A circuit breaker and photovoltaic system

Abstract

The application provides a kind of photovoltaic system and switch-off device, the input side and output side of the switch-off device are respectively arranged at the two sides of the power transmission branch in the switch-off device, and at least one first switch tube and at least one second switch tube are arranged in series in the power transmission branch; although the body diode or anti-parallel diode of the first switch tube allows reverse current to flow into the positive electrode of the input side of the switch-off device, when the control unit detects that the output current of the switch-off device is the reverse current, the second switch tube is controlled to be disconnected to cut off the reverse current; when the group string is connected in parallel with the group string of different voltage, even if the reverse current occurs, it can be cut off in time, and finally the reliable switch-off under the communication control scheme is realized.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a switch and a photovoltaic system. Background Technology

[0002] In photovoltaic (PV) systems, the series voltage of the PV array is typically very high. To improve system safety, the PV system needs to be able to quickly shut off. Therefore, current technology generally incorporates a shutdown device into the PV modules to change the power output of the PV modules by switching the shutdown device on and off. The internal structure of the shutdown device is as follows: Figure 1 As shown, it mainly controls the off state of the corresponding component by controlling the state of the switching transistor K located in the power supply circuit; the on and off state of the switching transistor K is driven and controlled by its control unit according to the instructions received by the communication unit.

[0003] There is also a solution in the existing technology that is a communication-free control solution, which saves... Figure 1 The communication unit in the system cannot communicate with other control units, so it cannot receive control information from other control units. It only determines whether the system is normal by detecting the output current and voltage of the shut-off device itself, and then executes the switching on and off of the shut-off device.

[0004] Therefore, when two photovoltaic strings with different voltages are connected in parallel, the circuit breaker in the high-voltage string will detect the presence of current and will not turn off; while the circuit breaker in the low-voltage string will detect reverse current and will actively turn off. However, due to the presence of its switching transistor K reverse parallel diode or body diode, it cannot block the reverse current path. At this time, the problem of current flowing back from the high-voltage string into the low-voltage string will occur. Summary of the Invention

[0005] In view of this, this application provides a switch and a photovoltaic system to achieve reliable shutdown in the case of different voltage groups connected in series and parallel in a communication control scheme.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] The first aspect of this application provides a switch, wherein the applied string is connected in parallel with another string of different voltages, the switch comprising: a control unit, a power transmission branch, and a bypass branch; wherein...

[0008] The two sides of the power transmission branch serve as the input side and output side of the switch, respectively.

[0009] The bypass branch is located between the two poles of the output side of the shut-off device;

[0010] The power transmission branch is provided with at least one first switch and at least one second switch connected in series; the conduction reverse of the body diode or anti-parallel diode of the first switch is the same as the reverse current flowing into the positive terminal of the input side of the switch.

[0011] The control unit is used to detect the output current of the shutdown device, and when the output current is the reverse current, it controls the second switch to open to cut off the reverse current.

[0012] Optionally, when the output current is a positive current flowing to the positive terminal of the output side of the switch and is greater than or equal to a preset threshold, all switching transistors are controlled to remain in the on state.

[0013] Optionally, the control unit is further configured to: control the first switch to disconnect when the output current is a positive current flowing to the positive terminal of the output side of the switch and is less than a preset threshold, or control all switches to disconnect.

[0014] Optionally, the control unit is further configured to: control the first switch to disconnect when the output current is the reverse current.

[0015] Optionally, the control unit is used to control the corresponding switch to turn off, specifically for delaying the turning off of the corresponding switch.

[0016] Optionally, the control unit is further configured to: when a start signal is detected from the input / output parameters of the shut-off device, control all switching transistors to be turned on.

[0017] Optionally, the second switch may have no body diode and anti-parallel diode, or the conduction direction of its body diode or anti-parallel diode may be opposite to the reverse current.

[0018] Optionally, the power transmission branch includes: a positive transmission branch and a negative transmission branch;

[0019] The positive transmission branch is connected between the positive input terminal and the positive output terminal of the switch;

[0020] The negative transmission branch is connected between the input negative terminal and the output negative terminal of the switch;

[0021] The first switch is disposed in the positive transmission branch or the negative transmission branch, and the second switch is disposed in the positive transmission branch or the negative transmission branch.

