Method for controlling DC bus voltage of two-stage conversion photovoltaic inverter and photovoltaic inverter

Abstract

The invention discloses a two-stage conversion photovoltaic inverter DC bus voltage control method and a photovoltaic inverter. The control method comprises the following steps: performing maximum power point tracking control on a DC / DC conversion module; the DC / DC conversion module and the photovoltaic module PV are simulated, so that the DC / DC conversion module and the photovoltaic module PV are equivalent to a photovoltaic output module PV ', and output is carried out according to the power voltage characteristic of the photovoltaic output module PV'; whether the DC bus voltage Vbus of the photovoltaic output module PV'after equivalence meets the grid-connected condition or not is judged, if the grid-connected condition is met, maximum power point tracking control is conducted on the DC / AC conversion module, and grid-connected current control is conducted on the DC / AC conversion module. The control method can remove the control loop switching process of the DC / DC conversion module.

Description

Technical Field

[0001] The present application belongs to the field of photovoltaic power generation control technology, and specifically refers to a control method for a DC bus voltage of a two-stage converted photovoltaic inverter and a photovoltaic inverter. Background Art

[0002] In the prior art, the DC side voltage control method of the two-stage photovoltaic inverter is that when the photovoltaic module PV generates electricity and the power generation voltage of the photovoltaic module PV exceeds the set allowable startup value, the DC / DC conversion module starts to work and establishes the DC bus voltage. When the DC bus voltage output by the DC / DC conversion module meets the grid connection conditions, the DC / AC conversion module of the subsequent stage starts to work. When the DC / AC conversion module of the subsequent stage completes the AC conversion and is connected to the grid, the photovoltaic inverter starts to perform maximum power point tracking control (Maximum power point tracking, referred to as MPPT) based on the output voltage of the photovoltaic module PV. At the same time, the DC side of the DC / AC conversion module of the subsequent stage performs voltage closed-loop control based on the DC bus voltage output by the DC / DC conversion module with reference to the given voltage. In this DC control method, when the photovoltaic inverter is operating stably, the photovoltaic module PV and the DC / DC conversion module can be equivalent to a DC voltage stabilizing source model.

[0003] During the operation of the two-stage photovoltaic inverter, there is a problem of control loop switching in the control of the DC / DC conversion module in the two-stage photovoltaic inverter. On the one hand, the loop switching of the control system will increase the instability of the system, and on the other hand, the loop switching process will cause the loss of photovoltaic power generation. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present application provides a control method for a DC bus voltage of a two-stage converted photovoltaic inverter and a photovoltaic inverter. The control method can eliminate the control loop switching process of a DC / DC conversion module.

[0005] The present invention provides a control method for a DC bus voltage of a two-stage photovoltaic inverter, the control method comprising:

[0006] Perform maximum power point tracking control on the DC / DC conversion module;

[0007] The DC / DC conversion module and the photovoltaic module PV are simulated so that the DC / DC conversion module and the photovoltaic module PV are equivalent to the photovoltaic output module PV', and the power voltage characteristics of the photovoltaic output module PV' are output;

[0008] Determine whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection conditions;

[0009] If the grid connection conditions are met, the DC / AC conversion module is subjected to maximum power point tracking control;

[0010] Perform grid-connected current control on the DC / AC conversion module.

[0011] According to the control method of the DC bus voltage of the two-stage conversion photovoltaic inverter provided by the present application, the step of simulating the DC / DC conversion module and the photovoltaic assembly module PV so that the DC / DC conversion module and the photovoltaic assembly module PV are equivalent to the photovoltaic output module PV', and outputting according to the power voltage characteristics of the photovoltaic output module PV' also includes:

[0012] Determine the open circuit voltage Vc of the equivalent photovoltaic output module PV', the maximum voltage Vb allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point, and the minimum voltage Va allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point;

[0013] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of 0-Va;

[0014] The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb;

[0015] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

[0016] According to the control method of the DC bus voltage of the two-stage photovoltaic inverter provided in the present application, the step of judging whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection condition includes:

[0017] Determine the peak voltage of the grid-connected voltage;

[0018] It is determined whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' is greater than the peak voltage of the grid-connected voltage.

