A load-limited operation method for an inverter system

Abstract

The present application discloses a load-limited operation method for an inverter system, comprising the following steps: determining the current load-limited operation power of the inverter system at the first position 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 maintains the load-limited operation at the first position, otherwise the inverter system will switch to the second position of the working curve. Beneficial effects of the present application: 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, thereby effectively balancing the loss of the inverter system. The entire switching process is implemented in a pure software manner, which can effectively improve the smoothness of the switching.

Description

Technical Field

[0001] The present application relates to the field of renewable energy power generation, and in particular to a load-limited operation method for an inverter system. Background Art

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

[0003] like Figure 2 As shown, Figure 1 The photovoltaic working curve corresponding to the photovoltaic inverter system in operation. The curve can be divided from the MPPT position of the highest point 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-allocation is serious and the light intensity is large, the system needs to be load-limited. Generally, the load can be limited to the left slope of the curve, or the right slope of the curve.

[0004] When the system is running on the right slope with limited load, the corresponding bus voltage is higher, which means that the loss of the DC / AC unit is higher and the loss of the DC / DC unit is relatively smaller. When the system is running on the left slope with limited load, the corresponding bus voltage is lower, which means that under the same power condition, the input current of the DC / DC unit is larger, which leads to a relatively higher loss of the DC / DC unit. Therefore, how to ensure the loss balance of the system during the load-limited operation is a technical problem to be solved by those skilled in the art. Summary of the invention

[0005] One of the objectives of the present application is to provide a load-limited operation method for an inverter system that can solve at least one of the defects in the above-mentioned background technology.

[0006] In order to achieve at least one of the above-mentioned purposes, the technical solution adopted in the present application is: a load-limited operation method of an inverter system, comprising the following steps: determining the current load-limited operating power of the inverter system at a first position in a 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 maintains the load-limited operation at the first position, otherwise the inverter system will switch to the second position of the working curve; wherein the load-limited 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.

[0007] Preferably, the current operation data of the inverter system includes temperature data of the power unit; the inverter system is suitable for judging the loss of the inverter system at the current first position based on 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 located 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 the current temperature of the DC / AC unit is less than the set second threshold value, the loss of the inverter system does not meet the preset value, and the load-limited operation position of the inverter system will switch from the left slope to the right slope; 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 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 meet the preset value, and the load-limited 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 operating data of the inverter system, and the loss of the inverter system in the second position is predicted according to the obtained loss prediction model; the predicted result is used as a preset value to compare with the loss of the inverter system in the first position; if the loss of the inverter system in 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 maintain load-limited operation in the first position.

[0010] Preferably, 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.

[0011] Preferably, the process of switching the inverter system 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 a set number, each group includes at least one power generation unit; all the power generation units of one group are short-circuited, and then the short-circuited power generation units are subjected to MPPT tracking of the left slope until the operating power of all the power generation 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 power of all the power generation units of the inverter system are at the second position.

[0012] Preferably, the process of switching the inverter system 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 the power generation units of the inverter system by ΔP to a third position on the same side of the first position; dividing the multiple power generation units of the inverter system into multiple groups according to a set number, each group including at least one power generation unit; raising the operating power of all the power generation units of one group to the highest point along the right slope, and then reducing the operating power along the left slope to a fourth position with the same power as the third position; repeating 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 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.

[0013] Preferably, the total number of power generation units of the inverter system is N, and the operating power of the power generation unit when the power is not reduced is P limit ; The value of the number of power generation units in each group is: X≤N·ΔP / (P MPPT -P limit ), where P MPPT Indicates the power value corresponding to the highest point of the working curve.

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

[0015] Preferably, the process of switching the inverter system 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 the power generation units of the inverter system by ΔP to the third position on the same side of the first position; dividing the multiple power generation units of the inverter system into multiple groups according to a set number, setting a sequence for the multiple groups of power generation units, and each group includes at least one power generation unit; raising the operating power of all the power generation units of the first group to the highest point along the left slope, and then reducing the operating power along the right slope to a fourth position with the same power as the third position; opening all the power generation units of the second group so that all the power generation units of the second group work at the fifth position of the right slope, and 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 for the remaining power generation unit groups in sequence 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 beneficial effects of this application are:

[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, thereby effectively balancing the loss of the inverter system. The entire switching process is implemented in a pure software manner, which can effectively improve the smoothness of the switching. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0020] Figure 3 The figure is a schematic diagram of the overall workflow of this application.

[0021] Figure 4 This is a schematic diagram of the process of switching to load-limited operation based on temperature monitoring of the power unit in this application.

[0022] Figure 5 This is a flow chart of the load-limited operation switching based on loss prediction in this application.

