Photovoltaic grid-connected inverter and control method thereof

Abstract

The embodiment of the present invention discloses a photovoltaic grid-connected inverter and a control method thereof, and the control method of the photovoltaic grid-connected inverter includes: obtaining the working parameters of the inverter; the working parameters include at least one of the bus sampling voltage, the output power of the inverter, and the input voltage; judging whether the inverter meets the preset conditions according to the relationship between the working parameters and the corresponding preset parameters; wherein the preset conditions are used to determine the preset working mode of the inverter; if the inverter meets the preset conditions, the current working mode of the inverter is switched to the preset working mode. The technical solution provided by the embodiment of the present invention can give full play to the performance advantages of the inverter by quickly switching the working mode to carry out targeted control, so that the inverter can balance the input and output power in time when power limitation or recovery is performed, and is conducive to improving work efficiency, reducing inverter stress, enhancing system stability and reliability, and reducing hardware costs.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of photovoltaic power generation, and in particular to a photovoltaic grid-connected inverter and a control method thereof. Background Art

[0002] With the development of photovoltaic power generation technology, photovoltaic grid-connected inverters, as an important component of photovoltaic power generation systems, play a vital role.

[0003] When the photovoltaic grid-connected inverter is performing power limitation and recovery, the system efficiency is low and the stress of the inverter is large, which is not conducive to the stable operation of the system. Summary of the invention

[0004] The embodiment of the present invention provides a photovoltaic grid-connected inverter and a control method thereof, so as to improve the working efficiency of the inverter and reduce the stress of the inverter.

[0005] According to one aspect of the present invention, a control method for a photovoltaic grid-connected inverter is provided, wherein the inverter is connected to at least one photovoltaic module, the photovoltaic module is used to provide input voltage for the inverter, the inverter comprises at least one voltage conversion circuit, a bus and an inverter circuit, the voltage conversion circuit, the bus and the inverter circuit are connected in sequence, and the photovoltaic module is connected to the voltage conversion circuit in a one-to-one correspondence; the control method for the photovoltaic grid-connected inverter comprises:

[0006] Acquiring operating parameters of the inverter; the operating parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage;

[0007] According to the relationship between the operating parameter and the corresponding preset parameter, judging whether the inverter meets the preset condition; wherein the preset condition is used to determine the preset operating mode of the inverter;

[0008] If the inverter meets the preset condition, the current working mode of the inverter is switched to the preset working mode.

[0009] Optionally, the relationship between the operating parameter and the corresponding preset parameter includes: the relationship between the bus sampling voltage and the bus reference voltage, the relationship between the maximum value of the input voltage and the minimum value of the input voltage, and the relationship between the limiting power of the inverter and the output power of the inverter;

[0010] The preset conditions include:

[0011] A first preset condition, wherein the first preset condition is used to determine that a preset working mode of the inverter is a constant voltage mode;

[0012] A second preset condition, wherein the second preset condition is used to determine that the preset working mode of the inverter is a maximum power tracking mode;

[0013] A third preset condition, wherein the third preset condition is used to determine that the preset working mode of the inverter is a voltage sharing mode.

[0014] Optionally, judging whether the inverter meets a preset condition according to a relationship between the operating parameter and a corresponding preset parameter includes:

[0015] Determine whether the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value;

[0016] If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the preset condition currently satisfied by the inverter is the first preset condition.

[0017] Optionally, if the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the preset condition currently satisfied by the inverter is the first preset condition, which includes:

[0018] If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the count value of the first counter is controlled to be incremented by 1;

[0019] When the count value of the first counter is greater than a first pre-designed value, it is determined that the preset condition currently satisfied by the inverter is the first preset condition, and the first counter is controlled to be reset.

[0020] Optionally, judging whether the inverter meets a preset condition according to a relationship between the operating parameter and a corresponding preset parameter includes:

[0021] When the difference between the bus sampling voltage and the bus reference voltage is less than or equal to a first preset voltage value, determine whether the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or whether the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, wherein the first preset voltage value is greater than the second preset voltage value;

[0022] If the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or the absolute value of the difference between the limiting power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition.

[0023] Optionally, if the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition, which includes:

[0024] If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared;

[0025] When the count value of the second counter is greater than a second preset value, it is determined that the preset condition currently satisfied by the inverter is the second preset condition, and the count values ​​of the first counter and the second counter are controlled to be cleared;

[0026] Alternatively, if the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition, including:

[0027] If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared;

[0028] Determine whether the difference between the bus reference voltage and the bus sampling voltage is greater than a third preset voltage;

[0029] If the difference between the bus reference voltage and the bus sampling voltage is greater than a third preset voltage, the count value of the third counter is controlled to be incremented by 1; if the difference between the bus reference voltage and the bus sampling voltage is less than or equal to the third preset voltage, the count value of the third counter is controlled to remain unchanged;

[0030] When the count value of the second counter is greater than the second pre-designed value, or the count value of the third counter is greater than the third pre-designed value, it is determined that the preset condition currently satisfied by the inverter is the second preset condition, and the count values ​​of the first counter, the second counter and the third counter are controlled to be cleared;

[0031] The third preset voltage value is greater than the second preset voltage value and less than the first preset voltage value.

[0032] Optionally, judging whether the inverter meets a preset condition according to a relationship between the operating parameter and a corresponding preset parameter includes:

[0033] When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than or equal to a fourth preset voltage value, determining whether the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than a fifth preset voltage value;

[0034] When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than the fifth preset voltage value, determining whether the absolute value of the difference between the limit power of the inverter and the output power of the inverter is less than a second preset power value;

[0035] If the absolute value of the difference between the limit power of the inverter and the output power of the inverter is less than the second preset power value, the preset condition currently satisfied by the inverter is the third preset condition;

[0036] The fifth preset voltage value is greater than the fourth preset voltage value, and the fourth preset voltage value is greater than zero; the fifth preset voltage value and the fourth preset voltage value are separated by at least one disturbance step of the maximum power tracking mode.

[0037] Optionally, switching the current working mode of the inverter to the preset working mode includes:

[0038] Based on the preset working mode, determining a loop control strategy corresponding to the preset working mode;

[0039] The voltage and current loops are controlled to generate drive signals according to the loop control strategy, so as to control the inverter to operate in the preset working mode.

