Impedance characteristic scanning circuit, detection device, and detection system

Abstract

An impedance characteristic scanning circuit, a detection device and a detection system, the impedance characteristic scanning circuit comprises a power module and a harmonic module, which are used for connecting a box-type transformer and a string inverter, the power module and the harmonic module are used for receiving a system rated voltage output by the box-type transformer, the power module is used for outputting a power frequency fundamental voltage to the string inverter according to the system rated voltage, and the harmonic module is used for outputting a harmonic disturbance voltage to the string inverter according to the system rated voltage, so that the harmonic disturbance voltage is directly applied to the string inverter, interference of the harmonic voltage received by the box-type transformer is avoided, and the measurement accuracy of the impedance characteristic of the string inverter is improved.

Description

Technical Field

[0001] This utility model relates to the field of new energy stability control technology, specifically to an impedance characteristic scanning circuit, detection equipment, and detection system. Background Technology

[0002] String inverters have become the mainstream technology for centralized photovoltaic power plants due to their excellent economic efficiency, flexible configuration, and higher power generation efficiency. The stability of a photovoltaic power plant is closely related to the impedance characteristics of the string inverter. Accurately obtaining its impedance characteristics is of great significance for analyzing power plant oscillations, optimizing control strategies, and ensuring the safe and stable operation of the power grid. Currently, obtaining the impedance characteristics of string inverters mainly relies on hardware-in-the-loop (HIL) simulation technology in a laboratory environment. Although this method can simulate the working characteristics of string inverters to a certain extent, it has the limitation of low consistency between laboratory test results and field test structures. In field testing of string inverters, harmonic signals are usually input into the high-voltage side of a box-type transformer. The harmonic signals must pass through the box-type transformer to be transmitted to the low-voltage side of the string inverter. The electromagnetic characteristics of the transformer, such as magnetizing inductance and leakage inductance, will severely attenuate and distort the injected harmonic signals and introduce the transformer's own impedance characteristics, resulting in low accuracy in measuring the impedance characteristics of string inverters. Utility Model Content

[0003] The purpose of this invention is to provide an impedance characteristic scanning circuit, detection equipment, and detection system to solve the problem of low accuracy in impedance characteristic measurement of string inverters.

[0004] To achieve the objectives of this utility model, the following technical solution is provided:

[0005] In a first aspect, this utility model provides an impedance characteristic scanning circuit for connecting a box-type transformer and a string inverter. The impedance characteristic scanning circuit includes: a power module comprising a first DC positive bus, a first DC negative bus, a first rectifier unit, a first filter unit, and a first inverter unit, wherein the first rectifier unit, the first filter unit, and the first inverter unit are arranged sequentially, and the DC side of the first rectifier unit, the first filter unit, and the first inverter unit are all connected between the first DC positive bus and the first DC negative bus; and a harmonic module comprising a second DC positive bus, a second DC negative bus, a second rectifier unit, a second filter unit, and a second inverter unit, wherein the second rectifier unit and the second filter unit... The first and second inverter units are arranged sequentially. The DC side of the second rectifier unit, the second filter unit, and the DC side of the second inverter unit are all connected between the second positive DC bus and the second negative DC bus. The AC side of the first rectifier unit and the AC side of the second rectifier unit are both electrically connected to the low-voltage side of the box-type transformer to receive the system rated voltage output by the box-type transformer. The AC side of the first inverter unit and the AC side of the second inverter unit are both electrically connected to the AC side of the string inverter. The power module is used to output the power frequency fundamental voltage to the string inverter according to the system rated voltage. The harmonic module is used to output harmonic disturbance voltage to the string inverter according to the system rated voltage.

[0006] In one embodiment, the first rectifier unit includes a first rectifier structure, a second rectifier structure, and a third rectifier structure. The DC side of the first rectifier structure, the DC side of the second rectifier structure, and the DC side of the third rectifier structure are all connected between the first DC positive bus and the first DC negative bus. The AC side of the first rectifier structure is used to be electrically connected to phase A of the low-voltage side of the box-type transformer. The AC side of the second rectifier structure is used to be electrically connected to phase B of the low-voltage side of the box-type transformer. The AC side of the third rectifier structure is used to be electrically connected to phase C of the low-voltage side of the box-type transformer.

[0007] In one embodiment, the first rectifier structure includes a first power rectifier switch and a second power rectifier switch. The collector of the first power rectifier switch is electrically connected to the first DC positive bus, and the emitter of the second power rectifier switch is electrically connected to the first DC negative bus. The emitter of the first power rectifier switch is also electrically connected to the collector of the second power rectifier switch. Both the emitter of the first power rectifier switch and the collector of the second power rectifier switch are used to be electrically connected to the low-voltage side A phase of the box-type transformer.

[0008] In one embodiment, the first filter unit includes a first capacitor, the positive terminal of the first capacitor being electrically connected to the first DC positive bus, and the negative terminal of the first capacitor being connected to the first DC negative bus.

[0009] In one embodiment, the first inverter unit includes a first inverter structure, a second inverter structure, and a third inverter structure. The DC side of the first inverter structure, the DC side of the second inverter structure, and the DC side of the third inverter structure are all connected between the first DC positive bus and the first DC negative bus. The AC side of the first inverter structure is electrically connected to phase A of the AC side of the string inverter, the AC side of the second inverter structure is electrically connected to phase B of the AC side of the string inverter, and the AC side of the third inverter structure is electrically connected to phase C of the AC side of the string inverter.

