Photovoltaic inverter

Abstract

The utility model provides a photovoltaic inverter which is characterized in that a direct current side interface is connected with the direct current side of a DC / AC conversion circuit through a first DC / DC conversion circuit; furthermore, when EL detection needs to be carried out on the photovoltaic string, the photovoltaic string can be reversely operated in a rectification mode through the DC / AC conversion circuit, and then EL power supply is provided for the photovoltaic string to be detected through the first DC / DC conversion circuit; the power supply process can be automatically realized by the controller in the photovoltaic inverter, so that the problems of tedious and inconvenient detection process and high error rate caused by a manual detection scheme can be avoided, and the operation cost and the labor cost of detection personnel can be saved. Besides, due to the existence of the first DC / DC conversion circuit, a first-stage voltage reduction function can be provided for the reverse flow process, and a relatively high voltage obtained after reverse rectification of the DC / AC conversion circuit can be reduced, so that the finally obtained voltage is matched with a photovoltaic group string with a relatively low open-circuit voltage level, and the photovoltaic equipment is further prevented from being damaged due to relatively high reverse flow voltage.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a photovoltaic inverter. Background Art

[0002] EL (Electroluminescence) detection technology can effectively detect defects such as hidden cracks, fragments, broken edges, poor solder joints, and broken grids inside photovoltaic modules, which has guiding significance for power station operation and maintenance. During the detection process, it is necessary to transmit electrical energy to the photovoltaic modules (hereinafter referred to as reverse injection) to make the photovoltaic modules heat up, that is, emit light.

[0003] At present, the conventional backfeeding method is: the inspector unplugs the photovoltaic connector (such as the MC4 terminal) of the photovoltaic string from the location connected to the photovoltaic inverter (such as the input side of the combiner box), and inserts it into the built-in rectifier, which draws power from the grid, outputs DC energy according to the voltage and current set by the inspector, and transmits it to the photovoltaic string. However, this solution has the problems of inconvenient transportation, cumbersome process of plugging and unplugging terminals, and easy to make mistakes when plugging back in, resulting in confusion of string numbers and even possible faults such as short circuits.

[0004] In addition, there is also a solution in the prior art that uses the power converter itself to obtain energy from the power grid for backfeeding operations, which can solve the above-mentioned problems brought about by the manual detection solution; however, this solution is only applicable to systems with higher photovoltaic string voltages. For photovoltaic strings with lower open-circuit voltage levels, the photovoltaic equipment will be damaged due to the larger backfeeding voltage. Utility Model Content

[0005] In view of this, the present application provides a photovoltaic inverter to prevent a large backflow voltage from damaging photovoltaic equipment.

[0006] To achieve the above objectives, this application provides the following technical solutions:

[0007] The present application provides a photovoltaic inverter, comprising: a controller, a DC / AC conversion circuit and a first DC / DC conversion circuit; wherein:

[0008] The first side of the first DC / DC conversion circuit is used to connect the corresponding photovoltaic string through the DC side interface of the photovoltaic inverter;

[0009] The second side of the first DC / DC conversion circuit is connected to the DC side of the DC / AC conversion circuit;

[0010] The operating mode of the first DC / DC converter circuit includes transmitting electric energy from the second side thereof to the first side;

[0011] The AC side of the DC / AC conversion circuit serves as the AC side of the photovoltaic inverter;

[0012] The DC / AC conversion circuit and the first DC / DC conversion circuit are both controlled by the controller.

[0013] Optionally, the first DC / DC conversion circuit is: a Buck circuit;

[0014] The input end of the Buck circuit serves as the second side of the first DC / DC conversion circuit;

[0015] The output end of the Buck circuit serves as the first side of the first DC / DC conversion circuit.

[0016] Optionally, when the photovoltaic inverter operates in a reverse feeding mode and the reverse feeding setting voltage is lower than the peak value of the grid line voltage:

[0017] The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than or equal to the peak value of the grid line voltage;

[0018] The Buck circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage.

[0019] Optionally, when the photovoltaic inverter operates in a reverse feeding mode and the reverse feeding setting voltage is higher than the peak value of the grid line voltage:

[0020] The DC / AC conversion circuit works in a rectification mode, and the reference voltage on its DC side is the reverse injection setting voltage; the Buck circuit is in a closed state;

[0021] Alternatively, the DC / AC conversion circuit operates in a rectification mode, and a reference voltage on its DC side is greater than the feedback setting voltage; the Buck circuit operates in a step-down mode, and a reference voltage at its output end is the feedback setting voltage.

