Photovoltaic inverter and dynamic protection method thereof
By dynamically adjusting the output current limit value and overcurrent protection threshold of the photovoltaic inverter, the problem of mismatch between the output current and the protection threshold under high bus voltage and high current steady-state operating conditions is solved, and the steady-state grid-connected operation of the inverter and the dynamic protection of the power switch tube is realized.
Patent Information
- Application Number
- CN202411981537.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-04-25
AI Technical Summary
Under high bus voltage and high current steady-state operating conditions, the output current of the photovoltaic inverter does not match the overcurrent protection threshold, resulting in wave-by-wave current limit timeout or hardware overcurrent failure shutdown, affecting the steady-state grid-connected operation of the inverter and the dynamic protection of the power switch tube.
By obtaining the DC voltage of the photovoltaic inverter, dynamically adjusting the output current limit value and overcurrent protection threshold to achieve limiting and overcurrent protection of the output current. The specific method includes using linear or step methods to reduce the output current limit and the overcurrent protection threshold when the DC voltage is higher than a certain set threshold.
It effectively avoids the problem that the output current does not match the overcurrent protection threshold under high bus voltage and high current steady-state operating conditions, prevents wave-by-wave current limiting timeout or hardware overcurrent failure shutdown, and ensures the stable operation of the inverter and the user's power generation benefits.
Smart Images
Figure CN119891725A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of photovoltaic inverters, and in particular to a photovoltaic inverter and a dynamic protection method thereof. Background Art
[0002] The inverter is an important component of the photovoltaic power generation system. The inverter can convert the direct current of the photovoltaic panel into alternating current and send it to the power grid. The core component of the inverter is the DCAC inverter unit composed of power switch tubes. Affected by factors such as the over-matching of the series / parallel connection of photovoltaic panels, the power switch tubes often work under high bus voltage and high current conditions, which makes the voltage stress of the power switch tube in the switching state worse. Extreme conditions such as flicker and high and low penetration of the power grid may cause damage to the power switch tube.
[0003] Although the wave-by-wave current limiting and hardware overcurrent protection can reduce the probability of power switch damage to a certain extent, in actual engineering applications, due to the influence of comprehensive factors such as the difference in power switch devices, the degree of over-matching of photovoltaic panels in series / parallel connection, the attenuation of the inductance of AC filter inductors under large currents, and the size of inductor current ripple, it is difficult to obtain appropriate values for the wave-by-wave current limiting and hardware overcurrent protection thresholds. When the wave-by-wave current limiting and hardware overcurrent protection thresholds are too high, the power switch cannot be effectively protected under high bus voltage and high current conditions; when the wave-by-wave current limiting and hardware overcurrent protection thresholds are too low, although the power switch can be effectively protected, under the influence of factors such as over-matching of photovoltaic panels in series / parallel connection and the sharp attenuation of the inductance of AC filter inductors under large currents, the output current may not match the overcurrent protection threshold under high bus voltage and high current steady-state conditions, thereby triggering the wave-by-wave current limiting timeout or hardware overcurrent fault shutdown, seriously affecting the user's power generation income. Therefore, how to take into account both the steady-state grid-connected operation of the inverter and the dynamic protection of the power switch is a technical problem that needs to be solved urgently. Summary of the invention
[0004] In view of this, the purpose of the present application is to provide a photovoltaic inverter and a dynamic protection method thereof, so as to solve the problem that under high bus voltage and large current steady-state conditions, the output current does not match the overcurrent protection threshold, resulting in triggering wave-by-wave current limiting timeout or hardware overcurrent fault shutdown, while taking into account both the steady-state grid-connected operation of the inverter and the dynamic protection of the power switch tube.
[0005] The technical solutions adopted by this application to solve the above technical problems are as follows:
[0006] On one hand, the present application provides a dynamic protection method for a photovoltaic inverter, the dynamic protection method comprising:
[0007] Obtaining a DC voltage of the photovoltaic inverter;
[0008] According to the DC voltage, adjusting the output current limit value of the photovoltaic inverter to limit the output current of the photovoltaic inverter;
[0009] According to the DC voltage, an overcurrent protection threshold of the photovoltaic inverter is adjusted to achieve overcurrent protection of the photovoltaic inverter.
