A method for limiting load operation of an inverter system

Abstract

The application discloses a load-limiting operation method of an inverter system, comprising the following steps: determining a first position of current load-limiting operation power of the inverter system in a working curve; collecting current operation data of the inverter system to determine 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 keeps the load-limiting operation at the first position, otherwise, the inverter system switches to a second position of the working curve. The application has the beneficial effects that: through the collection of the current operation data of the inverter system, the loss data of the inverter system at different positions can be determined, and then the inverter system can switch to a lower loss position, so that the loss of the inverter system can be effectively balanced. The whole switching process is realized by a pure software mode, and the smoothness of switching can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of new energy power generation, and in particular to a load-limiting operation method for an inverter system. Background Technology

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

[0003] like Figure 2 As shown, Figure 1 The photovoltaic (PV) operating curve corresponds to the PV system's operation. The curve can be divided based on the MPPT (Maximum Per Second) point; the curve segment to the left of the highest point can be defined as the left slope, and the curve segment to the right of the highest point as the right slope. When PV oversizing is severe, and the solar irradiance is high, the system needs to be operated under load limiting conditions. Generally, load limiting can be implemented on either the left or right slope of the curve.

[0004] When the system operates under load limiting on the right slope, the corresponding bus voltage is higher, which means that the losses of the DC / AC unit are higher, while the losses of the DC / DC unit are relatively lower. When the system operates under load limiting on the left slope, the corresponding bus voltage is lower, which means that under the same power conditions, the input current of the DC / DC unit is larger, resulting in relatively higher losses of the DC / DC unit. Therefore, how to ensure the balance of losses during system operation under load limiting is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] One objective of this application is to provide a load-limiting operation method for an inverter system that can solve at least one of the defects in the aforementioned background art.

[0006] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: a load-limiting operation method for an inverter system, comprising the following steps: determining the first position of the current load-limiting operation power of the inverter system on the operating curve; collecting the current operating data of the inverter system to determine 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 load-limiting operation at the first position; otherwise, the inverter system will switch to the second position of the operating curve; wherein, the load-limiting power values ​​at the first position and the second position are equal but located on both sides of the highest point of the operating curve.

[0007] Preferably, the current operating data of the inverter system comprises temperature data of the power unit; the inverter system is adapted to make the loss judgment of the inverter system at the current first position according to comparison between the current temperature of the power unit and a threshold value.

[0008] Preferably, the power unit of the inverter system comprises a DC / DC unit and a DC / AC unit; when the first position is located on the left slope left of the highest point of the operating curve, if the current temperature of the DC / DC unit is greater than a set first threshold value and the current temperature of the DC / AC unit is less than a set second threshold value, the loss of the inverter system does not conform to the preset value, and the load-limiting operating position of the inverter system will be switched from the left slope to the right slope; when the first position is located on the right slope right of the highest point of the operating curve, if the current temperature of the DC / DC unit is less than the set first threshold value and the current temperature of the DC / AC unit is greater than the set second threshold value, the loss of the inverter system does not conform to the preset value, and the load-limiting operating position of the inverter system will be switched 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 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 prediction result is compared with the loss of the inverter system at the first position as the preset value; if the loss of the inverter system at the first position is greater than the preset value, the inverter system will be switched from the first position to the second position, otherwise the inverter system will remain in the load-limiting operation at the first position.

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

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

[0012] Preferably, the inverter system performs the process of switching from the right slope corresponding to the first position to the left slope corresponding to the second position as follows: lowering the operating power of all the power generating units of the inverter system by ΔP to a third position on the same side of the first position; dividing the power generating units of the inverter system into multiple groups according to a set number, each group including at least one power generating unit; raising the operating power of all the power generating units in one group along the right slope to the highest point, and then lowering the operating power along the left slope to a fourth position with the same power as the third position; repeating the above process in order for the remaining groups of power generating units until the operating power of all the power generating units of the inverter system is located at the fourth position; raising the operating power of all the power generating units of the inverter system by ΔP so that the operating power of all the power generating units is raised from the fourth position to the second position.