[0022] Optionally, the first DC / DC conversion circuit is: a Buck-Boost circuit;

[0023] The input end of the Buck-Boost circuit serves as the second side of the first DC / DC conversion circuit;

[0024] The output end of the Buck-Boost circuit serves as the first side of the first DC / DC conversion circuit.

[0025] Optionally, when the photovoltaic inverter operates in a reverse feeding mode and the reverse feeding setting voltage is lower than the peak value of the grid line voltage:

[0026] The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than or equal to the peak value of the grid line voltage;

[0027] The Buck-Boost circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage.

[0028] Optionally, when the photovoltaic inverter operates in a reverse feeding mode and the reverse feeding setting voltage is higher than the peak value of the grid line voltage:

[0029] The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is the reverse injection setting voltage; the Buck-Boost circuit is in a closed state;

[0030] Alternatively, the DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than the feedback setting voltage; the Buck-Boost circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage;

[0031] Alternatively, the DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is the peak value of the grid line voltage; the Buck-Boost circuit operates in a boost mode, and the reference voltage at its output end is the feedback setting voltage.

[0032] Optionally, a corresponding bypass switch is connected between at least one pole on both sides of the first DC / DC conversion circuit.

[0033] Optionally, the photovoltaic inverter further includes: at least one second DC / DC conversion circuit and at least one bypass switch; wherein,

[0034] The input end of the second DC / DC conversion circuit is used as a DC side corresponding circuit interface of the photovoltaic inverter to connect the corresponding photovoltaic string;

[0035] The output end of the second DC / DC conversion circuit is connected to the first side of the first DC / DC conversion circuit;

[0036] The second DC / DC conversion circuit has a bypass switch connected between at least one of its input and output ends;

[0037] The second DC / DC conversion circuit and the bypass switch are both controlled by the controller.

[0038] Optionally, when the photovoltaic inverter operates in a reverse charging mode, the bypass switch connected to the photovoltaic string to be detected is in a closed state.

[0039] Optionally, the photovoltaic inverter further includes: an AC power supply;

[0040] The input end of the AC power source draws power from the power grid;

[0041] The output end of the AC power supply is connected to the DC side of the DC / AC conversion circuit;

[0042] The AC power source is controlled by the controller.

[0043] The photovoltaic inverter provided by the present application has a DC side interface, which is connected to the DC side of the DC / AC conversion circuit through a first DC / DC conversion circuit; further, when it is necessary to perform EL detection on the photovoltaic string, the DC / AC conversion circuit can be reversely operated in the rectification mode, and then the first DC / DC conversion circuit can be used to provide EL power supply for the photovoltaic string to be detected; the power supply process can be automatically realized by the controller in the photovoltaic inverter, thereby avoiding the cumbersome and inconvenient detection process and the error-prone problems brought about by the manual detection scheme, and can also save the operating cost and manpower cost of the detection personnel. In addition, the existence of the first DC / DC conversion circuit can provide a first-level voltage reduction function for the reverse injection process, and can reduce the higher voltage obtained after the reverse rectification of the DC / AC conversion circuit, so that the final voltage is adapted to the photovoltaic string with a lower open circuit voltage level, thereby avoiding the large reverse injection voltage and damaging the photovoltaic equipment; and, by reducing the voltage of the first DC / DC conversion circuit to achieve soft start during EL detection, the second DC / DC conversion circuit in the string inverter can also select a unidirectional DC / DC conversion circuit, thereby reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings to be used in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0045] Figure 1 A schematic diagram of the structure of a photovoltaic inverter provided in an embodiment of the present application;

[0046] Figure 2 Another structural schematic diagram of a photovoltaic inverter provided in an embodiment of the present application;

[0047] Figure 3 A schematic diagram of a reverse IV characteristic curve of a photovoltaic module provided in an embodiment of the present application;

[0048] Figure 4 Another structural schematic diagram of a photovoltaic inverter provided in an embodiment of the present application;

[0049] Figure 5 Another schematic diagram of the structure of the photovoltaic inverter provided in the embodiment of the present application. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0051] In this application, the terms "comprises", "comprising" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0052] The present application provides a photovoltaic inverter to prevent a large backflow voltage from damaging photovoltaic equipment.

