A test circuit

Abstract

The present invention discloses a test circuit, comprising: a first adjustable load, connected to an inverter to be tested, for simulating residual current; a second adjustable load, connected to the inverter to be tested, for simulating the generation of inrush current; a first measuring device, for measuring the first measuring current of the first adjustable load and / or the second adjustable load; a second measuring device, for measuring the second measuring current of the first adjustable load and / or the second adjustable load, the first test device and the second test device having different measuring ranges; a selection switch circuit, for selecting the connection relationship between the first adjustable load and / or the second adjustable load and the first test device and the second test device through the action of the selection switch; a test switch circuit, for controlling the enabling / disconnecting of the first adjustable load and the second adjustable load in the test circuit. The resistor series-parallel connection technology and the capacitor parallel connection technology are used to realize the generation of a wide range of simulated residual electricity, which can better simulate various inverter conditions.

Description

Technical Field

[0001] The invention relates to the field of electronic technology, and in particular to a test circuit. Background Art

[0002] The function of the photovoltaic inverter is to convert the DC voltage, DC current, and DC power generated by the photovoltaic array under sunlight into industrial frequency AC to supply power to electrical equipment, or directly connect the industrial frequency power to the grid for power generation. As the quality of photovoltaic component materials continues to improve, its operating voltage is also constantly increasing to improve the power transmission efficiency of the photovoltaic array. The current operating voltage of the photovoltaic array specified by the latest international standards has reached 1500VDC, which is far higher than the 60VDC human safety voltage specified by international standards. As a high-power power transmission and transformation equipment, photovoltaic transformers are not only used in desert power stations, but are also gradually popularized to households. Preventing overheating and fire is also an important safety regulatory requirement. Therefore, the international standard provides technical requirements for personal safety protection and property protection for photovoltaic inverters, requiring the installation of residual current monitoring circuit breakers in the inverter to cut off the circuit when the residual current flowing through the inverter's accessible parts to the ground, including the residual current with inrush current, exceeds the specified value; the residual current flowing through the inverter's conductive parts reaches the fire hazard limit; the insulation resistance of the DC input terminal to the ground is lower than the specified value; the human body contact current exceeds the standard specified value, etc.

[0003] In the prior art, when detecting the working status of the installed inverter residual current monitoring circuit breaker in various protection scenarios, a single tester is used for testing. However, due to the different conditions of various scenarios and equipment, the multiple current ranges have different loads, the measurement range is wide, and it is easy to output large currents and voltages during the test, causing equipment damage, which is not convenient for actual testing. Summary of the invention

[0004] The technical problem to be solved by the embodiments of the present invention is how to satisfy a wider test range through a single circuit structure setting.

[0005] According to a first aspect, an embodiment of the present invention provides a test circuit, comprising: a first adjustable load, connected to the inverter to be tested, for simulating residual current; a second adjustable load, connected to the inverter to be tested, for simulating the generation of inrush current; a first measuring device, for measuring a first measurement current of the first adjustable load and / or the second adjustable load; a second measuring device, for measuring a second measurement current of the first adjustable load and / or the second adjustable load, wherein the measurement range of the first test device is different from that of the second test device; a selection switch circuit, with a built-in selection switch, connected to the first test circuit and the second test circuit, wherein the connection relationship between the first adjustable load and / or the second adjustable load and the first test device and the second test device is selected through the action of the selection switch; and a test switch circuit, for controlling the enabling / disabling of the first adjustable load and the second adjustable load in the test circuit.

[0006] Optionally, the first adjustable load includes: a first sub-load, including at least two resistance units connected in series, the resistance unit including a digital resistor and at least one counting resistor connected in parallel with the digital resistor in sequence according to the gear order, wherein the digital resistors of different resistance units are always in a series state, the digital resistors are used to characterize the bit information of the resistance value of the load, and the counting resistor is used to characterize the counting information of the resistance value of the load at the current bit; at least a first gear switch, which is respectively connected in series with the counting resistor, and the first gear switches corresponding to different counting resistors are connected in series, and the counting information at the current bit is adjusted by adjusting the opening and closing state of the first gear switch.

[0007] Optionally, the first adjustable load includes: a third adjustable sub-load, and the third adjustable sub-load includes a first sliding adjustable load.

[0008] Optionally, the second adjustable load includes: a second sliding adjustable load.

[0009] Optionally, the test circuit further comprises: a contact current simulation module, which is connected to a selection switch circuit and is connected to the first measuring device through the action of the selection switch.

