Direct-current component sampling method and system

Abstract

The invention discloses a direct current component sampling method and system. The direct-current component sampling method is realized by a direct-current component sampling system, and the direct-current component sampling system comprises a calibration platform, at least one first sampling module and a controller; the direct-current component sampling method comprises the steps that before the inverter is started, the calibration platform sets the direct-current component of the isolation voltage source to be zero; after the inverter is started, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output end of the inverter according to the initial common-mode voltage; when the inverter works, the controller determines the actual common-mode voltage of the inverter and determines a corresponding common-mode error according to the actual common-mode voltage and the common-mode error gain; and the direct current component of each first output end of the inverter is determined according to the actual sampling voltage, the zero point error, the differential mode gain and the common mode error output by the first sampling module. According to the technical scheme, the accuracy of direct-current component acquisition is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage acquisition, and in particular to a direct current component sampling method and system. Background Art

[0002] When the solar-storage inverter works in the inverter off-grid mode, the DC component of the inverter output AC voltage needs to be controlled within a certain value to meet the requirements of parallel operation or transformer load. Therefore, it is necessary to sample the DC component of the AC output voltage for control.

[0003] In order to accurately collect the DC component voltage, the existing sampling calibration method calibrates the zero point error and the differential mode gain ratio under fixed conditions. However, different input voltages and different input paths in the photovoltaic system will make the common mode voltage different, and the error caused by different common mode voltages is different. The existing calibration method can only adapt to the error caused by the calibration compensation fixed common mode voltage and the error caused by the differential mode gain error. It cannot adapt to the situation where the common mode voltage changes continuously during the working process, and cannot compensate for different common mode errors, so it is impossible to accurately collect the DC component in the AC voltage output by the inverter. Summary of the invention

[0004] The present invention provides a DC component sampling method and system to solve the problem that the existing sampling method cannot accurately sample the DC component in the AC voltage output by the inverter.

[0005] According to one aspect of the present invention, a DC component sampling method is provided, and the DC component sampling method is implemented by a DC component sampling system, and the DC component sampling system includes a calibration platform, at least one first sampling module and a controller; the first sampling module is respectively connected to a first output end of an inverter, a second output end of the inverter and the controller; wherein the inverter includes at least one first output end; the first sampling module corresponds to the first output end of the inverter one by one;

[0006] The DC component sampling method comprises:

[0007] Before the inverter is turned on, the calibration platform sets the DC component of the isolation voltage source to zero;

[0008] After the inverter is powered on, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage;

[0009] When the inverter is working, the controller determines the actual common-mode voltage of the inverter, and determines the corresponding common-mode error according to the actual common-mode voltage and the common-mode error gain; and determines the DC component of each first output terminal of the inverter according to the actual sampling voltage, zero-point error, differential-mode gain and common-mode error output by the first sampling module.

[0010] Optionally, the first sampling module includes a first operational amplifier and a second operational amplifier; the first input end of the first operational amplifier is connected to the first output end of the inverter, the second input end of the first operational amplifier is connected to the second output end of the inverter, and the second operational amplifier is connected between the output end of the first operational amplifier and the controller;

[0011] The controller determines the DC component of each first output terminal of the inverter according to the actual sampling voltage output by the first sampling module, the zero point error, the differential mode gain and the common mode error, including:

[0012] The controller subtracts the bias voltage of the second operational amplifier and the zero-point error from the actual sampled voltage to obtain a first difference, divides the first difference by the amplification factor of the second operational amplifier, subtracts the common-mode error to obtain a second difference, and divides the second difference by the differential-mode gain to obtain the DC component.

[0013] Optionally, the controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, including:

[0014] The controller determines a corresponding common-mode error gain according to the initial common-mode voltage, the zero-point error, and an initial sampling voltage output by the first sampling module.

[0015] Optionally, before the calibration platform sets the DC component of the isolation voltage source to zero, the method further includes:

[0016] The calibration platform sets the DC component of the isolated voltage source connected to the inverter to zero to determine the zero-point error; the calibration platform sets the DC component of the isolated voltage source to a preset value to determine the differential mode gain.

[0017] Optionally, the DC component sampling system further includes a second sampling module; the second sampling module is respectively connected to the second output terminal of the inverter and the first ground wire of the inverter control module corresponding to the inverter, and the second sampling module is connected to the controller;

[0018] The controller determines an actual common mode voltage of the inverter, including:

[0019] The controller obtains the actual common mode voltage from the second sampling module.

[0020] Optionally, the DC component sampling system further includes a third sampling module; the third sampling module is respectively connected to the first busbar and the second busbar of the inverter, the first ground wire and the second ground wire of the inverter control module corresponding to the inverter, each first output terminal of the inverter and the second output terminal of the inverter; the third sampling module is connected to the controller;

[0021] The controller determines an actual common mode voltage of the inverter, including:

[0022] The controller obtains the input voltage of the inverter, the first bus voltage of the first bus, the ground voltage of the second ground line, and the second output voltage of the second output end of the inverter from the third sampling module; and determines the actual common mode voltage of the inverter according to the input voltage of the inverter, the first bus voltage, the ground voltage of the second ground line, the second output voltage and parameter information of the third sampling module.

[0023] Optionally, after the controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, the controller further includes:

[0024] The controller stores the common mode error gain.

[0025] According to another aspect of the present invention, a DC component sampling system is provided, and the DC component sampling system is used to execute the DC component sampling method described in any embodiment of the present invention; the DC component sampling system includes: a calibration platform, at least one first sampling module and a controller; the first sampling module is respectively connected to the first output end of the inverter, the second output end of the inverter and the controller; wherein the inverter includes at least one first output end; the first sampling module corresponds one-to-one to the first output end of the inverter.

[0026] Optionally, the DC component sampling system further includes a second sampling module; the second sampling module is respectively connected to the second output terminal of the inverter and the first ground wire of the inverter control module corresponding to the inverter, and the second sampling module is connected to the controller;

[0027] Alternatively, the DC component sampling system also includes a third sampling module; the third sampling module is respectively connected to the first bus, the second bus, the first ground wire, the second ground wire of the inverter control module corresponding to the inverter, the first output terminals of the inverter and the second output terminal of the inverter; the third sampling module is connected to the controller.

[0028] Optionally, the second sampling module includes a third operational amplifier, a fourth operational amplifier and a first voltage source;

[0029] The first input terminal of the third operational amplifier is connected to the second output terminal of the inverter, and the first input terminal of the third operational amplifier is connected to the first ground line; the second input terminal of the third operational amplifier is connected to the output terminal of the third operational amplifier;

[0030] The first input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier, the first input terminal of the fourth operational amplifier is connected to the first voltage source, and the second input terminal of the fourth operational amplifier is connected to the output terminal of the fourth operational amplifier;

[0031] The controller is connected to the output terminal of the fourth operational amplifier.

