Photovoltaic power generation control method, inverter, main control device and photovoltaic system

Abstract

A photovoltaic power generation control method, an inverter, a main control device and a photovoltaic system. The method comprises: determining whether there is a power converter in a voltage-limiting state in a photovoltaic string connected to an inverter, wherein the photovoltaic string comprises a plurality of power converters connected in series, and photovoltaic direct-current power sources correspondingly connected to the power converters; and if so, sending a communication signal to the photovoltaic string where the power converter in the voltage-limiting state is located, wherein the communication signal comprises an adjustment instruction, and the adjustment instruction is used for controlling at least one corresponding power converter in the photovoltaic string to adjust an output voltage characteristic value thereof.

Description

Control methods, inverters, main control equipment, and photovoltaic systems for photovoltaic power generation

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on July 26, 2024, application number 202411018500.8, entitled "Control method for photovoltaic power generation, inverter, main control equipment 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, inverter, main control equipment and photovoltaic system for photovoltaic power generation. 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 each power converter on the photovoltaic string needs to be lower than the upper limit of the DC input voltage of the inverter. Therefore, it is necessary to set an output voltage characteristic value for the power converter to limit its output voltage external characteristics. In related technologies, this output voltage characteristic value of the power converter is a fixed value and cannot be adjusted, resulting in low power generation efficiency of the photovoltaic system. Summary of the Invention

[0006] According to various embodiments of this application, a photovoltaic power generation control method, inverter, main control equipment, and photovoltaic system are provided.

[0007] In a first aspect, embodiments of this application propose a control method for photovoltaic power generation, the method comprising:

[0008] Determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state. The photovoltaic string includes multiple power converters connected in series and photovoltaic DC power supplies connected to the corresponding power converters.

[0009] If so, a communication signal is sent to the photovoltaic string containing the power converter in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0010] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristics.

[0011] In some embodiments, the adjustment command is used to control the power converter in the photovoltaic string that is in a voltage-limiting state to adjust its output voltage characteristic value, and the power converter in the MPPT state to automatically adjust its output voltage characteristic value.

[0012] In some embodiments, the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to its preset adjustment coefficient;

[0013] Alternatively, the communication signal carries an adjustment coefficient, and the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to the adjustment coefficient.

[0014] In some embodiments, the adjustment factor is the ratio of the upper limit of the DC input voltage of the inverter to the current DC input voltage.

[0015] In some embodiments, each power converter is provided with an output voltage characteristic value, and the adjustment command controls the output voltage characteristic value of the power converter to be adjusted to the product of the current output voltage of the power converter and the adjustment coefficient.

[0016] In some embodiments, each of the power converters is provided with a plurality of output voltage characteristic values, and the adjustment command controls the power converter to adjust at least a portion of its output voltage characteristic values ​​according to the adjustment coefficient.

[0017] In some embodiments, if the output voltage characteristic value obtained according to the adjustment coefficient is greater than the maximum output voltage characteristic value among the multiple output voltage characteristic values ​​before adjustment, then the output voltage characteristic value is adjusted to the maximum output voltage characteristic value.

[0018] Alternatively, if the output voltage characteristic value obtained according to the adjustment coefficient is greater than the upper limit value of the output voltage of the power converter, then the output voltage characteristic value shall be adjusted to the upper limit value of the output voltage.

[0019] In some embodiments, the adjustment command controls the maximum output voltage characteristic value among the plurality of output voltage characteristic values ​​to be adjusted to the product of the current output voltage and the adjustment coefficient, while the other output voltage characteristic values ​​are adjusted proportionally or according to the minimum output voltage characteristic value and the adjusted maximum output voltage characteristic value among the plurality of output voltage characteristic values.

[0020] In some embodiments, a disturbance is applied in the direction of increasing and / or decreasing DC input voltage, and the presence of a power converter in a voltage-limiting state is determined based on the change in DC input power of the inverter before and after the disturbance.

[0021] Secondly, embodiments of this application propose an inverter applied to a photovoltaic system, wherein the photovoltaic system further includes at least one photovoltaic string connected to the inverter, the photovoltaic string including a plurality of power converters connected in series and photovoltaic DC power supplies corresponding to the power converters, and the inverter including:

[0022] The first state determination module is used to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state.

[0023] The first signal transmitting module is used to send a communication signal to the photovoltaic string containing the power converter in the voltage-limited state when there is a power converter in the photovoltaic string in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0024] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristic values, or the adjustment command is used to control the power converters in the photovoltaic string that are in a voltage-limiting state to adjust their output voltage characteristic values, and the power converters in the MPPT state automatically adjust their output voltage characteristic values.

[0025] In some embodiments, the first state determination module applies a disturbance in the direction of increasing and / or decreasing DC input voltage, and determines whether there is a power converter in a voltage-limiting state based on the change in DC input power of the inverter before and after the disturbance.

[0026] Thirdly, embodiments of this application propose a method for controlling photovoltaic power generation, the method comprising:

[0027] Send a status judgment command, which is used to control the inverter to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state. The photovoltaic string includes multiple power converters connected in series and photovoltaic DC power supplies connected to the power converters respectively.

