A turn-off protection system

Abstract

The present invention discloses a turn-off protection system, which includes a phase current sensor group for respectively detecting the currents of each phase line on the grid side; a bus current sensor for detecting the current i of the negative bus on the photovoltaic side bus ; a protection control module adapted to respectively compare the currents of each phase line with a preset phase line threshold I x_ref , and compare the current i bus with a preset bus threshold I bus_ref . When there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side, and the current of the phase line is less than the preset phase line threshold I x_ref , the protection control module can switch the grid-connected switch corresponding to the phase line with a current less than the preset phase line threshold I x_ref to the open state, so as to more safely cut off the short-circuit loop when a photovoltaic side-to-ground short-circuit fault occurs in the photovoltaic system.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy power generation, and particularly relates to a shutdown protection system. Background Art

[0002] Due to reasons such as line aging, a photovoltaic side-to-ground short circuit fault may occur in a photovoltaic system. Even if the switching devices of the inverter circuit of the photovoltaic system are all switched to the open state, a short circuit loop may be formed by the anti-parallel diodes of the switching devices. Furthermore, a relatively large short circuit current may damage the switching devices, causing secondary damage to the photovoltaic system.

[0003] In some related technologies, the grid-connected switch is directly turned off to cut off the short circuit loop, but arcing may occur, even causing a safety accident; in other related technologies, a shunt circuit is set up to improve the current-carrying capacity of the photovoltaic system, thereby reducing the risk of damage to the switching devices of the inverter circuit caused by the short circuit current. However, the short circuit loop is not cut off, so there may still be a relatively large short circuit current, which may damage the switching devices. Summary of the Invention

[0004] An object of the present invention is to provide a shutdown protection system that can more safely cut off the short circuit loop when a photovoltaic side-to-ground short circuit fault occurs in a photovoltaic system.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a shutdown protection system, including: a phase current sensor group for respectively detecting the currents of each phase line on the grid side; a bus current sensor for detecting the current i of the negative bus on the photovoltaic side bus ; a protection control module adapted to respectively compare the current of each phase line with a preset phase line threshold I x_ref , and compare the current i bus with a preset bus threshold I bus_ref . When there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side, and the current of the phase line is less than the preset phase line threshold I x_ref , the protection control module can switch the grid-connected switch corresponding to the phase line with a current less than the preset phase line threshold I x_ref to the open state.

[0006] As a preference, the protection control module includes a number of shutdown devices, and each shutdown device is provided with a phase current comparator, a bus current comparator and an AND gate unit; the phase current comparator is used to judge whether the current of the phase line flows from the photovoltaic side to the grid side, and judge whether the current of the phase line is less than the preset phase line threshold I x_ref ; the bus current comparator is used to judge the current i busWhether it flows from the photovoltaic side to the grid side, and determines the current i bus is greater than a preset bus threshold I bus_ref ; One input terminal of the AND gate unit is used to receive the output signal of the phase current comparator, and the other input terminal of the AND gate unit is used to receive the output signal of the bus current comparator. The AND gate unit is adapted to output an intermediate signal D x_ctl , the intermediate signal D x_ctl acts on the grid-connected switch, so that when there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side and the current of the phase line is less than the preset phase line threshold I x_ref , the grid-connected switch is switched to the open state.

[0007] As a preference, the negative input terminal of the phase current comparator is used to receive the detected value I of the phase line current output by the phase current sensor group x , the positive input terminal of the phase current comparator is used to receive the preset phase line threshold I x_ref , when the current of the phase line is greater than the preset phase line threshold I x_ref , the output signal of the phase current comparator is set to high level; when the current of the phase line is less than the preset phase line threshold I x_ref , the output signal of the phase current comparator is set to low level.

[0008] As a preference, the negative input terminal of the bus current comparator is used to receive the detected value I of the bus current output by the bus current sensor bus , the positive input terminal of the bus current comparator is used to receive the preset bus threshold I bus_ref , when the current i bus is greater than the preset bus threshold I bus_ref , the output signal of the phase current comparator is set to high level; when the current i bus is less than the preset bus threshold I bus_ref , the output signal of the phase current comparator is set to low level.

