Electric power system, inverter, power converter and control method

Abstract

The invention discloses a power system, an inverter, a power converter and a control method. The power system comprises an inverter and at least one path of direct current string, the direct-current string comprises a plurality of power converters; each power converter comprises a direct-current input end and a direct-current output end, the direct-current input end of each power converter is used for connecting a corresponding direct-current power supply, and the direct-current output end of each power converter in the direct-current string is connected in series to the inverter; and aiming at the same direct current group string, if at least one power converter of which the output voltage is less than or equal to a preset threshold exists, the inverter is used for reducing the output voltage set value of the second type of power converter in the direct current group string and increasing the output voltage set value of the first type of power converter in the direct current group string. By adjusting the output voltage set value of the power converter, the power converter can be prevented from being limited by the output voltage set value in the process of tracking the maximum power point, so that the power converter works at the maximum power point.

Description

TECHNICAL FIELD

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

[0002] In a photovoltaic power system, the positive input end and the negative input end of the power converter are connected to the positive output end and the negative output end of the photovoltaic module respectively, so as to track the maximum power point (MPP) of the photovoltaic module in real time, thereby solving the problem of reduced power generation of the photovoltaic system caused by shadow shielding, differences in module orientation or inconsistent module attenuation, realizing maximum power output and online monitoring of the photovoltaic module, and improving system efficiency.

[0003] In the related art, the output end of the direct current group string is connected to the inverter. When the photovoltaic module in the direct current group string ages, is damaged or the power converter fails, the output voltage of the corresponding power converter decreases, and the output voltage of other power converters increases, so that the MPP point needs to be re-tracked by the passive increase of the output voltage of the power converter. However, in order to protect the inverter at the back end of the direct current group string, each power converter is provided with an upper limit value of the output voltage, which may cause the power converter to fail to track the MPP point. SUMMARY

[0004] Based on the above problems, the present application provides a power system, an inverter, a power converter and a control method, which can track the MPP point by redistributing the output voltage setting value in the direct current group string.

[0005] The embodiments of the present application disclose the following technical solutions:

[0006] In a first aspect, the embodiments of the present application provide a power system, comprising: an inverter and at least one direct current group string.

[0007] The direct current group string comprises a plurality of power converters; the power converter comprises a direct current input end and a direct current output end, the direct current input end of the power converter is used to connect to a corresponding direct current power supply, and the direct current output ends of the power converters in the direct current group string are connected in series to the inverter;

[0008] The inverter is configured to: if there is at least one power converter whose output voltage is less than or equal to a preset threshold value, decrease the output voltage set value of a second type of power converter in the DC string and increase the output voltage set value of a first type of power converter in the DC string; the first type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value; the second type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value; the second difference value is greater than the first difference value; the sum of the output voltage set values of all the power converters in the DC string is equal to the maximum input voltage of the inverter; and the difference between the total amount of decrease of the output voltage set value of the second type of power converter and the total amount of increase of the output voltage set value of the first type of power converter is less than or equal to a third difference value.

[0009] Optionally, the inverter is configured to: after the output voltage set values of all the second type of power converters are decreased, increase the output voltage set values of the first type of power converters.

[0010] Optionally, the inverter is configured to: sequentially increase the output voltage set values of the first type of power converters in the order of the difference between the output voltage set value and the output voltage of the first type of power converters from small to large.

[0011] Optionally, the rated output power of at least two power converters in the same DC string is different.

[0012] Optionally, the inverter is further configured to: obtain the output voltage set values of the power converters according to the number of the power converters and the maximum input voltage of the inverter.

[0013] In a second aspect, an embodiment of the present application provides an inverter, including an inverter circuit and a controller.

[0014] The DC side of the inverter circuit is configured to connect at least one DC string; the DC string includes a plurality of power converters; the power converter includes a DC input end and a DC output end; the DC input end of the power converter is configured to connect a corresponding DC power supply; and the DC output ends of the power converters in the DC string are connected in series to the inverter.

[0015] The controller is configured to: if there is at least one power converter with an output voltage less than or equal to a preset threshold, decrease the output voltage set value of a second type of power converter in the DC string and increase the output voltage set value of a first type of power converter in the DC string; wherein the first type of power converter includes a power converter with a difference between the output voltage set value and the output voltage less than or equal to a first difference; the second type of power converter includes a power converter with a difference between the output voltage set value and the output voltage greater than or equal to a second difference; the second difference is greater than the first difference; the sum of the output voltage set values of all the power converters in the DC string is equal to the maximum input voltage of the inverter; and the difference between the total amount of decrease in the output voltage set value of the second type of power converter and the total amount of increase in the output voltage set value of the first type of power converter is less than or equal to a third difference.

[0016] In a third aspect, an embodiment of the present application provides a power converter, comprising: a first DC-DC circuit and a controller.

[0017] The input end of the first DC-DC circuit is configured to be connected to a DC power supply, and the output end of the first DC-DC circuit is connected in series with the output end of at least one second DC-DC circuit to an inverter.

