A photovoltaic inverter

Abstract

The present invention discloses a photovoltaic inverter, comprising: at least one group of MPPT modules and DC / DC units connected in sequence, wherein the MPPT modules have a first mode, a second mode, and a third mode; the number of connected strings of the MPPT modules in the second mode is less than the number of connected strings of the MPPT modules in the first mode and the third mode; within the same time period, the output maximum current of the MPPT modules in the third mode exceeds the current upper limit value i pv_max The number of times is higher than the first mode and the second mode; the second mode is distinguished by judging the output current of each string of the MPPT module, and the maximum output current of the MPPT module within the time length T exceeds the current upper limit value i pv_max times to distinguish the first mode from the third mode; a control module, used to output a PWMDC / DC signal to control the DC / DC unit, so that the photovoltaic inverter operates in a steady-state mode, a current limiting mode, a load limiting mode, or a strong light start-up mode. The input of the control module is adjusted according to the type of the MPPT module to adapt to the specifications of the photovoltaic module.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic energy, and in particular to a photovoltaic inverter. Background Art

[0002] In the field of photovoltaic energy, photovoltaic modules are the core components of the system, and their performance and specifications directly affect the efficiency and stability of the entire photovoltaic system. With the rapid development of photovoltaic technology, a variety of photovoltaic modules of different specifications have appeared on the market, such as square modules and rectangular modules of different specifications. These photovoltaic modules have significant differences in size, power output, voltage and current characteristics, and therefore require photovoltaic inverter systems with different software architectures to adapt.

[0003] However, in order to adapt to photovoltaic modules of different specifications, the system architecture and control strategy must be developed separately, which not only increases the R&D costs and the costs of subsequent operation and maintenance, but also limits the versatility and scalability of the system architecture and control strategy, which is not conducive to quickly adapting to market changes and the application of new technologies. Summary of the invention

[0004] An object of the present invention is to provide a photovoltaic inverter adapted to photovoltaic modules of different specifications.

[0005] To achieve at least one of the above purposes, the technical solution adopted by the present invention is: a photovoltaic inverter, comprising: at least one set of MPPT modules and DC / DC units connected in sequence, the MPPT module having a first mode, a second mode, and a third mode; the second mode is distinguished by judging the output current of each string of the MPPT module, and the maximum output current of the MPPT module exceeds the current upper limit value i within a time period T. pv_max times to distinguish the first mode from the third mode; a control module, used to output a PWMDC / DC signal to control the DC / DC unit, so that the photovoltaic inverter operates in a steady-state mode, a current limiting mode, a load limiting mode, or a strong light start-up mode, and the input of the control module is adjusted according to the mode of the MPPT module to adapt to the specifications of the photovoltaic module.

[0006] As a preferred embodiment, the control module includes a DC voltage loop, a current limiting loop, a load limiting loop and a DC current loop, wherein the DC voltage loop is used to output a first reference value i pv1_1* The current limiting loop is used to output a second reference value i pv1_2* The load limit ring is used to output a third reference value i pv1_3* , the first reference value i pv1_1* The second reference value i pv1_2* and the third reference value i pv1_3* The minimum value among the three is taken as the given value i pv* , the given value ipv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC Signal.

[0007] As a preferred embodiment, when the output current of at least one string of each DC / DC unit is 0A, it is determined that the MPPT module adopts the second mode; on the basis that the output current of each string of each DC / DC unit is greater than 0A, the number of times X of triggering the current limiting loop within the time length T is counted, and when the number X is greater than or equal to the set number X max When the MPPT module adopts the third mode, the number of times X is less than the set number of times X. max When the MPPT module adopts the first mode, it is determined that the MPPT module adopts the first mode.

[0008] As a preferred embodiment, the input voltage sampling value v of the DC / DC unit is pv And the input current sampling value i pv As the input of the MPPT module, the MPPT module is used to output the PV side voltage reference v pv* , the PV side voltage reference v pv* As the input of the DC voltage loop, the DC voltage loop is used to compare v pv* With the input voltage sampling value v pv To obtain the first reference value i pv1_1* The load limit ring is used to compare the upper limit value v of the bus voltage BUS_max And the sampling value of bus voltage v BUS , to output the third reference value i pv1_3* .

[0009] As a preferred embodiment, the current limiting loop is used to set the current upper limit value i pv_max As i pv1_2* Output, the current upper limit value i pv_max Adjustments are made according to the mode adopted by the MPPT module.

[0010] As a preferred embodiment, at the first reference value i pv1_1* Exceeding the current upper limit i pv_max When the output of the DC voltage loop is modified to the current upper limit value i pv_max ; In the third reference value i pv1_3* Exceeding the current upper limit i pv_max When the output of the load limit ring is modified to the current upper limit value i pv_max , the current upper limit value i pv_max Adjustments are made according to the mode adopted by the MPPT module.

[0011] As a preferred embodiment, in the steady-state mode, the DC voltage loop outputs a first reference value i pv1_1* , the current limiting loop outputs a second reference value i pv1_2* , the first reference value i pv1_1* and the second reference value i pv1_2* The minimum value of the two is taken as the given value i pv* , the fixed value i pv* Acting on the DC current loop.