[0032] According to the technical solution of the embodiment of the present invention, before the inverter leaves the factory, the controller can determine the common-mode error gain and store it, so that after the inverter actually works, the controller can calibrate the DC component of the AC voltage output by the collected inverter according to the common-mode error gain, thereby improving the accuracy of DC component collection. When the inverter actually works after leaving the factory, the controller can determine the actual common-mode voltage of the inverter in real time or periodically, and determine the common-mode error corresponding to each phase output voltage of the inverter according to the actual common-mode voltage and the common-mode error gain corresponding to each phase output voltage of the inverter. When determining the DC component, the common-mode error can be subtracted to achieve compensation for the DC component, so that a more accurate DC component can be obtained, thereby improving the accuracy of DC component collection.

[0033] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 is a flow chart of a DC component sampling method provided by an embodiment of the present invention;

[0036] Figure 2 is a flow chart of another DC component sampling method provided by an embodiment of the present invention;

[0037] Figure 3 is a flow chart of another DC component sampling method provided by an embodiment of the present invention;

[0038] Figure 4 is a structural schematic diagram of a DC component sampling system provided by an embodiment of the present invention;

[0039] Figure 5 is a schematic diagram of a circuit structure of a first sampling module provided by an embodiment of the present invention;

[0040] Figure 6 is a structural schematic diagram of another DC component sampling system provided by an embodiment of the present invention;

[0041] Figure 7 is a structural schematic diagram of another DC component sampling system provided by an embodiment of the present invention;

[0042] Figure 8 is a schematic diagram of a circuit structure of a second sampling module provided by an embodiment of the present invention;

[0043] Fig. 9 It is a schematic diagram of the circuit structure of a third sampling module provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0045] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0046] The present invention provides a DC component sampling method, which is implemented by a DC component sampling system. The DC component sampling system includes a calibration platform, at least one first sampling module and a controller; the first sampling module is respectively connected to the first output end of an inverter, the second output end of the inverter and the controller; wherein the inverter includes at least one first output end; the first sampling module corresponds to the first output end of the inverter one by one.

[0047] Among them, the calibration platform can be an automatic test calibration platform. The inverter can be a photovoltaic storage inverter. The inverter includes an inverter circuit. The input side of the inverter can be connected to a photovoltaic string or an energy storage battery, and the inverter can convert the direct current output by the photovoltaic string or the energy storage battery into an alternating current output. The first output end of the inverter can be connected to the live wire of the power grid, and the second output end of the inverter can be connected to the neutral wire of the power grid. The inverter includes at least one first output end, that is, the inverter can output at least one phase voltage. By setting the first sampling module to correspond to the first output end of the inverter one by one, the sampled voltage of the first output end of each inverter can be collected, so that the DC component of the AC voltage output by the first output end of each inverter can be determined, that is, the DC component of each phase AC voltage output by the inverter is determined, so as to facilitate the control of the DC component of each phase AC voltage. The controller can be a digital signal processor (digital signal processor, DSP), or a field programmable gate array (Field Programmable Gate Array, FPGA), etc., which is not limited in this embodiment. In the inverter system, the inverter is connected to the inverter control module, and the inverter control module can control the output voltage of the inverter. For example, the inverter control module is a controller, or the inverter control module and the controller are two control devices, which is not limited in this embodiment. In the inverter system, the voltage at the second output terminal of the inverter is equal to half of the voltage difference between the first bus and the second bus. Because the inverter control module is provided with many high-resistance differential amplification sampling circuits for voltage sampling of the inverter power end, after the sampling resistor divides the voltage, there is a situation where the voltage of the first ground line of the inverter control module is not equal to the voltage of the second output terminal of the inverter, then the second output terminal of the inverter has a common mode voltage generated to the first ground line.

[0048] Figure 1 is a flow chart of a DC component sampling method provided by an embodiment of the present invention, with reference to Figure 1 , DC component sampling methods include:

[0049] S110. Before the inverter is turned on, the calibration platform sets the DC component of the isolation voltage source to zero.

[0050] Specifically, before the inverter leaves the factory, the calibration platform can control whether the inverter is turned on. Before the inverter is turned on (i.e. when the calibration platform controls the inverter to shut down), the calibration platform can set input and output conditions for the inverter, such as setting a single battery fixed voltage of 400V input and no photovoltaic string voltage input. Set the inverter to grid-connected mode, connect the output terminals (first output terminal and second output terminal) of the inverter to an isolated voltage source, and the calibration platform sets the DC component of the isolated voltage source to zero, that is, the DC component of the AC voltage output by the inverter is zero.

[0051] S120: After the inverter is powered on, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage.

[0052] Specifically, before the inverter leaves the factory, after the inverter is turned on and runs stably, the controller can determine the initial common-mode voltage of the inverter, which can be determined based on the voltage parameters and current parameters of the inverter, or the initial common-mode voltage can be obtained from the common-mode voltage acquisition circuit, which is not limited in this embodiment. The controller can determine the common-mode error gain corresponding to each first output terminal of the inverter based on the initial common-mode voltage, for example, the common-mode error gain corresponding to each first output terminal of the inverter can be determined based on the output voltage of each first output terminal of the inverter and the initial common-mode voltage. The controller can store the determined common-mode error gain, so that after the inverter actually works, the controller can calibrate the DC component of the AC voltage output by the collected inverter based on the common-mode error gain, thereby improving the accuracy of DC component acquisition.

[0053] S130. When the inverter is working, the controller determines the actual common-mode voltage of the inverter, and determines the corresponding common-mode error based on the actual common-mode voltage and the common-mode error gain; determines the DC component of each first output terminal of the inverter based on the actual sampling voltage, zero-point error, differential-mode gain and common-mode error output by the first sampling module.

[0054] Specifically, when the inverter is working, that is, when the inverter is actually working after leaving the factory, the controller can determine the actual common-mode voltage of the inverter in real time or periodically, so as to facilitate calibration of the collected DC component according to the actual common-mode voltage. Therefore, when the number of input voltage paths of the inverter is different and / or the magnitude of the input voltage is different, the accurate actual common-mode voltage can be determined, thereby improving the applicability and accuracy of DC component collection.

[0055] After the controller determines the actual common-mode voltage of the inverter, the controller can determine the corresponding common-mode error according to the actual common-mode voltage and the common-mode error gain, that is, determine the common-mode error corresponding to each phase output voltage of the inverter according to the actual common-mode voltage and the common-mode error gain corresponding to each phase output voltage of the inverter. For example, the product of the actual common-mode voltage and the common-mode error gain is used as the common-mode error of the corresponding phase.

