Voltage fluctuation control method, grid-connected inverter and grid-connected system

Abstract

The invention discloses a voltage fluctuation control method, a grid-connected inverter and a grid-connected system, and the voltage fluctuation control method comprises the steps: obtaining each phase voltage in a three-phase power grid, carrying out the function conversion of each phase voltage, and carrying out the calculation to obtain a voltage change value; wherein the phase voltage is the voltage of a grid-connected point of the electrical equipment with the grid-connected function; when any voltage change value is greater than a first preset threshold value and less than a second preset threshold value, adjusting a grid-connected voltage output to a grid-connected point of the electrical equipment so as to maintain grid-connected operation of the electrical equipment; wherein the second preset threshold value is greater than the first preset threshold value. The problem that response is not timely due to the fact that voltage fluctuation of the power grid voltage is not easy to judge in the grid-connected operation process at present can be solved.

Description

Technical Field

[0001] The present application relates to the field of electronic technologies, and particularly relates to a voltage fluctuation control method, a grid-connected inverter, and a grid-connected system. Background Art

[0002] LCRT (Low Voltage Ride Through) and HVRT (High Voltage Ride Through) refer to a capability in a power system, especially in wind power generation and photovoltaic power generation systems. It refers to the ability of a power generation device to continue grid-connected operation without disconnecting from the grid when there is a short-term abnormality in the grid voltage (such as a voltage dip or a voltage surge). This ability is crucial for maintaining the stability and reliability of the power grid.

[0003] Both the three-phase power grid and the inverter have AC outputs. When there is a voltage fluctuation in the power grid voltage, it is not easy to judge. Then, for the situation of voltage fluctuation, there will be a problem of inability to respond in a timely manner.

[0004] Therefore, the current technology still needs to be improved and enhanced. Summary of the Invention

[0005] The present application provides a voltage fluctuation control method, a grid-connected inverter, and a grid-connected system, which can alleviate the problem that it is not easy to judge when there is a voltage fluctuation in the grid voltage during grid-connected operation, resulting in untimely response.

[0006] The present application provides a voltage fluctuation control method, and the voltage fluctuation control method includes the following steps:

[0007] Obtain each phase voltage in the three-phase power grid, and calculate a voltage change value after performing a function conversion on each of the phase voltages; wherein, the phase voltage is the voltage at the grid connection point of an electrical device with grid connection function.

[0008] When any one of the voltage change values is greater than a first preset threshold and less than a second preset threshold, adjust the grid-connected voltage output to the grid connection point of the electrical device to maintain the grid-connected operation of the electrical device; wherein, the second preset threshold is greater than the first preset threshold.

[0009] In the voltage fluctuation control method in some embodiments, the step of obtaining each phase voltage in the three-phase power grid and calculating a voltage change value after performing a function conversion on each of the phase voltages includes:

[0010] Obtain each phase voltage in the three-phase power grid, and obtain a corresponding voltage detection value after taking the derivative of each of the phase voltages.

[0011] Calculate the voltage change value according to the voltage detection value and the corresponding phase voltage.

[0012] In the voltage fluctuation control method in some embodiments, the step of obtaining the corresponding voltage detection value after taking the derivative of each phase voltage includes:

[0013] Take the first derivative of each phase voltage to obtain the corresponding first derivative value;

[0014] Take the second derivative of the first derivative value to obtain the voltage detection value corresponding to the phase voltage.

[0015] In the voltage fluctuation control method in some embodiments, after the step of calculating the voltage change value after performing function conversion on each phase voltage, the following further includes:

[0016] When any one of the voltage change values is greater than the second preset threshold, control the electrical device to stop grid connection.

[0017] In the voltage fluctuation control method in some embodiments, the electrical device includes an air conditioner.

