Impedance measurement method, device and equipment for network-forming inverter and storage medium

Abstract

The invention belongs to the field of electric power, and discloses an impedance measurement method, device and equipment for a network-forming inverter and a storage medium, and the method comprises the steps: obtaining an active power reference instruction and a filter capacitor voltage amplitude of an impedance test inverter, and a filter capacitor voltage amplitude of a tested inverter; based on the deviation between the active power reference instruction and the actually measured active power, virtual synchronous machine control is carried out through an active power control module to generate a dynamic power angle difference; inputting the active power reference instruction, the dynamic power angle difference, the filter capacitor voltage amplitude of the impedance test inverter and the filter capacitor voltage amplitude of the tested inverter into a line impedance calculation module; and according to a preset impedance calculation formula, the line impedance calculation module calculates the resistance and inductive reactance of a connection line between the impedance test inverter and the tested inverter.

Description

Technical Field

[0001] This invention belongs to the field of power, and particularly relates to an impedance measurement method, device, equipment and storage medium for a grid-connected inverter. Background Technology

[0002] As a core power electronic device for grid-connected renewable energy, grid-connected inverters possess active voltage and frequency regulation capabilities, and can provide auxiliary services such as inertia support and damping to the power grid. Compared to traditional grid-following inverters, grid-connected inverters, thanks to their phase self-synchronization capability, can achieve grid-connected operation without a phase-locked loop, and exhibit better stability under weak grid conditions.

[0003] In microgrids and other high-proportion renewable energy applications, multiple grid-connected inverters are often operated in parallel to improve system capacity, reliability, and modularity. However, due to the varying distances of each inverter from the point of common coupling, the impedance of their connecting lines differs. This can lead to difficulties in evenly distributing reactive power among the parallel inverters, potentially causing circulating currents, system oscillations, and even equipment damage. Therefore, accurately estimating line impedance is crucial for achieving power distribution and analyzing system stability.

[0004] In related technologies, impedance measurement schemes are mainly divided into passive and active techniques. Passive techniques use devices such as Kalman filters and phasor measurement units to collect the inherent harmonic signals of the port under test for impedance estimation. However, this method relies too heavily on random events in the power grid, resulting in low measurement accuracy and poor real-time performance. Active techniques, on the other hand, actively inject specific disturbance signals (such as harmonics, pulses, etc.) into the system and calculate the impedance by measuring the response. This method has higher accuracy, but the design of the injection device increases the system complexity and cost, and inappropriate disturbances may pollute the power quality of the power grid, affecting the stable operation of the system. Summary of the Invention

[0005] In view of this, the present invention discloses an impedance measurement method, device, equipment and storage medium for a grid-connected inverter, which can solve the shortcomings of related technologies.

[0006] To achieve the above objectives, the present invention discloses the following technical solution: According to a first aspect of the present invention, an impedance measurement method for a grid-connected inverter is provided. The method is applied in a controller of a parallel grid-connected inverter system, the parallel grid-connected inverter system comprising an impedance test inverter and a test inverter connected in parallel, both connected to a common junction point via a connecting line. Each of the impedance test inverter and the test inverter includes a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The controller includes a power calculation module, an active power control module, a reactive power control module, a voltage and current dual closed-loop control module, and a line impedance calculation module. These modules are connected sequentially or in parallel to form a closed-loop control circuit for power and voltage / current. The method includes: Obtain the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test; Based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and through the active power control module, a virtual synchronous machine is controlled to generate a dynamic power angle difference δg. The active power reference command Pg_ref, the dynamic power angle difference δg, the voltage amplitude of the filter capacitor of the impedance test inverter vgf_ref, and the voltage amplitude of the filter capacitor of the inverter under test vtf_ref are input into the line impedance calculation module. According to the preset impedance calculation formula, the line impedance calculation module calculates the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test; wherein, the impedance calculation formula is: ; .

