A method for determining whether a string of a power supply floating ground system is connected

Abstract

The application discloses a method for judging whether a photovoltaic string is connected to a power supply floating ground system, comprising the following steps: voltage control or detection is performed on the system, and the port voltage of the photovoltaic string is detected; if the port voltage of the photovoltaic string changes within a set threshold range, it is determined that the photovoltaic string is connected to the system, otherwise, it is determined that the photovoltaic string is not connected to the system. The application has the beneficial effects that the judgment on whether the photovoltaic string is connected can be completed by adding a small number of elements or without adding elements, the judgment accuracy can be effectively improved while the cost is saved, and the implementation mode is simple.

Description

A method for determining unconnected strings in a power supply floating ground system Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a method for determining unconnected strings in a power supply floating ground system. Background Technology

[0002] Figure 1 shows a schematic diagram of an existing string photovoltaic (PV) system, comprising multiple PV strings. Each PV string is connected to the bus via a corresponding DC / DC circuit, and then connected to the grid via a DC / AC circuit. In this system, auxiliary power is typically drawn from the bus, as shown in Figure 2. After being drawn from the bus, power is obtained through an isolated DC / DC circuit to acquire low-voltage power. However, the low-voltage signal may not be connected to the negative terminal of the bus; this type of system is called a floating ground system. In a floating ground system, if any strings are not connected, due to the structure of the system, the ports corresponding to the unconnected strings will also generate voltage. This can cause errors in voltage judgment for unconnected strings, leading to system malfunctions. Summary of the Invention

[0003] One objective of this application is to provide a method for determining unconnected strings in a power floating system that can solve at least one of the defects in the aforementioned background art.

[0004] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: a method for determining whether a photovoltaic string in a floating power system is not connected, comprising the following steps: performing voltage control or detection on the system, and simultaneously detecting the port voltage of the photovoltaic string; if the port voltage change of the photovoltaic string is within a set threshold range, the photovoltaic string is determined to be connected to the system; otherwise, the photovoltaic string is determined to be not connected to the system.

[0005] Preferably, grounding control is implemented at the negative terminal of the DC bus. If the port voltage of the photovoltaic string drops to zero, it is determined that the photovoltaic string is not connected to the system.

[0006] Preferably, a control switch is installed between the negative terminal of the DC bus and the signal ground. The control switch is adapted to remain closed and conductive when making a decision on the connection of the photovoltaic string, and the control switch is adapted to remain open when the system is operating normally.

[0007] Preferably, the control switch is either a relay or a switching transistor.

[0008] Preferably, the system includes multiple photovoltaic strings to be tested. Any photovoltaic string to be tested is selected as the target photovoltaic string. The outputs of the remaining photovoltaic strings are blocked, and the port voltage of the target photovoltaic string is detected. If the port voltage of the target photovoltaic string is zero, it is determined that the target photovoltaic string is not connected to the system. If the port voltage of the target photovoltaic string is high, it is determined that the target photovoltaic string is connected to the system. The target photovoltaic string is reselected, and the above connection judgment process is repeated until all photovoltaic strings have completed the connection detection.

[0009] Preferably, the output of the photovoltaic string is short-circuited to achieve the blocking.

[0010] Preferably, the switching transistors of the DC / DC circuit corresponding to the photovoltaic string are set to constant continuity to complete the output short circuit of the photovoltaic string.

[0011] Preferably, the output shorting of the photovoltaic string is accomplished by setting a shorting circuit at the output end of the photovoltaic string.

[0012] Preferably, the output terminal of the photovoltaic string is disconnected to achieve the blocking.

[0013] Preferably, the voltage between the negative terminal of the DC bus and the signal ground of the system is detected; the detected voltage is used as a threshold and compared with the difference between the voltage at the port of each photovoltaic string; if the difference is less than or equal to the set threshold, the photovoltaic string is determined not to be connected to the system; if the port voltage of the photovoltaic string is greater than the voltage between the negative terminal of the DC bus and the signal ground, and the difference between the two is greater than the set threshold, the photovoltaic string is determined to be connected to the system.

[0014] Compared with the prior art, the beneficial effects of this application are as follows:

[0015] The determination of whether a photovoltaic string is connected can be completed by adding a few extra components or not adding any components. This saves costs, effectively improves the accuracy of the determination, and is simple to implement. Attached Figure Description

[0016] Figure 1 is a schematic diagram of the architecture of an existing string photovoltaic system.