[0018] The controller is configured to receive an instruction issued by the inverter and increase or decrease the output voltage set value of the first DC-DC circuit according to the instruction; wherein if there is at least one second DC-DC circuit with an output voltage less than or equal to a preset threshold and the first DC-DC circuit is a first type of DC-DC circuit, the instruction indicates to increase the output voltage set value of the first DC-DC circuit; or if there is at least one second DC-DC circuit with an output voltage less than or equal to a preset threshold and the first DC-DC circuit is a second type of DC-DC circuit, the instruction indicates to decrease the output voltage set value of the first DC-DC circuit; the first type of DC-DC circuit includes a DC-DC circuit with a difference between the output voltage set value and the output voltage less than or equal to a first difference; the second type of DC-DC circuit includes a DC-DC circuit with a difference between the output voltage set value and the output voltage greater than or equal to a second difference; the second difference is greater than the first difference; and the sum of the output voltage set value of the first DC-DC circuit and the output voltage set value of the second DC-DC circuit is equal to the maximum input voltage of the inverter.

[0019] In a fourth aspect, an embodiment of the present application provides a control method of a power system, applied to an inverter, the power system comprising the inverter and at least one DC string; wherein the DC string comprises a plurality of power converters; each power converter comprises a DC input end and a DC output end, the DC input end of each power converter is configured to be connected to a corresponding DC power supply, and the DC output ends of the power converters in the DC string are connected in series to the inverter.

[0020] The method comprises:

[0021] For the same DC group string, if there is at least one power converter whose output voltage is less than or equal to a preset threshold, the inverter is used to lower the output voltage set value of the second type of power converter in the DC group string and raise the output voltage set value of the first type of power converter in the DC group string; wherein the first type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference; the second type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; the sum of the output voltage set values of all the power converters in the DC group string is equal to the maximum input voltage of the inverter; the difference between the total amount of lowering of the output voltage set value of the second type of power converter and the total amount of raising of the output voltage set value of the first type of power converter is less than or equal to a third difference.

[0022] Optionally, the lowering of the output voltage set value of the second type of power converter in the DC group string and the raising of the output voltage set value of the first type of power converter in the DC group string specifically comprises:

[0023] Lowering the output voltage set value of the second type of power converter in the DC group string;

[0024] After the output voltage set values of all the second type of power converters are lowered, raising the output voltage set value of the first type of power converter.

[0025] Optionally, the raising of the output voltage set value of the first type of power converter specifically comprises:

[0026] Raising the output voltage set value of the first type of power converter in order from small to large according to the difference between the output voltage set value and the output voltage of the first type of power converter.

[0027] Optionally, for the same DC group string, the rated output power of at least two power converters is different.

[0028] Optionally, the method further comprises:

[0029] Obtaining the output voltage set value of each power converter according to the number of power converters and the maximum input voltage of the inverter.

[0030] In a fifth aspect, an embodiment of the present application provides a control method of a power system, applied to a power converter, the power system comprising an inverter and at least one DC group string; wherein the DC group string comprises a plurality of power converters; the power converter comprises a DC input end and a DC output end, the DC input end of the power converter being used to connect to a corresponding DC power supply, and the DC output ends of the power converters in the DC group string being connected in series to the inverter;

[0031] The method comprises:

[0032] For the same DC group string, the target power converter receives a first instruction issued by the inverter, and adjusts the output voltage set value of the target power converter according to the first instruction; wherein, if there is at least one power converter whose output voltage is less than or equal to a preset threshold, and the target power converter is a first type power converter, the first instruction indicates to increase the output voltage set value of the target power converter; if there is at least one power converter whose output voltage is less than or equal to a preset threshold, and the target power converter is a second type power converter, the first instruction indicates to decrease the output voltage set value of the target power converter; the first type power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference; the second type power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; and the sum of the output voltage set values of all power converters in the DC group string is equal to the maximum input voltage of the inverter.

[0033] After the output voltage set value of the target power converter is adjusted, a second instruction is sent to the inverter, so that the inverter determines the next target power converter in the same DC group string.

[0034] The power system provided by the embodiment of the present application comprises an inverter and at least one DC group string; the DC group string comprises a plurality of power converters; the power converter comprises a DC input end and a DC output end; the DC input end of the power converter is used to connect a corresponding DC power supply; the DC output ends of the power converters in the DC group string are connected in series to the inverter; for the same DC group string, if there is at least one power converter whose output voltage is less than or equal to a preset threshold, the inverter is used to decrease the output voltage set value of a second type power converter in the DC group string and increase the output voltage set value of a first type power converter in the DC group string. In the embodiment of the present application, the output voltage set values of the power converters in the same DC group string are redistributed in the following way: for a power converter that needs to track the MPP point by increasing the output voltage set value, the corresponding output voltage set value is increased; and for a power converter that does not need to track the MPP point by increasing the output voltage set value, the corresponding output voltage set value is decreased. Therefore, each power converter in the embodiment of the present application can track the MPP point. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without creative effort based on the accompanying drawings are within the protection scope of the present application.