[0053] See also Figure 1 The photovoltaic inverter may be a centralized inverter, which specifically includes: a controller (not shown in the figure), a first DC / DC conversion circuit 102 and a DC / AC conversion circuit 103; wherein:

[0054] The first side of the first DC / DC conversion circuit 102 is used to connect at least one photovoltaic string through the DC side interface of the photovoltaic inverter, and the photovoltaic string includes a plurality of photovoltaic modules connected in series (PV 1 To PV m ); In practical applications, the DC side interface of the photovoltaic inverter can be connected to multiple photovoltaic strings through at least one combiner box.

[0055] The second side of the first DC / DC conversion circuit 102 is connected to the DC side of the DC / AC conversion circuit 103. In addition, a corresponding capacitor (such as C shown in the figure) can be connected between the positive and negative electrodes of the DC side of the DC / AC conversion circuit 103. bus ).

[0056] The AC side of the DC / AC conversion circuit 103 serves as the AC side of the photovoltaic inverter. In practical applications, at least one grid-connected switch may be provided between the AC side of the DC / AC conversion circuit 103 and the AC side of the photovoltaic inverter. Figure 1Two grid-connected switches (S inv_R , S inv_S , S inv_T , and,S g_R , S g_S , S g_T ) is used as an example to demonstrate, connecting the phases R, S, and T of the power grid respectively.

[0057] The DC / AC conversion circuit 103 and the first DC / DC conversion circuit 102 are both controlled by a controller.

[0058] In practical applications, the photovoltaic inverter can also be a string inverter, see Figure 2 , which is Figure 1 The invention also includes: at least one (n is shown as an example in the figure, where n is a positive integer) second DC / DC conversion circuit 101 and at least one bypass switch (S shown in the figure) 1 To S n );in:

[0059] The input end of the second DC / DC conversion circuit 101 is used as the DC side corresponding interface of the photovoltaic inverter, and is used to connect the corresponding photovoltaic string; the second DC / DC conversion circuit 101 can be connected to at least one photovoltaic string. When the number of photovoltaic strings connected to it is greater than 1, each photovoltaic string is connected in parallel and serves as a photovoltaic string connected to the photovoltaic inverter. Moreover, the positive and negative electrodes of the input end of the second DC / DC conversion circuit 101 can be connected with corresponding capacitors (such as the C capacitors shown in the figure). pv ).

[0060] The output end of the second DC / DC conversion circuit 101 is connected to the first side of the first DC / DC conversion circuit 102; Figure 2 As shown in , the output ends of the n second DC / DC conversion circuits 101 are connected in parallel to the first side of the first DC / DC conversion circuit 102 .

[0061] Furthermore, a corresponding bypass switch is connected between at least one of the input and output terminals of the second DC / DC conversion circuit 101; for each second DC / DC conversion circuit 101, Figure 2 As shown in the figure, a corresponding bypass switch (S shown in the figure) is connected between the positive pole of its input end and the positive pole of its output end. 1 To S n ); or, a corresponding bypass switch may be connected between the negative pole of its input terminal and the negative pole of its output terminal; or, a corresponding bypass switch may be connected between the positive pole of its input terminal and the positive pole of its output terminal, and between the negative pole of its input terminal and the negative pole of its output terminal; it depends on the specific application environment and is within the protection scope of this application.

[0062] Each second DC / DC conversion circuit 101 and each bypass switch are controlled by a controller.

[0063] It is worth noting that for the mainstream inverters currently used in the prior art, their topology determines that they will boost voltage when they are reverse rectified, that is, their DC bus voltage is at least the peak value of the grid line voltage. Therefore, for some special power stations, such as 320G2 with a 1500V DC system equipped with a 1000V system, there is a risk of damaging the PV modules when performing EL testing. The reason is that the reverse IV characteristic curve of the PV module is nonlinear, such as Figure 3 As shown in , when the actual reverse voltage applied is greater than a certain threshold, the reverse current is too large and there is a risk.

