Control method for power converter, power converter, and photovoltaic system

Abstract

A control method for a power converter, a power converter, and a photovoltaic system. The method comprises: on the basis of a set power control curve, using a single power loop to control the output power of a power converter, wherein the power control curve comprises a first interval, a second interval, and a third interval that are smoothly connected; in the first interval, the output power of the power converter increases as the output voltage increases; in the third interval, the output power of the power converter decreases as the output voltage increases; and in the second interval, an amplitude change of the output power of the power converter is less than a first threshold.

Description

Control methods for power converters, power converters and photovoltaic systems

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on July 26, 2024, with application number 202411022836.1, entitled "Control method for power converter, power converter and photovoltaic system", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of photovoltaic power generation, and in particular to a control method for a power converter, a power converter, and a photovoltaic system. Background Technology

[0004] Due to the renewable and clean nature of solar energy, photovoltaic (PV) power generation technology has developed rapidly. String PV systems have been widely used in the PV power generation field due to their mature technology, high conversion efficiency, and low cost. To avoid the "weakest link" effect that occurs when PV modules are directly connected in series, resulting in power loss, each PV module is typically equipped with a power converter. The outputs of multiple power converters are connected in series to form a PV string, which is then connected to the input of an inverter. The power converter can adjust the output voltage and current of the PV modules to achieve maximum power point tracking (MPPT) and improve the system's power generation efficiency.

[0005] For the safe operation of the system, the sum of the output voltages of all power converters on the photovoltaic string must be lower than the input voltage limit of the inverter. Therefore, an output voltage limit needs to be set for the power converters. In related technologies, a fixed output voltage limit V is typically set for the power converter. lim0 As shown in Figure 1, however, when using this power converter, it is impossible to smoothly and efficiently control the output power of the power converter. Summary of the Invention

[0006] According to various embodiments of this application, a control method for a power converter, a power converter, and a photovoltaic system are provided.

[0007] In a first aspect, embodiments of the present invention provide a control method for a power converter, the method comprising:

[0008] Based on the set power control curve, the output power of the power converter is controlled by a single power loop.

[0009] The power control curve includes a first interval, a second interval, and a third interval that are smoothly connected. In the first interval, the output power of the power converter increases with the increase of the output voltage. In the third interval, the output power of the power converter decreases with the increase of the output voltage. In the second interval, the amplitude change of the output power of the power converter is less than a first threshold.

[0010] In some embodiments, the power control curve is obtained based on Fourier series decomposition of the output PV curve of the power converter.

[0011] In some embodiments, the power control curve is obtained by periodically expanding the output PV curve of the power converter and then performing Fourier series decomposition.

[0012] In some embodiments, the power control curve is determined based on the electrical parameters of the photovoltaic DC power supply connected to the power converter, or based on the electrical parameters of the photovoltaic DC power supply connected to the power converter and the electrical parameters of the photovoltaic system connected to the power converter.

[0013] In some embodiments, the maximum voltage value of the third interval is the first output voltage limit value of the power converter, the minimum voltage value of the third interval is the second output voltage limit value of the power converter, and the first output voltage limit value is less than or equal to the hardware voltage limit value of the power converter.

[0014] In some embodiments, the power converter is used in a photovoltaic system, the photovoltaic system including a photovoltaic string consisting of a plurality of the power converters connected in series and an inverter connected to the photovoltaic string;

[0015] The first output voltage limit value is determined based on the input voltage limit value of the corresponding inverter in the photovoltaic system and the number of power converters in the photovoltaic string; or, it is determined based on the open-circuit voltage of the photovoltaic DC power supply connected to the power converter.

[0016] In some embodiments, in the second interval, the input power of the power converter is equal to the maximum output power of the photovoltaic DC power supply connected to its input terminal.

[0017] In some embodiments, controlling the output power of the power converter using a single power loop includes:

[0018] The output power reference value of the power converter is determined based on the output voltage of the power converter and the power control curve.

[0019] Based on the output power reference value and the output power, a control signal is generated through the power loop to control the power converter, so that it operates along the power control curve throughout the entire operating voltage range.