[0036] Figure 1 is an output characteristic curve diagram of a photovoltaic module;

[0037] Figure 2 is a structural schematic diagram of an electric power system provided by an embodiment of the present application;

[0038] Figure 3 is a schematic diagram of power converter classification provided by an embodiment of the present application;

[0039] Figure 4 is a structural schematic diagram of an inverter provided by an embodiment of the present application;

[0040] Figure 5 is a structural schematic diagram of a power converter provided by an embodiment of the present application;

[0041] Figure 6 is a flowchart of a control method of an electric power system provided by an embodiment of the present application;

[0042] Figure 7 is a flowchart of another control method of an electric power system provided by an embodiment of the present application;

[0043] Figure 8 is a flowchart of still another control method of an electric power system provided by an embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without creative effort based on the accompanying drawings are within the protection scope of the present application.

[0045] The terms "first" and "second" and the like in the specification and claims of the present application are used to distinguish different objects, rather than to describe a specific order of the objects. For example, first data and second data are used to distinguish different data, rather than to describe a specific order of the data.

[0046] In the present embodiments, the word "exemplary" or "for example" is used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "for example" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "for example" is intended to present concepts in a concrete manner.

[0047] In the description of the present embodiments, unless otherwise stated "a plurality of" means two or more, for example, a plurality of processing units means two or more processing units, and the like; a plurality of elements means two or more elements, and the like.

[0048] In order to understand the present application, first, the basic principles involved in the present application are introduced.

[0049] The power system described in the present application is composed of an inverter and at least a DC string, and the input end of each power converter in the DC string is connected to a DC power source, and the output end of each power converter is connected in series to the inverter. Taking one DC string as an example, the output voltage of the DC string is fixed (the maximum input voltage of the inverter), when one of the power converters in the DC string is aged or damaged due to the photovoltaic module, its output voltage is reduced, resulting in the output voltage of other power converters rising and needing to retrace the MPP point.

[0050] Referring to Figure 1 , the figure is an output characteristic curve diagram of a photovoltaic module provided by the present embodiments.

[0051] Among them, Figure 1 The vertical axis P in the figure represents the output power of the photovoltaic module, and the horizontal axis V represents the output voltage of the photovoltaic module.

[0052] As Figure 1 shown, Vm is the output voltage of the photovoltaic module at the MPP point (the input voltage of the power converter at the MPP point), and V0 is the output voltage of the photovoltaic module after deviating from the MPP point (the input voltage of the power converter when deviating from the MPP point). When the input voltage of the power converter is V0, the inverter needs to track the MPP point by reducing the input voltage of the power converter, accompanied by the reduction of the input voltage of the power converter, the output voltage of the power converter will rise. However, the output voltage of the power converter is fixed, resulting in limited space for the output voltage of the power converter to rise, further resulting in the power converter failing to track the MPP point.

[0053] To this end, in the DC string, by redistributing the output voltage of the power converter, for the power converter that needs to track the MPP point by increasing the output voltage set value, the corresponding output voltage set value is increased; correspondingly, for the power converter that does not need to track the MPP point by increasing the output voltage set value, the corresponding output voltage set value is decreased. Thus, each power converter in the DC string can track the MPP point.

[0054] Referring to Figure 2 , the figure is a structural schematic diagram of a power system provided by an embodiment of the present application.

[0055] As Figure 2 shown, the power system comprises an inverter 110 and at least one DC string 120;

[0056] The DC string 120 comprises a plurality of power converters; the power converter comprises a DC input end and a DC output end, the DC input end of the power converter is used to connect the corresponding DC power supply, and the DC output ends of the power converters in the DC string 120 are connected in series to the inverter 110;

[0057] For the same DC string 120, if there is at least one power converter whose output voltage is less than or equal to a preset threshold value, the inverter is used to down-regulate the output voltage set value of the second type of power converter in the DC string and up-regulate the output voltage set value of the first type of power converter in the DC string; wherein the first type of power converter comprises a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value; the second type of power converter comprises a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value; the second difference value is greater than the first difference value; the sum of the output voltage set values of all the power converters in the DC string is equal to the maximum input voltage of the inverter; the difference between the total amount of down-regulation of the output voltage set value of the second type of power converter and the total amount of up-regulation of the output voltage set value of the first type of power converter is less than or equal to a third difference value.

[0058] Exemplarily, the DC power supply can be a photovoltaic module, and the power converter can be a DCDC circuit. It should be understood that the DCDC circuit can be any one of a Buck, a Boost, and a Buck-Boost circuit, wherein the Buck and the Buck-Boost are mostly used in small-power power systems, and the user can select the corresponding DCDC circuit according to the power of the power system, and the type of the DCDC circuit is not limited in the embodiment.

[0059] Exemplarily, as Figure 2As shown, the power system includes DC group string 1, DC group string 2, …, DC group string m, DC group string 1 includes a plurality of power converters, for example, power converter 11, power converter 12, power converter 13, …, power converter 1n; DC group string 2 includes a plurality of power converters, for example, power converter 21, power converter 22, power converter 23, …, power converter 2n; DC group string m includes a plurality of power converters, for example, power converter m1, power converter m2, power converter m3, …, power converter mn.