[0018] The embodiment of the present application also provides a grid-connected inverter, and the grid-connected inverter includes:

[0019] An inverter module, the inverter module is used to connect to a power generation device, and the inverter module is used to invert the DC voltage output by the power generation device into an AC voltage;

[0020] A switch module, the switch module is used to connect to the grid connection point of the electrical device, and the switch module is used to output the AC voltage as the grid-connected voltage;

[0021] A control module, the control module is respectively connected to the inverter module and the switch module, and the control module is used to execute the above voltage fluctuation control method.

[0022] In the grid-connected inverter in some embodiments, the grid-connected inverter further includes a filtering module, the filtering module is connected in series between the inverter module and the switch module, and the filtering module is used to perform filtering processing on the AC voltage output by the inverter module.

[0023] In the grid-connected inverter in some embodiments, the filtering module includes an LCL filter, the LCL filter is connected in series between the inverter module and the switch module, and the LCL filter is used to perform filtering processing on the AC voltage output by the inverter module.

[0024] In some embodiments of the grid-connected inverter, the control module includes a digital signal processor, and the digital signal processor is respectively connected to the inverter module and the switch module.

[0025] An embodiment of the present application also provides a grid-connected system, which includes a power generation device, an electrical device, and the grid-connected inverter as described above. The grid-connected inverter is connected between the power generation device and the electrical device; the grid-connected inverter is configured to invert the DC voltage output by the power generation device into an AC voltage to provide a grid-connected voltage for the electrical device.

[0026] A voltage fluctuation control method, a grid-connected inverter, and a grid-connected system provided by the present application. The voltage fluctuation control method calculates a voltage change value by obtaining each phase voltage in a three-phase power grid and performing a function conversion on each of the phase voltages; when any voltage change value is greater than a first preset threshold and less than a second preset threshold, the grid-connected voltage at the grid connection point output to the electrical device is adjusted to maintain the grid-connected operation of the electrical device. In the present application, by performing a function conversion on the voltages of the three-phase power grid, it is helpful to quickly identify the voltage change, so as to start protection and achieve a fast response to voltage fluctuations, improving the reliability of the grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The following will make the technical solutions and other beneficial effects of the present application obvious by describing the specific embodiments of the present application in detail with reference to the drawings.

[0028] Figure 1 It is a schematic flowchart of the voltage fluctuation control method provided by an embodiment of the present application.

[0029] Figure 2 It is a schematic flowchart of step 100 in the voltage fluctuation control method provided by an embodiment of the present application.

[0030] Figure 3 It is a schematic flowchart of step 110 in the voltage fluctuation control method provided by an embodiment of the present application.

[0031] Figure 4 It is a first structural block diagram of the grid-connected inverter provided by an embodiment of the present application.

[0032] Figure 5 It is a second structural block diagram of the grid-connected inverter provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0034] 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 specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the present application, "a plurality" means two or more, unless otherwise specifically defined.

[0035] Currently, it is judged according to the effective value of the AC voltage or the quadrature-axis voltage value in the rotating coordinate system. Judgment of the effective value of the AC voltage: Since the AC effective value is for one power frequency cycle such as 1 / 50 second, the calculation speed is slow, the voltage crossing time is fast, and the judgment is not timely, resulting in out-of-control; in the rotating coordinate system, if only one phase voltage drops among the three phases, the response speed of the direct-axis voltage is also slow and cannot achieve a fast response effect.

[0036] Please refer to Figure 1 , the embodiments of the present application provide a voltage fluctuation control method, and the voltage fluctuation control method includes the following steps:

[0037] 100. Obtain each phase voltage in the three-phase power grid, and calculate the voltage change value after performing function conversion on each of the phase voltages;

[0038] 200. When any one of the voltage change values is greater than a first preset threshold and less than a second preset threshold, adjust the grid-connected voltage output to the grid connection point of the electrical equipment to maintain the grid-connected operation of the electrical equipment; wherein, the second preset threshold is greater than the first preset threshold.

