Control method of power converter, power converter and photovoltaic system

Abstract

The invention relates to the technical field of photovoltaic power generation, in particular to a control method of a power converter, the power converter and a photovoltaic system. The method comprises the following steps: sampling output parameters of the power converter, wherein the output parameters comprise a first parameter and a second parameter; when the sampling value of the first parameter is larger than or equal to the upper limit value of the first parameter, the upper limit value is controlled to be increased along with decreasing of the second parameter, the first parameter is one of the output voltage and the output current, and the second parameter is the other one of the output voltage and the output current. The output parameters of the power converter are sampled, and when the sampling value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to be increased along with the decrease of the second parameter, so that the problem of power fluctuation caused by the fact that the output voltage or the output current of the power converter is reduced to be too low when the output of the power converter is limited is avoided; and the stability of the system is improved.

Description

Technical Field

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

[0002] Due to the renewable and clean nature of solar energy, photovoltaic power generation technology has developed rapidly. String photovoltaic systems have been widely used in the field of photovoltaic power generation due to their mature technology, high conversion efficiency, and low price. As the rated power of string inverters continues to increase, in order to give full play to the power performance of the inverter, a single string is often equipped with more power converters to convert the DC output of the photovoltaic module into DC first.

[0003] In order to maintain system stability, a constant output limit is generally set as the upper limit for the output parameter of the power converter (such as the output voltage or output current of the power converter). When the value of the output parameter rises to the output limit, it cannot rise further. However, due to reasons such as component precision and manufacturing differences, the actual output limits of the same batch of power converters vary. In actual use, if all power converters are set with a uniform output limit, only the power converter with the smallest actual output limit will always be in a restricted state, which may cause its output voltage or output current to be too small, thus affecting the stable control of the power converter. Summary of the invention

[0004] Based on this, it is necessary to provide a control method of a power converter, a power converter and a photovoltaic system to address the above technical problems.

[0005] In a first aspect, an embodiment of the present invention provides a control method for a power converter, wherein the power converter is used for performing DC conversion, and the method includes:

[0006] Sampling an output parameter of the power converter, the output parameter comprising a first parameter and a second parameter;

[0007] When the sampling value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to increase as the second parameter decreases, wherein the first parameter is one of the output voltage and the output current, and the second parameter is the other of the output voltage and the output current.

[0008] In some embodiments, the first parameter is the output current, the second parameter is the output voltage, and the upper limit value of the output current is controlled to increase as the output voltage decreases.

[0009] In some embodiments, the first parameter is the output voltage, the second parameter is the output current, and the upper limit value of the output voltage is controlled to increase as the output current decreases.

[0010] In some embodiments, controlling the upper limit value to increase as the second parameter decreases comprises:

[0011] The upper limit value of the first parameter is controlled to increase linearly or nonlinearly as the second parameter decreases.

[0012] In some embodiments, controlling the upper limit value to increase as the second parameter decreases comprises:

[0013] The upper limit value of the first parameter is controlled to increase stepwise as the second parameter decreases.

[0014] In some embodiments, the upper limit value of the first parameter is greater than or equal to a first threshold value and less than or equal to a second threshold value.

[0015] In some embodiments, the second threshold is less than or equal to a hardware limit of the power converter.

[0016] In some embodiments, when the sample value of the first parameter is less than the first threshold, the upper limit value of the first parameter is set to be equal to the first threshold.

[0017] In some embodiments, the upper limit value is controlled to increase as the second parameter decreases until the adjusted upper limit value of the first parameter is greater than the sampled value of the first parameter.

[0018] In a second aspect, an embodiment of the present invention provides a power converter, the power converter comprising:

[0019] A DC conversion circuit, used for performing DC conversion;

[0020] A control circuit is used to execute the steps of the method described in the first aspect.

[0021] In some embodiments, the DC conversion circuit includes a buck circuit, a boost circuit or a buck-boost circuit.

[0022] In a third aspect, an embodiment of the present invention proposes a photovoltaic system, comprising an inverter and at least one photovoltaic string connected to the inverter, wherein the photovoltaic string comprises a plurality of power converters and a photovoltaic DC power supply correspondingly connected to the power converters, and the power converter performs the steps of the method described in the first aspect.