[0013] Preferably, the total number of power generating units of the inverter system is N, and the operating power of the power generating units when not performing power lowering is P limit ; the value of the number X of power generating units in each group is: X≤N·ΔP / (P MPPT -P limit ); wherein P MPPT represents the power value corresponding to the highest point of the operating curve.

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

[0015] Preferably, the inverter system performs the switching process from the left slope corresponding to the first position to the right slope corresponding to the second position as follows: lowering the operating power of all the power generation units of the inverter system by ΔP to a third position on the same side of the first position; dividing the plurality of power generation units of the inverter system into a plurality of groups according to a set number, setting a sequence for the plurality of groups, each group including at least one power generation unit; raising the operating power of all the power generation units of the first group along the left slope to a highest point, and then lowering the operating power along the right slope to a fourth position with the same power as the third position; opening the circuit of all the power generation units of the second group, so that all the power generation units of the second group work at a fifth position on the right slope, performing MPPT tracking on the right slope for 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; repeating the switching process of the second group of power generation units according to the sequence for the remaining groups of power generation units until all the power generation units of the inverter system are operating at the fourth position; raising 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.

[0016] Compared with the prior art, the application has the beneficial effects that:

[0017] By collecting the current operating data of the inverter system, the loss data of the inverter system at different positions can be determined, and then the inverter system can be switched to a lower loss position, so that the loss of the inverter system can be effectively balanced. The entire switching process is realized by pure software, which can effectively improve the smoothness of switching. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a schematic diagram of the architecture of an existing photovoltaic inverter system.

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

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

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

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

[0023] Figure 6 It is a schematic diagram of the working curve of one of the examples of the inverter system of the application for right slope to left slope load limiting operation switching.

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

[0025] Figure 8 The schematic diagram of the short-circuit architecture for PV string PV#1 in the inverter system of the present application. Figure 6 The schematic diagram of the control flow of the control loop in the switching process shown.

[0026] Figure 9 The schematic diagram of the working curve for another example of the right slope to left slope limited load operation switching in the inverter system of the present application.

[0027] Figure 10 The schematic diagram of the working curve for another example of the right slope to left slope limited load operation switching in the inverter system of the present application. Figure 9 The schematic diagram of the control flow of the control loop in the switching process shown.

[0028] Figure 11 The schematic diagram of the working curve for another example of the right slope to left slope limited load operation switching in the inverter system of the present application.

[0029] Figure 12 The schematic diagram of the working curve for another example of the right slope to left slope limited load operation switching in the inverter system of the present application. Figure 1 .

[0030] Figure 13 The schematic diagram of the working curve for another example of the right slope to left slope limited load operation switching in the inverter system of the present application. Figure 2 . DETAILED DESCRIPTION

[0031] In the following, the present application will be further described with reference to the specific embodiments. It is to be noted that the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" in the description of the present application means that the specific feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. The illustrative representations of the above terms in the present specification 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. Furthermore, the person skilled in the art can combine and combine different embodiments or examples described in the present specification.

[0032] In the description of the application, it should be noted that, for orientation words, such as the terms "center", "transverse", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation and positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and cannot be understood as limiting the specific protection scope of the application.

[0033] It should be noted that the terms "first", "second", etc. in the specification and claims of the application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0034] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example, it can be connected, or it can be detachably connected, or it can be integrated; it can be mechanical connection, or it can be electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0035] In the present application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the first feature "on", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0036] The terms "include" and "have" in the specification and claims of the present application, as well as any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can 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 is as follows Figure 3As shown, a method for limiting load operation of an inverter system includes the following steps: determining a first position of current limiting load operation power of the inverter system in a working curve. Collecting current operation data of the inverter system to determine 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 remains limiting load operation at the first position, otherwise the inverter system will switch to a second position of the working curve. Wherein the limiting load power values of the first position and the second position are equal but 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 heat loss of the power device, that is, the loss of the inverter system increases, and the heat generated by the power device in unit time increases. Since the power device is installed in a relatively closed environment, the increased heat of the power device due to power loss will cause the temperature of the installation space to rise sharply until the working temperature threshold of the power device is exceeded and the power device is burned out.