[0012] As a preferred embodiment, in the second reference value i pv1_2* Greater than the first reference value i pv1_1* When the photovoltaic inverter is in current limiting mode, the current limiting loop outputs a second reference value i pv1_2* , the second reference value i pv1_2* As a given value i pv* , the fixed value i pv* Acting on the DC current loop.

[0013] As a preferred embodiment, in the load limiting mode, the current limiting loop is used to output the second reference value i pv1_2* The load limit ring is used to output a third reference value i pv1_3* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value of the two is taken as the given value i pv* , the fixed value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC signal, causing the output power on the PV side to decrease.

[0014] As a preferred embodiment, the control module further includes a bus voltage loop, which is used to compare the set value v of the bus voltage BUS* And the sampling value of bus voltage v BUS , to output the fourth reference value i pv1_4* In the strong light start mode, when the MPPT module adopts the third mode, the current limiting loop is used to output the second reference value i pv1_2* , the bus voltage loop is used to output the fourth reference value i pv1_4* , the second reference value ipv 1_2* and the fourth reference value i pv1_4* The minimum value of the two is taken as the given value i pv* , the fixed value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DCsignal; when the MPPT module adopts the first mode or the second mode, the bus voltage loop is used to output the fourth reference value i pv1_4* , the fourth reference value i pv1_4* As a given value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC Signal.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) By judging that the output current of each string and the maximum output current of the MPPT module within the time T exceeds the current upper limit i pv_max The number of times can distinguish whether the MPPT module adopts the first mode, the second mode or the third mode, thereby facilitating the adjustment of the input of the control module so that the photovoltaic inverter is adapted to photovoltaic modules of different specifications;

[0017] (2) The control module enables the photovoltaic inverter to operate in a steady-state mode, a current limiting mode, a load limiting mode, or a strong light start-up mode, so as to play the role of current load limiting and current amplitude limiting, which is conducive to the safe and reliable operation of the photovoltaic inverter;

[0018] (3) The input of the control module is adjusted according to the mode of the MPPT module, that is, the current upper limit value i is adjusted according to the determined mode of the MPPT module. pv_max , which helps to avoid overshoot of the DC voltage loop output, thereby improving the stability and performance of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of a photovoltaic inverter when the MPPT module of some embodiments of the present application adopts the first mode.

[0020] Figure 2 This is a schematic diagram of a photovoltaic inverter when the MPPT module of some embodiments of the present application adopts the second mode.

[0021] Figure 3 This is a schematic diagram of a photovoltaic inverter when the MPPT module of some embodiments of the present application adopts the third mode.

[0022] Figure 4 is a schematic diagram of a photovoltaic inverter according to some embodiments of the present application.

[0023] Figure 5 It is a control strategy diagram of a control module of a photovoltaic inverter in some embodiments of the present application.

[0024] Figure 6It is a control strategy diagram of a control module of a photovoltaic inverter in other embodiments of the present application.

[0025] Figure 7 This is a mode judgment flow chart of the MPPT module of the photovoltaic inverter in some embodiments of the present application.

[0026] Figure 8 This is a schematic diagram of input current sampling of a DC / DC module 1 of a photovoltaic inverter in some embodiments of the present application.

[0027] Fig. 9 It is a control strategy diagram of the control module in some embodiments of the present application in steady-state mode.

[0028] Fig.10 It is a control strategy diagram of the control module in the current limiting mode in some embodiments of the present application.

[0029] Fig.11 It is a control strategy diagram of the control module in some embodiments of the present application under load limiting mode.

[0030] Fig.12 This is a control strategy diagram of the control module in the strong light startup mode when the PMMT module of some embodiments of the present application adopts the third mode.

[0031] Fig.13 It is a control strategy diagram of the control module in the strong light startup mode when the PMMT module of some embodiments of the present application adopts the first mode or the second mode.

[0032] Fig.14 This is a control strategy diagram of the control loop of some embodiments of the present application in the strong light startup mode.

[0033] Fig.15 This is a control strategy diagram of the control loop of some embodiments of the present application after the strong light startup is completed.

[0034] In the figure: 101, control module; 201, MPPT module; 202, DC voltage loop; 203, DC current loop; 204, first PWM generation module; 205, current limiting loop; 206, load limiting loop; 207, bus voltage loop; 102, control loop; 208, second PWM generation module. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0036] 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.

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

[0038] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, a contact connection, or an indirect connection through an intermediate medium, and it can be the internal communication of 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.

[0039] A photovoltaic inverter, such as Figure 1-Figure 4 As shown, it includes: at least one group of MPPT modules 201 and DC / DC units connected in sequence, the MPPT module 201 has a first mode, a second mode, and a third mode; the second mode is distinguished by judging the output current of each string of the MPPT module 201, and the maximum output current of the MPPT module 201 within the time length T exceeds the current upper limit value i pv_max The control module 101 is used to output PWM DC / DC The signal controls the DC / DC unit so that the photovoltaic inverter operates in a steady-state mode, a current limiting mode, a load limiting mode, or a strong light start-up mode. The input of the control module 101 is adjusted according to the mode of the MPPT module 201 to adapt to the specifications of the photovoltaic module.