[0060] As shown, the power system includes DC group string 1, DC group string 2, …, DC group string m, DC group string 1 includes a plurality of power converters, for example, power converter 11, power converter 12, power converter 13, …, power converter 1n; DC group string 2 includes a plurality of power converters, for example, power converter 21, power converter 22, power converter 23, …, power converter 2n; DC group string m includes a plurality of power converters, for example, power converter m1, power converter m2, power converter m3, …, power converter mn.

[0061] It should be noted that the number of power converters in each DC group string is not limited in the embodiments of the present application. For example, DC group string 1 includes 15 power converters, and DC group string 2 includes 10 power converters. Further, the rated output power of the power converters in each DC group string can also be different.

[0062] In a possible implementation, for the same DC group string, the inverter determines the type of the power converter according to the difference between the output voltage set value and the output voltage of the power converter.

[0063] As an example, the type of the power converter includes a first type of power converter and a second type of power converter, the first type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value; the second type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value; wherein the second difference value is greater than the first difference value.

[0064] It should be understood that the first difference value and the second difference value described in the embodiments can be set or adjusted according to the user's needs.

[0065] For ease of understanding, the embodiments of the present application provide a schematic diagram of power converter classification, as shown in Figure 3 .

[0066] For example, the direct current group string 1 includes 15 group string connected power converters P11, P12, P13, P14, P15, P16, P17, P18, P19, P110, P111, P112, P113, P114 and P115. Among them, the power converters P11, P12, P13, P14, P15, P16, P17 and P18 meet the requirements of the first power converter, that is, the difference between the output voltage set value and the output voltage is less than or equal to the first difference; the power converters P110, P111, P112, P113, P114 and P115 meet the requirements of the second power converter, that is, the difference between the output voltage set value and the output voltage is greater than or equal to the second difference; wherein the output voltage of the power converter P19 is less than or equal to the preset threshold value, indicating that the power converter fails, or the photovoltaic module corresponding to the power converter is aged or damaged. Wherein, the preset threshold value can be set or adjusted according to the user's demand.

[0067] In a possible implementation, if there is at least one power converter with an output voltage less than or equal to a preset threshold value, for example, P19, the output voltage set value of the second type of power converter (P110, P111, P112, P113, P114 and P115) is sequentially adjusted downward, and after the output voltage set value of all second type of power converters is adjusted, the output voltage set value of the first type of power converter (P11, P12, P13, P14, P15, P16, P17 and P18) is sequentially adjusted upward. Wherein, the difference between the total amount of downward adjustment of the output voltage set value of the second type of power converter (P110, P111, P112, P113, P114 and P115) and the total amount of upward adjustment of the output voltage set value of the first type of power converter (P11, P12, P13, P14, P15, P16, P17 and P18) is less than or equal to a third difference.

[0068] It should be understood that the third difference described in the embodiment can be set or adjusted according to the user's demand. Wherein, in an ideal case, the third difference tends to be 0.

[0069] Further, in order to avoid the temporary rise of the direct current group string voltage during the adjustment process, which causes the first type of power converter to fail to track the MPP point, the embodiment of the present application can sort the first type of power converter, and sequentially adjust the output voltage set value of the first type of power converter in the order of the difference between the output voltage set value and the output voltage from small to large.

[0070] For example, the first type of power converter (P11, P12, P13, P14, P15, P16, P17 and P18) is in the order of the difference between the output voltage set value and the output voltage from small to large, P12, P13, P14, P11, P15, P17, P16 and P18. The inverter sends a command to P12, and P12 adjusts the output voltage set value according to the received command. After the output voltage set value of P12 is adjusted, the inverter returns the corresponding command to indicate that the adjustment is complete. Then, the inverter sends a command to P13, and P13 adjusts the output voltage set value according to the received command. After the adjustment is complete, the inverter returns the corresponding command to indicate that the adjustment is complete. In this way, the inverter receives the command sent by P18 to indicate that P18 completes the adjustment of the output voltage set value.

[0071] It should be understood that for the same DC string, for the first type of power converter with a smaller difference between the output voltage set value and the output voltage, the corresponding output voltage set value has a relatively larger up-regulation amplitude. For the first type of power converter with a larger difference between the output voltage set value and the output voltage, the corresponding output voltage set value has a relatively smaller up-regulation amplitude. Conversely, for the same DC string, for the second type of power converter with a smaller difference between the output voltage set value and the output voltage, the corresponding output voltage set value has a relatively smaller down-regulation amplitude. For the second type of power converter with a larger difference between the output voltage set value and the output voltage, the corresponding output voltage set value has a relatively larger down-regulation amplitude.

[0072] To further avoid the temporary rise of the DC string voltage during the adjustment process causing the first type of power converter to fail to track the MPP point, in the embodiment of the application, the output voltage set value of the second type of power converter can be alternately adjusted downward and the output voltage set value of the first type of power converter can be alternately adjusted upward.