[0020] In some embodiments, the power control curve further includes a fourth interval that is smoothly connected to the third interval; in the fourth interval, the output voltage of the power converter remains constant or changes by less than a second threshold.

[0021] In some embodiments, the method further includes:

[0022] The power control curve is dynamically adjusted according to the received adjustment instructions.

[0023] In some embodiments, dynamically adjusting the power control curve includes:

[0024] Adjust the range of the third interval and / or the amplitude of the power control curve according to the adjustment instructions.

[0025] Secondly, embodiments of the present invention provide a power converter, characterized in that the power converter comprises:

[0026] A DC-DC converter circuit is used to perform DC-DC conversion.

[0027] Control circuit, which controls the DC-DC converter circuit to perform DC-DC conversion;

[0028] The control circuit also uses a single power loop to control the output power of the power converter according to the set power control curve.

[0029] The power control curve includes a first interval, a second interval, and a third interval that are smoothly connected. In the first interval, the output power of the power converter increases with the increase of the output voltage. In the third interval, the output power of the power converter decreases with the increase of the output voltage. In the second interval, the amplitude change of the output power of the power converter is less than a first threshold.

[0030] In some embodiments, the control circuit includes:

[0031] The power control unit is used to obtain the duty cycle signal through power loop control based on the power control curve, the output voltage of the power converter, and the output power of the power converter.

[0032] The PWM control unit generates a PWM control signal for controlling the DC-DC converter circuit based on the duty cycle signal.

[0033] In some embodiments, the power converter further includes:

[0034] The communication unit is used to receive adjustment instructions;

[0035] The control circuit dynamically adjusts the power control curve according to the adjustment command.

[0036] In some embodiments, the control circuit further includes:

[0037] An adjustment unit is used to dynamically adjust the range of the third interval and / or the amplitude of the power control curve according to the adjustment command.

[0038] The power control unit also includes:

[0039] The power control curve generation module is used to regenerate the power control curve based on the adjusted range and / or amplitude.

[0040] Thirdly, embodiments of the present invention provide a photovoltaic system, including an inverter and at least one photovoltaic string connected to the inverter, the photovoltaic string including a plurality of power converters connected in series and a photovoltaic DC power supply corresponding to the power converters, the power converters performing the steps of the method described in the first aspect.

[0041] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the published drawings without creative effort.

[0043] Figure 1 is a schematic diagram of the output PV curve of a power converter in related technologies.

[0044] Figure 2 is a schematic diagram of the structure of a photovoltaic system in some embodiments provided in this application.

[0045] Figure 3 is a schematic diagram of the control method of the power converter in some embodiments provided in this application.

[0046] Figure 4 is a schematic diagram of the output PV curve in some embodiments provided in this application.

[0047] Figure 5 is a schematic diagram of power control curves in some embodiments provided in this application.

[0048] Figure 6 is a flowchart illustrating the control method of the power converter in some other embodiments provided in this application.

[0049] Figure 7 is a schematic diagram of the method for adjusting the output voltage limit value in some embodiments provided in this application.

[0050] Figure 8 is a schematic diagram of the power converter structure in some embodiments provided in this application.

[0051] Figure 9 is a schematic diagram of the power converter in some other embodiments provided in this application. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application. Furthermore, it is understood that although the efforts made in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, modifications to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0053] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0054] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; 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 not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application means two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The terms “first,” “second,” “third,” etc., used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0055] Figure 2 is a schematic diagram of the structure of a photovoltaic system in some embodiments provided in this application. As shown in Figure 2, the photovoltaic system includes at least one photovoltaic string 100 and an inverter 200 connected to the photovoltaic string 100. The photovoltaic string 100 includes a plurality of power converters 102 connected in series and a photovoltaic DC power supply 101 corresponding to the power converters 102.

[0056] The photovoltaic DC power supply 101 is connected to the input terminal of the power converter 102 to provide DC power. The photovoltaic DC power supply 101 is, for example, any one of a single photovoltaic module, a single photovoltaic cell substring, multiple photovoltaic modules connected in series and / or in parallel, or multiple photovoltaic cell substrings connected in series and / or in parallel.

