String misconnection judgment method for power floating system

Abstract

The invention discloses a string misconnection judgment method for a power supply floating system, and the method comprises the following steps: carrying out the voltage control or detection of the system, and detecting the port voltage of a photovoltaic string at the same time; and if the port voltage change of the photovoltaic string is within a set threshold range, determining that the photovoltaic string is connected to the system, otherwise, determining that the photovoltaic string is not connected to the system. The method has the advantages that whether the photovoltaic string is connected or not can be judged by additionally adding a small number of elements or not, the cost is saved, meanwhile, the judgment precision can be effectively improved, and the implementation mode is simple.

Description

Technical Field

[0001] The present application relates to the technical field of new energy power generation, and particularly relates to a method for judging the disconnection of a string in a power supply floating ground system. Background Art

[0002] As Figure 1 shown, it is a schematic diagram of the architecture of an existing string-type photovoltaic system, including a plurality of photovoltaic strings. Each photovoltaic string is connected to a bus through a corresponding DC / DC circuit, and then is connected to the grid through a DC / AC circuit. In the system, the auxiliary power supply generally takes power from the bus. As Figure 2 shown, after taking power from the bus, a isolated DC / DC circuit is used to obtain a weak power supply. However, the weak electrical signal may not be connected to the negative terminal of the bus. Such a system is called a power supply floating ground system. In the power supply floating ground system, if a string is not connected, based on the structure of the power supply floating ground system, a voltage will also be generated at the port corresponding to the unconnected string, which will cause an error in judging the voltage of the unconnected string, and further lead to disorder in the system operation. Summary of the Invention

[0003] One of the purposes of the present application is to provide a method for judging the disconnection of a string in a power supply floating ground system that can solve at least one defect in the above background art.

[0004] To achieve at least one of the above purposes, the technical solution adopted by the present application is: a method for judging the disconnection of a string in a power supply floating ground system, including the following steps: controlling or detecting the voltage of the system, and simultaneously detecting the port voltage of the photovoltaic string; if the change in the port voltage of the photovoltaic string is 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.

[0005] Preferably, the negative terminal of the DC side bus is grounded. 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 side bus and the signal ground. The control switch is adapted to be closed and conducting when judging the connection of the photovoltaic string, and the control switch is adapted to be open when the system is working normally.

[0007] Preferably, the control switch is one of a relay and a switching tube.

[0008] Preferably, the system includes multiple photovoltaic strings to be detected. Select any one of the photovoltaic strings to be detected as the target photovoltaic string; block the outputs of the remaining photovoltaic strings and detect the port voltage of the target photovoltaic string. 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 a high voltage, it is determined that the target photovoltaic string is connected to the system. Re-select the target photovoltaic string and repeat the above connection judgment process until all photovoltaic strings complete the connection detection.

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

[0010] Preferably, the switching tube of the DC / DC circuit corresponding to the photovoltaic string is set to be constantly on to complete the short-circuit of the output of the photovoltaic string.

[0011] Preferably, a short-circuit circuit is arranged at the output end of the photovoltaic string to complete the short-circuit of the output of the photovoltaic string.

[0012] Preferably, the output end of the photovoltaic string is opened to complete the blocking.

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

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

[0015] By adding a small number of additional components or no components, the judgment on whether the photovoltaic string is connected can be completed. While saving costs, the judgment accuracy can be effectively improved, and the implementation method is simple. Description of the Drawings

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

[0017] Figure 2 It is a schematic diagram of the structure of an existing power supply floating ground system.

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

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

[0020] Figure 5 Schematic diagram of the work flow of one embodiment of the present application.

[0021] Figure 6 For the present application Figure 5 Schematic diagram of the specific architecture of the illustrated embodiment.

[0022] Figure 7 For the present application Figure 6 Schematic diagram of the equivalent circuit structure of the illustrated architecture.

[0023] Figure 8 Schematic diagram of the work flow of another embodiment of the present application.