[0009] As a preference, the turn-off device further includes an OR gate unit. One input terminal of the OR gate unit is used to receive the intermediate signal D output by the AND gate unit x_ctl , the other input terminal of the OR gate unit is used to receive the switch signal S output by the controller of the photovoltaic system x_ctl , the OR gate unit is adapted to output a control signal K x_ctl , the control signal K x_ctl acts on the grid-connected switch, so that under the condition that the photovoltaic side of the photovoltaic system does not have a ground short-circuit fault, the switch signal S x_ctlThe grid-connected switch can be controlled to remain in the closed state; when there is a current flowing from the PV side to the grid side on the negative bus of the PV side and the current of the phase line is less than the preset phase line threshold I x_ref under the condition that, the intermediate signal D x_ctl can cause the grid-connected switch to switch to the open state.

[0010] As a preference, the phase current sensor group includes a first phase current sensor, a second phase current sensor and a third phase current sensor. The first phase current sensor is used to detect the current i a of phase A on the grid side, the second phase current sensor is used to detect the current i b of phase B on the grid side, and the third phase current sensor is used to detect the current i c of phase C on the grid side.

[0011] As a preference, the several turn-off devices include a first turn-off device, a second turn-off device and a third turn-off device. When there is a current flowing from the PV side to the grid side on the negative bus of the PV side and the current i a of phase A is less than the preset phase line threshold I x_ref under the condition that, the first turn-off device can cause the grid-connected switch S a of phase A to switch to the open state; when there is a current flowing from the PV side to the grid side on the negative bus of the PV side and the current i b of phase B is less than the preset phase line threshold I x_ref under the condition that, the second turn-off device can cause the grid-connected switch S b of phase B to switch to the open state; when there is a current flowing from the PV side to the grid side on the negative bus of the PV side and the current i c of phase C is less than the preset phase line threshold I x_ref under the condition that, the third turn-off device can cause the grid-connected switch S c of phase C to switch to the open state.

[0012] As a preference, the turn-off protection system further includes a DC switch group and a current sensor CT. The DC switch group is connected between the positive terminal of the PV module PV and the MPPT circuit, and between the negative terminal of the PV module PV and the MPPT circuit. The current sensor CT is connected between the negative terminal of the PV module PV and the MPPT circuit and is used to detect the current of the MPPT circuit. When there is a current flowing from the negative terminal of the PV module PV to the grid side in the MPPT circuit, the DC switch group switches to the open state to disconnect the PV module PV from the MPPT circuit.

[0013] As a preference, when a ground short-circuit fault occurs in the PV system and the switching devices of the inverter circuit of the PV system are in the open state, the protection control module can make the current less than the preset phase line threshold Ix_ref The grid - connected switches corresponding to the phase lines are switched to the open state one by one.

[0014] As an optimization, under the condition that all the grid - connected switches corresponding to the phase lines are in the open state, the controller of the photovoltaic system disconnects the photovoltaic modules PV with current flowing from the negative terminal of the photovoltaic module PV to the grid side from the MPPT circuit, and restarts the photovoltaic system.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] When a photovoltaic - side ground - short - circuit fault occurs in the photovoltaic system, through the protection control module, the grid - connected switches corresponding to the phase lines are closed under the condition that the phase - line current is less than the preset phase - line threshold value I x_ref On this basis, while cutting off the short - circuit loop, the risk of arcing is reduced, and the safety is improved. Description of the Drawings

[0017] Figure 1 It is the architecture diagram of the photovoltaic system in the related art.

[0018] Figure 2 It is the schematic diagram of the ground - short - circuit fault occurring at the positive terminal of the photovoltaic module PV1 in the photovoltaic system of the related art.

[0019] Figure 3 It is for the photovoltaic module PV in the photovoltaic system of the related art n The schematic diagram of the ground - short - circuit fault occurring at the negative terminal.

[0020] Figure 4 It is the architecture diagram of the photovoltaic system and the shutdown protection system in some embodiments of the present application.