[0010] On the other hand, the present application provides a photovoltaic inverter, which includes a control unit, the control unit includes a memory and a processor, the memory is configured to store a computer program, and the processor implements the dynamic protection method of the photovoltaic inverter when executing the computer program.
[0011] The photovoltaic inverter and its dynamic protection method provided by the present application adjust the output current limit value and overcurrent protection threshold of the photovoltaic inverter according to the DC voltage; solve the problem that the output current does not match the overcurrent protection threshold under high bus voltage and large current steady-state conditions, resulting in triggering wave-by-wave current limiting timeout or hardware overcurrent fault shutdown, ensure the stable operation of the inverter and the user's power generation revenue, and take into account both the steady-state grid-connected operation of the inverter and the dynamic protection of the power switch tube. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 A schematic diagram of a photovoltaic inverter provided in an embodiment of the present application;
[0013] Figure 2 A schematic diagram of a dynamic protection method for a photovoltaic inverter provided in an embodiment of the present application;
[0014] Figure 3 A schematic diagram of reducing the output current limit value of a photovoltaic inverter in a linear manner provided in an embodiment of the present application;
[0015] Figure 4 A schematic diagram of reducing the output current limit value of a photovoltaic inverter in a step-by-step manner provided in an embodiment of the present application;
[0016] Figure 5 A schematic diagram of reducing the overcurrent protection threshold of a photovoltaic inverter in a linear manner provided in an embodiment of the present application;
[0017] Figure 6 A schematic diagram of reducing the overcurrent protection threshold of a photovoltaic inverter in a step-by-step manner provided in an embodiment of the present application.
[0018] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.
[0020] like Figure 1 As shown, the photovoltaic inverter provided in the embodiment of the present application includes an inverter unit, a positive DC bus BUS+, a negative DC bus BUS- and a bus midpoint O1 arranged on the DC side of the inverter unit, a positive bus capacitor C1 connected between the positive DC bus BUS+ and the bus midpoint O1, a negative bus capacitor C2 connected between the negative DC bus BUS- and the bus midpoint O1, a filter unit and a grid-connected switch arranged on the AC side of the inverter unit, the filter unit includes a filter inductor (shown in L1 to L3 in the figure) and a filter capacitor (shown in Cf1 to Cf3 in the figure), the three-phase filter capacitor is star-connected and the center point of the star connection is O2, the grid-connected switch includes a first grid-connected switch S1 (shown in K1, K3, and K5 in the figure) and a second grid-connected switch S2 (shown in K2, K4, and K6 in the figure) connected in series, and a current sampling module for collecting the three-phase current (shown in Ia, Ib, and Ic in the figure) flowing through the grid-connected switch.
[0021] Among them, the topological structure of the inverter unit is not limited, and the figure shows a three-level topological structure. The first grid-connected switch S1 and the second grid-connected switch S2 both include three-phase independent relays, for example, the first grid-connected switch S1 includes three-phase independent relays K1, K3, K5, and the second grid-connected switch S2 includes three-phase independent relays K2, K4, K6, and each group of three-phase independent relays is driven together, and the relays between the same phases are connected in series, for example, relay K1 is connected in series with relay K2. The current sampling module is arranged between the filtering unit and the three-phase grid-connected switch.
[0022] In one example, the photovoltaic inverter further includes a control unit (not shown in the figure), the control unit includes a memory and a processor, the memory is configured to store a computer program, and the processor implements a dynamic protection method for the photovoltaic inverter when executing the computer program.
[0023] like Figure 2 As shown, in one example, the dynamic protection method of the photovoltaic inverter includes the following steps:
[0024] S11, obtaining a DC voltage of the photovoltaic inverter;
[0025] Among them, the DC voltage includes but is not limited to the MPPT (maximum power point tracking) input voltage of the string inverter and the bus voltage, the input voltage of the centralized inverter, the input voltage of the distributed inverter, and the MPPT input voltage of the distributed combiner box.