[0017] Figure 2 is a schematic diagram of the existing power floating system.

[0018] Figure 3 is a schematic diagram of the architecture of an existing string photovoltaic system considering the measurement resistance.

[0019] Figure 4 is a schematic diagram of the equivalent circuit structure of the photovoltaic module PV#2 in Figure 3 when it is not connected.

[0020] Figure 5 is a schematic diagram of the workflow of one embodiment of this application.

[0021] Figure 6 is a schematic diagram of the specific architecture of the embodiment shown in Figure 5 of this application.

[0022] Figure 7 is a schematic diagram of the equivalent circuit structure of the architecture shown in Figure 6 of this application.

[0023] Figure 8 is a schematic diagram of the workflow of another embodiment of this application.

[0024] Figure 9 is a schematic diagram of the specific architecture of the embodiment shown in Figure 8 of this application.

[0025] Figure 10 is a schematic diagram of the equivalent circuit structure of the architecture shown in Figure 9 of this application.

[0026] Figure 11 is a schematic diagram of the specific architecture of another embodiment of this application.

[0027] Figure 12 is a schematic diagram of the equivalent circuit structure of the architecture shown in Figure 11 of this application. Detailed Implementation

[0028] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0029] In the description of this application, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this application.

[0030] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0031] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0032] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0033] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0034] To facilitate understanding of the technical solution of this application, a simple analysis of the port voltage calculation process when the photovoltaic string is not connected to the system will be provided below.

[0035] As shown in Figure 3, to simplify the analysis, the number of photovoltaic strings in a string photovoltaic system is taken as two strings, namely photovoltaic string PV#1 and photovoltaic string PV#2. The voltage measurement resistor corresponding to photovoltaic string PV#1 is R. PV1+ and R PV1- The voltage measurement resistor corresponding to photovoltaic string PV#2 is R. PV2+ and R PV2- .

[0036] Figure 4 shows the equivalent circuit structure of the string photovoltaic system corresponding to Figure 3. Assume that photovoltaic string PV#1 is connected to the system, while photovoltaic string PV#2 is not connected; then photovoltaic string PV#1 can be considered as a power source, with a corresponding output voltage of V. PV1 At this time, the photovoltaic string PV#1 has a measured resistance of R. PV1+ and RPV1- These can form a series circuit. Simultaneously, the measured resistance is R. PV1+ and R PV1- The midpoint of the series branch and the measured resistance R PV2+ and R PV2- The midpoints of the series branches are all grounded, and the negative terminals of photovoltaic strings PV#1 and PV#2 are both connected to the DC side negative bus BUS-.

[0037] Based on the equivalent circuit shown in Figure 4, the port voltage V of the photovoltaic string PV#2 can be obtained. PV2_mes The expression is: V PV2_mes =R PV- ×V PV1 / (R PV+ +R PV- ).

[0038] Among them, R PV+ R represents the total resistance of all photovoltaic strings corresponding to the positive measured resistance. PV- This represents the total resistance value of the negative measured resistors corresponding to all photovoltaic strings.

[0039] As can be seen from the above expression, when photovoltaic string PV#1 is connected to the system and generating electricity, even if photovoltaic string PV#2 is not connected to the system, its port still has voltage, and the voltage value can be regarded as the measured resistance R. PV2- The voltage drop is due to the voltage drop across the system. When testing a traditional power supply floating ground system, this voltage value may cause the photovoltaic string PV#2 to be misjudged as being connected to the system, resulting in an error in the system's judgment.

[0040] Based on this, this application provides a method for determining whether a photovoltaic string is not connected in a power floating ground system. By controlling or detecting the system voltage and simultaneously detecting the port voltage of the photovoltaic string, if the port voltage change of the photovoltaic string is within a set threshold range, the photovoltaic string is considered to be connected to the system; otherwise, the photovoltaic string is considered not connected to the system. This method can accurately identify whether a photovoltaic string is connected to the system.

[0041] It is understandable that there are various specific implementation methods for voltage control or detection of the system, and thus various ways to determine the connection to the system based on the port voltage of the photovoltaic string; for ease of understanding, three specific embodiments will be described in detail below.