[0040] Optionally, the determining, based on the preset working mode, a loop control strategy corresponding to the preset working mode includes:

[0041] When the preset working mode is the constant voltage mode, determining whether the inverter enters the constant voltage mode for the first time;

[0042] If yes, after saving the input voltage in the current working mode of the inverter, determining a loop control strategy corresponding to the constant voltage mode;

[0043] If not, directly determine the loop control strategy corresponding to the constant pressure mode;

[0044] When the preset working mode is the constant voltage mode, controlling the voltage and current loop to generate a drive signal according to the loop control strategy to control the inverter to operate in the preset working mode includes:

[0045] The bus reference voltage and the bus actual voltage are used as input parameters of the voltage loop, and are converted into a reference current through the voltage loop;

[0046] The reference current and the input current of the inverter are used as input parameters of a current loop, and a corresponding driving signal is generated through the current loop to control the inverter to operate in the constant voltage mode.

[0047] According to another aspect of the present invention, there is provided a photovoltaic grid-connected inverter, comprising:

[0048] At least one voltage conversion circuit, a busbar, and an inverter circuit, wherein the input end of the voltage conversion circuit is connected to the photovoltaic modules in a one-to-one correspondence, the output end of the voltage conversion circuit is connected to the input end of the inverter circuit via the busbar, and the output end of the inverter circuit is connected to the power grid; and

[0049] A control device, wherein the control device is used to execute the control method of the photovoltaic grid-connected inverter provided by any embodiment of the present invention.

[0050] The technical solution provided by the embodiment of the present invention determines whether the inverter meets the preset conditions according to the relationship between the obtained working parameters of the inverter and the corresponding preset parameters. The preset conditions are used to determine the preset working mode of the inverter. If the inverter meets the preset conditions, the current working mode of the inverter is switched to the preset working mode. Since the working parameters of the inverter are different in different working modes, the corresponding control strategies are also different. Therefore, by switching the working mode, the performance advantages of the inverter can be fully utilized for targeted control, so that the inverter can balance the input power and output power in time when power limitation or recovery is performed, and it is beneficial to improve work efficiency and reduce inverter stress. It is not necessary to use a controller with too high a main frequency to achieve rapid switching of the working mode, which is beneficial to enhancing the stability and reliability of the system and reducing hardware costs.

[0051] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0053] Figure 1 A schematic diagram of the structure of a photovoltaic system provided by an embodiment of the present invention;

[0054] Figure 2 A flow chart of a control method for a photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0055] Figure 3 A flow chart of another control method of a photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0056] Figure 4 A flowchart of inverter working mode switching provided by an embodiment of the present invention;

[0057] Figure 5 A flow chart of another control method of a photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0058] Figure 6 A flowchart of another inverter operating mode switching provided by an embodiment of the present invention;

[0059] Figure 7 A flow chart of another control method of a photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0060] Figure 8 A flowchart of another inverter operating mode switching provided by an embodiment of the present invention;

[0061] Fig. 9 A flow chart of another control method of a photovoltaic grid-connected inverter provided by an embodiment of the present invention;

[0062] Fig.10 A logic block diagram of a control strategy in a constant voltage mode provided by an embodiment of the present invention;

[0063] Fig.11 A schematic diagram of loop control in a constant voltage mode provided by an embodiment of the present invention;

[0064] Fig.12 A logic block diagram of a control strategy in a maximum power tracking mode provided by an embodiment of the present invention;

[0065] Fig.13 A schematic diagram of loop control in a maximum power tracking mode provided by an embodiment of the present invention;

[0066] Fig.14 A logic block diagram of a control strategy in a pressure equalization mode provided by an embodiment of the present invention;

[0067] Fig.15 A flowchart of another inverter operating mode switching provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0068] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0069] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0070] When the existing photovoltaic grid-connected inverter performs power limitation and recovery, it usually controls the photovoltaic output voltage to limit the inverter output power. By calculating the average power value of a certain period, the photovoltaic reference voltage is quickly adjusted to control the current photovoltaic output voltage to achieve the purpose of controlling the output power. Alternatively, the output power is directly limited, and the bus voltage is controlled in the front-stage DC-DC circuit to prevent the bus voltage from overshooting. In the first method, it is necessary to ensure that the power calculation and control logic operation cycle is fast enough, so a controller with a faster main frequency must be used, which increases the hardware cost. In the second method, it is easy to cause the bus voltage to be too high and the voltage difference between the bus voltage and the input voltage to be too large, resulting in reduced system efficiency, increased stress on the switching devices inside the inverter, severe heating, and other problems, and the good performance of the inverter cannot be guaranteed.

[0071] In view of the above problems, an embodiment of the present invention provides a control method for a photovoltaic grid-connected inverter to improve the performance of the inverter. Figure 1 A schematic diagram of a photovoltaic system according to an embodiment of the present invention is provided. Figure 1The photovoltaic system includes a photovoltaic module 10, an inverter and a power grid 40. The inverter is connected to at least one photovoltaic module 10. The inverter includes at least one voltage conversion circuit 102, a bus 20 and an inverter circuit 30. The voltage conversion circuit 102, the bus 20 and the inverter circuit 30 are connected in sequence. The photovoltaic module 10 is connected to the voltage conversion circuit 102 in a one-to-one correspondence. The photovoltaic module 10 is used to provide input voltage for the inverter. After the input voltage is converted by the voltage conversion circuit 102, it is transmitted to the bus 20. The bus 20 provides the bus voltage for the inverter circuit 30. The inverter circuit 30 converts the bus voltage into an AC voltage and then connects to the power grid 40.

[0072] Figure 2 A flow chart of a control method for a photovoltaic grid-connected inverter provided by an embodiment of the present invention, referring to Figure 1 The control method of the photovoltaic grid-connected inverter provided in this embodiment includes:

[0073] S110, obtaining working parameters of the inverter; the working parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage.