[0010] In one embodiment, the first inverter structure includes a first power inverter switch and a second power inverter switch. The collector of the first power inverter switch is electrically connected to the first DC positive bus, the emitter of the second power inverter switch is electrically connected to the first DC negative bus, and the emitter of the first power inverter switch is electrically connected to the collector of the second power inverter switch. Both the emitter of the first power inverter switch and the collector of the second power inverter switch are used to be electrically connected to the AC side A phase of the string inverter.

[0011] In one embodiment, the power module further includes a first unloading unit, which is disposed between the first rectifier unit and the first inverter unit. The first unloading unit includes a first unloading switch and a first resistor. The collector of the first unloading switch is electrically connected to the first DC positive bus, and the first resistor is connected in series with the emitter of the first unloading switch and the first DC negative bus.

[0012] In one embodiment, the impedance characteristic scanning circuit further includes a control module, which is electrically connected to the first rectifier unit, the first inverter unit, the second rectifier unit, and the second inverter unit. The control module is used to control the operation of each of the first rectifier unit, the first inverter unit, the second rectifier unit, and the second inverter unit.

[0013] Secondly, the present invention also provides an impedance characteristic detection device, including a sensor, a processor, and an impedance characteristic scanning circuit as described in any one of the embodiments of the first aspect, wherein the sensor is electrically connected to the processor, and the sensor is electrically connected to both the AC side of the first inverter unit and the AC side of the second inverter unit.

[0014] Thirdly, this utility model also provides an impedance characteristic detection system, including a box-type transformer, a string inverter, and an impedance characteristic detection device as described in any one of the embodiments of the second aspect, wherein the impedance characteristic detection device is electrically connected to both the box-type transformer and the string inverter.

[0015] An impedance characteristic scanning circuit is used to connect a box-type transformer and a string inverter. The impedance characteristic scanning circuit includes a power module and a harmonic module. The power module includes a first DC positive bus, a first DC negative bus, a first rectifier unit, a first filter unit, and a first inverter unit, arranged sequentially. The DC side of the first rectifier unit, the first filter unit, and the first inverter unit are all connected between the first DC positive bus and the first DC negative bus. The harmonic module includes a second DC positive bus, a second DC negative bus, a second rectifier unit, a second filter unit, and a second inverter unit, arranged sequentially. The DC side of the second rectifier unit, the second filter unit, and the second inverter unit are all connected between the first DC positive bus and the first DC negative bus. The DC sides of both the first and second inverter units are connected between the second positive DC bus and the second negative DC bus. The AC sides of both the first and second rectifier units are electrically connected to the low-voltage side of the box-type transformer to receive the system rated voltage output by the box-type transformer. The AC sides of both the first and second inverter units are electrically connected to the AC side of the string inverter. The power module is used to output the fundamental frequency voltage to the string inverter according to the system rated voltage. The harmonic module is used to output harmonic disturbance voltage to the string inverter according to the system rated voltage, so that the harmonic disturbance voltage is directly applied to the string inverter, avoiding interference from the box-type transformer and improving the measurement accuracy of the impedance characteristics of the string inverter. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model 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 this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of an impedance characteristic detection system according to one embodiment;

[0018] Figure 2 This is a schematic diagram of an impedance characteristic scanning circuit according to one embodiment.

[0019] Explanation of reference numerals in the attached figures:

[0020] 10000 - Impedance Characteristic Testing System;

[0021] 1000 - Impedance characteristic testing equipment;

[0022] 100-Impedance characteristic scanning circuit;

[0023] 10-Power module, 11-First DC positive bus, 12-First DC negative bus, 13-First rectifier unit, 131-First rectifier structure, MA1-First power rectifier switch, MA2-Second power rectifier switch, 132-Second rectifier structure, MB1-Third power rectifier switch, MB2-Fourth power rectifier switch, 133-Third rectifier structure, MC1-Fifth power rectifier switch, MC2-Sixth power rectifier switch, 14-First filter unit, C1-First capacitor, 15-First inverter unit, 151-First inverter structure, MA3-First power inverter switch, MA4-Second power inverter switch, 152-Second inverter structure, MB3-Third power inverter switch, MB4-Fourth power inverter switch, 153-Third inverter structure, MC3-Fifth power inverter switch, MC4-Sixth power inverter switch, 16-First unloading unit, M1-First unloading switch, R1-First resistor;

[0024] 20 - Harmonic module, 21 - Second DC positive bus, 22 - Second DC negative bus, 23 - Second rectifier unit, 231 - Fourth rectifier structure, MA5 - First harmonic rectifier switch, MA6 - Second harmonic rectifier switch, 232 - Fifth rectifier structure, MB5 - Third harmonic rectifier switch, MB6 - Fourth harmonic rectifier switch, 233 - Sixth rectifier structure, MC5 - Fifth harmonic rectifier switch, MC6 - Sixth harmonic rectifier switch, 24 - Second filter unit Element, C2 - second capacitor, 25 - second inverter unit, 251 - fourth inverter structure, MA7 - first harmonic inverter switch, MA8 - second harmonic inverter switch, 252 - fifth inverter structure, MB7 - third harmonic inverter switch, MB8 - fourth harmonic inverter switch, 253 - sixth inverter structure, MC7 - fifth harmonic inverter switch, MC8 - sixth harmonic inverter switch, 26 - second unloading unit, M2 - second unloading switch, R2 - second resistor;

[0025] 200-sensor;

[0026] 300-processor;

[0027] 2000-Box-type transformer;

[0028] 3000-String Inverter. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

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

[0032] The following detailed description, in conjunction with the accompanying drawings, outlines some embodiments of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] The core purpose of conducting impedance scanning of the string inverter 3000 is to address the increasingly prominent oscillation stability problem in high-proportion renewable energy power plants. The impedance characteristics of the string inverter 3000 are not fixed values, but rather a dynamic frequency response determined by its internal phase-locked loop, current loop, and other control algorithms. Only by accurately measuring this characteristic can impedance stability criteria be applied to predict in advance whether a mismatch will occur between the inverter and the grid background impedance, potentially leading to resonance.