[0042] Example 1:

[0043] A method for determining if a string of photovoltaic (PV) modules is not connected in a floating ground power supply system is disclosed. This method is applied to a string PV system, the specific structure of which is described in the background section and will not be repeated here. As shown in Figure 5, a preferred embodiment includes the following steps: voltage variation control is performed between the negative terminal of the DC bus and the signal ground of the system, while simultaneously detecting the port voltage of each PV module. If the port voltage variation of the PV module is within a set threshold range, the PV module is considered connected to the system; otherwise, it is considered not connected.

[0044] As can be understood from the aforementioned analysis, when the photovoltaic (PV) string is connected to the system, its port voltage is primarily affected by the voltage output from the PV string's conversion of light energy into electrical energy. Conversely, when the PV string is disconnected from the system, its port voltage is primarily affected by the voltage between the negative terminal of the DC bus and ground. Therefore, when determining whether a PV string is connected to the system, the change in port voltage of each PV string can be identified by altering the voltage between the negative terminal of the DC bus and ground. PV strings with significant voltage changes can be considered disconnected from the system, while those with insignificant changes (i.e., voltage changes within a set threshold range) can be considered connected to the system.

[0045] It should be understood that the specific value of the set threshold range can be selected by those skilled in the art based on their actual needs.

[0046] In this embodiment, there are various specific methods for controlling the voltage change between the negative terminal of the DC bus and the signal ground. To further increase the impact of the voltage change between the negative terminal of the DC bus and the signal ground on the port voltage of photovoltaic strings not connected to the system, this embodiment preferably implements grounding control on the negative terminal of the DC bus. Therefore, when determining whether a photovoltaic string is connected to the system, the voltage at the negative terminal of the DC bus can be clamped to zero by shorting it to ground. If the port voltage of a photovoltaic string drops to zero at this time, it can be determined that the photovoltaic string is not connected to the system.

[0047] Specifically, in order to control the grounding of the negative terminal of the DC bus, a control switch can be installed between the negative terminal of the DC bus and the signal ground. The control switch can remain closed and conducting when judging the access of photovoltaic strings, and can remain open when the system is working normally.

[0048] To facilitate understanding, the following detailed explanation will use a photovoltaic system corresponding to two photovoltaic strings, PV#1 and PV#2, as an example. As shown in Figure 6, a control switch S is installed between the negative terminal of the DC bus and the signal ground. The control switch S can be a relay or a switching transistor, etc., whichever is appropriate for the needs of those skilled in the art. When the inverter of the photovoltaic system is powered on to detect whether any photovoltaic strings are not connected, the control switch S can be closed, at which point the signal ground is clamped to the negative terminal of the DC bus. Assuming that photovoltaic string PV#2 is not connected to the system, the port voltage corresponding to photovoltaic string PV#2 will drop to zero. When the photovoltaic system is operating normally, the control switch S is in the open state, thus not affecting the normal operation of the photovoltaic system.

[0049] To further facilitate understanding, an equivalent circuit analysis can be performed on the architecture shown in Figure 6; where photovoltaic string PV#1 is connected to the system, and photovoltaic string PV#2 is not connected. As shown in Figure 7, when the photovoltaic string connection detection is performed, the control switch S is closed. At this time, all negative measuring resistors can be regarded as short-circuited. From the aforementioned analysis process, it can be seen that the port voltage V of photovoltaic string PV#2 is... PV2_mes =0, while the port voltage of photovoltaic string PV#1 remains at V. PV1 This ensures accurate identification of whether photovoltaic strings are connected, preventing misjudgments.

[0050] Example 2:

[0051] A method for determining unconnected strings in a power supply floating ground system is disclosed, applicable to string photovoltaic (PV) systems. The specific structure of a string PV system is described in the background section and will not be repeated here. As shown in Figure 8, a preferred embodiment includes the following steps: The system includes multiple PV strings to be tested. Any PV string to be tested is selected as the target PV string. The outputs of the remaining PV strings are blocked, and the port voltage of the target PV string is detected. If the port voltage of the target PV string is zero, it is determined that the target PV string is not connected to the system. If the port voltage of the target PV string is high, it is determined that the target PV string is connected to the system. A new target PV string is selected, and the above connection determination process is repeated until all PV strings have completed the connection detection.

