Load limiting operation method of inverter system

Abstract

The invention discloses a load-limiting operation method of an inverter system. The method comprises the following steps: determining a first position of the current load-limiting operation power of the inverter system in a working curve; collecting the current operation data of the inverter system to judge the loss of the inverter system at the first position; and if the loss of the inverter system at the first position accords with a preset value, the inverter system keeps load-limited operation at the first position, otherwise, the inverter system is switched to a second position of the working curve. The method has the beneficial effects that the loss data of the inverter system at different positions can be judged by collecting the current operation data of the inverter system, so that the inverter system can be switched to a low-loss position, and the loss of the inverter system can be effectively balanced. The whole switching process is realized in a pure software mode, and the switching smoothness can be effectively improved.

Description

Technical Field

[0001] The present application relates to the field of new energy power generation, and particularly to a method for limiting the load operation of an inverter system. Background Art

[0002] Taking photovoltaic power generation as an example, as Figure 1 shown is a schematic diagram of the architecture of a typical photovoltaic inverter system in the prior art. Each photovoltaic string in the front stage is connected to a corresponding DC / DC unit, and then all the DC / DC units are connected in parallel at the bus, and are connected to the grid through a DC / AC unit.

[0003] As Figure 2 shown, it is Figure 1 the corresponding photovoltaic working curve when the photovoltaic inverter system is working. The curve can be divided from the highest point MPPT position of the curve. The curve segment on the left side of the highest point can be defined as the left slope, and the curve segment on the right side of the highest point can be defined as the right slope. When the photovoltaic over-matching is serious and the light intensity is relatively large, it is necessary to limit the load operation of the system at this time. Generally, the load can be limited to operate on the left slope of the curve, or it can be limited to operate on the right slope of the curve.

[0004] When the system is limited to operate on the right slope, the corresponding bus voltage is relatively high, which means that the loss of the DC / AC unit is relatively high, and the loss of the DC / DC unit is relatively small. When the system is limited to operate on the left slope, the corresponding bus voltage is relatively low, which means that under the same power condition, the input current of the DC / DC unit is relatively large, and thus the loss of the DC / DC unit is relatively high. Therefore, how to ensure the loss balance of the system during the load-limiting operation is a technical problem to be solved by those skilled in the art. Summary of the Invention

[0005] One of the purposes of the present application is to provide a method for limiting the load operation of an inverter system that can solve at least one defect in the above background art.

[0006] To achieve at least one of the above purposes, the technical solution adopted by the present application is: a method for limiting the load operation of an inverter system, including the following steps: determining a first position of the current load-limiting operation power of the inverter system in the working curve; collecting the current operation data of the inverter system to judge the loss of the inverter system at the first position; if the loss of the inverter system at the first position meets a preset value, the inverter system maintains the load-limiting operation at the first position, otherwise the inverter system will switch to a second position of the working curve; wherein, the load-limiting power values at the first position and the second position are equal but are respectively located on both sides of the highest point of the working curve.

[0007] Preferably, the current operation data of the inverter system includes the temperature data of the power unit; the inverter system is adapted to judge the loss of the inverter system at the current first position according to the comparison between the current temperature of the power unit and the threshold value.

[0008] Preferably, the power unit of the inverter system includes a DC / DC unit and a DC / AC unit; when the first position is on the left slope to the left of the highest point of the working curve, if the current temperature of the DC / DC unit is greater than the set first threshold value, and at the same time the current temperature of the DC / AC unit is less than the set second threshold value, at this time the loss of the inverter system does not meet the preset value, and the load-limiting operation position of the inverter system will switch from the left slope to the right slope; when the first position is on the right slope to the right of the highest point of the working curve, if the current temperature of the DC / DC unit is less than the set first threshold value, and at the same time the current temperature of the DC / AC unit is greater than the set second threshold value, at this time the loss of the inverter system does not meet the preset value, and the load-limiting operation position of the inverter system will switch from the right slope to the left slope.

[0009] Preferably, a loss prediction model of the inverter system is constructed based on the electrical parameters of the current operation data of the inverter system, and the loss of the inverter system at the second position is predicted according to the obtained loss prediction model; the predicted result is used as the preset value to compare with the loss of the inverter system at the first position; if the loss of the inverter system at the first position is greater than the preset value, the inverter system will switch from the first position to the second position, otherwise the inverter system remains in load-limiting operation at the first position.

[0010] Preferably, the electrical parameters of the current operation data of the inverter system include the grid voltage, the operating power of the inverter system, and the output voltage of the power generation unit in the inverter system.