[0023] The present application samples the output parameters of the power converter, wherein the output parameters include a first parameter and a second parameter, wherein the first parameter is one of the output voltage and the output current, and the second parameter is the other of the output voltage and the output current; when the sampled value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to increase as the second parameter decreases, so as to avoid the problem of power fluctuation caused by the output voltage or output current of the power converter dropping too low when the output is limited, thereby improving the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the structure of a photovoltaic system in some embodiments provided in this application;

[0025] Figure 2 A schematic diagram of the structure of a photovoltaic system in some other embodiments provided in this application;

[0026] Figure 3 A schematic diagram of a control method for a power converter in some embodiments provided in the present application;

[0027] Figure 4 A schematic diagram showing how the output current limiting value of a power converter varies with the output voltage value in the first exemplary embodiment provided by the present application;

[0028] Figure 5 A schematic diagram of an output characteristic curve of a power converter in a first exemplary embodiment provided in the present application;

[0029] Figure 6 A schematic diagram showing how the output current limiting value of a power converter varies with the output voltage value in the second exemplary embodiment provided by the present application;

[0030] Figure 7 A schematic diagram showing how the output voltage limit value of the power converter varies with the output current value in the third exemplary embodiment provided by the present application;

[0031] Figure 8 This is a schematic diagram of an output characteristic curve of a power converter in a third exemplary embodiment provided in the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for ordinary technicians in the field related to the contents disclosed in the present application, some changes such as design, manufacturing or production based on the technical contents disclosed in the present application are only conventional technical means, and should not be understood as insufficient contents disclosed in the present application.

[0033] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0034] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to greater than or equal to two. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, "A and / or B" can represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are merely used to distinguish similar objects and do not represent a specific ordering of the objects.

[0035] Figure 1 The following is a schematic diagram of the structure of a photovoltaic system in some embodiments provided in this application. Figure 1As shown, the photovoltaic system includes at least one photovoltaic string 100 and an inverter 200 connected to the photovoltaic string 100 , and the photovoltaic string 100 includes n power converters 102 connected in series and n photovoltaic DC power supplies 101 correspondingly connected to the power converters 102 .

[0036] The photovoltaic DC power supply 101 is connected to the input end of the power converter 102 for providing DC power. The photovoltaic DC power supply 101 is, for example, any one of a single photovoltaic module, a single photovoltaic cell substring, a plurality of photovoltaic modules connected in series and / or in parallel, and a plurality of photovoltaic cell substrings connected in series and / or in parallel.

[0037] The power converter 102 is used to realize DC conversion. The output ends of multiple power converters 102 are connected in series and then connected to the DC input end of the inverter 200, so as to provide the DC power output by the photovoltaic DC power source 101 to the inverter 200. The power converter 102 can adjust the working point of the photovoltaic DC power source 101 so that the photovoltaic DC power source 101 works at the maximum power point, for example, it can be realized by using buck, boost, buck-boost circuits, etc.

[0038] The inverter 200 is used to invert the direct current provided by the photovoltaic string 100 into alternating current, and provide the alternating current to the grid or load.

[0039] Figure 2 The following are schematic diagrams of the structure of photovoltaic systems in some other embodiments provided in this application. Figure 2 As shown, the photovoltaic system includes at least one photovoltaic string 100 and an inverter 200 connected to the photovoltaic string 100 , and the photovoltaic string 100 includes n power converters 102 connected in parallel and n photovoltaic DC power supplies 101 correspondingly connected to the power converters 102 .

[0040] The control loop of the power converter generally includes an MPPT (Maximum Power Point Track) control loop, a voltage limiting loop, and a current limiting loop. When the power converter operates in the MPPT state, the MPPT control loop of the power converter works to control the corresponding connected photovoltaic DC power supply to operate at the maximum power point; when the power converter operates in the voltage limiting state, the voltage limiting loop of the power converter works to control the output voltage of the power converter to be equal to the output voltage limiting value; when the power converter operates in the current limiting state, the current limiting loop of the power converter works to control the output current of the power converter to be equal to the output current limiting value.

[0041] against Figure 1In the photovoltaic system shown in which multiple power converters are connected in series, due to reasons such as component precision and manufacturing differences, the actual output current limiting values ​​of the power converters in the same photovoltaic string may be different. For example, the actual output current limiting value of the nth power converter 102 is smaller than the actual output current limiting values ​​of other power converters. For example, when the nth power converter 102 samples its output current, if the sampled value of the output current is greater than the actual output current due to reasons such as component precision, when the sampled value is greater than the output current limiting value, the current limiting loop will be triggered in advance to take effect. At this time, if all power converters on the same photovoltaic string are set with a unified output current limiting value, only the nth power converter 102 is always in a current limiting state, which may cause its output voltage to be too small and cause power fluctuations, thereby affecting the stable control of the power converter.