[0028] If so, a communication signal is sent to the photovoltaic string containing the power converter in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0029] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristic values;

[0030] Alternatively, the power converters in the photovoltaic string that are in voltage limiting state can adjust their output voltage characteristic values, while the power converters in MPPT state can automatically adjust their output voltage characteristic values.

[0031] In some embodiments, the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to its preset adjustment coefficient;

[0032] Alternatively, the communication signal carries an adjustment coefficient, and the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to the adjustment coefficient.

[0033] Fourthly, this application provides a master control device applied to a photovoltaic system. The photovoltaic system further includes at least one photovoltaic string and an inverter connected to the photovoltaic string. The photovoltaic string includes multiple power converters connected in series and photovoltaic DC power supplies corresponding to the power converters. The master control device includes:

[0034] The second signal transmission module is used to send a status judgment command to the inverter. The status judgment command is used to control the inverter to apply a disturbance to its DC input and to control the inverter to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state.

[0035] The third signal transmission module is used to send a communication signal to the photovoltaic string containing the power converter in the voltage-limited state when there is a power converter in the photovoltaic string in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0036] Fifthly, embodiments of this application propose a control method for a power converter, the method comprising:

[0037] If the power converter is in a voltage limiting state, the output voltage characteristic value of the power converter is adjusted according to the received communication signal including the adjustment command;

[0038] If the power converter is in MPPT state, the output voltage characteristic value of the power converter is automatically adjusted.

[0039] In a sixth aspect, embodiments of this application propose a photovoltaic system including an inverter and at least one photovoltaic string connected to the inverter. The photovoltaic string includes a plurality of power converters connected in series and a photovoltaic DC power supply corresponding to each power converter. The inverter performs the steps of the method described in the first aspect.

[0040] In a seventh aspect, embodiments of this application propose a photovoltaic system, including an inverter, at least one photovoltaic string connected to the inverter, and a main control device connected to the inverter. The photovoltaic string includes a plurality of power converters connected in series and photovoltaic DC power supplies corresponding to the power converters. The main control device performs the steps of the method described in the third 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 structure of the photovoltaic system in the first embodiment provided in this application.

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

[0045] Figure 3 is a flowchart illustrating a photovoltaic power generation control method in one embodiment of this application.

[0046] Figure 4 is a schematic diagram of the method for adjusting the output voltage characteristic value in some embodiments provided in this application.

[0047] Figure 5 is a schematic diagram of the method for adjusting the output voltage characteristic value in some other embodiments provided in this application.

[0048] Figure 6 is a schematic diagram of the inverter provided in this application.

[0049] Figure 7 is a flowchart illustrating a photovoltaic power generation control method in another embodiment provided in this application.

[0050] Figure 8 is a schematic diagram of the main control device in one embodiment provided in this application.

[0051] Figure 9 is a flowchart illustrating the control method of a power converter in one embodiment of 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 1 is a schematic diagram of the structure of the photovoltaic system in the first embodiment provided in this application. As shown in Figure 1, 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 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] Furthermore, the power converter 102 is generally equipped with a switchable MPPT (Maximum Power Point Track) control loop and an output voltage control loop. When the power converter 102 operates in MPPT mode, the MPPT control loop of the power converter 102 is activated to control the corresponding connected photovoltaic DC power supply 101 to operate at the maximum power point, thereby maximizing the utilization of the photovoltaic DC power supply energy. At this time, the actual output voltage of the power converter 102 is less than a characteristic value of the output voltage of the power converter 102, which can be the upper limit of the output voltage of the power converter 102. When the power converter 102 operates in voltage limiting mode, the output voltage control loop of the power converter 102 is activated, controlling the output voltage of the power converter 102 to be equal to the characteristic value of the output voltage. At this time, the output power of the photovoltaic DC power supply is limited, and there will be energy loss.

[0060] For safe system operation, the sum of the output voltages of each power converter must be less than the upper limit of the inverter's DC input voltage (the maximum input voltage allowed for normal inverter operation). The sum of the characteristic values ​​of the output voltages of each power converter can be equal to or less than the upper limit of the inverter's DC input voltage. The DC input voltage is generally controlled by the inverter and stabilized at a set value (this set value is less than the upper limit of the inverter's DC input voltage). During system operation, each power converter operates in MPPT state. When the photovoltaic DC power supply is abnormal (such as being shaded or malfunctioning) or when a power converter is disconnected due to a fault, the output voltage of some power converters will rise. When it rises to the corresponding characteristic value of the output voltage, the power converter operates in a voltage-limiting state, resulting in a loss of power generation. At this time, it is necessary to adjust the output voltage characteristic value of the power converter in the voltage-limiting state to switch it to MPPT state.

[0061] Figure 2 is a schematic diagram of the photovoltaic system in the second embodiment provided in this application. As shown in Figure 2, the photovoltaic system includes at least one photovoltaic string 100, an inverter 200 connected to the photovoltaic string 100, and a main control device 300. The main control device 300 is connected to the inverter 200. The photovoltaic string 100 includes multiple power converters 102 connected in series and photovoltaic DC power supplies 101 connected to the power converters 102 respectively.