[0022] Optionally, the bypass branch includes a third switch controlled by the control unit.

[0023] Optionally, the bypass branch includes: a diode;

[0024] The negative terminal of the diode is connected to the positive terminal of the output side of the switch;

[0025] The positive terminal of the diode is connected to the negative terminal of the output side of the switch.

[0026] Optionally, the control unit includes: a processor and a drive circuit;

[0027] The processor is used to control the on / off state of the corresponding switching transistor through the driving circuit based on the input / output parameters of the acquired switch.

[0028] The first aspect of this application provides a photovoltaic system, characterized in that it comprises: a photovoltaic array, at least one inverter, and N switchgear; N is greater than or equal to 2; wherein,

[0029] The inverter has at least one string connected to its DC side;

[0030] The string includes at least two shutdown devices connected in series via their respective output sides; and the input side of each shutdown device is connected to a corresponding photovoltaic module in the photovoltaic array.

[0031] At least one of the shutdown devices in the said string is a shutdown device as described in any of the first aspects above.

[0032] Optionally, at least two strings are connected in parallel on the DC side of the inverter, wherein the shutdown device in at least one string with a lower voltage is a shutdown device as described in any of the first aspects above.

[0033] The power transmission branch of the present application provides a power switch, with its two sides serving as the input and output sides respectively. The power transmission branch includes at least one first switch and at least one second switch connected in series. Although the body diode or anti-parallel diode of the first switch allows reverse current to flow into the positive terminal of the power switch's input side, the control unit, upon detecting that the output current of the power switch is the reverse current, controls the second switch to open to cut off the reverse current. Furthermore, when the power switch string is connected in parallel with strings of different voltages, even if a reverse current occurs, it can be cut off in time, ultimately achieving reliable power-off without communication control. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 A schematic diagram of the structure of a switch provided in the prior art;

[0036] Figure 2 This is a schematic diagram of the structure of the shut-off device provided in the embodiments of this application;

[0037] Figure 3a , Figure 3b , Figure 3c , Figure 3d and Figure 3e Five circuit diagrams of the shut-off device provided in the embodiments of this application are shown respectively.

[0038] Figure 4 This is a schematic diagram of the long and short groups connected in series and parallel according to an embodiment of this application;

[0039] Figure 5 A schematic diagram of the long and short series-parallel connection structure provided for existing technology. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0042] This application provides a switch to achieve reliable shutdown in the case of different voltage groups connected in series and parallel in a communication-free control scheme.

[0043] The string to which this switch is applied is connected in parallel with another string of different voltages, see [link to relevant documentation]. Figure 2 The circuit breaker specifically includes: a control unit 10, a power transmission branch 20, and a bypass branch 30; wherein:

[0044] The two sides of the power transmission branch 20 serve as the input and output sides of the switch. The input and output sides of the switch have positive and negative terminals, respectively. That is, the positive and negative terminals on one side of the power transmission branch 20 serve as the input positive and negative terminals of the switch, connecting to the corresponding photovoltaic module. The positive and negative terminals on the other side of the power transmission branch 20 serve as the output positive and negative terminals of the switch, outputting the electrical energy of the corresponding photovoltaic module.

[0045] The bypass branch 30 is located between the two poles of the output side of the shut-off device; specifically, the bypass branch 30 may include a diode D, such as... Figure 3a As shown, the cathode of diode D is connected to the anode of the switch output, and the anode of diode D is connected to the cathode of the switch output; alternatively, the bypass branch 30 may also include a switching transistor, such as... Figure 3b The K12 shown here may vary depending on the specific application environment, and all are within the scope of protection of this application.

[0046] like Figure 3a or Figure 3b As shown, the power transmission branch 20 in the switch includes a positive transmission branch 201 and a negative transmission branch 202; wherein, the positive transmission branch 201 is connected between the positive input terminal and the positive output terminal of the switch; and the negative transmission branch 202 is connected between the negative input terminal and the negative output terminal of the switch.

[0047] In the power transmission branch 20, such as its positive transmission branch 201, at least one first switch and at least one second switch are connected in series. The number of both is not specifically limited. Each of the following figures is shown using one as an example.