[0042] against Figure 2 In the photovoltaic system shown in which multiple power converters are connected in parallel, due to reasons such as component precision and manufacturing differences, the actual output voltage limiting values ​​of the power converters at the same input port may be different. For example, the actual output voltage limiting value of the nth power converter 102 is smaller than the actual output voltage limiting values ​​of other power converters. For example, when the nth power converter 102 samples the output voltage, if the sampled value of the output voltage is greater than the actual output voltage due to reasons such as component precision, when the sampled value is greater than the output voltage limiting value, the voltage limiting loop will be triggered in advance to take effect. At this time, if all power converters on the same input port are set to a uniform voltage limiting value, only the nth power converter 102 is always in a voltage limiting state, which may cause its output current to be too small and cause power fluctuations, thereby affecting the stable control of the power converter.

[0043] In order to solve the above technical problems, the present application proposes a control method for a power converter, such as Figure 3 As shown, the method includes:

[0044] S302: Sampling output parameters of the power converter.

[0045] The output parameters include a first parameter and a second parameter.

[0046] S304: When the sampling value of the first parameter is greater than or equal to the upper limit value of the first parameter, control the upper limit value to increase as the second parameter decreases.

[0047] The first parameter is one of the output voltage and the output current, and the second parameter is the other of the output voltage and the output current.

[0048] Correspondingly, the upper limit value may be an output voltage limit value or an output current limit value of the power converter.

[0049] In some specific embodiments, the upper limit value is controlled to increase as the second parameter decreases until the adjusted upper limit value of the first parameter is greater than the sampled value of the first parameter.

[0050] In some specific embodiments, for example, when the power converter is used Figure 1 In the case of the series photovoltaic system shown, the first parameter may be the output current, and the second parameter may be the output voltage. The upper limit value of the output current is controlled to increase as the output voltage decreases.

[0051] In some embodiments, for example, when the power converter is used Figure 2 In the parallel photovoltaic system shown, the first parameter may be the output voltage, the second parameter may be the output current, and the upper limit value of the output voltage is controlled to increase as the output current decreases.

[0052] The increasing trend may be a linear increase or a nonlinear increase.

[0053] In some embodiments, the upper limit value of the first parameter may be controlled to increase linearly or nonlinearly as the second parameter decreases.

[0054] In some other embodiments, the upper limit value of the first parameter may be controlled to increase in a step-by-step manner as the second parameter decreases.

[0055] Based on the above steps S302-S304, by sampling the output parameters of the power converter, when the sampling value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to increase as the second parameter decreases, so as to avoid the problem of power fluctuation caused by the output parameter of the power converter dropping too low when the output is limited, thereby improving the stability of the system.

[0056] The control method of the present application will be described in detail below with reference to the accompanying drawings.

[0057] Specifically, in the first exemplary embodiment, when the power converter is used Figure 1 In the photovoltaic system shown in FIG. 1 , a plurality of power converters are connected in series, the first parameter is the output current of the power converter, the second parameter is the output voltage of the power converter, the corresponding hardware limit value of the power converter is the hardware current limit value of the power converter, and the upper limit value of the output current of the power converter is the output current limit value of the power converter. Figure 4 The output current limit value of the power converter changes with its output voltage. Figure 4 As shown, I 1 is the first threshold value of the output current limit value of the power converter, that is, the minimum output current limit value of the power converter; I 2is the second threshold of the output current limit value of the power converter, that is, the maximum output current limit value of the power converter; V 1 The power converter is in normal operation until the sampled value of the output current reaches the first threshold value I 1 Output voltage at 2 is the minimum output voltage of the power converter during current limiting, where I 1 2 ≤ the hardware current limit value of the power converter. As can be seen from the figure, the sampling value of the output current of the self-power converter reaches the first threshold value I 1 When the power converter is in the current limiting state, the upper limit of the output current of the power converter is in the voltage range [V 2 ,V 1 ] increases linearly with the decrease of the output voltage of the power converter, and increases when the output voltage decreases to V 2 When the upper limit of the output current increases to the second threshold value I 2 .

[0058] Specifically, when the sampled value of the output current of the power converter reaches the first threshold value I 1 When the power converter enters the current limiting state, Figure 4 The curve shown adjusts the upper limit value of the output current of the power converter. When the sampled value of the output current is less than the adjusted upper limit value of the output current, the power converter exits the current limiting state and starts normal operation, such as performing MPPT control.

[0059] At this time, the output characteristic curve of the power converter is Figure 5 The constant current limit curve S 1 Transformed into variable current limiting value curve S 2 , and ensure that the output voltage is greater than V 2 .