[0011] Preferably, the process of the inverter system switching from the right slope corresponding to the first position to the left slope corresponding to the second position is as follows: the multiple power generation units of the inverter system are divided into multiple groups according to the set quantity, and each group includes at least one power generation unit; all the power generation units in one group are short-circuited, and then the MPPT tracking of the left slope is carried out on the short-circuited power generation units until the operating power of all the power generation units in this group reaches the second position; the above process is repeated in sequence for the remaining multiple groups of power generation units until the operating powers of all the power generation units of the inverter system are located at the second position.

[0012] Preferably, the process of the inverter system switching from the right slope corresponding to the first position to the left slope corresponding to the second position is as follows: the operating power of all the power generation units of the inverter system is decreased by ΔP to the third position on the same side as the first position; the multiple power generation units of the inverter system are divided into multiple groups according to a set number, and each group includes at least one power generation unit; the operating power of all the power generation units in one group is lifted along the right slope to the highest point, and then the operating power is decreased along the left slope to the fourth position with the same power as the third position; the above process is sequentially repeated for the remaining multiple groups of power generation units until the operating power of all the power generation units of the inverter system is located at the fourth position; the operating power of all the power generation units of the inverter system is lifted by ΔP so that the operating power of all the power generation units rises from the fourth position to the second position.

[0013] Preferably, let the total number of power generation units of the inverter system be N, and the operating power of the power generation units before power reduction be P limit ; the value of the number of power generation units X in each group is: X ≤ N·ΔP / (P MPPT - P limit ); where, P MPPT represents the power value corresponding to the highest point of the working curve.

[0014] Preferably, the process of the inverter system switching from the left slope corresponding to the first position to the right slope corresponding to the second position is as follows: first, drive blocking is performed on all the power units of the inverter system so that all the power generation units operate at the open-circuit voltage position; then, the drive blocking of all the power units of the inverter system is released for grid feeding, and MPPT tracking of the right slope is performed on the inverter system until the operating power of all the power generation units is located at the second position.

[0015] Preferably, the process of the inverter system switching from the left slope corresponding to the first position to the right slope corresponding to the second position is as follows: the operating power of all the power generation units of the inverter system is decreased by ΔP to the third position on the same side as the first position; the multiple power generation units of the inverter system are divided into multiple groups according to a set number, a sequence is set for the multiple groups, and each group includes at least one power generation unit; the operating power of all the power generation units in the first group is lifted along the left slope to the highest point, and then the operating power is decreased along the right slope to the fourth position with the same power as the third position; all the power generation units in the second group are opened, so that all the power generation units in the second group operate at the fifth position on the right slope, and MPPT tracking on the right slope is performed on all the power generation units in the second group until the operating power of all the power generation units in the second group is at the fourth position; the switching process of the second group of power generation units is repeated for the remaining power generation unit groups in sequence until all the power generation units of the inverter system operate at the fourth position; the operating power of all the power generation units of the inverter system is lifted by ΔP, so that the operating power of all the power generation units rises from the fourth position to the second position.

[0016] Compared with the prior art, the beneficial effects of the present application are as follows:

[0017] By collecting the current operating data of the inverter system, the loss data of the inverter system at different positions can be judged. Furthermore, the inverter system can switch to a position with lower loss, thereby effectively balancing the loss of the inverter system. The entire switching process is realized by a pure software method, which can effectively improve the smoothness of the switching. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of a conventional photovoltaic inverter system.

[0019] Figure 2 It is a schematic diagram of a photovoltaic working curve corresponding to the operation of a conventional photovoltaic inverter system.

[0020] Figure 3 It is a schematic diagram of the overall working process of the present application.

[0021] Figure 4 It is a schematic diagram of the process of load limit operation switching based on the temperature monitoring of the power unit in the present application.

[0022] Figure 5 It is a schematic diagram of the process of load limit operation switching based on loss prediction in the present application.

[0023] Figure 6 It is a schematic diagram of the working curve of one example of the load limit operation switching of the inverter system in the present application from the right slope to the left slope.

[0024] Figure 7Schematic diagram of the short - circuit architecture of the PV string PV#1 in the inverter system of the present application.

[0025] Figure 8 For the inverter system of the present application during Figure 6 Schematic diagram of the control flow of the control loop during the switching process shown.

[0026] Figure 9 Schematic diagram of the working curve of another example of the load - limit operation switching from the right slope to the left slope of the inverter system of the present application.

[0027] Figure 10 For the inverter system of the present application during Figure 9 Schematic diagram of the control flow of the control loop during the switching process shown.