[0039] However, the prior art does not adjust the limiting load position of the inverter system when the inverter system is in limiting load operation; that is, when the inverter system is in left slope of the working curve at the beginning of limiting load operation, the inverter system will always remain in left slope limiting load operation. As can be known from the analysis content of the background art, when the inverter system operates in the left slope, the corresponding bus voltage is relatively low, so that the input current of the DC / DC unit is relatively large, thereby causing the loss of the DC / DC unit to be relatively high, and long-time left slope operation may cause the DC / DC unit to be burned out. Similarly, when the inverter system is in right slope of the working curve at the beginning of limiting load operation, the inverter system will always remain in right slope limiting load operation, and long-time right slope operation may cause the DC / AC unit to be burned out.

[0040] Therefore, in the embodiment, the limiting 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 determined according to the current operation data of the inverter system, and then the inverter system can switch to a lower loss position, thereby effectively balancing the loss of the inverter system; and the entire switching process is realized by a pure software manner, which can effectively improve the smoothness of switching. In a popular way, the core idea of the present application is to judge which one of the left slope and the right slope has smaller loss based on the current operation power of the inverter system, and then switch to the position corresponding to the smaller loss, so that the inverter system can always work in a region with smaller loss, thereby ensuring the operation safety of the power device. For the convenience of understanding, the following can be described in detail.

[0041] Specifically, if the first position of the current operation of the inverter system is located on the left slope, and the loss of the inverter system at the first position is greater than the loss of the inverter system at the second position on the right slope, it indicates that the working temperature of the DC / DC unit is relatively high, and the working temperature of the DC / AC unit is relatively low, that is, the DC / AC unit has a certain temperature rising interval; 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 to reduce the working temperature, and the DC / AC unit can work within the temperature rising interval. When the working temperature of the DC / AC unit rises to exceed the upper limit of the temperature rising interval, the DC / DC unit also has a certain temperature rising interval due to the temperature drop, at which 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 load limiting operation process, so that the loss of the inverter system can be balanced to protect the use safety of the power unit of the inverter system.

[0042] It can be understood that, as known from the foregoing, the loss of the inverter system is mainly thermal power loss, so the loss judgment of the inverter system at the current load limiting operation position can be directly realized by monitoring the temperature of the power device; of course, the thermal power loss can also be calculated by the electrical parameters of the inverter system, that is, the loss judgment of the inverter system at the current load limiting operation position can also be realized by calculating the electrical parameters of the inverter system. For the convenience of understanding, the following will be described in detail by specific examples for the above two different implementation manners. It should be noted that the technical solution of the present application can be applied not only to the field of photovoltaic power generation, but also to the fields of wind power generation and hydroelectric power generation. In order to simplify 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 a photovoltaic string PV.

[0043] Example one: as shown in Figure 4 The current operation data of the inverter system includes the temperature data of the power unit; then the inverter system can compare the current temperature of the power device with the threshold value to judge the loss of the inverter system at the current first position.

[0044] It can be understood that the power unit of the inverter system includes the DC / DC unit and the DC / AC unit, and the temperature data of the power unit collected by the inverter system during the operation stage can only include the temperature data of the DC / DC unit, or only include the temperature data of the DC / AC unit, or include the temperature data of 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, the temperature of the DC / DC unit and the DC / AC unit is monitored simultaneously in the present example to judge the loss.

[0045] Specifically, asFigure 4 As shown, when the first position is located 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 Greater than the set first threshold value T DC-DC_th Meanwhile, the current temperature T of the DC / AC unit DC-AC Less than the set second threshold value T DC-AC_th This indicates that the DC / DC unit's temperature is exceeding the limit, while the DC / AC unit's temperature still has a certain range of potential increase, specifically within the range of T. DC-AC_th -T DC-AC At this point, the inverter system's losses at the first position on the left slope do not meet the preset value, and the inverter system's load-limited operating position will switch from the left slope to the second position on the right slope.