[0048] The conduction reverse of the body diode or anti-parallel diode of the first switching transistor is the same as the reverse current flowing into the positive terminal of the input side of the switch, such as... Figures 3a to 3c K10 is shown in the figure.

[0049] The second switching transistor can be its body diode or an anti-parallel diode whose conduction direction is opposite to the reverse current (e.g., ...). Figure 3a or Figure 3b K11 as shown in the figure, or it may not have a body diode and an anti-parallel diode (such as K11). Figure 3c As shown in the figure, K11; as long as the output current of the shut-off device is the reverse current, the disconnection of the second switch K11 can cut off the reverse current, which is within the protection scope of this application.

[0050] Furthermore, the placement and series connection order of these two switching transistors K10 and K11 are not limited. Figures 3a to 3cThis is just one example where both switches K10 and K11 are located in the positive transmission branch 201. In practical applications, both switches K10 and K11 can also be located in the negative transmission branch 202 (e.g., Figure 3d As shown in the figure, they can also be set in different transmission branches (such as...). Figure 3e As shown in the figure, as long as the on / off control of the circuit breaker can be achieved, it is within the protection scope of this application; in addition, the series connection order of these two switching transistors K10 and K11 can also be interchanged. Figures 3a to 3e These are just some examples; combinations of the above features or variations such as switches of other numbers will not be illustrated one by one.

[0051] The control unit 10 is used to detect the output current of the switch, and when the output current is the aforementioned reverse current, it controls the second switch K11 to open. Alternatively, it can control both switches K10 and K11 to open, as long as the reverse current can be cut off and its reverse flow into the corresponding photovoltaic module can be blocked. All of these are within the protection scope of this application.

[0052] Specifically, when different voltage strings are connected in parallel, for example, if the voltage of the photovoltaic modules connected to the switch in different strings is different, or if the number of series-connected modules in different strings is different (e.g., ... Figure 4 As shown in the figure, a high-voltage string with a higher voltage and a low-voltage string with a lower voltage will appear. Due to the parallel connection, the high-voltage string will cause reverse current to flow into the low-voltage string, and the circuit breaker in the low-voltage string will detect the reverse current.

[0053] Figure 4 Two series-connected strings with different numbers of components are connected in parallel, and the switch adopts... Figure 3b The structure shown below will be used as an example for demonstration:

[0054] The first string consists of two circuit breakers connected in series, while the second string contains only one circuit breaker. In the first string, the power transmission branch 20 of the first circuit breaker contains a first switch K10 and a second switch K11; the power transmission branch 20 of the second circuit breaker contains a first switch K20 and a second switch K21; and the power transmission branch 20 of the circuit breakers in the second string contains a first switch K30 and a second switch K31. The bypass branches 30 of the three circuit breakers each contain a corresponding third switch K12, K22, and K32.

[0055] When the irradiation conditions of the three photovoltaic modules are similar, there is a difference in the output voltage of the modules between the two strings. The high-voltage string will backflow current into the low-voltage string through the parallel connection points (points P and N). At this time, even if the circuit breaker in the high-voltage string does not turn off, the circuit breaker in the low-voltage string will at least control the second switch K31 in the corresponding power transmission branch 20 to be in the open state because its control unit 10 detects that the output current of the circuit breaker is a reverse current. Then, the diode or body diode connected in parallel with the second switch K31 will block the backflow current due to reverse cutoff, and finally achieve reliable turn-off.

[0056] The series and parallel connection cases of different voltage groups with other numbers of series components are similar and will not be elaborated further. Additionally, for Figure 3c The switch structure shown in the diagram, when a reverse current occurs, the second switch K11 is turned off, directly cutting off the path between the input and output sides of the switch, and thus also cutting off the reverse current.

[0057] The shutdown device provided in this embodiment, through the above principle, enables the shutdown device in the low-voltage string to detect the reverse current through its control unit 10 when different voltage strings are connected in parallel, and actively shuts off the second switch in its power transmission branch 20, thereby cutting off the reverse current and ultimately achieving reliable shutdown under the communication-free control scheme.

[0058] In practical applications, regardless of whether the circuit breaker adopts any of the structures described in the previous embodiment, the control unit 10 of the circuit breaker can be specifically used for:

[0059] (1) When a start signal is detected from the input and output parameters of the shut-off device, all switching transistors are turned on.