[0028] Figure 11 Schematic diagram of the working curve of one example of the load - limit operation switching from the left slope to the right slope of the inverter system of the present application.

[0029] Figure 12 For another example of the load - limit operation switching from the left slope to the right slope of the inverter system of the present application, the working curve is shown Figure 1 .

[0030] Figure 13 For another example of the load - limit operation switching from the left slope to the right slope of the inverter system of the present application, the working curve is shown Figure 2 . Detailed implementation manners

[0031] Next, in combination with the detailed implementation manners, the present application will be further described. It should be noted that in the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above - mentioned terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0032] In the description of the present application, it should be noted that for orientation terms, such as the terms "center", "horizontal", "vertical", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the indicated orientation and positional relationship are based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of the present application.

[0033] 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 do not necessarily have to be used to describe a specific order or sequence.

[0034] In the present application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In the present application, unless otherwise clearly specified and limited, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or may include the first and second features not being in direct contact but being in contact through other features between them. Moreover, the first feature being "above", "over", and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath", and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the first feature has a lower horizontal height than the second feature.

[0036] The terms "including" and "having" in the description and claims of the present application, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0037] One preferred embodiment of the present application, such as Figure 3As shown in the figure, a method for limited-load operation of an inverter system includes the following steps: Determine the first position of the current limited-load operation power of the inverter system in the working curve. Collect the current operation data of the inverter system to judge the loss of the inverter system at the first position. If the loss of the inverter system at the first position meets the preset value, the inverter system maintains the limited-load operation at the first position; otherwise, the inverter system will switch to the second position of the working curve. Among them, the limited-load power values at the first position and the second position are equal but are respectively located on both sides of the highest point of the working curve.

[0038] It should be known that the loss of the inverter system mainly refers to the thermal loss of the power devices, that is, when the loss of the inverter system increases, the heat generated by the power devices per unit time increases. Since the power devices are all installed in a relatively enclosed environment, the heat increased due to power loss of the power devices will cause the temperature of the installation space to rise more severely until it exceeds the working temperature threshold of the power devices and causes the power devices to be burned out.

[0039] However, in the prior art, the limited-load operation position of the inverter system will not be adjusted during the limited-load operation of the inverter system; that is, if the inverter system is at the left slope of the working curve at the beginning of the limited-load operation, then the inverter system will always maintain the limited-load operation at the left slope. From the analysis content of the background technology, it can be seen that the bus voltage corresponding to the inverter system operating at the left slope is relatively low, which makes the input current of the DC / DC unit relatively large, and thus the loss of the DC / DC unit is relatively high. Long-term operation at the left slope may cause the DC / DC unit to be burned out. Similarly, when the inverter system is at the right slope of the working curve at the beginning of the limited-load operation, then the inverter system will always maintain the limited-load operation at the right slope. Long-term operation at the right slope may cause the DC / AC unit to be burned out.

[0040] Therefore, in this embodiment, the limited-load operation position of the inverter system can be determined first, and then the loss data of the inverter system at different positions can be judged according to the current operation data of the inverter system. Furthermore, the inverter system can switch to the position with lower loss, so as to effectively balance the loss of the inverter system; and the entire switching process is realized by a pure software method, which can effectively improve the smoothness of the switching. Generally speaking, the core idea of this application is to judge which loss of the inverter system at the left slope and the right slope is smaller based on the current operation power and then switch to the corresponding position with smaller loss, so as to ensure that the inverter system always works in the area with smaller loss, thereby ensuring the operation safety of the power devices. For the convenience of understanding, the following can be specifically described.

[0041] Specifically, if the first operating position of the inverter system is currently on the left slope and the loss of the inverter system at the first position is greater than the loss at the second position on the right slope, it indicates that the operating temperature of the DC / DC unit is relatively high at this time, while the operating temperature of the DC / AC unit is relatively low, that is, the DC / AC unit has a certain temperature rise range. Then, the inverter system can be switched from the left slope to the right slope, so that the loss of the DC / DC unit is reduced and the operating temperature is decreased. At the same time, the DC / AC unit can increase its operating temperature within the temperature rise range. When the operating temperature of the DC / AC unit rises above the upper limit of the temperature rise range, the DC / DC unit also has a certain temperature rise range due to the temperature drop. At this time, the inverter system can be switched from the right slope to the left slope again. The inverter system repeats the above switching process during the entire operation under load, so as to achieve the loss balance of the inverter system and protect the safe use of the power unit of the inverter system.