[0039] Among them, the phase voltage is the voltage at the grid connection point of the electrical equipment with grid connection function. In this embodiment, by obtaining each phase voltage in the three-phase power grid, the voltage change value is calculated after performing a function conversion on each phase voltage, so as to determine the magnitude of the voltage change during the grid-connected operation of the electrical equipment according to the voltage change value. Among them, the second preset threshold is greater than the first preset threshold. When the voltage change value is greater than the first preset threshold and less than the second preset threshold, that is, when the voltage change value is between the first preset threshold and the second preset threshold, the grid-connected voltage can be adjusted to be synchronized with the voltage at the grid connection point to maintain the grid-connected operation state of the electrical equipment. In this embodiment, by performing a function conversion on the phase voltage of the three-phase power grid and calculating the voltage change value, it helps to quickly identify the rapid change of the voltage, so as to quickly start the protection and achieve a rapid response to the voltage fluctuation, improving the reliability of the grid-connected system.

[0040] Please refer to Figure 2 , in some embodiments, step 100 includes:

[0041] 110. Obtain each phase voltage in the three-phase power grid, and obtain the corresponding voltage detection value after taking the derivative of each phase voltage;

[0042] 120. Calculate the voltage change value according to the voltage detection value and the corresponding phase voltage.

[0043] In a specific embodiment, the process of performing a function conversion on the phase voltage can be to take the derivative operation on each phase voltage to obtain the voltage detection value, and then compare the voltage detection value with the phase voltage corresponding to the voltage detection value to calculate the voltage change value, which helps to quickly identify whether the voltage at the grid connection point fluctuates, so as to realize a rapid response to the voltage fluctuation subsequently and improve the reliability of the grid-connected system.

[0044] Please refer to Figure 3 , in some embodiments, step 110 includes:

[0045] 111. Take the first derivative of each phase voltage to obtain the corresponding first derivative value;

[0046] 112. Take the second derivative of the first derivative value to obtain the detection value of the corresponding phase voltage.

[0047] Assume that the grid voltage is 230V, the voltages of the three-phase power grid are sinusoidal voltages with a phase difference of 120°, and the grid frequency is 50Hz. As shown in formula (1), where Va, Vb, and Vc are the three-phase voltages, A is the voltage amplitude, w = 2πf is the angular frequency, θ0 is the initial angle of the power grid, and f is the grid frequency. Taking the derivative of the three-phase voltages to obtain the first derivative value as shown in formula (2), taking the second derivative of the first derivative value to obtain the voltage detection value as shown in formula (3), and obtaining formula (4) according to formula (3).

[0048]

[0049] When there is no fluctuation in the three-phase voltage, the values in formula (4) are the same as those in formula (1). If the three-phase voltage fluctuates, it means that the amplitude A fluctuates. Since the amplitude drops significantly per unit time when the voltage changes, its first derivative value is large, and the voltage detection value obtained by the second derivative value increases quadratically. Therefore, when there is a small voltage fluctuation, its second derivative will increase, and the change of the second derivative assignment is used to determine whether the grid voltage fluctuates. This method can quickly respond to the drop situation in order to achieve the purpose of starting rapid protection.

[0050] If the first preset threshold is set as A VRT1 , and the second preset threshold is A VRT2 ; Subtracting formula (1) from formula (4) gives formula (5). As shown in formula (5), normally subtracting formula (1) from formula (4) gives zero. When the absolute value of △Va or △Vb or △Vc exceeds the first preset threshold, it is considered that a voltage fluctuation has occurred. If it is less than the second preset threshold, it indicates that the voltage fluctuation is not very large. Thus, the grid-connected voltage can be quickly adjusted on the grid-connected system side to achieve a rapid response to voltage fluctuations and improve the reliability of grid-connected operation.

[0051]

[0052] In some embodiments, after step 200 in the voltage fluctuation control method, it further includes: when any voltage change value is greater than the second preset threshold, controlling the electrical device to stop grid connection. When the absolute value of △Va or △Vb or △Vc exceeds the second preset threshold, it is considered that it may not be possible to achieve synchronization with the phase voltage by adjusting the grid-connected voltage at this time. Then, in order to improve the safety of grid connection, the electrical device can be directly controlled to stop grid connection, so that the electrical device stops grid-connected operation.