[0056] The controller determines the DC component of each first output terminal of the inverter according to the actual sampling voltage, zero-point error, differential-mode gain and common-mode error output by the first sampling module, that is, determines the DC component corresponding to each phase output voltage of the inverter, so as to subtract the common-mode error and compensate for the DC component, thereby obtaining a more accurate DC component and improving the accuracy of DC component acquisition.

[0057] The technical solution of this embodiment is that before the inverter leaves the factory, the controller can determine the common-mode error gain and store it, so that after the inverter actually works, the controller can calibrate the DC component of the AC voltage output by the collected inverter according to the common-mode error gain, thereby improving the accuracy of DC component collection. When the inverter actually works after leaving the factory, the controller can determine the actual common-mode voltage of the inverter in real time or periodically, and determine the common-mode error corresponding to each phase output voltage of the inverter according to the actual common-mode voltage and the common-mode error gain corresponding to each phase output voltage of the inverter. When determining the DC component, the common-mode error can be subtracted to achieve compensation for the DC component, so that a more accurate DC component can be obtained, thereby improving the accuracy of DC component collection.

[0058] Based on the above technical solution, the first sampling module includes a first operational amplifier and a second operational amplifier; the first input end of the first operational amplifier is connected to the first output end of the inverter, the second input end of the first operational amplifier is connected to the second output end of the inverter, and the second operational amplifier is connected between the output end of the first operational amplifier and the controller.

[0059] Figure 2 is a flowchart of another DC component sampling method provided by an embodiment of the present invention. Optionally, refer to Figure 2 , DC component sampling methods include:

[0060] S210. Before the inverter is turned on, the calibration platform sets the DC component of the isolation voltage source to zero.

[0061] S220: After the inverter is powered on, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage.

[0062] S230: When the inverter is working, the controller determines an actual common-mode voltage of the inverter, and determines a corresponding common-mode error according to the actual common-mode voltage and a common-mode error gain.

[0063] S240, the controller subtracts the bias voltage and zero-point error of the second operational amplifier from the actual sampled voltage to obtain a first difference, divides the first difference by the gain of the second operational amplifier, subtracts the common-mode error to obtain a second difference, and divides the second difference by the differential-mode gain to obtain a DC component.

[0064] Among them, the first operational amplifier is a first-stage operational amplifier, which can amplify or reduce the voltage input to the first operational amplifier, and the second operational amplifier is a second-stage operational amplifier, which can reduce and bias the voltage output by the first operational amplifier, thereby avoiding the first sampling module from outputting a negative voltage.

[0065] Specifically, the first input terminal of the first operational amplifier is connected to the first output terminal of the inverter, and the voltage of the first input terminal of the first operational amplifier is proportional to the DC component U d The second input terminal of the first operational amplifier is connected to the second output terminal of the inverter, and there is a common mode voltage between the second output terminal of the inverter and the first ground line of the inverter control module corresponding to the inverter, that is, the voltage of the second input terminal of the first operational amplifier is equal to the common mode voltage U c The voltage U output by the first operational amplifier is o1 It can be expressed as U o1 =U c ×A c +U d ×A d , where A c is the common-mode error gain, A d is the differential mode gain. For example, if the bias voltage of the second operational amplifier is 1.5V, the zero point can be biased to 1.5V, and the gain of the second operational amplifier is Zero point error is V oz , then the actual sampling voltage output by the second operational amplifier is The DC component That is, the actual sampling voltage is subtracted from the bias voltage and zero-point error of the second operational amplifier to obtain a first difference, the first difference is divided by the amplification factor of the second operational amplifier, the common-mode error is subtracted to obtain a second difference, and the second difference is divided by the differential-mode gain to obtain a DC component. In this way, the common-mode error can be subtracted to achieve compensation for the DC component, so that a more accurate DC component can be obtained, thereby improving the accuracy of DC component acquisition.

[0066] On the basis of the above technical solution, optionally, the controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, including:

[0067] The controller determines a corresponding common mode error gain according to the initial common mode voltage, the zero point error and the initial sampling voltage output by the first sampling module.

[0068] Specifically, the common-mode error gain can be calculated based on the output voltage of the first sampling module (the actual sampling voltage U o2 ) is determined by the calculation formula. The zero point error is V oz , the initial common mode voltage is Uco , the initial sampling voltage output by the first sampling module is U s1 , the calibration platform sets the DC component of the isolated voltage source to zero, then the common-mode error gain In this way, the common-mode error gain can be determined before the inverter is actually applied, which facilitates determination of the common-mode error when the inverter is actually applied.

[0069] Based on the above technical solutions, Figure 3 is a flowchart of another DC component sampling method provided by an embodiment of the present invention. Optionally, refer to Figure 3 , DC component sampling methods include:

[0070] S310. Before the inverter is turned on, the calibration platform sets the DC component of the isolated voltage source connected to the inverter to zero to determine the zero point error; the calibration platform sets the DC component of the isolated voltage source to a preset value to determine the differential mode gain.

[0071] Specifically, before the inverter is turned on (i.e., when the calibration platform controls the inverter to shut down), the calibration platform first sets the inverter to bypass mode, the inverter is connected to the isolated voltage source, the relay in the inverter is not closed, and the second output terminal of the inverter is not connected to the bus midpoint. Because the inverter does not output voltage, each phase is balanced. For example, if the inverter outputs a three-phase voltage, the three phases are balanced, so that the common-mode voltage is 0 and the common-mode error is 0. By setting the DC component of the isolated voltage source connected to the inverter to zero on the calibration platform, the zero-point error can be determined. For example, the DC component (the DC component is zero at this time) and the common-mode voltage (the common-mode voltage is zero at this time) are substituted into the voltage output by the second operational amplifier (the actual sampling voltage U o2 ) is used to determine the zero-point error, so that the zero-point error can be calibrated to make the zero-point error more accurate, which is convenient for the subsequent accurate determination of the common-mode error gain. Then, the differential-mode gain can be calibrated by setting the DC component of the isolated voltage source to a preset value through the calibration platform, that is, the differential-mode gain can be determined, for example, the determined zero-point error and common-mode voltage (the common-mode voltage is zero at this time) are substituted into the voltage output by the second operational amplifier (the actual sampling voltage U o2 ) is used to determine the differential mode gain, making the differential mode gain more accurate and facilitating the subsequent accurate determination of the common mode error gain.

[0072] In this way, the calibration of the zero-point error and the differential-mode gain is achieved, which facilitates the subsequent accurate determination of the common-mode error gain, and further accurately determines the common-mode error when the inverter is actually working, thereby improving the accuracy of DC component acquisition.