[0046] Similarly, when the first position is located 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 Less than the set first threshold value T DC-DC th Meanwhile, the current temperature T of the DC / AC unit DC-AC Greater than the set second threshold value T DC-AC_th This indicates that the temperature of the DC / AC unit is exceeding the limit, while the DC / DC unit's temperature still has a certain range of potential increase, specifically T. DC-DC_th -T DC-DC At this point, the inverter system's losses at the first position on the right slope do not meet the preset value, and the inverter system's load-limited operating position will switch from the right slope to the second position on the left slope.

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

[0048] Example 2: such as Figure 5As shown, the 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 compared with the loss of the inverter system at the first position as a preset value; if the loss of the inverter system at the first position is greater than the preset value, the inverter system will be switched from the first position to the second position, otherwise the inverter system will remain in the first position in the limited load operation. Specifically, if the first position is located on the left slope, and the loss of the right slope is predicted to be less than the loss of the left slope, the inverter system will be switched from the left slope to the second position of the right slope; if the first position is located on the right slope, and the loss of the left slope is predicted to be less than the loss of the right slope, the inverter system will be switched from the right slope to the second position of 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 first position operation; then 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 determine the size of the two.

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

[0051] In this embodiment, it can be known from the working curve of the inverter system that the working voltage corresponding to the left slope is lower than that of the right slope; therefore, the working voltage needs to be increased when the inverter system is switched from the left slope to the right slope, and the working voltage needs to be reduced when the inverter system is switched from the right slope to the left slope. The increase of the working voltage and the decrease of the working voltage have different effects on the overall inverter system, so the specific way of switching the inverter system from the left slope to the right slope and from the right slope to the left slope is also different; in order to facilitate understanding, the specific switching process of the inverter system will be described in detail below for the switching from the left slope to the right slope and from the right slope to the left slope.

[0052] I. 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 many specific implementation methods to realize the above switching direction, in order to facilitate understanding, two specific examples will be described in detail below.

[0054] Example one: as shown in FIG. 2, the inverter system is switched from the right slope to the left slope. Figure 6 and Figure 7As shown, the plurality of power generation units of the inverter system is divided into multiple groups according to a set number, and each group includes at least one power generation unit. All power generation units in one group are short-circuited, and then the short-circuited power generation units are subjected to left-slope MPPT tracking until the operating power of all power generation units in the group reaches the second position. The above process is repeated in sequence for the remaining groups of power generation units until the operating power of all power generation units of the inverter system is located at the second position.

[0055] It should be understood that, since the short-circuiting of the power generation unit will cause the corresponding load-limited operating power of the power generation unit to be reduced to 0, this will cause the bus voltage of the inverter system to instantaneously drop. Therefore, the position switching of the power generation units of the inverter system cannot be performed simultaneously, and needs to be performed in sequence after grouping. Although the bus voltage of the inverter system will still drop, since the number of power generation units in each group is small, the drop of the bus voltage will not be large. The specific number of power generation units in each group can be selected by the person skilled in the art according to actual needs. For example, a lower limit of the instantaneous drop of the bus voltage can be set. Assuming that the lower limit of the instantaneous drop of the bus voltage 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 number of power generation units in each group is at most two.

[0056] For the convenience of understanding, the specific switching process of the photovoltaic string PV#1 of the photovoltaic inverter system shown in Figure 7 will be described in detail below. Assuming that the current load-limited operating power of the photovoltaic string PV#1 is P limit , a horizontal line can be drawn in the operating curve shown in Figure 6 according to the power P limit . The intersection A of the horizontal line and the right-slope operating curve is the first position of the photovoltaic string PV#1 in the operating curve, and the intersection B of the horizontal line and the left-slope operating curve is the target position of the photovoltaic string PV#1 for the load-limited operating power switching, i.e., the second position.