[0023] Figure 6 A schematic diagram of a working curve of one example of switching from right-slope to left-slope load-limited operation of the inverter system of the present application.

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

[0025] Figure 8 The inverter system of this application is in progress Figure 6 Schematic diagram of the control flow of the control loop during the switching process shown.

[0026] Fig. 9 A schematic diagram of another example of a working curve for switching the inverter system of the present application from right slope to left slope load limited operation.

[0027] Fig.10 The inverter system of this application is in progress Fig. 9 Schematic diagram of the control flow of the control loop during the switching process shown.

[0028] Fig.11 A schematic diagram of a working curve of one example of switching from left-slope to right-slope load-limited operation of the inverter system of the present application.

[0029] Fig.12 Another example of the working curve diagram of the inverter system of the present application switching from left slope to right slope load limited operation Figure 1 .

[0030] Fig.13 Another example of the working curve diagram of the inverter system of the present application switching from left slope to right slope load limited operation Figure 2 . DETAILED DESCRIPTION

[0031] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0032] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application.

[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 are not necessarily used to describe a specific order or sequence.

[0034] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be connected, detachably connected, or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0036] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0037] One of the preferred embodiments of the present application is as follows: Figure 3As shown, a load-limited operation method of an inverter system includes the following steps: determining the current load-limited operation power of the inverter system at the first position in the working curve. Collecting the 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 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-limited 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.

[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 per unit time increases. Since the power devices are installed in a relatively closed environment, the heat increased by the power loss of the power device will cause the temperature of the installation space to rise sharply, until it exceeds the operating temperature threshold of the power device and causes the power device to burn out.

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

[0040] Therefore, in this embodiment, the load-limited operating position of the inverter system can be determined first, and then the loss data of the inverter system at different positions can be determined based on the current operating data of the inverter system, and then the inverter system can be switched to a lower loss position, thereby effectively balancing the loss of the inverter system; and the entire switching process is implemented in a pure software manner, which can effectively improve the smoothness of the switching. In layman's terms, the core idea of ​​this application is to determine which of the losses of the inverter system on the left slope and the right slope is smaller based on the current operating power, and then switch to the corresponding position with lower loss, so as to ensure that the inverter system always works in an area with lower loss, thereby ensuring the safe operation of the power device. For ease of understanding, a specific description can be given below.

[0041] Specifically, if the first position of the current operation of the inverter system is on the left slope, and the loss of the inverter system in the first position is greater than the loss when the inverter system is in the second position on the right slope, it means that the operating temperature of the DC / DC unit is high, 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 reduced, and at the same time, the DC / AC unit can increase the operating temperature within the temperature rise range. When the operating temperature of the DC / AC unit rises to exceed the upper limit of the temperature rise range, the DC / DC unit also has a certain temperature rise range due to the temperature drop, and 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-limited operation process, so that the loss balance of the inverter system can be achieved to 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, so the loss judgment of the inverter system at the current load-limited operation position can be directly achieved by temperature monitoring of the power device; 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 load-limited operation position can also be achieved by calculating the electrical parameters of the inverter system. For ease of understanding, the following will provide a detailed description of the above two different implementation methods through specific examples. 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 fields such as wind power generation and hydropower generation. However, in order to simplify the description of subsequent content, the subsequent content will be described using photovoltaic power generation as an example, and the power generation unit of the inverter system is the photovoltaic string PV.

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

[0044] It is understandable that the power unit of the inverter system includes a DC / DC unit and a DC / AC unit. The temperature data of the power unit collected during the operation phase of the inverter system may include only the temperature data of the DC / DC unit, only the temperature data of the DC / AC unit, or both the temperature data of the DC / DC unit and the DC / AC unit. Of course, in order to further ensure the accuracy of the judgment of the loss of the inverter system, it is preferred in this example to monitor the temperature of the DC / DC unit and the DC / AC unit at the same time to make a loss judgment.

[0045] Specifically, Figure 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 first threshold value T DC-DC_th , while the current temperature of the DC / AC unit T DC-AC Less than the set second threshold value T DC-AC_th This means that the temperature of the DC / DC unit exceeds the standard, while the temperature of the DC / AC unit still has a certain temperature rise range, which 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 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 first threshold value T DC-DC_th , while the current temperature of the DC / AC unit T DC-AC Greater than the set second threshold value T DC-AC_th This means that the temperature of the DC / AC unit exceeds the standard, and the temperature of the DC / DC unit still has a certain temperature rise range, which is specifically 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 first threshold value T DC-DC_th and the second threshold value T DC-AC_th The specific value of can be adaptively selected according to 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 the DC / DC unit as an example, the DC / DC unit includes a variety of different 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: Figure 5As shown, 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 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 will maintain load-limited operation at the first position. 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 switch 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 switch 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 based on the electrical parameters currently running at the first position; and 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 based on 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 known 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, namely, 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; therefore, the working voltage needs to be increased when the inverter system switches from the left slope to the right slope, and the working voltage needs to be reduced when the inverter system switches from the right slope to the left slope. The increase in working voltage and the reduction in working voltage have different overall effects on the inverter system, so the specific methods of switching the inverter system from the left slope to the right slope and from the right slope to the left slope are also different; for ease of understanding, the specific switching process of the inverter system will be described in detail below for switching from the left slope to the right slope and from the right slope to the left slope.

