Inverter, control method thereof and photovoltaic system

Abstract

The invention relates to an inverter, a control method thereof and a photovoltaic system. The control method comprises the steps of obtaining a first parameter corresponding to an inverter in a grid-connected operation process of the inverter in a first modulation mode; and if it is determined that the modulation mode of the inverter needs to be switched to a second modulation mode based on the first parameter, controlling the inverter to operate in a grid-connected manner based on the second modulation mode, wherein the leakage current of the inverter does not exceed a preset inverter shutdown protection threshold value in the grid-connected operation process of the inverter in the second modulation mode; in this way, the inverter, the control method thereof and the photovoltaic system can improve the situation that the inverter breaks down and trips due to the fact that leakage current exceeds the standard frequently.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic power generation, in particular to an inverter, a control method thereof and a photovoltaic system. BACKGROUND

[0002] A photovoltaic system is a new type of power generation system that converts solar radiation energy into electrical energy by using the photovoltaic effect of photovoltaic solar panels. An inverter is one of the main components of a photovoltaic system. The inverter can convert the variable direct current voltage generated by the photovoltaic components connected thereto into alternating current of a power frequency, and output the alternating current to a power grid for use by the power grid. The energy conversion efficiency and power quality directly affect the power generation efficiency of the photovoltaic system.

[0003] In the above photovoltaic system, based on the inverter, there is an electrical connection between the photovoltaic component unit and the power grid, and there is a certain parasitic impedance between the photovoltaic component unit and the grounded metal frame. When the inverter is running, the common mode component of the output voltage of the inverter can form a common mode current, i.e. a leakage current, on the total impedance, wherein the total impedance is the sum of the parasitic impedance and the internal common mode impedance of the inverter.

[0004] In related technologies, when the inverter is running, the leakage current often exceeds the standard, causing the inverter to trip off, which seriously affects the normal power generation of the photovoltaic system. SUMMARY

[0005] Therefore, it is necessary to provide an inverter, a control method thereof and a photovoltaic system capable of improving the situation that the leakage current often exceeds the standard, causing the inverter to trip off.

[0006] In a first aspect, the present application provides a control method of an inverter, the control method comprising:

[0007] acquiring a first parameter corresponding to the inverter during the process that the inverter is running in a first modulation mode and connected to a power grid;

[0008] if it is determined based on the first parameter that the modulation mode of the inverter needs to be switched to a second modulation mode, controlling the inverter to run in the power grid based on the second modulation mode;

[0009] wherein the leakage current of the inverter does not exceed a preset inverter trip-off protection threshold during the process that the inverter is running in the power grid in the second modulation mode.

[0010] In one of the embodiments, the first parameter comprises at least one of the following:

[0011] the operating parameter of the inverter, the working condition parameter of the photovoltaic component unit connected to the inverter, and the environmental parameter of the environment in which the inverter is located.

[0012] In one of the embodiments, the method further comprises:

[0013] determining whether the first parameter is in a target switching interval of the at least one switching interval, if yes, determining that the modulation mode of the inverter needs to be switched, and taking the modulation mode corresponding to the target switching interval as the second modulation mode.

[0014] In one of the embodiments, the method further comprises:

[0015] determining the at least one switching interval according to the first modulation mode.

[0016] In one of the embodiments, the method further comprises:

[0017] determining the modulation mode corresponding to the first parameter, if the modulation mode corresponding to the first parameter is not the first modulation mode, determining that the modulation mode of the inverter needs to be switched, and taking the modulation mode corresponding to the first parameter as the second modulation mode.

[0018] In one of the embodiments, the method further comprises:

[0019] comparing the first parameter with a first reference parameter, if the comparison result meets a preset condition, determining that the modulation mode of the inverter needs to be switched, and determining the second modulation mode according to the comparison result.

[0020] In one of the embodiments, the first parameter is multiple, and the method further comprises:

[0021] obtaining a weight corresponding to each of the first parameters;

[0022] determining a first weighted parameter according to each of the first parameters and the weight corresponding to each of the first parameters;

[0023] determining the modulation mode corresponding to the first weighted parameter, if the modulation mode corresponding to the first weighted parameter is not the first modulation mode, determining that the modulation mode of the inverter needs to be switched, and taking the modulation mode corresponding to the first weighted parameter as the second modulation mode.

[0024] In one of the embodiments, the method further comprises:

[0025] if it is determined based on the first parameter that the modulation mode of the inverter does not need to be switched, continuing to control the inverter to operate in grid-connected mode based on the first modulation mode.

[0026] In one of the embodiments, the method further comprises:

[0027] In a start-up phase of the inverter, a second parameter corresponding to the inverter is acquired;

[0028] A third modulation mode is determined according to the second parameter, wherein a leakage current of the inverter does not exceed a preset inverter shutdown protection threshold in a process in which the inverter starts up in the third modulation mode;

[0029] The inverter is controlled to start up based on the third modulation mode.

[0030] In one of the embodiments, the second parameter includes at least one of the following:

[0031] An operating condition parameter of a photovoltaic module unit connected to the inverter and an environmental parameter of an environment in which the inverter is located.

[0032] In one of the embodiments, the third modulation mode is determined according to the second parameter, including:

[0033] A modulation mode corresponding to the second parameter is determined, and the modulation mode corresponding to the second parameter is taken as the third modulation mode.

[0034] In one of the embodiments, the third modulation mode is determined according to the second parameter, including:

[0035] The second parameter is compared with a second reference parameter, and the third modulation mode is determined according to a comparison result.

[0036] In one of the embodiments, the second parameter is multiple, and the third modulation mode is determined according to the second parameter, including:

[0037] A weight corresponding to each of the second parameters is acquired;

[0038] A second weighted parameter is determined according to each of the second parameters and the weight corresponding to each of the second parameters;

[0039] A modulation mode corresponding to the second weighted parameter is determined, and the modulation mode corresponding to the second weighted parameter is taken as the third modulation mode.

[0040] In one of the embodiments, the method further includes:

[0041] In the start-up phase of the inverter, the inverter is controlled to start up based on a preset default modulation mode.