[0034] Therefore, conducting on-site impedance scanning is crucial. It overcomes the limitations of laboratory simulations and the differences in hardware and software between laboratory and field equipment, and also avoids the inaccuracies caused by transformer impedance "contamination" of results during high-voltage side testing in transformer substations. This precise testing, performed directly at the inverter ports, is a key technology for enabling photovoltaic power plants to shift from "passively handling faults" to "actively predicting risks," and has irreplaceable value in ensuring power generation revenue and grid security.

[0035] Please refer to Figure 1This utility model provides an impedance characteristic detection system 10000, including a box-type transformer 2000, a string inverter 3000, and an impedance characteristic detection device 1000 in the embodiment of this utility model. The impedance characteristic detection device 1000 is electrically connected to both the box-type transformer 2000 and the string inverter 3000.

[0036] In a specific implementation, the impedance characteristic testing device 1000 is electrically connected to phases A, B, and C of the low-voltage side of the box-type transformer 2000 to receive the system rated voltage of the box-type transformer 2000. The system rated voltage is the 800V, 50Hz three-phase AC power converted from the grid voltage by the box-type transformer 2000, which is used to power the impedance characteristic testing device 1000.

[0037] The impedance characteristic testing device 1000 is used to electrically connect to phases A, B, and C of the AC side of the string inverter 3000. After rectification, filtering, and inversion, the rated voltage of the system is processed and output to the string inverter 3000 as the power frequency fundamental voltage. The power frequency fundamental voltage is a pure and stable 800V, 50Hz fixed-frequency three-phase sinusoidal voltage, so that the string inverter 3000 can start up normally and operate under ideal conditions.

[0038] In addition, the impedance characteristic testing device 1000 will output harmonic disturbance voltage to the string inverter 3000 after the system rated voltage has been rectified, filtered and inverted. The harmonic disturbance voltage is a three-phase sinusoidal voltage with a small amplitude and a frequency that can be precisely controlled between 1-3000Hz, so as to measure the impedance characteristics of the string inverter 3000 according to the response of the string inverter 3000 at different frequencies.

[0039] The impedance characteristic detection system 10000 provided by this utility model, by setting the impedance characteristic detection device 1000 in the embodiment of this utility model, the impedance characteristic detection device 1000 is electrically connected to the box transformer 2000 and the string inverter 3000, and the accurate measurement of the impedance characteristics of the string inverter 3000 is realized.

[0040] Please refer to Figure 1 The present invention also provides an impedance characteristic detection device 1000, including a sensor 200, a processor 300 and an impedance characteristic scanning circuit 100 in the embodiment of the present invention. The sensor 200 is electrically connected to the processor 300, and the sensor 200 is electrically connected to the AC side of the first inverter unit 15 and the AC side of the second inverter unit 25.

[0041] In a specific embodiment, sensor 200 includes a voltage sensor 200 and a current sensor 200. The voltage sensor 200 is electrically connected to phases A, B, and C of the AC side of the string inverter 3000, and is also electrically connected to the neutral wire or ground wire to obtain the voltages on phases A, B, and C of the AC side of the string inverter 3000. The current sensor 200 is connected in series with phases A, B, and C of the AC side of the string inverter 3000 to obtain the currents on phases A, B, and C of the AC side of the string inverter 3000. The processor 300 uses the amplitude and phase relationship of the voltage and current on the AC side of the string inverter 3000 acquired by the sensor 200 to calculate the impedance value of the string inverter 3000. For example, when the impedance characteristic scanning circuit 100 outputs a harmonic disturbance voltage of a specific frequency, the processor 300 calculates the voltage and current harmonic components of the string inverter 3000 at that frequency and obtains the impedance characteristic curve of the string inverter 3000 through Fourier analysis.

[0042] In a specific embodiment, the impedance characteristic testing device 1000 includes a first connector for pluggable connection to the low-voltage side of the box-type transformer 2000 and a second connector for pluggable connection to the AC side of the string inverter 3000, so as to realize flexible testing of the string inverter 3000 by the impedance characteristic testing device 1000 and improve the practicality of the impedance characteristic testing device 1000.

[0043] The impedance characteristic detection device 1000 provided by this utility model, by setting up a sensor 200, a processor 300 and an impedance characteristic scanning circuit 100 in the embodiment of this utility model, wherein the sensor 200 is electrically connected to the processor 300, and the sensor 200 is electrically connected to the AC side of the first inverter unit 15 and the AC side of the second inverter unit 25, realizes accurate measurement of the impedance characteristics of the string inverter 3000.