[0052] As can be understood from the aforementioned analysis, the port voltage of the photovoltaic string not connected to the system mainly comes from the voltage division of the output voltage of the photovoltaic string connected to the system; that is, the photovoltaic string connected to the system can be regarded as the power source of the entire equivalent circuit. Therefore, if the photovoltaic string connected to the system is blocked so that its output voltage is zero, the port voltage of the photovoltaic string not connected to the system will also be reduced to zero. At this time, it is only necessary to detect whether the port voltage of the photovoltaic string is zero to determine the connection status of the photovoltaic string.

[0053] It should be noted that since the access status of the photovoltaic strings is unknown, each photovoltaic string needs to be treated as a target photovoltaic string to complete an access determination. This way, all photovoltaic strings can be traversed to complete the access determination.

[0054] In this embodiment, there are several ways to block the photovoltaic strings other than the target photovoltaic string, which can be mainly divided into two types: the first is to short-circuit the photovoltaic strings other than the target photovoltaic string to complete the blocking, and the second is to disconnect the output terminal of the photovoltaic strings other than the target photovoltaic string to complete the blocking. For ease of understanding, these two blocking methods will be described in detail below.

[0055] There are also various specific implementation methods for the first type of blocking. To facilitate understanding, two specific examples will be used to explain in detail below.

[0056] Example 1: Short-circuiting is achieved by setting the switching transistor of the DC / DC circuit corresponding to the photovoltaic string to be constantly on. It should be noted that the DC / DC circuit uses a Boost circuit, and the switching transistors of the DC / DC circuit are connected in parallel between the positive and negative output terminals of the photovoltaic string. Therefore, setting the switching transistors to be constantly on can achieve a short circuit of the photovoltaic string output.

[0057] Specifically, the following will use two photovoltaic strings, PV#1 and PV#2, as examples to illustrate this in detail; where PV#1 is connected to the system, and PV#2 is not connected. As shown in Figure 9, if PV#2 is taken as the target photovoltaic string, the switching transistor of the DC / DC circuit corresponding to PV#1 can be set to constant on when determining the connection of PV#2. The corresponding equivalent circuit is shown in Figure 10. At this time, PV#1 can be equivalent to a wire in the equivalent circuit, and the voltage across the measuring resistor of PV#2 will also be reduced to zero, i.e., V. PV2_mes =0. This allows for accurate identification of whether photovoltaic string PV#2 is connected, and similarly, other photovoltaic strings can be identified, thus preventing misjudgments.

[0058] Example 2: Short-circuiting is achieved by setting a short-circuit circuit at the output terminal of the photovoltaic string; that is, a short-circuit circuit controlled by a switch is set at the positive and negative output terminals of the photovoltaic string. Thus, when determining whether to connect the target photovoltaic string, the output of the photovoltaic string is short-circuited by closing the switch; and when the photovoltaic string is operating normally, the short-circuit circuit can be opened by the switch to avoid affecting the normal operation of the photovoltaic string.

[0059] II. There are several specific implementation methods for the second blocking method. The following will explain in detail using a specific example. Specifically, switches can be installed at the positive and / or negative output terminals of each photovoltaic (PV) string. When the PV string is operating normally, the switches are closed and conducting, allowing the PV string to output voltage normally. However, when determining whether a PV string is connected, the switches corresponding to the output terminals of other PV strings (excluding the target PV string) can be disconnected, putting other PV strings in an open-circuit state. In this case, no power can be generated in the equivalent circuit to supply power to the target PV string. Therefore, when the target PV string is not connected, its port voltage can be detected as zero.

[0060] Example 3:

[0061] A method for determining if a string of photovoltaic (PV) modules in a floating ground power system is disclosed, applicable to a string PV system. The specific structure of the string PV system is described in the background section and will not be repeated here. One preferred embodiment includes the following steps: detecting the voltage between the negative terminal of the DC bus and signal ground, and comparing it with the port voltage of each PV string. If the difference is less than a set threshold, the PV string is determined to be unconnected to the system; if the port voltage of the PV string is greater than the voltage between the negative terminal of the DC bus and signal ground, and the difference is greater than the set threshold, the PV string is determined to be connected to the system.