[0062] In some implementations, the main control device 300 includes an MCU (Micro Controller Unit) and a communication module. The main control device 300 is communicatively connected to the inverter 200 and communicates with the inverter 200 through the communication module, for example, via a PLC (Power Line Communication) or wirelessly. The communication module is implemented using a communication chip, for example.

[0063] In some implementations, the master control device 300 is communicatively connected to each power converter 102. The master control device 300 can communicate with each power converter 102, for example, through a PLC (Power Line Communication) or wireless means. The master control device 300 can provide control signals to each power converter to control the operating state of each power converter. When needed, it can quickly shut down the power output of each power converter. The master control device 300 can be, for example, a transmitter.

[0064] This application proposes a control method for photovoltaic power generation, which can be applied to the inverter in the first embodiment described above to control and adjust the output voltage characteristic value of the corresponding power converter. As shown in Figure 3, the method includes:

[0065] S302: Determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state.

[0066] In some embodiments, the inverter applies a disturbance to its DC input at certain preset intervals to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limited state.

[0067] S304: If so, a communication signal is sent to the photovoltaic string containing the power converter in the voltage limiting state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0068] In some embodiments, the inverter can broadcast communication signals to the photovoltaic string where the power converter is located, which is in a voltage-limited state, via PLC, wireless or other communication methods.

[0069] Based on the above steps S302-S304, by determining whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limited state, a communication signal is sent to the photovoltaic string where the power converter in the voltage-limited state is located. The power converter responds to the received communication signal and adjusts its output voltage characteristic value according to the adjustment command included in the communication signal. This allows for timely adjustment of the output voltage characteristic value, ensuring that the power generation of the photovoltaic system is not affected by the output voltage characteristic value of the power converter and can still generate power at the maximum power under the current conditions. This is beneficial to improving the system's power generation efficiency. At the same time, this application issues the adjustment command when there is a power converter in a voltage-limited state, reducing the occupation of the communication channel and the amount of data on the communication link, which can reduce the possibility of errors in the adjustment of the output voltage characteristic value and improve accuracy.

[0070] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristics.

[0071] All power converters in the photovoltaic string respond to the communication signal upon receiving it, adjusting their output voltage characteristic values ​​according to the adjustment instructions included in the communication signal. This allows for timely adjustment of the output voltage characteristic values, ensuring that the power generation of the photovoltaic system is not affected by the output voltage characteristic values ​​of the power converters.

[0072] In some embodiments, the communication signal carries an adjustment coefficient, and the power converter can adjust its output voltage characteristic value according to the adjustment coefficient in the communication signal. For example, the adjusted output voltage characteristic value is the product of the current output voltage of the power converter and the adjustment coefficient.

[0073] In some other embodiments, the communication signal does not include an adjustment coefficient, and the power converter adjusts its output voltage characteristic value according to its own preset adjustment coefficient. For example, the adjusted output voltage characteristic value is the product of the power converter's current output voltage and the adjustment coefficient.

[0074] In some embodiments, the adjustment factor in the communication signal is equal to its own preset adjustment factor.

[0075] In some embodiments, under normal circumstances, both the adjustment factor in the communication signal and the preset adjustment factor of the power converter are greater than 1. When the inverter needs to lower the upper limit of the DC input voltage, the adjustment factor may be less than 1.

[0076] In some embodiments, the adjustment factor is, for example, the ratio of the upper limit of the inverter's DC input voltage to the current DC input voltage.

[0077] When a photovoltaic DC power supply is obstructed, under the adjustment command, the power converter connected to the abnormal photovoltaic DC power supply (the obstructed photovoltaic DC power supply) will lower its output voltage characteristic value, while the power converter connected to a normal photovoltaic DC power supply will raise its output voltage characteristic value. However, when the power converter connected to the abnormal photovoltaic DC power supply fails to receive the adjustment command due to communication failure or other problems, its output voltage characteristic value remains unchanged (i.e., it is not lowered). When the abnormal photovoltaic DC power supply returns to normal, an overvoltage problem may occur in the output voltage of the photovoltaic string.

[0078] To address the aforementioned technical issues, in some embodiments, the adjustment command is used to control the power converter in the photovoltaic string that is in a voltage-limiting state to adjust its output voltage characteristic value, and the power converter in the MPPT state automatically adjusts its output voltage characteristic value at regular intervals.

[0079] Although a power converter in MPPT state will receive adjustment commands, it will not respond to them. A power converter in MPPT state automatically adjusts its output voltage characteristics according to its own settings, and is not controlled by adjustment commands.

[0080] A power converter in MPPT state, for example, actively adjusts its own output voltage characteristic value at regular intervals.

[0081] A power converter in MPPT state adjusts its output voltage characteristic value according to its output voltage and a preset adjustment coefficient. For example, the adjusted output voltage characteristic value is equal to the product of the current output voltage and the adjustment coefficient.

[0082] A power converter in a voltage-limiting state can adjust its output voltage characteristic value according to the adjustment coefficient in the communication signal, or according to its own preset adjustment coefficient.