[0044] Please refer to Figure 2This utility model provides an impedance characteristic scanning circuit 100 for connecting a box-type transformer 2000 and a string inverter 3000. The impedance characteristic scanning circuit 100 includes a power module 10 and a harmonic module 20. The power module 10 includes a first DC positive bus 11, a first DC negative bus 12, a first rectifier unit 13, a first filter unit 14, and a first inverter unit 15. The first rectifier unit 13, the first filter unit 14, and the first inverter unit 15 are arranged sequentially. The DC side of the first rectifier unit 13, the first filter unit 14, and the first inverter unit 15 are all connected between the first DC positive bus 11 and the first DC negative bus 12. The harmonic module 20 includes a second DC positive bus 21, a second DC negative bus 22, a second rectifier unit 23, a second filter unit 24, and a second inverter unit 25. The first rectifier unit 23, the second filter unit 24, and the second inverter unit 25 are arranged sequentially. The DC side of the second rectifier unit 23, the second filter unit 24, and the second inverter unit 25 are all connected between the second positive DC bus 21 and the second negative DC bus 22. The AC side of the first rectifier unit 13 and the AC side of the second rectifier unit 23 are both used to be electrically connected to the low-voltage side of the box transformer 2000 to receive the system rated voltage output by the box transformer 2000. The AC side of the first inverter unit 15 and the AC side of the second inverter unit 25 are both used to be electrically connected to the AC side of the string inverter 3000. The power module 10 is used to output the power frequency fundamental voltage to the string inverter 3000 according to the system rated voltage. The harmonic module 20 is used to output harmonic disturbance voltage to the string inverter 3000 according to the system rated voltage.

[0045] In a specific embodiment, the impedance characteristic scanning circuit 100 further includes a control module, which is electrically connected to the first rectifier unit 13, the first unloading unit 16, the first inverter unit 15, the second rectifier unit 23, the second unloading unit 26, and the second inverter unit 25. The control module is used to control the operation of each of the first rectifier unit 13, the first unloading unit 16, the first inverter unit 15, the second rectifier unit 23, the second unloading unit 26, and the second inverter unit 25.

[0046] Specifically, the first rectifier unit 13 is used to convert the three-phase AC power input from the box transformer 2000 into pulsating DC power, and output the pulsating DC power to the first filter module through the first DC positive bus 11 and the first DC negative bus 12. The first filter module is used to smooth the pulsating DC power input from the first rectifier unit 13, so that the DC power input to the first inverter module is stable DC power. The first inverter module then converts the DC power into the power frequency fundamental voltage and inputs it to the string inverter 3000.

[0047] The second rectifier unit 23 is used to convert the three-phase AC power input from the box transformer 2000 into pulsating DC power, and output the pulsating DC power to the second filter module through the second DC positive bus 21 and the second DC negative bus 22. The second filter module is used to smooth the pulsating DC power input from the second rectifier unit 23, so that the DC power input to the second inverter module is stable DC power. The second inverter module then converts the DC power into harmonic disturbance voltage and inputs it to the string inverter 3000.

[0048] In a specific embodiment, the first rectifier unit 13 includes a first rectifier structure 131, a second rectifier structure 132, and a third rectifier structure 133. The DC side of the first rectifier structure 131, the DC side of the second rectifier structure 132, and the DC side of the third rectifier structure 133 are all connected between the first DC positive bus 11 and the first DC negative bus 12. The AC side of the first rectifier structure 131 is used to be electrically connected to the low-voltage side A phase of the box-type transformer 2000. The AC side of the second rectifier structure 132 is used to be electrically connected to the low-voltage side B phase of the box-type transformer 2000. The AC side of the third rectifier structure 133 is used to be electrically connected to the low-voltage side C phase of the box-type transformer 2000.

[0049] In a specific embodiment, the first rectifier structure 131 includes a first power rectifier switch MA1 and a second power rectifier switch MA2. The collector of the first power rectifier switch MA1 is electrically connected to the first DC positive bus 11, the emitter of the second power rectifier switch MA2 is electrically connected to the first DC negative bus 12, and the emitter of the first power rectifier switch MA1 is electrically connected to the collector of the second power rectifier switch MA2. Both the emitter of the first power rectifier switch MA1 and the collector of the second power rectifier switch MA2 are used to be electrically connected to the low-voltage side A phase of the box-type transformer 2000.

[0050] In a specific embodiment, the second rectifier structure 132 includes a third power rectifier switch MB1 and a fourth power rectifier switch MB2. The collector of the third power rectifier switch MB1 is electrically connected to the first DC positive bus 11, the emitter of the fourth power rectifier switch MB2 is electrically connected to the first DC negative bus 12, and the emitter of the third power rectifier switch MB1 is electrically connected to the collector of the fourth power rectifier switch MB2. Both the emitter of the third power rectifier switch MB1 and the collector of the fourth power rectifier switch MB2 are used to be electrically connected to the low-voltage side B phase of the box-type transformer 2000.

[0051] In a specific embodiment, the third rectifier structure 133 includes a fifth power rectifier switch MC1 and a sixth power rectifier switch MC2. The collector of the fifth power rectifier switch MC1 is electrically connected to the first DC positive bus 11, the emitter of the sixth power rectifier switch MC2 is electrically connected to the first DC negative bus 12, and the emitter of the fifth power rectifier switch MC1 is electrically connected to the collector of the sixth power rectifier switch MC2. Both the emitter of the fifth power rectifier switch MC1 and the collector of the sixth power rectifier switch MC2 are used to be electrically connected to the low-voltage side C phase of the box-type transformer 2000.