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

[0053] 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.

[0054] Example 1: Figure 6 and Figure 7As shown, 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 the 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 the power generation 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 power of all the power generation units of the inverter system is at the second position.

[0055] It should be known that the short circuit of the power generation unit will cause the corresponding load-limited operating power of the power generation unit to be reduced to 0, which will cause the bus voltage of the inverter system to drop instantaneously. Therefore, the power generation units of the inverter system cannot be switched at the same time, and need to be grouped and switched in sequence. In this way, although the bus voltage of the inverter system will still drop, the drop in the bus voltage will not be large due to the small number of power generation units in a single group. The specific number of power generation units in each group can be selected according to the actual needs of technical personnel in this field. 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 circuit of each power generation unit can cause the bus voltage to drop instantly by 2%, the number of power generation units in each group is at most two.

[0056] For ease of understanding, the following Figure 7 The specific switching process of the photovoltaic string PV#1 of the photovoltaic inverter system shown in FIG. 1 is described in detail as an example. Assume that the current load-limited operating power of the photovoltaic string PV#1 is P limit , then you can Figure 6 The working curve shown is based on the power P limit Draw a horizontal line. The intersection point A of the 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 of the photovoltaic string PV#1 for load-limited operation power switching, that is, the second position.

[0057] Then in the process of switching the running position, if Figure 7 As shown in the figure, PV string PV#1 can be short-circuited first, and the other PV strings remain normally connected. Then PV string PV#1 Figure 6 The position in the working curve shown is changed from point A to point 0 of the working curve. In order to realize the operation power of photovoltaic string PV#1 is changed from point A of the working curve to point 0, as shown in FIG. Figure 8 As shown, the control loop of the DC / DC unit corresponding to the photovoltaic string PV#1 keeps the drive constant high during the transformation from point A to point 0, thereby controlling the switch device S of the DC / DC unit. 11 and S 12 Short-circuit PV string PV#1.

[0058] Since the 0 point position of the working curve is the left slope endpoint position of the working curve, if Figure 8 As shown, the photovoltaic string PV#1 can perform left slope MPPT tracking through the control loop of the corresponding DC / DC unit until the load-limited operating power of the photovoltaic string PV#1 is reduced by Figure 6 The 0 point position in the diagram rises along the left slope to the B point position, 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 known that during the switching process from point 0 to point B, 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 described 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 described in detail here.

[0060] Example 2: Fig. 9 As shown, the operating power of all power generation units of the inverter system is reduced by ΔP to the 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 the set number, and each group includes at least one power generation unit. The operating power of all power generation units of one group is raised to the highest point along the right slope, and then the operating power is reduced along the left slope to the fourth position with the same power as the third position. The above process is repeated for the remaining multiple groups of power generation units in sequence until the operating power of all power generation units of the inverter system is at the fourth position; the operating power of all power generation units of the inverter system is raised by ΔP, so that the operating power of all power generation units is increased from the fourth position to the second position.

[0061] It is understandable that, since the power generation unit needs to pass through the highest point of the working curve, i.e., the MPPT point, during the position switching process, this is a power increase for the power generation unit, which will cause the load-limited operating power of the inverter system to rise to a value exceeding the limit. Therefore, in this example, the operating power of all power generation units is reduced before the position switching of the power generation unit is performed, so that it can be ensured that when the operating power of the power generation unit reaches the MPPT point, the load-limited operating power of the inverter system will not exceed the limit. Of course, all power generation units of the inverter system cannot be switched at the same time, otherwise the load-limited operating power of the inverter system will still exceed the limit.

[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 safe operation 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 the requirement of X≤N·ΔP / (P MPPT -P limit ), where N represents the total number of power generation units of the inverter system, Plimit Indicates the operating power of the power generation unit when no power reduction is performed, P MPPT Indicates 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 of this group of power generation units when raising the power to the MPPT point must be less than or equal to the total power decrease of the inverter system beforehand.