[0010] Optionally, the test circuit further comprises: an analysis module connected to at least one of the first adjustable load, the second adjustable load and the inverter cut-off action detection module, and comparing the cut-off signal with the time of the inrush current access to obtain the inverter on-off protection action time;

[0011] The first measuring device 103 is connected to monitor whether the unweighted output voltage of the weighted network exceeds the standard requirement.

[0012] Optionally, the test circuit further comprises: an alarm module connected to the inverter cut-off action detection module, and configured to alarm when the inverter cut-off action occurs.

[0013] Optionally, the test circuit also includes: a sampling module, which is respectively connected to the second adjustable load, the contact current input terminal, and the calibration module, and is used to collect current and voltage information of the second adjustable load, the contact current input terminal, and the calibration module.

[0014] This application realizes the wide range generation of simulated residual power through resistor series series-parallel technology and capacitor parallel technology, which can better simulate various inverter conditions. In addition, this application realizes different logical functions in the same test circuit according to the different switch closures through the logical setting of the functional switch, and concentrates the functions of multiple test units in this test circuit. Finally, the test circuit integrates multiple functions such as residual current and protection action time, human contact current, and insulation resistance threshold protection action time required by international standards and European standards, and is widely applicable to various power levels, grid-connected, off-grid photovoltaic inverter product manufacturers, testing institutions and scientific research laboratories. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the structure of a test circuit according to an embodiment of the present invention is shown;

[0017] Figure 2 A schematic diagram showing the structure of a first adjustable load in a test circuit according to an embodiment of the present invention is shown;

[0018] Figure 3 A schematic diagram showing the structure of a first adjustable load in a test circuit according to an embodiment of the present invention is shown;

[0019] Figure 4 A schematic diagram showing the structure of a first adjustable load in a test circuit according to an embodiment of the present invention is shown;

[0020] Figure 5 A schematic diagram of port connection of a first adjustable load in a test circuit according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] As described in the background technology, in the prior art, when detecting the working state of the installed inverter residual current monitoring circuit breaker in each protection scenario, the method of testing by a single tester has the problem that due to the different situations of each scenario and equipment, the load of multiple current ranges is different, the measurement range is wide, and it is easy to output a large current and voltage during the test, causing equipment damage, which is not convenient for actual testing. Therefore, the inventor found through research that a wider simulated residual current generation range can be generated by simulating loads in series and parallel resistors and capacitors. In the test circuit, a selection switch circuit is set to integrate multiple measurement circuits into one measurement circuit, so that residual currents of different magnitudes can be generated according to actual measurement requirements, and the required measurements can be performed according to preset rules according to the measurement method selected by the selection switch, and a single circuit design can be used to realize multi-functional measurement functions, which increases operability and saves time and space costs.

[0023] However, in the actual implementation process, the inventors also found that during the test, due to the different properties of the parameters to be measured, the current parameter range of each property is relatively wide. For example, the residual current of the inverter is usually 0-1A, and the human body contact current and ground current are usually 1-10A. The traditional single design method cannot meet the measurement requirements. In order to solve this problem, it is necessary to design measurement ranges with different accuracy requirements and different ranges. Specifically, the inventors designed a dual-channel, dual-range measurement method, using two measurement devices with different channels to measure measurement data of different ranges and accuracies, respectively, to achieve data measurement with a wide range and different accuracies.

[0024] For ease of understanding, the following is an explanation with reference to the accompanying drawings. Figure 1 A schematic diagram of a test circuit according to an embodiment of the present invention is shown in FIG. Figure 1 As shown, the adjustable load includes: a first adjustable load 101, connected to the inverter to be tested, for simulating residual current;

[0025] Specifically, the first adjustable load can be composed of load components such as resistors and capacitors and connected to the inverter to be tested. Since changes in the power supply load will cause changes in the power supply output, as the load increases, the output decreases, and conversely, as the load decreases, the output increases, the load is used to adjust the current output by the inverter to generate different load outputs and simulate residual currents under different test requirements.

[0026] A second adjustable load 102 is connected to the inverter to be tested and is used to simulate the generation of an inrush current;

[0027] Specifically, the second adjustable load has the same principle as the first adjustable load. It can be composed of load components such as resistors and capacitors and connected to the inverter to be tested. Because changes in the power load will cause changes in the power output, as the load increases, the output decreases. On the contrary, as the load decreases, the output increases. Therefore, the load is used to adjust the current output by the inverter to simulate the inrush current under different conditions.