[0042] It can be understood that from the foregoing content, the loss of the inverter system is mainly thermal power loss. Therefore, the loss judgment of the inverter system at the current operating position under load can be directly achieved by monitoring the temperature of the power devices. Of course, the thermal power loss can also be calculated through the electrical parameters of the inverter system, that is, the loss judgment of the inverter system at the current operating position under load can also be achieved through the calculation of the electrical parameters of the inverter system. For the convenience of understanding, the following will be described in detail through specific examples for the above two different implementation methods. It should be noted that the technical solution of this application can be applied not only to the field of photovoltaic power generation, but also to the fields of wind power generation and hydropower generation, etc. However, for the sake of simplifying the description of the subsequent content, the subsequent content will be described by taking photovoltaic power generation as an example, and the power generation unit of the inverter system is the photovoltaic string PV.

[0043] Example 1: As Figure 4 shown, the current operating data of the inverter system includes the temperature data of the power unit. Then, the inverter system can judge the loss at the current first position according to the comparison between the current temperature of the power device and the threshold value.

[0044] It can be understood that the power unit of the inverter system includes a DC / DC unit and a DC / AC unit. For the temperature data of the power unit collected during the operation of the inverter system, it can include only the temperature data of the DC / DC unit, or only the temperature data of the DC / AC unit, or also include the temperature data of both the DC / DC unit and the DC / AC unit. Of course, in order to further ensure the accuracy of the loss judgment of the inverter system, in this example, it is preferably to monitor the temperatures of both the DC / DC unit and the DC / AC unit simultaneously for loss judgment.

[0045] Specifically, asFigure 4 As shown, when the first position is on the left slope to the left of the highest point of the working curve, if the current temperature T of the DC / DC unit DC-DC is greater than the set first threshold value T DC-DC_th , and at the same time the current temperature T of the DC / AC unit DC-AC is less than the set second threshold value T DC-AC_th . This indicates that the temperature of the DC / DC unit exceeds the standard at this time, while the temperature of the DC / AC unit still has a certain temperature increase range, and the specific temperature increase range is T DC-AC_th -T DC-AC . At this time, the loss of the inverter system at the first position on the left slope does not meet the preset value, and the load-limited operation position of the inverter system will be switched from the left slope to the second position on the right slope.

[0046] Similarly, when the first position is on the right slope to the right of the highest point of the working curve, if the current temperature T of the DC / DC unit DC-DC is less than the set first threshold value T DC-DC th , and at the same time the current temperature T of the DC / AC unit DC-AC is greater than the set second threshold value T DC-AC_th . This indicates that the temperature of the DC / AC unit exceeds the standard at this time, while the temperature of the DC / DC unit still has a certain temperature increase range, and the specific temperature increase range is T DC-DC_th -T DC-DC . At this time, the loss of the inverter system at the first position on the right slope does not meet the preset value, and the load-limited operation position of the inverter system will be switched from the right slope to the second position on the left slope.

[0047] It should be known that the specific values of the first threshold value T DC-DC_th and the second threshold value T DC-AC_th can be adaptively selected according to the type of power device, and generally it is the upper limit of the lowest operating temperature of all power devices in the corresponding power unit. Taking the DC / DC unit as an example, the DC / DC unit includes various types of power devices, and the upper limit values of the operating temperatures of each type of power device are different; the minimum value of the upper limit values of the operating temperatures can be selected as the first threshold value T DC-DC_th in this example.

[0048] Example 2: As Figure 5As shown in the figure, a loss prediction model of the inverter system is constructed based on the electrical parameters of the current operating data of the inverter system, and the loss of the inverter system at the second position is predicted according to the obtained loss prediction model; the predicted result is used as a preset value and compared with the loss of the inverter system at the first position; if the loss of the inverter system at the first position is greater than the preset value, the inverter system will switch from the first position to the second position, otherwise the inverter system will operate under load limit at the first position. Specifically, if the first position is on the left slope and the predicted loss of the right slope is less than the loss of the left slope, the inverter system will switch from the left slope to the second position on the right slope; if the first position is on the right slope and the predicted loss of the left slope is less than the loss of the right slope, the inverter system will switch from the right slope to the second position on the left slope.

[0049] It can be understood that the inverter system can obtain the corresponding electrical parameters of the inverter system at the second position from the working curve according to the electrical parameters of the current operation at the first position; furthermore, the electrical parameters of the inverter system at the second position can be substituted into the loss prediction model to predict the loss of the inverter system at the second position; at the same time, the inverter system can also calculate the loss of the first position according to the electrical parameters of the first position; finally, the predicted value of the second position can be compared with the calculated value of the first position to judge the size of the two.