[0040] That is, by judging the output current of each string and whether the maximum output current of the MPPT module 201 exceeds the current upper limit i within the time T, pv_max The number of times can distinguish whether the MPPT module 201 adopts the first mode, the second mode or the third mode, and then it is convenient to adjust the input of the control module 101, so that the photovoltaic inverter is adapted to photovoltaic modules of different specifications. And through the control module 101, the photovoltaic inverter can be switched between the steady-state mode, the current limiting mode, the load limiting mode or the strong light start mode to play the role of current load limiting and current amplitude limiting, which is conducive to the safe and reliable operation of the photovoltaic inverter.

[0041] For ease of understanding, a simple example can be given below to illustrate. Commonly used bifacial photovoltaic modules include 182 square modules, 210 square modules, and 182×210 rectangular modules. Table 1 shows the parameters of 182 square modules, Table 2 shows the parameters of 210 square modules, and Table 3 shows the parameters of 182×210 rectangular modules. When using bifacial photovoltaic modules, it is necessary to consider the back current superposition, that is, the actual output current of the photovoltaic module is the sum of the front output current and the back output current, and the back output current is the product of the front output current and the back current gain. The back current gain is usually 5%, 10%, and 15%.

[0042] Table 1 Parameters of 182 square components

[0043]

[0044] Table 2 Parameters of 210 square modules

[0045]

[0046] Table 3 Parameters of 182×210 rectangular modules

[0047]

[0048] In this example, it is assumed that the maximum bus voltage is 1100V, the grid-connected rated power is 150KW, the photovoltaic inverter has 7 MPPT modules 201, each MPPT module 201 is suitable for connecting to 3 strings at most, and the set current upper limit i of each MPPT module 201 is pv_max To save costs.

[0049] It can be understood that, in combination with Table 1 and Figure 1 As shown, the open circuit voltage V of the 182-gauge square component OC The maximum power point voltage V of the square module with a specification of 182 is about 53V. mpp The voltage of each string is about 44V, so each string of the MPPT module 201 can be connected to 19 square modules of 182 specifications, so that the voltage of each string is less than the maximum voltage of the busbar. The maximum power P of the square module of 182 specifications is max It is about 590W, so the MPPT module 201 can be connected to 3 strings, so that the capacity ratio of the photovoltaic inverter is about 1.6, which is beneficial to improve the flexibility of the photovoltaic inverter and reduce the cost of the photovoltaic inverter.

[0050] Combining Table 2 and Figure 2 As shown, the open circuit voltage V of the 210-gauge square module OCAll are less than 49V, the maximum power point voltage V of the 210 specification square module mpp The voltage of each string is about 41V, so each string of the MPPT module 201 can be connected to 21 square modules of 182 specifications, so that the voltage of each string is less than the maximum voltage of the busbar. The maximum power P of the square module of 210 specifications max The power consumption of each MPPT module 201 is about 715W, so the MPPT module 201 can be connected to two strings, making the capacity ratio of the photovoltaic inverter about 1.4, which is conducive to improving the flexibility of the photovoltaic inverter and reducing the cost of the photovoltaic inverter. In other words, each MPPT module 201 has one string that is not connected.

[0051] Combining Table 3 and Figure 3 As shown, the open circuit voltage V of the 182×210 rectangular component OC All are less than 49.5V, the maximum power point voltage V of the rectangular component with a specification of 182×210 mpp The voltage of each string is about 41V, so each string of the MPPT module 201 is connected to 21 rectangular modules of 182×210 specifications, so that the voltage of each string is less than the maximum voltage of the busbar. However, the maximum power P of the rectangular modules of 182×210 specifications is max It is about 625W. If the MPPT module 201 is connected to 2 strings, the capacity ratio of the photovoltaic inverter is about 1.2. In order to improve the capacity ratio of the system, the number of photovoltaic modules on each string needs to be increased, but it will cause the bus voltage to be too high, resulting in the system being unable to operate. Therefore, the MPPT module 201 is connected to 3 strings. It is worth mentioning that when the MPPT module 201 is connected to 3 strings, the output current of the MPPT module 201 may exceed the current upper limit i pv_max .

[0052] It can be understood that the connection method of the above-mentioned 182-specification square components is suitable for adopting the first mode MPPT module 201, the connection method of the 210-specification square components is suitable for adopting the second mode MPPT module 201, and the connection method of the 182×210-specification rectangular components is suitable for adopting the third mode MPPT module 201.

[0053] Specifically, when the photovoltaic module is a square module of specification 210, each MPPT module 201 has one path that is not connected to a string, and one path of the string current is 0A, that is, the number of strings actually connected to the MPPT module 201 is less than the maximum number that the MPPT module 201 is suitable for connecting, so that the square module of specification 210 can be distinguished from the square module of specification 182 and the rectangular module of specification 182×210, that is, the MPPT module 201 of the second mode can be distinguished from the MPPT module 201 of the first mode and the MPPT module 201 of the third mode.