[0028] A first measuring device 103, used to measure a first measurement current of the first adjustable load and / or the second adjustable load;

[0029] Specifically, a current and voltage test device is provided, and the measuring range is obviously different from that of the second measuring device, and the first adjustable load 101 and the second adjustable load 102 are connected to the selection switch circuit 105 and the test switch 106 respectively, such as Figure 1 As shown, after the photovoltaic positive electrode (PV+) input voltage of the inverter under test enters, it is regulated by the first adjustable load to output a simulated residual current, and then it is selected by the selection switch circuit 105 and the test switch 106, and is separated into two paths according to the range of the first measuring device 103 and the second measuring device 104. If it meets the range of the first measuring device 103, it enters the first measuring device 103 for measurement. After the PV+ input voltage enters, it is regulated by the second adjustable load 102 to output a simulated inrush current, and it is also selected by the selection switch circuit 105 and the test switch 106 to separate into two paths according to the range of the first measuring device 103 and the second measuring device 104. If it meets the range of the first measuring device 103, it enters the first measuring device 103 for measurement. After the PV+ input voltage enters, the residual current of the analog output is adjusted by the first adjustable load 103, the selection switch circuit 105, and the test switch 106, and the inrush current of the analog output is adjusted by the first adjustable load 103, the selection switch circuit 105, and the test switch 106. If it meets the range of the first measuring device 103, it enters the first measuring device 103 for measurement.

[0030] A second measuring device 104, used to measure a second measuring current of the first adjustable load and / or the second adjustable load, wherein the first measuring device 103 and the second measuring device 104 have different measuring ranges;

[0031] Specifically, similar to the working principle of the first measuring device 103, when the first adjustable load 101 is simulated and generated, the residual current range of the simulated output adjusted by the selection switch circuit 105 and the test switch 106 does not meet the range of the first measuring device 103 but meets the range of the second measuring device 104. The current enters the second measuring device 104 for measurement. When the range of the second measuring device 104 is met, the second measuring device 104 can also be used to measure the inrush current simulated by the second adjustable load 102 and adjusted by the selection switch circuit 105 and the test switch 16. When the range of the second measuring device 104 is met, the second measuring device 104 can also be used to measure the simulated residual current simulated by the first adjustable load 103 and adjusted by the selection switch circuit 105 and the test switch 106, and the superimposed current after the superimposition of the simulated inrush current simulated by the first adjustable load 103 and adjusted by the selection switch circuit 105 and the test switch 106.

[0032] A selection switch circuit 105 has a built-in selection switch, is connected to the first test device and the second test device, and selects the connection relationship between the first adjustable load and / or the second adjustable load and the first test device and the second test device through the action of the selection switch;

[0033] Specifically, multiple sets of switches are built into the selection switch circuit 105, and the simulated residual current and simulated inrush current generated in the first adjustable load 101 and / or the second adjustable load 102 are output to the first measuring device 103 or the second measuring device 104 through the switch logic on-off sequence control. Figure 1 As shown, in the present invention, if the simulated residual current generated by the first adjustable load 101 needs to be output to the first measuring device 103, the contact pairs 11-12 and 17-18 set in the switch circuit 105 are selected to enter the first measuring device 103 for measurement. Similarly, if the value needs to be output to the second measuring device 104, the contact pair 15-16 set in the switch circuit 105 is selected to enter the second measuring device 104 for measurement.

[0034] The test switch circuit 106 is used to control the enabling / disabling of the first adjustable load 101 and the second adjustable load 102 in the test circuit.

[0035] Specifically, multiple groups of switches are set in the test switch circuit 106, and the first adjustable load 101 and the second adjustable load 102 are enabled / disconnected in the test circuit by controlling the contact states of the multiple groups of switches. The enabled / disconnected state of the first adjustable load 101 is adjusted by controlling the state of the contact pair of k3-k4. When k3-k4 is connected, the adjustable load 101 is enabled for measuring the simulated residual current alone. The enabled / disconnected state of the second adjustable load 102 is adjusted by controlling the state of the contact pair of k1-k2 and k5-k6. When the contact pair of k1-k2 and the contact pair of k5-k6 are connected, the second adjustable load is enabled alone for measuring the simulated inrush current alone. Similarly, when k3-k4, k1-k2, and k5-k6 in the test switch 106 are connected at the same time, the first adjustable load 101 and the second adjustable load 102 are enabled at the same time for measuring the superimposed current of the simulated residual current and the simulated inrush current.