[0073] For example, the second type of power converter (P110, P111, P112, P113, P114 and P115) is in the order of the difference between the output voltage set value and the output voltage from large to small, P112, P113, P114, P110, P111 and P115. The first type of power converter (P11, P12, P13, P14, P15, P16, P17 and P18) is in the order of the difference between the output voltage set value and the output voltage from small to large, P12, P13, P14, P11, P15, P17, P16 and P18.

[0074] In a possible implementation, the output voltage set value of P112, P113 and P114 is sequentially lowered, the output voltage set value of P12 is raised; the output voltage set value of P110 is lowered, and the output voltage set value of P13 and P14 is sequentially raised, and so on, until the output voltage set value of all the first type power converters is adjusted.

[0075] It should be understood that the above example is merely exemplary, and the adjustment order of the output voltage set value of the power converter can be determined according to the difference between the output voltage set value and the output voltage of each power converter; for example, the difference between the output voltage set value and the output voltage of P112 is P, the difference between the output voltage set value and the output voltage of P12 is Q, and P≥Q, then the output voltage set value of P112 is lowered, and then the output voltage set value of P12 is lowered.

[0076] In this embodiment, by advancing the adjustment time of the output voltage set value of the first type power converter (compared to adjusting the output voltage set value of the first type power converter after the output voltage set value of all the second type power converters is lowered), the problem that the first type power converter cannot track the MPP point due to the temporary rise of the DC string voltage during the adjustment process can be further avoided.

[0077] In a possible implementation, for the same DC string, the initial output voltage set value of each power converter can be determined according to the number of power converters in the string and the maximum input voltage of the inverter.

[0078] As an example, the rated output power of each power converter in the DC string is the same, then the output voltage set value of each power converter is obtained by dividing the maximum input voltage of the inverter by the number of power converters.

[0079] As an example, the rated output power of each power converter in the DC string is not the same, then the corresponding output voltage set value is obtained by the maximum input voltage of the inverter and the rated output power of each power converter.

[0080] It should be understood that for the power converter with relatively high rated output power, the corresponding output voltage set value is also relatively high; for the power converter with relatively low rated output power, the corresponding output voltage set value is also relatively low. The output voltage set value of the power converter is allocated as needed (the higher the rated output power of the power converter, the higher the demand for the output voltage set value), so that each power converter in the DC string can be operated at full power.

[0081] In the embodiments of the present application, the output voltage set value of the power converter in the DC string is redistributed. For the power converter that needs to track the MPP point by increasing the output voltage set value, the corresponding output voltage set value is increased. Conversely, for the power converter that can track the MPP point without increasing the output voltage set value, the corresponding output voltage set value is decreased. Therefore, each power converter in the embodiments of the present application can track the MPP point.

[0082] In the application scenarios corresponding to the foregoing embodiments, the inverter does not adjust the upper limit of the output voltage of the DC string (the upper limit of the output voltage of the DC string remains unchanged) to ensure that the power generation of the power system is not affected. In addition, in the embodiments of the present application, the inverter can also adjust the output voltage of the DC string so that the power converter in the DC string is not affected by other power converters, thereby enabling the power converter to work at the MPP point.

[0083] Referring to Figure 4 , the figure is a structural schematic diagram of an inverter provided by the embodiments of the present application.

[0084] As Figure 4 shown, the inverter 400 includes an inverter circuit 410 and a controller 420;

[0085] The DC side of the inverter circuit 410 is used to connect at least one DC string; wherein the DC string contains a plurality of power converters; the power converter contains a DC input end and a DC output end, the DC input end of the power converter is used to connect a corresponding DC power supply, and the DC output ends of the power converters in the DC string are connected in series to the DC side of the inverter circuit 410;

[0086] The controller 420 is used to down-regulate the output voltage set value of the second type of power converter in the DC string and up-regulate the output voltage set value of the first type of power converter in the DC string if there is at least one power converter whose output voltage is less than or equal to a preset threshold value; wherein the first type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value; the second type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value; the second difference value is greater than the first difference value; the sum of the output voltage set values of all the power converters in the DC string is equal to the maximum input voltage of the inverter; the difference between the total down-regulation amount of the output voltage set value of the second type of power converter and the total up-regulation amount of the output voltage set value of the first type of power converter is less than or equal to a third difference value.

[0087] Optionally, the controller 420 is specifically configured to increase the output voltage setting value of the first type of power converter after the output voltage setting value of all the second type of power converters is decreased.

[0088] Optionally, the controller 420 is specifically configured to increase the output voltage setting value of the first type of power converter in the order of the difference between the output voltage setting value and the output voltage of the first type of power converter from small to large.

[0089] Optionally, the rated output power of the at least two power converters is different for the same DC string.

[0090] Optionally, the controller 420 is further configured to obtain the output voltage setting value of each power converter according to the number of power converters and the maximum input voltage of the inverter.

[0091] Referring to Figure 5 , the figure is a structural schematic diagram of a power converter provided by the embodiment of the application.

[0092] As Figure 5 shown, the power converter 500 includes a first DC-DC circuit 510 and a controller 520;

[0093] The input end of the first DC-DC circuit 510 is configured to be connected to a DC power supply, and the output end of the first DC-DC circuit 510 is connected in series with the output end of at least one second DC-DC circuit to an inverter;

[0094] The controller 520 is configured to receive an instruction issued by the inverter and increase or decrease the output voltage setting value of the first DC-DC circuit 510 according to the instruction.