[0057] Power converter 102 is used to realize DC-DC conversion. The output terminals of multiple power converters 102 are connected in series and then connected to the DC input terminal of inverter 200 to provide the DC power output from photovoltaic DC power supply 101 to inverter 200. Power converter 102 can adjust the operating point of photovoltaic DC power supply 101 so that photovoltaic DC power supply 101 operates at the maximum power point, for example, by using buck, boost, buck-boost circuits, etc.

[0058] Inverter 200 is used to invert the DC power provided by photovoltaic string 100 into AC power and supply it to the grid or load.

[0059] For system safety, the sum of the output voltages of each power converter must be less than the input voltage limit of the inverter (the maximum voltage allowed for normal inverter operation). Therefore, an output voltage limit needs to be set for the power converter. If the power converter shown in Figure 1 is used, when the inverter is operating in power-limited mode, the output of the photovoltaic string is approximately a rigid voltage source, and the inverter cannot limit the output power of the photovoltaic string by raising its output voltage.

[0060] This application proposes a control method for a power converter, as shown in Figure 3. The method includes:

[0061] S302: Based on the set power control curve, the output power of the power converter is controlled by a single power loop.

[0062] The power control curve includes a first interval, a second interval, and a third interval that are smoothly connected. In the first interval, the output power of the power converter increases with the increase of the output voltage. In the third interval, the output power of the power converter decreases with the increase of the output voltage. In the second interval, the amplitude change of the output power of the power converter is less than a first threshold.

[0063] In the above embodiments, the output power of the power converter is controlled according to the set power control curve, so that the power converter outputs power along the power control curve, which can smoothly and efficiently control the output power of the power converter. Therefore, when the output power of the inverter 200 is limited and the input power needs to be reduced, the output power of the photovoltaic string can be limited by increasing the output voltage of the photovoltaic string, thereby reducing the input power of the inverter 200.

[0064] In other related technologies, the control loop of a power converter generally includes an MPPT (Maximum Power Point Track) control loop and an output voltage control loop. When the power converter operates in MPPT mode, the MPPT control loop of the power converter is activated to control the corresponding connected photovoltaic DC power supply to operate at the maximum power point. When the power converter operates in voltage limiting mode, the output voltage control loop of the power converter is activated to control the output voltage of the power converter to be equal to the output voltage limit value.

[0065] In the above embodiments of this application, a single power loop is used to control the output power of the power converter. Compared with the MPPT control loop and output voltage control loop used in related technologies, loop switching is not required, making the control simpler.

[0066] In some embodiments, the power control curve is obtained based on Fourier series decomposition of the output PV curve of the power converter.

[0067] To improve the accuracy of power control curve fitting, in some embodiments, the power control curve is obtained by periodically expanding the output PV curve of the power converter and then performing Fourier series decomposition.

[0068] In some embodiments, the power control curve of the power converter is determined based on the electrical parameters of the photovoltaic DC power supply or based on the electrical parameters of the photovoltaic DC power supply and the electrical parameters of the photovoltaic system.

[0069] The electrical parameters of the photovoltaic DC power supply include the open-circuit voltage, maximum power point power, and maximum power point voltage. The electrical parameters of the photovoltaic system include the input voltage limit of the inverter and the number of power converters in the photovoltaic string.

[0070] The method for determining the power control curve will be explained below with reference to Figures 4 and 5.

[0071] First, the output PV curve of the power converter is determined based on the electrical parameters of the photovoltaic DC power supply or based on the electrical parameters of the photovoltaic DC power supply and the electrical parameters of the photovoltaic system, for example, curve S1 in Figure 4.

[0072] In some specific embodiments, for example, the first output voltage limit V of the power converter is determined based on the open-circuit voltage of the photovoltaic DC power supply. lim1 The maximum output power P is determined based on the maximum power point power of the photovoltaic DC power supply. mpp The second output voltage limit V of the power converter is determined based on the voltage at the maximum power point. lim2 The lower limit of the output voltage V when the maximum power output is achieved. mpp1 It can be set according to actual needs.

[0073] First output voltage limit V lim1 For example, D1 is the open-circuit voltage of the photovoltaic DC power supply, where D1 is the proportional coefficient, which can be determined according to the hardware circuit of the power converter.