[0060] The start signal can be either a power line carrier signal or an analog pulse signal, depending on the specific application environment, as long as it can achieve communication-free control.

[0061] (2) When the output current is the positive current flowing to the positive terminal of the output side of the shut-off device and is greater than or equal to the preset threshold, control all switching transistors to maintain the on state.

[0062] (3) When the output current is the positive current flowing to the positive terminal of the output side of the shut-off device and is less than the preset threshold, control the first switch to open, or control all switches to open.

[0063] (4) When the output current is reverse current, control the second switch to turn off, or control all switches to turn off.

[0064] Moreover, when the control unit 10 controls the corresponding switch to turn off, it can specifically control the corresponding switch to turn off with a delay. That is, the corresponding switch will only be controlled to turn off after the output current has been maintained in the corresponding state for a preset time.

[0065] Specifically, during normal grid connection, the control unit 10 of the circuit breaker first initiates a startup operation based on a power line carrier signal or analog pulse signal, controlling the two switches K10 and K11 in the power transmission branch 20 to be in a conducting state, thereby enabling the normal output of the corresponding photovoltaic modules. Then, by detecting the input and output parameters of the circuit breaker, such as the voltage and / or current on the input and / or output sides, it determines whether a fault has occurred. For example, when the circuit breaker detects a normal-sized forward current, it considers the system normal, i.e., without a fault, and controls switches K10 and K11 to be in a conducting state, thus maintaining the circuit breaker's conducting state. When the detected forward current is too small, it considers a fault to have occurred and controls the first switch K10 to be disconnected, or controls both switches K10 and K11 to be disconnected. When a reverse current is detected, it is also determined to be a fault, and controls the second switch K11 to be disconnected, or controls both switches K10 and K11 to be disconnected; thus achieving a communication-free shutdown.

[0066] It is worth noting that, in existing technologies, to meet the requirements of the photovoltaic power generation industry regarding single-point failures, some solutions connect two switching transistors in series on the power transmission branch of the shutdown device, such as... Figure 5 The K1 and K2 shown are used to control the switching on and off of the circuit breaker by controlling the switching on and off of these two switching transistors K1 and K2. However, when two photovoltaic strings with different voltages are connected in parallel, even if the downstream inverter fails, the high-voltage string will still send a reverse current into the low-voltage string. The high-voltage string detects the current and therefore will not turn off; while the low-voltage string detects the reverse current and can actively turn off, the presence of the reverse parallel diodes or body diodes of the switching transistors K1 and K2 cannot block the reverse current path, so it cannot reliably turn off.

[0067] The switch provided in this embodiment has the ability to block reverse current. In a system with long and short series connected in parallel, when the inverter is turned off and the long series flows back into the short series, the switch in the short series detects the reverse current and blocks the reverse current path. The switch in the long series will also automatically turn off after detecting that the current is zero, thus ensuring reliable shutdown.

[0068] In addition, the control unit 10 in the above embodiment may specifically include: a processor and a drive circuit; wherein, the processor is used to control the on / off state of the switching transistor through the drive circuit according to the input and output parameters of the acquired switch.

[0069] In practical applications, the circuit breaker may also include: an auxiliary power supply for the processor, a floating voltage elimination device located between the positive and negative terminals of the circuit breaker output side, and a voltage and current sampling module located on the input and output sides of the circuit breaker. These can all be found in existing technologies and will not be described in detail here.

[0070] Another embodiment of this application also provides a photovoltaic system, which includes: a photovoltaic array, at least one inverter, and N turn-off devices; N is greater than or equal to 2, such that each turn-off device is divided into at least two groups, which can form at least two strings.

[0071] The inverter has at least one string connected to its DC side.

[0072] Each string includes at least two turn-off switches connected in series through their respective output sides; and the input side of each turn-off switch is connected to the corresponding photovoltaic module in the photovoltaic array.

[0073] Each switch in at least one string is a switch as described in any of the above embodiments. The structure and principle of the switch are explained in the above embodiments and will not be repeated here.

