonic order according to the following formula:

[0253]

[0254] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power This represents the effective value of the output voltage of the three-phase inverter. To preset the harmonic order, This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis.

[0255] In one feasible embodiment, the main controller 3 further includes a fourth calculation module 35 for calculating the harmonic power of a preset harmonic order by combining the harmonic power of other inverter control units in communication, and obtaining a harmonic power sharing controller for the preset harmonic order. The fourth calculation module 35 includes:

[0256] The sixth calculation submodule is used to calculate the harmonic power sharing controller for the preset harmonic order according to the following formula:

[0257]

[0258] In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller For coupling gain, Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the relationship with the first A collection of inverter control units that are communicatively connected to each other. To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power.

[0259] In one feasible implementation, the main controller 3 includes a fifth calculation module 36, which is used to obtain the harmonic voltage gain coefficient through a PI controller based on the harmonic power sharing controller, and calculate the harmonic component of the outer loop reference voltage of a preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient; the fifth calculation module 36 includes:

[0260] The seventh calculation submodule is used to obtain the harmonic voltage gain coefficient according to the following formula:

[0261]

[0262] In the formula, Represents the harmonic voltage gain coefficient. It is the first The proportional gain of each inverter control unit It is the first Integral gain of each inverter control unit, For complex frequencies, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller To preset the harmonic order;

[0263] The eighth calculation submodule is used to calculate the harmonic components of the outer loop reference voltage according to the following formula:

[0264]

[0265] In the formula, This indicates that the harmonic components of the outer loop reference voltage are in Transformation values ​​in the coordinate system Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is Transformation values ​​in the coordinate system.

[0266] In one feasible implementation, the main controller 3 includes a control module 37, which is used to obtain the corresponding control voltage for the three-phase inverter bridge by employing a dual-loop control based on a PR controller for the voltage outer loop reference voltage; the control module 37 includes:

[0267] The first control submodule is used to calculate the difference between the outer voltage loop reference voltage and the corresponding three-phase inverter output voltage, and then uses the calculated voltage difference to obtain the inner current loop reference value through the first PR controller. The first PR controller is:

[0268]

[0269] In the formula, This is the transfer function of the first PR controller. For proportional gain, The fundamental resonant coefficient, for Subharmonic resonance coefficient For the rated frequency, It is a complex frequency;

[0270] The second control submodule is used to calculate the difference between the reference value of the inner current loop and the output current of the corresponding three-phase inverter, and to pass the calculated current difference through the second PR controller to obtain the control voltage of the three-phase inverter bridge. The second PR controller is:

[0271]

[0272] In the formula, This is the transfer function for the second PR controller. It is proportional gain. It is the fundamental frequency resonance coefficient.

[0273] The present invention also provides a distributed harmonic control method for a multi-inverter system. The multi-inverter system includes multiple inverter control units, each of which is connected to a three-phase inverter. Adjacent inverter control units are communicatively connected to form a ring network. Each inverter control unit includes a voltage sensor, a current sensor, and a main controller. The voltage sensor is used to acquire the output voltage of the corresponding connected three-phase inverter, and the current sensor is used to acquire the output current of the corresponding connected three-phase inverter. The method is executed by the main controller.

[0274] Figure 8 A flowchart of a distributed harmonic control method for a multi-inverter system, executed by a main controller, is shown in an embodiment of the present invention.

[0275] like Figure 8 As shown, the method includes:

[0276] Step S10: Obtain the output voltage collected by the voltage sensor and the output current collected by the current sensor, and separate the fundamental frequency and harmonic frequency of the output voltage and the output current to obtain the corresponding fundamental frequency and harmonic frequency components.

[0277] Step S20: Calculate the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculate the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power.

[0278] Step S30: Calculate the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combine it with the harmonic power of the preset harmonic order of other inverter control units connected in communication to obtain the harmonic power distribution controller of the preset harmonic order.

[0279] Step S40: According to the harmonic power sharing controller, the harmonic voltage gain coefficient is obtained through the PI controller, and the harmonic components of the outer loop reference voltage of the preset harmonic order are calculated based on the harmonic current components and the harmonic voltage gain coefficient.

[0280] Step S50: Calculate the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, use dual-loop control of the outer loop current and inner loop based on the PR controller to obtain the corresponding control voltage of the three-phase inverter bridge.

[0281] The present invention also provides a distributed harmonic control device for a multi-inverter system, comprising:

[0282] A memory for storing instructions; wherein the instructions are for implementing the present invention. Figure 8 The distributed harmonic control method for multi-inverter systems is shown.

[0283] A processor for executing instructions in the memory.

[0284] The present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the present invention. Figure 8 The distributed harmonic control method for multi-inverter systems is shown.

[0285] In the above embodiments of the present invention, adjacent inverter control units communicate to form a ring network, which is unaffected by grid interference and feeder impedance mismatch. By combining the harmonic power of other inverter control units connected in the communication, a harmonic power sharing controller is calculated, thereby realizing the sharing of harmonic power. The outer voltage reference voltage is then calculated, and based on the calculated outer voltage reference voltage, a dual-loop control of the outer voltage loop current and inner current loop is performed to determine the control voltage of the three-phase inverter bridge. This can compensate for voltage distortion caused by nonlinear loads, achieve precise harmonic power distribution between DGs, improve the voltage quality at the PCC, and also ensure the safe and stable operation of the microgrid.