[0042] In a second aspect, the application further provides an inverter configured to implement the control method of the inverter according to the first aspect.

[0043] In a third aspect, the present application also provides a photovoltaic system, comprising a controller and at least one inverter; each of the inverters is connected with the controller, and the controller is configured to implement the control method of the inverter according to the first aspect.

[0044] The above inverter, control method thereof and photovoltaic system, in the process of grid-connected operation of the inverter in the first modulation mode, the first parameter corresponding to the inverter is obtained, if it is determined based on the first parameter that the modulation mode of the inverter needs to be switched to the second modulation mode, the inverter is controlled to operate in the grid-connected mode based on the second modulation mode, and the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold value in the process of grid-connected operation of the inverter in the second modulation mode; in this way, in the process of grid-connected operation of the inverter, the first parameter corresponding to the inverter is obtained in real time, so that the modulation mode of the inverter is adjusted in real time based on the first parameter, so that the leakage current of the inverter always does not exceed the preset inverter shutdown protection threshold value, thereby ensuring that the inverter will not be tripped due to the leakage current exceeding the preset inverter shutdown protection threshold value in the process of grid-connected operation, and the present application thus avoids the situation that the inverter is tripped due to the leakage current exceeding the standard in the process of grid-connected operation of the inverter, thereby improving the power generation efficiency of the photovoltaic system. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other related drawings can be obtained by those skilled in the art without creative labor.

[0046] Figure 1 A schematic diagram of a topology structure of a three-phase photovoltaic inverter in an embodiment;

[0047] Figure 2 A schematic diagram of a flow of an inverter control method in an embodiment;

[0048] Figure 3 A schematic diagram of a flow of an inverter control method in an embodiment;

[0049] Figure 4 A schematic diagram of a flow of an inverter control method in an embodiment;

[0050] Figure 5 A schematic diagram of a flow of an inverter control method in an embodiment;

[0051] Figure 6 A schematic diagram of a modulation mode switching in an inverter control method in an embodiment;

[0052] Figure 7 This is the fifth flowchart of an inverter control method in one embodiment;

[0053] Figure 8 This is the sixth flowchart of an inverter control method in one embodiment;

[0054] Figure 9 This is the seventh flowchart of an inverter control method in one embodiment;

[0055] Figure 10 This is the eighth flowchart of an inverter control method in one embodiment;

[0056] Figure 11 This is the ninth flowchart of an inverter control method in one embodiment. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0058] The inverter control method provided in this application embodiment is applicable to the regulation of inverter leakage current and can be executed by a controller integrated inside the inverter or by a control circuit located outside the inverter. The inverter is, for example, but not limited to, a three-phase photovoltaic inverter, such as... Figure 1 This diagram illustrates only one exemplary topology of a three-phase photovoltaic inverter, which includes three-phase bridge arm circuits and bus capacitors. The three-phase bridge arm circuits have identical structures; for example, the first phase bridge arm circuit includes switches Sa1-Sa4 and inductor La, the second phase bridge arm circuit includes switches Sb1-Sb4 and inductor Lb, and the third phase bridge arm circuit includes switches Sc1-Sc4 and inductor Lc. The photovoltaic module unit PV is connected to the bus and outputs a DC voltage Upv. The input terminals of the three-phase bridge arm circuits are all connected to the midpoint of bus capacitors Cde1 and Cdc2. The output voltages Usa, Usb, and Usc of the three-phase bridge arm circuits can be input to the mains power grid.

[0059] In one exemplary embodiment, reference is made to Figure 2 This paper provides a control method for an inverter, which can be applied to... Figure 1 The following steps, S202~S204, are used as an example to illustrate the topology structure.

[0060] S202, during the grid-connected operation of the inverter in the first modulation mode, the first parameter corresponding to the inverter is obtained.

[0061] The modulation mode of the inverter (also referred to as a modulation algorithm) acts on each switch tube of the three-phase bridge arm circuit, and is used to regulate the output voltages Usa, Usb and Usc of the three-phase bridge arm circuit.

[0062] There are many modulation modes of the inverter, such as but not limited to sinusoidal modulation, space vector modulation, discontinuous pulse width modulation, carrier superposition modulation, and specific harmonic elimination modulation. Under the same conditions, different modulation modes have their respective advantages, such as small switching loss, high efficiency, few current harmonics, high utilization rate of DC voltage, etc. Moreover, under the same conditions, the leakage current generated by different modulation modes is also different. Accordingly, in combination with the background technology, it can be understood that the size of the leakage current of the inverter is affected by the size of the parasitic impedance and the modulation mode.

[0063] During the process of the inverter operating in parallel with the grid in the first modulation mode, the modulation mode of the inverter at the current time is the first modulation mode. In the embodiments of the present application, the modulation mode of the inverter at the next time may still be the first modulation mode, or may be switched to the second modulation mode, wherein the second modulation mode and the first modulation mode are different modulation modes.

[0064] During the process of the inverter operating in parallel with the grid in a certain modulation mode, the first parameter corresponding to the inverter can include the size of the parasitic impedance, and / or parameters that can directly or indirectly reflect and / or affect the size of the parasitic impedance.

[0065] In S204, if it is determined based on the first parameter that the modulation mode of the inverter needs to be switched to the second modulation mode, the inverter is controlled to operate in parallel with the grid based on the second modulation mode, wherein the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold during the process of the inverter operating in parallel with the grid in the second modulation mode.

[0066] In the embodiments of the present application, during the process of the inverter operating in parallel with the grid in a certain modulation mode (i.e. the first modulation mode) at the current time, the first parameter corresponding to the inverter is obtained, so that based on the obtained first parameter corresponding to the inverter, it can be determined whether the modulation mode of the inverter needs to be switched to another modulation mode (i.e. the second modulation mode) at the next time, or the modulation mode of the inverter at the next time continues to be the modulation mode at the current time (i.e. the first modulation mode) to control the inverter to operate in parallel with the grid, so that the leakage current of the inverter always does not exceed the preset inverter shutdown protection threshold, thereby ensuring that the inverter will not be tripped due to the leakage current exceeding the preset inverter shutdown protection threshold during the process of operating in parallel with the grid. The embodiments of the present application thus avoid the situation that the leakage current exceeds the standard, resulting in the inverter tripping during the process of operating in parallel with the grid, and thus improve the power generation efficiency of the photovoltaic system.