[0026] S12, adjusting the output current limit value of the photovoltaic inverter according to the DC voltage to limit the output current of the photovoltaic inverter;
[0027] The output current amplitude limit value may be a total output current amplitude limit value, or may be an amplitude limit value of an active current and a reactive current.
[0028] In one example, adjusting the output current limit value of the photovoltaic inverter according to the DC voltage includes:
[0029] If the DC voltage is higher than the first set voltage threshold, the output current limit value of the photovoltaic inverter is reduced.
[0030] Among them, the first set voltage threshold is greater than or equal to the full-load MPPT input voltage upper limit or the full-load MPPT bus voltage upper limit, and is less than or equal to the software or hardware overvoltage protection threshold.
[0031] In a specific implementation, reducing the output current limit value of the photovoltaic inverter includes:
[0032] The output current limit value of the photovoltaic inverter is reduced in a linear manner or in a step manner.
[0033] like Figure 3-Figure 4 As shown in the two implementations, the horizontal axis is the bus voltage V bus The vertical axes are all output current limit values, and the difference lies in the method of reducing the output current limit values.
[0034] like Figure 3 The linear mode shown, V BUS1 Corresponding to the upper limit of the full-load MPPT bus voltage range, V BUS2 The value is the busbar overvoltage protection threshold, and the vertical coordinate point I lmt1 For V BUS1 The corresponding output current limit value, the vertical coordinate point I lmt2 For V BUS2 The corresponding output current limit value, V BUS1 With V BUS2 The output current limit value between changes linearly.
[0035] like Figure 4 The step method shown, V BUS1 Corresponding to the upper limit of the full-load MPPT bus voltage range, V BUS3The value is the busbar overvoltage protection threshold, V BUS2 The value is a point between the upper limit of the full-load MPPT bus voltage range and the bus overvoltage protection threshold. BUS Less than V BUS1 When the output current is limited to I lmt Maintain the original output current limit value I lmt1 unchanged; V BUS Between V BUS1 and V BUS2 When the output current is limited to I lmt Keep as I lmt2 ; V BUS Between V BUS2 and V BUS3 When the output current is limited to I lmt Keep as I lmt3 .
[0036] In one example, limiting the output current of the photovoltaic inverter includes:
[0037] If the output current of the photovoltaic inverter is higher than the output current limit value of the photovoltaic inverter, a current limiting action is performed to reduce the output current of the photovoltaic inverter;
[0038] If the output current of the photovoltaic inverter is lower than the output current limit value of the photovoltaic inverter, the photovoltaic inverter is controlled to continue to operate at the current output current.
[0039] In a specific implementation, limiting the output current of the photovoltaic inverter includes:
[0040] According to the output current limit value of the photovoltaic inverter, the current loop given quantity of the photovoltaic inverter is limited.
[0041] That is, by using the current limit value to limit the current loop set value of the photovoltaic inverter, when the current loop set value of the photovoltaic inverter is higher than the output current limit value of the photovoltaic inverter, the current loop set value of the photovoltaic inverter will be limited to the current limit value, so that the current loop feedback amount, that is, the output current of the photovoltaic inverter, is rapidly reduced; conversely, when the output current of the photovoltaic inverter is lower than the output current limit value of the photovoltaic inverter, the photovoltaic inverter continues to operate with the current output current, at this time the corresponding current loop set value of the photovoltaic inverter is lower than the current limit value, and the inverter continues to operate with the current current loop set value, that is, maintains the current output current operation.
[0042] S13. Adjusting an overcurrent protection threshold of the photovoltaic inverter according to the DC voltage to implement overcurrent protection of the photovoltaic inverter.
[0043] The second set voltage threshold is greater than or equal to the upper limit of the full-load MPPT input voltage or the upper limit of the full-load MPPT bus voltage, and is less than or equal to the software or hardware overvoltage protection threshold. The overcurrent protection threshold includes but is not limited to the wave-by-wave current limiting protection threshold, the hardware overcurrent protection threshold, and the software overcurrent protection threshold.
[0044] In one example, adjusting the overcurrent protection threshold of the photovoltaic inverter according to the DC voltage includes:
[0045] If the DC voltage is higher than the second set voltage threshold, the overcurrent protection threshold of the photovoltaic inverter is reduced.