[0057] Then, in the process of operating position switching, as shown in Figure 7 , the photovoltaic string PV#1 can be short-circuited first, and the remaining photovoltaic strings remain normally connected. The position of the photovoltaic string PV#1 in the operating curve shown in Figure 6 changes from the point A to the 0-point position of the operating curve. In order to realize the change of the operating power of the photovoltaic string PV#1 from the point A to the 0-point of the operating curve, as shown in Figure 8 , the control loop of the DC / DC unit corresponding to the photovoltaic string PV#1 keeps driving the constant high during the change from the point A to the 0-point, so as to control the switching devices S 11 and S 12 of the DC / DC unit to be short-circuited for the photovoltaic string PV#1.

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

[0059] It should be understood that the specific working process of the control loop of the DC / DC unit in the switching process from the 0-point to the B-point position is known to those skilled in the art, and therefore will not be described in detail here. Meanwhile, the specific structure of the control loop of the DC / DC unit is also known to those skilled in the art, and therefore will not be described in detail here.

[0060] Example II: As shown in Figure 9 , the operating power of all the power generation units of the inverter system is lowered by ΔP to a third position on the same side of the first position. The plurality of power generation units of the inverter system is 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 raised along the right slope to the highest point, and then lowered along the left slope to a fourth position with the same power as the third position. The above process is repeated in the order 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 raised by ΔP, so that the operating power of all the power generation units is raised from the fourth position to the second position.

[0061] It can be understood that since the highest point, i.e. the MPPT point, of the working curve needs to be passed during the position switching of the power generation units, which is a power increase for the power generation units, and thus will cause the load-limited operating power of the inverter system to rise to exceed the limit value. Therefore, the operating power of all the power generation units is lowered before the position switching of the power generation units in this example, so that when the operating power of the power generation units is raised to the MPPT point, the load-limited operating power of the inverter system will not exceed the limit value. Of course, all the power generation units of the inverter system cannot be simultaneously switched in position, otherwise the load-limited operating power of the inverter system will still exceed the limit value.

[0062] It should be understood that the specific number of power generation units in each group can be selected by those skilled in the art according to actual needs; but in order to ensure the safe operation of the inverter system during the position switching of each group of power generation units, the value of the number of power generation units X 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 P represents the operating power of the power generation unit without power reduction. MPPT This represents the power value corresponding to the highest point of the operating curve. In other words, the total power increase of the inverter system brought about by the power boosting of this group of generator units to the MPPT point must be less than or equal to the total power decrease of the inverter system beforehand.

[0063] To facilitate understanding, the following detailed explanation will use the specific switching process of one of the power generation units as an example. Figure 9 As shown, assume the current load-limited operating power of this power generation unit is P. limit Then you can in such Figure 9 The working curve shown is based on power P limit Draw a horizontal line. The intersection point A of this line and the right slope of the working curve is the first position of the power generation unit on the working curve. The intersection point B of this line and the left slope of the working curve is the target position, i.e., the second position, for the power generation unit to switch to load-limited operation. For example... Figure 9 As shown, the corresponding power P limit Subtracting ΔP yields the power P. limit ′, in the working curve according to power P limit Draw a horizontal line; the intersection point C of this line and the right slope of the working curve is the third position, and the intersection point D of this 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] like Figure 10 As shown, when the power generation unit switches from path A to C, the control loop of the corresponding DC / DC unit can perform right-hill MPPT power point tracking to power P. limit When the power generation unit switches from path C to M, the control loop of the corresponding DC / DC unit can perform right-hill MPPT maximum power point tracking. When the power generation unit switches from path M to D, the control loop of the corresponding DC / DC unit can perform left-hill MPPT power point tracking to power P. limit When the power generation unit switches from path D to B, the control loop of the corresponding DC / DC unit can perform left-hill MPPT power point tracking to P. limit .