[0074] Among them, the bus sampling voltage refers to the voltage obtained after sampling the bus voltage. For example, the bus 20 can be sampled in real time by a voltage sensor to obtain the bus sampling voltage. The output power of the inverter directly determines the amount of power that the inverter can provide to the load. The output power can assist in judging whether the inverter is operating normally. The output power of the inverter can be obtained by a power sensor or a voltage and current in a calculation circuit. The input voltage refers to the input voltage of the inverter, that is, the output voltage of the photovoltaic module 10. The photovoltaic module 10 may include a photovoltaic cell, and the output voltage of the photovoltaic cell is the input voltage of the inverter. The input voltage can be provided to the bus 20 after being boosted by the voltage conversion circuit 102, and then input to the inverter circuit 30. The input voltage can also be obtained by a voltage sensor.

[0075] S120, judging whether the inverter meets the preset conditions according to the relationship between the working parameters and the corresponding preset parameters;

[0076] The preset condition is used to determine the preset working mode of the inverter.

[0077] Specifically, the working mode of the inverter may include Maximum Power Point Tracking (MPPT) mode, Constant Voltage (CV) mode and Balance Voltage (BV) mode. Based on the relationship between the working parameters obtained above and the corresponding preset parameters, it is determined whether the inverter meets the preset conditions. When the inverter meets the corresponding preset conditions, the preset working mode of the inverter is determined according to the preset conditions met by the inverter. Among them, the preset working mode is one of the MPPT mode, CV mode and BV mode.

[0078] S130: If the inverter meets the preset condition, switch the current working mode of the inverter to the preset working mode.

[0079] Specifically, the preset condition may be that the relationship between the above working parameter and the preset parameter satisfies a certain value greater than or less than a certain value. When the inverter satisfies the preset condition, the working mode that the inverter is about to enter can be determined, and the controller inside the inverter controls the inverter to switch its current working mode to the preset working mode.

[0080] The technical solution provided by the embodiment of the present invention determines whether the inverter meets the preset conditions according to the relationship between the obtained working parameters of the inverter and the corresponding preset parameters. The preset conditions are used to determine the preset working mode of the inverter. If the inverter meets the preset conditions, the current working mode of the inverter is switched to the preset working mode. Since the working parameters of the inverter are different in different working modes, the corresponding control strategies are also different. Therefore, by switching the working mode, the performance advantages of the inverter can be fully utilized for targeted control, so that the inverter can balance the input power and output power in time when power limitation or recovery is performed, and it is beneficial to improve work efficiency and reduce inverter stress. It is not necessary to use a controller with too high a main frequency to achieve rapid switching of the working mode, which is beneficial to enhancing the stability and reliability of the system and reducing hardware costs.

[0081] Optionally, in this embodiment, the relationship between the operating parameters and the corresponding preset parameters includes: the relationship between the bus sampling voltage and the bus reference voltage, the relationship between the maximum input voltage and the minimum input voltage, and the relationship between the inverter's limiting power and the inverter's output power.

[0082] In this embodiment, the bus sampling voltage can be a filtered voltage obtained by filtering the bus voltage to eliminate the interference of the bus ripple, thereby ensuring the accuracy of determining the preset working mode of the inverter. The bus reference voltage can be set according to actual needs. The limited power of the inverter refers to the maximum output power that the inverter can output under certain conditions is limited to a certain range of power, and the specific limit of the power can be set according to actual needs.

[0083] Figure 3 A flowchart of another photovoltaic grid-connected inverter control method provided by an embodiment of the present invention, referring to Figure 3 Based on the above embodiment, optionally, the control method of the photovoltaic grid-connected inverter provided in this embodiment includes:

[0084] S110, obtaining working parameters of the inverter; the working parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage.

[0085] S1201. Determine whether the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value.

[0086] S1202: If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the preset condition currently satisfied by the inverter is the first preset condition.

[0087] S1211. When the difference between the bus sampling voltage and the bus reference voltage is less than or equal to the first preset voltage value, determine whether the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or whether the absolute value of the difference between the inverter's limiting power and the inverter's output power is greater than the first preset power value, wherein the first preset voltage value is greater than the second preset voltage value.

[0088] S1212: If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the inverter limit power and the inverter output power is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition.

[0089] S1221. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than or equal to the fourth preset voltage value, determine whether the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than a fifth preset voltage value.

[0090] S1222. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than the fifth preset voltage value, determine whether the absolute value of the difference between the inverter limit power and the inverter output power is less than the second preset power value.

[0091] S1223: If the absolute value of the difference between the limiting power of the inverter and the output power of the inverter is less than the second preset power value, the preset condition currently satisfied by the inverter is the third preset condition.

[0092] S130: If the inverter meets the preset condition, switch the current working mode of the inverter to the preset working mode.

[0093] In this embodiment, the preset conditions include: a first preset condition, a second preset condition and a third preset condition. The first preset condition is used to determine that the preset working mode of the inverter is a constant voltage mode, the second preset condition is used to determine that the preset working mode of the inverter is an MPPT mode, and the third preset condition is used to determine that the preset working mode of the inverter is a voltage-balanced mode.

[0094] Figure 4 A flowchart of an inverter operation mode switching provided by an embodiment of the present invention, referring to Figure 4 Based on the above embodiment, optionally, after the inverter is initialized, the process of determining the working mode is performed. Compare the bus sampling voltage V bus-filter With bus reference voltage V bus-ref If the bus sampling voltage V bus-filter With bus reference voltage V bus-ref If the difference is greater than the first preset voltage value A1, the preset condition currently satisfied by the inverter is the first preset condition, and the current working mode of the inverter is switched to the constant voltage mode.

[0095] When the bus sampling voltage V bus-filter With bus reference voltage V bus-ref When the difference between the bus sampling voltage V bus-filter With bus reference voltage V bus-ref Is the difference less than the second preset voltage value A2, or the inverter's limit power P limit The output power P of the inverter fact Is the absolute value of the difference greater than the first preset power value B1? If the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference is less than the second preset voltage value A2, or the inverter's limit power P limit The output power P of the inverter fact If the absolute value of the difference between the first and second preset power values ​​is greater than the first preset power value B1, the preset condition currently satisfied by the inverter is the second preset condition, and the current working mode of the inverter is switched to the maximum power tracking mode.