[0067] In one exemplary embodiment, reference is made to Figure 3The control method of the inverter further includes step S206. If it is determined based on the first parameter that the modulation mode of the inverter does not need to be switched, the inverter continues to be controlled based on the first modulation mode to operate in grid connection.

[0068] In the embodiment of the present application, in the case that it is determined based on the first parameter that the modulation mode of the inverter does not need to be switched at the next moment and the first modulation mode continues to be used to control the inverter to operate in grid connection, it is illustrated that the first modulation mode continues to be used to control the inverter to operate in grid connection at the next moment, and the leakage current does not exceed the preset inverter shutdown protection threshold to cause a fault trip.

[0069] In the case that it is determined based on the first parameter that the modulation mode of the inverter needs to be switched to the second modulation mode at the next moment, if the modulation mode of the inverter is not switched to the second modulation mode at the next moment, the leakage current of the inverter is likely to exceed the preset inverter shutdown protection threshold to cause a fault trip in the grid connection operation at the next moment and thereafter; and if the modulation mode of the inverter is switched to the second modulation mode at the next moment, the leakage current exceeding the preset inverter shutdown protection threshold to cause a fault trip can be avoided.

[0070] In addition, the control method of the inverter provided by the embodiment of the present application is not only applicable to the grid connection operation scenario of the inverter, but also applicable to any other operation scenario of the inverter, which is not limited herein.

[0071] Optionally, during the grid connection operation of the inverter in a certain modulation mode, the first parameter corresponding to the inverter can include at least one of the following: a working condition parameter of a photovoltaic component unit connected to the inverter, an operation parameter of the inverter, and an environmental parameter of an environment in which the inverter is located.

[0072] For example, the working condition parameter of the photovoltaic component unit connected to the inverter can include a parasitic impedance of the photovoltaic component unit connected to the inverter; the operation parameter of the inverter can include at least one of the following: a leakage current of the inverter, a power generation power of the inverter, and a maximum power point voltage of the inverter; and the environmental parameter of the environment in which the inverter is located can include at least one of the following: an environmental humidity, an environmental temperature, and an environmental weather.

[0073] The leakage current of the inverter can directly reflect the size of the parasitic impedance, the power generation power of the inverter, the maximum power point voltage of the inverter, the environmental temperature, and the environmental weather can directly reflect the light condition, the light condition can directly reflect the environmental humidity, and the environmental humidity can directly affect the size of the parasitic impedance; in other words, the power generation power of the inverter, the maximum power point voltage of the inverter, the environmental temperature, and the environmental weather can indirectly reflect the size of the parasitic impedance.

[0074] In an exemplary embodiment, reference is made to Figure 4The inverter control method further includes step S402, determining whether the first parameter is within a target switching interval in at least one switching interval; if it is, determining that the modulation mode of the inverter needs to be switched, and using the modulation mode corresponding to the target switching interval as the second modulation mode.

[0075] Specifically, for one or more first parameters, there can be at least one switching interval, and the target switching interval is one of these at least one switching intervals. Each switching interval corresponds to a modulation scheme, and different switching intervals correspond to different modulation schemes. If the first parameter is within one of the at least one switching intervals, i.e., within the target switching interval, then it is determined that the inverter's modulation scheme needs to be switched, and the modulation scheme corresponding to the target switching interval is used as the second modulation scheme. If the first parameter is not within any of the at least one switching intervals, then it is determined that the inverter's modulation scheme does not need to be switched, and the inverter can continue to operate in grid-connected mode based on the first modulation scheme.

[0076] In one exemplary embodiment, reference is made to Figure 5 The inverter control method further includes step S401, which determines at least one switching interval according to the first modulation scheme.

[0077] Since each switching interval corresponds to a modulation scheme, and different switching intervals correspond to different modulation schemes, at least one switching interval can be determined based on the first modulation scheme.

[0078] The following example, using the inverter's leakage current as the first parameter, further illustrates this embodiment:

[0079] As mentioned above, under the same conditions, different modulation methods produce different amounts of leakage current. Accordingly, four modulation methods are pre-stored for example. Under the same conditions, these four modulation methods can be sorted in ascending order of the leakage current they produce, resulting in, for example, the leakage current produced by modulation method S1, modulation method S2, modulation method S3, and modulation method S4 increasing sequentially. Furthermore, the leakage current threshold values ​​T1, T2, T3, and T4 of modulation method S1, S2, S3, and S4 increase sequentially, i.e., T1 < T2 < T3 < T4.

[0080] refer to Figure 6 When the first modulation method is modulation method S1, the switching interval includes at least switching interval 1, where switching interval 1 is the interval where the leakage current is less than T1; if the obtained leakage current is in switching interval 1, then switching interval 1 can be used as the target switching interval, and the modulation method S2 corresponding to the target switching interval can be used as the second modulation method.

[0081] It can be understood that, in the process of inverter grid-connected operation in the modulation mode S1: if the obtained leakage current is less than T1, the modulation mode can be switched to a modulation mode with slightly larger leakage current, for example, from the modulation mode S1 to the modulation mode S2; if the obtained leakage current is much less than T1, the modulation mode can be switched to a modulation mode with larger leakage current, for example, from the modulation mode S1 to the modulation mode S3; if the obtained leakage current is equal to or greater than T1, it is determined that the modulation mode does not need to be switched, and the inverter continues to be controlled to operate in the grid-connected mode in the modulation mode S1; in this way, it is ensured that the leakage current in the process of inverter grid-connected operation is moderate and does not exceed the preset inverter shutdown protection threshold.

[0082] With reference back to Figure 6 In the case where the first modulation mode is the modulation mode S2, the switching interval at least includes the switching interval 2 and the switching interval 3, wherein the switching interval 2 is an interval in which the leakage current is less than T2, and the switching interval 3 is an interval in which the leakage current is greater than T3; if the obtained leakage current is in the switching interval 2, the switching interval 2 can be used as the target switching interval, and the modulation mode S3 corresponding to the target switching interval can be used as the second modulation mode; if the obtained leakage current is in the switching interval 3, the switching interval 3 can be used as the target switching interval, and the modulation mode S1 corresponding to the target switching interval can be used as the second modulation mode.