[0286] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and modules described above can be referred to the corresponding processes in the foregoing method embodiments, and the specific beneficial effects of the systems, devices, and modules described above can be referred to the corresponding beneficial effects in the foregoing method embodiments, and will not be repeated here.

[0287] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or modules may be electrical, mechanical, or other forms.

[0288] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0289] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated modules described above can be implemented in hardware or as software functional modules.

[0290] If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0291] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A distributed harmonic control method for a multi-inverter system, characterized in that, The multi-inverter system includes multiple inverter control units, each inverter control unit is connected to a three-phase inverter, and adjacent inverter control units are communicatively connected to form a ring network. The method includes: The inverter control unit collects the output voltage and output current of the connected three-phase inverter; The inverter control unit separates the fundamental and harmonic components of the collected output voltage and output current to obtain the corresponding fundamental and harmonic components. The inverter control unit calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power. The inverter control unit calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order. The inverter control unit obtains the harmonic voltage gain coefficient through the PI controller according to the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order according to the harmonic current component and the harmonic voltage gain coefficient. The inverter control unit calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

2. The distributed harmonic control method for a multi-inverter system according to claim 1, characterized in that, The process of separating the fundamental and harmonic frequencies of the acquired output voltage and output current includes: The A-phase voltage of the collected output voltage is passed through a phase-locked loop to obtain the angular frequency. The collected output current is passed through Matrix transformation to In the coordinate system, the DC component is obtained. and Based on the real-time phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. Transform to obtain the corresponding fundamental current component; Based on the real-time harmonic phase of the phase-locked loop By transforming the matrix For the DC component and Calculate and obtain the corresponding shaft current and The shaft current is separated by a low-pass filter. The DC component of the shaft current will be obtained The DC component of the shaft current is transformed by the inverse transformation matrix. The transformation yields the harmonic current components of the corresponding preset harmonic order, where... This indicates the preset harmonic order.

3. The distributed harmonic control method for a multi-inverter system according to claim 2, characterized in that, The calculation of the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component includes: Calculate the fundamental active power and reactive power using the following formulas: In the formula, Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental reactive power calculated by each inverter control unit This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental voltage component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis, Indicates the first The fundamental current component of the three-phase inverter output connected to the inverter control unit is in coordinate system Transformation values ​​on the axis.

4. The distributed harmonic control method for a multi-inverter system according to claim 3, characterized in that, The calculation of the fundamental component of the outer loop reference voltage based on the fundamental active power and reactive power includes: Calculate the first Fundamental active power co-controller of each inverter control unit: In the formula, Indicates the first The fundamental active power coordinated controller of the inverter control unit. For coupling gain, It indicates the first The fundamental active power droop factor of each inverter control unit. It indicates the first The fundamental active power droop factor of each inverter control unit. Indicates the first The fundamental active power calculated by each inverter control unit Indicates the first The fundamental active power calculated by each inverter control unit To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit; The calculation is based on the fundamental active power co-controller. Reference frequency of each inverter control unit: In the formula, Indicates the first The reference frequency of each inverter control unit, Indicates the first The nominal frequency of each inverter control unit; According to the first The reference frequency of each inverter control unit is calculated using the following formula to determine the fundamental component of the outer loop reference voltage: In the formula, This indicates the fundamental component of the outer loop reference voltage. For the first The reference voltage of each inverter control unit, For the first The phase angle of each inverter control unit, Indicates time, This represents the initial phase angle of the three-phase inverter. The obtained fundamental component of the outer loop reference voltage is obtained through... Matrix transformation to In the coordinate system, the fundamental component of the outer voltage loop reference voltage is obtained. Transformation values ​​in the coordinate system.

5. The distributed harmonic control method for a multi-inverter system according to claim 2, characterized in that, The step of calculating the harmonic power of the preset harmonic order based on the obtained harmonic current components includes: The harmonic power of the preset harmonic order is calculated using the following formula: In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power This represents the effective value of the output voltage of the three-phase inverter. To preset the harmonic order, This is the cutoff frequency of the low-pass filter. For complex frequencies, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis, Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is coordinate system Transformation values ​​on the axis.

6. The distributed harmonic control method for a multi-inverter system according to claim 5, characterized in that, The harmonic power sharing controller for the preset harmonic order, calculated by combining the harmonic power of other inverter control units connected in communication, includes: The harmonic power distribution controller for preset harmonic orders is calculated using the following formula: In the formula, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller For coupling gain, Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the first Harmonic droop coefficient of each inverter control unit Indicates the relationship with the first A collection of inverter control units that are communicatively connected to each other. To indicate the first The inverter control unit to the first Dynamic edge weights of each inverter control unit Indicates the first The inverter control unit is connected to the three-phase inverter Subharmonic power.

