DC bias detection method, apparatus and device, and medium

Abstract

The invention discloses a DC bias detection method and device, equipment and a medium, and belongs to the technical field of photovoltaic grid connection, and the method comprises the steps: obtaining the output voltage and / or output current and / or output power of a PV side of a photovoltaic system during the grid-connected operation of an inverter, and obtaining target operation data; according to the target operation data, determining data variable quantities of a positive half cycle and a negative half cycle of the PV side of the photovoltaic system in the target fundamental frequency cycle, and obtaining a target variable quantity; and determining the direct current bias when the inverter and the power grid are connected according to the target variable quantity. Therefore, when the DCI in the inverter network access current is eliminated by using a closed-loop correction method, the DC bias of the inverter network access current does not need to be detected by using a current sensor, so that the influence of the null drift phenomenon of the current sensor when the DC bias of the inverter network access current is detected by using the current sensor can be avoided. Through the method, safe and efficient grid connection of the inverter can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic grid-connected technology, and in particular to a direct current bias detection method, device, equipment and medium. Background Art

[0002] At present, in order to avoid the adverse effects of power frequency isolation transformers on the volume, cost and energy conversion efficiency of products, many inverters use transformer-free non-isolated inverter technology. After the transformer is removed from the inverter, DCI (Direct Current Injection) problems will occur. DCI will not only cause corrosion of underground equipment and transformer saturation on the grid side, but also cause poor operation of electrical equipment. The national standard GBT30427-2013 stipulates that the DC current component fed by the inverter to the grid cannot exceed 0.5% of its output current rating or 5mA, whichever is greater.

[0003] In order to enable the inverter to be connected to the grid safely and efficiently, it is necessary to reduce the DCI of the inverter's grid-connected current. In the prior art, two methods are mainly used to reduce the DCI of the inverter's grid-connected current. One method is to use a current sensor to detect the DC bias of the grid-connected current, and eliminate the DCI in the inverter's grid-connected current through a closed-loop correction method. However, when using a current sensor to detect the DC bias of the inverter's grid-connected current, the detection result will be affected by the zero drift phenomenon of the current sensor, which will affect the accuracy of the DCI elimination control logic. Another method is not to detect the inverter's grid-connected current, but to directly use a preset control law to perform open-loop control on the inverter's grid-connected current, which makes the inverter's grid-connected current even more uncontrollable. At present, there is no more effective solution to this technical problem.

[0004] It can be seen that how to detect the DC bias of the inverter grid-connected current without using a current sensor is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method, device, equipment and medium for detecting DC bias, so as to solve the problem that the DC bias in the inverter grid current can only be detected by relying on a current sensor in the prior art. The specific scheme is as follows:

[0006] In order to solve the above technical problems, the present invention provides a method for detecting a DC bias, comprising:

[0007] When the inverter is connected to the grid, the output voltage and / or output current and / or output power of the photovoltaic system PV side is obtained to obtain target operation data;

[0008] Determine the data change amount of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data, and obtain the target change amount;

[0009] A DC bias when the inverter is connected to a power grid is determined according to the target change amount.

[0010] Preferably, determining the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data to obtain the target variation comprises:

[0011] Extracting the output voltage of the photovoltaic system PV side from the target operation data to obtain target voltage data;

[0012] The data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle is determined according to the target voltage data to obtain the target variation.

[0013] Preferably, it also includes:

[0014] Creating a target model of the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias; wherein the target DC bias is the DC bias when the inverter is connected to the power grid;

[0015] Correspondingly, determining the DC bias of the inverter when it is connected to the power grid according to the target variation includes:

[0016] A DC bias when the inverter is connected to the power grid is determined according to the target model and the target variation.

[0017] Preferably, the target model for creating the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias includes:

[0018] The target model of the correlation relationship between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias is created according to the equivalent circuit of the inverter when it is connected to the grid.

[0019] Preferably, the equivalent circuit comprises: a decoupling capacitor, a DC / DC converter, a bus capacitor and a DC / AC converter;

[0020] The first end and the second end of the decoupling capacitor are connected to PV+ and PV- respectively, the first end and the second end of the decoupling capacitor are connected to the first input end and the second input end of the DC / DC converter respectively, the first output end of the DC / DC converter is connected to the first end of the bus capacitor and the first input end of the DC / AC converter respectively, the second output end of the DC / DC converter is connected to the second end of the bus capacitor and the second input end of the DC / AC converter respectively, and the first output end and the second output end of the DC / AC converter are both connected to the power grid.