[0073] S320, the calibration platform sets the DC component of the isolation voltage source to zero.

[0074] S330: After the inverter is powered on, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage.

[0075] S340. When the inverter is working, the controller determines the actual common-mode voltage of the inverter, and determines the corresponding common-mode error based on the actual common-mode voltage and the common-mode error gain; determines the DC component of each first output terminal of the inverter based on the actual sampling voltage, zero-point error, differential-mode gain and common-mode error output by the first sampling module.

[0076] Based on the above technical solutions, the following describes a method in which the controller determines the actual common-mode voltage, but this is not intended to limit the present application.

[0077] In one embodiment, the DC component sampling system further includes a second sampling module; the second sampling module is respectively connected to the second output terminal of the inverter and the first ground wire of the inverter control module corresponding to the inverter, and the second sampling module is connected to the controller. The inverter control module can control the inverter, thereby controlling the output voltage of the inverter. The inverter control module is connected to the first ground wire.

[0078] Optionally, the controller determines an actual common mode voltage of the inverter, including:

[0079] The controller obtains the actual common mode voltage from the second sampling module.

[0080] Specifically, the second sampling module is a common mode voltage sampling circuit, and the second sampling module can collect the actual common mode voltage in real time or periodically. The controller can obtain the actual common mode voltage from the second sampling module, thereby determining the actual common mode voltage.

[0081] In another embodiment, the DC component sampling system further includes a third sampling module; the third sampling module is respectively connected to the first busbar, the second busbar, the first ground wire, the second ground wire of the inverter control module corresponding to the inverter, each first output terminal of the inverter and the second output terminal of the inverter; the third sampling module is connected to the controller. The first busbar can be a positive busbar, and the second busbar is a negative busbar. The first busbar can connect multiple photovoltaic strings and energy storage batteries.

[0082] Optionally, the controller determines an actual common mode voltage of the inverter, including:

[0083] The controller obtains the input voltage of the inverter, the first bus voltage of the first bus, the ground voltage of the second ground line and the second output voltage of the second output end of the inverter from the third sampling module; and determines the actual common mode voltage of the inverter according to the input voltage of the inverter, the first bus voltage, the ground voltage of the second ground line, the second output voltage and the parameter information of the third sampling module.

[0084] Specifically, for example, if the third sampling module includes multiple sampling resistors, the parameter information of the third sampling module includes the resistance value of each sampling resistor. The input voltage of the inverter may include the output voltage of each photovoltaic string and the output voltage of the energy storage battery. After obtaining the input voltage of the inverter, the first bus voltage of the first bus, the ground voltage of the second ground wire, and the second output voltage of the second output terminal of the inverter, the voltage of each sampling node can be determined, and then the current relationship of the third acquisition module can be established according to the parameter information of the third sampling module (the resistance value of each sampling resistor), so that the controller can calculate and determine the actual common mode voltage of the inverter.

[0085] Based on the above technical solutions, optionally, after the controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, the method further includes:

[0086] The controller stores the common-mode error gain.

[0087] Specifically, after determining the common-mode error gain corresponding to each first output terminal of the inverter, that is, after determining the common-mode error gain corresponding to each phase output voltage of the inverter, the controller can store the common-mode error gain to facilitate subsequent determination of the common-mode error when the inverter is actually working.

[0088] The DC component collected by the related art is compared with the DC component collected by the DC component sampling method of the present invention. The related art only calibrates the zero point error and the differential mode gain ratio under fixed conditions.

[0089] Exemplarily, for example, under the conditions of a differential mode gain of 0.98217 and a common mode voltage of 81V, the zero point and the differential mode gain are calibrated using the relevant technology and the DC component sampling method of the present invention, respectively. After the inverter is connected to the grid and works stably, the DC component of each phase output voltage of the inverter under different working conditions is collected using the relevant technology and the DC component sampling method of the present invention. For example, the inverter outputs a three-phase AC voltage (phase A, phase B, and phase C). Different working conditions refer to different DC components and common mode voltages of the AC voltage output by the inverter. Table 1 shows the DC components collected by the relevant technology under different working conditions, and Table 2 shows the DC components collected by the DC component sampling method of the present invention under different working conditions.

[0090] Table 1 DC components collected by related technologies under different working conditions

[0091] Table 2 DC components collected by the DC component sampling method of the present invention under different working conditions

[0092]

[0093] As shown in Table 1 and Table 2, the sampling errors of the DC components of the three phases A, B, and C in the related technology vary greatly, and the errors vary according to the size of the common mode voltage. The maximum error is 212mV when the common mode voltage deviates from the calibration point; most of the errors in the present application are within 30mV. And the larger the common mode voltage variation range, the larger the error of the related technology solution, while the common mode voltage variation of the present application solution is not affected. Therefore, the technical solution of the present invention can improve the accuracy of the DC component of the AC voltage output by the inverter.

[0094] An embodiment of the present invention further provides a DC component sampling system, which is used to execute the DC component sampling method provided by any implementation scheme of the present invention. Figure 4 is a schematic diagram of a DC component sampling system provided by an embodiment of the present invention, with reference to Figure 4 The DC component sampling system includes: a calibration platform 101, at least one first sampling module 102 and a controller 103; the first sampling module 102 is respectively connected to the first output end of the inverter 201, the second output end of the inverter 201 and the controller 103; wherein the inverter 201 includes at least one first output end; the first sampling module 102 corresponds to the first output end of the inverter 201 one by one.

[0095] Among them, before the inverter 201 leaves the factory, the calibration platform 101 is connected to the inverter 201, and the inverter 201 can be controlled, for example, whether the inverter 201 is turned on, and the input conditions and output conditions of the inverter 201. For example, the inverter 201 includes three first output terminals, that is, the inverter 201 outputs a three-phase voltage, and the three first output terminals of the inverter 201 include a first first output terminal L1, a second first output terminal L2, and a third first output terminal L3. The first first output terminal L1, the second first output terminal L2, and the third first output terminal L3 are respectively connected to the corresponding first sampling modules 102. The second output terminal N of the inverter 201 is connected to each first sampling module 102.

[0096] Specifically, before the inverter 201 leaves the factory, before the inverter 201 is turned on (i.e., when the calibration platform 101 controls the inverter 201 to shut down), the calibration platform 101 can set input and output conditions for the inverter 201, such as setting a single cell fixed voltage of 400V input, and no photovoltaic string voltage input. The inverter 201 is set to the grid-connected mode, and the output ends (the first output end and the second output end) of the inverter 201 are connected to the isolated voltage source. The calibration platform 101 sets the DC component of the isolated voltage source to zero, that is, the DC component of the AC voltage output by the inverter 201 is zero. Then the calibration platform 101 controls the inverter 201 to start up. After the inverter 201 is turned on and runs stably, the controller 103 can determine the initial common-mode voltage of the inverter 201. The controller 103 can determine the common-mode error gain corresponding to each first output end of the inverter 201 based on the initial common-mode voltage. The controller 103 may store the determined common-mode error gain, so that after the inverter actually works, the controller 103 calibrates the collected DC component of the AC voltage output by the inverter according to the common-mode error gain, thereby improving the accuracy of DC component collection.