[0096] If the above conditions are not met, the current judgment logic is exited and whether to enter the constant voltage mode or the maximum power tracking mode is re-judged.

[0097] Finally, determine the maximum value of the input voltage V pv_max With minimum value V pv_min Determine the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min Is the difference less than the fourth preset voltage value E1? If so, then exit the judgment logic of the voltage equalization mode and re-judge whether to enter the constant voltage mode or the maximum power tracking mode; if not, continue to judge the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min Is the difference greater than the fifth preset voltage value E2? pv_max With the minimum input voltage V pv_min The difference between the voltage and the limit power P of the inverter is greater than the fifth preset voltage value E2. limit The output power P of the inverter fact The absolute value of the difference is less than the second preset power value B2. If the inverter's limit power P limit The output power P of the inverter fact If the absolute value of the difference between the power consumption and the power consumption is less than the second preset power value B2, it is determined that the preset condition currently satisfied by the inverter is the third preset condition, and the current working mode of the inverter is switched to the voltage balancing mode; if the limit power P of the inverter is limit The output power P of the inverter fact If the absolute value of the difference is greater than or equal to the second preset power value B2, the judgment logic of the voltage equalization mode is exited, and it is re-judged whether to enter the constant voltage mode or the maximum power tracking mode.

[0098] The first preset voltage value A1 and the bus sampling voltage V bus-filter The sampling cut-off frequency is positively correlated. The smaller the sampling cut-off frequency, the smaller the first preset voltage value A1. The second preset voltage value A2 is equal to the input voltage V pv The maximum value V pv_max and bus sampling voltage V bus-filter The first preset voltage value A1 is greater than the second preset voltage value A2.

[0099] The fifth preset voltage value E2 is greater than the fourth preset voltage value E1, and the fourth preset voltage value E1 is greater than zero; the fifth preset voltage value E2 is associated with at least one of the stress and temperature rise of the transistor in the inverter, and the working efficiency of the inverter.

[0100] The fifth preset voltage value E2 is at least separated from the fourth preset voltage value E1 by a disturbance step of the maximum power tracking mode to prevent logic errors caused by a short interval between the fifth preset voltage value E2 and the fourth preset voltage value E1, thereby ensuring the normal operation of the judgment logic.

[0101] Optionally, the first preset power value B1 and the second preset power value B2 satisfy: , the first preset power value B1 is equal to the output power P of the inverter fact One percent of the maximum value to meet the grid 40 grid connection standard requirements. W is the output power P of the inverter fact The sampling accuracy error.

[0102] Optionally, Figure 5 A flowchart of another control method for a photovoltaic grid-connected inverter provided by an embodiment of the present invention, and specifically shows the specific methods of steps S1202 and S1212, refer to Figure 5 Based on the above embodiments, the control method of the photovoltaic grid-connected inverter provided in this embodiment includes:

[0103] S110, obtaining working parameters of the inverter; the working parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage.

[0104] S1201. Determine whether the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value.

[0105] S12021. If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, control the count value of the first counter to increase by 1.

[0106] S12022. When the count value of the first counter is greater than the first pre-designed value, determine that the preset condition currently satisfied by the inverter is the first preset condition, and control the first counter to be reset.

[0107] Specifically, Figure 6 Another flow chart of switching the inverter working mode provided by the embodiment of the present invention, combined with Figure 5 and Figure 6 , when the bus sampling voltage V bus-filter With bus reference voltage V bus-ref When the absolute value of the difference is greater than the first preset voltage value A1, the count value C1 of the first counter is controlled to be incremented by 1, and the count value C2 of the second counter can also be controlled to be cleared (to ensure the accuracy of the next program judgment), that is, C1+=1, C2=0, until the count value C1 of the first counter is greater than the first preset value D1, that is, C1>D1, the inverter is controlled to switch the current working mode to the constant voltage mode.

[0108] S1211. When the difference between the bus sampling voltage and the bus reference voltage is less than or equal to the first preset voltage value, determine whether the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or whether the absolute value of the difference between the inverter's limiting power and the inverter's output power is greater than the first preset power value, wherein the first preset voltage value is greater than the second preset voltage value.

[0109] S12121. If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the inverter's limiting power and the inverter's output power is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared.

[0110] S12122. When the count value of the second counter is greater than the second pre-designed value, determine that the preset condition currently satisfied by the inverter is the second preset condition, and control the count values ​​of the first counter and the second counter to be cleared.

[0111] Specifically, continue to refer to Figure 6 , when the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference is less than the second preset voltage value A2, or the inverter's limit power P limit The output power P of the inverter fact When the absolute value of the difference is greater than the first preset power value B1, the count value C1 of the first counter is controlled to be cleared, and the count value C2 of the second counter is self-added by 1, that is, C2+=1, C1=0. When the count value C2 of the second counter is greater than the second pre-designed value D2 (C2>D2), the inverter is controlled to switch the current working mode to the maximum power tracking mode. After that, the count value C1 of the first counter and the count value C2 of the second counter are controlled to be cleared to ensure the accuracy of the next program judgment.

[0112] S1221. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than or equal to the fourth preset voltage value, determine whether the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than a fifth preset voltage value.

[0113] S1222. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than the fifth preset voltage value, determine whether the absolute value of the difference between the inverter limit power and the inverter output power is less than the second preset power value.

[0114] S1223: If the absolute value of the difference between the limiting power of the inverter and the output power of the inverter is less than the second preset power value, the preset condition currently satisfied by the inverter is the third preset condition.

[0115] S130: If the inverter meets the preset condition, switch the current working mode of the inverter to the preset working mode.

[0116] The technical solution provided in this embodiment can also use a counter to count the number of times the relationship between the working parameters and the preset parameters meets the preset conditions during the process of determining the preset working mode of the inverter. When the preset number of times is met, it is determined to switch to the corresponding working mode to avoid errors caused by voltage or power instability and ensure the accuracy of determining the working mode.