[0021] Preferably, the bus capacitor is specifically a capacitor used as voltage support.

[0022] Preferably, the expression of the target model is:

[0023] ;

[0024] In the formula, is the 2-fold frequency amplitude of the decoupling capacitor output voltage, is the average value of the output current on the PV side of the photovoltaic system, is twice the frequency of the power grid, is the capacitance value of the decoupling capacitor, is the voltage amplitude of the power grid, is a DC bias when the inverter is connected to the power grid, is the average value of the output voltage on the PV side of the photovoltaic system.

[0025] In order to solve the above technical problems, the present invention further provides a DC bias detection device, comprising:

[0026] A data acquisition module is used to acquire the output voltage and / or output current and / or output power of the photovoltaic system PV side when the inverter is connected to the grid to obtain target operation data;

[0027] A variation determination module is used to determine the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data to obtain a target variation;

[0028] The bias calculation module is used to determine the DC bias of the inverter when it is connected to the power grid according to the target change amount.

[0029] In order to solve the above technical problem, the present invention further provides an electronic device, comprising:

[0030] Memory for storing computer programs;

[0031] A processor is used to implement the steps of a DC bias detection method disclosed above when executing the computer program.

[0032] In order to solve the above technical problem, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of a DC bias detection method disclosed above are implemented.

[0033] Beneficial effects: In the present invention, when the inverter is connected to the grid, the output voltage and / or output current and / or output power on the PV side of the photovoltaic system are first obtained to obtain target operating data; then, the data change amount of the positive half-cycle and the negative half-cycle on the PV side of the photovoltaic system within the target fundamental frequency cycle is determined according to the target operating data to obtain the target change amount; finally, the DC bias when the inverter is connected to the grid is determined according to the target change amount.

[0034] Compared with the prior art, the method described in the present invention does not require the use of a current sensor to detect the DC bias when the inverter is connected to the grid. The DC bias when the inverter is connected to the grid can be determined based on the change in the output voltage and / or output current and / or output power in the positive half-cycle and negative half-cycle of the photovoltaic system PV side within the target base frequency cycle. In this way, when using a closed-loop correction method to eliminate the DCI in the inverter grid current, there is no need to use a current sensor to detect the DC bias of the inverter grid current, thereby avoiding the influence of the current sensor zero drift phenomenon when using the current sensor to detect the DC bias of the inverter grid current. In addition, the method can also avoid the disadvantages caused by directly using a preset control law to perform open-loop control on the inverter grid current in a scenario without DC bias sampling, thereby enabling the inverter to be safely and efficiently connected to the grid.

[0035] Correspondingly, a DC bias detection device, equipment and medium provided by the present invention also have the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0037] Figure 1 A flow chart of a DC bias detection method provided by an embodiment of the present invention;

[0038] Figure 2It is a schematic diagram of the output parameters of the photovoltaic system PV side after injecting a forward DC bias on the reference current;

[0039] Figure 3 A structural diagram of an equivalent circuit of an inverter provided by an embodiment of the present invention when in grid-connected operation;

[0040] Figure 4 Schematic diagram of the changes of relevant parameters in the target model;

[0041] Figure 5 A schematic diagram showing the principle of calculating the DC bias of the inverter when it is connected to the grid;

[0042] Figure 6 When a single-channel DC bias is injected into the grid, Figure 3 The measurement effect diagram of the 2 times frequency amplitude extraction and DC bias of the decoupling capacitor output voltage;

[0043] Figure 7 A structural diagram of a DC bias detection device provided by an embodiment of the present invention;

[0044] Figure 8 A structural diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0046] See also Figure 1 , Figure 1 A flow chart of a DC bias detection method provided by an embodiment of the present invention, the method comprising:

[0047] Step S11: when the inverter is connected to the grid, the output voltage and / or output current and / or output power of the photovoltaic system PV side is obtained to obtain target operation data;

[0048] Step S12: determining the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data, and obtaining the target variation;

[0049] Step S13: determining the DC bias when the inverter is connected to the power grid according to the target variation.