[0036] As an exemplary embodiment, the first adjustable load includes: a first sub-load, which includes a resistor unit 21, including a digital resistor 22 and at least one counting resistor 23, and at least one first unit switch 24, which is used to constitute the minimum unit of the adjustable load; the digital resistor 22 is connected in series with other unit digital resistors, and is used to characterize the resistance value bit information of the resistor unit for the adjustable load; the counting resistor 23 is connected in parallel with the digital resistor 22 in a gear sequence, and is used to characterize the counting information of the resistance value of the adjustable load at the current bit; the first gear switch 24 is connected in series with the counting resistor 23, and the current bit is adjusted by adjusting the opening and closing state of the first gear switch 24 The counting information under the condition that the resistor unit 25 includes a digital resistor 26 and at least one counting resistor 27, and at least one first unit switch 28, which are used to constitute the minimum unit of the adjustable load; the digital resistor 26 is connected in series with the digital resistor 22, and is used to characterize the number of bits of the resistance value of the adjustable load in the resistor unit; the counting resistor 27 is connected in parallel with the digital resistor 22 in a gear sequence, and is used to characterize the counting information of the resistance value of the adjustable load under the current number of bits; the first gear switch 28 is connected in series with the counting resistor 27, and the counting information under the current number of bits is adjusted by adjusting the opening and closing state of the first gear switch 28; the resistor unit constitutes the adjustable load as the smallest overall unit.

[0037] Specifically, Figure 2The structural schematic diagram of a first adjustable load proposed in an embodiment of the present invention, taking two resistor units as an example, the resistor unit 21 includes a digital resistor 21 and a counting resistor 23, and a first gear switch 24; the resistor unit 25 includes a digital resistor 26 and a counting resistor 27, and a first gear switch 28. The series connection between the resistor units is formed by the constant series connection of the digital resistors in the units. Taking this embodiment as an example, the resistor unit 21 is connected in series with the resistor unit 25, and the digital resistor 22 included in the resistor unit 21 and the digital resistor 26 in the resistor unit 25 are in a constant series state. The digital resistor 22 is used to represent the resistance value bit information of the adjustable load corresponding to the resistor unit 21, and the digital resistor 26 is used to represent the resistance value bit information of the adjustable load corresponding to the resistor unit 25; the counting resistor 23 included in the resistor unit 21 is connected in series with the first gear switch 24, and then connected in parallel with the digital resistor 22 according to the gear sequence. The counting resistor 23 is used to represent the counting information of the resistance value of the adjustable load at the current bit, and the counting information at the current bit is adjusted by adjusting the on-off state of the first gear switch 24. Similarly, the connection mode and function effects of the components in the resistance unit 25 are the same as those of the resistance unit 21 and will not be described in detail.

[0038] As an exemplary embodiment, it is characterized in that the first adjustable load includes: a capacitor unit 31, including at least one unit capacitor 32, 33, and first gear switches 34, 35 corresponding to the unit capacitors, respectively, for constituting a minimum unit of the adjustable load.

[0039] Specifically, Figure 3 A schematic diagram of the structure of an adjustable load proposed in an embodiment of the present invention is shown in FIG. Figure 3 As shown, the capacitor unit, as the smallest overall unit, constitutes an adjustable load. In this embodiment, two capacitor units are taken as an example, capacitor unit 31A and capacitor unit 31B, wherein capacitor unit 31A contains different unit capacitors 32 and 33, and first gear switches 34 and 35, wherein capacitor unit 31B contains different unit capacitors 32B and 33B, and first gear switches 34B and 35B. Through the parallel connection between the capacitor units, the final output capacitance is the sum of the capacitances of the two capacitor units, capacitor unit 31A and capacitor unit 31B, wherein capacitor unit 31A contains different unit capacitors 32 and 33, and unit capacitors 32 and 33 are connected in parallel, and first gear switches 34 and 35 are connected in series with 32 and 33 respectively. By controlling the working state of the first gear switches 34 and 35, the enabling and switching out of unit capacitors 32 and 33 are adjusted, and then the output capacitance value of the capacitor unit is adjusted.

[0040] Similarly, the connection method and effects of the components in the capacitor unit 31B are the same as those in the resistor unit 31A, and will not be described in detail.

[0041] As an exemplary embodiment, it is characterized in that the first adjustable load includes: a third adjustable sub-load, and the third adjustable sub-load includes a first sliding adjustable load.