[0024] Figure 9 For the present application Figure 8 Schematic diagram of the specific architecture of the illustrated embodiment

[0025] Figure 10 For the present application Figure 9 Schematic diagram of the equivalent circuit structure of the illustrated architecture.

[0026] Figure 11 Schematic diagram of the specific architecture of yet another embodiment of the present application.

[0027] Figure 12 For the present application Figure 11 Schematic diagram of the equivalent circuit structure of the illustrated architecture. Detailed implementation manners

[0028] Next, in combination with the detailed implementation manners, the present application will be further described. It should be noted that in the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0029] In the description of the present application, it should be noted that for orientation terms, such as the terms "center", "horizontal", "vertical", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship are based on the orientation or positional relationship shown in the drawings. This is 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 should not be construed as limiting the specific protection scope of the present application.

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

[0031] In the present application, unless otherwise clearly defined and limited, the terms "installed", "connected", "joined", "fixed", etc. should be understood in a broad sense. For example, it can be a connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] In the present application, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but in contact through other features between them. Moreover, the first feature being "above", "over" and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "under" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0033] The terms "comprising" and "having" in the description and claims of the present application, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that comprises a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0034] For the convenience of understanding the technical solution of the present application, the following will conduct a simple analysis on the calculation process of the port voltage when the photovoltaic string is not connected to the system.

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

[0036] As Figure 4 shown, it is Figure 3 the schematic diagram of the equivalent circuit structure corresponding to the string-type photovoltaic system. Assume that photovoltaic string PV#1 is connected to the system while photovoltaic string PV#2 is not connected to the system; then photovoltaic string PV#1 can be equivalent to a power source, and its corresponding output voltage is V PV1 . At this time, photovoltaic string PV#1, the measurement resistor R PV1+ and R PV1- can form a series loop. At the same time, the midpoints of the series branches formed by the measurement resistors R PV1+ and R PV1- and the midpoints of the series branches formed by the measurement resistors R PV2+ and R PV2- are both grounded, and the negative ends of photovoltaic string PV#1 and photovoltaic string PV#2 are both connected to the negative DC bus BUS-.

[0037] According to the equivalent circuit as Figure 4 shown, the expression for the port voltage V PV2_mes of photovoltaic string PV#2 can be obtained as: V PV2_mes = R PV- ×V PV1 / (R PV+ + R PV- ).

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

[0039] It can be seen from the above expression that when photovoltaic string PV#1 is connected to the system and generates electricity, even if photovoltaic string PV#2 is not connected to the system, there is still a voltage at its port, and the voltage value can be regarded as the voltage division of the measurement resistor R PV2- ; this voltage value may cause photovoltaic string PV#2 to be misjudged as being in the connected state when detecting the traditional power source floating ground system, resulting in a misjudgment of the system.

[0040] Based on this, the present application provides a method for judging whether a string in a power floating ground system is connected or not. By controlling or detecting the voltage of the system and simultaneously detecting the port voltage of the photovoltaic string; if the change in the port voltage of the photovoltaic string is within the 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, which can accurately identify whether the photovoltaic string is connected to the system.

[0041] It can be understood that there are various specific implementation manners for controlling or detecting the voltage of the system, and thus there are various manners for judging whether to connect to the system according to the port voltage of the photovoltaic string; for the convenience of understanding, the following will be described in detail through three specific embodiments.

[0042] Embodiment 1:

[0043] A method for judging whether a string in a power floating ground system is connected or not is applied to a string-type photovoltaic system. The specific structure of the string-type photovoltaic system is as described in the background art, so it will not be repeated here. As Figure 5 shown, one preferred embodiment includes the following steps: Control the voltage change between the negative end of the DC side bus of the system and the signal ground, and simultaneously detect the port voltage of each photovoltaic string. If the change in the port voltage of the photovoltaic string is within the 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.