[0050] In this embodiment, a new DC bias detection method is provided. The DC bias of the inverter when it is connected to the grid can be detected without using a current sensor. At this time, combined with a closed-loop correction method, the DCI in the inverter grid current can be eliminated, thereby greatly reducing the damage of DC bias to electrical equipment and the impact on the transformer on the grid side.

[0051] See also Figure 2 , Figure 2 Schematic diagram of the PV-side output parameters of the photovoltaic system after injecting a forward DC bias on the reference current. Figure 2 Curves ①, ② and ③ in the figure respectively represent the output voltage, output current and output power of the photovoltaic system PV side over time, while curve ④ represents the reference current over time. The reference current refers to the reference value of the inverter grid current. Figure 2 It can be seen that in the positive half cycle of any fundamental frequency cycle, the 2 times frequency amplitude of the output voltage, output current and output power on the PV side of the photovoltaic system increases, while in the negative half cycle of any fundamental frequency cycle, the 2 times frequency amplitude of the output voltage, output current and output power on the PV side of the photovoltaic system decreases.

[0052] Based on this property characteristic of the PV side of the photovoltaic system, the DC bias of the inverter when it is connected to the grid can be calculated. Specifically, when the inverter is connected to the grid, it is first necessary to obtain the output voltage and / or output current and / or output power of the PV side of the photovoltaic system to obtain the target operation data. After that, the data change amount of any one or more parameter dimensions of the output voltage, output current and output power in the positive half-cycle and negative half-cycle of the PV side of the photovoltaic system within the target fundamental frequency cycle is determined according to the target operation data, and the DC bias of the inverter when it is connected to the grid can be determined based on the data change amount. Among them, the target fundamental frequency cycle refers to any fundamental frequency cycle of the inverter during operation.

[0053] In other words, in this embodiment, the DC bias of the inverter when connected to the grid can be determined according to the data change amount of the output voltage in the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle, or the DC bias of the inverter when connected to the grid can be determined according to the data change amount of the output current in the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle, or the DC bias of the inverter when connected to the grid can be determined according to the data change amount of the output power in the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle, or the DC bias of the inverter when connected to the grid can be determined according to the data change amount of the output voltage and output current in the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle, or the DC bias of the inverter when connected to the grid can be determined according to the data change amount of the output voltage, output current and output power in the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle.

[0054] Obviously, the method described in this embodiment does not need to use a current sensor to detect the DC bias when the inverter is connected to the grid. The DC bias when the inverter is connected to the grid can be determined based on the change in the output voltage and / or output current and / or output power in the positive half-cycle and negative half-cycle of the photovoltaic system PV side within the target base frequency cycle. In this way, when using a closed-loop correction method to eliminate the DCI in the inverter grid-connected current, there is no need to use a current sensor to detect the DC bias of the inverter grid-connected current, thereby avoiding the influence of the current sensor zero drift phenomenon when using the current sensor to detect the DC bias of the inverter grid-connected current. In addition, this method can also avoid the disadvantages caused by directly using a preset control law to perform open-loop control on the inverter grid-connected current in a scenario without DC bias sampling, thereby enabling the inverter to be safely and efficiently connected to the grid.

[0055] Based on the above embodiment, this embodiment further illustrates and optimizes the technical solution. As a preferred implementation mode, the above step: determining the data change amount of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data to obtain the target change amount includes:

[0056] Extract the output voltage of the photovoltaic system PV side from the target operation data to obtain the target voltage data;

[0057] The data variation of the positive half cycle and the negative half cycle of the PV side of the photovoltaic system within the target fundamental frequency cycle is determined according to the target voltage data to obtain the target variation.

[0058] When determining the data variation of the positive half cycle and the negative half cycle of the PV side of the photovoltaic system within the target base frequency cycle, the output voltage of the PV side of the photovoltaic system can be preferentially extracted from the target operation data to obtain the target voltage data, and the data variation of the positive half cycle and the negative half cycle of the PV side of the photovoltaic system within the target base frequency cycle can be determined based on the target voltage data to obtain the target variation. That is, the DC bias of the inverter when it is connected to the power grid can be preferentially determined based on the voltage variation of the positive half cycle and the negative half cycle of the PV side of the photovoltaic system within the target base frequency cycle.