[0083] It can be understood that, in the process of inverter grid-connected operation in the modulation mode S2: if the obtained leakage current is less than T2, the modulation mode can be switched to a modulation mode with slightly larger leakage current, for example, from the modulation mode S2 to the modulation mode S3; if the obtained leakage current is much less than T2, the modulation mode can be switched to a modulation mode with larger leakage current, for example, from the modulation mode S2 to the modulation mode S4; if the obtained leakage current is between T2 and T3, it is determined that the modulation mode does not need to be switched, and the inverter continues to be controlled to operate in the grid-connected mode in the modulation mode S2; if the obtained leakage current is greater than T3, the modulation mode can be switched to a modulation mode with slightly smaller leakage current, for example, from the modulation mode S2 to the modulation mode S1; in this way, it is also ensured that the leakage current in the process of inverter grid-connected operation is moderate and does not exceed the preset inverter shutdown protection threshold.

[0084] With reference back to Figure 6 In the case where the first modulation mode is the modulation mode S3, the switching interval at least includes the switching interval 4, wherein the switching interval 4 is an interval in which the leakage current is greater than T4; if the obtained leakage current is in the switching interval 4, the switching interval 4 can be used as the target switching interval, and the modulation mode S2 corresponding to the target switching interval can be used as the second modulation mode.

[0085] It can be understood that, in the process of the inverter operating in the modulation mode S3 in the grid-connected mode: if the obtained leakage current is less than T4, it is determined that the modulation mode does not need to be switched, and the inverter continues to operate in the grid-connected mode in the modulation mode S3; if the obtained leakage current is greater than T4, the modulation mode can be switched to a modulation mode with smaller leakage current, for example, from the modulation mode S3 to the modulation mode S2; if the obtained leakage current is much greater than T4, the modulation mode can be switched to a modulation mode with smaller leakage current, for example, from the modulation mode S3 to the modulation mode S1; in this way, it can also ensure that the leakage current in the process of the inverter operating in the grid-connected mode is moderate and does not exceed the preset inverter shutdown protection threshold.

[0086] In the embodiment of the application, the leakage current size of the modulation mode and the obtained leakage current size can be the effective value, the effective value after removing the direct current component, the instantaneous maximum value or the maximum value of the absolute value of the leakage current; wherein one of the effective value, the effective value after removing the direct current component, the instantaneous maximum value and the maximum value of the absolute value of the leakage current increases, and the rest increases accordingly, and one of them decreases, and the rest decreases accordingly.

[0087] In one exemplary embodiment, referring to Figure 7 The control method of the inverter further includes a step S702 of determining the modulation mode corresponding to the first parameter, and if the modulation mode corresponding to the first parameter is not the first modulation mode, it is determined that the modulation mode of the inverter needs to be switched, and the modulation mode corresponding to the first parameter is taken as the second modulation mode.

[0088] Wherein, different first parameters can correspond to different modulation modes, and the mapping relationship between the first parameter and the modulation mode can be pre-stored, and then the corresponding modulation mode can be determined according to the obtained first parameter and the pre-stored mapping relationship. If the modulation mode corresponding to the first parameter is not the first modulation mode, it means that the modulation mode needs to be switched from the first modulation mode to the modulation mode corresponding to the first parameter, that is, the modulation mode corresponding to the first parameter is taken as the second modulation mode, so as to ensure that the leakage current in the process of the inverter operating in the grid-connected mode is moderate and does not exceed the preset inverter shutdown protection threshold.

[0089] The first parameter is taken as the parasitic impedance, the environmental humidity or the environmental weather as an example to further supplement the embodiment:

[0090] In the case of the first parameter being the parasitic impedance, in the mapping relationship between the parasitic impedance and the modulation mode: the larger the parasitic impedance, the smaller the leakage current generated, and the smaller the parasitic impedance, the larger the leakage current. Therefore, the larger the parasitic impedance, the larger the leakage current of the modulation mode that can be used, and the smaller the parasitic impedance, the smaller the leakage current of the modulation mode that can be used, in other words, the larger the parasitic impedance, the larger the leakage current of the modulation mode that corresponds to, and the smaller the parasitic impedance, the smaller the leakage current of the modulation mode that corresponds to, so as to ensure that the leakage current in the process of the inverter operating in the grid-connected mode is moderate and does not exceed the preset inverter shutdown protection threshold.

[0091] For example, if the first modulation mode is modulation mode S1 and the obtained parasitic impedance is large, and the corresponding modulation mode in the mapping relationship is modulation mode S3, then it can be determined that the first modulation mode (modulation mode S1) needs to be switched to the second modulation mode (modulation mode S3); if the first modulation mode is S2 and the obtained parasitic impedance is small, and the corresponding modulation mode in the mapping relationship is modulation mode S1, then it can be determined that the first modulation mode (modulation mode S2) needs to be switched to the second modulation mode (modulation mode S1); if the first modulation mode is modulation mode S2 and the obtained parasitic impedance is small, and the corresponding modulation mode in the mapping relationship is modulation mode S2, then it is determined that the modulation mode does not need to be switched, and the first modulation mode (modulation mode S2) is continued to be used to control the inverter to operate in grid-connected mode.

[0092] In the case where the first parameter is the ambient humidity, in the mapping relationship between the ambient humidity and the modulation mode: the smaller the ambient humidity, the smaller the leakage current generated, and the larger the ambient humidity, the larger the leakage current. Therefore, the larger the ambient humidity, the smaller the leakage current that can be used, and the smaller the ambient humidity, the larger the leakage current that can be used. In other words, the larger the ambient humidity corresponds to the smaller leakage current modulation mode, and the smaller the ambient humidity corresponds to the larger leakage current modulation mode, so as to ensure that the leakage current during the grid-connected operation of the inverter is moderate and does not exceed the preset inverter shutdown protection threshold.

