A method for adaptive limiting control of output voltage of photovoltaic optimizer

Abstract

The present application discloses a method for adaptively limiting the output voltage of a photovoltaic optimizer, comprising the following steps: real-time collection of environmental parameters of the environment in which the photovoltaic module is located, and derivation of a voltage limit value update coefficient k of the photovoltaic optimizer based on the relationship between the environmental parameters, the photovoltaic module and the photovoltaic optimizer; in the operation stage of the photovoltaic optimizer, the output voltage limit value corresponding to the photovoltaic optimizer at the current moment is at least k times that of the previous moment. The beneficial effects of the present application: it can ensure that the output voltage of each photovoltaic optimizer rises slowly and is controllable in real time during the startup and operation of the photovoltaic optimizer, and the change trend of the output voltage of the photovoltaic module can be predicted in combination with the environmental parameters. In the whole working process, the voltage limit value update coefficient k changes adaptively with the environmental variables, which can significantly improve the accuracy of the output voltage limit control and ensure that the output voltage of the photovoltaic optimizer will not produce a large step.

Description

Technical Field

[0001] The present application relates to the technical field of renewable energy power generation, and in particular to a method for adaptively limiting output voltage of a photovoltaic optimizer. Background Art

[0002] In a user system with multiple PV modules connected in series, the maximum power points of each PV module are also quite different due to the large differences in lighting conditions, ambient temperature and shading conditions of different PV modules. A single inverter cannot achieve maximum power tracking of all PV modules at the same time. Therefore, it is necessary to add a PV optimizer to the PV module to achieve independent maximum power tracking of each PV module.

[0003] Existing photovoltaic optimizers use a control method in which the voltage limit value is given once. This control method may cause a large difference between the voltage limit value set in the voltage limit link and the stable voltage when the optimizer power is low during the startup phase. When the power of other optimizers changes significantly, the voltage will have a large step and there will be instability. In addition, the voltage limit value cannot be pre-adjusted according to environmental changes. Summary of the invention

[0004] One of the objectives of the present application is to provide a method for adaptively limiting output voltage of a photovoltaic optimizer that can solve at least one of the defects in the above-mentioned background technology.

[0005] In order to achieve at least one of the above-mentioned purposes, the technical solution adopted in the present application is: a method for adaptively limiting the output voltage of a photovoltaic optimizer, comprising the following steps: real-time collection of environmental parameters of the environment in which the photovoltaic components are located, and deriving a voltage limit value update coefficient k of the photovoltaic optimizer based on the relationship between the environmental parameters, the photovoltaic components and the photovoltaic optimizer; during the operation stage of the photovoltaic optimizer, the output voltage limit value corresponding to the photovoltaic optimizer at the current moment is at least k times that of the previous moment; wherein the voltage limit value update coefficient k is suitable for adaptively updating according to changes in environmental parameters at the current moment.

[0006] Preferably, the expression of the voltage limit value update coefficient k is as follows:

[0007] k = [ρ1·η·S·I rr [1-0.005(RH+25)]+ ρ2·T] / (U lim I m );

[0008] Among them, I rrrepresents the irradiation intensity, RH represents the air humidity, T represents the ambient temperature, ρ1 and ρ2 represent the correlation coefficients between the irradiation intensity and the ambient temperature and the output power of the photovoltaic module, η represents the efficiency factor of the photovoltaic module in converting solar energy into electrical energy, and S represents the surface area of ​​the photovoltaic module; I m Represents the output current of the photovoltaic optimizer, U lim Indicates the output voltage limit value at the previous moment.

[0009] Preferably, the derivation process of the voltage limit value update coefficient k is as follows:

[0010] Environmental parameters and the output power P of photovoltaic modules out The relationship between them is:

[0011] P out =ρ1·η·S·I rr [1-0.005(RH+25)]+ ρ2·T (1);

[0012] The output power of photovoltaic modules P out The relationship between it and the photovoltaic optimizer is:

[0013] P out =U m I m (2);

[0014] U m = k·U lim (3);

[0015] Combining equations (1), (2) and (3), we can obtain the expression of voltage limit value update coefficient k; where U m Represents the output voltage of the PV optimizer.

[0016] Preferably, in the process of the photovoltaic optimizer from startup to stable operation stage, the photovoltaic optimizer first performs a low-power startup stage with unlimited output voltage for a set time, and then limits the output voltage of the photovoltaic optimizer according to the updated voltage limit value update coefficient k until the photovoltaic optimizer enters the stable operation stage.