[0059] According to the power calculation formula, in order to determine the power change of the PV side of the photovoltaic system in the positive half-cycle and the negative half-cycle within the target fundamental frequency cycle, it is necessary not only to determine the output voltage of the PV side of the photovoltaic system in the positive half-cycle and the negative half-cycle within the target fundamental frequency cycle, but also to determine the output current of the PV side of the photovoltaic system in the positive half-cycle and the negative half-cycle within the target fundamental frequency cycle, which increases the calculation complexity of the DC bias.

[0060] In addition, compared with current detection, voltage detection is not easily affected by changes in resistance in the system. Moreover, voltage detection can be measured directly without the need for additional hardware to convert current signals into voltage signals. This not only ensures the accuracy of the voltage detection results, but also reduces the detection cost required for voltage detection.

[0061] Based on the above considerations, in this embodiment, the voltage variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle is used to determine the DC bias of the inverter when it is connected to the grid.

[0062] Obviously, the technical solution provided in this embodiment can not only reduce the computational complexity and detection cost of the DC bias detection method provided in this application, but also improve the accuracy of the DC bias detection result.

[0063] As a preferred embodiment, the method further comprises:

[0064] Create a target model for the correlation between the 2-fold frequency amplitude of the PV-side output voltage of the photovoltaic system and the target DC bias; wherein the target DC bias is the DC bias when the inverter is connected to the grid;

[0065] Accordingly, the DC bias of the inverter when it is connected to the grid is determined according to the target variation, including:

[0066] The DC bias of the inverter when it is connected to the power grid is determined according to the target model and the target variation.

[0067] In this embodiment, when determining the DC bias when the inverter is connected to the grid based on the voltage variation of the positive half cycle and the negative half cycle of the PV side of the photovoltaic system within the target base frequency cycle, a target model of the correlation between the 2 times frequency amplitude of the output voltage of the PV side of the photovoltaic system and the target DC bias can be created first; wherein the target DC bias is the DC bias when the inverter is connected to the grid. After the target model is established, the DC bias corresponding to any output voltage 2 times frequency amplitude of the PV side of the photovoltaic system can be determined based on the target model.

[0068] In this case, the mathematical expression of the DC bias corresponding to any output voltage 2 times the frequency amplitude on the PV side of the photovoltaic system can be derived based on the target model. Then, the mathematical expressions of the DC bias corresponding to the positive half-cycle and negative half-cycle of the PV side of the photovoltaic system in the target fundamental frequency cycle are subjected to difference processing, and the mathematical expression of the voltage change in the positive half-cycle and negative half-cycle of the PV side of the photovoltaic system in the target fundamental frequency cycle can be determined.

[0069] Since the mathematical expression of the voltage change in the positive half-cycle and the negative half-cycle on the PV side of the photovoltaic system within the target fundamental frequency cycle is a mathematical expression containing a DC bias parameter, the DC bias of the inverter when it is connected to the grid can be calculated by substituting the target change (that is, the voltage change in the positive half-cycle and the negative half-cycle on the PV side of the photovoltaic system within the target fundamental frequency cycle) into the target model.

[0070] Obviously, through the technical solution provided in this embodiment, the reliability of the DC bias calculation result can be guaranteed when the inverter is connected to the power grid.

[0071] As a preferred implementation, the above step of creating a target model of the correlation between the 2-fold frequency amplitude of the photovoltaic system PV side output voltage and the target DC bias includes:

[0072] According to the equivalent circuit of the inverter when it is connected to the grid, a target model of the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias is created.

[0073] It is understandable that because the equivalent circuit of the inverter when it is connected to the grid can characterize the complex circuit behavior of the inverter when it is connected to the grid, when the equivalent circuit of the inverter when it is connected to the grid is used to analyze the grid-connected operation behavior of the inverter, the entire inverter grid-connected process can be easier to understand and analyze.

[0074] Therefore, in this embodiment, when creating a target model of the correlation between the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias, the target model of the correlation between the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias is created based on the equivalent circuit when the inverter is connected to the grid.

[0075] Obviously, the technical solution provided by this embodiment can reduce the complexity in creating the target model.