[0007] According to a second aspect of the present invention, an impedance measurement device for a grid-connected inverter is provided. The device is installed in the controller of a parallel grid-connected inverter system, which includes parallel impedance testing inverters and inverters under test connected via a connection line to a common junction point. Each of the impedance testing inverters and the inverters under test includes a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The controller includes a power calculation module, an active power control module, a reactive power control module, a voltage and current dual closed-loop control module, and a line impedance calculation module. These modules are connected sequentially or in parallel to form a closed-loop control circuit for power and voltage / current. The device includes: Acquisition Unit: Acquires the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test; First control unit: Based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and through the active power control module, performs virtual synchronous machine control to generate dynamic power angle difference δg; Input unit: Input the active power reference command Pg_ref, the dynamic power angle difference δg, the voltage amplitude of the filter capacitor of the impedance test inverter vgf_ref, and the voltage amplitude of the filter capacitor of the inverter under test vtf_ref into the line impedance calculation module; First calculation unit: Based on a preset impedance calculation formula, the line impedance calculation module calculates the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test; wherein, the impedance calculation formula is: ; .

[0008] According to a third aspect of the present invention, an electronic device is provided, comprising: processor; Memory used to store processor-executable instructions; The processor implements the steps of the method as described in the first aspect by running the executable instructions.

[0009] According to a fourth aspect of the invention, a computer-readable storage medium is provided having computer instructions stored thereon that, when executed by a processor, implement the steps of the method as described in the first aspect.

[0010] As can be seen from the above technical solutions, the beneficial effects of the impedance measurement method, apparatus, equipment, and storage medium for grid-connected inverters disclosed in this invention are as follows: On the one hand, impedance estimation is performed based on the control logic and operating state of the grid-connected inverter itself, eliminating the need to inject any external disturbance signals into the grid, thus avoiding spectrum pollution and ensuring the stability and safety of system operation. On the other hand, there is no need to design and configure additional disturbance injection hardware (such as harmonic generators); the impedance calculation module only needs to be embedded in the existing inverter control algorithm, reducing system complexity and implementation costs. Furthermore, the impedance calculation formula originates from the fundamental physical equations of power transmission, has a clear physical meaning, and the required input quantities are all directly measurable or easily obtainable variables in the control system, making the calculation simple and enabling online, real-time, and dynamic impedance tracking. Attached Figure Description

[0011] Figure 1 This is an exemplary embodiment of an architecture diagram of a grid-connected inverter parallel system; Figure 2This is a flowchart of an impedance measurement method for a grid-type inverter provided in an exemplary embodiment; Figure 3 This is a schematic diagram of an impedance calculation module provided in an exemplary embodiment; Figure 4 This is a schematic diagram of an active power control module provided in an exemplary embodiment; Figure 5 This is a schematic diagram of a power calculation module provided in an exemplary embodiment; Figure 6 This is a schematic diagram of an exemplary embodiment of a power control module-free system. Figure 7 This is a schematic diagram of a voltage and current dual closed-loop control module provided in an exemplary embodiment; Figure 8 This is a schematic structural diagram of a device provided in an exemplary embodiment; Figure 9 This is a block diagram of an impedance measurement device for a grid-type inverter provided in an exemplary embodiment. Detailed Implementation

[0012] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with one or more embodiments of the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of one or more embodiments of the present invention as detailed in the appended claims.

[0013] It should be noted that in other embodiments, the corresponding methods are not necessarily performed in the order shown and described in this invention. The method comprises steps. In some other embodiments, the method may include more or fewer steps than those described in this invention. Furthermore, a single step described in this invention may be broken down into multiple steps in other embodiments; and multiple steps described in this invention may be combined into a single step in other embodiments.

[0014] As a core power electronic device for grid-connected renewable energy, grid-connected inverters possess active voltage and frequency regulation capabilities, and can provide auxiliary services such as inertia support and damping to the power grid. Compared to traditional grid-following inverters, grid-connected inverters, thanks to their phase self-synchronization capability, can achieve grid-connected operation without a phase-locked loop, and exhibit better stability under weak grid conditions.