[0064] For example, for the 320G2-HX model, the open circuit voltage V OC The effective value of the grid line voltage is 900V, and the effective value of the grid line voltage is 800V. When the inverter of this model is reversely rectified, its minimum actual reverse voltage is 800V*sqrt(2)=1131V, which is more than 1.25V. OC ;according to Figure 3 It can be seen that when the EL function is turned on, excessive current may be injected into the PV string, causing irreversible damage to the PV modules and even the risk of burning. Figure 3 middle, I pv is the current of the photovoltaic module, V pv is the voltage of the photovoltaic module, I SC is the short-circuit current of the photovoltaic module, V OC is the open circuit voltage of the PV module.

[0065] The photovoltaic inverter provided in this embodiment is additionally provided with a first DC / DC conversion circuit 102, and its working mode includes transmitting electric energy from its second side to the first side to solve the above problem; Figure 2 Taking the string inverter shown in the figure as an example, the working principle of EL detection is introduced:

[0066] When EL detection is required, in order to realize EL detection power supply for each photovoltaic module in the photovoltaic string to be detected, the controller can control the second DC / DC conversion circuit 101 connected to the photovoltaic string to be detected to stop working, and at the same time control the bypass switch connected to the photovoltaic string to be detected to be in a closed state; and control the DC / AC conversion circuit 103 to rectify the electric energy received from the power grid so that its DC side obtains a certain voltage value; and then control the first DC / DC conversion circuit 102 to run in reverse, that is, the first DC / DC conversion circuit 102 The electric energy received on its second side is transmitted to its first side, so that the electric energy is transmitted from the AC side to the DC side of the photovoltaic inverter; and when the controller controls the first DC / DC conversion circuit 102 to operate in reverse, it can specifically control it to reduce the voltage, thereby reducing the voltage difference between the photovoltaic string to be detected and the DC side of the DC / AC conversion circuit 103, reducing the backflow current to the photovoltaic string to be detected, realizing soft start of EL detection, and avoiding damage to photovoltaic equipment due to large backflow voltage; and then providing EL detection power supply for the photovoltaic string to be detected by closing the corresponding bypass switch.

[0067] For the string inverter, after the second DC / DC conversion circuits 101 of the photovoltaic strings are connected in parallel, they are connected to the DC side of the DC / AC conversion circuit 103 through the first DC / DC conversion circuit 102; and each second DC / DC conversion circuit 101 has a corresponding bypass switch connected between at least one pole of its input and output ends. Furthermore, when it is necessary to perform EL detection on the photovoltaic strings, the DC / AC conversion circuit 103 can be reversely operated in the rectification mode, and then the bypass switch of the first DC / DC conversion circuit 102 and the corresponding second DC / DC conversion circuit 101 is sequentially used to provide EL power supply for the photovoltaic strings to be detected. For the centralized inverter, after the DC / AC conversion circuit 103 is reversely rectified, the corresponding electric energy will directly provide EL power supply for the photovoltaic strings to be detected through the first DC / DC conversion circuit 102.

[0068] for Figure 1 and Figure 2 The power supply process of the EL detection of the photovoltaic inverter under the two structures shown can be automatically realized by the internal controller, thereby avoiding the cumbersome and inconvenient detection process and the problem of easy errors caused by the manual detection scheme. Moreover, the operating cost and manpower cost of the detection personnel can be saved. In addition, through the step-down control of the newly added first DC / DC conversion circuit 102, the risk of damaging the photovoltaic components due to excessive back-feeding voltage can be avoided, and EL detection can be performed on photovoltaic strings with lower open circuit voltage levels.

[0069] It is worth noting that for the traditional string inverter, the reverse operation of its original DC / DC conversion circuit (that is, the second DC / DC conversion circuit 101 in this embodiment) can also be used to achieve the step-down conversion of the DC bus voltage obtained by the reverse rectification of the DC / AC conversion circuit; however, this solution requires that these DC / DC conversion circuits all adopt bidirectional DC / DC conversion circuits to be implemented, and when the number of photovoltaic strings in the photovoltaic array is huge, all DC / DC conversion circuits corresponding to each photovoltaic string must be selected in this way, which will inevitably lead to a significant increase in cost.