[0083] Since the power converter in MPPT state can actively adjust its output voltage characteristic value without being controlled by adjustment commands sent by the main control equipment or inverter, it can prevent the inverter's DC input voltage from becoming overvoltaged due to the lack of adjustment command control, thus improving the reliability of the system.

[0084] The following section provides a detailed explanation of the method for determining whether a power converter in a photovoltaic string is in a voltage-limiting state.

[0085] Inverters can determine whether a power converter is in a voltage-limiting state by applying a disturbance to the inverter's DC input, such as by applying a disturbance to the DC input voltage, and by observing the change in the inverter's DC input power before and after the disturbance.

[0086] Specifically, in some embodiments, the inverter can apply a perturbation in the direction of increasing DC input voltage. If the DC input power of the inverter after the perturbation is less than the DC input power before the perturbation, it is considered that there is a power converter in the photovoltaic string in a voltage-limiting state; otherwise, it is considered that there is no power converter in the photovoltaic string in a voltage-limiting state.

[0087] In some embodiments, the inverter can apply a perturbation in the direction of decreasing DC input voltage. If the DC input power of the inverter after the perturbation is greater than the DC input power before the perturbation, it is considered that there is a power converter in the photovoltaic string in a voltage-limiting state; otherwise, it is considered that there is no power converter in the photovoltaic string in a voltage-limiting state.

[0088] In some embodiments, the inverter can apply perturbations in the directions of increasing and decreasing DC input voltage. If, when the perturbation is applied in the direction of increasing DC input voltage, the DC input power of the inverter after the perturbation is less than the DC input power before the perturbation, and when the perturbation is applied in the direction of decreasing DC input voltage, the DC input power of the inverter after the perturbation is greater than the DC input power before the perturbation, then it is considered that there is a power converter in the photovoltaic string in a voltage-limiting state; otherwise, it is considered that there is no power converter in the photovoltaic string in a voltage-limiting state. By applying perturbations in both directions of increasing and decreasing voltage and making judgments, the accuracy of the judgment can be improved.

[0089] The method for adjusting the output voltage characteristic value is explained in detail below with reference to Figures 4-5.

[0090] In some embodiments, each power converter is provided with an output voltage characteristic value, which is used as the upper limit of the power converter's output voltage. The PV curves of the power converter's output power P and output voltage Vo are shown in Figure 4. Between points a and b (the constant power range), the power converter operates in MPPT mode, with a maximum output power of Pmpp. Between points b and c (the voltage-limiting range), the power converter operates in voltage-limiting mode, with an output voltage characteristic value of Vlim0. In this range, the power converter's output voltage is limited to the output voltage characteristic value Vlim0. When adjusting the output voltage characteristic value, for example, it can be adjusted from Vlim0 to Vlim0', where Vlim0' is the product of the power converter's current output voltage and the adjustment coefficient. The adjusted PV curve is, for example, curve S1 in the figure.

[0091] In other embodiments, each power converter is provided with multiple output voltage characteristic values. The PV curves of the output power P and output voltage Vo of the power converter are shown in Figure 5. Between points d and e (the constant power interval), the power converter operates in MPPT state, with a maximum output power of Pmpp; between points e and f (the voltage limiting interval), the power converter operates in voltage limiting state, and the output power of the power converter at point f is 0. The power converter includes a minimum output voltage characteristic value Vlim1 at point e, a maximum output voltage characteristic value Vlim2 at point f, and any number of output voltage characteristic values ​​between the minimum output voltage characteristic value Vlim1 and the maximum output voltage characteristic value Vlim2, where the maximum output voltage characteristic value Vlim2 is the upper limit of the output voltage of the power converter.

[0092] When the output voltage characteristic value is adjusted, the adjustment command controls the power converter to adjust at least part of its output voltage characteristic value according to the adjustment coefficient.

[0093] In some embodiments, multiple output voltage characteristic values ​​of the power converter are adjusted proportionally, and the adjusted output voltage characteristic values ​​are, for example, curves S2 and S2' in Figure 5.

[0094] Specifically, the adjusted maximum output voltage characteristic value Vlim2 is the product of the current output voltage of the power converter and the adjustment coefficient. The other output voltage characteristic values ​​are adjusted proportionally, so that the drooping characteristics of the power converter's PV curve do not need to be changed, and the power drop rate remains consistent before and after the adjustment.

[0095] In some embodiments, multiple output voltage characteristic values ​​of the power converter can be adjusted in different proportions.

[0096] In some embodiments, if the output voltage characteristic value calculated based on a certain output voltage characteristic value and an adjustment coefficient is greater than the maximum output voltage characteristic value Vlim2, then the output voltage characteristic value is adjusted to the maximum output voltage characteristic value Vlim2, for example as shown by curve S3 in Figure 5, thereby ensuring that the DC input voltage of the inverter does not exceed the upper limit of the DC input voltage.

[0097] In some embodiments, the maximum output voltage characteristic value Vlim2 is kept constant, the minimum output voltage characteristic value Vlim1 is adjusted according to the adjustment coefficient, and other output voltage characteristic values ​​are determined according to the adjusted minimum output voltage characteristic value Vlim1, the maximum output voltage characteristic value Vlim2, the maximum output power Pmpp, and the slope of the PV curve determined by the three, as shown by curve S4 in Figure 5.