[0052] In a specific implementation, the first power rectifier switch MA1, the second power rectifier switch MA2, the third power rectifier switch MB1, the fourth power rectifier switch MB2, the fifth power rectifier switch MC1, and the sixth power rectifier switch MC2 are all insulated-gate bipolar thyristors. The gates of each of the first power rectifier switch MA1, the second power rectifier switch MA2, the third power rectifier switch MB1, the fourth power rectifier switch MB2, the fifth power rectifier switch MC1, and the sixth power rectifier switch MC2 are electrically connected to the control module. The control module is used to control the opening and closing of the first power rectifier switch MA1, the second power rectifier switch MA2, the third power rectifier switch MB1, the fourth power rectifier switch MB2, the fifth power rectifier switch MC1, and the sixth power rectifier switch MC2 to convert the three-phase AC power input from the box transformer 2000 into pulsating DC power.

[0053] In a specific embodiment, the first filter unit 14 includes a first capacitor C1. The positive terminal of the first capacitor C1 is electrically connected to the first DC positive bus 11, and the negative terminal of the first capacitor C1 is connected to the first DC negative bus 12. The first capacitor C1 is used to receive and charge the DC pulse voltages output by the first rectifier structure 131, the second rectifier structure 132, and the third rectifier structure 133, respectively. After the first capacitor C1 is fully charged, it outputs a stable DC power to the first inverter module.

[0054] In a specific embodiment, the first inverter unit 15 includes a first inverter structure 151, a second inverter structure 152, and a third inverter structure 153. The DC side of the first inverter structure 151, the DC side of the second inverter structure 152, and the DC side of the third inverter structure 153 are all connected between the first DC positive bus 11 and the first DC negative bus 12. The AC side of the first inverter structure 151 is used to be electrically connected to the AC side A phase of the string inverter 3000, the AC side of the second inverter structure 152 is used to be electrically connected to the AC side B phase of the string inverter 3000, and the AC side of the third inverter structure 153 is used to be electrically connected to the AC side C phase of the string inverter 3000.

[0055] In a specific embodiment, the first inverter structure 151 includes a first power inverter switch MA3 and a second power inverter switch MA4. The collector of the first power inverter switch MA3 is electrically connected to the first DC positive bus 11, the emitter of the second power inverter switch MA4 is electrically connected to the first DC negative bus 12, and the emitter of the first power inverter switch MA3 is electrically connected to the collector of the second power inverter switch MA4. Both the emitter of the first power inverter switch MA3 and the collector of the second power inverter switch MA4 are used to be electrically connected to the AC side A phase of the string inverter 3000.

[0056] In a specific embodiment, the second inverter structure 152 includes a third power inverter switch MB3 and a fourth power inverter switch MB4. The collector of the third power inverter switch MB3 is electrically connected to the first DC positive bus 11, the emitter of the fourth power inverter switch MB4 is electrically connected to the first DC negative bus 12, and the emitter of the third power inverter switch MB3 is electrically connected to the collector of the fourth power inverter switch MB4. Both the emitter of the third power inverter switch MB3 and the collector of the fourth power inverter switch MB4 are used to be electrically connected to the AC side B phase of the string inverter 3000.

[0057] In a specific implementation, the third inverter structure 153 includes a fifth power inverter switch MC3 and a sixth power inverter switch MC4. The collector of the fifth power inverter switch MC3 is electrically connected to the first DC positive bus 11, the emitter of the sixth power inverter switch MC4 is electrically connected to the first DC negative bus 12, and the emitter of the fifth power inverter switch MC3 is electrically connected to the collector of the sixth power inverter switch MC4. Both the emitter of the fifth power inverter switch MC3 and the collector of the sixth power inverter switch MC4 are used to be electrically connected to the AC side C phase of the string inverter 3000.

[0058] In a specific implementation, the first power inverter switch MA3, the second power inverter switch MA4, the third power inverter switch MB3, the fourth power inverter switch MB4, the fifth power inverter switch MC3, and the sixth power inverter switch MC4 are all insulated-gate bipolar thyristors. The gates of each of the first power inverter switch MA3, the second power inverter switch MA4, the third power inverter switch MB3, the fourth power inverter switch MB4, the fifth power inverter switch MC3, and the sixth power inverter switch MC4 are electrically connected to the control module. The control module is used to control the opening and closing of the first power inverter switch MA3, the second power inverter switch MA4, the third power inverter switch MB3, the fourth power inverter switch MB4, the fifth power inverter switch MC3, and the sixth power inverter switch MC4 to input the power frequency fundamental voltage to the string inverter 3000.

[0059] In a specific embodiment, the power module 10 further includes a first unloading unit 16, which is disposed between the first rectifier unit 13 and the first inverter unit 15. The first unloading unit 16 includes a first unloading switch M1 and a first resistor R1. The collector of the first unloading switch M1 is electrically connected to the first DC positive bus 11, and the first resistor R1 is connected in series with the emitter of the first unloading switch M1 and the first DC negative bus 12. The first unloading switch M1 is an insulated-gate bipolar thyristor, and the gate of the first unloading switch M1 is electrically connected to the control module.

[0060] Specifically, when the voltage across the first capacitor C1 is lower than a preset value, the control module controls the first unloading switch M1 to close, and at this time, the current does not pass through the first unloading unit 16. When the voltage across the first capacitor C1 is higher than the preset value, the control module controls the first unloading switch M1 to open, and at this time, the current passes through the first resistor R1 to reduce the voltage across the first capacitor C1 to below the preset value, preventing the first capacitor C1 from breaking down.