[0044] It can be understood that from the foregoing analysis process, when the photovoltaic string is in the state of being connected to the system, the port voltage of the photovoltaic string is mainly affected by the voltage output when the photovoltaic string converts light energy into electrical energy, and when the photovoltaic string is in the state of not being connected to the system, the port voltage of the photovoltaic string is mainly affected by the voltage between the negative end of the DC side bus and the ground. Therefore, when judging whether the photovoltaic string is connected to the system, the change in the port voltage of each photovoltaic string can be identified by changing the voltage between the negative end of the DC side bus and the ground. For the photovoltaic string with obvious change, it can be determined that it is in the state of not being connected to the system, and for the photovoltaic string with no obvious change, that is, the voltage change is within the set threshold range, it can be determined that it is connected to the system.

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

[0046] In this embodiment, there are various specific ways to control the voltage change between the negative terminal of the DC-side bus and the signal ground. To further increase the influence of the voltage change between the negative terminal of the DC-side bus and the signal ground on the port voltage of the photovoltaic string not connected to the system, this embodiment preferably performs grounding control on the negative terminal of the DC-side bus, so that when judging whether the photovoltaic string is connected to the system, the voltage of the negative terminal of the bus can be clamped to zero by shorting the negative terminal of the DC-side bus to the 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, to perform grounding control on the negative terminal of the DC-side bus, a control switch can be installed between the negative terminal of the DC-side bus and the signal ground. The control switch can remain closed and conducting when judging whether the photovoltaic string is connected, and the control switch can remain open when the system is operating normally.

[0048] For ease of understanding, the following will be described in detail by taking a photovoltaic system corresponding to two photovoltaic strings PV#1 and PV#2 as an example. As Figure 6 shown, a control switch S is installed between the negative terminal of the DC-side bus and the signal ground. The control switch S can be a relay or a switching tube, etc., and can be specifically selected according to the actual needs of those skilled in the art. When the inverter of the photovoltaic system is powered on to detect whether there is an unconnected photovoltaic string, the control switch S can be closed, and at this time the signal ground is clamped to the negative terminal of the DC-side bus. Assuming that the photovoltaic string PV#2 is in an unconnected state to the system, then the port voltage corresponding to the photovoltaic string PV#2 will drop to zero at this time. When the photovoltaic system is operating normally, the control switch S is in an open state, so as not to affect the normal operation of the photovoltaic system.

[0049] For further ease of understanding, the following can perform an equivalent circuit analysis on the Figure 6 shown architecture; among them, the photovoltaic string PV#1 is connected to the system, and the photovoltaic string PV#2 is not connected to the system. As Figure 7 shown, when detecting the connection of the photovoltaic string, the control switch S is closed. At this time, the negative measurement resistors can all be regarded as being short-circuited. Then, from the foregoing analysis process, it can be known that the port voltage V PV2_mes of the photovoltaic string PV#2 is 0 at this time, while the port voltage of the photovoltaic string PV#1 still remains at V PV1 , so that it is possible to accurately identify whether the photovoltaic string is connected and no misjudgment will occur.

[0050] Embodiment 2:

[0051] A method for judging the disconnection of a string in a floating-ground power supply system is applied to a string-type photovoltaic system. The specific structure of the string-type photovoltaic system is as described in the background art, so it will not be repeated here. As Figure 8As shown, one preferred embodiment includes the following steps: The system includes multiple photovoltaic strings to be detected, and any one of the photovoltaic strings to be detected is selected as the target photovoltaic string. Block the outputs of the remaining photovoltaic strings, and detect the port voltage of the target photovoltaic string. 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 a high voltage, it is determined that the target photovoltaic string is connected to the system. Re-select the target photovoltaic string and repeat the above access judgment process until the access detection of all photovoltaic strings is completed.

[0052] It can be understood that from the foregoing analysis process, the port voltage of the photovoltaic string not connected to the system is mainly 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. Then, block the photovoltaic string connected to the system so that the output voltage is zero, and 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 access situation of the photovoltaic string.

[0053] It should be known that since the access situation of the photovoltaic string is unknown, each photovoltaic string needs to be used as the target photovoltaic string to complete an access judgment once, so that all photovoltaic strings can be traversed to complete the judgment of the access situation.