[0070] In this embodiment, the reverse buck function of the first DC / DC conversion circuit 102 can reduce the DC bus voltage obtained by reverse rectification of the DC / AC conversion circuit 103 to a range that can be received by the photovoltaic string, thereby providing the condition of directly supplying power to the photovoltaic string through the bypass switch, and realizing the buck soft start during reverse injection; so that the second DC / DC conversion circuit 101 in the string inverter does not need to further perform reverse buck conversion on the DC bus voltage; therefore, each second DC / DC conversion circuit 101 only uses a unidirectional DC / DC conversion circuit, such as a Boost type conversion circuit, that is, it is only used to realize the boost conversion under the normal grid-connected state. That is, in this embodiment, only one additional first DC / DC conversion circuit 102 is needed to realize the reverse soft start of all photovoltaic strings, which can reduce the selection cost of the second DC / DC conversion circuit 101, and thus reduce the overall cost of the string inverter.

[0071] In addition, the photovoltaic inverter provided in this embodiment operates in a grid-connected mode during normal operation. At this time, the controller in the string inverter will control each second DC / DC conversion circuit 101 to perform MPPT (Maximum Power Point Tracking) on ​​the photovoltaic strings connected thereto, and the controllers in the string inverter and the centralized inverter will control the reverse conversion function of the first DC / DC conversion circuit 102 to be turned off, and at the same time control the DC / AC conversion circuit 103 to invert the DC power received on its DC side to obtain corresponding AC power, and then transmit it to the power grid through a closed grid-connected switch, thereby realizing the grid-connected function of the overall circuit.

[0072] Preferably, in the photovoltaic inverter, a corresponding bypass switch may also be connected between at least one pole on both sides of the first DC / DC conversion circuit 102. Figure 4 (In Figure 2 As shown in FIG. 1 , a bypass switch S is connected between the positive electrodes on both sides of the first DC / DC conversion circuit 102. n+1; so that the first DC / DC conversion circuit 102 can be bypassed when the photovoltaic inverter works in the grid-connected mode. In practical applications, a corresponding bypass switch can also be connected between the negative electrodes on both sides of the first DC / DC conversion circuit 102; or, a corresponding bypass switch can also be connected between the positive electrodes on both sides of the first DC / DC conversion circuit 102, and between the negative electrodes on both sides, respectively. This is not limited here, and it can be determined according to the specific application environment, and all are within the protection scope of this application.

[0073] It is worth noting that, in the above embodiment, the first DC / DC conversion circuit 102 in the string inverter and the centralized inverter is mainly used for reverse operation, that is, its working mode at least includes transmitting electric energy from its second side to the first side to realize EL detection power supply.

[0074] If the first DC / DC conversion circuit 102 can only operate in reverse, then when the photovoltaic inverter operates normally, the bypass switch (i.e. Figure 4 S n+1 ) to transmit electric energy. In practical applications, the first DC / DC conversion circuit 102 may also adopt a topology capable of bidirectional operation, that is, a bidirectional DC / DC conversion circuit, which can transmit electric energy from its second side to the first side during EL detection, and can also transmit electric energy from its first side to the second side during normal operation. Regardless of whether the first DC / DC conversion circuit 102 can only operate in reverse or can operate in bidirectional mode, as long as it can at least provide a step-down conversion function during reverse operation, it is within the protection scope of the present application.

[0075] The first DC / DC conversion circuit 102 may specifically adopt a buck circuit or a buck-boost circuit, which is not specifically limited here and can be determined according to the actual application environment, all of which are within the protection scope of this application.

[0076] For example, the first DC / DC conversion circuit 102 is a Buck circuit. At this time, the input end of the Buck circuit serves as the second side of the first DC / DC conversion circuit 102 ; the output end of the Buck circuit serves as the first side of the first DC / DC conversion circuit 102 .

[0077] Alternatively, the first DC / DC conversion circuit 102 is a Buck-Boost circuit; in this case, the input end of the Buck-Boost circuit serves as the second side of the first DC / DC conversion circuit 102; and the output end of the Buck-Boost circuit serves as the first side of the first DC / DC conversion circuit 102.

[0078] In addition, the first DC / DC conversion circuit 102 may also be implemented by using other forms of circuits, and circuits that can achieve the above functions are all within the protection scope of this application.

[0079] However, for the first DC / DC conversion circuit 102 with different circuit implementation forms, the specific control methods may also be different. The following takes two circuit implementation forms as examples for explanation. Assuming that the peak value of the grid line voltage is V peak ,have:

[0080] (1) When the first DC / DC conversion circuit 102 is a Buck circuit:

[0081] When the photovoltaic inverter works in the reverse feeding mode, the corresponding reverse feeding setting voltage refers to the EL supply voltage required by the photovoltaic string to be detected.