[0093] For example, if the first modulation mode is modulation mode S3 and the obtained ambient humidity is large, and the corresponding modulation mode in the mapping relationship is modulation mode S1, then it can be determined that the first modulation mode (modulation mode S3) needs to be switched to the second modulation mode (modulation mode S1); if the first modulation mode is S1 and the obtained ambient humidity is small, and the corresponding modulation mode in the mapping relationship is modulation mode S3, then it can be determined that the first modulation mode (modulation mode S1) needs to be switched to the second modulation mode (modulation mode S3); if the first modulation mode is modulation mode S2 and the obtained ambient humidity is small, and the corresponding modulation mode in the mapping relationship is modulation mode S2, then it is determined that the modulation mode does not need to be switched, and the first modulation mode (modulation mode S2) is continued to be used to control the inverter to operate in grid-connected mode.

[0094] In the case that the first parameter is the ambient weather, in the mapping relationship between the ambient weather and the modulation mode: the more sunny the ambient weather is, the smaller the leakage current generated is, and the more rainy the ambient weather is, the larger the leakage current is, so the more sunny the ambient weather is, the larger the leakage current is, the more rainy the ambient weather is, the smaller the leakage current is, in other words, the more sunny the ambient weather is, the larger the leakage current is, the more rainy the ambient weather is, the smaller the leakage current is, so as to ensure that the leakage current is moderate during the grid-connected operation of the inverter, and does not exceed the preset inverter shutdown protection threshold.

[0095] Exemplarily, if the first modulation mode is the modulation mode S1, and the ambient weather obtained is sunny, and the corresponding modulation mode in the mapping relationship is the modulation mode S3, then it can be determined that the modulation mode needs to be switched from the first modulation mode (the modulation mode S1) to the second modulation mode (the modulation mode S3); if the first modulation mode is the modulation mode S3, and the ambient weather obtained is rainy, and the corresponding modulation mode in the mapping relationship is the modulation mode S1, then it can be determined that the modulation mode needs to be switched from the first modulation mode (the modulation mode S3) to the second modulation mode (the modulation mode S1); if the first modulation mode is the modulation mode S2, and the ambient weather obtained is overcast, and the corresponding modulation mode in the mapping relationship is the modulation mode S2, then it is determined that the modulation mode does not need to be switched, and the inverter is continued to be controlled to operate in the grid-connected mode in the first modulation mode (the modulation mode S2).

[0096] In an exemplary embodiment, referring to Figure 8 The control method of the inverter further includes the step S802 of comparing the first parameter with a first reference parameter, and if the comparison result meets a preset condition, it is determined that the modulation mode of the inverter needs to be switched, and the second modulation mode is determined according to the comparison result.

[0097] The first reference parameter can be the first parameter recorded at the same period or at the same time in the past, and the modulation mode used at the same period or at the same time in the past can also be recorded. The first parameter obtained is compared with the first reference parameter, if the comparison result meets a preset condition, it is determined that the modulation mode of the inverter needs to be switched, and the second modulation mode is determined according to the comparison result, if the comparison result does not meet the preset condition, it is determined that the modulation mode does not need to be switched, and the inverter is continued to be controlled to operate in the grid-connected mode in the first modulation mode, or the modulation mode used at the same period or at the same time in the past is switched to.

[0098] The first parameter is taken as the ambient temperature, the power generated by the inverter, or the maximum power point voltage of the inverter, respectively, as examples to further supplement the embodiment:

[0099] In the case that the first parameter is the ambient temperature, the first reference parameter is the historical same period or historical same time ambient temperature. If the obtained ambient temperature is significantly less than the historical same period or historical same time ambient temperature, a modulation mode with smaller leakage current can be adopted; if the obtained ambient temperature is significantly greater than the historical same period or historical same time ambient temperature, a modulation mode with larger leakage current can be adopted; in this way, the leakage current during the grid-connected operation of the inverter is ensured to be moderate, not exceeding the preset inverter shutdown protection threshold.

[0100] Exemplarily, if the first modulation mode is S3 and the obtained ambient temperature is significantly less than the historical same period or historical same time ambient temperature, a modulation mode with smaller leakage current, for example, modulation mode S1, needs to be adopted, and at this time it can be determined that the first modulation mode (modulation mode S3) needs to be switched to the second modulation mode (modulation mode S1); if the first modulation mode is S1 and the obtained ambient temperature is significantly greater than the historical same period or historical same time ambient temperature, a modulation mode with larger leakage current, for example, modulation mode S3, needs to be adopted, and at this time it can be determined that the first modulation mode (modulation mode S1) needs to be switched to the second modulation mode (modulation mode S3); if the first modulation mode is modulation mode S2 and the obtained ambient temperature is equal to or close to the historical same period or historical same time ambient temperature, it can be determined that the modulation mode does not need to be switched and the first modulation mode (modulation mode S2) continues to control the grid-connected operation of the inverter.

[0101] Similarly, in the case that the first parameter is the power generation power of the inverter, the first reference parameter is the historical same period or historical same time power generation power of the inverter. If the obtained power generation power of the inverter is significantly less than the historical same period or historical same time power generation power of the inverter, a modulation mode with smaller leakage current can be adopted; if the obtained power generation power of the inverter is significantly greater than the historical same period or historical same time power generation power of the inverter, a modulation mode with larger leakage current can be adopted; in this way, the leakage current during the grid-connected operation of the inverter is ensured to be moderate, not exceeding the preset inverter shutdown protection threshold.

[0102] Similarly, in the case that the first parameter is the maximum power point voltage of the inverter, the first reference parameter is the historical same period or historical same time maximum power point voltage of the inverter. If the obtained maximum power point voltage of the inverter is significantly less than the historical same period or historical same time maximum power point voltage of the inverter, a modulation mode with smaller leakage current can be adopted; if the obtained maximum power point voltage of the inverter is significantly greater than the historical same period or historical same time maximum power point voltage of the inverter, a modulation mode with larger leakage current can be adopted; in this way, the leakage current during the grid-connected operation of the inverter is ensured to be moderate, not exceeding the preset inverter shutdown protection threshold.