[0054] In this embodiment, there are various ways to block the remaining photovoltaic strings except the target photovoltaic string, which can be mainly divided into two types; the first is to short-circuit the remaining photovoltaic strings except the target photovoltaic string to complete the block, and the second is to open the output end of the remaining photovoltaic strings except the target photovoltaic string to complete the block. For the convenience of understanding, the following will specifically describe these two blocking methods.

[0055] I. There are also various specific implementation manners for the first blocking method. For the convenience of understanding, the following will be described in detail through two specific examples.

[0056] Example 1: The short circuit is completed by setting the switch tube of the DC / DC circuit corresponding to the photovoltaic string to be constantly on. It should be known that the DC / DC circuit adopts a Boost circuit, and the switch tubes of the DC / DC circuit are installed in parallel between the positive and negative output terminals of the photovoltaic string. Therefore, setting the switch tube to be constantly on can achieve the short circuit of the output of the photovoltaic string.

[0057] Specifically, the following will take the photovoltaic system corresponding to two photovoltaic strings PV#1 and PV#2 as an example for detailed description; among them, the photovoltaic string PV#1 is connected to the system, and the photovoltaic string PV#2 is not connected to the system. As Figure 9As shown in the figure, taking the PV string PV#2 as the target PV string, when judging the connection of the PV string PV#2, the switching tube of the DC / DC circuit corresponding to the PV string PV#1 can be set to be constantly on. The corresponding equivalent circuit is as follows Figure 10 As shown, at this time, the PV string PV#1 can be equivalent to a wire in the equivalent circuit. Then, the voltage of the measuring resistor of the PV string PV#2 is also reduced to zero, that is, V PV2_mes = 0. In this way, it is possible to accurately identify whether the PV string PV#2 is connected. By analogy, other PV strings can be judged, so that misjudgment will not occur.

[0058] Example 2: Short-circuiting is performed by setting a short-circuit circuit at the output end of the PV string; that is, a short-circuit circuit controlled by a switch is set at the positive and negative output ends of the PV string. Thus, when judging the connection of the target PV string, the output of the PV string is short-circuited by closing the switch; when the PV string is operating normally, the short-circuit circuit can be disconnected by the switch to avoid affecting the normal operation of the PV string.

[0059] Second, there are also various specific implementation manners for the second blocking method. The following will be described in detail through a specific example. Specifically, switches can be installed at the positive output end / or negative output end of each PV string. When the PV string is operating normally, the switch is in the closed and conducting state so that the PV string can output voltage normally. When judging the connection of the PV string, the switches corresponding to the output ends of other PV strings except the target PV string can be disconnected, so that other PV strings are in an output open-circuit state. At this time, a power supply cannot be formed in the equivalent circuit to supply power to the target PV string. Furthermore, when the target PV string is not connected, the port voltage of the target PV string can be detected to be zero.

[0060] Embodiment 3:

[0061] A method for judging the disconnection of a string in a power supply floating ground system, which is applied to a string-type PV system. The specific structure of the string-type PV system is as described in the background art, so it will not be repeated here. One preferred embodiment includes the following steps: detecting the voltage between the negative terminal of the DC side bus of the system and the signal ground, and comparing it with the port voltage of each PV string. If the difference between the two is less than the set threshold, it is determined that the PV string is not connected to the system; if the port voltage of the PV string is greater than the voltage between the negative terminal of the DC side bus and the signal ground, and the difference between the two is greater than the set threshold, it is determined that the PV string is connected to the system.

[0062] It can be understood that from the foregoing analysis process, when the PV string is not connected to the system, the port voltage of the PV string is theoretically equal to the voltage V between the negative terminal of the DC side bus and the signal groundCND_BUS Considering that there may be certain errors in voltage detection, a threshold with a relatively small value can be set. Then, only the difference between the port voltage of the photovoltaic string and voltage V CND_BUS needs to be compared with the threshold. If the difference between the two is within the threshold range, then the port voltage of the photovoltaic string can be equivalently considered equal to voltage V CND_BUS . When the photovoltaic string is connected to the system, the voltage output by the photovoltaic string 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 value range of the threshold can be selected according to the actual needs of those skilled in the art.