[0095] In a possible implementation, if there is at least one second DC-DC circuit with an output voltage less than or equal to a preset threshold value, and the first DC-DC circuit 510 is a first type of DC-DC circuit, the instruction indicates to increase the output voltage setting value of the first DC-DC circuit 510.

[0096] The first type of DC-DC circuit includes a DC-DC circuit with a difference between the output voltage setting value and the output voltage less than or equal to a first difference value; the second type of DC-DC circuit includes a DC-DC circuit with a difference between the output voltage setting value and the output voltage greater than or equal to a second difference value; the second difference value is greater than the first difference value; and the sum of the output voltage setting value of the first DC-DC circuit 510 and the output voltage setting value of the second DC-DC circuit is equal to the maximum input voltage of the inverter.

[0097] In another possible implementation, if there is at least one second DC-DC circuit whose output voltage is less than or equal to a preset threshold value, and the first DC-DC circuit 510 is a second type of DC-DC circuit, the instruction indicates to lower the output voltage set value of the first DC-DC circuit 510.

[0098] Referring to Figure 6 FIG. 4 is a flowchart of a control method of a power system according to an embodiment of the present application.

[0099] The method is applied to an inverter, and the power system includes the inverter and at least one DC string; the DC string includes a plurality of power converters; each power converter includes a DC input end and a DC output end, the DC input end of each power converter is used to connect to a corresponding DC power supply, and the DC output ends of the power converters in the DC string are connected in series to the inverter.

[0100] As shown in Figure 6 The method includes:

[0101] S610: Obtain the output voltage of each power converter, and determine the type of each power converter according to the output voltage set value and the output voltage of the power converter.

[0102] The type of the power converter includes a first type of power converter and a second type of power converter. The first type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value; the second type of power converter includes a power converter whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value; and the second difference value is greater than the first difference value.

[0103] S620: For the same DC string, if there is at least one power converter whose output voltage is less than or equal to a preset threshold value, lower the output voltage set value of the second type of power converter in the DC string and raise the output voltage set value of the first type of power converter in the DC string; and the difference between the total amount of lowering of the output voltage set value of the second type of power converter and the total amount of raising of the output voltage set value of the first type of power converter is less than or equal to a third difference value.

[0104] Optionally, the inverter is specifically used to raise the output voltage set value of the first type of power converter after the output voltage set value of all the second type of power converter is lowered.

[0105] Optionally, the inverter is specifically used to raise the output voltage set value of the first type of power converter in the order from small to large of the difference between the output voltage set value and the output voltage of the first type of power converter.

[0106] Optionally, for the same DC string, the rated output power of at least two power converters is different.

[0107] Optionally, the inverter is further configured to obtain the output voltage setting value of each power converter according to the number of power converters and the maximum input voltage of the inverter.

[0108] Referring to Figure 7 FIG. 6 is a flowchart of another method for controlling a power system according to an embodiment of the present application.

[0109] As shown in Figure 7 the method comprises the following steps.

[0110] S710: determining the upper limit of the output voltage of the DC string according to the maximum input voltage of the inverter.

[0111] S720: determining the number of power converters in the DC string for the same DC string.

[0112] S730: obtaining the output voltage setting value of each power converter according to the upper limit of the output voltage of the DC string and the number of power converters.

[0113] In one possible implementation, the rated output power of each power converter is equal, and the output voltage setting value corresponding to each power converter is equal to the upper limit of the output voltage of the DC string divided by the number of power converters, and the output voltage setting value of each power converter is consistent.

[0114] In one possible implementation, the rated output power of each power converter is not equal, and the output voltage setting value corresponding to each power converter is obtained according to the upper limit of the output voltage of the DC string, the number of power converters and the rated output power of the power converter.

[0115] It should be understood that the output voltage setting value of the power converter is positively correlated with the rated output power of the power converter.

[0116] S740: obtaining the output voltage of each power converter.

[0117] S750: updating the output voltage setting value of each power converter.

[0118] It should be understood that the output voltage setting value of the power converter is determined according to the upper limit of the output voltage of the DC string and the number of power converters only when the first adjustment is made; and each subsequent adjustment is made on the basis of the output voltage setting value of the power converter of the previous adjustment.

[0119] As an example, the output voltage set value of the power converter P11 is y1 before adjustment, and the output voltage set value of the power converter P11 is y11 after adjustment. When the output voltage set value of the power converter P11 needs to be adjusted again, the adjustment is based on y11.

[0120] S760: Adjust the output voltage set value of each power converter according to the output voltage of each power converter.

[0121] In a possible implementation, the power converters are classified according to the relationship between the output voltage of the power converter and the output voltage set value. The types of the power converters include first-type power converters and second-type power converters. The first-type power converters include power converters whose difference between the output voltage set value and the output voltage is less than or equal to a first difference value. The second-type power converters include power converters whose difference between the output voltage set value and the output voltage is greater than or equal to a second difference value. The second difference value is greater than the first difference value.