[0021] Figure 5 It is the architecture diagram of the protection control module of the present application.

[0022] Figure 6 It is the architecture diagram of the shutdown device of the present application.

[0023] Figure 7 It is the architecture diagram of the photovoltaic system and the shutdown protection system in other embodiments of the present application.

[0024] Figure 8 It is the voltage and current waveforms on the grid side when a ground - short - circuit fault occurs at the negative terminal of the photovoltaic module PV of the present application.

[0025] Figure 9 It is the turn - off control timing diagram of the grid - connected switch when a ground - short - circuit fault occurs at the negative terminal of the photovoltaic module PV of the present application.

[0026] Figure 10This is the restart control timing diagram when a ground short - circuit fault occurs at the PV negative terminal of the present application.

[0027] In the figure: 101, DC / DC unit; 1011, MPPT circuit; 102, DC / AC unit; 103, grid - connection switch group; 104, protection control module; 1041, cut - off device; 1042, phase - current comparator; 1043, bus - current comparator; 1044, AND - gate unit; 1045, OR - gate unit; 105, phase - current sensor group; 106, bus - current sensor; 107, DC switch group; 108, controller. Specific embodiments

[0028] Next, in combination with specific embodiments, the present invention will be further described. It should be noted that, on the premise of no conflict, the following described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0029] 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 need to describe a specific order or sequence.

[0030] 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 includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0031] In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "installed", "connected", "linked" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or connected by contact or indirectly through an intermediate medium, and can be the internal communication of two components. 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] For the convenience of understanding the following method, the present application will be described through a photovoltaic system. As Figure 1As shown, it is a three-phase grid-connected photovoltaic system with n-channel MPPT in the related art, mainly including n photovoltaic modules PV, a DC / DC unit 101, a DC / AC unit 102, and a grid-connected switch group 103. Among them, the photovoltaic module PV is connected to the DC bus through the DC / DC unit 101, and the DC bus is connected to the grid through a bus capacitor, the DC / AC unit 102, a filter inductor, and the grid-connected switch group 103. Specifically, the DC / DC unit 101 is composed of n parallel MPPT circuits 1011, and each MPPT circuit 1011 is respectively connected to a photovoltaic module PV. For example, the first MPPT circuit 1011 is connected to the photovoltaic module PV1, and the nth MPPT circuit 1011 is connected to the photovoltaic module PV n . Further, the DC / AC unit 102 is composed of switching devices S1 to S6, and the switching devices S1 to S6 are controlled by the controller 108 of the photovoltaic system to switch between the open state and the closed state respectively, so as to convert the direct current on the photovoltaic side into alternating current on the grid side. It should be understood that, as Figure 1 shown, the circuit structure of the photovoltaic system is only for the convenience of explaining the subsequent scheme. The DC / AC unit 102 can also be a single-phase inverter circuit or a three-level three-phase inverter circuit, etc. The present application does not make specific restrictions on this.

[0033] Taking the photovoltaic module PV1 as an example, it should be understood that the same applies to other photovoltaic modules PV. As Figure 2 shown, under the condition that a ground short-circuit fault occurs at the positive terminal of the photovoltaic module PV1, due to the function of the diode D1 in the first MPPT circuit 1011, the loop flowing from the grid side to the photovoltaic side is blocked, that is, it is beneficial to avoid the generation of short-circuit current.

[0034] Further, taking the photovoltaic module PV n as an example, it should be understood that the same applies to other photovoltaic modules PV. As Figure 3 shown, under the condition that a ground short-circuit fault occurs at the negative terminal of the photovoltaic module PV n , taking phase A as an example, even if the switching devices S1 to S6 are in the open state, a short-circuit loop may be formed from the negative terminal of the photovoltaic module PV n through the switching device S4, the filter inductor L a , the grid-connected switch S a , the grid, and the ground in sequence. It is worth mentioning that the current I in the short-circuit loop = V ga / Z eq , where V ga is the grid voltage of phase A, and Z eqis the equivalent impedance of the short - circuit loop. That is to say, there is a large current in the short - circuit loop, which may damage the switching device S4 and then cause secondary damage to the photovoltaic system. It should be understood that the above - mentioned short - circuit loop is also applicable to phases B and C, and will not be elaborated in detail here.