[0042] Specifically, Figure 1 When the first adjustable load 11 set in the test circuit cannot meet the load requirements, a third sub-load can be connected externally in CN1 in the figure to simulate the residual current. When the power of the inverter under test is greater than 250kVA, a specially designed sliding-wire adjustable power resistor is used as the simulated load. A four-unit synchronous adjustable power resistor is used. Each power resistor is rated at 0-200Ω and rated at 2.5A / 600V, that is, the full-scale power of each power resistor is 1500W; different residual current measurements require different load resistance values. 2.5A-10A at a working voltage of 600V, the resistance value adjustment range is from 240Ω-50Ω, and the specific logic is shown in Table 1;

[0043] 2.5 5 7.5 10 Resistance Range 0-240Ω 0-120Ω 0-75Ω 0-55Ω Current range ≤2.5A ≤5A ≤7.5A ≤10A Resistance method Single channel Two-way parallel connection Three-way parallel connection Four-way parallel Maximum input voltage 600V 600V 560V 550V

[0044] Table 1

[0045] The structure of the sliding line adjustable power resistor is as follows Figure 4 , a four-unit high-power sliding wire resistor box is used for series-parallel connection. When measuring high current, the four sliding wire power resistors are divided into four grades according to the test requirements, and the resistance, power, current and maximum working voltage of the four grades are calculated. Then, the four sliding wire resistors are connected in parallel. The connection relationship of the combination switch is as follows: Figure 5 .

[0046] As an exemplary embodiment, it is characterized in that the second adjustable load includes: a second sliding adjustable load.

[0047] Specifically, changes in the power supply load will cause changes in the power supply output. When the load increases, the output decreases, and vice versa, when the load decreases, the output increases.

[0048] As an exemplary embodiment, the test circuit further includes: an inverter cut-off action detection module 41, which is used to output a cut-off signal when a cut-off action occurs in the inverter.

[0049] Specifically, Figure 1 As shown, when the current and voltage in the test circuit meet the inverter cut-off conditions, in this embodiment, that is, when the sum of the simulated residual current value output by the first adjustable load 101 and the simulated inrush current value of the second adjustable load 102 is greater than the preset value, the inverter will cut off the input. At this time, the inverter cut-off action detection module 41 detects the action and starts to continuously output a cut-off signal to the outside as an inverter cut-off signal identifier.

[0050] As an exemplary embodiment, the test circuit further includes: a contact current simulation module 51, which is connected to the selection switch 105 circuit and selects connection with the first test device 103 or the second test device 104 through the action of the selection switch.

[0051] Specifically, Figure 1 As shown, the contact current simulation module 51 is connected to the selection switch circuit 105, and the current is output from the positive end of the terminal CN1, and is measured in the first measuring device 103 through the 9-10 contacts of the selection switch 105 to obtain test data.

[0052] As an exemplary embodiment, the test circuit also includes: an analysis module 61, which is connected to at least one of the first adjustable load 101, the second adjustable load 102 and the inverter cut-off action detection module 41, compares the cut-off signal with the time of inrush current access, and obtains the inverter on-off protection action time; connected to the first measuring device 103, monitors whether the unweighted output voltage of the weighted network exceeds the standard requirements.

[0053] Specifically, when the current and voltage in the test circuit meet the inverter cut-off condition, in this embodiment, that is, when the sum of the simulated residual current value output by the first adjustable load and the simulated inrush current value of the second adjustable load is greater than the preset value, the inverter will cut off the input, and at this time, the inverter cut-off action detection module detects the action and starts to continuously output a cut-off signal to the outside as an inverter cut-off signal identifier; when the analysis module receives the cut-off signal identifier, the output time of the superimposed signal of the first adjustable load and the second adjustable load received in the analysis module is compared to obtain the inverter on-off protection action time. Or it is connected to the first measuring device 103 to monitor whether the unweighted output voltage of the weighted network exceeds the standard requirements.

[0054] As an exemplary embodiment, the test circuit further includes: an alarm module 81 connected to the inverter cut-off action detection module 41, and configured to generate an alarm when the inverter cut-off action occurs.

[0055] Specifically, Figure 1 As shown, the alarm module 81 is connected to the inverter stage action module 41. When the current and voltage in the test circuit meet the inverter cut-off conditions, in this embodiment, that is, when the sum of the simulated residual current value output by the first adjustable load and the simulated inrush current value of the second adjustable load is greater than the preset value, the inverter will cut off the input. At this time, the inverter cut-off action detection module detects the action and starts to continuously output a cut-off signal to the outside as an inverter cut-off signal identifier; when the alarm module receives the inverter cut-off signal identifier, an alarm is issued.