[0122] As an example, the output voltage set value of the second-type power converter is first adjusted downward, and the output voltage set value of the first-type power converter is adjusted upward after the output voltage set value of all the second-type power converters is adjusted. The first-type power converters are adjusted in the order of the difference between the output voltage set value and the output voltage from small to large.

[0123] As an example, the output voltage set value of the second-type power converter and the output voltage set value of the first-type power converter are adjusted alternately.

[0124] S770: Confirm that the output voltage set value of the power converter is adjusted, and continue to issue the instruction.

[0125] It should be understood that the output voltage set value of the power converter is adjusted one by one. After the output voltage set value of a power converter is adjusted, the inverter returns an instruction indicating that the output voltage set value of the power converter is adjusted, and then issues an adjustment instruction to the next power converter.

[0126] S780: Determine whether the output voltage set value of all the power converters is adjusted. If yes, perform S750; if not, perform S760.

[0127] Referring to Figure 8 The figure is a flowchart of another control method of the power system provided by the embodiment of the application.

[0128] The method is applied to a power converter, and the power system comprises an inverter and at least one direct current group string; wherein the direct current group string comprises a plurality of power converters; the power converter comprises a direct current input end and a direct current output end, the direct current input end of the power converter is used for connecting a corresponding direct current power supply, and the direct current output ends of the power converters in the direct current group string are connected in series to the inverter.

[0129] As shown in Figure 8 , the method comprises:

[0130] S810: For the same direct current group string, the target power converter receives a first instruction issued by the inverter, and adjusts the output voltage set value of the target power converter according to the first instruction.

[0131] In a possible implementation, if there is at least one power converter with an output voltage less than or equal to a preset threshold value, and the target power converter is a first type of power converter, the first instruction indicates to increase the output voltage set value of the target power converter.

[0132] In another possible implementation, if there is at least one power converter with an output voltage less than or equal to a preset threshold value, and the target power converter is a second type of power converter, the first instruction indicates to decrease the output voltage set value of the target power converter.

[0133] It should be noted that the first type of power converter includes a power converter with a difference between the output voltage set value and the output voltage less than or equal to a first difference value; the second type of power converter includes a power converter with a difference between the output voltage set value and the output voltage greater than or equal to a second difference value; the second difference value is greater than the first difference value; and the sum of the output voltage set values of all the power converters in the same direct current group string is equal to the maximum input voltage of the inverter.

[0134] It should be understood that the first instruction comprises identification information of the target power converter, so that the inverter sends the first instruction to the target power converter.

[0135] S820: After the output voltage set value of the target power converter is adjusted, a second instruction is sent to the inverter, so that the inverter determines the next target power converter in the same direct current group string.

[0136] For example, the direct current group string 1 includes 15 group string connected power converters P11, P12, P13, P14, P15, P16, P17, P18, P19, P110, P111, P112, P113, P114 and P115. If P11 is the target power converter, P11 adjusts the output voltage set value according to the received first instruction; after the output voltage set value is adjusted, the second instruction is returned to the inverter to indicate that the output voltage set value of P11 is adjusted; the inverter determines the next target power converter, for example, P12, according to the received second instruction.

[0137] It should be understood that the foregoing describes the order of the power converter adjusting the output voltage set value, which will not be described again.

[0138] It should be understood that the foregoing describes the order of the power converter adjusting the output voltage set value, which will not be described again.

[0139] The above describes only one specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application without creative labor, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A power system, characterized in that, include: Inverter and at least one DC string; The DC string includes multiple power converters; each power converter includes a DC input terminal and a DC output terminal, the DC input terminal of the power converter is used to connect to a corresponding DC power supply, and the DC output terminal of each power converter in the DC string is connected in series to the inverter. For the same DC string, if there is at least one power converter with an output voltage less than or equal to a preset threshold, the inverter is used to lower the output voltage setting value of the second type of power converter in the DC string and raise the output voltage setting value of the first type of power converter in the DC string; wherein, the first type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is less than or equal to a first difference; the second type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; the sum of the output voltage setting values ​​of all the power converters in the DC string is equal to the maximum input voltage of the inverter; the difference between the total downward adjustment of the output voltage setting value of the second type of power converter and the total upward adjustment of the output voltage setting value of the first type of power converter is less than or equal to a third difference.

2. The power system according to claim 1, characterized in that, The inverter is specifically used to increase the output voltage setting value of the first type of power converter after all the output voltage setting values ​​of the second type of power converter have been lowered.

3. The power system according to claim 2, characterized in that, The inverter is specifically used to sequentially increase the output voltage setting value of the first type of power converter in order of increasing the difference between the output voltage setting value and the output voltage.

4. The power system according to any one of claims 1-3, characterized in that, For the same DC string, at least two of the power converters have different rated output powers.

5. The power system according to claim 4, characterized in that, The inverter is also used to obtain the output voltage setting value of each power converter based on the number of power converters and the maximum input voltage of the inverter.