[0015] In microgrids and other high-proportion renewable energy applications, multiple grid-connected inverters are often operated in parallel to improve system capacity, reliability, and modularity. However, due to the varying distances of each inverter from the point of common coupling, the impedance of their connecting lines differs. This can lead to difficulties in evenly distributing reactive power among the parallel inverters, potentially causing circulating currents, system oscillations, and even equipment damage. Therefore, accurately estimating line impedance is crucial for achieving power distribution and analyzing system stability.

[0016] In related technologies, impedance measurement schemes are mainly divided into passive and active techniques. Passive techniques use devices such as Kalman filters and phasor measurement units to collect the inherent harmonic signals of the port under test for impedance estimation. However, this method relies too heavily on random events in the power grid, resulting in low measurement accuracy and poor real-time performance. Active techniques, on the other hand, actively inject specific disturbance signals (such as harmonics, pulses, etc.) into the system and calculate the impedance by measuring the response. This method has higher accuracy, but the design of the injection device increases the system complexity and cost, and inappropriate disturbances may pollute the power quality of the power grid, affecting the stable operation of the system.

[0017] To address the shortcomings in related technologies, this invention proposes an impedance measurement method, apparatus, equipment, and storage medium for grid-connected inverters.

[0018] Figure 1 This is an exemplary embodiment of an architecture diagram of a grid-connected inverter parallel system. The circuit consists of two grid-connected inverters: one is an impedance testing inverter, and the other is the inverter under test (DUT). Their connection point is connected to the three-phase load Rpcc. Both inverters include a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The LCL filter of the impedance testing inverter consists of an inverter-side inductor Lgi, a filter capacitor Cgf, and a grid-side inductor Lgg, with connection impedances to the PCC point of Rcs and Lcs, respectively. The LCL filter of the DUT consists of an inverter-side inductor Lti, a filter capacitor Ctf, and a grid-side inductor Ltg. The control structure consists of a power calculation module, an active power control module, a reactive power control module, and a voltage and current dual closed-loop control module. The power calculation module can calculate the transmitted power on the line in real time and feed it back to the active / reactive power control module to achieve closed-loop power control. Active / reactive power control features inertia and damping, providing frequency and voltage support while dynamically adjusting the voltage reference required by the inner loop. The voltage-current dual closed-loop control, based on the voltage reference, outputs a PWM modulated signal after two PI controls. Parallel line impedance estimation is performed by the impedance calculation module.

[0019] Figure 2This is a flowchart illustrating an impedance measurement method for a grid-connected inverter, provided in an exemplary embodiment. The method is applied in a controller of a parallel grid-connected inverter system. The parallel grid-connected inverter system includes an impedance test inverter and a test inverter connected in parallel, both connected to a common junction point via a connecting line. Each of the impedance test inverter and the test inverter includes a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The controller includes a power calculation module, an active power control module, a reactive power control module, a voltage and current dual closed-loop control module, and a line impedance calculation module. These modules are connected sequentially or in parallel to form a closed-loop control circuit for power and voltage / current, such as... Figure 2 As shown, the method may include the following steps: Step 201: Obtain the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test; Step 202: Based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and through the active power control module, a virtual synchronous machine is controlled to generate a dynamic power angle difference δg; Step 203: Input the active power reference command Pg_ref, the dynamic power angle difference δg, the voltage amplitude of the filter capacitor of the impedance test inverter vgf_ref, and the voltage amplitude of the filter capacitor of the inverter under test vtf_ref into the line impedance calculation module; Step 204: According to the preset impedance calculation formula, the line impedance calculation module calculates the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test.

[0020] like Figure 3 As shown, the impedance calculation formula is: ; .

[0021] In this embodiment, on the one hand, impedance estimation is performed based on the control logic and operating state of the grid-connected inverter itself, without injecting any external disturbance signals into the grid, thus avoiding spectrum pollution and ensuring the stability and safety of system operation. On the other hand, there is no need to design and configure additional disturbance injection hardware devices (such as harmonic generators); only an impedance calculation module needs to be embedded in the existing inverter control algorithm, reducing system complexity and implementation costs. Furthermore, the impedance calculation formula originates from the fundamental physical equations of power transmission, has a clear physical meaning, and the required input quantities are all variables that can be directly measured or easily obtained in the control system, making the calculation simple and enabling online, real-time, and dynamic impedance tracking.