[0054] Furthermore, when the photovoltaic module is a square module of 182 specifications, the MPPT module 201 is connected to 3 strings. Since the maximum power point current I mpp The output current of the MPPT module 201 is not more than 16A, so it is not easy to exceed the upper current limit i pv_max However, when the photovoltaic module is a rectangular module with a specification of 182×210, although the MPPT module 201 is also connected to three strings, due to the maximum power point current I mpp will exceed 16A, causing the output current of the MPPT module 201 to exceed the current upper limit i pv_max Then, by determining whether the maximum output current of the MPPT module 201 exceeds the current upper limit i within the time period T, pv_max The number of times is used to distinguish the square components of 182 specifications and the rectangular components of 182×210 specifications, that is, to distinguish the MPPT modules 201 of the first mode and the MPPT modules 201 of the third mode.

[0055] It is worth mentioning that the specifications of the photovoltaic modules are not limited to 182 square modules, 210 square modules and 182×210 rectangular modules. The above examples are only for ease of understanding. In other embodiments, photovoltaic modules of other specifications can also be used. The number of MPPT modules 201 of the photovoltaic inverter and the maximum number of MPPT modules 201 suitable for connecting to the string can also be adjusted according to the actual application scenario, and this application does not impose specific restrictions on this.

[0056] In some embodiments, Figure 5 and Figure 6 As shown, the control module 101 includes a DC voltage loop 202, a current limiting loop 205, a load limiting loop 206 and a DC current loop 203. The DC voltage loop 202 is used to output a first reference value i pv1_1* , the current limiting loop 205 is used to output the second reference value i pv1_2* , the load limit ring 206 is used to output the third reference value i pv1_3* , the first reference value i pv1_1* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value among the three is taken as the given value i pv* , given value i pv* Acting on the DC current loop 203, the DC current loop 203 is used to output the duty cycle d DC / DC , to control PWM DC / DC It can be understood that the first reference value i pv1_1* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value among the three is taken as the given value ipv* , which can play the role of current load limitation and current amplitude limitation, which is conducive to the safe and reliable operation of the photovoltaic inverter.

[0057] In some embodiments, the DC current loop 203 includes a comparator 2 and a PI controller 2. Specifically, the comparator 2 is used to compare the PV side voltage reference v pv* and given value i pv* The output of comparator 2 is used as the input of PI controller 2, which is used to output duty cycle d DC / DC , duty cycle d DC / DC Used to control the first PWM generation module 204, the first PWM generation module 204 is used to output PWM DC / DC The signal acts on the DC / DC unit.

[0058] In some embodiments, Figure 5 and Figure 6 As shown, the input voltage sampling value v of the DC / DC unit pv And the input current sampling value i pv As the input of MPPT module 201, MPPT module 201 is used to output PV side voltage reference v pv* , PV side voltage reference v pv* As the input of DC voltage loop 202, DC voltage loop 202 is used to compare v pv* With the input voltage sampling value v pv , to obtain the first reference value i pv1_1* .

[0059] In at least one embodiment, the DC voltage loop 202 includes a comparator 1 and a PI controller 1. Specifically, the comparator 1 is used to compare the PV side voltage reference v pv* And the input voltage sampling value v pv The output result of comparator 1 is used as the input of PI controller 1, and PI controller 1 is used to output the first reference value i pv1_1* It can be understood that the PV side voltage reference v output by the MPPT module 201 is compared by the DC voltage loop 202. pv* And the input voltage sampling value v pv , and outputs a first reference value for controlling PWM DC / DC The signal is beneficial to improve the dynamic response speed of the photovoltaic inverter in steady-state mode, so that the photovoltaic inverter can adapt to load changes and light intensity changes more quickly.

[0060] In some embodiments, Figure 5 and Figure 6 As shown, the load limit ring 206 is used to compare the upper limit value v of the bus voltage. BUS_max And the sampling value of bus voltage v BUS, to output the third reference value i pv1_3* It is understandable that when the PV inverter needs to limit the output power, the DC / AC unit side of the PV inverter reduces the output power, but the output power of the DC / DC unit side changes slower than that of the DC / AC unit side, which causes the electric energy to be stored on the bus, resulting in an increase in the bus voltage. Further, the bus voltage can be reduced by reducing the output power on the PV side. Specifically, at the sampling value v of the bus voltage BUS Higher than the upper limit of bus voltage v BUS_max When the load limit ring 206 compares the upper limit value v of the bus voltage BUS_max And the sampling value of bus voltage v BUS , to output the third reference value i pv1_3* , which reduces the output power on the PV side, helps avoid grid overload and improves the reliability and safety of the photovoltaic system.

[0061] In at least one embodiment, the load limit loop 206 includes a comparator 3 and a PI controller 3. Specifically, the comparator 3 is used to compare the upper limit value v of the bus voltage. BUS_max And the sampling value of bus voltage v BUS The output result of the comparator 3 is used as the input of the PI controller 3, and the PI controller 3 is used to output the third reference value i pv1_3* .