[0035] It should be understood that if the grid - connected switch group 103 is directly turned off to cut off the short - circuit loop, arcing may occur, and even safety accidents may be caused. If a shunt circuit is set to improve the current - passing capacity of the photovoltaic system, since the short - circuit loop is not cut off, there may still be a large short - circuit current, which may damage the switching devices S1 to S6.

[0036] Based on the above, in order to more safely cut off the short - circuit loop when a photovoltaic - side ground - short - circuit fault occurs in the photovoltaic system, one aspect of the present application provides a turn - off protection system, as Figure 4 shown, including: a phase - current sensor group 105, a bus - current sensor 106, and a protection control module 104. The phase - current sensor group 105 is used to detect the currents of each phase line on the grid side respectively; the bus - current sensor 106 is used to detect the current i bus of the negative bus on the photovoltaic side; the protection control module 104 is adapted to compare the current of each phase line with a preset phase - line threshold I x_ref , and compare the current i bus with a preset bus threshold I bus_ref . When there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side, and the current of the phase line is less than the preset phase - line threshold I x_ref , the protection control module 104 can switch the grid - connected switch corresponding to the phase line with a current less than the preset phase - line threshold I x_ref to the open state. It should be understood that through the protection control module 104, the grid - connected switch corresponding to the phase line can be turned off under the condition that the phase - line current is less than the preset phase - line threshold I x_ref , so as to reduce the risk of arcing and improve safety on the basis of cutting off the short - circuit loop.

[0037] Specifically, the current i bus of the negative bus on the photovoltaic side can be detected through the bus - current sensor 106, and it can be judged through the protection control module 104 whether there is a current i bus flowing from the photovoltaic side to the grid side, that is, it can detect whether a ground - short - circuit fault occurs at the negative end of the photovoltaic module PV. It should be understood that under the condition that a ground - short - circuit fault occurs at the negative end of the photovoltaic module PV, when the voltage of one of the phases on the grid side is in the negative half - cycle, the bus - current sensor 106 can detect the current i bus。Further, the current of each phase wire on the grid side is detected by the phase current sensor group 105, and the protection control module 104 determines whether the current of the phase wire is less than the preset phase wire threshold I x_ref , and then, under the condition that the current of one of the phase wires on the grid side is less than the preset phase wire threshold I x_ref , the protection control module 104 switches the grid-connected switch corresponding to the phase wire to the open state.

[0038] For example, under the condition that the current of the A-phase wire is less than the preset phase wire threshold I x_ref , the protection control module 104 switches the grid-connected switch SA a of the A phase to the open state, while the grid-connected switches SB b and SC c of the B and C phases remain in the closed state; further, under the condition that the current of the B-phase wire is also less than the preset phase wire threshold I x_ref , the protection control module 104 switches the grid-connected switch SB b of the B phase to the open state as well, while the grid-connected switch SC c of the C phase remains in the closed state; furthermore, under the condition that the current of the C-phase wire is also less than the preset phase wire threshold I x_ref , the protection control module 104 switches the grid-connected switch SC c of the C phase to the open state as well to cut off the short-circuit loop. That is to say, the protection control module 104 switches the grid-connected switches corresponding to the phase wires with currents less than the preset phase wire threshold I x_ref to the open state one by one. It should be understood that the order in which the grid-connected switches in the grid-connected switch group 103 are switched to the open state is only an example, and the present application does not specifically limit this.