7. The distributed harmonic control method for a multi-inverter system according to claim 1, characterized in that, The step of obtaining the harmonic voltage gain coefficient through a PI controller based on the harmonic power sharing controller, and calculating the outer loop reference voltage harmonic component of the preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient, includes: The harmonic voltage gain coefficient is obtained using the following formula: In the formula, Represents the harmonic voltage gain coefficient. It is the first The proportional gain of each inverter control unit It is the first Integral gain of each inverter control unit, For complex frequencies, Indicates the first The inverter control unit is connected to the three-phase inverter. Subharmonic power sharing controller To preset the harmonic order; The harmonic components of the outer loop reference voltage are calculated using the following formula: In the formula, This indicates that the harmonic components of the outer loop reference voltage are in Transformation values ​​in the coordinate system Indicates the first The output of the three-phase inverter connected to the inverter control unit The subharmonic current component is Transformation values ​​in the coordinate system.

8. The distributed harmonic control method for a multi-inverter system according to claim 1, characterized in that, For the aforementioned outer voltage reference voltage, a dual-loop control based on a PR controller (outer voltage loop and inner current loop) is employed to obtain the corresponding control voltage for the three-phase inverter bridge, including: The difference between the outer voltage loop reference voltage and the corresponding three-phase inverter output voltage is calculated. This calculated voltage difference is then passed through a first PR controller to obtain the inner current loop reference value. The first PR controller is: In the formula, This is the transfer function of the first PR controller. For proportional gain, The fundamental resonant coefficient, for Subharmonic resonance coefficient For the rated frequency, It is a complex frequency; The difference between the reference value of the inner current loop and the corresponding output current of the three-phase inverter is calculated. This calculated current difference is then passed through a second PR controller to obtain the control voltage for the three-phase inverter bridge. The second PR controller is: In the formula, This is the transfer function for the second PR controller. It is proportional gain. It is the fundamental frequency resonance coefficient.

9. A multi-inverter system with a nonlinear load, characterized in that, The multi-inverter system includes multiple inverter control units, each inverter control unit is connected to a three-phase inverter, and adjacent inverter control units are communicatively connected to form a ring network. Each inverter control unit includes: A voltage sensor is used to collect the output voltage of the corresponding connected three-phase inverter. A current sensor is used to collect the output current of the corresponding connected three-phase inverter; The main controller is used to separate the fundamental and harmonic components of the acquired output voltage and output current to obtain the corresponding fundamental and harmonic components. The main controller calculates the corresponding fundamental active power and reactive power based on the obtained fundamental voltage component and fundamental current component, and calculates the fundamental component of the voltage outer loop reference voltage based on the fundamental active power and reactive power. The main controller calculates the harmonic power of the preset harmonic order based on the obtained harmonic current components, and combines the harmonic power of the preset harmonic order of other inverter control units connected in communication to calculate the harmonic power distribution controller of the preset harmonic order. The main controller obtains the harmonic voltage gain coefficient through the PI controller based on the harmonic power sharing controller, and calculates the voltage outer loop reference voltage harmonic component of the preset harmonic order based on the harmonic current component and the harmonic voltage gain coefficient. The main controller calculates the outer loop reference voltage based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

10. A distributed harmonic control method for a multi-inverter system, characterized in that, The multi-inverter system includes multiple inverter control units, each of which is connected to a three-phase inverter. Adjacent inverter control units are communicatively connected to form a ring network. Each inverter control unit includes a voltage sensor, a current sensor, and a main controller. The voltage sensor is used to acquire the output voltage of the corresponding connected three-phase inverter, and the current sensor is used to acquire the output current of the corresponding connected three-phase inverter. The method is executed by the main controller, and the method includes: The output voltage collected by the voltage sensor and the output current collected by the current sensor are acquired, and the fundamental and harmonic components of the output voltage and the output current are separated to obtain the corresponding fundamental and harmonic components. The corresponding fundamental active power and reactive power are calculated based on the obtained fundamental voltage component and fundamental current component, and the fundamental component of the voltage outer loop reference voltage is calculated based on the fundamental active power and reactive power. The harmonic power of the preset harmonic order is calculated based on the obtained harmonic current components. Combined with the harmonic power of the preset harmonic order of other inverter control units connected in communication, the harmonic power distribution controller of the preset harmonic order is calculated. According to the harmonic power equalization controller, the harmonic voltage gain coefficient is obtained through the PI controller, and the harmonic current component and the harmonic voltage gain coefficient are used to calculate the voltage outer loop reference voltage harmonic component of the preset harmonic order. The outer loop reference voltage is calculated based on the fundamental component and harmonic component of the outer loop reference voltage. For the outer loop reference voltage, a dual-loop control of the outer loop current and inner loop based on the PR controller is adopted to obtain the corresponding control voltage of the three-phase inverter bridge.

11. A distributed harmonic control device for a multi-inverter system, characterized in that, include: A memory for storing instructions; wherein the instructions are used to implement the distributed harmonic control method for a multi-inverter system as described in claim 10; A processor for executing instructions in the memory.

12. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the distributed harmonic control method for a multi-inverter system as described in claim 10.

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