[0082] If the PV inverter operates in the reverse mode and the reverse setting voltage is lower than the peak value of the grid line voltage V peak , then: the DC / AC conversion circuit 103 can be made to work in the rectification mode, and the reference voltage on the DC side is the peak value of the grid line voltage V peak The Buck circuit works in the step-down mode, and the reference voltage at its output end is the feedback setting voltage. Alternatively, the DC / AC conversion circuit 103 can also work in the rectification mode, and the reference voltage on its DC side is greater than the peak value of the grid line voltage V peak The Buck circuit operates in step-down mode, and the reference voltage at its output is the feedback setting voltage.

[0083] If the PV inverter operates in the reverse mode and the reverse setting voltage is higher than the peak value of the grid line voltage V peak , then: the DC / AC conversion circuit 103 can be operated in the rectification mode, and the reference voltage on its DC side is the feedback setting voltage; and the Buck circuit is in the off state. Alternatively, the DC / AC conversion circuit 103 can be operated in the rectification mode, and the reference voltage on its DC side is greater than the feedback setting voltage; and the Buck circuit can be operated in the step-down mode, and the reference voltage at its output end is the feedback setting voltage.

[0084] Taking the string inverter as an example, when the photovoltaic string to be detected is powered by EL detection, the bypass switch (i.e., S i ) is closed. If the reverse feed setting voltage is lower than the peak value of the grid line voltage V peak , the DC / AC conversion circuit 103 performs reverse rectification, and can directly control the bus voltage on its DC side to the peak value of the grid line voltage V peak, or the bus voltage on the DC side can be controlled to be higher than the peak value of the grid line voltage V peak , and then the first DC / DC conversion circuit 102 controls the photovoltaic string side voltage to be the reverse injection setting voltage. If the reverse injection setting voltage is higher than the peak value of the grid line voltage V peak , the first DC / DC conversion circuit 102 can be turned off, and the actual feedback voltage is controlled by the reverse rectification of the DC / AC conversion circuit 103; or the DC / AC conversion circuit 103 and the first DC / DC conversion circuit 102 can be made to run in reverse, and the feedback setting voltage is realized by two-stage step-down.

[0085] (2) When the first DC / DC conversion circuit 102 is a Buck-Boost circuit:

[0086] If the PV inverter operates in the reverse mode and the reverse setting voltage is lower than the peak value of the grid line voltage V peak , then: the DC / AC conversion circuit 103 can be made to work in the rectification mode, and the reference voltage on the DC side is the peak value of the grid line voltage V peak The Buck-Boost circuit works in the step-down mode, and the reference voltage at its output end is the reverse injection setting voltage. Alternatively, the DC / AC conversion circuit 103 can also work in the rectification mode, and the reference voltage on its DC side is greater than the peak value of the grid line voltage V peak ; The Buck-Boost circuit works in the step-down mode, and the reference voltage at its output end is the feedback setting voltage.

[0087] If the PV inverter operates in the reverse mode and the reverse setting voltage is higher than the peak value of the grid line voltage V peak , then: the DC / AC conversion circuit 103 can be operated in the rectification mode, the reference voltage on its DC side is the reverse injection setting voltage, and the Buck-Boost circuit is in the off state; or, the DC / AC conversion circuit 103 works in the rectification mode, the reference voltage on its DC side is greater than the reverse injection setting voltage; the Buck-Boost circuit works in the step-down mode, and the reference voltage at its output end is the reverse injection setting voltage; or, the DC / AC conversion circuit 103 works in the rectification mode, and the reference voltage on its DC side is the peak value of the grid line voltage V peak , and the Buck-Boost circuit works in the boost mode, and the reference voltage at its output end is the feedback setting voltage.