[0065] In this example, the switching process from path A to C is performed simultaneously by all power generation units; however, there are two main methods for the switching process from path M to B. Method 1: All power generation units switch sequentially from point M to point D, and then simultaneously switch from point D to point B. Method 2: First, the power generation units in the first part switch sequentially from point M to point D, then the remaining power generation units in the second part switch directly from point M to point B sequentially, and finally, the power generation units in the first part switch simultaneously from point D to point B. Those skilled in the art can choose the appropriate method for the switching process from path M to B based on actual needs; however, it should be noted that the prerequisite for implementing Method 2 is that the total power decrease 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, i.e., 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. For the inverter system, switch from the left slope corresponding to the first position to the right slope corresponding to the second position.

[0067] There are various specific implementation methods to achieve the above-mentioned direction switching. For ease of understanding, two specific examples will be used to illustrate this in detail below.

[0068] Example 1: such as Figure 11 As shown, firstly, all power units of the inverter system are driven and locked, so that all power generation units operate at the open-circuit voltage position; then, the drive lock of all power units of the inverter system is released to feed into the grid, and the inverter system is subjected to right-slope MPPT tracking until the operating power of all power generation units is at the second position.

[0069] To facilitate understanding, the following detailed explanation will use the specific switching process of one of the power generation units as an example. Figure 11 As shown, assume the current load-limited operating power of this power generation unit is P. limit Then you can in such Figure 11 The working curve shown is based on power P limit Draw a horizontal line. The intersection point B of this line and the left slope of the working curve is the first position of the generator unit on the working curve. The intersection point A of the line and the right slope of the working curve is the target position, i.e., the second position, for the generator unit to switch to load-limited operation power. When the DC / DC and DC / AC units of the inverter system are locked, the switching devices in the DC / DC and DC / AC units can be considered as open circuits. At this time, the output voltage of the generator unit can be considered as an open-circuit voltage without load, i.e., the corresponding... Figure 11The switching path of the power generation unit is B—E—A.

[0070] Example two: as shown in Figure 12 and Figure 13 , the operating power of all the power generation units of the inverter system is decreased by ΔP to a third position on the same side of the first position. The power generation units of the inverter system are divided into multiple groups according to a set number, and a sequence order is set for the multiple groups, each group including at least one power generation unit. The operating power of all the power generation units of the first group is increased along the left slope to a highest point, and then decreased along the right slope to a fourth position with the same power as the third position. All the power generation units of the second group are opened to make all the power generation units of the second group work at a fifth position on 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. The switching process of the second group of power generation units is repeated in sequence order for the remaining groups of power generation units 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 increased by ΔP to make the operating power of all the power generation units increase 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 increase the bus voltage to a certain extent; so that when the second group and subsequent power generation units are opened, the open circuit voltage of the second group and subsequent power generation units is not directly at the maximum value U oc at the position, which can effectively suppress the bus voltage surge of the inverter system. Since the power generation units of the second group pass through the highest point of the working curve, i.e. the MPPT point, when the position switching is performed, in order to ensure that the inverter system does not exceed the limit load power during switching, the operating power of all the power generation units needs to be decreased first.

[0072] For the convenience of understanding, the power generation units of the first two groups will be taken as an example for detailed description.

[0073] As shown in Figure 12 , it is assumed that the current limit load operating power of the first group of power generation units is P limit , a horizontal line is drawn in the working curve as shown in Figure 12 according to the power P limit . The intersection 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 A of the horizontal line and the right slope of the working curve is the target position of the limit load operating power switching of the power generation unit, i.e. the second position. The power P limit is decreased by ΔP to obtain the power P limit ', and the power P limitDraw a horizontal line; the intersection point D of this line and the left slope of the working curve is the third position, and the intersection point C of this 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] like Figure 13 As shown, assume the current load-limited operating power of the second group of power generation units is P. limit Then you can in such Figure 13 The working curve shown is based on power P limit Draw a horizontal line. The intersection point B of this line and the left slope of the working curve is the first position of the power generation unit on the working curve. The intersection point A of the line and the right slope of the working curve is the target position, i.e., the second position, for the power generation unit to switch to load-limited operation. Then, assign the corresponding power P... limit Subtracting ΔP yields the power P. limit ′, in the working curve according to power P limit Draw a horizontal line; the intersection point D of this line and the left slope of the working curve is the third position, and the intersection point C of this line and the right slope of the working curve is the fourth position. When the second group of generator units is driven and blocked, because the first group of generator units is already at the fourth position (point C) and has raised the bus voltage, the open-circuit voltage V of the second group of generator units... bus Point F, located below point C on the operating curve, is the fifth position. Therefore, the position switching path for the second group of power generation units is B—D—F—C—A.