[0074] Second output voltage limit value V lim2 For example, D2 is the voltage at the maximum power point of the photovoltaic DC power supply, where D2 is the proportional coefficient, which can be determined according to the hardware circuit of the power converter.

[0075] In some other specific embodiments, the input voltage limit value Vin of the corresponding inverter in the photovoltaic system can also be used. lim The first output voltage limit V is determined by the number of power converters n in the photovoltaic string. lim1 For example, V lim1 =Vin lim / n.

[0076] As shown in Figure 4, the output PV curve includes three intervals, starting at the second output voltage limit value V. lim2 and the first output voltage limit V lim1 Between (in [V]) lim2 V lim1 Within the specified range, the output power of the power converter decreases as its output voltage increases.

[0077] At the lower limit value V mpp1 Second output voltage limit V lim2 Between (in [V]) mpp1 V lim2 Within the specified range, the output power of the power converter remains basically unchanged, corresponding to the maximum power point power of the corresponding connected photovoltaic DC power supply, and basically maintaining the maximum power output.

[0078] At 0 and the lower limit value V mpp1 Between (in [0, V) mpp1 Within the specified range, the output power of the power converter gradually increases with the increase of the output voltage.

[0079] Furthermore, the output PV curve of the power converter is periodically extended, with an extension period of V1, where V1 is greater than or equal to the first output voltage limit value V. lim1 Then, Fourier series decomposition is performed to obtain the expression for the power control curve, P = f a (v), the corresponding curve is shown in Figure 5.

[0080] For example, after performing Fourier series decomposition on the output PV curve S1, we obtain:

[0081] Where k is an integer, k = 1, 2, 3, ..., m, the larger m is, the better the fitting effect of the power control curve.

[0082] Finally, the power control curve P = f is obtained according to equations (1) and (2). a (v):

[0083] It is understandable that the power control curve is a smooth curve obtained by fitting the output PV curve. It also includes three intervals, which correspond one-to-one with the intervals of the output PV curve. The power control curve is the target power curve of the power converter. Through power loop control, the operating point of the power converter is located on or close to the power control curve.

[0084] As shown in Figure 5, the interval between points A and B of the power control curve corresponds to the second interval of the PV curve, the interval between points B and C of the power control curve corresponds to the third interval of the PV curve, and the interval between point A of the power control curve and the origin corresponds to the first interval of the PV curve.

[0085] Within the second interval, the input power of the power converter is equal to the maximum output power of the photovoltaic DC power supply connected to its input terminal.

[0086] In some other embodiments, the output PV curve of the power converter is determined based on the open-circuit voltage, maximum power point power, and maximum power point voltage of the photovoltaic DC power supply, as shown by curve S1' in Figure 4. Compared with curve S1, a fourth interval is also included, in which the output voltage of the power converter remains constant or the change value is less than the second threshold.

[0087] Then, following the same steps as above, the corresponding power control curve can be fitted.

[0088] During the operation of a photovoltaic system, when the output power of the inverter is unrestricted, if the photovoltaic DC power supply is abnormal (such as being blocked or malfunctioning) or the power converter is disconnected due to a fault, the output voltage of some power converters will increase. The output power of the power converter controlled by the power loop will begin to decrease as the output voltage increases, which will cause the corresponding photovoltaic DC power supply to be unable to work at the maximum power point, resulting in a loss of power generation. At this time, it is necessary to adjust the output voltage limit of the power converter in this state to increase its output power.

[0089] Based on this, in some embodiments, as shown in FIG6, the control method further includes:

[0090] S304: Dynamically adjust the power control curve according to the received adjustment command.

[0091] The adjustment command can be provided by the inverter or issued by other control devices.

[0092] In some implementations, the adjustment command is an output voltage limit adjustment command. The range of the third interval is dynamically adjusted according to the received output voltage limit adjustment command, so that the power generation of the photovoltaic DC power supply is not affected by the output voltage limit of the power converter, and the photovoltaic DC power supply can still generate power at the maximum power under the current conditions.