[0039] In some embodiments, as shown in Figure 5 and Figure 6 , the protection control module 104 includes a number of turn-off devices 1041, and each turn-off device 1041 is provided with a phase current comparator 1042, a bus current comparator 1043, and an AND gate unit 1044; the phase current comparator 1042 is used to determine whether the current of the phase wire flows from the photovoltaic side to the grid side, and to determine whether the current of the phase wire is less than the preset phase wire threshold I x_ref ; the bus current comparator 1043 is used to determine whether the current i bus flows from the photovoltaic side to the grid side, and to determine whether the current i bus is greater than the preset bus threshold I bus_ref ; one input terminal of the AND gate unit 1044 is used to receive the output signal of the phase current comparator 1042, the other input terminal of the AND gate unit 1044 is used to receive the output signal of the bus current comparator 1043, and the AND gate unit 1044 is adapted to output an intermediate signal Dx_ctl and the intermediate signal D x_ctl acts on the grid-connection switch so that when there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side and the current of the phase line is less than the preset phase-line threshold I x_re f, the grid-connection switch switches to the open state.

[0040] It should be understood that the phase-current comparator 1042 can compare the current of the phase line measured by the phase-current sensor group 105 with the preset phase-line threshold I x_ref , and the bus-current comparator 1043 can compare the current i of the negative bus of the photovoltaic side bus with the preset bus threshold I bus_ref . Further, the output signal of the phase-current comparator 1042 and the output signal of the bus-current comparator 1043 jointly act on the AND gate unit 1044, and then when there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side and the current of the phase line is less than the preset phase-line threshold I x_ref , the intermediate signal D output by the AND gate unit 1044 x_ctl can make the grid-connection switch switch to the open state to cut off the short-circuit loop.

[0041] It should be known that the specific structure and working principle of the AND gate unit 1044 are well-known technologies to those skilled in the art, so they will not be elaborated in detail here; the working logic of the AND gate unit 1044 is to output a high level only when both input terminals are at a high level.

[0042] In some embodiments, as Figure 5 and Figure 6 shown, the turn-off device 1041 further includes an OR gate unit 1045. One input terminal of the OR gate unit 1045 is used to receive the intermediate signal D output by the AND gate unit 1044 x_ctl , and the other input terminal of the OR gate unit 1045 is used to receive the switch signal S output by the controller 108 of the photovoltaic system x_ctl , and the OR gate unit 1045 is adapted to output a control signal K x_ctl , and the control signal K x_ctl acts on the grid-connection switch so that when the photovoltaic side of the photovoltaic system does not have a ground short-circuit fault, the switch signal S x_ctl can control the grid-connection switch to remain in the closed state; when there is a current flowing from the photovoltaic side to the grid side on the negative bus of the photovoltaic side and the current of the phase line is less than the preset phase-line threshold I x_ref , the intermediate signal D x_ctl can make the grid-connection switch switch to the open state.

[0043] It should be understood that when the photovoltaic side of the photovoltaic system does not have a ground short-circuit fault, the grid-connection switch is controlled by the switch signal S output by the controller 108 x_ctlfunctions to remain in a closed state; and the switching devices S1 to S6 are respectively controlled by the controller 108 to switch between an open state and a closed state, so that the direct current on the photovoltaic side is converted into alternating current on the grid side. Further, under the condition that a ground short - circuit fault occurs at the negative terminal of the photovoltaic module PV of the photovoltaic system, the switching devices S1 to S6 are controlled by the controller 108 to remain in an open state, and the grid - connection switch is controlled by the intermediate signal D of the protection control module 104 x_ctl functions to achieve a current less than the preset phase - line threshold I x_ref The grid - connection switches corresponding to the phase lines with the above - mentioned conditions are switched to the open state one by one to cut off the short - circuit loop.

[0044] In at least one embodiment, under the condition that no ground short - circuit fault occurs on the photovoltaic side of the photovoltaic system, the intermediate signal D output by the AND gate unit 1044 x_ctl remains at a low level, so that the control signal K output by the OR gate unit 1045 x_ctl and the switch signal S output by the controller 108 x_ctl remain consistent. Furthermore, the grid - connection switch is affected by the switch signal S output by the controller 108 x_ctl functions to switch between an open state and a closed state to achieve the normal grid - connection operation of the photovoltaic system. Further, under the condition that a ground short - circuit fault occurs at the negative terminal of the photovoltaic module PV of the photovoltaic system, the switch signal S output by the controller 108 x_ctl remains at a low level, so that the control signal K output by the OR gate unit 1045 x_ctl and the intermediate signal D output by the AND gate unit 1044 x_ctl remain consistent. Furthermore, the grid - connection switch is controlled by the protection control module 104 to achieve that the grid - connection switches corresponding to the phase lines with a current less than the preset phase - line threshold I x_ref are switched to the open state one by one.