[0061] In a specific implementation, the harmonic module 20 has a similar structure to the power module 10. Specifically, the second rectifier unit 23 includes a fourth rectifier structure 231, a fifth rectifier structure 232, and a sixth rectifier structure 233. The DC side of the fourth rectifier structure 231, the DC side of the fifth rectifier structure 232, and the DC side of the sixth rectifier structure 233 are all connected between the second DC positive bus 21 and the second DC negative bus 22. The AC side of the fourth rectifier structure 231 is used to connect to the low-voltage A phase of the box-type transformer 2000. The AC side of the fifth rectifier structure 232 is used to connect to the low-voltage B phase of the box-type transformer 2000. The AC side of the sixth rectifier structure 233 is used to connect to the low-voltage C phase of the box-type transformer 2000.

[0062] In a specific implementation, the fourth rectifier structure 231 includes a first harmonic rectifier switch MA5 and a second harmonic rectifier switch MA6. The collector of the first harmonic rectifier switch MA5 is electrically connected to the second DC positive bus 21, the emitter of the second harmonic rectifier switch MA6 is electrically connected to the second DC negative bus 22, and the emitter of the first harmonic rectifier switch MA5 is electrically connected to the collector of the second harmonic rectifier switch MA6. Both the emitter of the first harmonic rectifier switch MA5 and the collector of the second harmonic rectifier switch MA6 are used to be electrically connected to the low-voltage side A phase of the box-type transformer 2000.

[0063] In a specific implementation, the fifth rectifier structure 232 includes a third harmonic rectifier switch MB5 and a fourth harmonic rectifier switch MB6. The collector of the third harmonic rectifier switch MB5 is electrically connected to the second DC positive bus 21, the emitter of the fourth harmonic rectifier switch MB6 is electrically connected to the second DC negative bus 22, and the emitter of the third harmonic rectifier switch MB5 is electrically connected to the collector of the fourth harmonic rectifier switch MB6. Both the emitter of the third harmonic rectifier switch MB5 and the collector of the fourth harmonic rectifier switch MB6 are used to be electrically connected to the low-voltage side B phase of the box-type transformer 2000.

[0064] In a specific implementation, the sixth rectifier structure 233 includes a fifth harmonic rectifier switch MC5 and a sixth harmonic rectifier switch MC6. The collector of the fifth harmonic rectifier switch MC5 is electrically connected to the second DC positive bus 21, the emitter of the sixth harmonic rectifier switch MC6 is electrically connected to the second DC negative bus 22, and the emitter of the fifth harmonic rectifier switch MC5 is electrically connected to the collector of the sixth harmonic rectifier switch MC6. Both the emitter of the fifth harmonic rectifier switch MC5 and the collector of the sixth harmonic rectifier switch MC6 are used to be electrically connected to the low-voltage side C phase of the box-type transformer 2000.

[0065] In a specific implementation, the first harmonic rectifier switch MA5, the second harmonic rectifier switch MA6, the third harmonic rectifier switch MB5, the fourth harmonic rectifier switch MB6, the fifth harmonic rectifier switch MC5, and the sixth harmonic rectifier switch MC6 are all insulated-gate bipolar thyristors. The gates of each of the first harmonic rectifier switch MA5, the second harmonic rectifier switch MA6, the third harmonic rectifier switch MB5, the fourth harmonic rectifier switch MB6, the fifth harmonic rectifier switch MC5, and the sixth harmonic rectifier switch MC6 are electrically connected to the control module. The control module is used to control the opening and closing of the first harmonic rectifier switch MA5, the second harmonic rectifier switch MA6, the third harmonic rectifier switch MB5, the fourth harmonic rectifier switch MB6, the fifth harmonic rectifier switch MC5, and the sixth harmonic rectifier switch MC6 to convert the three-phase AC power input from the box-type transformer 2000 into pulsating DC power.

[0066] In a specific embodiment, the second filter unit 24 includes a second capacitor C2. The positive terminal of the second capacitor C2 is electrically connected to the second DC positive bus 21, and the negative terminal of the second capacitor C2 is connected to the second DC negative bus 22. The second capacitor C2 is used to receive and charge the DC pulse voltages output by the fourth rectifier structure 231, the fifth rectifier structure 232, and the sixth rectifier structure 233, respectively. After the second capacitor C2 is fully charged, it outputs a stable DC power to the first inverter module.

[0067] In a specific embodiment, the first inverter unit 15 includes a fourth inverter structure 251, a fifth inverter structure 252, and a sixth inverter structure 253. The DC side of the fourth inverter structure 251, the DC side of the fifth inverter structure 252, and the DC side of the sixth inverter structure 253 are all connected between the second DC positive bus 21 and the second DC negative bus 22. The AC side of the fourth inverter structure 251 is used to be electrically connected to the AC side A phase of the string inverter 3000, the AC side of the fifth inverter structure 252 is used to be electrically connected to the AC side B phase of the string inverter 3000, and the AC side of the sixth inverter structure 253 is used to be electrically connected to the AC side C phase of the string inverter 3000.