[0076] See also Figure 3 , Figure 3 This is a structural diagram of an equivalent circuit of a photovoltaic system in grid-connected operation provided by an embodiment of the present invention. As a preferred implementation, the equivalent circuit includes: a decoupling capacitor C1, a DC / DC converter 101, a bus capacitor C2 and a DC / AC converter 102;

[0077] Among them, the first end and the second end of the decoupling capacitor C1 are connected to PV+ and PV- respectively, the first end and the second end of the decoupling capacitor C1 are connected to the first input end and the second input end of the DC / DC converter 101 respectively, the first output end of the DC / DC converter 101 is connected to the first end of the bus capacitor C2 and the first input end of the DC / AC converter 102 respectively, the second output end of the DC / DC converter 101 is connected to the second end of the bus capacitor C2 and the second input end of the DC / AC converter 102 respectively, and the first output end and the second output end of the DC / AC converter 102 are both connected to the power grid.

[0078] In this embodiment, the internal structure of the equivalent circuit when the inverter is connected to the grid is specifically described. The equivalent circuit when the inverter is connected to the grid is mainly composed of a decoupling capacitor C1, a DC / DC converter 101, a bus capacitor C2 and a DC / AC converter 102. Figure 3 middle, Indicates the average value of the output voltage on the PV side of the photovoltaic system. Represents the grid voltage. Because the bus capacitor C2 has a very small capacitance and only provides voltage support but does not store energy or exchange power, the impact of the bus capacitor C2 on the target model can be ignored.

[0079] It should be noted that the direction of the output power of the photovoltaic system can be determined according to the direction of the output current of the photovoltaic system. The current consumed by the DC / DC converter 101 is diverted by the decoupling capacitor C1 node. and the current absorbed by the decoupling capacitor C1 The power of the photovoltaic system on the inverter side is mainly determined by the grid voltage And the inverter current output by the photovoltaic system Give a description.

[0080] Obviously, when the equivalent circuit of the inverter when connected to the grid is constructed using decoupling capacitors, DC / DC converters, bus capacitors and DC / AC converters, the difficulty of analyzing the inverter when connected to the grid can be reduced.

[0081] As a preferred implementation, the expression of the above target model is:

[0082] ;

[0083] In the formula, is the 2-fold frequency amplitude of the decoupling capacitor output voltage. is the average value of the output current on the PV side of the photovoltaic system, is twice the frequency of the power grid, is the capacitance value of the decoupling capacitor, is the voltage amplitude of the power grid, It is the DC bias when the inverter is connected to the grid. It is the average value of the output voltage on the PV side of the photovoltaic system.

[0084] In this embodiment, the mathematical expression of the target model is specifically described. Figure 4 , Figure 4 This is a schematic diagram of the changes in relevant parameters in the target model. Figure 4 In the figure, curve ① represents Figure 3 The curve of the 2 times frequency amplitude of the decoupling capacitor output voltage changing with time, curve ② represents the coupled fundamental frequency component of the DC bias when the inverter is connected to the grid, and curve ③ represents the AC power output by the inverter when it is connected to the grid. Among them, the output voltage of the decoupling capacitor can be approximately regarded as the voltage on the PV side of the photovoltaic system.

[0085] from Figure 4 It can be seen that in the time period [0, 0.01], the 2-fold frequency amplitude of the decoupling capacitor output voltage is in the range of [0, ], and in the time period [0, 0.01] when the inverter is connected to the grid, the coupling fundamental frequency component of the DC bias is in the range of [0, ], the AC superposition amplitude is equivalent to: the 2-fold frequency amplitude of the decoupling capacitor output voltage plus 0.707 times the fundamental frequency amplitude, which is generally too large. In the time period [0.01, 0.02], the AC superposition amplitude is equivalent to: the 2-fold frequency amplitude of the decoupling capacitor output voltage minus 0.707 times the fundamental frequency amplitude, which is generally too small.

[0086] In this case, the DC bias of the inverter when it is connected to the grid can be determined by extracting the voltage variation of the decoupling capacitor in the positive half cycle and the negative half cycle in the [0, 0.02] time period. That is, by extracting the 2 times frequency amplitude of the output voltage of the decoupling capacitor in the [0, 0.01] and [0.01, 0.02] time periods, and subtracting the 2 times frequency amplitude of the output voltage of the decoupling capacitor in the [0, 0.01] and [0.01, 0.02] time periods, the DC bias of the inverter when it is connected to the grid can be determined.

[0087] Specifically, the difference between the 2 times frequency amplitude of the output voltage of the decoupling capacitor in the time period [0, 0.01] and [0.01, 0.02] can be obtained. .