[0019] According to the control method of the DC bus voltage of the two-stage photovoltaic inverter provided in the present application, the DC / DC conversion module is a step-down (Buck) circuit, a step-up (Boost) circuit, or one or more combinations of a step-up and step-down (Buck-Boost) circuit.

[0020] According to the control method of the DC bus voltage of the two-stage conversion photovoltaic inverter provided in the present application, the DC / AC conversion module is one or more combinations of single-phase or three-phase full-bridge circuits.

[0021] According to the control method of the DC bus voltage of the two-stage photovoltaic inverter provided in the present application, the maximum power point tracking control step of the DC / AC conversion module includes:

[0022] Compare the operating power of PV modules at different DC bus points;

[0023] The input voltage is controlled to make the photovoltaic module work in a maximum power state.

[0024] The present application also provides a photovoltaic inverter using the control method of the DC bus voltage of the photovoltaic inverter with two-stage conversion provided by the present application, wherein the photovoltaic inverter comprises a photovoltaic module PV, a DC / DC conversion module and a DC / AC conversion module; the photovoltaic module PV is connected to the DC / DC conversion module, the DC / DC conversion module is connected to the DC / AC conversion module, and the DC / AC conversion module is connected to a power grid;

[0025] The photovoltaic assembly PV and the DC / DC conversion module are simulated and equivalent to the photovoltaic output module PV' according to the control method of the DC bus voltage of the photovoltaic inverter with two-stage conversion as claimed in any one of claims 1 to 6.

[0026] According to the photovoltaic inverter provided in the present application, the open circuit voltage of the equivalent photovoltaic output module PV' is Vc, the maximum voltage allowed when the equivalent photovoltaic output module PV' is operated at the maximum power point is Vb, and the minimum voltage allowed when the equivalent photovoltaic output module PV' is operated at the maximum power point is Va;

[0027] Among them, the output voltage of the equivalent photovoltaic output module PV' is limited to operate in the range of 0-Va;

[0028] The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb;

[0029] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

[0030] According to the photovoltaic inverter provided by the present application, the DC / AC conversion module adopts maximum power point tracking control.

[0031] The beneficial effects of the present invention are as follows: according to the control method of the DC bus voltage of a two-stage photovoltaic inverter provided by the present application, by simulating the DC / DC conversion module and the photovoltaic assembly module PV, which are equivalent to the photovoltaic output module PV', and independently controlling the DC / AC conversion module of the subsequent stage according to the single-stage photovoltaic inverter, it is possible to remove the control loop switching process in the DC / DC conversion module, and also to realize that the DC / DC conversion module and the DC / AC conversion module do not need to agree on the DC working voltage so that they can operate independently. The system stability is improved, and the MPPT control of the DC bus is performed independently, and the DC bus has the maximum power segment output characteristic, so that the DC bus voltage fluctuation will not affect the system MPPT control effect, which is helpful to improve the efficiency of photovoltaic power generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0033] Figure 1 It is a structural schematic diagram of a two-stage photovoltaic inverter in the prior art.

[0034] Figure 2 The figure is a schematic diagram of the working process of a two-stage conversion photovoltaic inverter in the prior art.

[0035] Figure 3 It is a power-voltage curve diagram of the photovoltaic module PV in the prior art.

[0036] Figure 4 A schematic diagram of the working process of the method for controlling the DC bus voltage of a photovoltaic inverter with two-stage conversion provided in this embodiment.

[0037] Figure 5 This is a schematic diagram of the equivalent photovoltaic output module PV' provided in this embodiment.