[0017] Preferably, during the operation phase of the photovoltaic optimizer, it is suitable to predict the output voltage of the photovoltaic module according to the collected environmental parameters, and then perform a preset update of the voltage limit value update coefficient k according to the predicted output voltage of the photovoltaic module.

[0018] Preferably, the output voltage prediction of the photovoltaic module includes the following process: fitting the radiation intensity change curve and the temperature change curve of the environment according to the collected environmental parameters; predicting the output voltage change trend of the photovoltaic module based on the slope change of the radiation intensity change curve and the temperature change curve.

[0019] Preferably, during the operation stage of the PV optimizer, if a sudden output power unloading occurs in some PV optimizers in a multi-PV optimizer scenario of a PV array, the PV optimizers that have not experienced a sudden output power unloading adjust the voltage limit value update coefficient k according to the state of the PV optimizers that have experienced a sudden output power unloading after a set time, so that the bus voltage of the system remains consistent before and after the sudden output power unloading of the PV optimizer.

[0020] Preferably, adjusting the voltage limit value update coefficient k based on the state of the photovoltaic optimizer in which a sudden output power unloading has occurred includes the following specific processes: obtaining the irradiation intensity change curve and the temperature change curve corresponding to the photovoltaic optimizer in which a sudden output power unloading has occurred; judging the change in the slope of the obtained irradiation intensity change curve and the temperature change curve; if the slopes of the irradiation intensity change curve and the temperature change curve slowly decrease, slowly increasing the voltage limit value update coefficient k corresponding to the photovoltaic optimizer in which a sudden output power unloading has not occurred; if the slopes of the irradiation intensity change curve and the temperature change curve rapidly decrease, rapidly increasing the voltage limit value update coefficient k corresponding to the photovoltaic optimizer in which a sudden output power unloading has not occurred by a constant multiple.

[0021] Preferably, in the initial startup stage of the photovoltaic optimizer, it is suitable to give an initial limiting value through the output voltage limiting link, so that the photovoltaic optimizer updates the output voltage limiting value according to the given initial limiting value after entering the startup stage; in the maximum power stage of the photovoltaic optimizer, if the output voltage of the photovoltaic optimizer is less than or equal to the current output voltage limiting value, the updating of the voltage limiting value update coefficient k will be stopped, so that the current output voltage limiting value remains constant.

[0022] Preferably, the working modes of the photovoltaic optimizer include MPPT mode and voltage adaptive limiting mode; in MPPT mode, the corresponding duty cycle is output according to the sampled values ​​of the output voltage and output current of the photovoltaic optimizer after passing through the MPPT loop; in voltage adaptive mode, the corresponding duty cycle is output according to the comparison result of the output voltage and voltage limiting value of the photovoltaic optimizer; the DC / DC unit corresponding to the photovoltaic optimizer performs switch tube control according to the minimum value of the duty cycles outputted respectively by the MPPT mode and the voltage adaptive limiting mode.

[0023] Preferably, the photovoltaic optimizer output voltage adaptive limiting control method is applied to a photovoltaic power generation system or a photovoltaic storage power generation system.

[0024] Compared with the prior art, the beneficial effects of this application are:

[0025] It can ensure that the output voltage of each photovoltaic optimizer rises slowly and is controllable in real time during the startup and operation of the photovoltaic optimizer, and the change trend of the output voltage of the photovoltaic module can be predicted in combination with the environmental parameters. During the whole working condition, the voltage limit value update coefficient k changes adaptively with the environmental variables, which can significantly improve the accuracy of the output voltage limit control and ensure that the output voltage of the photovoltaic optimizer will not produce a large step. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a control flow diagram of this application.

[0027] Figure 2 This is a schematic diagram of the installation structure of the environmental sensor in this application.

[0028] Figure 3 Voltage and power variation curves for a single voltage limit for a traditional PV optimizer.

[0029] Figure 4 The voltage and power variation curve diagram of the photovoltaic optimizer of the present application performing adaptive voltage limiting.

[0030] Figure 5 This is a schematic diagram of the control loop structure of one of the photovoltaic optimizers in this application.

[0031] Figure 6 The voltage and power variation curve diagram of the voltage limit of the photovoltaic optimizer of the present application when a sudden load occurs in other photovoltaic optimizers. DETAILED DESCRIPTION

[0032] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0033] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application.