[0097] When the inverter 201 is actually working after leaving the factory, the controller 103 can determine the actual common-mode voltage of the inverter in real time or periodically, so as to calibrate the collected DC component according to the actual common-mode voltage. Therefore, when the number of input voltage paths of the inverter is different and / or the magnitude of the input voltage is different, the accurate actual common-mode voltage can be determined, thereby improving the applicability and accuracy of DC component collection.

[0098] After the controller 103 determines the actual common-mode voltage of the inverter, the controller 103 may determine the corresponding common-mode error according to the actual common-mode voltage and the common-mode error gain, that is, determine the common-mode error corresponding to each phase output voltage of the inverter according to the actual common-mode voltage and the common-mode error gain corresponding to each phase output voltage of the inverter. For example, the product of the actual common-mode voltage and the common-mode error gain is used as the common-mode error of the corresponding phase.

[0099] The controller 103 determines the DC component of each first output terminal of the inverter according to the actual sampling voltage, zero point error, differential mode gain and common mode error output by the first sampling module 102, that is, determines the DC component corresponding to each phase output voltage of the inverter, so as to subtract the common mode error and compensate for the DC component, thereby obtaining a more accurate DC component and improving the accuracy of DC component acquisition.

[0100] Based on the above technical solutions, Figure 5 is a schematic diagram of a circuit structure of a first sampling module provided by an embodiment of the present invention, with reference to Figure 5The first sampling module 102 includes a first operational amplifier U1 and a second operational amplifier U2; the first input end of the first operational amplifier U1 is connected to the first output end of the inverter 201, the second input end of the first operational amplifier U1 is connected to the second output end N of the inverter 201, and the second operational amplifier U2 is connected between the output end of the first operational amplifier U1 and the controller 103.

[0101] in, Figure 5 FIG. 2 shows a situation where the first sampling module 102 is connected to the first output terminal (the first output terminal L1 ) of the inverter 201 .

[0102] Specifically, the first operational amplifier U1 is a first-stage operational amplifier, which can amplify or reduce the voltage input to the first operational amplifier U1, and the second operational amplifier U2 is a second-stage operational amplifier, which can reduce and bias the voltage output by the first operational amplifier U1, thereby preventing the first sampling module 102 from outputting a negative voltage. The first input terminal of the first operational amplifier is connected to the first output terminal of the inverter, and the voltage of the first input terminal of the first operational amplifier is proportional to the DC component U d The second input terminal of the first operational amplifier is connected to the second output terminal of the inverter, and there is a common mode voltage between the second output terminal of the inverter and the first ground line of the inverter control module corresponding to the inverter, that is, the voltage of the second input terminal of the first operational amplifier is equal to the common mode voltage U c The voltage U output by the first operational amplifier is o1 It can be expressed as U o1 =U c ×A c +U d ×A d , where A c is the common-mode error gain, A d is the differential mode gain. For example, if the bias voltage of the second operational amplifier is 1.5V, the zero point can be biased to 1.5V, and the gain of the second operational amplifier is Zero point error is V oz , then the actual sampling voltage output by the second operational amplifier is The DC component That is, the bias voltage and zero-point error of the second operational amplifier are subtracted from the actual sampled voltage to obtain a first difference, the first difference is divided by the amplification factor of the second operational amplifier, the common-mode error is subtracted to obtain a second difference, and the second difference is divided by the differential-mode gain to obtain a DC component. In this way, the common-mode error can be subtracted to achieve compensation for the DC component, so that a more accurate DC component can be obtained, thereby improving the accuracy of DC component acquisition.

[0103] Optionally, refer to Figure 5, the first sampling module 102 also includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a second voltage source U3; the first resistor R1 is connected between the first output terminal of the inverter 201 and the first input terminal of the first operational amplifier U1, the second resistor R2 is connected between the output terminal of the first operational amplifier U1 and the first input terminal of the first operational amplifier U1, the third resistor R3 is connected between the second output terminal of the inverter 201 and the second input terminal of the first operational amplifier U1, and the fourth resistor R4 is connected between the second input terminal of the first operational amplifier U1 and the first ground line GND;

[0104] The first input terminal of the second operational amplifier U2 is connected to the output terminal of the first operational amplifier U1 through the fifth resistor R5, the first input terminal of the second operational amplifier U2 is connected to the second voltage source U3 through the sixth resistor R6, and the output terminal of the second operational amplifier U2 is connected to the controller.

[0105] Specifically, the first resistor R1, the third resistor R3, the fourth resistor R4 and the fifth resistor R5 have a voltage dividing effect, and the second resistor R2 can form a feedback circuit. The sixth resistor R6 can divide the voltage provided by the second voltage source U3. By setting the second voltage source U3, a bias voltage can be provided, so that the second operational amplifier U2 can bias the voltage output by the first operational amplifier U1, and the negative voltage output by the first operational amplifier U1 can be adjusted to a positive voltage, so as to avoid the first sampling module 102 outputting a negative voltage.

[0106] For example, if the resistance of the first resistor R1 and the third resistor R3 is R, and the resistance of the second resistor R2 and the fourth resistor R4 is G×R, then the differential mode gain is Ideally, the common-mode gain is zero. Although the common-mode rejection ratio of the op amp is very large, the impact of the various parameters of the op amp is very small, and the impact of the op amp can be ignored, the common-mode gain caused by the external resistor accuracy error problem cannot be ignored. For example, the error coefficient of the first resistor R1 is k1, the error coefficient of the second resistor R2 is k2, the error coefficient of the third resistor R3 is k3, and the error coefficient of the fourth resistor R4 is k4. The actual resistance of the first resistor R1 is k1×R, the actual resistance of the second resistor R2 is k2×G×R, the actual resistance of the third resistor R3 is k3×R, and the actual resistance of the fourth resistor R4 is k4×G×R. According to the virtual short and virtual open principles of the operational amplifier, the output voltage of the first operational amplifier U1 can be obtained. Among them, U c is the common mode voltage, that is, the voltage difference between the voltage of the second output terminal N of the inverter 201 and the voltage of the first ground line GND, U dis the DC component of the AC voltage output by the inverter 201, that is, the DC component of the voltage at the first output terminal of the inverter 201. After simplification, we can get From the expression of the output voltage of the first operational amplifier U1, it can be seen that if the resistance error accuracy is 1%, the influence on the differential mode gain ratio is the largest. If the differential mode gain A d =1, then the common-mode error gain is A c =0.02. If the common-mode voltage is as large as 100V, the output caused by the common-mode voltage is 2V. Therefore, in the sampling of high common-mode voltage and small differential-mode signals, the common-mode voltage and resistance accuracy have a great influence on the sampling system.