[0098] In some embodiments, the minimum output voltage characteristic value Vlim1 can be kept constant, while the maximum output voltage characteristic value Vlim2 can be adjusted according to the adjustment coefficient. The adjusted maximum output voltage characteristic value Vlim2 can be the product of the current output voltage of the power converter and the adjustment coefficient. Other output voltage characteristic values ​​are determined according to the minimum output voltage characteristic value Vlim1, the adjusted maximum output voltage characteristic value Vlim2, the maximum output power Pmpp, and the slope of the PV curve determined by the three.

[0099] The above-mentioned adjustment method of at least one output voltage characteristic value, under the premise of ensuring that the DC input voltage of the inverter does not exceed the upper limit, adjusts the rate of change of the DC input power of the inverter by adjusting the slope of the redefined PV curve, so as to adapt to different application scenarios and improve the application range.

[0100] Furthermore, to prevent the unrestricted adjustment of the output voltage characteristic value of the power converter in MPPT state from causing overvoltage of the inverter's DC input voltage, an upper limit value can be set for the output voltage characteristic value of each power converter, as shown by the upper limit value Voh in Figures 4 and 5. When the output voltage characteristic value calculated by the power converter based on the current output voltage and the adjustment coefficient is greater than the upper limit value Voh, the output voltage characteristic value is set as the upper limit value Voh, for example, as shown by curve S5 in Figure 5.

[0101] The upper limit of the output voltage, Voh, is, for example, the rated output voltage of the power converter.

[0102] The following example illustrates how the control method provided in this application (taking the setting of only one output voltage characteristic value, which is the upper limit of the output voltage of the power converter) can quickly adjust the output voltage characteristic value when the photovoltaic DC power supply is blocked or malfunctions.

[0103] Assume a photovoltaic string includes 20 photovoltaic DC power supplies, of which 10 photovoltaic DC power supplies have a maximum power point of 250W (hereinafter referred to as the first photovoltaic DC power supply), and 10 photovoltaic DC power supplies have a maximum power point of 150W (hereinafter referred to as the second photovoltaic DC power supply). The upper limit of the inverter's DC input voltage is set to 880V, the operating voltage is set to 800V, and the adjustment coefficient is 1.1.

[0104] If all power converters are operating in MPPT state, the DC input voltage of the inverter is controlled by the inverter to be 800V. At this time, the photovoltaic string current is 5A. The output voltage of the power converter connected to the first photovoltaic DC power supply is 50V, and the output voltage of the power converter connected to the second photovoltaic DC power supply is 30V. Since each power converter is operating in MPPT state, it actively updates its own output voltage characteristic value. The output voltage characteristic value = current output voltage * 1.1. Therefore, the output voltage characteristic value of the power converter connected to the first photovoltaic DC power supply is 55V, and the output voltage characteristic value of the power converter connected to the second photovoltaic DC power supply is 33V.

[0105] When the second photovoltaic DC power supply malfunctions, such as due to shading, and its output power drops to 70W, the inverter's DC input voltage stabilizes at 800V. At this time, the photovoltaic string current drops to (250W*10+70W*10) / 800V=4A. The output voltage of the power converter connected to the first photovoltaic DC power supply rises to 62.5V, while the output voltage of the power converter connected to the malfunctioning photovoltaic DC power supply (second photovoltaic DC power supply) drops to 17.5V. Since the characteristic value of the output voltage of the power converter connected to the first photovoltaic DC power supply is 55V, which is less than the ideal output voltage of 62.5V, it switches from MPPT state to voltage limiting state. The output voltage of the power converter connected to the malfunctioning photovoltaic DC power supply (second photovoltaic DC power supply) is less than the characteristic value of the output voltage and still operates in MPPT state.

[0106] In actual operation, the output voltage of the power converter connected to the first photovoltaic DC power supply is limited to 55V. The output voltage of the power converter connected to the abnormal photovoltaic DC power supply is (800V-55V*10) / 10=25V. At this time, the photovoltaic string current is 70W / 25V=2.8A. The actual output power of the photovoltaic string is 2240W (154W*10+70W*10), which is less than the ideal output power of the photovoltaic string of 3200W (250W*10+70W*10), resulting in power generation loss.

[0107] By employing the control method described in this application, the inverter applies a disturbance to the DC input to determine if there is a power converter in the photovoltaic string that is in a voltage-limiting state. It then sends a communication signal including an adjustment command. After two adjustments, the power converter in the voltage-limiting state adjusts its output voltage characteristic value to 66.5V (55V*1.1*1.1) according to the adjustment command, which is greater than 62.5V. The power converter in the voltage-limiting state then exits the voltage-limiting state and enters the MPPT state.

[0108] Because the abnormal photovoltaic DC power supply is always working in MPPT state, it actively adjusts its output voltage characteristic value. After adjustment, its output voltage characteristic value is adjusted to ((800V-62.5V*10) / 10)*1.1=19.25V.

[0109] At this time, the actual output power of the photovoltaic string is equal to the ideal output power of 3200W.