[0045] It should be known that the specific structure and working principle of the OR gate unit 1045 are well - known technologies to those skilled in the art, so they will not be elaborated in detail here; the working logic of the OR gate unit 1045 is to output a high level when at least one input terminal is at a high level and output a low level when all input terminals are at a low level.

[0046] In some embodiments, as shown in Figure 5 and Figure 6 the negative input terminal of the phase - current comparator 1042 is used to receive the phase - line current detection value I output by the phase - current sensor group 105 x , and the positive input terminal of the phase - current comparator 1042 is used to receive the preset phase - line threshold I x_ref , when the current of the phase line is greater than the preset phase - line threshold I x_refUnder the condition that, the output signal of the phase current comparator 1042 is set to a high level so as to be suitable for making the grid connection switch in a closed state; when the current in the phase line is less than the preset phase line threshold I x_ref Under the condition that, the output signal of the phase current comparator 1042 is set to a low level so as to be suitable for making the grid connection switch in an open state.

[0047] In at least one embodiment, the phase current sensor group 105 takes the current flowing from the grid side to the photovoltaic side as the forward current, and takes the current flowing from the photovoltaic side to the grid side as the reverse current, and the detected value I of the phase line current x Decreases as the reverse current increases. That is to say, under the condition that the current in the phase line flows from the grid side to the photovoltaic side, the detected value I of the phase line current output by the phase current sensor group 105 x Is a positive number, and under the condition that the current in the phase line flows from the photovoltaic side to the grid side, the detected value I of the phase line current output by the phase current sensor group 105 x Is a negative number. It should be understood that the greater the reverse current, the greater the absolute value of the detected value I of the phase line current x The detected value I of the phase line current x And the detected value I of the phase line current x The absolute values are opposite numbers, and further the detected value I of the phase line current x Is smaller.

[0048] In at least one embodiment, in order to realize switching the grid connection switch to the open state when the reverse current is small, the preset phase line threshold I x_ref Is set to 0 or a negative number. It is worth mentioning that when the preset phase line threshold I x_ref Is set to a negative number, the "under the condition that the current in the phase line is greater than the preset phase line threshold I x_ref " mentioned above means that the current in the phase line is greater than the absolute value of the preset phase line threshold I x_ref The preset phase line threshold I x_ref Can be adjusted according to the actual working conditions, and the present application does not make specific limitations on this.

[0049] Furthermore, under the condition that the input value at the negative input terminal of the phase current comparator 1042 is less than the input value at the positive input terminal, the output signal of the phase current comparator 1042 is set to a high level; under the condition that the input value at the negative input terminal of the phase current comparator 1042 is greater than the input value at the positive input terminal, the output signal of the phase current comparator 1042 is set to a low level. Specifically, when there is a reverse current in the phase line and the reverse current is large, that is, when the reverse current is greater than the absolute value of the preset phase line threshold I x_ref The smaller the detected value I of the phase line current output by the phase current sensor, that is, the detected value I of the phase line current x Is smaller, that is, the detected value I of the phase line current x Is less than the preset phase line threshold I x_ref, and then the output signal of the phase current comparator 1042 is set to a high level, so as to make the grid-connected switch in a closed state; when there is a reverse current in the phase line and the reverse current is small, that is, the reverse current is less than the absolute value of the preset phase line threshold I x_ref , the phase line current detection value I x output by the phase current sensor is larger, that is, the phase line current detection value I x is greater than the preset phase line threshold I x_ref , and then the output signal of the phase current comparator 1042 is set to a low level, so as to make the grid-connected switch in a closed state.