[0088] That is, formula 1: ;

[0089] In the formula, It represents the difference between the output voltage double frequency amplitude of the decoupling capacitor in the time period [0, 0.01] and [0.01, 0.02], It represents the 2-fold frequency amplitude of the output voltage of the decoupling capacitor in the time period [0, 0.01]. It indicates the 2 times frequency amplitude of the output voltage of the decoupling capacitor in the time period [0.01, 0.02].

[0090] After simplifying formula 1, we can get formula 2:

[0091] Formula 2: ;

[0092] By transforming Formula 2, we can get the DC bias of the inverter when it is connected to the grid, and thus get Formula 3.

[0093] Formula 3: .

[0094] See also Figure 5 , Figure 5 This is a schematic diagram of the principle of calculating the DC bias of the inverter when it is connected to the power grid. Figure 5 First, we need to wait for the half-cycle zero-crossing signal to trigger the extraction of the PV side output voltage of the photovoltaic system. When calculating the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system, it is necessary to first calculate the average value of the output voltage of the decoupling capacitor in the positive half cycle to obtain the amplitude average value. , and then calculate the difference between the original signal of the decoupling capacitor output voltage and the average amplitude to obtain the AC component of the decoupling capacitor output voltage Then, the peak detection method is used to obtain the AC component amplitude of the output voltage of the decoupling capacitor in the positive half cycle, thereby obtaining the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system in the positive half cycle. , caches the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system in the positive half cycle.

[0095] Using the same method, using the hysteresis module ( Indicates a lag of half a cycle) It is also possible to calculate the 2 times frequency amplitude of the output voltage on the PV side of the photovoltaic system in the negative half cycle After that, the difference between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system in the positive half cycle and the negative half cycle is calculated to obtain Then, the average output voltage of the photovoltaic system PV side is , the voltage amplitude of the power grid , twice the frequency of the power grid And the capacitance value of the decoupling capacitor Substituting into formula 3, we can get the DC bias of the inverter when it is connected to the grid: .

[0096] It should be noted that in Figure 5 middle, That is , That is .

[0097] See also Figure 6 , Figure 6 When a single-channel DC bias is injected into the grid, Figure 3 The measurement effect diagram of the 2 times frequency amplitude extraction and DC bias of the decoupling capacitor output voltage. Figure 6 In the figure, the DC bias injected into the power grid is 0A~0.4A. Among them, curve ① represents the output voltage of the decoupling capacitor, curve ② represents the extracted 2 times frequency amplitude of the decoupling capacitor output voltage, curve ③ represents the injected DC bias (curve ③ is a neat step curve, indicating that the injected DC bias is updated once per second with a step size of 0.05A), and curve ④ represents the DC bias The actual measured value (curve ④ is a step-like curve with a lot of jitter). Ioffset represents the bias current, and Err represents the error. Figure 6 It can be seen that the actual measurement shows that the DC bias of the inverter when it is connected to the grid is The error is less than 0.015A, which means that the technical solution provided by the present application can accurately detect the DC bias of the inverter when it is connected to the power grid.

[0098] Obviously, through the technical solution provided in this embodiment, the DC bias of the inverter when it is connected to the power grid can be accurately and reliably detected.

[0099] See also Figure 7 , Figure 7 A structural diagram of a DC bias detection device provided by an embodiment of the present invention, the device comprising:

[0100] The data acquisition module 21 is used to acquire the output voltage and / or output current and / or output power of the photovoltaic system PV side when the inverter is connected to the grid to obtain target operation data;

[0101] The variation determination module 22 is used to determine the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data, and obtain the target variation;

[0102] The bias calculation module 23 is used to determine the DC bias when the inverter is connected to the power grid according to the target variation.

[0103] Preferably, the variation determination module 22 includes:

[0104] A data extraction unit, used for extracting the output voltage of the photovoltaic system PV side from the target operation data to obtain target voltage data;

[0105] The variation determination unit is used to determine the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target voltage data to obtain the target variation.

[0106] Preferably, it also includes:

[0107] A model creation module, used to create a target model of the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias; wherein the target DC bias is the DC bias when the inverter is connected to the power grid;

[0108] Accordingly, the bias calculation module 23 includes:

[0109] A bias calculation unit is used to determine a DC bias when the inverter is connected to the power grid according to the target model and the target variation.