[0110] The inverter then applies another disturbance, determines that there are no power converters in the photovoltaic string that are in a voltage-limiting state, and stops issuing adjustment commands. At this time, each power converter is in MPPT state and actively adjusts its own output voltage characteristic value at regular intervals.

[0111] According to an embodiment of this application, an inverter that implements the above-described control method is also provided, applied to the photovoltaic system shown in Figure 1. As shown in Figure 6, the inverter includes:

[0112] The first state determination module 202 is used to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state.

[0113] The first signal transmitting module 204 is used to send a communication signal to the photovoltaic string where the power converter in the voltage-limited state is located when there is a power converter in the photovoltaic string in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0114] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristics.

[0115] In some embodiments, the adjustment command is used to control the power converter in the photovoltaic string that is in a voltage-limiting state to adjust its output voltage characteristic value, and the power converter in the MPPT state to automatically adjust its output voltage characteristic value.

[0116] In some embodiments, the first state determination module applies a disturbance in the direction of increasing and / or decreasing DC input voltage, and determines whether there is a power converter in a voltage-limiting state based on the change in DC input power of the inverter before and after the disturbance.

[0117] The first state determination module 202 and the first signal transmission module 204 can be implemented by corresponding processors, such as a first state determination processor and a first signal transmitter. Since the processing and functions implemented by the inverter in the above embodiments correspond to the embodiments, principles, and examples of the aforementioned control method, any details not elaborated in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0118] This application proposes another control method for photovoltaic power generation, which can be applied to the main control device in the second embodiment above, as shown in Figure 7. The method includes the following steps:

[0119] S702: Send a status judgment command. The status judgment command is used to control the inverter to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state. The photovoltaic string includes multiple power converters connected in series and photovoltaic DC power supplies connected to the power converters respectively.

[0120] S704: If so, a communication signal is sent to the photovoltaic string containing the power converter in the voltage limiting state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0121] In some embodiments, the adjustment command is used to control all power converters in the photovoltaic string to adjust their output voltage characteristic values, or to control the power converters in the photovoltaic string that are in a voltage-limiting state to adjust their output voltage characteristic values, and the power converters in the MPPT state to automatically adjust their output voltage characteristic values.

[0122] In some embodiments, the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to its preset adjustment coefficient; or, the communication signal carries the adjustment coefficient, and the adjustment command controls the corresponding power converter to adjust the output voltage characteristic value according to the adjustment coefficient.

[0123] It should be noted that the inverter in this embodiment is only used to apply disturbances and determine whether there is a power converter in a voltage-limiting state. In addition to sending status judgment commands, the main control device also sends communication signals to the photovoltaic string where the power converter in the voltage-limiting state is located based on the inverter's judgment result, so as to control the corresponding power converter to adjust the output voltage characteristic value.

[0124] According to an embodiment of this application, a main control device for implementing the above control method is also provided, applied to the photovoltaic system shown in FIG2. As shown in FIG8, the main control device includes:

[0125] The second signal sending module 302 is used to send a status judgment instruction, which is used to control the inverter to determine whether there is a power converter in the photovoltaic string connected to the inverter that is in a voltage-limiting state.

[0126] The third signal transmitting module 304 is used to send a communication signal to the photovoltaic string where the power converter in the voltage-limited state is located when there is a power converter in the photovoltaic string in the voltage-limited state; the communication signal includes an adjustment command, which is used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

[0127] The second signal transmitting module 302 and the third signal transmitting module 304 can be implemented by corresponding processors, such as a second signal transmitter and a third signal transmitter. Since the processing and functions implemented by the main control device in the above embodiments correspond to the embodiments, principles, and examples of the aforementioned control methods, any details not fully described in this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0128] This application proposes a control method for a power converter, which is applied to the power converter in the first or second embodiment described above. The power converter can dynamically adjust its output voltage characteristic value. As shown in Figure 9, the method includes the following steps:

[0129] S902: If the power converter is in a voltage limiting state, adjust the output voltage characteristic value of the power converter according to the received communication signal including the adjustment command;

[0130] S904: If the power converter is in MPPT state, automatically adjust the output voltage characteristic value of the power converter.

[0131] In this embodiment, since the power converter in MPPT state can actively adjust its output voltage characteristic value without being controlled by the adjustment command sent by the main control device or the inverter, it can prevent the inverter from losing control due to the lack of adjustment command, which may lead to overvoltage of the DC input voltage of the inverter, thus improving the reliability of the system.

[0132] In some embodiments, a power converter in a voltage-limiting state receives an adjustment command, responds to the adjustment command, and adjusts the output voltage characteristic value according to its preset adjustment coefficient;

[0133] In some embodiments, the communication signal carries an adjustment coefficient, and the power converter in the voltage-limiting state responds to the adjustment command and adjusts the output voltage characteristic value according to the adjustment coefficient carried in the communication signal.

[0134] Although a power converter in MPPT state will receive communication signals, it will not respond to them. A power converter in MPPT state will automatically adjust its output voltage characteristics, independent of adjustment commands.

[0135] In some embodiments, a power converter in MPPT state actively adjusts its output voltage characteristic value according to a preset adjustment coefficient at regular intervals.