[0038] Figure 6 This is a power-voltage curve diagram of the equivalent photovoltaic output module PV' provided in this embodiment. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0040] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0041] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0042] The embodiments of the present application are now further described in conjunction with the accompanying drawings and specific implementation methods.

[0043] Figure 1 It is a structural schematic diagram of a two-stage photovoltaic inverter in the prior art. Figure 2 This is the working process of a two-stage conversion photovoltaic inverter in the prior art. Figure 3 It is the power-voltage curve of the photovoltaic module PV in the prior art.

[0044] like Figures 1 to 3 As shown, in the prior art, after the PV module starts to generate electricity, the DC / DC conversion module starts to output a DC voltage Vbus at a constant voltage. Then it is determined whether the DC voltage Vbus is greater than the preset DC working voltage Vbusref; if the DC voltage Vbus is greater than the preset DC working voltage Vbusref, the DC / DC conversion module starts to work according to the maximum power point tracking control. The DC / AC conversion module at the subsequent stage starts to work, inputs the DC voltage Vbus, outputs the DC voltage to the grid, and performs grid-connected current control.

[0045] like Figure 3 As shown, in the prior art, when the output of the front-stage DC / DC conversion module reaches the set voltage point A, the inversion of the rear-stage DC / AC conversion module takes the voltage at point A as the control target. If the DC bus voltage deviates from the set voltage A, the system enters a power-limited operation state. The control of the voltage at point A involves a process of switching from the control of the DC / DC conversion module to the control of the DC / AC conversion module, and there is a control loop process in the working mode. On the one hand, the loop switching of the control system will increase the instability of the system, and on the other hand, the loop switching process will cause the loss of photovoltaic power generation power.

[0046] Therefore, if Figure 4 As shown, this embodiment proposes a control method for a DC bus voltage of a photovoltaic inverter with two-stage conversion, and the control method includes:

[0047] Perform maximum power point tracking control on the DC / DC conversion module;

[0048] The DC / DC conversion module and the photovoltaic module PV are simulated so that the DC / DC conversion module and the photovoltaic module PV are equivalent to the photovoltaic output module PV', and the power voltage characteristics of the photovoltaic output module PV' are output;

[0049] Determine whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection conditions;

[0050] If the grid connection conditions are met, the DC / AC conversion module is subjected to maximum power point tracking control;

[0051] Perform grid-connected current control on the DC / AC conversion module.

[0052] Specifically, if Figure 5 As shown, the front-stage DC / DC conversion module and the photovoltaic component module PV are simulated and equivalent together, which is equivalent to the photovoltaic output module PV'.

[0053] In the two-stage conversion photovoltaic inverter in the prior art, the photovoltaic component module PV serves as the input of the front-stage DC / DC conversion module, and the front-stage DC / DC conversion module externally presents a DC voltage source characteristic.

[0054] In this embodiment, the DC / DC conversion module and the photovoltaic assembly module PV are simulated together to be equivalent to a photovoltaic output module PV', and the front-stage DC / DC conversion module and the photovoltaic assembly module PV together present the power-voltage characteristics of the improved photovoltaic output module PV'.

[0055] like Figure 6As shown, the step of simulating the DC / DC conversion module and the photovoltaic module PV so that the DC / DC conversion module and the photovoltaic module PV are equivalent to the photovoltaic output module PV', and outputting according to the power voltage characteristics of the photovoltaic output module PV' also includes:

[0056] Determine the open circuit voltage Vc of the equivalent photovoltaic output module PV', the maximum voltage Vb allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point, and the minimum voltage Va allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point;

[0057] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of 0-Va;

[0058] The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb;

[0059] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

[0060] Specifically, in this embodiment, the DC / DC conversion module is a buck circuit, a boost circuit, or a combination of one or more buck-boost circuits. The DC / AC conversion module is a combination of one or more single-phase or three-phase full-bridge circuits. The DC / DC conversion module has a variety of topological structures. In this embodiment, the power voltage characteristics of the DC / DC conversion module with buck-boost function after equivalent control are as follows: Figure 6 shown.