[0117] Optionally, Figure 7 A flowchart of another control method for a photovoltaic grid-connected inverter provided by an embodiment of the present invention, and specifically shows the specific methods of steps S1202 and S1212, refer to Figure 7 Based on the above embodiments, the control method of the photovoltaic grid-connected inverter provided in this embodiment includes:

[0118] S110, obtaining working parameters of the inverter; the working parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage.

[0119] S1201. Determine whether the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value.

[0120] S12021. If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, control the count value of the first counter to increase by 1.

[0121] S12022. When the count value of the first counter is greater than the first pre-designed value, determine that the preset condition currently satisfied by the inverter is the first preset condition, and control the first counter to be reset.

[0122] S1211. When the difference between the bus sampling voltage and the bus reference voltage is less than or equal to the first preset voltage value, determine whether the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or whether the absolute value of the difference between the inverter's limiting power and the inverter's output power is greater than the first preset power value, wherein the first preset voltage value is greater than the second preset voltage value.

[0123] S12121. If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the inverter's limiting power and the inverter's output power is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared.

[0124] S12123. Determine whether the difference between the bus reference voltage and the bus sampling voltage is greater than a third preset voltage.

[0125] S12124. If the difference between the bus reference voltage and the bus sampling voltage is greater than the third preset voltage, the count value of the third counter is controlled to increase by 1; if the difference between the bus reference voltage and the bus sampling voltage is less than or equal to the third preset voltage, the count value of the third counter is controlled to remain unchanged.

[0126] S12125. When the count value of the second counter is greater than the second pre-designed value, or the count value of the third counter is greater than the third pre-designed value, it is determined that the preset condition currently satisfied by the inverter is the second preset condition, and the count values ​​of the first counter, the second counter and the third counter are controlled to be cleared.

[0127] S1221. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than or equal to the fourth preset voltage value, determine whether the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than a fifth preset voltage value.

[0128] S1222. When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than the fifth preset voltage value, determine whether the absolute value of the difference between the inverter limit power and the inverter output power is less than the second preset power value.

[0129] S1223: If the absolute value of the difference between the limiting power of the inverter and the output power of the inverter is less than the second preset power value, the preset condition currently satisfied by the inverter is the third preset condition.

[0130] S130: If the inverter meets the preset condition, switch the current working mode of the inverter to the preset working mode.

[0131] Specifically, Figure 7 The control method of the photovoltaic grid-connected inverter shown in FIG. Figure 5 The control method of the photovoltaic grid-connected inverter shown is different in that Figure 7 In the control method shown, when judging the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference is less than the second preset voltage value A2, or the inverter's limit power P limit The output power P of the inverter fact After the absolute value of the difference between the power and the power is greater than the first preset power value B1, the bus reference voltage V bus-ref and bus sampling voltage V bus-filter to improve the flexibility of the judgment conditions.

[0132] Figure 8 Another flow chart of switching the inverter working mode provided by the embodiment of the present invention, combined with Figure 7 and Figure 8 , when the bus sampling voltage V bus-filterWith bus reference voltage V bus-ref When the difference is greater than the first preset voltage value A1, the count value C1 of the first counter is controlled to be incremented by 1, and the count value C2 of the second counter and the count value C3 of the third counter can also be controlled to be cleared (to ensure the accuracy of the next program judgment), that is, C1+=1, C2=0, C3=0, until the count value C1 of the first counter is greater than the first preset value D1, that is, C1>D1, the inverter is controlled to switch the current working mode to the constant voltage mode.

[0133] When the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference is less than the second preset voltage value A2, or the inverter's limit power P limit The output power P of the inverter fact When the absolute value of the difference is greater than the first preset power value B1, the count value C1 of the first counter is controlled to be cleared, and the count value C2 of the second counter is incremented by 1, that is, C1=0, C2+=1. After that, the bus reference voltage V bus-ref and bus sampling voltage V bus-filter Is the difference greater than the third preset voltage value A3? bus-ref and bus sampling voltage V bus-filter When the difference between φ and φ is greater than the third preset voltage value A3, the count value C3 of the third counter is controlled to be incremented by 1, that is, C3+=1.

[0134] When the count value C2 of the second counter is greater than the second pre-designed value D2 (C2>D2), or when the count value C2 of the second counter is less than or equal to the second pre-designed value D2 (C2≤D2), and the count value C3 of the third counter is greater than the third pre-designed value D3 (C3>D3), the working mode of the inverter is controlled to switch to the maximum power tracking mode.

[0135] The technical solution provided by this embodiment also has the beneficial effects described in the above embodiments. Among them, the first preset voltage value A1 is greater than the second preset voltage value A2, and greater than the third preset voltage value A3, and the third preset voltage value A3 is greater than the second preset voltage value A2, that is, A1>A3>A2.

[0136] The second pre-designed value D2 is greater than the third pre-designed value D3, and the third pre-designed value D3 is greater than the first pre-designed value D1. In this embodiment, the values ​​of the first pre-designed value D1, the second pre-designed value D2, and the third pre-designed value D3 depend on the capacitance of the busbar. The larger the capacitance, the smaller the values ​​of the three.

[0137] Optionally, if the bus sampling voltage V bus-filter With bus reference voltage V bus-refThe difference between the voltage and the inverter is greater than or equal to the second preset voltage value A2 or the inverter limit power P limit The output power P of the inverter fact If the absolute value of the difference is less than or equal to the first preset power value B1, the count value C1 of the first counter, the count value C2 of the second counter and the count value C3 of the third counter are all cleared, that is, C1=0, C2=0, C3=0, and the preset conditions satisfied by the inverter are re-determined.

[0138] Fig. 9 A flowchart of another photovoltaic grid-connected inverter control method provided by an embodiment of the present invention, referring to Fig. 9 Based on the above embodiments, optionally, the control method of the photovoltaic grid-connected inverter provided in this embodiment includes:

[0139] S110, obtaining working parameters of the inverter; the working parameters include at least one of a bus sampling voltage, an output power of the inverter, and an input voltage.

[0140] S120. Determine whether the inverter meets preset conditions according to the relationship between the operating parameters and the corresponding preset parameters.

[0141] S1301: If the inverter meets the preset conditions, determine a loop control strategy corresponding to the preset working mode based on the preset working mode.