[0093] In some specific implementations, the power converter can adjust its first output voltage limit and / or second output voltage limit based on a first voltage adjustment coefficient in the output voltage limit adjustment command. For example, the adjusted first output voltage limit is the product of the power converter's current output voltage and the first voltage adjustment coefficient, or the adjusted second output voltage limit is the product of the power converter's current output voltage and the first voltage adjustment coefficient. If the output voltage limit adjustment command does not include a first voltage adjustment coefficient, the power converter adjusts its first output voltage limit and / or second output voltage limit based on its own preset second voltage adjustment coefficient.

[0094] Optionally, the first voltage adjustment factor is equal to the second voltage adjustment factor.

[0095] In other specific implementations, although the power converter operating in the second range will also receive the output voltage limit adjustment command, it will not respond to the output voltage limit adjustment command. The power converter operating in the second range will automatically adjust its output voltage limit, and will not be controlled by the output voltage limit adjustment command.

[0096] In other implementations, the adjustment command is a power adjustment command, and the power converter can adjust the amplitude of the power control curve according to the power adjustment command.

[0097] For example, power adjustment coefficients can be set according to lighting conditions, and power control curves can be updated in a timely manner, so that the power converter can be adapted to different operating conditions, such as when the photovoltaic DC power supply is shaded or the lighting is relatively weak.

[0098] The adjusted power control curve is, for example: P = hf a (v), where h represents the power adjustment coefficient, and h>0.

[0099] Figure 7 illustrates a schematic diagram of output voltage limit adjustment in some embodiments. As shown in Figure 7, when adjusting the output voltage limit, for example, the first output voltage limit V is... lim1 Second output voltage limit V lim2 All are adjusted proportionally according to the adjustment coefficient. After adjustment, the curves S2 and S2' in Figure 7 are shown, for example.

[0100] Optional, second output voltage limit value V lim2 Keeping the first output voltage limit value V unchanged lim1 Adjusting according to the adjustment coefficient, as shown by curve S3 in Figure 7, can be applied to scenarios where the input voltage limit of the inverter needs to be adjusted.

[0101] Optional, first output voltage limit value V lim1 Keeping the second output voltage limit value V unchanged lim2 Adjust according to the adjustment factor, as shown by curve S4 in Figure 7.

[0102] Optionally, if the calculated first output voltage limit value V lim1 The voltage exceeds the hardware limit V of the power converter. oh Then the first output voltage limit value V will be set. lim1 Adjust to the hardware voltage limit value of the power converter, as shown by curve S5 in Figure 7.

[0103] Finally, the latest power control curve is obtained by refitting the adjusted PV curve.

[0104] In some embodiments, controlling the output power of the power converter according to the power control curve of the power converter includes: determining a reference value for the output power of the power converter based on the output voltage and the power control curve of the power converter; and generating a control signal for controlling the power converter through a power loop based on the reference value and the output power, so that the power converter operates along the power control curve throughout the entire operating voltage range.

[0105] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0106] According to an embodiment of this application, a power converter implementing the above control method is also provided, applied to the photovoltaic system shown in FIG1. ​​As shown in FIG8, the power converter 102 includes:

[0107] DC-DC converter circuit 1021 is used for DC-DC conversion;

[0108] The control circuit 1022 is connected to the DC-DC converter circuit 1021 and controls the DC-DC converter circuit 1021 to perform DC-DC conversion.

[0109] The control circuit 1022 also uses a single power loop to control the output power of the power converter according to the set power control curve.

[0110] The power control curve includes a first interval, a second interval, and a third interval that are smoothly connected. In the first interval, the output power of the power converter increases with the increase of the output voltage. In the third interval, the output power of the power converter decreases with the increase of the output voltage. In the second interval, the amplitude change of the output power of the power converter is less than a first threshold.

[0111] In some embodiments, the power control curve is obtained based on Fourier series decomposition of the output PV curve of the power converter.

[0112] In some embodiments, the power control curve is determined based on the parameters of the photovoltaic DC power supply or based on the electrical parameters of the photovoltaic DC power supply and the electrical parameters of the photovoltaic system.