[0053] As an embodiment, the electrical device includes an air conditioner.

[0054] Please refer to Figure 4 , this application embodiment also provides a grid-connected inverter 1. The grid-connected inverter 1 includes an inversion module 11, a switching module 12, and a control module 13. The inversion module 11 is used to connect to the power generation device 2, the switching module 12 is used to connect to the grid connection point B of the electrical device 3, and the control module 13 is respectively connected to the inversion module 11 and the switching module 12.

[0055] Among them, the inverter module 11 is used to invert the DC voltage output by the power generation device 2 into an AC voltage, and the switch module 12 is used to output the AC voltage as a grid-connected voltage to the grid side to realize the grid-connected operation of the electrical equipment 3 on the grid side. The control module 13 is used to execute the above voltage fluctuation control method. In this embodiment, the control module 13 calculates the voltage change value by performing function conversion on the phase voltages of the three-phase power grid, which helps to quickly identify the rapid change of the voltage, so as to quickly start protection, achieve a rapid response to voltage fluctuations, and improve the reliability of the grid-connected system.

[0056] Please refer to Figure 5 , in some embodiments, the grid-connected inverter 1 further includes a filtering module 14. The filtering module 14 is connected in series between the inverter module 11 and the switch module 12, and the filtering module 14 is used to filter the AC voltage output by the inverter module 11. For example, the inverter module 11 converts the DC voltage output by the power generation device 2 into a square-wave AC voltage, and the AC voltage is processed by the filtering module 14 to obtain a sine-wave output to the grid side.

[0057] As an embodiment, the filtering module 14 is an LCL filter. The LCL filter is connected in series between the inverter module 11 and the switch module 12, and the LCL filter is used to filter the AC voltage output by the inverter module 11. The LCL filter has the characteristics of strong harmonic suppression ability, good filtering effect, small volume, and light weight. This filter can filter out high-order harmonics, improve the power quality, prevent the influence of harmonics on the power grid, and at the same time can also suppress electromagnetic interference and protect sensitive equipment from interference.

[0058] In some embodiments, the control module 13 includes a digital signal processor, which is respectively connected to the inverter module 11 and the switch module 12. Among them, the switch module 12 can be a relay switch. When the digital signal processor detects that any one of the voltage change values is greater than the first preset threshold and less than the second preset threshold, the AC voltage output by the inverter module 11 is adjusted accordingly, thereby realizing the adjustment of the grid-connected voltage at the grid connection point B. When the digital signal processor detects that any one of the voltage change values is greater than the second preset threshold, the relay is controlled to disconnect, and then the power generation device 2 is controlled to stop outputting the grid-connected voltage, so that the electrical equipment 3 exits the grid-connected operation state.

[0059] For example, after the inverter module 11 converts the direct current output by the power generation device 2 into alternating current, it is filtered by the LCL filter and then output to the grid side through the switch module 12, enabling the electrical device 3 connected to the grid side to enter the grid-connected operation mode. During the process of regulating the grid-connected voltage, the digital signal processor will acquire the actual output current such as the inverter currents ia, ib, and ic, and perform coordinate transformation on the inverter currents such as Clarke transformation and Park transformation to obtain the actual feedback currents id and iq. At the same time, the digital signal processor will also acquire the phase voltages in the three-phase power grid such as Va, Vb, and Vc, perform coordinate transformation on the phase voltages such as Clarke transformation and Park transformation to obtain the actual feedback voltages ud and uq, and perform phase-locked processing on the actual feedback voltages to obtain the synchronous rotation angle. The digital signal processor will also acquire the bus voltage output by the power generation device 2, output the reference current idref according to the bus voltage, and then output the first control voltages such as ud_c and uq_c according to the reference current, the actual feedback current, the actual feedback voltage, and the synchronous rotation angle. After that, the first control voltage is subjected to inverse Park transformation to obtain the second control voltages such as uα-c and uβ-c, and then the switching control signals such as Ta, Tb, and Tc are modulated according to the second control voltages and output to the inverter module 11 to adjust the alternating voltage output by the inverter module 11, thereby realizing the regulation of the grid-connected voltage, ensuring that the grid-connected voltage is synchronized with the phase voltages of the three-phase power grid, and further improving the reliability of grid-connected operation. It should be noted that the process of the digital signal processor regulating the grid-connected voltage is known content and will not be elaborated here.