[0062] As can be understood from the aforementioned analysis, when the photovoltaic string is not connected to the system, the port voltage of the photovoltaic string is theoretically equal to the voltage V between the negative terminal of the DC bus and the signal ground. CND_BUS Considering the potential for error in voltage detection, a threshold with a small value can be set. Therefore, it is only necessary to compare the port voltage of the photovoltaic string with the voltage V. CND_BUS The difference is compared with a threshold. If the difference is within the threshold range, then it can be equivalent to the port voltage of the photovoltaic string being equal to voltage V. CND_BUS When photovoltaic strings are connected to the system, the voltage output by the photovoltaic strings converting light energy into electrical energy is much greater than the voltage between the negative terminal of the DC bus and the signal ground. The specific range of the threshold value can be selected by those skilled in the art based on their actual needs.

[0063] For ease of understanding, as shown in Figures 11 and 12, the following detailed explanation will use a photovoltaic system corresponding to two photovoltaic strings, PV#1 and PV#2, as an example. In this example, PV#1 is connected to the system, while PV#2 is not connected, and the threshold value is zero. When determining the connection of the photovoltaic strings, the port voltages of PV#1 and PV#2 can be collected, along with the voltage between the negative terminal of the DC bus and the signal ground. This yields the port voltage V of PV#1. PV1 >V CND_BUS The port voltage V of photovoltaic string PV#2 PV2_mes =V CND_BUS .

[0064] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for determining unconnected strings in a power supply floating ground system, characterized in that, The process includes the following steps: voltage control or detection of the system, and simultaneous detection of the port voltage of the photovoltaic string; if the port voltage of the photovoltaic string is within a set threshold range, the photovoltaic string is considered connected to the system; otherwise, the photovoltaic string is considered not connected to the system; voltage control or detection of the system includes installing a control switch between the negative terminal of the DC bus and signal ground, the control switch being adapted to remain closed and conducting during photovoltaic string connection determination, and adapted to remain open during normal system operation; grounding control of the negative terminal of the DC bus of the system is performed through the control switch; if the port voltage of the photovoltaic string drops to zero, the photovoltaic string is considered not connected to the system.

2. The method for determining unconnected strings in a power supply floating ground system as described in claim 1, characterized in that, The control switch is either a relay or a switching transistor.

3. A method for determining unconnected strings in a power supply floating ground system, characterized in that, The process includes the following steps: Voltage control or detection of the system, and simultaneous detection of the port voltage of the photovoltaic (PV) strings; if the port voltage of the PV string is within a set threshold range, the PV string is considered connected to the system; otherwise, it is considered not connected. The system includes multiple PV strings to be detected, and any PV string to be detected is selected as the target PV string; voltage control or detection of the system includes blocking the output of the remaining PV strings; the port voltage of the target PV string is detected; if the port voltage of the target PV string is zero, it is considered not connected to the system; if the port voltage of the target PV string is high, it is considered connected to the system; a new target PV string is selected, and the above connection judgment process is repeated until all PV strings have completed the connection detection.

4. The method for determining unconnected strings in a power supply floating ground system as described in claim 3, characterized in that, The output of the photovoltaic string is short-circuited to complete the blocking.

5. The method for determining unconnected strings in a power supply floating ground system as described in claim 4, characterized in that, The switching transistors of the DC / DC circuit corresponding to the photovoltaic string are set to be constantly on to complete the output short circuit of the photovoltaic string.

6. The method for determining unconnected strings in a power supply floating ground system as described in claim 4, characterized in that, A shorting circuit is set at the output end of the photovoltaic string to complete the output shorting of the photovoltaic string.

7. The method for determining unconnected strings in a power supply floating ground system as described in claim 3, characterized in that, The output terminal of the photovoltaic string is disconnected to complete the blocking.

8. A method for determining unconnected strings in a power supply floating ground system, characterized in that, The process includes the following steps: voltage control or detection of the system, and simultaneous detection of the port voltage of the photovoltaic (PV) strings; if the port voltage of the PV strings is within a set threshold range, the PV strings are considered connected to the system; otherwise, the PV strings are considered not connected to the system; voltage control or detection of the system includes detecting the voltage between the negative terminal of the DC bus and signal ground; the detected voltage is used as a threshold and compared with the difference between the threshold voltage and the port voltage of each PV string; if the difference is less than or equal to a set error range, the PV strings are considered not connected to the system; if the port voltage of the PV strings is greater than the voltage between the negative terminal of the DC bus and signal ground, and the difference is greater than a set error range, the PV strings are considered connected to the system.

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