[0022] In one embodiment, the virtual synchronous machine (VSM) control via the active power control module includes: normalizing the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and inputting it into a transfer function of 1 / (2H). g A VSM controller (s + Dg) is used to obtain the per-unit frequency deviation Δfg_pu; where H g Dg is the virtual inertia coefficient, and Dg is the damping coefficient; the frequency deviation Δfg_pu is inversely scalarized and integrated to obtain the dynamic power angle difference δg.

[0023] like Figure 4 As shown, the active power Pg output from the power calculation module and its reference command Pg_ref are used as inputs. The deviation between the two is normalized before VSM control is applied. Based on the droop relationship between active power and frequency, the output frequency can be changed by altering Pg_ref. The virtual inertia Hs converts electrical energy into virtual kinetic energy for transient energy storage and release, providing frequency support. The damping Dg simulates the damping characteristics of a synchronous generator, suppressing power and frequency oscillations. The frequency deviation of the denormalized output is converted to an angular frequency deviation, and after integration, the power angle difference δg is obtained. The output frequency deviation is added to the reference frequency and converted to an angular frequency, which is then integrated to obtain the voltage phase reference command θg. In the figure, the virtual inertia Hs coefficient of VSM control is 10 s, and the damping Dg coefficient is 300. The transfer function of the active power control system is: .

[0024] In one embodiment, the method further includes: Figure 5 As shown, the power calculation module acquires the filter capacitor voltage v_gf_abc and grid-side inductor current i_gg_abc of the impedance test inverter, and performs a dq coordinate transformation on the filter capacitor voltage and grid-side inductor current based on the voltage phase command θg output by the active power control module to obtain their DC components in the dq rotating coordinate system; based on the DC components, the actual active power Pg and reactive power Qg transmitted by the line are calculated.

[0025] Specifically, the formulas for calculating active power Pg and reactive power Qg are as follows: ; ; Where vgf_d and vgf_q are the d-axis and q-axis components of the filter capacitor voltage, respectively, and igg_d and igg_q are the d-axis and q-axis components of the grid-side inductor current, respectively.

[0026] Furthermore, it also includes: the reactive power control module normalizes the deviation between the reactive power reference command Qg_ref and the actual measured reactive power Qg, and obtains the voltage deviation in per-unit value through PI control; the per-unit value of the voltage deviation is inversely normalized and added to the rated voltage amplitude Vg_ref to generate the voltage loop d-axis voltage amplitude reference command vgf_d_ref.

[0027] like Figure 6 As shown, the reactive power Qg output by the power calculation module and its reference command Qg_ref are used as inputs. The deviation between the two is normalized and then PI control is applied. PI control can achieve zero steady-state error tracking, meaning that Qg can reach Qg_ref under stable conditions. Since the inverter outputs inductive reactive power, the voltage of the parallel nodes will increase; conversely, it outputs capacitive reactive power, and the voltage of the parallel nodes will decrease. The voltage amplitude deviation directly reflects the imbalance between reactive power supply and demand. Therefore, the reactive power deviation, after being reverse-normalized by the PI controller, can be obtained as Δvg. This Δvg is added to the given voltage amplitude Vg_ref to obtain the voltage loop d-axis amplitude reference command vgf_d_ref. In the figure, the proportional coefficient of the PI control is 0.1, and the integral coefficient is 1.

[0028] Furthermore, the method also includes: using the voltage amplitude reference command vgf_d_ref generated by the voltage and current dual closed-loop control module in the reactive power control step as the d-axis voltage reference and 0 as the q-axis voltage reference, subtracting the voltage deviation from the capacitor voltage components on the dq axes respectively; performing PI control on the voltage deviation to generate the dq-axis reference component of the grid-side inductor current; subtracting the current reference component from the dq-axis component of the inverter-side inductor current obtained through coordinate transformation to obtain the current deviation; and performing PI control on the current deviation to generate a pulse width modulation signal for driving the impedance test inverter.