[0060] The embodiment of the present application also provides a grid-connected system, and the grid-connected system includes a power generation device, an electrical device, and the above grid-connected inverter. Since the above grid-connected inverter has been described in detail, it will not be elaborated here.

[0061] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0062] The above has introduced in detail the voltage fluctuation control method provided by the embodiments of the present application. In this article, specific examples are used to elaborate on the principle and implementation manner 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; those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A voltage fluctuation control method, characterized in that, The voltage fluctuation control method includes the following steps: Obtain the voltage of each phase in the three-phase power grid, and calculate the voltage change value after performing function conversion on each of the phase voltages; wherein, the phase voltage is the voltage at the grid connection point of the electrical equipment with grid connection function. When any one of the voltage change values is greater than the first preset threshold and less than the second preset threshold, adjust the grid-connected voltage output to the grid connection point of the electrical equipment to maintain the grid-connected operation of the electrical equipment; wherein, the second preset threshold is greater than the first preset threshold.

2. The voltage fluctuation control method according to claim 1, wherein The step of obtaining the voltage of each phase in the three-phase power grid and calculating the voltage change value after performing function conversion on each of the phase voltages includes: Obtain the voltage of each phase in the three-phase power grid, and obtain the corresponding voltage detection value after differentiating each of the phase voltages. Calculate the voltage change value according to the voltage detection value and the corresponding phase voltage.

3. The voltage fluctuation control method according to claim 2, wherein The step of obtaining the corresponding voltage detection value after differentiating each of the phase voltages includes: Perform a first derivative on each of the phase voltages to obtain the corresponding first derivative value. Perform a second derivative on the first derivative value to obtain the voltage detection value corresponding to the phase voltage.

4. The voltage fluctuation control method according to any one of claims 1-3, characterized in that, After the step of calculating the voltage change value after performing function conversion on each of the phase voltages, it further includes: When any one of the voltage change values is greater than the second preset threshold, control the electrical equipment to stop grid connection.

5. The voltage fluctuation control method according to claim 4, characterized in that, The electrical equipment includes an air conditioner.

6. A grid-connected inverter, characterized in that, The grid-connected inverter includes: An inversion module, which is used to connect to the power generation equipment and is used to invert the DC voltage output by the power generation equipment into an AC voltage. A switch module, which is used to connect to the grid connection point of the electrical equipment and is used to output the AC voltage as the grid-connected voltage. A control module, which is respectively connected to the inversion module and the switch module, and is used to execute the voltage fluctuation control method according to any one of claims 1-5.

7. The grid-connected inverter according to claim 6, wherein The grid-connected inverter further includes a filtering module, which is connected in series between the inversion module and the switch module, and is used to filter the AC voltage output by the inversion module.

8. The grid-connected inverter according to claim 7, wherein, The filtering module includes an LCL filter, which is connected in series between the inversion module and the switch module, and is used to filter the AC voltage output by the inversion module.

9. The grid-connected inverter according to claim 8, characterized in that, The control module includes a digital signal processor, which is respectively connected to the inversion module and the switch module.

10. A grid-connected system, characterized in that, The grid-connected system includes a power generation equipment, an electrical equipment and a grid-connected inverter according to any one of claims 6-9, and the grid-connected inverter is connected between the power generation equipment and the electrical equipment; the grid-connected inverter is used to invert the DC voltage output by the power generation equipment into an AC voltage to provide the grid-connected voltage for the electrical equipment.

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