[0062] In some embodiments, Figure 5 As shown, the current limiting loop 205 is used to set the current upper limit value i pv_max As i pv1_2* Output, so that the input current of the DC / DC unit does not exceed the current upper limit i pv_max It can be understood that the first reference value i pv1_1* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value among the three is taken as the given value i pv* Acting on the DC current loop 203, that is, the current limiting loop 205 can ensure that the input current of the DC / DC unit does not exceed the current upper limit i pv_max This helps to avoid damage to the photovoltaic inverter or load unit due to excessive current.

[0063] In other embodiments, Figure 6 As shown, at the first reference value i pv1_1* Exceeding the current upper limit i pv_max When the output of the DC voltage loop 202 is modified to the current upper limit value i pv_max ; At the third reference value i pv1_3* Exceeding the current upper limit i pv_max When the load limit ring 206 output is modified to the current upper limit value i pv_max, and thus can play the same role as setting the current limiting ring 205. In other words, the current upper limit i pv_max , the third reference value i pv1_3* and the current upper limit i pv_max The minimum value among the three is taken as the given value i pv* Acting on the DC current loop 203, so that the input current of the DC / DC unit does not exceed the current upper limit i pv_max .

[0064] It is worth mentioning that the output current capabilities of the MPPT modules 201 of different modes are also different. If the output current, that is, the input current i of the DC / DC unit pv Compared with the current upper limit i pv_max If it is too small, then when the DC voltage loop 202 outputs overshoot, the response speed of the photovoltaic inverter will be reduced, thereby affecting the system stability and performance of the photovoltaic inverter.

[0065] For example, in the example described above, the MPPT module 201 in the second mode is connected to only two strings, which may cause the input current i pv Therefore, the upper limit of the current i pv_max The current upper limit value i is adjusted according to the mode adopted by the MPPT module 201. That is, after completing the mode recognition of the MPPT module 201, the current upper limit value i pv_max Adjustments are made, and then the DC / DC unit is adapted to the MPPT module 201 through adjustments of the control module 101 .

[0066] For ease of understanding, the above example is used for explanation. The connection method of the square assembly of 182 specifications is suitable for the MPPT module 201 of the first mode. The current of the square assembly of 182 specifications is about 15A. Each MPPT module 201 is connected to 3 strings, and the input current i of the DC / DC unit is pv Around 45A.

[0067] The connection method of the above-mentioned rectangular components of 182×210 specifications is suitable for the MPPT module 201 using the third mode. The current of the rectangular components of 182×210 specifications is about 16A to 17A. Each MPPT module 201 is connected to 3 strings. Through the control of the current limiting loop 205, the input current i of the DC / DC unit is pv Not exceeding 48A.

[0068] The connection method of the square assembly of the 210 specification is suitable for the MPPT module 201 of the second mode. The current of the square assembly of the 210 specification is about 18A to 20A. Each MPPT module 201 is only connected to 2 strings, so the input current i of the DC / DC unit is pvAround 40A. In other words, the input current i of the DC / DC unit is pv Small, so the current upper limit value i needs to be adjusted pv_max , so that the MPPT module 201 has a good response speed.

[0069] In at least one embodiment, when the MPPT module 201 is determined to be in the first mode or the third mode, the current upper limit value i pv_max When the MPPT module 201 is determined to adopt the first mode or the third mode, the current upper limit value i pv_max It is 42A.

[0070] Furthermore, how to implement the pattern recognition of the MPPT module 201 is described in conjunction with the above-mentioned control module 101 .

[0071] like Figure 7 As shown, when the output current of at least one string in each DC / DC unit is 0A, it is determined that the MPPT module 201 adopts the second mode. Further, on the basis that the output current of each string of each DC / DC unit is greater than 0A, the number of times X that the current limiting loop 205 is triggered within the time length T is counted, and when the number X is greater than or equal to the set number X max When the MPPT module 201 adopts the third mode, the number of times X is less than the set number of times X. max When the MPPT module 201 adopts the first mode, the first mode, the second mode and the third mode are distinguished.

[0072] That is to say, after starting up, the output current of each string of each MPPT module 201 is detected. If the output current of at least one string of each DC / DC unit is 0A, that is, at least one string of the MPPT module 201 is not connected, then it is determined that the MPPT module 201 adopts the second mode. Otherwise, the number of times X that the current limiting loop 205 is triggered within the time length T is counted, that is, the given value i within the time length T is pv* The value is the second reference value i pv1_2* If the number of times X is greater than or equal to the set number of times X max , determine that the MPPT module 201 adopts the third mode, if the number X is less than the set number X max When the MPPT module 201 is determined to adopt the first mode.