[0103] In one exemplary embodiment, the first parameter is multiple, and the referenceFigure 9 The control method of the inverter further includes steps S902-S906.

[0104] S902, a weight corresponding to each first parameter is obtained.

[0105] Exemplarily, the obtained multiple first parameters are at least two of the leakage current, the parasitic impedance, the environmental humidity, the environmental weather, the environmental temperature, the power generation of the inverter and the maximum power point voltage of the inverter. Each first parameter corresponds to a preset weight. The weights of different first parameters can be different or the same. The specific size of the weight can be preset according to the actual situation. The weight value can be a positive number, a negative number or zero.

[0106] S904, a first weighted parameter is determined according to each first parameter and the weight corresponding to each first parameter.

[0107] Exemplarily, each first parameter can be converted into a leakage current value according to a preset conversion relationship between each first parameter and the leakage current size. The converted leakage current value will correspond to the preset weight one by one. Then, the sum of the product of each leakage current value and the corresponding weight is taken as the first weighted parameter.

[0108] S906, a modulation mode corresponding to the first weighted parameter is determined. If the modulation mode corresponding to the first weighted parameter is not the first modulation mode, it is determined that the modulation mode of the inverter needs to be switched, and the modulation mode corresponding to the weighted parameter is taken as the second modulation mode.

[0109] Exemplarily, based on the leakage current size of the modulation mode, different modulation modes correspond to different weighted parameter intervals. For example, the weighted parameter intervals corresponding to the modulation mode S1, the modulation mode S2, the modulation mode S3 and the modulation mode S4 are the weighted parameter interval 1, the weighted parameter interval 2, the weighted parameter interval 3 and the weighted parameter interval 4 respectively. If the first modulation mode is the modulation mode S1 and the first weighted parameter is in the weighted parameter interval 3, the modulation mode corresponding to the first weighted parameter is the modulation mode S3. At this time, it can be determined that the first modulation mode (the modulation mode S1) needs to be switched to the second modulation mode (the modulation mode S3). If the first modulation mode is the modulation mode S4 and the first weighted parameter is in the weighted parameter interval 4, the modulation mode corresponding to the first weighted parameter is the modulation mode S4. It can be determined that the modulation mode does not need to be switched, and the inverter is continued to be controlled by the first modulation mode (the modulation mode S4) to operate in parallel. In this way, it is ensured that the leakage current is moderate during the parallel operation of the inverter, and does not exceed the preset inverter shutdown protection threshold.

[0110] In the related art, in addition to the situation that the leakage current exceeds the threshold value frequently in the grid-connected operation of the inverter, causing the inverter to trip, the leakage current also exceeds the threshold value in the starting stage of the inverter, causing the inverter to trip, especially when the inverter starts with an inappropriate modulation method, which is prone to cause the leakage current to exceed the threshold value, causing the inverter to trip. The starting stage of the inverter can be understood as the stage before the grid relay is completely closed.

[0111] Therefore, in an exemplary embodiment, the control method of the inverter further includes the following steps S1002-S1006. Figure 10

[0112] S1002, in the starting stage of the inverter, the second parameter corresponding to the inverter is obtained.

[0113] In the starting stage of the inverter, the second parameter corresponding to the inverter can include the size of the parasitic impedance and / or parameters that can directly or indirectly reflect and / or affect the size of the parasitic impedance.

[0114] S1004, the third modulation method is determined according to the second parameter, wherein the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold value in the process of starting the inverter in the third modulation method.

[0115] The modulation method matched and adapted to the second parameter of the inverter can be determined according to the second parameter of the inverter as the third modulation method, so that the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold value in the process of starting the inverter in the third modulation method.

[0116] S1006, the inverter is started based on the third modulation method.

[0117] In the starting stage of the inverter, the second parameter corresponding to the inverter is obtained in the embodiment of the application, so that the third modulation method is determined according to the second parameter, and the inverter is started based on the third modulation method, so that the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold value in the starting stage of the inverter, thereby ensuring that the inverter does not trip due to the leakage current exceeding the preset inverter shutdown protection threshold value in the starting stage.

[0118] Optionally, the second parameter includes at least one of the following: a working condition parameter of a photovoltaic component unit connected to the inverter, and an environmental parameter of an environment in which the inverter is located.

[0119] For example, the working condition parameter of the photovoltaic component unit connected to the inverter can include the parasitic impedance of the photovoltaic component unit connected to the inverter; the environmental parameter of the environment in which the inverter is located can include at least one of the following: environmental humidity, environmental temperature, and environmental weather.

[0120] ​The environment temperature and the environment weather can directly reflect the light condition, the light condition can directly reflect the environment humidity, and the environment humidity can directly affect the size of the parasitic impedance. In other words, the environment temperature and the environment weather can indirectly reflect the size of the parasitic impedance.

[0121] In an example embodiment, the step S1004 comprises: determining the modulation mode corresponding to the second parameter as the third modulation mode.

[0122] The different second parameters can correspond to different modulation modes, and the mapping relationship between the second parameters and the modulation modes can be pre-stored, so that the corresponding modulation mode can be determined according to the obtained second parameter and the pre-stored mapping relationship, to ensure that the leakage current in the inverter starting process is moderate and does not exceed the preset inverter shutdown protection threshold.

[0123] The first parameter is taken as the parasitic impedance, the environment humidity or the environment weather as an example to further supplement the embodiment as follows:

[0124] In the case of the second parameter being the parasitic impedance, in the mapping relationship between the parasitic impedance and the modulation mode: the larger the parasitic impedance is, the smaller the leakage current generated is, and the smaller the parasitic impedance is, the larger the leakage current is. Therefore, the larger the parasitic impedance is, the larger the leakage current is, and the smaller the parasitic impedance is, the smaller the leakage current is. In other words, the larger the parasitic impedance is, the larger the leakage current is, and the smaller the parasitic impedance is, the smaller the leakage current is, to ensure that the leakage current in the inverter starting process is moderate and does not exceed the preset inverter shutdown protection threshold.

[0125] For example, if the obtained parasitic impedance is large, the corresponding modulation mode in the mapping relationship is modulation mode S3, and then modulation mode S3 can be taken as the third modulation mode. If the obtained parasitic impedance is small, the corresponding modulation mode in the mapping relationship is modulation mode S1, and then modulation mode S1 can be taken as the third modulation mode.