[0107] The technical solution of this embodiment is to adjust the common mode error gain A before the inverter 201 leaves the factory. c Perform calibration to determine the common-mode error gain A c By determining the actual common-mode voltage during the actual operation of the inverter 201 after leaving the factory, the common-mode error caused by the accurate common-mode voltage can be obtained, so that the DC component of the AC voltage output by the inverter 201 can be determined more accurately.

[0108] Based on the above technical solution, in one implementation mode, Figure 6 is a schematic diagram of the structure of another DC component sampling system provided by an embodiment of the present invention. Figure 6 The DC component sampling system further includes a second sampling module 104 ; the second sampling module 104 is respectively connected to the second output terminal N of the inverter 201 and the first ground wire GND of the inverter control module corresponding to the inverter 201 , and the second sampling module 104 is connected to the controller 103 .

[0109] Specifically, the common-mode voltage exists between the first ground wire GND and the second output terminal N of the inverter 201. By setting a second sampling module 104, the second sampling module 104 is respectively connected to the second output terminal N of the inverter 201 and the first ground wire GND of the inverter control module corresponding to the inverter 201, so that the actual common-mode voltage can be collected and transmitted to the controller 103. Then, the controller 103 does not need to calculate the actual common-mode voltage, which can reduce the amount of calculation of the controller 103 and facilitate improving the control efficiency.

[0110] In another embodiment, Figure 7 is a schematic diagram of the structure of another DC component sampling system provided by an embodiment of the present invention. Figure 7The DC component sampling system further includes a third sampling module 105; the third sampling module 105 is respectively connected to the first bus BUS+, the second bus BUS- of the inverter 201, the first ground GND, the second ground PE of the inverter control module corresponding to the inverter 201, each first output terminal of the inverter and the second output terminal N of the inverter; the third sampling module 105 is connected to the controller 103. The second ground PE is the shell ground of the inverter.

[0111] Specifically, for example, the inverter 201 includes three first output terminals, that is, the inverter 201 outputs a three-phase voltage, and the three first output terminals of the inverter 201 include a first first output terminal L1, a second first output terminal L2, and a third first output terminal L3. The first first output terminal L1, the second first output terminal L2, and the third first output terminal L3 are respectively connected to the third sampling module 105. The input voltage of the inverter 201 may include the output voltage of each photovoltaic string and the output voltage of the energy storage battery. The controller 103 can obtain the input voltage of the inverter 201, the first bus voltage of the first bus BUS+, the grounding voltage of the second ground line PE, and the second output voltage of the second output terminal N of the inverter 201 from the third sampling module 105; and determine the actual common mode voltage of the inverter according to the input voltage of the inverter 201, the first bus voltage, the grounding voltage of the second ground line PE, the second output voltage, and the parameter information of the third sampling module 105 (for example, the resistance value of each sampling resistor in the third sampling module 105).

[0112] After obtaining the input voltage of the inverter 201, the first bus voltage of the first bus BUS+, the ground voltage of the second ground line PE, and the second output voltage of the second output terminal N of the inverter 201, the voltage of each sampling node can be determined, and then the current relationship of the third acquisition module 105 can be established according to the parameter information of the third sampling module 105 (for example, the resistance value of each sampling resistor), so that the controller 103 can calculate and determine the actual common mode voltage of the inverter 201.

[0113] Figure 8 is a schematic diagram of a circuit structure of a second sampling module provided in an embodiment of the present invention. Figure 8 , the second sampling module 104 includes a third operational amplifier U4, a fourth operational amplifier U5 and a first voltage source U6;

[0114] The first input terminal of the third operational amplifier U4 is connected to the second output terminal N of the inverter 201, and the first input terminal of the third operational amplifier U4 is connected to the first ground line GND; the second input terminal of the third operational amplifier U4 is connected to the output terminal of the third operational amplifier U4;

[0115] A first input terminal of the fourth operational amplifier U5 is connected to the output terminal of the third operational amplifier U4, a first input terminal of the fourth operational amplifier U5 is connected to the first voltage source U6, and a second input terminal of the fourth operational amplifier U5 is connected to the output terminal of the fourth operational amplifier U5;

[0116] The controller 103 is connected to the output terminal of the fourth operational amplifier U5.

[0117] Specifically, by setting the first voltage source U6, a bias voltage can be provided so that the fourth operational amplifier U5 can bias the voltage output by the third operational amplifier U4, and the negative voltage output by the third operational amplifier U4 can be adjusted to a positive voltage, thereby preventing the second sampling module 104 from outputting a negative voltage.

[0118] By setting the first input terminal of the third operational amplifier U4 to be connected to the second output terminal N of the inverter 201, and the first input terminal of the third operational amplifier U4 to be connected to the first ground line GND, the third operational amplifier U4 can collect the actual common-mode voltage between the second output terminal N of the inverter 201 and the first ground line GND, and the fourth operational amplifier U5 can be biased to output the actual common-mode voltage to the controller 103.

[0119] Optionally, refer to Figure 8 The second sampling module 104 further includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9 and a tenth resistor R10, wherein the seventh resistor R7 is connected between the second output terminal N of the inverter 201 and the first input terminal of the third operational amplifier U4, the eighth resistor R8 is connected between the first ground wire GND and the first input terminal of the third operational amplifier U4, the ninth resistor R9 is connected between the output terminal of the third operational amplifier U4 and the first input terminal of the fourth operational amplifier U5; and the tenth resistor R10 is connected between the first voltage source U6 and the first input terminal of the fourth operational amplifier U5. The seventh resistor R7, the eighth resistor R8, the ninth resistor R9 and the tenth resistor R10 have a voltage dividing effect, which can prevent the third operational amplifier U4 and the fourth operational amplifier U5 from being damaged by a large voltage.