[0136] In some embodiments, the adjustment coefficient can be a preset value greater than 1, such as the ratio of the upper limit of the DC input voltage of the inverter to the current DC input voltage.

[0137] In some embodiments, when the communication signal carries an adjustment coefficient, the power converter in the MPPT state updates its internal preset adjustment coefficient to the adjustment coefficient carried in the communication signal.

[0138] In some embodiments, the power converter is provided with an output voltage characteristic value, the adjusted output voltage characteristic value being equal to the product of the current output voltage of the power converter and the adjustment coefficient.

[0139] In some other embodiments, the power converter has multiple output voltage characteristic values. When the output voltage characteristic values ​​are adjusted, the power converter adjusts at least a portion of its output voltage characteristic values ​​according to an adjustment factor.

[0140] If the output voltage characteristic value obtained according to the adjustment coefficient is greater than the maximum output voltage characteristic value among the multiple output voltage characteristic values ​​before adjustment, then the output voltage characteristic value is adjusted to the maximum output voltage characteristic value; if the output voltage characteristic value obtained according to the adjustment coefficient is greater than the upper limit of the output voltage of the power converter, then the output voltage characteristic value is adjusted to the upper limit of the output voltage.

[0141] In some embodiments, the power converter adjusts the minimum output voltage characteristic value among a plurality of output voltage characteristic values ​​to the product of the current output voltage and the adjustment coefficient, and adjusts the other output voltage characteristic values ​​proportionally or according to the maximum output voltage characteristic value and the adjusted minimum output voltage characteristic value among a plurality of output voltage characteristic values.

[0142] In other embodiments, the power converter adjusts the maximum output voltage characteristic value among a plurality of output voltage characteristic values ​​to the product of the current output voltage and the adjustment coefficient, and adjusts the other output voltage characteristic values ​​proportionally or according to the minimum output voltage characteristic value among a plurality of output voltage characteristic values ​​and the adjusted maximum output voltage characteristic value.

[0143] Since the control method of the power converter in the above embodiments corresponds to the embodiments, principles and examples of the control method for photovoltaic power generation described above, any details not covered in the description of this embodiment can be found in the relevant descriptions in the foregoing embodiments, and will not be repeated here.

[0144] This application proposes a power converter applied to the first or second embodiment described above, wherein the power converter adjusts its output voltage characteristic value. The power converter includes: a voltage limiting adjustment module, used to adjust the output voltage characteristic value of the power converter; if the power converter is in a voltage limiting state, adjusting the output voltage characteristic value of the power converter according to a received communication signal including an adjustment command; if the power converter is in an MPPT state, automatically adjusting the output voltage characteristic value of the power converter.

[0145] 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 corresponding to the power converters 102. The inverter 200 performs the steps of the photovoltaic power generation control method shown in FIG3.

[0146] 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.

[0147] This application proposes a photovoltaic system, as shown in FIG2, including an inverter 200, at least one photovoltaic string 100 connected to the inverter 200, and a main control device 300 connected to the inverter 200. The photovoltaic string 100 includes a plurality of power converters 102 connected in series and photovoltaic DC power supplies 101 connected to the power converters 102 respectively. The main control device 300 executes the steps of the photovoltaic power generation control method shown in FIG7.

[0148] 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.

[0149] 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.

[0150] 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 photovoltaic power generation, characterized by, The method comprises: judging whether there is a power converter in a voltage limiting state in a photovoltaic string connected with an inverter, the photovoltaic string comprising a plurality of power converters connected in series and photovoltaic direct-current power sources connected with the power converters correspondingly; if yes, sending a communication signal to the photovoltaic string in which the power converter in the voltage limiting state is located; the communication signal comprises an adjustment instruction for controlling at least one corresponding power converter in the photovoltaic string to adjust an output voltage characteristic value thereof.

2. The method of claim 1, wherein, The adjustment instruction is used for controlling all the power converters in the photovoltaic string to adjust the output voltage characteristic value thereof.

3. The method of claim 1, wherein, The adjustment instruction is used for controlling the power converter in the voltage limiting state in the photovoltaic string to adjust the output voltage characteristic value thereof and the power converter in the MPPT state to automatically adjust the output voltage characteristic value thereof.

4. The method of claim 1, wherein, The adjustment instruction controls the corresponding power converter to adjust the output voltage characteristic value according to a preset adjustment coefficient thereof. Or, the adjustment coefficient is carried in the communication signal, and the adjustment instruction controls the corresponding power converter to adjust the output voltage characteristic value according to the adjustment coefficient.

5. The method of claim 4, wherein, The adjustment coefficient is a ratio of an upper limit value of a direct-current input voltage of the inverter to a current direct-current input voltage.

6. The method of claim 4, wherein, Each of the power converters is provided with one output voltage characteristic value, and the adjustment instruction controls the output voltage characteristic value of the power converter to be the product of the current output voltage of the power converter and the adjustment coefficient.

7. The method of claim 4, wherein, Each of the power converters is provided with a plurality of output voltage characteristic values, and the adjustment instruction controls the power converter to adjust at least part of the output voltage characteristic values thereof according to the adjustment coefficient.