[0068] In a specific implementation, the fourth inverter structure 251 includes a first harmonic inverter switch MA7 and a second harmonic inverter switch MA8. The collector of the first harmonic inverter switch MA7 is electrically connected to the second DC positive bus 21, the emitter of the second harmonic inverter switch MA8 is electrically connected to the second DC negative bus 22, and the emitter of the first harmonic inverter switch MA7 is electrically connected to the collector of the second harmonic inverter switch MA8. Both the emitter of the first harmonic inverter switch MA7 and the collector of the second harmonic inverter switch MA8 are used to be electrically connected to the AC side A phase of the string inverter 3000.

[0069] In a specific implementation, the fifth inverter structure 252 includes a third harmonic inverter switch MB7 and a fourth harmonic inverter switch MB8. The collector of the third harmonic inverter switch MB7 is electrically connected to the second DC positive bus 21, the emitter of the fourth harmonic inverter switch MB8 is electrically connected to the second DC negative bus 22, and the emitter of the third harmonic inverter switch MB7 is electrically connected to the collector of the fourth harmonic inverter switch MB8. Both the emitter of the third harmonic inverter switch MB7 and the collector of the fourth harmonic inverter switch MB8 are used to be electrically connected to the AC side B phase of the string inverter 3000.

[0070] In a specific implementation, the sixth inverter structure 253 includes a fifth harmonic inverter switch MC7 and a sixth harmonic inverter switch MC8. The collector of the fifth harmonic inverter switch MC7 is electrically connected to the second DC positive bus 21, the emitter of the sixth harmonic inverter switch MC8 is electrically connected to the second DC negative bus 22, and the emitter of the fifth harmonic inverter switch MC7 is electrically connected to the collector of the sixth harmonic inverter switch MC8. Both the emitter of the fifth harmonic inverter switch MC7 and the collector of the sixth harmonic inverter switch MC8 are used to be electrically connected to the AC side C phase of the string inverter 3000.

[0071] In a specific implementation, the first harmonic inverter switch MA7, the second harmonic inverter switch MA8, the third harmonic inverter switch MB7, the fourth harmonic inverter switch MB8, the fifth harmonic inverter switch MC7, and the sixth harmonic inverter switch MC8 are all insulated-gate bipolar thyristors. The gates of each of the first harmonic inverter switch MA7, the second harmonic inverter switch MA8, the third harmonic inverter switch MB7, the fourth harmonic inverter switch MB8, the fifth harmonic inverter switch MC7, and the sixth harmonic inverter switch MC8 are electrically connected to the control module. The control module is used to control the opening and closing of the first harmonic inverter switch MA7, the second harmonic inverter switch MA8, the third harmonic inverter switch MB7, the fourth harmonic inverter switch MB8, the fifth harmonic inverter switch MC7, and the sixth harmonic inverter switch MC8 to input harmonic disturbance voltage to the string inverter 3000.

[0072] In a specific embodiment, the power module 10 further includes a second unloading unit 26, which is disposed between the second rectifier unit 23 and the first inverter unit 15. The second unloading unit 26 includes a second unloading switch M2 and a second resistor R2. The collector of the second unloading switch M2 is electrically connected to the second DC positive bus 21, and the second resistor R2 is connected in series with the emitter of the second unloading switch M2 and the second DC negative bus 22. The second unloading switch M2 is an insulated-gate bipolar thyristor, and the gate of the second unloading switch M2 is electrically connected to the control module.

[0073] Specifically, when the voltage across the second capacitor C2 is lower than a preset value, the control module controls the second unloading switch M2 to close, and at this time, the current does not pass through the second unloading unit 26. When the voltage across the second capacitor C2 is higher than the preset value, the control module controls the second unloading switch M2 to open, and at this time, the current passes through the second resistor R2 to reduce the voltage across the second capacitor C2 to below the preset value, preventing the second capacitor C2 from breaking down.

[0074] An impedance characteristic scanning circuit 100 is used to connect a box-type transformer 2000 and a string inverter 3000. The impedance characteristic scanning circuit 100 includes a power module 10 and a harmonic module 20. The power module 10 includes a first DC positive bus 11, a first DC negative bus 12, a first rectifier unit 13, a first filter unit 14, and a first inverter unit 15. The first rectifier unit 13, the first filter unit 14, and the first inverter unit 15 are arranged sequentially. The DC side of the first rectifier unit 13, the first filter unit 14, and the first inverter unit 15 are all connected between the first DC positive bus 11 and the first DC negative bus 12. The harmonic module 20 includes a second DC positive bus 21, a second DC negative bus 22, a second rectifier unit 23, a second filter unit 24, and a second inverter unit 25. The second rectifier unit 23, the second filter unit 24, and the second inverter unit 25 are arranged sequentially. The DC side of the second rectifier unit 23... The DC sides of the first rectifier unit 13, the second rectifier unit 24, and the second inverter unit 25 are all connected between the second positive DC bus 21 and the second negative DC bus 22. The AC sides of the first rectifier unit 13 and the second rectifier unit 23 are both electrically connected to the low-voltage side of the box transformer 2000 to receive the system rated voltage output by the box transformer 2000. The AC sides of the first inverter unit 15 and the second inverter unit 25 are both electrically connected to the AC side of the string inverter 3000. The power module 10 is used to output the power frequency fundamental voltage to the string inverter 3000 according to the system rated voltage. The harmonic module 20 is used to output the harmonic disturbance voltage to the string inverter 3000 according to the system rated voltage, so that the harmonic disturbance voltage is directly applied to the string inverter 3000, avoiding the interference of the box transformer 2000 on the harmonic voltage, and improving the measurement accuracy of the impedance characteristics of the string inverter 3000.