6. An inverter, characterized in that, include: Inverter circuit and controller; The DC side of the inverter circuit is used to connect at least one DC string; wherein, the DC string includes multiple power converters; the power converter includes a DC input terminal and a DC output terminal, the DC input terminal of the power converter is used to connect to a corresponding DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the DC side of the inverter circuit. The controller is configured to, if at least one power converter has an output voltage less than or equal to a preset threshold, lower the output voltage setting value of the second type of power converter in the DC string and raise the output voltage setting value of the first type of power converter in the DC string; wherein, the first type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is less than or equal to a first difference; the second type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; the sum of the output voltage setting values ​​of all the power converters in the DC string is equal to the maximum input voltage of the inverter; the difference between the total amount of lowering the output voltage setting value of the second type of power converter and the total amount of raising the output voltage setting value of the first type of power converter is less than or equal to a third difference.

7. A power converter, characterized in that, include: First DC circuit and controller; The input terminal of the first DC-DC circuit is used to connect to a DC power supply, and the output terminal of the first DC-DC circuit is connected in series with the output terminal of at least one second DC-DC circuit to the inverter. The controller is configured to receive instructions from the inverter and, according to the instructions, increase or decrease the output voltage setting value of the first DC-DC circuit. Specifically, if there is at least one second DC-DC circuit with an output voltage less than or equal to a preset threshold, and the first DC-DC circuit is a first type of DC-DC circuit, the instruction indicates an increase in the output voltage setting value of the first DC-DC circuit; if there is at least one second DC-DC circuit with an output voltage less than or equal to the preset threshold, and the first DC-DC circuit is a second type of DC-DC circuit, the instruction indicates a decrease in the output voltage setting value of the first DC-DC circuit. The first type of DC-DC circuit includes DC-DC circuits where the difference between the output voltage setting value and the output voltage is less than or equal to a first difference; the second type of DC-DC circuit includes DC-DC circuits where the difference between the output voltage setting value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; and the sum of the output voltage setting values ​​of the first DC-DC circuit and the second DC-DC circuit is equal to the maximum input voltage of the inverter.

8. A control method for a power system, characterized in that, The invention is applied to an inverter, wherein the power system includes an inverter and at least one DC string; wherein the DC string includes multiple power converters; the power converter includes a DC input terminal and a DC output terminal, the DC input terminal of the power converter is used to connect to a corresponding DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the inverter; The method includes: For the same DC string, if at least one power converter has an output voltage less than or equal to a preset threshold, the output voltage setting value of the second type of power converter in the DC string is lowered and the output voltage setting value of the first type of power converter in the DC string is raised; wherein, the first type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is less than or equal to a first difference; the second type of power converter includes power converters whose difference between the output voltage setting value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; the sum of the output voltage setting values ​​of all the power converters in the DC string is equal to the maximum input voltage of the inverter; the difference between the total downward adjustment of the output voltage setting value of the second type of power converter and the total upward adjustment of the output voltage setting value of the first type of power converter is less than or equal to a third difference.

9. The method according to claim 8, characterized in that, The steps of lowering the output voltage setting value of the second type of power converter in the DC string and raising the output voltage setting value of the first type of power converter in the DC string specifically include: Lower the output voltage setting value of the second type of power converter in the DC string; After all the output voltage settings of the second type of power converters have been lowered, the output voltage settings of the first type of power converters are raised.

10. The method according to claim 9, characterized in that, The adjustment of the output voltage setting value of the first type of power converter specifically includes: The output voltage setting values ​​of the first type of power converter are sequentially increased according to the difference between the output voltage setting value and the output voltage, from smallest to largest.

11. The method according to any one of claims 8-10, characterized in that, For the same DC string, at least two of the power converters have different rated output powers.

12. The method according to claim 11, characterized in that, The method further includes: The output voltage setting value of each power converter is obtained based on the number of power converters and the maximum input voltage of the inverter.

13. A control method for a power system, characterized in that, The invention is applied to a power converter, wherein the power system includes an inverter and at least one DC string; wherein the DC string includes multiple power converters; the power converter includes a DC input terminal and a DC output terminal, the DC input terminal of the power converter is used to connect to a corresponding DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the inverter; The method includes: For the same DC string, the target power converter receives a first instruction from the inverter and adjusts its output voltage setting value upwards or downwards according to the first instruction. Specifically, if at least one power converter has an output voltage less than or equal to a preset threshold, and the target power converter is a first-type power converter, the first instruction instructs an upward adjustment of the target power converter's output voltage setting value; if at least one power converter has an output voltage less than or equal to the preset threshold, and the target power converter is a second-type power converter, the first instruction instructs a downward adjustment of the target power converter's output voltage setting value. The first-type power converter includes power converters whose difference between the output voltage setting value and the output voltage is less than or equal to a first difference; the second-type power converter includes power converters whose difference between the output voltage setting value and the output voltage is greater than or equal to a second difference; the second difference is greater than the first difference; and the sum of the output voltage settings of all power converters in the DC string is equal to the maximum input voltage of the inverter. Once the output voltage setting of the target power converter has been adjusted, a second command is sent to the inverter so that the inverter can determine the next target power converter in the same DC string.

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