[0073] In the example above, the connection mode of the square components of the 182 specifications is suitable for the MPPT module 201 of the first mode, and the input current ipv of the DC / DC unit is about 45A; the connection mode of the square components of the 210 specifications is suitable for the MPPT module 201 of the second mode, and the input current ipv of the DC / DC unit is about 40A. Further, when the MPPT module 201 adopts the first mode, the current upper limit value i is set. pv_max is 48A. When the MPPT module 201 adopts the second mode, the current upper limit value i pv_max It is 42A. It can be understood that the MPPT module 201 triggers the current limiting loop 205 less times when using the first mode and the second mode, so that it can work at the maximum power point for a long time. Furthermore, the connection method of the above-mentioned 182×210 rectangular components is suitable for the MPPT module 201 using the third mode. It is necessary to control the current limiting loop 205 so that the input current i of the DC / DC unit pv No more than 48A, that is to say, the number of times the current limiting ring 205 is triggered is relatively large, and thus it can be set by setting a reasonable number of times X max To distinguish the first mode from the third mode.

[0074] In some embodiments, the input current i of the DC / DC unit is pv Sampling is performed, and the input current i obtained by sampling is pv Adjust the current upper limit value i pv_max .

[0075] In a specific embodiment, Figure 8 As shown, the zero point of the triangular modulation wave is selected as the sampling point to obtain the input current i pv The average value of the input current i pv Adjust the current upper limit value i based on the average value of pv_max , so that the input current i pv The average value does not exceed the current upper limit i pv_max .

[0076] It is worth mentioning that the input current i can also be sampled pv The peak value of the input current i pv The current upper limit value is adjusted based on the peak value i pv_max , so that the input current i pv The peak value does not exceed the upper limit of the current i pv_max Alternatively, the input current i can be obtained by sampling pv The input current i is obtained by calculating the mean value and design parameters pv peak value.

[0077] Furthermore, the working conditions of the control module 101 in the steady-state mode, the current limiting mode, the load limiting mode, and the strong light startup mode are described.

[0078] In some embodiments, Fig. 9 As shown, in the steady-state mode, the DC voltage loop 202 outputs the first reference value i pv1_1* , the current limiting loop 205 outputs a second reference value i pv1_2* , the first reference value i pv1_1* and the second reference value i pv1_2* The minimum value of the two is taken as the given value i pv* , constant value i pv* Acting on the DC current loop 203.

[0079] That is, in the steady-state mode, the load limit loop 206 does not work, the DC voltage loop 202, the current limit loop 205 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 is pv* is the first reference value i pv1_1* and the second reference value i pv1_2* The smaller value of the two, thus ensuring that the input current i of the DC / DC unit is pv Do not exceed the current upper limit i pv_max , which helps to avoid damage to the photovoltaic inverter or load unit due to excessive current.

[0080] In some embodiments, Fig.10 As shown, at the second reference value i pv1_2* Greater than the first reference value i pv1_1* When the photovoltaic inverter is in current limiting mode, the current limiting loop 205 outputs the second reference value i pv1_2* , the second reference value i = as given value i pv* , constant value i pv* Acting on the DC current loop 203.

[0081] That is, in the current limiting mode, the DC voltage loop 202 and the load limiting loop 206 do not work, and the current limiting loop 205 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 is pv* is the second reference value i pv1_2* , thereby ensuring the input current i of the DC / DC unit pv Do not exceed the current upper limit i pv_max Until the DC voltage loop 202 outputs the first reference value i pv1_1* is less than the second reference value i output by the current limiting loop 205 pv1_2* , so that the photovoltaic inverter enters the steady-state mode; or until the third reference value i output by the load limit loop 206 is pv1_3* is less than the second reference value i output by the current limiting loop 205pv1_2* , so that the PV inverter enters load limiting mode.

[0082] In some embodiments, Fig.11 As shown, in the load limiting mode, the current limiting loop 205 is used to output the second reference value i pv1_2* , the load limit ring 206 is used to output the third reference value i pv1_3* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value of the two is taken as the given value i pv* , given value i pv* Acting on the DC current loop 203, the DC current loop 203 is used to output the duty cycle d DC / DC , to control PWM DC / DC signal, causing the output power on the PV side to decrease.

[0083] That is, the MPPT module 201 and the DC voltage loop 202 do not work, and the current limiting loop 205, the load limiting loop 206 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 is pv* is the second reference value i pv1_2* and the second reference value i pv1_2* The smaller value of the two, thereby ensuring that the input current i of the DC / DC unit is pv Do not exceed the current upper limit i pv_max , which helps to avoid damage to the photovoltaic inverter or load unit due to excessive current.

[0084] In some embodiments, Fig.12 and Fig.13 As shown, the control module 101 also includes a bus voltage loop 207, which is used to compare the set value v of the bus voltage. BUS* And the sampling value of bus voltage v BUS , to output the fourth reference value i pv1_4* .

[0085] In at least one embodiment, the bus voltage loop 207 includes a comparator 4 and a PI controller 4, wherein the comparator 4 is used to compare the set value v of the bus voltage. BUS* And the sampling value of bus voltage v BUS , to perform error analysis, the output result of comparator 4 is used as the input of PI controller 4, and PI controller 4 is used to output the fourth reference value i pv1_4* .

[0086] It is understandable that when the machine is started under sufficient sunlight, the output current of the MPPT module 201 during the startup process, that is, the input current i of the DC / DC unit pv The current limit may be exceededpv_max , so it is necessary to adopt the current limiting starting method.