[0034] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0035] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be connected, detachably connected, or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0037] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0038] One of the preferred embodiments of the present application is as follows: Figure 1As shown, a method for adaptively limiting the output voltage of a photovoltaic optimizer includes the following steps: collecting the environmental parameters of the photovoltaic module in real time, and deriving the voltage limit value update coefficient k of the photovoltaic optimizer based on the power relationship between the environmental parameters, the photovoltaic module and the photovoltaic optimizer. In the operation stage of the photovoltaic optimizer, the output voltage limit value corresponding to the photovoltaic optimizer at the current moment is at least k times that of the previous moment; wherein the voltage limit value update coefficient k can be adaptively updated according to the change of the environmental parameters at the current moment.

[0039] It is understandable that in the traditional photovoltaic optimizer control method, the output voltage limit value of the photovoltaic optimizer is given once; then in order to ensure that the photovoltaic optimizer can work stably, the given output voltage limit value generally corresponds to the maximum output voltage of the photovoltaic module, that is, the maximum output voltage of the photovoltaic optimizer cannot exceed the maximum output voltage of the photovoltaic module, thereby preventing the photovoltaic optimizer from overvoltage operation when the output power of some photovoltaic modules in the photovoltaic array is suddenly unloaded.

[0040] However, the output voltage limit of the above-mentioned traditional photovoltaic optimizer is only applicable to the scenario when the photovoltaic module works at the MPPT point, that is, the scenario when the photovoltaic optimizer works at the maximum output voltage. However, during the startup to stable operation stage of the photovoltaic optimizer, the photovoltaic modules in the photovoltaic array may experience a sudden unloading of output power. Since the output voltage limit value of the photovoltaic optimizer is much larger than the output voltage of the photovoltaic optimizer at this time, the output voltage of the photovoltaic optimizer that has not experienced a sudden unloading of output power will undergo an instantaneous mutation, which may cause circuit failure of the photovoltaic system.

[0041] In this embodiment, the voltage limit value update coefficient k related to the parameters of the photovoltaic module and the photovoltaic optimizer itself can be derived according to the environmental parameters of the photovoltaic module and the power relationship between the environmental parameters and the photovoltaic module and the photovoltaic optimizer. Then, during the normal operation of the photovoltaic optimizer, the voltage limit value update coefficient k can be adjusted in real time to ensure that the output voltage of the photovoltaic optimizer at any time corresponds to the output voltage limit value calculated by the voltage limit value update coefficient k, that is, close to it. Then, when the output power of some photovoltaic modules of the photovoltaic array is suddenly unloaded, for the photovoltaic optimizer that has not suddenly unloaded the output power, its output voltage will be limited by the corresponding output voltage limit value, and then the voltage limit value update coefficient k will reasonably adjust the output voltage limit value according to the current situation of the photovoltaic array to ensure that the photovoltaic optimizer that has not suddenly unloaded the output power can gradually raise the output voltage to avoid causing an instantaneous sudden shock to the output voltage, thereby protecting the working safety of the photovoltaic system.

[0042] Specifically, the photovoltaic optimizer output voltage adaptive limit control method of the present application can ensure that the output voltage of each photovoltaic optimizer rises slowly and is controllable in real time during the startup and operation of the photovoltaic optimizer. During the full working condition, the voltage limit value update coefficient k changes adaptively with the environmental variables, which can significantly improve the accuracy of the output voltage limit control and ensure that the output voltage of the photovoltaic optimizer will not produce a large step.

[0043] It should be known that the environmental parameters of the environment in which the photovoltaic modules are located include irradiation intensity, air humidity and ambient temperature. The above-mentioned environmental parameters can be collected by corresponding sensors; for example, the irradiation intensity can be collected by a light intensity sensor, the air humidity can be collected by a humidity sensor, and the ambient temperature can be collected by a temperature sensor. The specific structure and working principle of the light intensity sensor, humidity sensor and temperature sensor are well-known technologies to those skilled in the art, so they will not be elaborated here in detail. For the specific installation position of the light intensity sensor, humidity sensor and temperature sensor, the technicians in this field can determine it by themselves according to the actual installation environment. For the convenience of understanding, a specific example will be given below.