[0113] In some embodiments, the control circuit 1022 includes a power control unit and a PWM (Pulse Width Modulation) control unit. The power control unit is used to obtain a duty cycle signal through power loop control based on the power control curve, the output voltage Vo of the power converter, and the output power Po of the power converter. The PWM control unit generates a PWM control signal for controlling the DC-DC converter 1021 based on the duty cycle signal.

[0114] In some embodiments, the power control unit includes a power reference value calculation module and a power loop. The power reference value calculation module stores the power control curve and determines a power reference value Pref based on the power control curve. The power loop generates a duty cycle signal based on the output power Po of the power converter and the power reference value Pref.

[0115] For example, the power loop obtains the difference between the output power Po and the power reference value Pref, and adjusts the duty cycle signal in one direction. If the absolute value of the difference between the output power Po and the power reference value Pref increases, the duty cycle signal is adjusted in the opposite direction, but this is not the only possibility.

[0116] The output power Po can be calculated, for example, from the output voltage Vo and output current of the power converter, or from the input voltage Vi and input current of the power converter, or it can be obtained through other methods.

[0117] The DC-DC converter circuit 1021 can be a buck circuit, a boost circuit, a buck-boost circuit, etc.

[0118] In a specific implementation, the control circuit 1022 can be any of the following: a microcontroller unit (MCU), a central processing unit (CPU), a field-programmable gate array (FPGA), or a digital signal processor (DSP). Of course, the specific form of the control circuit is not limited to the examples above.

[0119] In some embodiments, as shown in FIG9, the power converter further includes: a communication unit for receiving adjustment commands; and a control circuit for dynamically adjusting the power control curve according to the adjustment commands.

[0120] The communication unit is implemented, for example, using a communication chip.

[0121] Specifically, the control circuit also includes: an adjustment unit, used to adjust the range of the third interval of the power control curve and / or the amplitude of the power control curve according to the adjustment command; the power control unit also includes: a power control curve generation module, used to regenerate the power control curve according to the adjusted range of the third interval and / or the amplitude of the power control curve.

[0122] All the aforementioned units and modules can be implemented using hardware such as processors. Since the processing and functions implemented by the power converter in the above embodiments correspond to the embodiments, principles, and examples of the aforementioned control methods, any details not elaborated in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0123] In one example embodiment, suppose a photovoltaic string includes 10 photovoltaic DC power supplies with identical characteristic parameters. The maximum power point of the photovoltaic DC power supply is 800W, and the input voltage limit of the inverter is 880V. If the output power of the inverter is unrestricted and each power converter operates in the second range, the input voltage of the inverter is controlled by the inverter to be 800V. At this time, the photovoltaic string current is 10A, and the output voltage of each power converter is 80V. If the inverter needs to reduce the output power, for example, to limit the output power to 6475W, the inverter's power limiting loop will raise the input voltage of the inverter to 850V. At this time, the output voltage of each power converter needs to be raised to 85V, and the output power of each power converter needs to be reduced to 647.5W. However, the power converter with a fixed output voltage limit cannot reduce the output power while increasing the output voltage. Therefore, the power converter is not suitable for this operating condition.

[0124] By using the power converter and control method of this application, the second output voltage limit value of each power converter is set to 83V and the first output voltage limit value is set to 88V. Each power converter can increase its output voltage to 85V, while the output power of each power converter decreases to 647.5W. Therefore, it can be applied to the power-limited state of the inverter, thus expanding the application range.

[0125] This application proposes a photovoltaic system, as shown in FIG1, including an inverter 200 and at least one photovoltaic string 100 connected to the inverter 200. The photovoltaic string 100 includes a plurality of power converters 102 connected in series and a photovoltaic DC power supply 101 correspondingly connected to the power converters 102. The power converters 102 execute the steps of the control method of the power converter.

[0126] Since the processing and functions implemented by the photovoltaic system in the above embodiments correspond to the embodiments, principles and examples of the aforementioned control methods, any details not covered in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0127] The technical features of the above embodiments can be combined in any way. For the sake of brevity, 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.