[0110] Preferably, the model creation module includes:

[0111] A model creation unit is used to create the target model of the correlation relationship between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias according to the equivalent circuit of the inverter when it is connected to the grid.

[0112] A DC bias detection device provided in an embodiment of the present invention has the beneficial effects of the DC bias detection method disclosed above.

[0113] See also Figure 8 , Figure 8 A structural diagram of an electronic device provided by an embodiment of the present invention, the electronic device comprising:

[0114] A memory 31, used for storing computer programs;

[0115] The processor 32 is used to implement the steps of a DC bias detection method disclosed above when executing a computer program.

[0116] An electronic device provided by an embodiment of the present invention has the beneficial effects of the above-disclosed method for detecting direct current bias.

[0117] Correspondingly, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of a DC bias detection method disclosed above are implemented.

[0118] A computer-readable storage medium provided in an embodiment of the present invention has the beneficial effects of the aforementioned DC bias detection method.

[0119] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0120] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0121] The above is a detailed introduction to a DC bias detection method, device, equipment and medium provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for detecting a DC bias, characterized in that: include: When the inverter is connected to the grid, the output voltage and / or output current and / or output power of the photovoltaic system PV side is obtained to obtain target operation data; Determine the data change amount of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data, and obtain the target change amount; A DC bias when the inverter is connected to a power grid is determined according to the target change amount.

2. A method for detecting a DC bias according to claim 1, characterized in that: The step of determining the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data to obtain the target variation comprises: Extracting the output voltage of the photovoltaic system PV side from the target operation data to obtain target voltage data; The data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle is determined according to the target voltage data to obtain the target variation.

3. A method for detecting a DC bias according to claim 2, characterized in that: Also includes: Creating a target model of the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias; wherein the target DC bias is the DC bias when the inverter is connected to the power grid; Correspondingly, determining the DC bias of the inverter when it is connected to the power grid according to the target variation includes: A DC bias when the inverter is connected to the power grid is determined according to the target model and the target variation.

4. A method for detecting a DC bias according to claim 3, characterized in that: The target model for creating the correlation between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias includes: The target model of the correlation relationship between the 2-fold frequency amplitude of the output voltage on the PV side of the photovoltaic system and the target DC bias is created according to the equivalent circuit of the inverter when it is connected to the grid.

5. A method for detecting a DC bias according to claim 4, characterized in that: The equivalent circuit includes: a decoupling capacitor, a DC / DC converter, a bus capacitor and a DC / AC converter; The first end and the second end of the decoupling capacitor are connected to PV+ and PV- respectively, the first end and the second end of the decoupling capacitor are connected to the first input end and the second input end of the DC / DC converter respectively, the first output end of the DC / DC converter is connected to the first end of the bus capacitor and the first input end of the DC / AC converter respectively, the second output end of the DC / DC converter is connected to the second end of the bus capacitor and the second input end of the DC / AC converter respectively, and the first output end and the second output end of the DC / AC converter are both connected to the power grid.

6. A method for detecting a DC bias according to claim 5, characterized in that: The bus capacitor is specifically a capacitor used as voltage support.

7. A method for detecting a DC bias according to claim 6, characterized in that: The expression of the target model is: ； In the formula, is the 2-fold frequency amplitude of the decoupling capacitor output voltage, is the average value of the output current on the PV side of the photovoltaic system, is twice the frequency of the power grid, is the capacitance value of the decoupling capacitor, is the voltage amplitude of the power grid, is a DC bias when the inverter is connected to the power grid, is the average value of the output voltage on the PV side of the photovoltaic system.

8. A DC bias detection device, characterized in that: include: A data acquisition module is used to acquire the output voltage and / or output current and / or output power of the photovoltaic system PV side when the inverter is connected to the grid to obtain target operation data; A variation determination module is used to determine the data variation of the positive half cycle and the negative half cycle of the photovoltaic system PV side within the target fundamental frequency cycle according to the target operation data to obtain a target variation; The bias calculation module is used to determine the DC bias of the inverter when it is connected to the power grid according to the target change amount.

9. An electronic device, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of a DC bias detection method as claimed in any one of claims 1 to 7 when executing the computer program.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of a DC bias detection method as claimed in any one of claims 1 to 7 are implemented.

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