[0044] Specifically, Figure 2 As shown, the number of photovoltaic modules is n and they are marked as PV#1 to PV#n, and each photovoltaic module is connected to the DC / AC unit through the corresponding DC / DC unit. The light intensity sensor, humidity sensor and temperature sensor can be collectively referred to as environmental sensors, and each photovoltaic module corresponds to an environmental sensor. The environmental sensors corresponding to each photovoltaic module can be marked as environmental sensor #1 to environmental sensor #n; each environmental sensor is powered by the DC / DC unit of the corresponding photovoltaic module.

[0045] In this embodiment, for ease of understanding, the derivation process of the voltage output limit value update coefficient k may be described in detail below.

[0046] Environmental parameters and the output power P of photovoltaic modules out The relationship between them is:

[0047] P out =ρ1·η·S·I rr [1-0.005(RH+25)]+ ρ2·T (1).

[0048] Wherein, ρ1 and ρ2 represent the correlation coefficients between the irradiation intensity and the ambient temperature and the output power of the photovoltaic module, respectively. The specific values ​​can be set according to the actual needs of technicians in this field. η represents the efficiency factor of the photovoltaic module in converting solar energy into electrical energy. S represents the surface area of ​​the photovoltaic module. I rrrepresents the radiation intensity, RH represents the air humidity, and T represents the ambient temperature.

[0049] When the output voltage of the PV optimizer is not limited, the output power P of the PV module out The output voltage U of the photovoltaic optimizer m And the output current I m The relationship between them is:

[0050] P out =U m I m (2).

[0051] From the above content, it can be seen that the output voltage limit value U of the photovoltaic optimizer at the current moment is lim _0=k·U lim , U lim Indicates the output voltage limit value at the previous moment.

[0052] The most ideal state of this embodiment is that the output voltage of the photovoltaic optimizer is equal to the corresponding output voltage limit value at any time, that is, the photovoltaic optimizer works in the current limit voltage state at any time, which can most effectively suppress the output voltage step of the photovoltaic optimizer. Based on the above ideal state scenario, the following relationship can be obtained:

[0053] U m = k·U lim (3).

[0054] Combining the above equations (1), (2) and (3), we can get the expression of the voltage limit value update coefficient k as follows:

[0055] k = [ρ1·η·S·I rr [1-0.005(RH+25)]+ ρ2·T] / (U lim I m ).

[0056] It should be known that the above-mentioned derivation process of the voltage limit value update coefficient k is for the case of a single photovoltaic optimizer. For the scenarios of multiple photovoltaic optimizers corresponding to multiple photovoltaic components of a photovoltaic array, a separate derivation process can be performed on each photovoltaic optimizer when the photovoltaic array is operating normally to obtain the corresponding voltage limit value update coefficient k.

[0057] In this embodiment, the photovoltaic optimizer mainly includes the initial limit value given stage, the voltage unlimited low power start-up stage and the voltage limit value constant stage when the power reaches the upper limit from startup to stable operation. For easy understanding, the specific working process of the photovoltaic optimizer in each stage will be described in detail below.

[0058] In the initial limit value setting stage of the photovoltaic optimizer, that is, the photovoltaic optimizer is in the initial startup stage, the built-in output voltage limit link of the photovoltaic optimizer can be given an initial limit value. The given initial limit value can be compared with the output voltage of the current photovoltaic module. If the output voltage of the photovoltaic module is greater than the given initial limit value, a new initial limit value can be reassigned. After the photovoltaic optimizer enters the startup stage, the output voltage limit value can be updated according to the given initial limit value.

[0059] After the photovoltaic optimizer completes the setting of the initial limit value, it enters the low-power startup stage with unlimited voltage. Since the startup of the photovoltaic optimizer is basically synchronized with the startup of the photovoltaic module, that is, the photovoltaic module starts to output voltage after the irradiation intensity meets the startup requirements, the photovoltaic optimizer will also start to track the maximum output power of the photovoltaic module. Since the output power of the photovoltaic module is relatively low in the initial startup stage, even if a sudden unloading of the output power occurs, it will not have a significant impact on the output voltage of the photovoltaic optimizer. Therefore, in this stage, the photovoltaic optimizer can first perform a low-power startup with unlimited output voltage for a set time; this can effectively avoid unnecessary updates to the voltage limit value update coefficient k. The setting time for the photovoltaic optimizer to perform the low-power startup stage with unlimited voltage can be determined by the actual needs of those skilled in the art.