[0063] For easy understanding, as shown in Figure 11 and Figure 12 , a photovoltaic system corresponding to two photovoltaic strings PV#1 and PV#2 will be used as an example for detailed description below. Among them, the photovoltaic string PV#1 is connected to the system, the photovoltaic string PV#2 is not connected to the system, and the value of the threshold is zero. When making a judgment on the connection of the photovoltaic string, the port voltages of the photovoltaic strings PV#1 and PV#2 can be collected, and at the same time, the voltage between the negative terminal of the DC bus and the signal ground can be collected. At this time, the port voltage V of the photovoltaic string PV#1 can be obtained PV1 > V CND_BUS , the port voltage V of the photovoltaic string PV#2 PV2_mes = V CND_BUS .

[0064] The above describes the basic principle, main features, and advantages of the present application. Those skilled in the art of this industry should understand that the present application is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A method for judging the disconnection of a string in a power supply floating ground system, characterized in that, The method includes the following steps: Perform voltage control or detection on the system, and at the same time, detect the port voltage of the photovoltaic string; If the port voltage of the photovoltaic string is within the 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.

2. The method for judging disconnection of the string in the power supply floating ground system according to claim 1, wherein Perform grounding control on the negative terminal of the DC side bus of the system; if the port voltage of the photovoltaic string drops to zero, it is determined that the photovoltaic string is not connected to the system.

3. The method for judging the disconnection of the string in the power supply floating ground system according to claim 2, characterized in that, Install a control switch between the negative terminal of the DC side bus and the signal ground. The control switch is adapted to remain closed and conducting when judging the connection of the photovoltaic string, and the control switch is adapted to remain open when the system is operating normally.

4. The method for judging the disconnection of a string in the power supply floating ground system according to claim 3, wherein, The control switch adopts one of a relay and a switching tube.

5. The method for judging the disconnection of the string of the power floating ground system according to claim 1, wherein The system includes multiple photovoltaic strings to be detected. Select any one of the photovoltaic strings to be detected as the target photovoltaic string; Block the outputs of the remaining photovoltaic strings and detect the port voltage of the target photovoltaic string; 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 a high voltage, it is determined that the target photovoltaic string is connected to the system; Re-select the target photovoltaic string and repeat the connection judgment process until the connection detection of all photovoltaic strings is completed.

6. The method for judging the disconnection of a string in the power supply floating ground system according to claim 5, characterized in that, Short-circuit the output of the photovoltaic string to complete the blocking.

7. The method for judging the disconnection of a string in the power supply floating ground system according to claim 6, wherein, Set the switching tube of the DC / DC circuit corresponding to the photovoltaic string to be constantly on to complete the short-circuit of the output of the photovoltaic string.

8. The method for judging the disconnection of the string in the power supply floating ground system according to claim 6, characterized in that, Set a short-circuit circuit at the output end of the photovoltaic string to complete the short-circuit of the output of the photovoltaic string.

9. The method for judging the disconnection of the string in the power supply floating ground system according to claim 5, wherein Open the circuit at the output end of the photovoltaic string to complete the blocking.

10. The method for judging the disconnection of the string of the power floating ground system according to claim 1, wherein Detect the voltage between the negative terminal of the DC side bus of the system and the signal ground; Use the detected voltage as a threshold to compare the difference with the port voltage of each photovoltaic string; If the difference between the two is less than or equal to the set error range, it is determined that the photovoltaic string is not connected to the system; If the port voltage of the photovoltaic string is greater than the voltage between the negative terminal of the DC side bus and the signal ground, and the difference between the two is greater than the set error range, it is determined that the photovoltaic string is connected to the system.

Images