[0061] Specifically, in this embodiment, the step of determining whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection condition includes:

[0062] Determine the peak voltage of the grid-connected voltage;

[0063] It is determined whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' is greater than the peak voltage of the grid-connected voltage.

[0064] The step of performing maximum power point tracking control on the DC / AC conversion module includes:

[0065] Compare the operating power of PV modules at different DC bus points;

[0066] The input voltage is controlled to make the photovoltaic module work in a maximum power state.

[0067] Specifically, since the DC / DC conversion module and the photovoltaic module module PV of the front stage are simulated together to be equivalent to the photovoltaic output module PV', the photovoltaic output module PV' has the power voltage characteristics of the photovoltaic module, so the maximum power point tracking control can be performed on the DC / AC conversion module of the rear stage. Maximum power point tracking control is the control of the DC bus voltage. By comparing the photovoltaic operating power at different DC bus points, the input voltage is controlled to make the photovoltaic module work at the maximum power state, so as to maximize the photovoltaic power generation benefits.

[0068] In this embodiment, a photovoltaic inverter using the control method of the DC bus voltage of the photovoltaic inverter with two-stage conversion provided in this embodiment is also provided, wherein the photovoltaic inverter comprises a photovoltaic module PV, a DC / DC conversion module and a DC / AC conversion module; the photovoltaic module PV is connected to the DC / DC conversion module, the DC / DC conversion module is connected to the DC / AC conversion module, and the DC / AC conversion module is connected to a power grid;

[0069] The photovoltaic assembly PV and the DC / DC conversion module are simulated and equivalent to the photovoltaic output module PV' according to the control method of the DC bus voltage of the photovoltaic inverter with two-stage conversion as claimed in any one of claims 1 to 6.

[0070] Specifically, the open circuit voltage of the equivalent photovoltaic output module PV' is Vc, the maximum voltage allowed when the equivalent photovoltaic output module PV' is at the maximum power point is Vb, and the minimum voltage allowed when the equivalent photovoltaic output module PV' is at the maximum power point is Va;

[0071] Among them, the output voltage of the equivalent photovoltaic output module PV' is limited to operate in the range of 0-Va;

[0072] The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb;

[0073] The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

[0074] The DC / AC conversion module adopts maximum power point tracking control.

[0075] According to a control method for the DC bus voltage of a two-stage photovoltaic inverter provided by the present application, by simulating the DC / DC conversion module and the photovoltaic assembly module PV, which are equivalent to the photovoltaic output module PV', and independently controlling the DC / AC conversion module of the rear stage according to the single-stage photovoltaic inverter, it is possible to remove the control loop switching process in the DC / DC conversion module, and it is also possible to realize that the DC / DC conversion module and the DC / AC conversion module do not need to agree on the DC working voltage so that they can operate independently. Improve the system stability, and independently control the DC bus with MPPT, and the DC bus has the maximum power segment output characteristics, so that the DC bus voltage fluctuation will not affect the system MPPT control effect, which helps to improve the photovoltaic power generation efficiency. Similarly, the photovoltaic inverter provided by the embodiment of the present application is completely decoupled between the DC / DC conversion module of the front stage and the DC / AC conversion module of the rear stage, and each can work independently. In particular, the DC / DC conversion module of the front stage does not need to switch the control mode during the entire working process, which improves the stability of the system. The DC bus can perform MPPT control independently, and the DC bus has the maximum power range output characteristics, so that the DC bus voltage fluctuation will not affect the system MPPT control effect, which helps to improve the efficiency of photovoltaic power generation.