[0060] After completing the low-power startup phase with no voltage limit for the photovoltaic optimizer, the output voltage of the photovoltaic optimizer can be limited according to the updated voltage limit update coefficient k until the photovoltaic optimizer enters the stable operation phase. When the photovoltaic optimizer runs to the maximum power phase, if the output voltage of the photovoltaic optimizer is less than or equal to the current output voltage limit value, the update of the voltage limit update coefficient k will be stopped to keep the current output voltage limit value constant; this can further avoid unnecessary updates of the voltage limit update coefficient k. At this time, the photovoltaic optimizer is in the constant voltage limit phase where the power reaches the upper limit.

[0061] For ease of understanding, the specific working processes of the traditional photovoltaic optimizer and the photovoltaic optimizer of the present application may be briefly described below.

[0062] For the case of a single voltage limit of a traditional photovoltaic optimizer, such as Figure 3 As shown. When the output power of any photovoltaic module increases from time T1 to time T S When the time reaches a constant, the single voltage limit value can be given the corresponding voltage limit value U according to the voltage value corresponding to the maximum output power that the photovoltaic module can achieve. mi_lim Then, when the output voltage of the photovoltaic optimizer increases with the output power of the photovoltaic module, the output voltage U miWith the given voltage limit value U mi_lim The difference ΔU mi In the initial stage, it is larger, as the PV optimizer output voltage U mi The increase in the difference ΔU mi Gradually decreases to 0. During this process, the output power P of the photovoltaic optimizer PVi Equal to the output power of the PV panel.

[0063] When the adaptive voltage limiting method of the present application is adopted, Figure 4 As shown in the figure, when the output power of any photovoltaic module increases from time T1 to T S In the process of reaching a constant value at the moment, from moment T1 to moment T2, due to the low output voltage of the photovoltaic optimizer, the photovoltaic optimizer can enter the low-power startup phase with unlimited voltage. The voltage limit value U corresponding to the photovoltaic optimizer in this phase mi_lim Keep updated but always slightly larger than the output voltage U of the PV optimizer mi Until time T2, the output voltage U mi Equal to the corresponding voltage limit value U mi_lim Then the PV optimizer enters the stable operation stage. During this stage, the voltage limit value U mi_lim are updated once so that the output voltage U mi Step up, thus ensuring the output voltage U of the photovoltaic optimizer mi And the corresponding voltage limit value U mi_lim The difference ΔU at any time mi Very small or equal to 0, which can effectively suppress the occurrence of voltage steps.

[0064] In this embodiment, the working modes of the photovoltaic optimizer include the MPPT mode and the voltage adaptive limiting mode. The DC / DC unit connected to the photovoltaic optimizer is comprehensively controlled by the MPPT mode and the voltage adaptive limiting mode of the photovoltaic optimizer, which specifically includes the following control process:

[0065] like Figure 5 As shown in the figure, for the MPPT mode, when the actual output power of the PV module is less than the rated power of the DC / DC unit, and the output voltage of the PV module is less than the rated output voltage, the PV optimizer uses the MPPT algorithm to track the maximum power point of the PV module. At this time, the output power of the PV optimizer is controlled to operate at the maximum power point. mi and output current I mi The sampling value is output after passing through the MPPT loop to control the duty cycle of each switch tube in the corresponding DC / DC unit.

[0066] For the voltage adaptive limiting mode, it corresponds to the voltage unlimited low-power startup stage and the voltage limiting stage of stable operation of the photovoltaic optimizer. During the voltage limiting stage, the photovoltaic optimizer can automatically update the voltage limit value according to the environmental parameters. The specific update formula is as described above. During the voltage unlimited low-power startup stage, the voltage limit value is updated after the set time to a voltage limit value that no longer exceeds the voltage amplitude, and there is always a voltage limit value that is less than the maximum input voltage of the photovoltaic module in this stage; that is, Figure 4 In the low-power startup phase with no voltage limit from time T1 to T2, the voltage limit value is always less than the voltage input from the PV module to the PV optimizer at time T2. mi And the corresponding voltage limit value U mi_lim The comparison result output controls the duty cycle of each switch tube in the corresponding DC / DC unit.

[0067] Finally, the minimum value of the duty cycles output by the MPPT mode and the voltage adaptive mode can be taken as the actual duty cycle of each switch in the corresponding DC / DC unit.