[0063] For ease of understanding, the following will take the specific switching process of one power generation unit as an example for detailed description. Fig. 9 As shown, assuming that the current load-limited operating power of the power generation unit is P limit , then you can Fig. 9 The working curve shown is based on the power P limit Draw a horizontal line. The intersection point A of the horizontal line and the right slope of the working curve is the first position of the generating 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 of the generating unit for load-limited operation power switching, that is, the second position. Fig. 9 As shown, the corresponding power P limit Subtract ΔP to get the power P limit ´, in the working curve according to the power P limit Draw a horizontal line; the intersection point C of the horizontal line and the right slope of the working curve is the third position, and the intersection point D of the horizontal line and the left slope of the working curve is the fourth position. Let M be the highest point of the working curve, then the position switching path of the power generation unit is A—C—M—D—B.

[0064] like Fig.10 As shown, when the power generation unit switches from path A to path C, the control loop of the DC / DC unit corresponding to the power generation unit can track the power limit of the right slope MPPT to the power P limit When the power generation unit switches from path C to M, the control loop of the DC / DC unit corresponding to the power generation unit can track the maximum power point of the right slope MPPT. When the power generation unit switches from path M to D, the control loop of the DC / DC unit corresponding to the power generation unit can track the power limit of the left slope MPPT to power P limit When the power generation unit switches from path D to path B, the control loop of the DC / DC unit corresponding to the power generation unit can track the left slope MPPT power limit 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: Fig.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. Fig.11 As shown, assuming that the current load-limited operating power of the power generation unit is P limit , then you can Fig.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 Fig.11The voltage corresponding to the endpoint E of the right slope; then the switching path of the power generation unit is B-E-A.

[0070] Example 2: Fig.12 and Fig.13 As shown, the operating power of all power generation units of the inverter system is reduced 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 the set number, and the order of priority is set for the multiple groups of power generation units, and each group includes at least one power generation unit. The operating power of all power generation units of the first group is raised to the highest point along the left slope, and then the operating power is reduced to the fourth position with the same power as the third position along the right slope. All power generation units of the second group are open-circuited so that all power generation units of the second group work at the fifth position of the right slope, and all power generation units of the second group are tracked by MPPT on the right slope until the operating power of all 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 order until all power generation units of the inverter system are running 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 first raise the bus voltage to a certain extent; so that when the second and subsequent groups of power generation units are open-circuited, the open-circuit voltage of the second and subsequent groups of power generation units will not directly reach the maximum value U due to the influence of the first group of power generation units. oc Position can effectively suppress the bus voltage burst 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, when switching positions, in order to ensure that the inverter system does not exceed the load limit power during the switching process, all power generation units need to be reduced in power first.

[0072] For ease of understanding, the following will be described in detail using the first two groups of power generation units as an example.

[0073] like Fig.12 As shown, assuming that the current load-limited operating power of the first group of power generation units is P limit , then you can Fig.12 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 generating 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 generating unit for load-limited operation power switching, that is, the second position. limit Subtract ΔP to get the power P limit ´, in the working curve according to the power P limitDraw a horizontal line; the intersection point D of the horizontal line and the left slope of the working curve is the third position, and the intersection point C of the horizontal line and the right slope of the working curve is the fourth position. Let M be the highest point of the working curve, then the position switching path of the first group of power generation units is B—D—M—C—A.

[0074] like Fig.13 As shown, assuming that the current load-limited operating power of the second group of power generation units is P limit , then you can Fig.13 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 generating 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 generating unit for load-limited operation power switching, that is, the second position. limit Subtract ΔP to get the power P limit ´, in the working curve according to the power P limit ' draw a horizontal line; the intersection D of the horizontal line and the left slope of the working curve is the third position, and the intersection C of the horizontal line and the right slope of the working curve is the fourth position. When the second group of generating units is driven and blocked, the first group of generating units is already at the fourth position of point C, which raises the bus voltage, making the open circuit voltage V bus The point F below the point C of the working curve is the fifth position. The position switching path of the second group of power generation units is B—D—F—C—A.

[0075] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A 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; The current operation data of the inverter system includes temperature data of the power unit; the inverter system is suitable for judging 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; The power unit of the inverter system includes a DC / DC unit and a DC / AC unit; 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 of the DC / DC unit is greater than the set first threshold value, and the current temperature of the DC / AC unit is less than the set second threshold value, the loss of the inverter system 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 right slope; 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 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 meet the preset value, and the load-limited operation position of the inverter system will switch from the right slope to the left slope.

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: Reduce the operating power of all power generation units in the inverter system 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; Increase the operating power of all power generation units in the inverter system , so that the operating power of all 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 generating units X in each group is: ; 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: Reduce the operating power of all power generation units in the inverter system 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; Increase the operating power of all power generation units in the inverter system , so that the operating power of all power generation units increases from the fourth position to the second position.

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