[0126] In the case of the second parameter being the environment humidity, in the mapping relationship between the environment humidity and the modulation mode: the smaller the environment humidity is, the smaller the leakage current generated is, and the larger the environment humidity is, the larger the leakage current is. Therefore, the larger the environment humidity is, the smaller the leakage current is, and the smaller the environment humidity is, the larger the leakage current is. In other words, the larger the environment humidity is, the smaller the leakage current is, and the smaller the environment humidity is, the larger the leakage current is, to ensure that the leakage current in the inverter starting process is moderate and does not exceed the preset inverter shutdown protection threshold.

[0127] Exemplarily, if the acquired environmental humidity is large, and the corresponding modulation mode in the mapping relationship is modulation mode S1, then modulation mode S1 can be taken as the third modulation mode; if the acquired environmental humidity is small, and the corresponding modulation mode in the mapping relationship is modulation mode S3, then modulation mode S3 can be taken as the third modulation mode.

[0128] In the case where the second parameter is environmental weather, in the mapping relationship between environmental weather and modulation mode: the more sunny the environmental weather is, the smaller the leakage current is, and the more rainy the environmental weather is, the larger the leakage current is, so the more sunny the environmental weather is, the larger the leakage current can be adopted, and the more rainy the environmental weather is, the smaller the leakage current can be adopted, in other words, the more sunny the environmental weather is, the larger the leakage current corresponding modulation mode is, and the more rainy the environmental weather is, the smaller the leakage current corresponding modulation mode is, so as to ensure that the leakage current in the inverter starting process is moderate and does not exceed the preset inverter shutdown protection threshold.

[0129] Exemplarily, if the acquired environmental weather is sunny, and the corresponding modulation mode in the mapping relationship is modulation mode S3, then modulation mode S3 can be taken as the third modulation mode; if the acquired environmental weather is rainy, and the corresponding modulation mode in the mapping relationship is modulation mode S1, then modulation mode S1 can be taken as the third modulation mode.

[0130] In an exemplary embodiment, step S1004 comprises: comparing the second parameter with a second reference parameter, and determining the third modulation mode according to the comparison result.

[0131] The second reference parameter can be the recorded historical same period or historical same time second parameter, and the modulation mode adopted at the historical same period or historical same time can also be recorded. The acquired second parameter is compared with the second reference parameter, and the third modulation mode is determined according to the comparison result.

[0132] The first parameter is taken as an example of environmental temperature for further supplementary description of this embodiment:

[0133] In the case where the second parameter is environmental temperature, the second reference parameter is the historical same period or historical same time environmental temperature. If the acquired environmental temperature is obviously smaller than the historical same period or historical same time environmental temperature, a smaller leakage current modulation mode can be adopted; if the acquired environmental temperature is obviously larger than the historical same period or historical same time environmental temperature, a larger leakage current modulation mode can be adopted; in this way, the leakage current in the inverter starting process is ensured to be moderate and does not exceed the preset inverter shutdown protection threshold.

[0134] Exemplarily, if the obtained ambient temperature is obviously less than the historical same period or historical same time ambient temperature, a modulation mode with smaller leakage current, for example, the modulation mode S1, needs to be adopted, and at this time, the modulation mode S1 can be taken as the third modulation mode; if the obtained ambient temperature is obviously greater than the historical same period or historical same time ambient temperature, a modulation mode with greater leakage current, for example, the modulation mode S3, needs to be adopted, and at this time, the modulation mode S3 can be taken as the third modulation mode.

[0135] In one exemplary embodiment, the second parameters are multiple, and the step S1004 comprises the following steps S1102-S1106. Figure 11

[0136] S1102, weights corresponding to respective second parameters are obtained.

[0137] Exemplarily, the obtained multiple second parameters are at least two of the parasitic impedance, the ambient humidity, the ambient weather and the ambient temperature. Each second parameter corresponds to a preset weight, and the weights of different second parameters can be different or the same, and the specific size of the weight can be preset according to the actual situation, wherein the weight value can be a positive number, a negative number or zero.

[0138] S1104, a second weighted parameter is determined according to the respective second parameters and the weights corresponding to the respective second parameters.

[0139] Exemplarily, each second parameter can be converted into a leakage current value according to a preset conversion relationship between the respective second parameters and the leakage current size, the converted leakage current value will correspond to the preset weight one by one, and then the sum of the product of each leakage current value and the corresponding weight is taken as the second weighted parameter.

[0140] S1106, a modulation mode corresponding to the second weighted parameter is determined, and the modulation mode corresponding to the second weighted parameter is taken as the third modulation mode.

[0141] Exemplarily, based on the leakage current size of the modulation mode, different modulation modes correspond to different weighted parameter intervals, for example, the modulation mode S1, the modulation mode S2, the modulation mode S3 and the modulation mode S4 correspond to the weighted parameter interval 1, the weighted parameter interval 2, the weighted parameter interval 3 and the weighted parameter interval 4 respectively. If the second weighted parameter is in the weighted parameter interval 3, the modulation mode corresponding to the second weighted parameter is the modulation mode S3, and at this time, the modulation mode S3 can be taken as the third modulation mode; if the second weighted parameter is in the weighted parameter interval 4, the modulation mode corresponding to the second weighted parameter is the modulation mode S4, and at this time, the modulation mode S4 can be taken as the third modulation mode; in this way, it is ensured that the leakage current in the inverter starting process is moderate and does not exceed the preset inverter shutdown protection threshold. ​

[0142] In an example embodiment, the control method of the inverter further comprises: in the starting stage of the inverter, controlling the inverter to start based on the preset default modulation mode.

[0143] Among the modulation modes, a modulation mode can be selected and pre-stored as the preset default modulation mode according to the principle of ensuring that the leakage current in the starting process of the inverter does not exceed the preset inverter shutdown protection threshold. In the starting stage of the inverter, for example, in the case that the program code for determining the third modulation mode is tampered with and errors, the inverter can be directly controlled to start based on the preset default modulation mode.