[0050] It should be known that the electrical parameters that can be used for the loss calculation of the inverter system mainly include the grid voltage, the operating power of the inverter system, and the output voltage of the power generation unit in the inverter system, that is, the PV voltage.

[0051] In this embodiment, it can be seen from the working curve of the inverter system that the working voltage corresponding to the left slope is lower than the working voltage of the right slope; then the working voltage needs to increase when the inverter system switches from the left slope to the right slope, and the working voltage needs to decrease when the inverter system switches from the right slope to the left slope. The increase and decrease of the working voltage have different overall effects on the inverter system, so the specific methods when the inverter system switches from the left slope to the right slope and from the right slope to the left slope are also different; for the convenience of understanding, the specific switching processes of the inverter system for the switching from the left slope to the right slope and from the right slope to the left slope will be described in detail below.

[0052] 1. For the inverter system to switch from the right slope corresponding to the first position to the left slope corresponding to the second position.

[0053] There are various specific implementation methods to achieve the above switching direction. For the convenience of understanding, the following will be described in detail through two specific examples.

[0054] Example 1: As Figure 6 and Figure 7As shown, multiple power generation units of the inverter system are divided into multiple groups according to a set number, and each group includes at least one power generation unit. All the power generation units in one group are short-circuited, and then the short-circuited power generation units are subjected to MPPT tracking on the left slope until the operating power of all the power generation units in this group reaches the second position. The above process is sequentially repeated for the remaining multiple groups of power generation units until the operating power of all the power generation units of the inverter system is located at the second position.

[0055] It should be known that since the short-circuiting of the power generation unit will cause the limited load operating power corresponding to this power generation unit to be reduced to 0, which will cause an instantaneous drop in the bus voltage of the inverter system. Therefore, the position switching of the power generation units of the inverter system cannot be carried out simultaneously, and grouping and sequential switching are required. In this way, although the bus voltage of the inverter system will still drop, due to the small number of power generation units in a single group, the drop in the bus voltage will not be large. The specific number of power generation units in each group can be selected according to the actual needs of those skilled in the art. For example, the lower limit of the instantaneous drop of the bus voltage can be set; assuming that the lower limit of the instantaneous drop is 5% of the bus voltage, if the short-circuiting of each power generation unit can cause the bus voltage to instantaneously drop by 2%, then the maximum number of power generation units in each group is two.

[0056] For the convenience of understanding, the following will take Figure 7 the specific switching process of the photovoltaic string PV#1 of the photovoltaic inverter system shown as an example for a detailed description. Assume that the current limited load operating power of the photovoltaic string PV#1 is P limit , then a horizontal line can be drawn in the working curve as shown in Figure 6 according to the power P limit . The intersection point A of this horizontal line and the right slope of the working curve is the first position of the photovoltaic string PV#1 in the working curve, and the intersection point B of the horizontal line and the left slope of the working curve is the target position for the limited load operating power switching of the photovoltaic string PV#1, that is, the second position.

[0057] Then, during the process of performing the operating position switching, as shown in Figure 7 , the photovoltaic string PV#1 can be short-circuited first, and the remaining photovoltaic strings are kept normally connected. Then the position of the photovoltaic string PV#1 in the working curve shown in Figure 6 changes from point A to the 0 point position of the working curve. In order to realize the change of the operating power of the photovoltaic string PV#1 from point A to point 0 of the working curve, as shown in Figure 8 , the control loop of the DC / DC unit corresponding to the photovoltaic string PV#1 keeps the drive constantly high during the process of changing from point A to point 0, and then the switching devices S 11 and S 12 of the DC / DC unit can be controlled to short-circuit the photovoltaic string PV#1.

[0058] Since the 0 - point position of the working curve is the left - slope end - point position of the working curve, then as Figure 8 shown, the photovoltaic string PV#1 can perform left - slope MPPT tracking through the control loop of the corresponding DC / DC unit until the limited - load operating power of the photovoltaic string PV#1 rises from the 0 - point position in Figure 6 along the left slope to the B - point position, finally realizing the switching of the limited - load operating power position of the photovoltaic string PV#1 from the right slope to the left slope.

[0059] It should be known that during the switching process from the 0 - point to the B - point position, the specific working process of the control loop of the DC / DC unit is well - known to those skilled in the art, so it will not be elaborated in detail here; at the same time, the specific structure of the control loop of the DC / DC unit is also well - known to those skilled in the art, so it will not be elaborated in detail here.