[0142] S1302: Control the voltage and current loops to generate drive signals according to the loop control strategy to control the inverter to operate in a preset working mode.

[0143] Specifically, after determining the preset working mode of the inverter according to the preset conditions satisfied by the inverter, determine the loop control strategy corresponding to the preset working mode, and control the inverter to operate in the preset working mode based on the determined loop control strategy. In the preset working mode, the control parameters of the inverter (including the working parameters of the inverter) can be dynamically adjusted through the corresponding loop control strategy to give full play to the performance advantages of the inverter and perform targeted control, which is conducive to improving work efficiency and improving the stability and reliability of the inverter operation.

[0144] In an optional implementation provided in this embodiment, step S1301 includes: when the preset operating mode is the constant voltage mode, determining whether the inverter enters the constant voltage mode for the first time, and if so, determining the loop control strategy corresponding to the constant voltage mode after saving the input voltage under the current operating mode of the inverter; if not, directly determining the loop control strategy corresponding to the constant voltage mode.

[0145] Step S1302 includes: using the bus reference voltage and the bus actual voltage as input parameters of the voltage loop, and converting them into a reference current through the voltage loop; using the reference current and the input current of the inverter as input parameters of the current loop, and generating a corresponding drive signal through the current loop to control the inverter to operate in constant voltage mode.

[0146] Specifically, Fig.10 A logic block diagram of a control strategy in a constant voltage mode provided by an embodiment of the present invention, refer to Fig.10 When it is determined that the current working mode of the inverter is the constant voltage mode, determine whether it is the first time to enter the constant voltage mode. If so, it is necessary to save the input voltage V in the previous working mode. pv , then determine the loop control strategy corresponding to the constant voltage mode and enter the loop control, such as entering the first loop control; if not, directly determine the loop control strategy corresponding to the constant voltage mode and enter the first loop control. Here, save the input voltage V pv The purpose is to save the input voltage V pv As a reference value, when entering the constant voltage mode again, you can compare the current input voltage V pv Compared with the input voltage V in the previous working mode pv , better adjust the loop control strategy. Under the first loop control, by limiting the input power of the inverter, the input power and output power P fact Achieve balance, thereby achieving the effect of quickly limiting power and preventing bus voltage overshoot.

[0147] Fig.11 A loop control schematic diagram in a constant voltage mode provided by an embodiment of the present invention is based on the above embodiment and combined with Fig.11 In the loop control strategy corresponding to the constant voltage mode, the outer loop is the voltage control loop, with the bus voltage V bus and bus reference voltage V bus-ref As input, it is controlled by the first PI controller, and then limited to the first maximum input current Imax1 and enters the inner loop control. The inner loop control is a current control loop, which uses the first maximum input current Imax1 output by the voltage loop and the input current I pv As input, it is PI controlled by the second PI controller and the amplitude is limited to N times the maximum PWM1 signal output, N Here, the N-fold maximum PWM1 signal is the first type driving signal, under the control of the first type driving signal, the inverter operates in a constant voltage mode.

[0148] Optionally, when the current operating mode of the inverter is the maximum power tracking mode, a loop control strategy corresponding to the maximum power tracking mode is determined, and loop control is entered, such as entering the second loop control, and a second type of drive signal is generated under the control strategy of the second loop control to control the inverter to perform power limitation and recovery.

[0149] Specifically, Fig.12 A logic block diagram of a control strategy in a maximum power tracking mode provided by an embodiment of the present invention, referring to Fig.12 When it is determined that the current working mode of the inverter is the maximum power tracking mode, the second loop control is directly entered. Through the maximum power tracking algorithm, the input power is increased, the bus 20 is charged, and more active power is output, so that the inverter reaches the maximum output power more quickly.

[0150] Fig.13 A schematic diagram of loop control in a maximum power tracking mode provided by an embodiment of the present invention, combined with Fig.13 In the second loop control strategy, the outer loop is a voltage control loop, with the input voltage V pv and input reference voltage V pv_ref As input, it is PI controlled by the third PI controller, and then limited to the second maximum input current Imax2 before entering the inner loop control. The inner loop control is a current control loop, which takes the second maximum input current Imax2 output by the voltage loop and the input current Ipv of the inverter as input, and is PI controlled by the fourth PI controller, and limited to N times the maximum PWM2 signal output, N Here, the N-fold maximum PWM2 signal is the second type driving signal, under the control of the second type driving signal, the inverter operates in the maximum power tracking mode.

[0151] Optionally, when the current operating mode of the inverter is the voltage equalizing mode, a loop control strategy corresponding to the voltage equalizing mode is determined, and loop control is entered, such as entering the third loop control, and a third type of drive signal is generated under the control strategy of the third loop control to control the inverter to operate in the voltage equalizing mode.

[0152] Specifically, Fig.14 A logic block diagram of a control strategy in a pressure equalization mode provided by an embodiment of the present invention, refer to Fig.14 When it is determined that the current working mode of the inverter is the voltage-sharing mode, the third loop control is directly entered. By adjusting the input voltage V pv , the maximum input voltage V pv_max With the minimum input voltage V pv_min The difference is reduced while ensuring the output power P fact stability, so that the inverter has the best working efficiency.

[0153] The third loop control strategy is the same as the second loop control strategy. For details, please refer to Fig.13 The relevant description in will not be repeated here.

[0154] Fig.15 Another flowchart of inverter operation mode switching provided by an embodiment of the present invention is shown in FIG. Fig.15 Based on the above embodiments, optionally, the specific working process of switching the working mode of the inverter provided in this embodiment is as follows:

[0155] After the inverter is initialized, it first enters the maximum power tracking mode, and then determines whether the working mode needs to be switched to determine the preset working mode of the inverter.

[0156] When the inverter is in the maximum power tracking mode, if the bus sampling voltage V bus-filter With bus reference voltage V bus-ref If the difference between the input power and the output power P is greater than the first preset voltage value A1, the inverter is controlled to switch its working mode from the maximum power tracking mode to the constant voltage mode. After entering the constant voltage mode, the input power of the inverter is limited so that the input power of the inverter is equal to the output power P fact Balance, thereby achieving the effect of quickly limiting power and preventing bus voltage from rising.