[0068] It should be known to those skilled in the art that it takes time to update the voltage limit update coefficient k. Since the ideal state of this embodiment is that the output voltage of the photovoltaic optimizer is close to or consistent with the output voltage limit value, during the process of updating the voltage limit update coefficient k, the output voltage of the photovoltaic module may be greater than the output voltage of the photovoltaic optimizer, that is, the photovoltaic optimizer may have a hysteresis in tracking the MPPT point of the photovoltaic module. Therefore, in this embodiment, during the operation stage of the photovoltaic optimizer, the output voltage of the photovoltaic module can be predicted based on the collected environmental parameters, and then the voltage limit update coefficient k is preset and updated based on the predicted output voltage of the photovoltaic module, so as to ensure that the photovoltaic optimizer can accurately and quickly track the MPPT point of the photovoltaic module.

[0069] In this embodiment, the process of using environmental parameters to predict the output voltage of the photovoltaic module includes the following steps: fitting the radiation intensity change curve and the temperature change curve of the environment in which the photovoltaic module is located according to the environmental parameters of the environment in which the photovoltaic module is located collected by the sensor. The output voltage change trend of the photovoltaic module is predicted based on the slope changes of the radiation intensity change curve and the temperature change curve.

[0070] Specifically, when the slopes of the irradiation intensity change curve and the temperature change curve both rise significantly, it can be judged that the output power of the photovoltaic module will be greatly improved, and the corresponding output voltage will also be greatly improved. At this time, the value of the voltage limit value update coefficient k corresponding to the photovoltaic optimizer is relatively large. When the slopes of the irradiation intensity change curve and the temperature change curve both rise slowly, it can be judged that the output power of the photovoltaic module will increase slowly, and the corresponding output voltage will also increase slowly. At this time, the value of the voltage limit value update coefficient k corresponding to the photovoltaic optimizer is relatively small. When the slopes of the irradiation intensity change curve and the temperature change curve both begin to decrease, it can be judged that the output power of the photovoltaic module will decrease. At this time, the value of the voltage limit value update coefficient k corresponding to the photovoltaic optimizer also needs to be reduced to achieve precise control of the output voltage of the photovoltaic optimizer.

[0071] In this embodiment, for the multi-PV optimizer scenario of the PV array, the bus voltage U Bus The relationship between them is: Bus =U m1 +U m2 +……+ U mn ; Where n represents the number of PV optimizers corresponding to all PV modules in the PV array.

[0072] It should be noted that during the operation phase of the PV optimizer, if the output power of some PV optimizers in the multi-PV optimizer scenario corresponding to the PV array is suddenly unloaded, in order to ensure the working stability of the system, the bus voltage U Bus For ease of understanding, we can use U m1 The corresponding photovoltaic module is used as an example for a brief explanation. m1 When the corresponding photovoltaic assembly is blocked and the output power is suddenly unloaded, the output power of the corresponding photovoltaic optimizer will also be suddenly unloaded, and the output voltage of the corresponding photovoltaic optimizer will drop suddenly. Based on the need for stable operation of the system, the output power of the remaining photovoltaic optimizers needs to be increased, and the corresponding output voltage also needs to be increased, which may cause a step in the output voltage of the photovoltaic optimizer that has not experienced a sudden output power unloading. In this embodiment, due to the existence of the output voltage limit value, the instantaneous change of the output voltage of the photovoltaic optimizer that has not experienced a sudden output power unloading will be limited, thereby avoiding a large step in the output voltage of the photovoltaic optimizer.

[0073] In order to ensure the normal operation of the system, in this embodiment, the photovoltaic optimizer that has not experienced a sudden output power unloading adjusts the voltage limit value update coefficient k after a set time according to the state of the photovoltaic optimizer that has experienced a sudden output power unloading, so that the bus voltage of the system remains consistent before and after the sudden output power unloading of the photovoltaic optimizer occurs.

[0074] It should be noted that when the photovoltaic array is working, the output power of the photovoltaic module is not necessarily the maximum output power under the current irradiation intensity. The specific output power needs to be adjusted according to the system load power. Therefore, when the output power of some photovoltaic modules is suddenly unloaded, the remaining photovoltaic modules still have room for output power increase.