[0088] In practical applications, when the photovoltaic string to be detected is powered by EL detection, the bypass switch (ie, S i ) is closed. If the reverse feed setting voltage is lower than the peak value of the grid line voltage Vpeak , the DC / AC conversion circuit 103 performs reverse rectification and can directly control the bus voltage on its DC side to the peak value of the grid line voltage V peak , or the bus voltage on the DC side can be controlled to be higher than the peak value of the grid line voltage V peak , and the first DC / DC conversion circuit 102 is used to control the voltage on the photovoltaic string side to be the reverse injection setting voltage. If the reverse injection setting voltage is higher than the peak value of the grid line voltage V peak , then: the DC / AC conversion circuit 103 can control the bus voltage on its DC side to the peak value of the grid line voltage V peak Or it can be controlled to be greater than the set feedback voltage, and then the set feedback voltage is obtained through the first DC / DC conversion circuit 102; or the first DC / DC conversion circuit 102 can be turned off, and the actual feedback voltage is controlled by reverse rectification of the DC / AC conversion circuit 103.

[0089] It should be noted that whether to increase Figure 4 The bypass switch S shown in n+1 , which is related to the specific topology adopted by the first DC / DC conversion circuit 102. For example, when the Buck-Boost circuit adopts the FSBB (Four Switch Buck-Boost, four-switch Buck-Boost) topology, since bidirectional operation can be achieved, there is no need to add the bypass switch S n+1 , and energy flow in the reverse direction can also be achieved during normal operation; when the Buck-Boost circuit adopts other topologies, such as SEPIC (Single Ended Primary Inductor Converter), since it can only run in the reverse direction, it is necessary to add the bypass switch S n+1 , so that the photovoltaic inverter can realize the inverter function during normal operation.

[0090] When the first DC / DC conversion circuit 102 adopts circuits in other implementation forms, its control principle can be deduced by analogy, and will not be described in detail here.

[0091] That is, the existence of the first DC / DC conversion circuit 102 can provide a suitable supply voltage for the EL detection of the photovoltaic string with a low open circuit voltage level to avoid damage to the photovoltaic components; however, when the photovoltaic inverter works in the reverse injection mode, it is not required that the first DC / DC conversion circuit 102 must perform a step-down conversion, for example, when the reverse injection setting voltage is higher than the peak value of the grid line voltage V peak In this case, the first DC / DC conversion circuit 102 can be operated in reverse buck mode or can be turned off; it depends on the specific application environment and is within the protection scope of this application.

[0092] It is worth mentioning that, as far as EL detection is concerned, since it is necessary to obtain infrared photos with clean background noise and high contrast for fault diagnosis, this detection technology is preferably carried out at night; and at night, when the reverse rectification of the DC / AC conversion circuit 103 is used to transmit electric energy to the photovoltaic components to make the photovoltaic components heat up and emit light, the DC / AC conversion circuit 103 DC side bus voltage needs to reach a certain value, so that the DC / AC conversion circuit 103 can receive electric energy from the power grid after soft start.

[0093] Therefore, this embodiment provides another photovoltaic inverter, which is based on the above embodiment, such as Figure 5 (In Figure 2 As shown in the figure, it also includes: an AC power supply 104; an input end of the AC power supply 104 draws power from the power grid; an output end of the AC power supply 104 is connected to the DC side of the DC / AC conversion circuit 103; and the AC power supply 104 is controlled by a controller.

[0094] Under this structure, through the control of the controller, the first DC / DC conversion circuit 102 can be turned off when there is light during the day, and the photovoltaic inverter can normally realize the grid-connected function. When EL detection is required at night, in one example, the first DC / DC conversion circuit 102 can be turned off first, and a dedicated AC power supply 104 can be used to draw power from the grid, and the bus voltage on the DC side of the DC / AC conversion circuit 103 can be raised to near the peak value of the grid line voltage, and then the grid-connected switch is controlled to close and connect to the grid to complete the soft start; after that, the first DC / DC conversion circuit 102 can be controlled to realize voltage control on the photovoltaic string side.

[0095] In this embodiment, an AC power supply 104 is added between the DC / AC conversion circuit 103 and the power grid, so that when performing EL detection of reverse injection, the bus voltage is first raised by the AC power supply 104, and then connected to the power grid to reduce the voltage difference and complete the soft start. Therefore, this embodiment can not only support EL detection of photovoltaic strings with low open circuit voltage levels, but also, unlike the prior art that can only perform EL detection during the day, this embodiment can also realize the EL function at night.

[0096] The same and similar parts between the various embodiments in this specification can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0097] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present utility model.