[0157] When the inverter is currently operating in constant voltage mode, if the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference between the voltage and the voltage is less than or equal to the first preset voltage value A1, and the bus sampling voltage V bus-filter With bus reference voltage V bus-ref If the difference between the voltages A and B is less than the second preset voltage value A2, the working mode of the inverter is controlled to switch from the constant voltage mode to the maximum power tracking mode.

[0158] Or, if the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference between is less than or equal to the first preset voltage value A1, and the bus reference voltage V bus-ref and bus sampling voltage V bus-filter If the difference between the voltages A and B is greater than the third preset voltage value A3, the working mode of the inverter is controlled to switch from the constant voltage mode to the maximum power tracking mode.

[0159] Or, if the bus sampling voltage V bus-filter With bus reference voltage V bus-ref The difference between the second preset voltage value A2 and the first preset voltage value A1 is greater than or equal to the second preset voltage value A2 and less than or equal to the first preset voltage value A1, and the inverter's limit power P limit The output power P of the inverter factIf the difference between the power supply voltage and the power supply voltage is greater than the first preset power value B1, the working mode of the inverter is controlled to switch from the constant voltage mode to the maximum power tracking mode.

[0160] In the maximum power tracking mode, the maximum power tracking algorithm is used to increase the input power, charge the bus 20, and output more active power, so that the output power of the inverter reaches the maximum.

[0161] When the inverter is currently operating in constant voltage mode, if the maximum input voltage V pv_max With the minimum input voltage V pv_min The difference between the voltage and the power consumption of the inverter is greater than or equal to the fifth preset voltage value E2, and the limit power P of the inverter is limit The output power P of the inverter fact If the absolute value of the difference between the input voltage V and the input voltage V is less than the second preset power value B2, the inverter is controlled to switch its working mode from the constant voltage mode to the voltage balancing mode. pv , the maximum input voltage V pv_max With the minimum input voltage V pv_min The difference is reduced while ensuring the output power P fact stability, so that the inverter has the best working efficiency.

[0162] When the inverter is in the voltage-sharing mode, the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min The difference between the fifth preset voltage value E2 and the fourth preset voltage value E1 is less than or equal to the fifth preset voltage value E2 or the fourth preset voltage value E1, or the inverter's limit power P limit The output power P of the inverter fact When the absolute value of the difference between the two is greater than or equal to the second preset power value B2, if the bus sampling voltage V bus-filter With bus reference voltage V bus-ref If the difference between the input power and the output power P is greater than the first preset voltage value A1, the working mode of the inverter is controlled to switch from the voltage-equalizing mode to the constant voltage mode. In the constant voltage mode, the input power of the inverter is limited so that the input power and the output power P fact Achieve balance, thereby achieving the effect of quickly limiting power and preventing bus voltage overshoot.

[0163] When the inverter is in the voltage-sharing mode, the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min The difference between the fifth preset voltage value E2 and the fourth preset voltage value E1 is less than or equal to the fifth preset voltage value E2 or the fourth preset voltage value E1, or the inverter's limit power P limit The output power P of the inverter fact When the absolute value of the difference is greater than or equal to the second preset power value B2, if the inverter power limit P is satisfiedlimit The output power P of the inverter fact The absolute value of the difference is greater than the first preset power value B1, the bus sampling voltage V bus-filter With bus reference voltage V pv_ref The difference is less than the second preset voltage value A2, the bus reference voltage V pv_ref and bus sampling voltage V bus-filter If the difference between the voltage and the voltage is greater than at least one of the third preset voltage value A3, the working mode of the inverter is controlled to switch from the voltage balancing mode to the maximum power tracking mode. In the maximum power tracking mode, the input power is increased through the maximum power tracking algorithm to charge the bus 20, thereby outputting more active power, so that the output power of the inverter reaches the maximum.

[0164] When the inverter is in the maximum power tracking mode, if the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min The difference between the voltage and the inverter is greater than the fifth preset voltage value E2, and the inverter limit power P limit The output power P of the inverter fact If the absolute value of the difference between the input voltage V and the output voltage V is less than the second preset power value B2, the inverter is controlled to switch its working mode from the maximum power tracking mode to the voltage balancing mode. pv , the maximum input voltage V pv_max With the minimum input voltage V pv_min The difference is reduced while ensuring the output power P fact stability, so that the inverter has maximum working efficiency.

[0165] The technical solution provided by the embodiment of the present invention can achieve rapid power limitation while taking into account the working efficiency of the inverter, and the maximum value of the input voltage V pv_max With the minimum input voltage V pv_min The difference between the switching voltages of the inverter and the switching voltages of the inverter can be reduced, thereby improving the performance of the inverter.

[0166] Optionally, the embodiment of the present invention further provides a photovoltaic grid-connected inverter, Figure 1The inverter includes at least one voltage conversion circuit 102, a bus 20 and an inverter circuit 30. The voltage conversion circuit 102, the bus 20 and the inverter circuit 30 are connected in sequence. The photovoltaic module 10 is connected to the input end of the voltage conversion circuit 102 in a one-to-one correspondence (e.g., the first photovoltaic module PV_1 is connected to the first voltage conversion circuit Boost_1, the second photovoltaic module PV_2 is connected to the second voltage conversion circuit Boost_2... the nth photovoltaic module PV_n is connected to the nth voltage conversion circuit Boost_n), the output end of the voltage conversion circuit 102 is connected to the input end of the inverter circuit 30 via the bus 20, and the output end of the inverter circuit 30 is connected to the power grid 40; and also includes a control device, which can be used to execute the control method of the photovoltaic grid-connected inverter provided in any embodiment of the present invention to meet the grid connection requirements. The photovoltaic grid-connected inverter provided in this embodiment also has the beneficial effects described in any of the above embodiments, which will not be repeated.