[0060] Example 2: As Figure 9 shown, reduce the operating power of all the power - generation units of the inverter system by ΔP to the third position on the same side as the first position. Divide the multiple power - generation units of the inverter system into multiple groups according to a set number, and each group includes at least one power - generation unit. Raise the operating power of all the power - generation units in one of the groups along the right slope to the highest point, and then lower the operating power along the left slope to the fourth position with the same power as the third position. Repeat the above process for the remaining multiple groups of power - generation units in sequence until the operating power of all the power - generation units of the inverter system is located at the fourth position; raise the operating power of all the power - generation units of the inverter system by ΔP so that the operating power of all the power - generation units rises from the fourth position to the second position.

[0061] It can be understood that since the power - generation units need to pass through the highest point of the working curve, that is, the MPPT point, during the position - switching process, which is a power - increase for the power - generation units, this will cause the limited - load operating power of the inverter system to rise above the limit value. Therefore, in this example, the operating power of all the power - generation units is reduced before the position - switching of the power - generation units, so as to ensure that when the power - generation units reach the MPPT point in terms of operating power increase, the limited - load operating power of the inverter system will not exceed the limit value. Of course, all the power - generation units of the inverter system cannot perform position - switching simultaneously, otherwise the limited - load operating power of the inverter system will still exceed the standard.

[0062] It should be known that the specific number of power - generation units in each group can be selected according to the actual needs of those skilled in the art; however, in order to ensure the operating safety of the inverter system during the position - switching process of each group of power - generation units, the value of the number X of power - generation units in each group needs to meet X≤N·ΔP / (P MPPT -P limit ); where, N represents the total number of power - generation units of the inverter system, Plimit represents the operating power of the power generation unit before power reduction, P MPPT represents the power value corresponding to the highest point of the working curve. That is, the total power increase of the inverter system brought about by the power generation unit group when the power is increased to the MPPT point should be less than or equal to the total power reduction of the inverter system beforehand.

[0063] For the convenience of understanding, the following will take the specific switching process of one of the power generation units as an example for detailed description. As Figure 9 shown, assume that the current limited-load operating power of this power generation unit is P limit , then a horizontal line can be drawn in the working curve as shown in Figure 9 at the power P limit . The intersection point A of this horizontal line and the right slope of the working curve is the first position of this power generation unit in the working curve, and the intersection point B of the horizontal line and the left slope of the working curve is the target position for the power generation unit to switch the limited-load operating power, that is, the second position. As Figure 9 shown, subtract ΔP from the corresponding power P limit to obtain the power P limit ′, and draw a horizontal line in the working curve at the power P limit ′; the intersection point C of this horizontal line and the right slope of the working curve is the third position, and the intersection point D of this horizontal line and the left slope of the working curve is the fourth position. Let the highest point of the working curve be M, then the position switching path of this power generation unit is A - C - M - D - B.

[0064] As Figure 10 shown, when this power generation unit makes the switch from path A to C, the control loop of the corresponding DC / DC unit of this power generation unit can perform power-limited tracking of the right-slope MPPT to the power P limit ′. When this power generation unit makes the switch from path C to M, the control loop of the corresponding DC / DC unit of this power generation unit can perform maximum power point tracking of the right-slope MPPT. When this power generation unit makes the switch from path M to D, the control loop of the corresponding DC / DC unit of this power generation unit can perform power-limited tracking of the left-slope MPPT to the power P limit ′. When this power generation unit makes the switch from path D to B, the control loop of the corresponding DC / DC unit of this power generation unit can perform power-limited tracking of the left-slope MPPT to P limit .

[0065] In this example, the process from path A to C is carried out by all power generation units at the same time; and there are two main ways for the switching process from path M to B. Method 1: All power generation units are switched from point M to point D in sequence, and then all power generation units are switched from point D to point B at the same time; Method 2: First, the power generation units of the first part are switched from point M to point D in sequence, and then the remaining power generation units of the second part are switched directly from point M to point B in sequence, and finally the power generation units of the first part are switched from point D to point B at the same time. For the switching process from path M to B, technicians in this field can make their own choices according to actual needs; but it should be noted that the implementation premise of Method 2 is that the total power reduction value of the first part of the power generation units must be greater than or equal to the total power increase brought by a single group of power generation units at the MPPT point, that is, K·ΔP≥X(P MPPT -P limit ), where K represents the number of power generation units in the first part, and the number of power generation units in the second part is NK.

[0066] 2. The inverter system is switched from the left slope corresponding to the first position to the right slope corresponding to the second position.