[0075] Specifically, the adjustment of the voltage limit value update coefficient k based on the state of the photovoltaic optimizer that has experienced a sudden output power unloading includes the following specific processes: obtaining the irradiation intensity change curve and the temperature change curve corresponding to the photovoltaic optimizer that has experienced a sudden output power unloading; judging the change in the slope of the obtained irradiation intensity change curve and the temperature change curve. If the slope of the irradiation intensity change curve and the temperature change curve slowly decreases, the voltage limit value update coefficient k corresponding to the photovoltaic optimizer that has not experienced a sudden output power unloading is slowly increased; if the slope of the irradiation intensity change curve and the temperature change curve rapidly decreases, the voltage limit value update coefficient k corresponding to the photovoltaic optimizer that has not experienced a sudden output power unloading is rapidly increased by a constant multiple.

[0076] It should be known that when some PV optimizers experience sudden output power unloading, the entire system needs to achieve power balance, that is, bus voltage balance, in a relatively short period of time. If the slopes of the irradiance intensity change curve and the temperature change curve slowly decrease, it means that the corresponding PV optimizer has a relatively slow sudden output power unloading, that is, the power drop of the PV module per unit time is relatively small. At this time, the voltage limit value update coefficient k corresponding to the PV optimizer that has not experienced sudden output power unloading only needs to be increased slowly, and the corresponding number of updates is also relatively small, so there is enough time to perform the update calculation of the voltage limit value update coefficient k. If the slopes of the irradiation intensity change curve and the temperature change curve drop rapidly, it means that the output power of the corresponding photovoltaic optimizer is unloaded quickly, that is, the power of the photovoltaic module drops more per unit time. At this time, the voltage limit value update coefficient k corresponding to the photovoltaic optimizer without output power unloading needs to be increased rapidly. If the voltage limit value update coefficient k is updated according to the aforementioned update calculation method, multiple updates may be required. In this case, the voltage limit value update coefficient k can be adjusted according to a constant multiple. After the output power unloading of the subsequent photovoltaic optimizer is eliminated, the voltage limit value update coefficient k can be updated and calculated again according to the environmental parameters.

[0077] For ease of understanding, a simple description of the voltage limit setting process when a sudden output power unloading occurs to some photovoltaic optimizers in a multi-photovoltaic optimizer scenario corresponding to a photovoltaic array is provided below.

[0078] Specifically, Figure 6As shown in the figure, when the output power of some photovoltaic optimizers in the multi-photovoltaic optimizer scenario corresponding to the photovoltaic array is suddenly unloaded at time T2. For the photovoltaic optimizers whose output power is not suddenly unloaded, the output voltage U mi is equal to the corresponding voltage limit value U mi_lim Therefore, at time T2, the output voltage U of the photovoltaic optimizer without sudden output power unloading mi There will not be a step immediately. Then, within the set time, according to the output power of the photovoltaic optimizer with sudden unloading, the output power increase of the photovoltaic optimizer without sudden unloading can be calculated, and then the voltage limit value U of the photovoltaic optimizer at the current moment based on the corresponding output power increase can be calculated. mi_lim , then the output voltage U of the PV optimizer mi The speed is increased according to the output power change degree of the photovoltaic optimizer that has sudden unloading, until T S When the output power of the photovoltaic optimizer reaches stability, the output voltage of the photovoltaic optimizer also reaches the corresponding U mi_lim of stable state.

[0079] In this embodiment, the photovoltaic optimizer output voltage adaptive limiting control method of the present application can be applied not only to photovoltaic power generation systems, but also to photovoltaic storage power generation systems. More specifically, when the photovoltaic optimizer output voltage adaptive limiting control method of the present application is applied to the above-mentioned power generation system, it can not only adapt to the scenario where all photovoltaic modules are equipped with photovoltaic optimizers, but also adapt to the scenario where some photovoltaic modules are equipped with photovoltaic optimizers.