[0098] With respect to the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other, so that professionals in the field can implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A photovoltaic inverter, characterized in that: include: controller, a DC / AC conversion circuit and a first DC / DC conversion circuit; wherein, The first side of the first DC / DC conversion circuit is used to connect the corresponding photovoltaic string through the DC side interface of the photovoltaic inverter; The second side of the first DC / DC conversion circuit is connected to the DC side of the DC / AC conversion circuit; The operating mode of the first DC / DC converter circuit includes transmitting electric energy from the second side thereof to the first side; The AC side of the DC / AC conversion circuit serves as the AC side of the photovoltaic inverter; The DC / AC conversion circuit and the first DC / DC conversion circuit are both controlled by the controller.

2. The photovoltaic inverter according to claim 1, characterized in that: The first DC / DC conversion circuit is a Buck circuit; The input end of the Buck circuit serves as the second side of the first DC / DC conversion circuit; The output end of the Buck circuit serves as the first side of the first DC / DC conversion circuit.

3. The photovoltaic inverter according to claim 2, characterized in that: When the photovoltaic inverter operates in the reverse feeding mode and the reverse feeding setting voltage is lower than the peak value of the grid line voltage: The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than or equal to the peak value of the grid line voltage; The Buck circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage.

4. The photovoltaic inverter according to claim 2, characterized in that: When the photovoltaic inverter operates in the reverse feeding mode and the reverse feeding setting voltage is higher than the peak value of the grid line voltage: The DC / AC conversion circuit works in a rectification mode, and the reference voltage on its DC side is the reverse injection setting voltage; the Buck circuit is in a closed state; Alternatively, the DC / AC conversion circuit operates in a rectification mode, and a reference voltage on its DC side is greater than the feedback setting voltage; the Buck circuit operates in a step-down mode, and a reference voltage at its output end is the feedback setting voltage.

5. The photovoltaic inverter according to claim 1, characterized in that: The first DC / DC conversion circuit is a Buck-Boost circuit; The input end of the Buck-Boost circuit serves as the second side of the first DC / DC conversion circuit; The output end of the Buck-Boost circuit serves as the first side of the first DC / DC conversion circuit.

6. The photovoltaic inverter according to claim 5, characterized in that: When the photovoltaic inverter operates in the reverse feeding mode and the reverse feeding setting voltage is lower than the peak value of the grid line voltage: The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than or equal to the peak value of the grid line voltage; The Buck-Boost circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage.

7. The photovoltaic inverter according to claim 5, characterized in that: When the photovoltaic inverter operates in the reverse feeding mode and the reverse feeding setting voltage is higher than the peak value of the grid line voltage: The DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is the reverse injection setting voltage; the Buck-Boost circuit is in a closed state; Alternatively, the DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is greater than the feedback setting voltage; the Buck-Boost circuit operates in a step-down mode, and the reference voltage at its output end is the feedback setting voltage; Alternatively, the DC / AC conversion circuit operates in a rectification mode, and the reference voltage on its DC side is the peak value of the grid line voltage; the Buck-Boost circuit operates in a boost mode, and the reference voltage at its output end is the feedback setting voltage.

8. The photovoltaic inverter according to any one of claims 1 to 7, characterized in that: A corresponding bypass switch is also connected between at least one pole on both sides of the first DC / DC conversion circuit.

9. The photovoltaic inverter according to any one of claims 1 to 7, characterized in that: Also includes: At least one second DC / DC conversion circuit and at least one bypass switch; wherein, The input end of the second DC / DC conversion circuit is used as a DC side corresponding circuit interface of the photovoltaic inverter to connect the corresponding photovoltaic string; The output end of the second DC / DC conversion circuit is connected to the first side of the first DC / DC conversion circuit; The second DC / DC conversion circuit has a bypass switch connected between at least one of its input and output ends; The second DC / DC conversion circuit and the bypass switch are both controlled by the controller.

10. The photovoltaic inverter according to claim 9, characterized in that: When the photovoltaic inverter operates in the reverse feeding mode, the bypass switch connected to the photovoltaic string to be detected is in a closed state.

11. The photovoltaic inverter according to any one of claims 1 to 7, characterized in that: Also includes: AC power supply; The input end of the AC power source draws power from the power grid; The output end of the AC power supply is connected to the DC side of the DC / AC conversion circuit; The AC power source is controlled by the controller.

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