[0075] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method of limiting the operation of an inverter system, characterized by, The method comprises the following steps: determining a first position of the current limited power of the inverter system in the working curve; collecting the current operating data of the inverter system to determine 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 remains the limited power at the first position, otherwise the inverter system will switch to a second position of the working curve; wherein the limited power values of the first position and the second position are equal but located on both sides of the highest point of the working curve respectively; constructing a loss prediction model of the inverter system based on the electrical parameters of the 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 with the loss of the inverter system at the first position as the preset value; 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 remain the limited power at the first position; the electrical parameters of the current operating data of the inverter system include grid voltage, operating power of the inverter system and output voltage of the power generation unit in the inverter system.

2. The load limit operation method of an inverter system according to claim 1, wherein The process of switching from the right slope corresponding to the first position to the left slope corresponding to the second position of the inverter system is as follows: 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; all power generation units in one group are short-circuited, and then the short-circuited power generation units are tracked by MPPT along the left slope until the operating power of all power generation units in the group reaches the second position; the above process is repeated in turn for the remaining multiple groups of power generation units according to the order until the operating power of all power generation units of the inverter system is located at the second position.

3. The method of claim 1, wherein, The process of switching from the right slope corresponding to the first position to the left slope corresponding to the second position of the inverter system is as follows: the operating power of all power generation units of the inverter system is lowered by ΔP to a third position on the same side of 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 power generation units in one group is lifted along the right slope to the highest point, and then lowered along the left slope to a fourth position with the same power as the third position; the above process is repeated in turn for the remaining multiple groups of power generation units according to the order until the operating power of all power generation units of the inverter system is located at the fourth position; the operating power of all power generation units of the inverter system is lifted by ΔP so that the operating power of all power generation units rises from the fourth position to the second position.

4. The method of claim 3, wherein the setting is performed when the output voltage of the inverter system is lower than a predetermined voltage. The total number of the power generation units of the inverter system is N, and the operating power of the power generation unit when power reduction is not performed is P limit ; The value of the number X of power generation units 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.

5. The method of claim 1, wherein, The process of switching from the left slope corresponding to the first position to the right slope corresponding to the second position of the inverter system is as follows: first, the driving lock of all power units of the inverter system is released so that all power generation units work at the open circuit voltage position; then, the driving lock of all power units of the inverter system is released to feed the grid; MPPT tracking of the inverter system is performed along the right slope until the operating power of all power generation units is located at the second position.

6. The method of claim 1, wherein, The process of switching from the left slope corresponding to the first position to the right slope corresponding to the second position of the inverter system is as follows: lowering the operating power of all the power generation units of the inverter system by ΔP to a third position on the same side of the first position; dividing the plurality of power generation units of the inverter system into a plurality of groups according to a set number, setting a sequence for the plurality of groups, and each group including at least one power generation unit; lifting the operating power of all the power generation units of the first group along a left slope to a highest point, and then lowering the operating power along a right slope to a fourth position with the same power as the third position; opening the circuit of all the power generation units of the second group to make all the power generation units of the second group work at a fifth position on the right slope, and performing MPPT tracking of all the power generation units of the second group on the right slope until the operating power of all the power generation units of the second group is at the fourth position; repeating the switching process of the second group of power generation units according to the sequence for the remaining groups of power generation units until all the power generation units of the inverter system are operating at the fourth position; lifting the operating power of all the power generation units of the inverter system by ΔP to make the operating power of all the power generation units rise from the fourth position to the second position.

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