[0067] There are many specific implementations that can achieve the above switching direction. For easy understanding, two specific examples are used below to provide a detailed description.

[0068] Example 1: Figure 11 As shown, first, all power units of the inverter system are driven and blocked, so that all power generation units work at the open circuit voltage position; then, the drive blockade of all power units of the inverter system is released to feed the grid, and the inverter system is tracked on the right slope of MPPT until the operating power of all power generation units is at the second position.

[0069] For ease of understanding, the following will take the specific switching process of one power generation unit as an example for detailed description. Figure 11 As shown, assuming that the current load-limited operating power of the power generation unit is P limit , then you can Figure 11 The working curve shown is based on the power P limit Draw a horizontal line. The intersection point B of the horizontal line and the left slope of the working curve is the first position of the power generation unit in the working curve, and the intersection point A of the horizontal line and the right slope of the working curve is the target position of the power generation unit for load-limited operation switching, that is, the second position. When the DC / DC unit and DC / AC unit of the inverter system are driven and blocked, the switching devices in the DC / DC unit and the DC / AC unit can be regarded as the disconnected state. At this time, the output voltage of the power generation unit can be regarded as the open circuit voltage without load, that is, the corresponding Figure 11The voltage corresponding to the right slope end point E; then the switching path of this power generation unit is B - E - A.

[0070] Example 2: As Figure 12 and Figure 13 shown, reduce the operating power of all power generation units of the inverter system by ΔP to the third position on the same side as the first position. Divide the multiple power generation units of the inverter system into multiple groups according to a set quantity, set a sequence for the multiple groups of power generation units, and each group includes at least one power generation unit. Raise the operating power of all power generation units in the first group along the left slope to the highest point, and then reduce the operating power along the right slope to the fourth position with the same power as the third position. Open the circuit of all power generation units in the second group, so that all power generation units in the second group work at the fifth position on the right slope, and perform MPPT tracking on the right slope for all power generation units in the second group until the operating power of all power generation units in the second group is at the fourth position. Repeat the switching process of the second group of power generation units for the remaining groups of power generation units in sequence until all power generation units of the inverter system operate at the fourth position. Raise the operating power of all power generation units of the inverter system by ΔP, so that the operating power of all power generation units rises from the fourth position to the second position.

[0071] It can be understood that the switching process of the first group of power generation units is to raise the bus voltage to a certain extent first; thus, when the second group and subsequent power generation units are opened, the open - circuit voltage of the second group and subsequent power generation units will not directly reach the maximum value U oc position due to the influence of the first group of power generation units, which can effectively suppress the sudden change of the bus voltage of the inverter system. Since the second group of power generation units will pass through the highest point of the working curve, that is, the MPPT point, during the position switching; therefore, in order to ensure that the inverter system does not exceed the limit load power during the switching process, it is necessary to first reduce the power of all power generation units.

[0072] For easy understanding, the following will take the first two groups of power generation units as an example for detailed description.

[0073] As Figure 12 shown, assume that the current limit - load operating power of the first group of power generation units is P limit , then a horizontal line can be drawn in the working curve as shown in Figure 12 according to the power P limit . The intersection point B of this horizontal line and the left slope of the working curve is the first position of this power generation unit in the working curve, and the intersection point A of the horizontal line and the right slope of the working curve is the target position for the limit - load operating power switching of this power generation unit, that is, the second position. Subtract ΔP from the corresponding power P limit to get the power P limit ′, and draw a horizontal line in the working curve according to the power P limit'Draw a horizontal line; the intersection point D of this horizontal line and the left slope of the working curve is the third position, and the intersection point C of this horizontal line and the right slope of the working curve is the fourth position. Let the highest point of the working curve be M, then the position switching path of the first group of power generation units is B - D - M - C - A.

[0074] As Figure 13 shown, assume that the current limited load operating power of the second group of power generation units is P limit , then a horizontal line can be drawn in the working curve as shown in Figure 13 according to the power P limit . The intersection point B of this horizontal line and the left slope of the working curve is the first position of this power generation unit in the working curve, and the intersection point A of the horizontal line and the right slope of the working curve is the target position for switching the limited load operating power of this power generation unit, that is, the second position. Subtract ΔP from the corresponding power P limit to obtain the power P limit ', and draw a horizontal line in the working curve according to the power P limit '. The intersection point D of this horizontal line and the left slope of the working curve is the third position, and the intersection point C of this horizontal line and the right slope of the working curve is the fourth position. When the drive of the second group of power generation units is blocked, due to the boost of the bus voltage by the first group of power generation units already at the fourth position C point, the open circuit voltage V bus of the second group of power generation units is at the F point position below the C point of the working curve, that is, the fifth position. Then the position switching path of the second group of power generation units is B - D - F - C - A.