[0029] like Figure 7As shown, the voltage amplitude reference commands vgf_d_ref and 0 output from the reactive power control module are used as the voltage reference commands for the d-axis and q-axis, respectively. The deviation is obtained by subtracting these values ​​from the dq-axis components after capacitor voltage coordinate transformation. The dq-axis deviation is then controlled by a PI controller to achieve zero steady-state error tracking. The output of this deviation serves as the current reference command for the dq-axis. This deviation is then subtracted from the dq-axis components of the inverter output current to obtain the current deviation, which is then controlled by a PI controller to output the PWM voltage control signal. The d-axis control incorporates a feedforward variable vgf_d_ref to improve the system's dynamic response speed and enhance its ability to suppress external disturbances. vdc represents the DC voltage amplitude. The output PWM voltage control signal is normalized, ultimately outputting the reference voltage command vref_n_dq0 in the dq coordinate system. The parameters of the two PI controls in the figure are identical: a voltage loop proportional gain of 0.05, a voltage loop integral gain of 20, and a current loop proportional gain of 3.

[0030] In one embodiment, the method further includes: controlling the active power transmitted between the impedance test inverter and the inverter under test by changing the active power reference command Pg_ref, so as to calculate the impedance of the connection line in real time during the power dynamic adjustment process and realize continuous tracking of the line impedance.

[0031] Figure 8 This is a schematic structural diagram of a device provided in an exemplary embodiment. Please refer to... Figure 8 At the hardware level, the device includes a processor 802, an internal bus 804, a network interface 806, memory 808, and non-volatile memory 810, and may also include other hardware required for its functions. One or more embodiments of the present invention can be implemented in software, for example, the processor 802 reads the corresponding computer program from the non-volatile memory 810 into memory 808 and then runs it. Of course, in addition to software implementation, one or more embodiments of the present invention do not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0032] Please refer to Figure 9 An impedance measurement device for a grid-type inverter can be applied to, for example... Figure 9 The device shown, in order to implement the technical solution of the present invention, includes: The acquisition unit 901 is used to acquire the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test. The first control unit 902 is used to generate a dynamic power angle difference δg by performing virtual synchronous machine control through the active power control module based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg. Input unit 903 is used to input the active power reference command Pg_ref, the dynamic power angle difference δg, the filter capacitor voltage amplitude vgf_ref of the impedance test inverter and the filter capacitor voltage amplitude vtf_ref of the inverter under test into the line impedance calculation module; The calculation unit 904 is used to calculate the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test according to a preset impedance calculation formula; wherein, the impedance calculation formula is: ; .

[0033] Optionally, the control unit 902 is specifically used for: The deviation between the active power reference command Pg_ref and the actual measured active power Pg is normalized and input into the transfer function 1 / (2H). g A VSM controller (s + Dg) is used to obtain the per-unit frequency deviation Δfg_pu; where H g Here, D is the virtual inertia coefficient, and Dg is the damping coefficient; The frequency deviation Δfg_pu is inversely scalarized and integrated to obtain the dynamic power angle difference δg.

[0034] Optional, also includes: The output unit 905 is used to acquire the filter capacitor voltage v_gf_abc and grid-side inductor current i_gg_abc of the impedance test inverter by the power calculation module, and based on the voltage phase command θg output by the active power control module; Transformation unit 906 is used to perform dq coordinate transformation on the filter capacitor voltage and the grid-side inductor current to obtain their DC components in the dq rotating coordinate system. The second calculation unit 907 is used to calculate the actual active power Pg and reactive power Qg transmitted by the line based on the DC component.

[0035] Furthermore, the formulas for calculating active power Pg and reactive power Qg are as follows: ; ; Where vgf_d and vgf_q are the d-axis and q-axis components of the filter capacitor voltage, respectively, and igg_d and igg_q are the d-axis and q-axis components of the grid-side inductor current, respectively.