8. The method of claim 7, wherein, If the output voltage characteristic value obtained according to the adjustment coefficient is greater than the maximum output voltage characteristic value among the plurality of output voltage characteristic values before adjustment, the output voltage characteristic value is adjusted to the maximum output voltage characteristic value. Or, if the output voltage characteristic value obtained according to the adjustment coefficient is greater than the upper limit value of the output voltage of the power converter, the output voltage characteristic value is adjusted to the upper limit value of the output voltage.

9. The method of claim 7, wherein, The adjustment instruction controls the maximum output voltage characteristic value among the plurality of output voltage characteristic values to be the product of the current output voltage and the adjustment coefficient, and other output voltage characteristic values are adjusted correspondingly or according to the minimum output voltage characteristic value among the plurality of output voltage characteristic values and the adjusted maximum output voltage characteristic value.

10. The method of claim 1, wherein, A perturbation is applied to the direction in which the direct-current input voltage increases and / or decreases, and whether there is a power converter in the voltage limiting state is judged according to the change of the direct-current input power of the inverter before and after the perturbation.

11. An inverter applied to a photovoltaic system, the photovoltaic system further comprising at least one photovoltaic string connected to the inverter, the photovoltaic string comprising a plurality of power converters connected in series and photovoltaic direct current power sources connected to the power converters correspondingly, characterized in that, The inverter comprises: a first state judging module for judging whether there is a power converter in a voltage limiting state in a photovoltaic string connected with the inverter; a first signal sending module for sending a communication signal to the photovoltaic string in which the power converter in the voltage limiting state is located when there is a power converter in the voltage limiting state in the photovoltaic string; the communication signal comprises an adjustment instruction for controlling at least one corresponding power converter in the photovoltaic string to adjust an output voltage characteristic value thereof.

12. The inverter of claim 11, wherein, The adjustment instruction is used to control all power converters in the photovoltaic string to adjust their output voltage characteristic values, or the adjustment instruction is used to control the power converters in the voltage-limited state in the photovoltaic string to adjust their output voltage characteristic values, and the power converters in the MPPT state to automatically adjust their output voltage characteristic values.

13. The inverter of claim 11, wherein, The first state judging module applies a perturbation to the direction of increase and / or decrease of the DC input voltage, and judges whether there is a power converter in the voltage-limited state according to the change of the DC input power of the inverter before and after the perturbation.

14. A control method of photovoltaic power generation, characterized by, The method comprises: sending a state judging instruction, the state judging instruction being used to control the inverter to judge whether there is a power converter in the voltage-limited state in the photovoltaic string connected to the inverter, the photovoltaic string comprising a plurality of series-connected power converters and photovoltaic DC power sources connected to the power converters correspondingly; if yes, sending a communication signal to the photovoltaic string in which the power converter in the voltage-limited state is located; the communication signal comprises an adjustment instruction, the adjustment instruction being used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

15. The method of claim 14, wherein, The adjustment instruction is used to control all power converters in the photovoltaic string to adjust their output voltage characteristic values; or, control the power converters in the voltage-limited state in the photovoltaic string to adjust their output voltage characteristic values, and the power converters in the MPPT state to automatically adjust their output voltage characteristic values.

16. The method of claim 14, wherein, The adjustment instruction controls the corresponding power converter to adjust the output voltage characteristic value according to the preset adjustment coefficient of the power converter; or, the adjustment instruction carries the adjustment coefficient in the communication signal, and controls the corresponding power converter to adjust the output voltage characteristic value according to the adjustment coefficient.

17. A master control device applied to a photovoltaic system, the photovoltaic system further comprising at least one photovoltaic string and an inverter connected to the photovoltaic string, the photovoltaic string comprising a plurality of power converters connected in series and photovoltaic direct-current power sources connected to the power converters correspondingly, characterized in that, The master control device comprises: a second signal sending module, used to send a state judging instruction, the state judging instruction being used to control the inverter to judge whether there is a power converter in the voltage-limited state in the photovoltaic string connected to the inverter; a third signal sending module, used to send a communication signal to the photovoltaic string in which the power converter in the voltage-limited state is located when there is a power converter in the voltage-limited state in the photovoltaic string; the communication signal comprises an adjustment instruction, the adjustment instruction being used to control at least one corresponding power converter in the photovoltaic string to adjust its output voltage characteristic value.

18. A control method of a power converter, characterized by, The method comprises: if the power converter is in the voltage-limited state, adjusting the output voltage characteristic value of the power converter according to the received communication signal comprising the adjustment instruction; if the power converter is in the MPPT state, automatically adjusting the output voltage characteristic value of the power converter.

19. A photovoltaic system characterized by, The inverter and at least one photovoltaic string connected to the inverter, the photovoltaic string comprising a plurality of series-connected power converters and photovoltaic DC power sources connected to the power converters correspondingly, the inverter performing the steps of the method according to any one of claims 1-10.

20. A photovoltaic system characterized by, An inverter, at least one photovoltaic string connected to the inverter, and a master device connected to the inverter, the photovoltaic string comprising a plurality of power converters connected in series and photovoltaic DC power sources connected to the power converters, the master device performing the steps of the method of any of claims 14-16.

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