[0120] Based on the above technical solutions, Fig. 9 is a schematic diagram of a circuit structure of a third sampling module provided in an embodiment of the present invention. Optionally, refer to Fig. 9The third sampling module 105 includes a first sampling resistor R11, a second sampling resistor R12, a third sampling resistor R13, a fourth sampling resistor R14, a fifth sampling resistor R15, a sixth sampling resistor R16, a seventh sampling resistor R17, an eighth sampling resistor R18, a ninth sampling resistor R19, a tenth sampling resistor R20, an eleventh sampling resistor R21, a twelfth sampling resistor R22, a thirteenth sampling resistor R23, a fourteenth sampling resistor R24, a fifteenth sampling resistor R25, a sixteenth sampling resistor R26, a seventeenth sampling resistor R27, an eighteenth sampling resistor R28, a nineteenth sampling resistor R29, a twentieth sampling resistor R30, a twenty-first sampling resistor R31, a twenty-second sampling resistor R32, a twenty-third sampling resistor R33 and a twenty-fourth sampling resistor R34;

[0121] A first end of the first sampling resistor R11 is connected to the first bus BUS+, a second end of the first sampling resistor R11 is connected to the first ground line GND, a first end of the second sampling resistor R12 is connected to the first ground line GND, and a second end of the second sampling resistor R12 is connected to the second bus BUS-;

[0122] A first end of the third sampling resistor R13 is connected to the first bus BUS+, a second end of the third sampling resistor R13 is connected to the first ground line GND, a first end of the fourth sampling resistor R14 is connected to the first ground line GND, and a second end of the fourth sampling resistor R14 is connected to the second bus BUS-;

[0123] A first end of the fifth sampling resistor R15 is connected to the first bus BUS+, a second end of the fifth sampling resistor R15 is connected to the first ground line GND, a first end of the sixth sampling resistor R16 is connected to the first ground line GND, and a second end of the sixth sampling resistor R16 is connected to the second bus BUS-;

[0124] A first end of the seventh sampling resistor R17 is connected to the first bus BUS+, a second end of the seventh sampling resistor R17 is connected to the first ground line GND, a first end of the eighth sampling resistor R18 is connected to the first ground line GND, and a second end of the eighth sampling resistor R18 is connected to the second bus BUS-;

[0125] A first end of the ninth sampling resistor R19 is connected to the first bus BUS+, a second end of the ninth sampling resistor R19 is connected to the first ground line GND, a first end of the tenth sampling resistor R20 is connected to the first ground line GND, and a second end of the tenth sampling resistor R20 is connected to the second bus BUS-;

[0126] The eleventh sampling resistor R21 is connected between the first ground line GND and the second bus line BUS-;

[0127] The twelfth sampling resistor R22 is connected between the first ground line GND and the second ground line PE;

[0128] The thirteenth sampling resistor R23 is connected between the first ground line GND and the second output terminal N of the inverter 201;

[0129] The fourteenth sampling resistor R24 ​​is connected between the first ground line GND and the second ground line PE;

[0130] The fifteenth sampling resistor R25 is connected between the first bus bar BUS+ and the first ground line GND, and the sixteenth sampling resistor R26 is connected between the first ground line GND and the second output terminal N of the inverter 201;

[0131] The seventeenth sampling resistor R27 is connected between the first ground line GND and the second bus line BUS-;

[0132] The eighteenth sampling resistor R28 is connected between the first ground line GND and the second output terminal N of the inverter 201; the nineteenth sampling resistor R29 is connected between the first ground line GND and the third first output terminal L3 of the inverter 201; the twentieth sampling resistor R30 is connected between the first ground line GND and the second first output terminal L2 of the inverter 201; the twenty-first sampling resistor R31 is connected between the first ground line GND and the first first output terminal L1 of the inverter 201; the twenty-second sampling resistor R32 is connected between the first ground line GND and the second output terminal N of the inverter 201; the twenty-third sampling resistor R33 is connected between the first ground line GND and the second output terminal N of the inverter 201; and the twenty-fourth sampling resistor R34 is connected between the first ground line GND and the second output terminal N of the inverter 201.

[0133] Specifically, the first sampling resistor R11 and the second sampling resistor R12 constitute a differential sampling circuit, which can obtain the voltage Upv1 of the first photovoltaic string input to the inverter 201, the third sampling resistor R13 and the fourth sampling resistor R14 constitute a differential sampling circuit, which can obtain the voltage Upv2 of the second photovoltaic string input to the inverter 201, the fifth sampling resistor R15 and the sixth sampling resistor R16 constitute a differential sampling circuit, which can obtain the voltage Upv3 of the third photovoltaic string input to the inverter 201, the seventh sampling resistor R17 and the eighth sampling resistor R18 constitute a differential sampling circuit, which can obtain the voltage Upv4 of the fourth photovoltaic string input to the inverter 201. The ninth sampling resistor R19 and the tenth sampling resistor R20 constitute a differential sampling circuit, which can collect the voltage Ubat input from the energy storage battery to the inverter 201. The eleventh sampling resistor R21 and the twelfth sampling resistor R22 are insulation impedance differential sampling resistors. The thirteenth sampling resistor R23 and the fourteenth sampling resistor R24 ​​are voltage differential sampling resistors between the second output terminal N of the inverter and the second ground line PE. The fifteenth sampling resistor R25 and the sixteenth sampling resistor R26 are positive half-bus differential sampling resistors, and the seventeenth sampling resistor R27 and the eighteenth sampling resistor R28 are negative half-bus differential sampling resistors. The nineteenth sampling resistor R29, the twentieth sampling resistor R30, the twenty-first sampling resistor R31, the twenty-second sampling resistor R32, the twenty-third sampling resistor R33 and the twenty-fourth sampling resistor R34 are three-phase AC voltage and DC component differential sampling equivalent resistors of the AC voltage.

[0134] It should be noted that Fig. 9 The circuit structure of the third sampling module 105 shown is an equivalent diagram of a high-resistance voltage divider network of each high-resistance sampling circuit of the inverter system. Fig. 9 The figure shows a situation where the inverter 201 is connected to four photovoltaic strings, but this is not a limitation.

[0135] Exemplarily, for example, the resistance values ​​of the first sampling resistor R11, the second sampling resistor R12, the third sampling resistor R13, the fourth sampling resistor R14, the fifth sampling resistor R15, the sixth sampling resistor R16, the seventh sampling resistor R17 and the eighth sampling resistor R18 are all Rp, the resistance values ​​of the ninth sampling resistor R19 and the tenth sampling resistor R20 are all Rt, and the resistance values ​​of the eleventh sampling resistor R21 and the twelfth sampling resistor R22 are all Ri;

[0136] The resistance values ​​of the thirteenth sampling resistor R23 and the fourteenth sampling resistor R24 ​​are both Re;

[0137] The resistance values ​​of the fifteenth sampling resistor R25, the sixteenth sampling resistor R26, the seventeenth sampling resistor R27 and the eighteenth sampling resistor R28 are all Rb;

[0138] The resistance values ​​of the nineteenth sampling resistor R29 , the twentieth sampling resistor R30 , the twenty-first sampling resistor R31 , the twenty-second sampling resistor R32 , the twenty-third sampling resistor R33 and the twenty-fourth sampling resistor R34 are all Ra.