[0056] As an exemplary embodiment, the test circuit also includes: a sampling module, which is respectively connected to the second adjustable load 102, the contact current simulation module 51, and the calibration module 71, and is used to collect current and voltage information of the second adjustable load 102, the contact current simulation module 51, and the calibration module 71.

[0057] Specifically, Figure 1 As shown, R46, R47, and R48 are sampling modules, wherein R46 is connected to the second adjustable load 102 for sampling the generated simulated inrush current information, R47 is connected to the first measuring device 103 for sampling the current and voltage information output by the first measuring device, and R48 is connected to the second measuring device 104 for using the current and voltage information output by the second measuring device.

[0058] This application realizes the wide range generation of simulated residual power through resistor series series-parallel technology and capacitor parallel technology, which can better simulate various inverter conditions. In addition, this application realizes different logical functions in the same test circuit according to the different switch closures through the logical setting of the functional switch, and concentrates the functions of multiple test units in this test circuit. Finally, the test circuit integrates multiple functions such as residual current and protection action time, human contact current, and insulation resistance threshold protection action time required by international standards and European standards, and is widely applicable to various power levels, grid-connected, off-grid photovoltaic inverter product manufacturers, testing institutions and scientific research laboratories.

[0059] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A test circuit for testing an inverter, characterized in that: include: A first adjustable load is connected to the inverter to be tested and is used to simulate a residual current; A second adjustable load is connected to the inverter to be tested and is used to simulate the generation of an inrush current; A first measuring device, used to measure a first measuring current of the first adjustable load and / or the second adjustable load; A second measuring device, used to measure a second measuring current of the first adjustable load and / or the second adjustable load, wherein the first measuring device and the second measuring device have different measuring ranges; A selection switch circuit, with a built-in selection switch, connected to the first test device and the second test device, and selecting a connection relationship between the first adjustable load and / or the second adjustable load and the first test device and the second test device through the action of the selection switch; The test switch circuit is used to control the enabling / disconnecting of the first adjustable load and the second adjustable load in the test circuit, and also includes: an inverter cut-off action detection module, which is used to output a cut-off signal when the inverter is cut off, and a contact current simulation module, which is connected to the selection switch circuit and selects to be connected to the first test device through the action of the selection switch.

2. The test circuit according to claim 1, characterized in that: The first adjustable load comprises: A first sub-load, comprising at least two resistance units connected in series, wherein the resistance unit comprises a digital resistor and at least one counting resistor sequentially connected in parallel with the digital resistor in a gear order, wherein the digital resistors of different resistance units are in a constant series state, the digital resistors are used to represent the bit information of the resistance value of the load, and the counting resistor is used to represent the counting information of the resistance value of the load at the current bit; At least a first gear switch is connected in series with the counting resistor, and the first gear switches corresponding to different counting resistors are connected in series, and the counting information at the current bit is adjusted by adjusting the opening and closing state of the first gear switch.

3. The test circuit according to claim 1, characterized in that: The first adjustable load comprises: A second sub-load, comprising at least one capacitor unit, different capacitor units are connected in parallel, the capacitor unit comprises at least one unit capacitor, wherein different unit capacitors are connected in parallel, and an output capacitance value of the capacitor unit is represented by an equivalent capacitance value after the unit capacitors are connected in parallel; At least a first gear switch is connected in series with the unit capacitors, and the first gear switches corresponding to different unit capacitors are connected in series, and the output capacitance value of the current capacitor unit is adjusted by adjusting the opening and closing states of the first gear switches.

4. The test circuit according to claim 1, characterized in that: The first adjustable load includes: a third adjustable sub-load, and the third adjustable sub-load includes a first sliding adjustable load.

5. The test circuit according to claim 1, characterized in that: The second adjustable load includes: a second sliding adjustable load.

6. The test circuit according to claim 5, characterized in that: Also includes: An analysis module is connected to at least one of the first adjustable load, the second adjustable load, and the inverter cut-off action detection module, and compares the cut-off signal with the time when the inrush current is connected to obtain the inverter on-off protection action time; Connected to the first measuring device 103, it monitors whether the unweighted output voltage of the weighted network exceeds the standard requirement.

7. The test circuit according to claim 6, characterized in that: include: The alarm module is connected to the inverter cut-off action detection module and is used for alarming when the inverter cut-off action occurs.

8. The test circuit according to claim 7, characterized in that: include: The sampling module is connected to the second adjustable load, the contact current input terminal and the calibration module respectively, and is used to collect current and voltage information of the second adjustable load, the contact current input terminal and the calibration module.

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