[0046] In a specific implementation, lowering the overcurrent protection threshold of the photovoltaic inverter includes:
[0047] The overcurrent protection threshold of the photovoltaic inverter is reduced in a linear manner or in a step manner.
[0048] like Figure 5-Figure 6 As shown in the two implementations, the horizontal axis is the bus voltage V bus The vertical axes are all over-current protection thresholds, and the difference lies in the method of lowering the over-current protection thresholds. Figure 5 It is a linear method. Figure 6 It is a step method, which is similar to the aforementioned method of reducing the output current limit value, and will not be described in detail here.
[0049] In one example, an output current limit value of the photovoltaic inverter corresponding to the same DC voltage point is lower than an overcurrent protection threshold of the photovoltaic inverter.
[0050] In this way, a certain margin can be left to ensure that the output current under steady-state conditions will not mistakenly trigger the wave-by-wave current limiting or overcurrent protection fault shutdown.
[0051] It should be noted that in the above description, “higher than” may mean greater than or equal to, or only greater than; and “lower than” may mean less than or equal to, or only less than.
[0052] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.
[0053] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.
[0054] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
[0055] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.
[0056] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk.
[0057] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.
Claims
1. A dynamic protection method for a photovoltaic inverter, characterized in that: The dynamic protection method comprises: Obtaining a DC voltage of the photovoltaic inverter; According to the DC voltage, adjusting the output current limit value of the photovoltaic inverter to limit the output current of the photovoltaic inverter; According to the DC voltage, an overcurrent protection threshold of the photovoltaic inverter is adjusted to achieve overcurrent protection of the photovoltaic inverter.
2. The dynamic protection method according to claim 1, characterized in that: The step of adjusting the output current limit value of the photovoltaic inverter according to the DC voltage includes: If the DC voltage is higher than the first set voltage threshold, the output current limit value of the photovoltaic inverter is reduced.
3. The dynamic protection method according to claim 2, characterized in that: The first set voltage threshold is greater than or equal to the full-load MPPT input voltage upper limit or the full-load MPPT bus voltage upper limit, and is less than or equal to the software or hardware overvoltage protection threshold.
4. The dynamic protection method according to claim 1, characterized in that: The limiting the output current of the photovoltaic inverter comprises: If the output current of the photovoltaic inverter is higher than the output current limit value of the photovoltaic inverter, a current limiting action is performed to reduce the output current of the photovoltaic inverter; If the output current of the photovoltaic inverter is lower than the output current limit value of the photovoltaic inverter, the photovoltaic inverter is controlled to continue to operate at the current output current.
5. The dynamic protection method according to claim 1, characterized in that: The limiting the output current of the photovoltaic inverter comprises: According to the output current limit value of the photovoltaic inverter, the current loop given quantity of the photovoltaic inverter is limited.
6. The dynamic protection method according to claim 1, characterized in that: The step of adjusting the overcurrent protection threshold of the photovoltaic inverter according to the DC voltage includes: If the DC voltage is higher than the second set voltage threshold, the overcurrent protection threshold of the photovoltaic inverter is reduced.
7. The dynamic protection method according to claim 6, characterized in that: The step of lowering the overcurrent protection threshold of the photovoltaic inverter comprises: The overcurrent protection threshold of the photovoltaic inverter is reduced in a linear manner or in a step manner.
8. The dynamic protection method according to claim 6, characterized in that: The second set voltage threshold is greater than or equal to the full-load MPPT input voltage upper limit or the full-load MPPT bus voltage upper limit, and is less than or equal to the software or hardware overvoltage protection threshold.
9. The dynamic protection method according to claim 1, characterized in that: The output current limit value of the photovoltaic inverter corresponding to the same DC voltage point is lower than the overcurrent protection threshold of the photovoltaic inverter.
10. A photovoltaic inverter, characterized in that: The photovoltaic inverter includes a control unit, the control unit includes a memory and a processor, the memory is configured to store a computer program, and the processor implements the dynamic protection method for the photovoltaic inverter according to any one of claims 1 to 9 when executing the computer program.