[0139] The second bus BUS- is the reference point 0V; Ubus is the voltage of the first bus, U n is the voltage of the N line (the second output terminal N of the inverter) to the second busbar BUS-. Upe is the voltage difference of the second ground line PE (the shell ground of the inverter) to the second output terminal N of the inverter, then U n +Upe is the voltage of the second ground wire PE to the second busbar BUS-, and Uac1, Uac2, and Uac3 are the voltages of the three-phase power to the second output terminal N of the inverter. Set the common mode voltage to U c , then the voltage of the first ground wire GND to the second bus bar BUS- is U n -U c .

[0140] Since the three-phase electricity is basically balanced, the small error can be ignored. Then the sum of the currents of the three-phase live wire currents entering the control terminal GND is

[0141] According to the balance of node current inflow and outflow, we can get:

[0142]

[0143] Simplified:

[0144]

[0145] The resistance of each sampling resistor is known, and each voltage can be sampled and calculated to determine the actual common-mode voltage U under different input voltages. c Therefore, when the number of input photovoltaic paths of the inverter is different, and / or the high-resistance sampling circuit is different, or the input voltage values ​​of the inverter are different, the actual common-mode voltage can be determined, thereby improving the applicability and accuracy of determining the actual common-mode voltage, and then the common-mode error can be accurately determined, which can improve the accuracy of determining the DC component of the inverter output AC voltage.

[0146] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0147] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC component sampling method, characterized in that: The DC component sampling method is implemented by a DC component sampling system, which includes a calibration platform, at least one first sampling module and a controller; the first sampling module is respectively connected to the first output end of the inverter, the second output end of the inverter and the controller; wherein the inverter includes at least one first output end; the first sampling module corresponds to the first output end of the inverter one by one; The DC component sampling method comprises: Before the inverter is turned on, the calibration platform sets the DC component of the isolation voltage source to zero; After the inverter is powered on, the controller determines an initial common-mode voltage of the inverter, and determines a common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage; When the inverter is working, the controller determines the actual common-mode voltage of the inverter, and determines the corresponding common-mode error according to the actual common-mode voltage and the common-mode error gain; and determines the DC component of each first output terminal of the inverter according to the actual sampling voltage, zero-point error, differential-mode gain and common-mode error output by the first sampling module.

2. The DC component sampling method according to claim 1, characterized in that: The first sampling module includes a first operational amplifier and a second operational amplifier; the first input end of the first operational amplifier is connected to the first output end of the inverter, the second input end of the first operational amplifier is connected to the second output end of the inverter, and the second operational amplifier is connected between the output end of the first operational amplifier and the controller; The controller determines the DC component of each first output terminal of the inverter according to the actual sampling voltage output by the first sampling module, the zero point error, the differential mode gain and the common mode error, including: The controller subtracts the bias voltage of the second operational amplifier and the zero-point error from the actual sampled voltage to obtain a first difference, divides the first difference by the amplification factor of the second operational amplifier, subtracts the common-mode error to obtain a second difference, and divides the second difference by the differential-mode gain to obtain the DC component.

3. The DC component sampling method according to claim 1, characterized in that: The controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, including: The controller determines a corresponding common-mode error gain according to the initial common-mode voltage, the zero-point error, and an initial sampling voltage output by the first sampling module.

4. The DC component sampling method according to claim 1, characterized in that: Before the calibration platform sets the DC component of the isolation voltage source to zero, the method further includes: The calibration platform sets the DC component of the isolated voltage source connected to the inverter to zero to determine the zero-point error; the calibration platform sets the DC component of the isolated voltage source to a preset value to determine the differential mode gain.

5. The DC component sampling method according to any one of claims 1 to 4, characterized in that: The DC component sampling system further includes a second sampling module; the second sampling module is respectively connected to the second output terminal of the inverter and the first ground wire of the inverter control module corresponding to the inverter, and the second sampling module is connected to the controller; The controller determines an actual common mode voltage of the inverter, including: The controller obtains the actual common mode voltage from the second sampling module.

6. The DC component sampling method according to any one of claims 1 to 4, characterized in that: The DC component sampling system further includes a third sampling module; the third sampling module is respectively connected to the first busbar and the second busbar of the inverter, the first ground wire and the second ground wire of the inverter control module corresponding to the inverter, each first output terminal of the inverter and the second output terminal of the inverter; the third sampling module is connected to the controller; The controller determines an actual common mode voltage of the inverter, including: The controller acquires the input voltage of the inverter, the first bus voltage of the first bus, the ground voltage of the second ground line, and the second output voltage of the second output end of the inverter from the third sampling module; The actual common mode voltage of the inverter is determined according to the input voltage of the inverter, the first bus voltage, the ground voltage of the second ground line, the second output voltage and parameter information of the third sampling module.

7. The DC component sampling method according to any one of claims 1 to 4, characterized in that: After the controller determines the common-mode error gain corresponding to each first output terminal of the inverter according to the initial common-mode voltage, the controller further includes: The controller stores the common mode error gain.

8. A DC component sampling system, characterized in that: The DC component sampling system is used to execute the DC component sampling method according to any one of claims 1 to 7; The DC component sampling system includes: a calibration platform, at least one first sampling module and a controller; the first sampling module is respectively connected to the first output end of the inverter, the second output end of the inverter and the controller; wherein the inverter includes at least one first output end; the first sampling module corresponds one-to-one to the first output end of the inverter.

9. The DC component sampling system according to claim 8, characterized in that: The DC component sampling system further includes a second sampling module; the second sampling module is respectively connected to the second output terminal of the inverter and the first ground wire of the inverter control module corresponding to the inverter, and the second sampling module is connected to the controller; Alternatively, the DC component sampling system also includes a third sampling module; the third sampling module is respectively connected to the first bus, the second bus, the first ground wire, the second ground wire of the inverter control module corresponding to the inverter, the first output terminals of the inverter and the second output terminal of the inverter; the third sampling module is connected to the controller.

10. The DC component sampling system according to claim 9, characterized in that: The second sampling module includes a third operational amplifier, a fourth operational amplifier and a first voltage source; The first input terminal of the third operational amplifier is connected to the second output terminal of the inverter, and the first input terminal of the third operational amplifier is connected to the first ground line; the second input terminal of the third operational amplifier is connected to the output terminal of the third operational amplifier; The first input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier, the first input terminal of the fourth operational amplifier is connected to the first voltage source, and the second input terminal of the fourth operational amplifier is connected to the output terminal of the fourth operational amplifier; The controller is connected to the output terminal of the fourth operational amplifier.

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