[0075] The above describes the basic principle, 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. What is described in the above embodiments and the specification is only the principle of the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A load-limited operation method for an inverter system, characterized in that: The steps include: Determine the first position of the current load-limited operating power of the inverter system in the working curve; Collecting current operating data of the inverter system to determine the loss of the inverter system at the first location; If the loss of the inverter system at the first position meets the preset value, the inverter system maintains the load-limited operation at the first position, otherwise the inverter system will switch to the second position of the working curve; The load limiting power values ​​of the first position and the second position are equal but are located on both sides of the highest point of the working curve; Building a loss prediction model of the inverter system based on electrical parameters of current operating data of the inverter system, and predicting the loss of the inverter system at the second position according to the obtained loss prediction model; comparing the predicted result as a preset value with the loss of the inverter system at the first position; If the loss of the inverter system in the first position is greater than a preset value, the inverter system will switch from the first position to the second position, otherwise the inverter system will maintain load-limited operation in the first position; The electrical parameters of the current operating data of the inverter system include the grid voltage, the operating power of the inverter system, and the output voltage of the power generation unit in the inverter system.

2. The load-limited operation method of the inverter system according to claim 1, characterized in that: The process of the inverter system switching from the right slope corresponding to the first position to the left slope corresponding to the second position is as follows: Dividing the plurality of power generation units of the inverter system into a plurality of groups according to a set number, each group including at least one power generation unit; Short-circuit all the generating units in one group, and then perform left-slope MPPT tracking on the short-circuited generating units until the operating power of all the generating units in the group reaches the second position; The above process is repeated for the remaining multiple groups of power generation units in sequence until the operating powers of all power generation units of the inverter system are at the second position.

3. The load-limited operation method of the inverter system according to claim 1, characterized in that: The process of the inverter system switching from the right slope corresponding to the first position to the left slope corresponding to the second position is as follows: reducing the operating power of all power generation units of the inverter system by ΔP to a third position on the same side as the first position; Dividing the plurality of power generation units of the inverter system into a plurality of groups according to a set number, each group including at least one power generation unit; Raise the operating power of all the generating units of one group along the right slope to the highest point, and then lower the operating power along the left slope to a fourth position having the same power as the third position; Repeat the above process for the remaining multiple groups of power generation units in order until the operating powers of all power generation units of the inverter system are at the fourth position; The operating power of all the power generation units of the inverter system is raised by ΔP, so that the operating power of all the power generation units increases from the fourth position to the second position.

4. The load-limited operation method of the inverter system according to claim 3, characterized in that: The total number of generating units in the inverter system is N, and the operating power of the generating units without power reduction is P limit ; The value of the number of power generation units in each group is: X≤N·ΔP / (P MPPT -P limit ); Among them, P MPPT Indicates the power value corresponding to the highest point of the working curve.

5. The load-limited operation method of the inverter system according to claim 1, characterized in that: The process of the inverter system switching from the left slope corresponding to the first position to the right slope corresponding to the second position is as follows: First, all power units of the inverter system are driven and blocked, so that all power generation units work at the open circuit voltage position; Then, the drive blocking of all power units of the inverter system is released to feed the grid; The inverter system is subjected to right slope MPPT tracking until the operating power of all power generation units is at the second position.

6. The load-limited operation method of the inverter system according to claim 1, characterized in that: The process of the inverter system switching from the left slope corresponding to the first position to the right slope corresponding to the second position is as follows: reducing the operating power of all power generation units of the inverter system by ΔP to a third position on the same side as the first position; Divide the multiple power generation units of the inverter system into multiple groups according to a set number, set a sequence for the multiple groups of power generation units, and each group includes at least one power generation unit; Raise the operating power of all the power generating units of the first group along the left slope to the highest point, and then lower the operating power along the right slope to a fourth position having the same power as the third position; All the power generation units of the second group are opened so that all the power generation units of the second group work at the fifth position of the right slope, and the MPPT tracking of the right slope is performed on all the power generation units of the second group until the operating power of all the power generation units of the second group is at the fourth position; Repeat the switching process of the second group of power generation units for the remaining power generation unit groups in sequence until all power generation units of the inverter system are operating in the fourth position; The operating power of all the power generation units of the inverter system is raised by ΔP, so that the operating power of all the power generation units increases from the fourth position to the second position.

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