[0060] like Figure 5 As shown, the power converter of the embodiment of the present application includes a constant current limit interval [0, V 2 ], variable current limiting range [V 2 ,V 1 ]、Constant power range [V 1 ,V 3 ], in the constant current limiting interval, the current limiting loop of the power converter is effective, and the power converter operates in a current limiting state; in the constant power interval, the current limiting loop of the power converter is ineffective, at this time, the power converter performs MPPT control, for example; in the variable current limiting interval, the working state of the power converter will switch between the current limiting state and the normal operating state (for example, the control loop of the power converter switches between the current limiting loop and the MPPT control loop).

[0061] ​In the constant current limit range, the upper limit value of the output current of the power converter is constant at I 2 .

[0062] In the variable current limit range, the upper limit of the output current of the power converter changes with the change of its output voltage. Specifically, when the output voltage is V 1 Gradually decrease to V 2 When the corresponding output current upper limit is I 1 The trend increases to I 2 .

[0063] In the variable current limiting range, the output power of the power converter decreases at a rate that is lower than the rate in the constant current limiting range as its output voltage decreases.

[0064] This embodiment controls the upper limit of the output current of the power converter to increase as its output voltage decreases, so as to avoid the problem that when the output current of the power converter is limited, the power converter always operates in a current limiting state, causing its output voltage to drop too low and causing power fluctuations, thereby improving the stability of the system.

[0065] In the second exemplary embodiment, when the power converter is used Figure 1 In the photovoltaic system shown in FIG. 1 , a plurality of power converters are connected in series, the first parameter is the output current of the power converter, the second parameter is the output voltage of the power converter, the corresponding hardware limit value of the power converter is the hardware current limit value of the power converter, and the upper limit value of the output current of the power converter is the output current limit value of the power converter. Figure 6 The output current limit value of the power converter changes with its output voltage. The difference from the first exemplary embodiment is that the upper limit value of the output current of the power converter is in the voltage range [V 2 ,V 1 ] increases step by step as the output voltage of the power converter decreases, which can further improve the stability of the system.

[0066] In the third exemplary embodiment, when the power converter is used Figure 2 In the photovoltaic system shown in FIG. 1 , a plurality of power converters are connected in parallel, the first parameter is the output voltage of the power converter, the second parameter is the output current of the power converter, the corresponding hardware limit value of the power converter is the hardware voltage limit value of the power converter, and the upper limit value of the output voltage of the power converter is the output voltage limit value of the power converter. Figure 7 The output voltage limit value of the power converter changes with its output current. Figure 7 As shown, V 4 is the first threshold of the output voltage limit value of the power converter, that is, the minimum output voltage limit value of the power converter; V 5is the second threshold of the output voltage limit value of the power converter, that is, the maximum output voltage limit value of the power converter; I 4 is the minimum output current of the power converter during voltage limiting; I 3 As the power converter goes from normal operation to reaching the first threshold V 4 The output current is 4 <V 5 ≤The hardware voltage limit value of the power converter. As can be seen from the figure, the sampling value of the output voltage of the self-power converter reaches the first threshold value V 4 When the power converter is in the voltage limiting state, the upper limit of the output voltage of the power converter is in the current range [I 4 ,I 3 ] increases linearly with the decrease of output current and increases when the output current drops to I 4 When it increases to the second threshold V 5 .

[0067] At this time, the output characteristic curve of the power converter is Figure 8 The constant limit pressure curve S 3 Transformed into variable pressure limit value curve S 4 , and ensure that the output current is greater than I under voltage limiting state 4 .

[0068] like Figure 8 As shown, the power converter of the embodiment of the present application includes a constant current limit interval [0, V 6 ]、Constant power range [V 6 ,V 4 ], variable voltage limit range [V 4 ,V 5 ] and constant voltage limit interval, where the interval corresponding to the point where the output voltage is V5 is the constant voltage limit interval. In the constant voltage limit interval, the voltage limit loop of the power converter works, the power converter works in the voltage limit state, and the output voltage is limited to V 5 ; In the constant power range, the voltage limiting loop of the power converter does not work. At this time, the power converter performs MPPT control for example; in the variable voltage limiting range, the working state of the power converter will switch between the voltage limiting state and the normal operating state (the control loop of the power converter, such as switching between the voltage limiting loop and the MPPT control loop).

[0069] In the variable voltage limit range, the output power of the power converter decreases at a rate that is lower than the rate in the constant voltage limit range as the output voltage decreases.

[0070] It should be noted that the power converter according to the embodiment of the present application may also include a variable current limiting interval as in the first exemplary embodiment or the second exemplary embodiment.