[0076] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concepts. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention. Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

[0077] The above is a detailed introduction to a control method for the DC bus voltage of a two-stage conversion photovoltaic inverter and a photovoltaic inverter provided in an embodiment of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solution and its core idea of ​​the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. A method for controlling the DC bus voltage of a two-stage photovoltaic inverter, characterized in that: The control method comprises: Perform maximum power point tracking control on the DC / DC conversion module; The DC / DC conversion module and the photovoltaic module PV are simulated so that the DC / DC conversion module and the photovoltaic module PV are equivalent to the photovoltaic output module PV', and the power voltage characteristics of the photovoltaic output module PV' are output; Determine whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection conditions; If the grid connection conditions are met, the DC / AC conversion module is subjected to maximum power point tracking control; Perform grid-connected current control on the DC / AC conversion module.

2. The method for controlling the DC bus voltage of a two-stage photovoltaic inverter according to claim 1, characterized in that: The step of simulating the DC / DC conversion module and the photovoltaic module PV so that the DC / DC conversion module and the photovoltaic module PV are equivalent to the photovoltaic output module PV', and outputting according to the power voltage characteristics of the photovoltaic output module PV' also includes: Determine the open circuit voltage Vc of the equivalent photovoltaic output module PV', the maximum voltage Vb allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point, and the minimum voltage Va allowed when the equivalent photovoltaic output module PV' is operating at the maximum power point; The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of 0-Va; The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb; The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

3. The method for controlling the DC bus voltage of a two-stage photovoltaic inverter according to claim 1, characterized in that: The step of judging whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' meets the grid connection condition includes: Determine the peak voltage of the grid-connected voltage; It is determined whether the DC bus voltage Vbus of the equivalent photovoltaic output module PV' is greater than the peak voltage of the grid-connected voltage.

4. The method for controlling the DC bus voltage of a two-stage photovoltaic inverter according to claim 1, characterized in that: The DC / DC conversion module is a step-down (Buck) circuit, a step-up (Boost) circuit, or a combination of one or more of a step-up and step-down (Buck-Boost) circuit.

5. The method for controlling the DC bus voltage of a two-stage photovoltaic inverter according to claim 1, characterized in that: The DC / AC conversion module is one or more combinations of single-phase or three-phase full-bridge circuits.

6. The method for controlling the DC bus voltage of a two-stage photovoltaic inverter according to claim 1, characterized in that: The step of performing maximum power point tracking control on the DC / AC conversion module includes: Compare the operating power of PV modules at different DC bus points; The input voltage is controlled to make the photovoltaic module work in a maximum power state.

7. A photovoltaic inverter using the method for controlling the DC bus voltage of a photovoltaic inverter with two-stage conversion according to any one of claims 1 to 6, characterized in that: The photovoltaic inverter comprises a photovoltaic module PV, a DC / DC conversion module and a DC / AC conversion module; the photovoltaic module PV is connected to the DC / DC conversion module, the DC / DC conversion module is connected to the DC / AC conversion module, and the DC / AC conversion module is connected to the power grid; The photovoltaic assembly PV and the DC / DC conversion module are simulated and equivalent to the photovoltaic output module PV' according to the control method of the DC bus voltage of the photovoltaic inverter with two-stage conversion as claimed in any one of claims 1 to 6.

8. The photovoltaic inverter according to claim 7, characterized in that: The open circuit voltage of the equivalent photovoltaic output module PV' is Vc, the maximum voltage allowed when the equivalent photovoltaic output module PV' is at the maximum power point is Vb, and the minimum voltage allowed when the equivalent photovoltaic output module PV' is at the maximum power point is Va; Among them, the output voltage of the equivalent photovoltaic output module PV' is limited to operate in the range of 0-Va; The output voltage of the equivalent photovoltaic output module PV' operates at a constant maximum power point within the range of Va-Vb; The output voltage of the equivalent photovoltaic output module PV' operates at limited power within the range of Vb-Vc.

9. The photovoltaic inverter according to claim 7, characterized in that: The DC / AC conversion module adopts maximum power point tracking control.

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