[0080] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A photovoltaic optimizer output voltage adaptive limiting control method, characterized in that: The steps include: Collect the environmental parameters of the environment where the photovoltaic modules are located in real time, and derive the voltage limit value update coefficient k of the photovoltaic optimizer based on the relationship between the environmental parameters, the photovoltaic modules and the photovoltaic optimizer; During the operation phase of the photovoltaic optimizer, the output voltage limit value corresponding to the photovoltaic optimizer at the current moment is at least k times that at the previous moment; wherein the voltage limit value update coefficient k is suitable for adaptively updating according to the change of the environmental parameters at the current moment; The expression of voltage limit value update coefficient k is as follows: ； Among them, I rr represents the irradiation intensity, RH represents the air humidity, T represents the ambient temperature, ρ1 and ρ2 represent the correlation coefficients between the irradiation intensity and the ambient temperature and the output power of the photovoltaic module, η represents the efficiency factor of the photovoltaic module in converting solar energy into electrical energy, S represents the surface area of ​​the photovoltaic module, and I m Represents the output current of the photovoltaic optimizer, U lim Indicates the output voltage limit value at the previous moment; During the operation phase of the PV optimizer, the output power of some PV optimizers in the multi-PV optimizer scenario of the PV array suddenly unloads; the PV optimizers that have not experienced a sudden unloading of output power adjust the voltage limit value update coefficient k according to the state of the PV optimizers that have experienced a sudden unloading of output power after a set time, so that the bus voltage of the system remains consistent before and after the sudden unloading of the output power of the PV optimizer; The adjustment of the voltage limit value update coefficient k based on the photovoltaic optimizer state where the output power sudden unloading has occurred includes the following specific processes: Obtaining the irradiance intensity change curve and temperature change curve corresponding to the photovoltaic optimizer that has experienced a sudden output power unloading; Determine the slope changes of the obtained irradiation intensity change curve and temperature change curve; If the slopes of the irradiance intensity change curve and the temperature change curve decrease slowly, the voltage limit value update coefficient k corresponding to the photovoltaic optimizer without output power sudden unloading is slowly increased; If the slopes of the irradiance intensity variation curve and the temperature variation curve decrease rapidly, the voltage limit value update coefficient k corresponding to the photovoltaic optimizer without sudden output power unloading is rapidly increased by a constant multiple.

2. The photovoltaic optimizer output voltage adaptive limiting control method according to claim 1, characterized in that: The derivation process of the voltage limit value update coefficient k is as follows: Environmental parameters and the output power P of photovoltaic modules out The relationship between them is: （1）； The output power of the photovoltaic module P out The relationship between it and the photovoltaic optimizer is: （2）； （3）； Combining equations (1), (2) and (3), we can obtain the expression of voltage limit value update coefficient k; where U m Represents the output voltage of the PV optimizer.

3. The photovoltaic optimizer output voltage adaptive limiting control method according to claim 1, characterized in that: In the process from the start-up to the stable operation stage of the photovoltaic optimizer, the photovoltaic optimizer first performs a low-power start-up stage with unlimited output voltage for a set time; Then, the output voltage of the photovoltaic optimizer is limited according to the updated voltage limit value update coefficient k until the photovoltaic optimizer enters a stable operation stage.

4. The photovoltaic optimizer output voltage adaptive limiting control method according to any one of claims 1 to 3, characterized in that: During the operation phase of the photovoltaic optimizer, it is suitable to predict the output voltage of the photovoltaic module according to the collected environmental parameters, and then perform a preset update of the voltage limit value update coefficient k according to the predicted output voltage of the photovoltaic module.

5. The photovoltaic optimizer output voltage adaptive limiting control method according to claim 4, characterized in that: The output voltage prediction of PV panels includes the following process: According to the collected environmental parameters, the radiation intensity change curve and temperature change curve of the environment are fitted; The output voltage variation trend of the photovoltaic module is predicted based on the slope changes of the radiation intensity variation curve and the temperature variation curve.

6. The photovoltaic optimizer output voltage adaptive limiting control method according to claim 1, characterized in that: In the initial startup phase of the photovoltaic optimizer, it is suitable to give an initial limit value through the output voltage limit link, so that the photovoltaic optimizer updates the output voltage limit value according to the given initial limit value after entering the startup phase; In the maximum power stage of the photovoltaic optimizer, if the output voltage of the photovoltaic optimizer is less than or equal to the current output voltage limit value, the updating of the voltage limit value update coefficient k will be stopped to keep the current output voltage limit value constant.

7. The photovoltaic optimizer output voltage adaptive limiting control method according to claim 1, characterized in that: The working modes of the photovoltaic optimizer include MPPT mode and voltage adaptive limiting mode; In MPPT mode, the corresponding duty cycle is output according to the sampled values ​​of the output voltage and output current of the photovoltaic optimizer after passing through the MPPT loop; In the voltage adaptive mode, the corresponding duty cycle is output according to the comparison result between the output voltage of the photovoltaic optimizer and the voltage limit value; The DC / DC unit corresponding to the photovoltaic optimizer performs switch control according to the minimum value of the duty cycle output by the MPPT mode and the voltage adaptive limiting mode respectively.

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