[0050] In some embodiments, as Figure 5 and Figure 6 shown, the negative input terminal of the bus current comparator 1043 is used to receive the bus current detection value I bus output by the bus current sensor 106, and the positive input terminal of the bus current comparator 1043 is used to receive the preset bus threshold I bus_ref . When the current i bus is greater than the preset bus threshold I bus_ref , the output signal of the phase current comparator 1042 is set to a high level, so as to make the grid-connected switch in a closed state; when the current i bus is less than the preset bus threshold I bus_ref , the output signal of the phase current comparator 1042 is set to a low level, so as to make the grid-connected switch in a closed state.

[0051] In at least one embodiment, the bus current sensor 106 group takes the current flowing from the grid side to the photovoltaic side as the positive current, and takes the current flowing from the photovoltaic side to the grid side as the reverse current, and the bus current detection value I bus decreases as the reverse current increases. That is to say, when the current i bus in the negative bus flows from the grid side to the photovoltaic side, the bus current detection value I bus output by the bus current sensor 106 group is a positive number, and when the current i bus in the negative bus flows from the photovoltaic side to the grid side, the bus current detection value I bus output by the bus current sensor 106 group is a negative number.

[0052] In at least one embodiment, in order to realize switching the grid-connected switch to an open state when a ground short-circuit fault occurs at the negative end of the photovoltaic module PV, that is, switching the grid-connected switch to an open state when the current i bus in the negative bus flows from the photovoltaic side to the grid side, the preset bus threshold I bus_ref is set to 0. It should be noted that the preset bus threshold I bus_ref can be adjusted according to the actual working conditions, and the present application does not make specific limitations on this.

[0053] Further, under the condition that the input value at the negative input terminal of the bus current comparator 1043 is less than the input value at the positive input terminal, the output signal of the bus current comparator 1043 is set to a high level; under the condition that the input value at the negative input terminal of the bus current comparator 1043 is greater than the input value at the positive input terminal, the output signal of the bus current comparator 1043 is set to a low level. Specifically, when there is a reverse current in the negative bus, that is, the detected bus current value I bus is less than the preset bus threshold I bus_ref , and then the output signal of the bus current comparator 1043 is set to a high level, so as to be suitable for enabling the intermediate signal D x_ctl output by the AND gate unit 1044 to be affected by the output signal of the phase current comparator 1042, and then it is possible to achieve that the grid connection switches corresponding to the phases where the current is less than the preset phase line threshold I x_ref are switched to the open state one by one; when there is a forward current in the negative bus, that is, the detected bus current value I bus is greater than the preset bus threshold I bus_ref , and then the output signal of the bus current comparator 1043 is set to a low level, so as to be suitable for enabling the intermediate signal D x_ctl output by the AND gate unit 1044 to remain at a low level, and then the control signal K x_ctl output by the OR gate unit 1045 and the switch signal S x_ctl output by the controller 108 are kept consistent, and the grid connection switch is affected by the switch signal S x_ctl output by the controller 108 and is switched between the open state and the closed state to achieve the normal grid connection operation of the photovoltaic system.

[0054] In some embodiments, the phase current sensor group 105 includes a first phase current sensor, a second phase current sensor, and a third phase current sensor. The first phase current sensor is used to detect the current i a of phase A on the grid side, the second phase current sensor is used to detect the current i b of phase B on the grid side, and the third phase current sensor is used to detect the current i c of phase C on the grid side. It should be understood that setting current sensors on each phase line on the grid side is beneficial to provide electrical isolation to improve the safety and reliability of the photovoltaic system.

[0055] In some embodiments, the plurality of turn-off devices 1041 include a first turn-off device, a second turn-off device, and a third turn-off device. When there is a current flowing from the photovoltaic side to the grid side in the negative bus of the photovoltaic side, and the current i a of phase A is less than the preset phase line threshold I a_ref , the first turn-off device enables the grid connection switch S aSwitch to the open state; when there is a current flowing from the PV side to the grid side on the negative bus of the PV side, and the current i of phase B b is less than the preset phase line threshold I b_ref , the second shutdown device enables the grid-connected switch S of phase B b to switch to the open state; when there is a current flowing from the PV side to the grid side on the negative bus of the PV side, and the current i of phase C c is less than the preset phase line threshold I c_ref , the third shutdown device enables the grid-connected switch S of phase C c to switch to the open state.