[0167] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0168] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for a photovoltaic grid-connected inverter, characterized in that: The inverter is connected to at least one photovoltaic module, and the photovoltaic module is used to provide input voltage for the inverter. The inverter includes at least one voltage conversion circuit, a bus and an inverter circuit. The voltage conversion circuit, the bus and the inverter circuit are connected in sequence, and the photovoltaic modules are connected to the voltage conversion circuit in a one-to-one correspondence; The control method of the photovoltaic grid-connected inverter includes: Acquire the operating parameters of the inverter; the operating parameters include at least one of a bus sampling voltage, an output power of the inverter, and the input voltage; According to the relationship between the operating parameter and the corresponding preset parameter, judging whether the inverter meets the preset condition; wherein the preset condition is used to determine the preset operating mode of the inverter; If the inverter meets the preset condition, switching the current working mode of the inverter to the preset working mode; The relationship between the working parameter and the corresponding preset parameter includes: the relationship between the bus sampling voltage and the bus reference voltage, the relationship between the maximum value of the input voltage and the minimum value of the input voltage, and the relationship between the limiting power of the inverter and the output power of the inverter; The preset conditions include: A first preset condition, wherein the first preset condition is used to determine that a preset working mode of the inverter is a constant voltage mode; A second preset condition, wherein the second preset condition is used to determine that the preset working mode of the inverter is a maximum power tracking mode; A third preset condition, wherein the third preset condition is used to determine that the preset working mode of the inverter is a voltage balancing mode; The determining, based on the relationship between the operating parameter and the corresponding preset parameter, whether the inverter meets the preset condition comprises: When the difference between the bus sampling voltage and the bus reference voltage is less than or equal to the first preset voltage value, determine whether the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or whether the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, wherein the first preset voltage value is greater than the second preset voltage value; If the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or the absolute value of the difference between the limiting power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition.

2. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The determining, based on the relationship between the operating parameter and the corresponding preset parameter, whether the inverter meets the preset condition comprises: Determine whether the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value; If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the preset condition currently satisfied by the inverter is the first preset condition.

3. The control method of the photovoltaic grid-connected inverter according to claim 2, characterized in that: If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the preset condition currently satisfied by the inverter is the first preset condition, which includes: If the difference between the bus sampling voltage and the bus reference voltage is greater than a first preset voltage value, the count value of the first counter is controlled to be incremented by 1; When the count value of the first counter is greater than a first pre-designed value, it is determined that the preset condition currently satisfied by the inverter is the first preset condition, and the first counter is controlled to be reset.

4. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition, which includes: If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared; When the count value of the second counter is greater than a second preset value, it is determined that the preset condition currently satisfied by the inverter is the second preset condition, and the count values ​​of the first counter and the second counter are controlled to be cleared; Alternatively, if the difference between the bus sampling voltage and the bus reference voltage is less than a second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the preset condition currently satisfied by the inverter is the second preset condition, including: If the difference between the bus sampling voltage and the bus reference voltage is less than the second preset voltage value or the absolute value of the difference between the limit power of the inverter and the output power of the inverter is greater than the first preset power value, the count value of the second counter is controlled to be incremented by 1, and the count value of the first counter is controlled to be cleared; Determine whether the difference between the bus reference voltage and the bus sampling voltage is greater than a third preset voltage; If the difference between the bus reference voltage and the bus sampling voltage is greater than a third preset voltage, the count value of the third counter is controlled to be incremented by 1; if the difference between the bus reference voltage and the bus sampling voltage is less than or equal to the third preset voltage, the count value of the third counter is controlled to remain unchanged; When the count value of the second counter is greater than the second pre-designed value, or the count value of the third counter is greater than the third pre-designed value, it is determined that the preset condition currently satisfied by the inverter is the second preset condition, and the count values ​​of the first counter, the second counter and the third counter are controlled to be cleared; The third preset voltage value is greater than the second preset voltage value and less than the first preset voltage value.

5. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The determining, based on the relationship between the operating parameter and the corresponding preset parameter, whether the inverter meets the preset condition comprises: When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than or equal to a fourth preset voltage value, determining whether the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than a fifth preset voltage value; When the absolute value of the difference between the maximum value of the input voltage and the minimum value of the input voltage is greater than the fifth preset voltage value, determining whether the absolute value of the difference between the limit power of the inverter and the output power of the inverter is less than a second preset power value; If the absolute value of the difference between the limit power of the inverter and the output power of the inverter is less than the second preset power value, the preset condition currently satisfied by the inverter is the third preset condition; The fifth preset voltage value is greater than the fourth preset voltage value, and the fourth preset voltage value is greater than zero; the fifth preset voltage value and the fourth preset voltage value are separated by at least one disturbance step of the maximum power tracking mode.

6. The control method of the photovoltaic grid-connected inverter according to claim 1, characterized in that: The switching of the current working mode of the inverter to the preset working mode comprises: Based on the preset working mode, determining a loop control strategy corresponding to the preset working mode; The voltage and current loops are controlled to generate drive signals according to the loop control strategy, so as to control the inverter to operate in the preset working mode.

7. The control method of the photovoltaic grid-connected inverter according to claim 6, characterized in that: The determining, based on the preset working mode, a loop control strategy corresponding to the preset working mode comprises: When the preset working mode is the constant voltage mode, determining whether the inverter enters the constant voltage mode for the first time; If yes, after saving the input voltage in the current working mode of the inverter, determining a loop control strategy corresponding to the constant voltage mode; If not, directly determine the loop control strategy corresponding to the constant pressure mode; When the preset working mode is the constant voltage mode, controlling the voltage and current loop to generate a drive signal according to the loop control strategy to control the inverter to operate in the preset working mode includes: The bus reference voltage and the bus actual voltage are used as input parameters of the voltage loop, and are converted into a reference current through the voltage loop; The reference current and the input current of the inverter are used as input parameters of a current loop, and a corresponding driving signal is generated through the current loop to control the inverter to operate in the constant voltage mode.

8. A photovoltaic grid-connected inverter, characterized in that: include: At least one voltage conversion circuit, a busbar and an inverter circuit, wherein the input end of the voltage conversion circuit is connected to the photovoltaic modules in a one-to-one correspondence, the output end of the voltage conversion circuit is connected to the input end of the inverter circuit via the busbar, and the output end of the inverter circuit is connected to the power grid; and A control device, wherein the control device is used to execute the control method of the photovoltaic grid-connected inverter according to any one of claims 1 to 7.

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