[0144] Based on the same inventive concept, in an example embodiment, the embodiments of the present application further provide an inverter configured to implement the control method of the inverter provided by any of the above embodiments.

[0145] The inverter and the control method of the inverter provided by the embodiments of the present application belong to the same inventive concept, can solve the same technical problems, and thus achieve the same technical effects. Repetitive content will not be repeated here.

[0146] Based on the same inventive concept, in an example embodiment, the embodiments of the present application further provide a photovoltaic system, which comprises a photovoltaic assembly unit, a controller and at least one inverter; each of the photovoltaic assembly units is connected to a corresponding inverter, and each of the inverters is connected to the controller, and the controller is configured to implement the control method of the inverter provided by any of the above embodiments.

[0147] In the embodiments of the present application, in the case that the photovoltaic system comprises multiple inverters, the controller can determine the first modulation mode, the second modulation mode and the third modulation mode for each inverter according to the first parameter and the second parameter of each inverter, or the controller can determine the first modulation mode, the second modulation mode and the third modulation mode according to the first parameter and the second parameter of a representative inverter and apply them to all inverters. The two cases can be implemented according to actual needs, and the embodiments of the present application do not make specific limitations thereon.

[0148] The photovoltaic system and the control method of the inverter provided by the embodiments of the present application belong to the same inventive concept, can solve the same technical problems, and thus achieve the same technical effects. Repetitive content will not be repeated here.

[0149] It should be understood that, although the steps in the flowcharts involved in the embodiments described above are shown in sequence according to the arrows, the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the execution of the steps is not strictly limited in sequence, and the steps can be executed in other sequences. Moreover, at least some of the steps in the flowcharts involved in the embodiments described above can include multiple steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of the steps or stages is not necessarily sequential, but can be executed in rotation or alternation with at least some of the other steps or the steps or stages in the other steps.

[0150] The technical features of the above embodiments can be combined in any manner. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, but it should be understood that any combination of the technical features is within the scope of the present application as long as the combination does not result in contradictions.

[0151] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A control method for an inverter, characterized in that, The control method includes: During the grid-connected operation of the inverter in the first modulation mode, the first parameter corresponding to the inverter is obtained; If it is determined based on the first parameter that the modulation mode of the inverter needs to be switched to the second modulation mode, then the inverter is controlled to operate in grid-connected mode based on the second modulation mode; During the grid-connected operation of the inverter in the second modulation mode, the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold.

2. The method according to claim 1, characterized in that, The first parameter includes at least one of the following: The operating parameters of the inverter, the operating condition parameters of the photovoltaic module unit connected to the inverter, and the environmental parameters of the environment in which the inverter is located.

3. The method according to claim 2, characterized in that, The method further includes: Determine whether the first parameter is within a target switching interval in at least one switching interval. If it is, determine that the modulation mode of the inverter needs to be switched, and use the modulation mode corresponding to the target switching interval as the second modulation mode.

4. The method according to claim 3, characterized in that, The method further includes: The at least one switching interval is determined according to the first modulation scheme.

5. The method according to claim 2, characterized in that, The method further includes: Determine the modulation method corresponding to the first parameter. If the modulation method corresponding to the first parameter is not the first modulation method, then determine that the modulation method of the inverter needs to be switched, and use the modulation method corresponding to the first parameter as the second modulation method.

6. The method according to claim 2, characterized in that, The method further includes: The first parameter is compared with the first reference parameter. If the comparison result meets the preset conditions, it is determined that the modulation mode of the inverter needs to be switched, and the second modulation mode is determined according to the comparison result.

7. The method according to claim 2, characterized in that, The first parameter can be multiple, and the method further includes: Obtain the weights corresponding to each of the first parameters; The first weighting parameter is determined based on each of the first parameters and the weights corresponding to each of the first parameters; The modulation scheme corresponding to the first weighting parameter is determined. If the modulation scheme corresponding to the first weighting parameter is not the first modulation scheme, it is determined that the modulation scheme of the inverter needs to be switched, and the modulation scheme corresponding to the weighting parameter is used as the second modulation scheme.

8. The method according to claim 1, characterized in that, The method further includes: If it is determined based on the first parameter that there is no need to switch the modulation mode of the inverter, then the inverter will continue to be controlled to operate in grid-connected mode based on the first modulation mode.

9. The method according to any one of claims 1 to 8, characterized in that, The method further includes: During the startup phase of the inverter, the second parameter corresponding to the inverter is obtained; The third modulation method is determined according to the second parameter, wherein the leakage current of the inverter does not exceed the preset inverter shutdown protection threshold during the startup process of the inverter using the third modulation method. The inverter is started up based on the third modulation method.

10. The method according to claim 9, characterized in that, The second parameter includes at least one of the following: Operating parameters of the photovoltaic module unit connected to the inverter, and environmental parameters of the environment in which the inverter is located.

11. The method according to claim 10, characterized in that, Determining the third modulation scheme based on the second parameter includes: Determine the modulation scheme corresponding to the second parameter, and use the modulation scheme corresponding to the second parameter as the third modulation scheme.

12. The method according to claim 10, characterized in that, Determining the third modulation scheme based on the second parameter includes: The second parameter is compared with the second reference parameter, and the third modulation method is determined based on the comparison result.

13. The method according to claim 10, characterized in that, The second parameter can be multiple, and determining the third modulation method based on the second parameter includes: Obtain the weights corresponding to each of the second parameters; The second weighting parameter is determined based on each of the second parameters and the weights corresponding to each of the second parameters; Determine the modulation scheme corresponding to the second weighting parameter, and use the modulation scheme corresponding to the second weighting parameter as the third modulation scheme.

14. The method according to any one of claims 1 to 8, characterized in that, The method further includes: During the startup phase of the inverter, the inverter is started up based on a preset default modulation method.

15. An inverter, characterized in that, The inverter is configured to implement the control method for the inverter as described in any one of claims 1-14.

16. A photovoltaic system, characterized in that, It includes a controller and at least one inverter; each of the inverters is connected to the controller, which is configured to implement the control method of the inverter according to any one of claims 1 to 14.

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