[0036] Furthermore, it also includes: The per-unit unit 908 is used by the reactive power control module to standardize the deviation between the reactive power reference command Qg_ref and the actual measured reactive power Qg, and obtain the per-unit value of the voltage deviation through PI control. The first generation unit 909 is used to reverse the per-unit scaling of the voltage deviation and add it to the rated voltage amplitude Vg_ref to generate the voltage loop d-axis voltage amplitude reference instruction vgf_d_ref.

[0037] Furthermore, it also includes: The first subtraction unit 910 is used to take the voltage amplitude reference command vgf_d_ref generated by the voltage and current dual closed-loop control module in the reactive power control step as the d-axis voltage reference and 0 as the q-axis voltage reference, and subtract it from the capacitor voltage components on the dq axis respectively to obtain the voltage deviation. The second generation unit 911 is used to perform PI control on the voltage deviation and generate the dq axis reference component of the grid-side inductor current. The second subtraction unit 912 is used to subtract the current reference component from the dq axis component of the inverter-side inductor current obtained by coordinate transformation to obtain the current deviation. The third generation unit 913 is used to perform PI control on the current deviation and generate a pulse width modulation signal to drive the impedance test inverter.

[0038] Optional, also includes: The second control unit 914 is used to control the active power transmitted between the impedance test inverter and the inverter under test by changing the active power reference command Pg_ref, so as to calculate the impedance of the connection line in real time during the power dynamic adjustment process and realize continuous tracking of the line impedance.

[0039] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer, which can take the form of a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email sending and receiving device, game console, tablet computer, wearable device, or any combination of these devices.

[0040] In a typical configuration, a computer includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0041] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0042] Computer-readable media, including both permanent and non-permanent, removable and non-removable media, can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage, quantum memory, graphene-based storage media or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0043] For any other form of computer-readable medium (or computer-readable storage medium) as described above, computer instructions may be stored thereon, which, when executed by a processor, implement one or more of the above embodiments, thereby realizing the technical solution of the present invention.

[0044] The present invention also proposes a computer program that, when executed by a processor, implements one or more of the embodiments described above, thereby realizing the technical solution of the present invention. This computer program may be specifically recorded on the above-described or other computer-readable media, and the present invention does not impose any limitations on this.

[0045] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0046] The foregoing has described specific embodiments of the invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0047] The terminology used in one or more embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in one or more embodiments of the invention and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0048] It should be understood that although the terms first, second, third, etc., may be used to describe various information in one or more embodiments of the present invention, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of one or more embodiments of the present invention, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0049] The above description is merely a preferred embodiment of one or more embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of the present invention should be included within the protection scope of one or more embodiments of the present invention.

Claims

1. A method for measuring the impedance of a grid-connected inverter, characterized in that, The method is applied to the controller of a grid-connected inverter parallel system, which includes an impedance testing inverter and a tested inverter connected in parallel. Both are connected to a common junction point via a connecting line. Each inverter includes a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The controller includes a power calculation module, an active power control module, a reactive power control module, a voltage and current dual closed-loop control module, and a line impedance calculation module. These modules are connected sequentially or in parallel to form a closed-loop control circuit for power and voltage / current. The method includes: Obtain the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test; Based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and through the active power control module, a virtual synchronous machine is controlled to generate a dynamic power angle difference δg. The active power reference command Pg_ref, the dynamic power angle difference δg, the voltage amplitude of the filter capacitor of the impedance test inverter vgf_ref, and the voltage amplitude of the filter capacitor of the inverter under test vtf_ref are input into the line impedance calculation module. According to the preset impedance calculation formula, the line impedance calculation module calculates the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test; wherein, the impedance calculation formula is: ； 。 2. The method according to claim 1, characterized in that, The virtual synchronous machine control via the active power control module includes: The deviation between the active power reference command Pg_ref and the actual measured active power Pg is normalized and input into the transfer function 1 / (2H). g A VSM controller (s + Dg) is used to obtain the per-unit frequency deviation Δfg_pu; where H g Here, D is the virtual inertia coefficient, and Dg is the damping coefficient; The frequency deviation Δfg_pu is inversely scalarized and integrated to obtain the dynamic power angle difference δg.