[0128] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A control method of a power converter, characterized by, The method comprises: controlling the output power of the power converter by a single power loop according to a set power control curve; wherein the power control curve comprises a first interval, a second interval and a third interval which are smoothly connected; in the first interval, the output power of the power converter increases with the increase of the output voltage; in the third interval, the output power of the power converter decreases with the increase of the output voltage; in the second interval, the amplitude variation of the output power of the power converter is less than a first threshold.

2. The method of claim 1, wherein, The power control curve is obtained based on Fourier series decomposition of an output PV curve of the power converter.

3. The method of claim 2, wherein, The power control curve is obtained based on Fourier series decomposition of an output PV curve of the power converter after period extension.

4. The method of claim 1, wherein, The power control curve is determined based on electrical parameters of a photovoltaic direct-current power source connected to the power converter, or based on electrical parameters of the photovoltaic direct-current power source and electrical parameters of a photovoltaic system connected to the power converter.

5. The method of claim 1, wherein, The maximum voltage of the third interval is a first output voltage limit of the power converter, and the minimum voltage of the third interval is a second output voltage limit of the power converter, and the first output voltage limit is less than or equal to a hardware voltage limit of the power converter.

6. The method of claim 5, wherein, The power converter is used in a photovoltaic system, the photovoltaic system comprising a photovoltaic string composed of a plurality of the power converters connected in series and an inverter connected to the photovoltaic string; The first output voltage limit is determined based on an input voltage limit of a corresponding inverter in the photovoltaic system and the number of the power converters in the photovoltaic string, or based on an open-circuit voltage of the photovoltaic direct-current power source connected to the power converter.

7. The method of claim 1, wherein, In the second interval, the input power of the power converter is equal to the maximum output power of the photovoltaic direct-current power source connected to the input of the power converter.

8. The method of claim 1, wherein, The controlling the output power of the power converter by a single power loop comprises: determining an output power reference value of the power converter according to the output voltage of the power converter and the power control curve; generating a control signal for the power converter by a power loop according to the output power reference value and the output power, so that the power converter works along the power control curve in the entire working voltage range.

9. The method of claim 1, wherein, The power control curve further comprises a fourth interval which is smoothly connected with the third interval; in the fourth interval, the output voltage of the power converter is maintained constant or varies by less than a second threshold.

10. The method of claim 1, wherein, The method further comprises: dynamically adjusting the power control curve according to a received adjustment instruction.

11. The method of claim 10, wherein, The dynamically adjusting the power control curve comprises: adjusting the interval range of the third interval and / or the amplitude of the power control curve according to the adjustment instruction.

12. A power converter, characterized by The power converter comprises: a direct-current conversion circuit for direct-current conversion; a control circuit for controlling the direct-current conversion circuit to perform direct-current conversion; wherein the control circuit controls the output power of the power converter by a single power loop according to a set power control curve; wherein the control circuit controls the output power of the power converter by a single power loop according to a set power control curve; The power control curve comprises a first interval, a second interval and a third interval which are connected smoothly; in the first interval, the output power of the power converter increases with the increase of the output voltage; in the third interval, the output power of the power converter decreases with the increase of the output voltage; in the second interval, the amplitude variation of the output power of the power converter is less than a first threshold.

13. The power converter of claim 12, wherein, The control circuit comprises: a power control unit configured to obtain a duty cycle signal by power loop control according to a power control curve, an output voltage of the power converter and an output power of the power converter; a PWM control unit configured to generate a PWM control signal for controlling the DC conversion circuit according to the duty cycle signal.

14. The power converter of claim 13, wherein, The power converter further comprises: a communication unit configured to receive an adjustment instruction; the control circuit is configured to dynamically adjust the power control curve according to the adjustment instruction.

15. The power converter of claim 14, wherein, The control circuit further comprises: an adjustment unit configured to dynamically adjust an interval range of the third interval and / or an amplitude of the power control curve according to the adjustment instruction; the power control unit further comprises: a power control curve generation module configured to regenerate the power control curve according to the adjusted interval range and / or amplitude.

16. A photovoltaic system characterized by, The inverter and at least one photovoltaic string connected with the inverter, the photovoltaic string comprising a plurality of power converters connected in series and photovoltaic DC power sources connected with the power converters correspondingly, the power converters performing the steps of the method according to any one of claims 1-11.

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