[0071] This embodiment controls the upper limit of the output voltage of the power converter to increase as its output current decreases, so as to avoid the problem that when the output voltage of the power converter is limited, the power converter always operates in a voltage-limited state, causing its output current to drop too low and causing power fluctuations, thereby improving the stability of the system.

[0072] In summary, the present application samples the output parameters of the power converter, wherein the output parameters include a first parameter and a second parameter, wherein the first parameter is one of the output voltage and the output current, and the second parameter is the other of the output voltage and the output current; when the sampled value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to increase as the second parameter decreases, so as to avoid the problem of power fluctuation caused by the output voltage or output current of the power converter dropping too low when the output is limited, thereby improving the stability of the system.

[0073] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0074] According to an embodiment of the present application, a power converter for implementing the above control method is also provided, which can be applied to Figure 1 and / or Figure 2 The photovoltaic system shown, the power converter comprises:

[0075] A DC conversion circuit, used for performing DC conversion;

[0076] The control circuit is used to execute the steps in the above method embodiment.

[0077] The DC conversion circuit may be a buck circuit, a boost circuit, a buck-boost circuit, or the like.

[0078] In specific implementation, the control circuit may include any one of a microcontroller unit (MCU), a central processing unit (CPU), a field programmable gate array (FPGA), and a digital signal processor (DSP). Of course, the specific form of the control circuit is not limited to the above examples.

[0079] Since the processing and functions implemented by the power converter in the above embodiment correspond to the embodiments, principles and examples of the above control method, for the details not fully described in this embodiment, please refer to the relevant descriptions in the above embodiment and will not be repeated here.

[0080] This application proposes a photovoltaic system, such as Figure 1 or Figure 2 As shown, it includes an inverter 200 and at least one photovoltaic string connected to the inverter 200, the photovoltaic string includes multiple power converters 102 and a photovoltaic DC power supply 101 correspondingly connected to the power converters 102, and the power converters perform the steps in the above method embodiment.

[0081] Multiple power converters 102 may be connected in series or in parallel.

[0082] Since the processing and functions implemented by the photovoltaic system of the above embodiment correspond to the embodiments, principles and examples of the above control method, for the details not fully described in this embodiment, please refer to the relevant descriptions in the above embodiment and will not be repeated here.

[0083] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A control method for a power converter, wherein the power converter is used for DC conversion, characterized in that: The method comprises: Sampling an output parameter of the power converter, the output parameter comprising a first parameter and a second parameter; When the sampling value of the first parameter is greater than or equal to the upper limit value of the first parameter, the upper limit value is controlled to increase as the second parameter decreases, wherein the first parameter is one of the output voltage and the output current, and the second parameter is the other of the output voltage and the output current.

2. The method according to claim 1, characterized in that: The first parameter is the output current, the second parameter is the output voltage, and the upper limit value of the output current is controlled to increase as the output voltage decreases.

3. The method according to claim 1, characterized in that The first parameter is the output voltage, the second parameter is the output current, and the upper limit value of the output voltage is controlled to increase as the output current decreases.

4. The method according to claim 1, characterized in that: The controlling the upper limit value to increase as the second parameter decreases comprises: The upper limit value of the first parameter is controlled to increase linearly or nonlinearly as the second parameter decreases.

5. The method according to claim 1, characterized in that The controlling the upper limit value to increase as the second parameter decreases comprises: The upper limit value of the first parameter is controlled to increase stepwise as the second parameter decreases.

6. The method according to claim 1, characterized in that The upper limit value of the first parameter is greater than or equal to a first threshold value and less than or equal to a second threshold value.

7. The method according to claim 6, characterized in that The second threshold is less than or equal to a hardware limit of the power converter.

8. The method according to claim 6, characterized in that When the sample value of the first parameter is less than the first threshold, the upper limit value of the first parameter is set to be equal to the first threshold.

9. The method according to claim 1, characterized in that: The upper limit value is controlled to increase as the second parameter decreases until the adjusted upper limit value of the first parameter is greater than the sampling value of the first parameter.

10. A power converter, characterized in that: The power converter comprises: A DC conversion circuit, used for performing DC conversion; A control circuit for executing the steps of the method according to any one of claims 1 to 9.

11. The power converter according to claim 10, characterized in that: The DC conversion circuit includes a buck circuit, a boost circuit or a buck-boost circuit.

12. A photovoltaic system, characterized in that: It includes an inverter and at least one photovoltaic string connected to the inverter, the photovoltaic string includes a plurality of power converters and a photovoltaic DC power supply correspondingly connected to the power converters, and the power converter performs the steps of the method described in any one of claims 1 to 9.

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