3. The method according to claim 1, characterized in that, Also includes: The power calculation module acquires the filter capacitor voltage v_gf_abc and grid-side inductor current i_gg_abc of the impedance test inverter, and calculates the voltage phase command θg output by the active power control module. The DC component of the filter capacitor voltage and the grid-side inductor current in the dq coordinate system is obtained by performing a dq coordinate transformation. Based on the DC component, the actual active power Pg and reactive power Qg transmitted by the line are calculated.

4. The method according to claim 3, characterized in that, The formulas for calculating active power Pg and reactive power Qg are as follows: ； ； Where vgf_d and vgf_q are the d-axis and q-axis components of the filter capacitor voltage, respectively, and igg_d and igg_q are the d-axis and q-axis components of the grid-side inductor current, respectively.

5. The method according to claim 3, characterized in that, Also includes: The reactive power control module normalizes the deviation between the reactive power reference command Qg_ref and the actual measured reactive power Qg, and obtains the per-unit value of the voltage deviation through PI control. The per-unit value of the voltage deviation is reverse-scaled and added to the rated voltage amplitude Vg_ref to generate the voltage loop d-axis voltage amplitude reference instruction vgf_d_ref.

6. The method according to claim 5, characterized in that, Also includes: The voltage amplitude reference command vgf_d_ref generated by the voltage and current dual closed-loop control module in the reactive power control step is used as the d-axis voltage reference, and 0 is used as the q-axis voltage reference. The voltage deviation is obtained by subtracting the capacitor voltage components on the d and q axes respectively. The voltage deviation is controlled by PI to generate the dq-axis reference component of the grid-side inductor current; The current deviation is obtained by subtracting the current reference component from the dq-axis component of the inverter-side inductor current obtained through coordinate transformation. The current deviation is controlled by a PI controller to generate a pulse width modulation signal, which is used to drive the impedance test inverter.

7. The method according to claim 1, characterized in that, Also includes: By changing the active power reference command Pg_ref, the active power transmitted between the impedance test inverter and the inverter under test is controlled, so as to calculate the impedance of the connection line in real time during the power dynamic adjustment process and realize continuous tracking of the line impedance.

8. An impedance measurement device for a grid-connected inverter, characterized in that, The device is installed in the controller of a grid-connected inverter parallel system. The grid-connected inverter parallel system includes an impedance testing inverter and a tested inverter connected in parallel, both connected to a common junction point via a connecting line. Each of the impedance testing inverter and the tested inverter includes a DC power supply, a three-phase full-bridge inverter, and an LCL filter. The controller includes a power calculation module, an active power control module, a reactive power control module, a voltage and current dual closed-loop control module, and a line impedance calculation module. These modules are connected sequentially or in parallel to form a closed-loop control circuit for power and voltage / current. The device includes: Acquisition Unit: Acquires the active power reference command Pg_ref of the impedance test inverter, the filter capacitor voltage amplitude vgf_ref, and the filter capacitor voltage amplitude vtf_ref of the inverter under test; First control unit: Based on the deviation between the active power reference command Pg_ref and the actual measured active power Pg, and through the active power control module, performs virtual synchronous machine control to generate dynamic power angle difference δg; Input unit: Input the active power reference command Pg_ref, the dynamic power angle difference δg, the voltage amplitude of the filter capacitor of the impedance test inverter vgf_ref, and the voltage amplitude of the filter capacitor of the inverter under test vtf_ref into the line impedance calculation module; First calculation unit: Based on a preset impedance calculation formula, the line impedance calculation module calculates the resistance Rcs and inductive reactance Xcs of the connection line between the impedance test inverter and the inverter under test; wherein, the impedance calculation formula is: ； 。 9. An electronic device, characterized in that, include: processor; Memory used to store processor-executable instructions; The processor implements the steps of the method as described in any one of claims 1-7 by executing the executable instructions.

10. A computer-readable storage medium storing computer instructions thereon, characterized in that, When executed by the processor, this instruction implements the steps of the method as described in any one of claims 1-7.

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