[0087] In some embodiments, Fig.12 As shown, in the strong light start mode, when the MPPT module 201 adopts the third mode, the current limiting ring 205 is used to output the second reference value i pv1_2* , bus voltage loop 207 is used to output a fourth reference value i pv1_4* , the second reference value i pv1_2* and the fourth reference value i pv1_4* The minimum value of the two is taken as the given value i pv* , constant value i pv* Acting on the DC current loop 203, the DC current loop 203 is used to output the duty cycle d DC / DC , duty cycle d DC / DC Acting on the first PWM generating module 204 to control the first PWM generating module 204 to output PWM DC / DC Signal.

[0088] That is, in the strong light start mode when the MPPT module 201 adopts the third mode, the DC voltage loop 202 and the load limit loop 206 do not work, and the bus voltage loop 207, the current limit loop 205 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 is pv* is the first reference value i pv1_1* and the fourth reference value i pv1_4* The smaller value of the two, thereby ensuring that the input current i of the DC / DC unit in the strong light startup mode pv Do not exceed the current upper limit i pv_max , which helps to avoid damage to the photovoltaic inverter or load unit due to excessive current.

[0089] In some embodiments, Fig.13 As shown, when the MPPT module 201 adopts the first mode or the second mode, the bus voltage loop 207 is used to output the fourth reference value i pv1_4* , the fourth reference value i pv1_4* As a given value i pv* Acting on the DC current loop 203, the DC current loop 203 is used to output the duty cycle d DC / DC , duty cycle d DC / DC Acting on the first PWM generating module 204 to control the first PWM generating module 204 to output PWM DC / DC Signal.

[0090] That is to say, in the strong light start mode, the MPPT module 201 using the first mode and the MPPT module 201 using the second mode will not trigger the current limiting loop 205, so the DC voltage loop 202, the current limiting loop 205 and the load limiting loop 206 do not work, and the bus voltage loop 207 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 pv* is the fourth reference value i pv1_4* .

[0091] It is worth mentioning that when starting the machine under weak light conditions, due to the weak light intensity, the output current of the MPPT module 201 during the startup process, that is, the input current i of the DC / DC unit pv is small, so the DC voltage loop 202, the current limiting loop 205 and the load limiting loop 206 do not work, and the bus voltage loop 207 and the DC current loop 203 work, so that the given value i of the input DC current loop 203 is pv* is the fourth reference value i pv1_4* .

[0092] In some embodiments, Fig.14 and Fig.15 As shown, the photovoltaic inverter also includes a DC / AC unit and a control loop 102 for controlling the DC / AC unit. Fig.14 As shown, the sampling value of the grid voltage v ga 、v gb and v gc After the phase-locked loop (PLL), the grid voltage frequency ω and phase θ are obtained. g Furthermore, the sampling value of the grid voltage v ga 、v gb and v gc After PARK transformation, v is obtained g0 、v gq and v gd , which is used to calculate the d-axis duty cycle d d , q-axis duty cycle d q and 0-axis duty cycle d 0 Then, the d-axis duty cycle dd, the q-axis duty cycle dq and the 0-axis duty cycle d0 are transformed by PARK to obtain the duty cycle d a d b and d c , duty cycle d a d b and d c Acting on the second PWM generation module 208 to output the control signal PWM DC / AC To control the DC / AC unit.

[0093] Further, such as Fig.15As shown in the figure, after the startup is completed, that is, after the output voltage of the DC / AC unit follows the grid voltage waveform, the grid-connected relay S a , S b and S c The control loop 102 for controlling the DC / AC unit is switched to closed-loop control, and the control module 101 for controlling the DC / DC unit remains unchanged.

[0094] Specifically, the control loop 102 includes a comparator 5, a PI controller 5, a comparator 6, a PI controller 6, a comparator 7, and a PI controller 7. The sampling value v of the grid voltage ga 、v gb and v gc After the phase-locked loop (PLL), the grid voltage frequency ω and phase θ are obtained. g , the sampling value of the three-phase current i a 、i b 、i c After PARK transformation, we get i 0 、i d and i q Comparator 5 is used to compare the set value v of the bus voltage BUS* And the sampling value of bus voltage v BUS The output result of the comparator 5 is used as the input of the PI controller 5, and the PI controller 5 is used to output the fifth reference value I d* The comparator 6 is used to compare the sampling values ​​of the three-phase current i d and the fifth reference value I d* The output of comparator 6 is used as the input of PI controller 6. Comparator 7 is used to compare the sampling values ​​of the three-phase current i q and the sixth reference value I q* The output of comparator 7 is used as the input of PI controller 7. The output of PI controller 6, the output of PI controller 7, v gq and v gd Used to calculate the d-axis duty cycle d d , q-axis duty cycle d q and 0-axis duty cycle d 0 , and then the d-axis duty cycle d d , q-axis duty cycle d q and 0-axis duty cycle d 0 , d-axis duty cycle d d , q-axis duty cycle d q and 0-axis duty cycle d 0 Obtain the duty cycle d through PARK transformation a ,d b and d c , duty cycle d a ,d b and d cActing on the second PWM generation module 208 to output the control signal PWM DC / AC To control the DC / AC unit.