[0075] In the description of the embodiments of this utility model, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and are not intended to indicate or imply that the circuit or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model.

[0076] The above-disclosed embodiments are merely preferred embodiments of the present utility model and should not be construed as limiting the scope of the present utility model. Those skilled in the art can understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present utility model are still within the scope of the present utility model.

Claims

1. An impedance characteristic scanning circuit, characterized in that, The impedance characteristic scanning circuit, used for connecting a box-type transformer and a string inverter, includes: The power module includes a first DC positive bus, a first DC negative bus, a first rectifier unit, a first filter unit, and a first inverter unit. The first rectifier unit, the first filter unit, and the first inverter unit are arranged sequentially. The DC side of the first rectifier unit, the DC side of the first filter unit, and the DC side of the first inverter unit are all connected between the first DC positive bus and the first DC negative bus. The harmonic module includes a second DC positive bus, a second DC negative bus, a second rectifier unit, a second filter unit, and a second inverter unit. The second rectifier unit, the second filter unit, and the second inverter unit are arranged sequentially. The DC side of the second rectifier unit, the DC side of the second filter unit, and the DC side of the second inverter unit are all connected between the second DC positive bus and the second DC negative bus. The AC sides of the first rectifier unit and the second rectifier unit are both electrically connected to the low-voltage side of the box-type transformer to receive the system rated voltage output by the box-type transformer. The AC sides of the first inverter unit and the second inverter unit are both electrically connected to the AC side of the string inverter. The power module is used to output the power frequency fundamental voltage to the string inverter according to the system rated voltage. The harmonic module is used to output harmonic disturbance voltage to the string inverter according to the system rated voltage.

2. The impedance characteristic scanning circuit according to claim 1, characterized in that, The first rectifier unit includes a first rectifier structure, a second rectifier structure, and a third rectifier structure. The DC side of the first rectifier structure, the DC side of the second rectifier structure, and the DC side of the third rectifier structure are all connected between the first DC positive bus and the first DC negative bus. The AC side of the first rectifier structure is used to be electrically connected to phase A of the low-voltage side of the box-type transformer. The AC side of the second rectifier structure is used to be electrically connected to phase B of the low-voltage side of the box-type transformer. The AC side of the third rectifier structure is used to be electrically connected to phase C of the low-voltage side of the box-type transformer.

3. The impedance characteristic scanning circuit according to claim 2, characterized in that, The first rectification structure includes a first power rectifier switch and a second power rectifier switch. The collector of the first power rectifier switch is electrically connected to the first DC positive bus, and the emitter of the second power rectifier switch is electrically connected to the first DC negative bus. The emitter of the first power rectifier switch is electrically connected to the collector of the second power rectifier switch. Both the emitter of the first power rectifier switch and the collector of the second power rectifier switch are used to be electrically connected to the low-voltage side A phase of the box-type transformer.

4. The impedance characteristic scanning circuit according to claim 1, characterized in that, The first filter unit includes a first capacitor, the positive terminal of the first capacitor is electrically connected to the first DC positive bus, and the negative terminal of the first capacitor is connected to the first DC negative bus.

5. The impedance characteristic scanning circuit according to claim 1, characterized in that, The first inverter unit includes a first inverter structure, a second inverter structure, and a third inverter structure. The DC side of the first inverter structure, the DC side of the second inverter structure, and the DC side of the third inverter structure are all connected between the first DC positive bus and the first DC negative bus. The AC side of the first inverter structure is used to be electrically connected to the AC side A phase of the string inverter, the AC side of the second inverter structure is used to be electrically connected to the AC side B phase of the string inverter, and the AC side of the third inverter structure is used to be electrically connected to the AC side C phase of the string inverter.

6. The impedance characteristic scanning circuit according to claim 5, characterized in that, The first inverter structure includes a first power inverter switch and a second power inverter switch. The collector of the first power inverter switch is electrically connected to the first DC positive bus, the emitter of the second power inverter switch is electrically connected to the first DC negative bus, and the emitter of the first power inverter switch is electrically connected to the collector of the second power inverter switch. Both the emitter of the first power inverter switch and the collector of the second power inverter switch are used to be electrically connected to the AC side A phase of the string inverter.

7. The impedance characteristic scanning circuit according to claim 1, characterized in that, The power module further includes a first unloading unit, which is disposed between the first rectifier unit and the first inverter unit. The first unloading unit includes a first unloading switch and a first resistor. The collector of the first unloading switch is electrically connected to the first DC positive bus, and the first resistor is connected in series with the emitter of the first unloading switch and the first DC negative bus.

8. The impedance characteristic scanning circuit according to any one of claims 1-7, characterized in that, The impedance characteristic scanning circuit further includes a control module, which is electrically connected to the first rectifier unit, the first inverter unit, the second rectifier unit, and the second inverter unit. The control module is used to control the operation of each of the first rectifier unit, the first inverter unit, the second rectifier unit, and the second inverter unit.

9. An impedance characteristic testing device, characterized in that, It includes a sensor, a processor, and an impedance characteristic scanning circuit as described in any one of claims 1-8, wherein the sensor is electrically connected to the processor and is electrically connected to both the AC side of the first inverter unit and the AC side of the second inverter unit.

10. An impedance characteristic detection system, characterized in that, It includes a box-type transformer, a string inverter, and an impedance characteristic testing device as described in claim 9, wherein the impedance characteristic testing device is electrically connected to both the box-type transformer and the string inverter.

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