[0074] When at least two strings are connected in parallel on the DC side of an inverter, the number of modules connected in series in each string connected to the DC side of the same inverter is preferably the same, and the irradiation conditions of the connected photovoltaic modules are also preferably the same. However, in practical applications, it is not impossible for different strings connected to the DC side of the same inverter to have different numbers of modules connected in series and / or different irradiation conditions; in this case, the following two settings are available:

[0075] (1) The switch in at least one of the lower voltage strings is a switch as described in any of the above embodiments; for example Figure 4 When the number of series components in different strings is different, the circuit breakers in the short strings all need to have reverse current interruption function.

[0076] (2) Alternatively, each switch in all strings may be a switch as described in any of the above embodiments. For example, if the number of switches in different strings is the same, but the voltage of the photovoltaic modules connected to each string is different, the voltage of each string may change depending on the irradiation conditions or time. In this case, it is preferable that all switches in all strings have reverse current interruption function.

[0077] Similar or identical parts between the various embodiments in this specification can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0078] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0079] The features described above regarding the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A switch, characterized in that, The applied string is connected in parallel with another string at a different voltage. The shutdown device includes: a control unit, a power transmission branch, and a bypass branch; wherein, The two sides of the power transmission branch serve as the input side and output side of the switch, respectively. The bypass branch is located between the two poles of the output side of the shut-off device; The power transmission branch is provided with at least one first switch and at least one second switch connected in series; the conduction direction of the body diode or anti-parallel diode of the first switch is the same as the direction of the reverse current flowing into the positive terminal of the input side of the switch. The control unit is used to detect the output current of the shutdown device, and when the output current is the reverse current, it controls the second switch to open to cut off the reverse current.

2. The switch according to claim 1, characterized in that, When the output current is a positive current flowing to the positive terminal of the output side of the switch and is greater than or equal to a preset threshold, all switches are controlled to remain in the on state.

3. The switch according to claim 1, characterized in that, The control unit is further configured to: control the first switch to disconnect when the output current is a positive current flowing to the positive terminal of the output side of the switch and is less than a preset threshold, or control all switches to disconnect.

4. The switch according to claim 1, characterized in that, The control unit is further configured to: control the first switch to disconnect when the output current is the reverse current.

5. The switch according to any one of claims 1 to 4, characterized in that, The control unit is used to control the corresponding switch to turn off, specifically for delaying the turn-off of the corresponding switch.

6. The switch according to any one of claims 1 to 4, characterized in that, The control unit is also used to: when a start signal is detected from the input and output parameters of the shutdown device, control all switching transistors to be turned on.

7. The switch according to any one of claims 1 to 4, characterized in that, The second switching transistor has no body diode and no anti-parallel diode, or the conduction direction of its body diode or anti-parallel diode is opposite to the direction of the reverse current.

8. The switch according to any one of claims 1 to 4, characterized in that, The power transmission branch includes: a positive transmission branch and a negative transmission branch; The positive transmission branch is connected between the positive input terminal and the positive output terminal of the switch; The negative transmission branch is connected between the input negative terminal and the output negative terminal of the switch; The first switch is disposed in the positive transmission branch or the negative transmission branch, and the second switch is disposed in the positive transmission branch or the negative transmission branch.

9. The switch according to any one of claims 1 to 4, characterized in that, The bypass branch includes a third switch controlled by the control unit.

10. The switch according to any one of claims 1 to 4, characterized in that, The bypass branch includes: a diode; The negative terminal of the diode is connected to the positive terminal of the output side of the switch; The positive terminal of the diode is connected to the negative terminal of the output side of the switch.

11. The switch according to any one of claims 1 to 4, characterized in that, The control unit includes: a processor and a drive circuit; The processor is used to control the on / off state of the corresponding switching transistor through the driving circuit based on the input / output parameters of the acquired switch.

12. A photovoltaic system, characterized in that, include: A photovoltaic array, at least one inverter, and N switch-off circuit breakers; N is greater than or equal to 2; where, The inverter has at least one string connected to its DC side; The string includes at least two shutdown devices connected in series via their respective output sides; and the input side of each shutdown device is connected to a corresponding photovoltaic module in the photovoltaic array. Each of the at least one of the shutdown devices in the said string is a shutdown device as described in any one of claims 1 to 11.

13. The photovoltaic system according to claim 12, characterized in that, The inverter has at least two strings connected in parallel on its DC side, wherein the shutdown device in at least one string with a lower voltage is a shutdown device as described in any one of claims 1 to 11.

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