[0095] The above describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention to be protected. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A photovoltaic inverter, characterized in that: include: At least one set of MPPT modules and DC / DC units connected in sequence, the MPPT module having a first mode, a second mode, and a third mode; The second mode is distinguished by judging the output current of each string of the MPPT module, and judging that the maximum output current of the MPPT module exceeds the current upper limit i within the time T. pv_max to distinguish the first mode from the third mode; Control module for PWM output DC / DC The signal is used to control the DC / DC unit so that the photovoltaic inverter operates in a steady-state mode, a current limiting mode, a load limiting mode, or a strong light start-up mode. The input of the control module is adjusted according to the mode of the MPPT module to adapt to the specifications of the photovoltaic module; When the output current of at least one string of each DC / DC unit is 0A, it is determined that the MPPT module adopts the second mode; the control module includes a current limiting loop, and on the basis that the output current of each string of each DC / DC unit is greater than 0A, the number of times X of triggering the current limiting loop within a time length T is counted, and when the number X is greater than or equal to the set number X max When the MPPT module adopts the third mode, the number of times X is less than the set number of times X. max When the MPPT module is determined to adopt the first mode; the corresponding current upper limit value i is set according to the mode of the MPPT module pv_max .

2. The photovoltaic inverter according to claim 1, characterized in that: The control module includes a DC voltage loop, a current limiting loop, a load limiting loop and a DC current loop. The DC voltage loop is used to output a first reference value i pv1_1* The current limiting loop is used to output a second reference value i pv1_2* The load limit ring is used to output a third reference value i pv1_3* , the first reference value i pv1_1* The second reference value i pv1_2* and the third reference value i pv1_3* The minimum value among the three is taken as the given value i pv* , the given value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC Signal.

3. The photovoltaic inverter according to claim 2, characterized in that: The input voltage sampling value v of the DC / DC unit pv And the input current sampling value i pv As the input of the MPPT module, the MPPT module is used to output the PV side voltage reference v pv* , the PV side voltage reference v pv* As the input of the DC voltage loop, the DC voltage loop is used to compare v pv* With the input voltage sampling value v pv To obtain the first reference value i pv1_1* ; The load limit ring is used to compare the upper limit value v of the bus voltage BUS_max And the sampling value of bus voltage v BUS , to output the third reference value i pv1_3* .

4. The photovoltaic inverter according to claim 2, characterized in that: The current limiting loop is used to set the current upper limit value i pv_max As i pv1_2* Output, the upper limit value i pv_max Adjustments are made according to the mode adopted by the MPPT module.

5. The photovoltaic inverter according to claim 2, characterized in that: At the first reference value i pv1_1* Exceeding the current upper limit i pv_max When the output of the DC voltage loop is modified to the current upper limit value i pv_max ; In the third reference value i pv1_3* Exceeding the current upper limit i pv_max When the output of the load limit ring is modified to the current upper limit value i pv_max , the upper limit value i pv_max Adjustments are made according to the mode adopted by the MPPT module.

6. The photovoltaic inverter according to any one of claims 2 to 5, characterized in that: In steady-state mode, the DC voltage loop outputs a first reference value i pv1_1* , the current limiting loop outputs a second reference value i pv1_2* , the first reference value i pv1_1* and the second reference value i pv1_2* The minimum value of the two is taken as the given value i pv* , the fixed value i pv* Acting on the DC current loop.

7. The photovoltaic inverter according to any one of claims 2 to 4, characterized in that: At the second reference value i pv1_2* Greater than the first reference value i pv1_1* When the photovoltaic inverter is in current limiting mode, the current limiting loop outputs a second reference value i pv1_2* , the second reference value i pv1_2* As a given value i pv* , the fixed value i pv* Acting on the DC current loop.

8. The photovoltaic inverter according to any one of claims 2 to 5, characterized in that: In the load limiting mode, the current limiting loop is used to output the second reference value i pv1_2* The load limit ring is used to output a third reference value i pv1_3* , the second reference value i pv1_2* and the third reference value i pv1_3* The minimum value of the two is taken as the given value i pv* , the given value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC signal, causing the output power on the PV side to decrease.

9. The photovoltaic inverter according to any one of claims 2 to 5, characterized in that: The control module also includes a bus voltage loop, which is used to compare the set value v of the bus voltage BUS* And the sampling value of bus voltage v BUS , to output the fourth reference value i pv1_4* ; In the strong light start mode, when the MPPT module adopts the third mode, the current limiting loop is used to output the second reference value i pv1_2* , the bus voltage loop is used to output the fourth reference value i pv1_4* , the second reference value i pv1_2* and the fourth reference value i pv1_4* The minimum value of the two is taken as the given value i pv* , the given value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC Signal; When the MPPT module adopts the first mode or the second mode, the bus voltage loop is used to output the fourth reference value i pv1_4* , the fourth reference value i pv1_4* As a given value i pv* Acting on the DC current loop, the DC current loop is used to output a duty cycle d DC / DC , to control the PWM DC / DC Signal.

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