[0056] It should be understood that by controlling the grid-connected switches S a , S b and S c respectively through the first shutdown device, the second shutdown device and the third shutdown device, it is beneficial to improve the reliability of the shutdown protection system. It is worth mentioning that the preset phase line threshold I x_ref includes the preset phase line threshold I of phase A a_ref , the preset phase line threshold I of phase B b_ref and the preset phase line threshold I of phase C c_ref , where the preset phase line thresholds I a_ref , I b_ref and I c_ref can be the same or different, and the present application does not make specific restrictions on this.

[0057] Taking the first shutdown device as an example, and assuming that the preset bus threshold I bus_ref is 0 and the preset phase line threshold I of phase A a_ref is negative. Under the condition that the PV system does not have a ground short circuit fault and the PV system is shut down, both the bus current comparator 1043 and the phase current comparator 1042 output low levels, and then the intermediate signal D x_ctl output by the AND gate unit 1044 remains low, and the control signal K x_ctl output by the OR gate unit 1045 and the switch signal S a_ctl output by the controller 108 are consistent, and the grid-connected switch Sa is affected by the switch signal S a_ctl output by the controller 108.

[0058] Under the condition that the PV system does not have a ground short circuit fault and the PV system is operating normally, there is a positive current in the negative bus, that is, the current flows from the grid side to the PV side, and the detected value I of the bus current busis positive and greater than 0. Consequently, the output signal of the bus current comparator 1043 is set to low level. Further, the magnitude and direction of the current in the phase line of phase A change continuously, and the output signal of the phase current comparator 1042 alternates between low level and high level. It should be understood that since the output signal of the bus current comparator 1043 is set to low, the intermediate signal D output by the AND gate unit 1044 x_ctl remains at low level, and the control signal K output by the OR gate unit 1045 x_ctl is consistent with the switch signal S output by the controller 108 a_ctl so that the grid-connected switch S a is affected by the switch signal S output by the controller 108 a_ctl .

[0059] Under the condition that a ground short-circuit fault occurs at the negative terminal of the photovoltaic module PV in the photovoltaic system, the switch signal S output by the controller 108 a_ctl remains at low level so that the control signal K output by the OR gate unit 1045 x_ctl is consistent with the intermediate signal D output by the AND gate unit 1044 x_ctl . Further, there is a reverse current in the negative bus, that is, the current flows from the grid side to the photovoltaic side, and the detected value I of the bus current bus is negative and less than 0. Consequently, the output signal of the bus current comparator 1043 is set to high level. Furthermore, the current in the phase line of phase A is a reverse current and its magnitude changes continuously. When the reverse current is greater than the absolute value of the preset phase line threshold I a_ref , the detected value I of the phase line current a is less than the preset phase line threshold I a_ref . Consequently, the output signal of the phase current comparator 1042 is set to high level. At this time, the intermediate signal D output by the AND gate unit 1044 x_ctl is at high level, and the control signal K output by the OR gate unit 1045 x_ctl is also at high level, and the grid-connected switch S a is in the closed state. When the reverse current is less than the absolute value of the preset phase line threshold I a_ref , the detected value I of the phase line current a is greater than the preset phase line threshold I a_ref . Consequently, the output signal of the phase current comparator 1042 is set to low level. At this time, the intermediate signal D output by the AND gate unit 1044 x_ctl is at low level, and the control signal K output by the OR gate unit 1045 x_ctl is also at low level, and the grid-connected switch S a switches to the open state to reduce the risk of arcing and improve safety on the basis of cutting off the short-circuit loop.

[0060] It should be understood that the above content applies to the second turn-off device of phase B and the third turn-off device of phase C, and will not be elaborated in detail here.

[0061] It is worth mentioning that in the above embodiment, the protection control module 104 is composed of hardware, which is beneficial to improving the response speed and reducing the occupation of resources of the controller 108 of the photovoltaic system.

[0062] It should be understood that the above logic can also be implemented through the algorithm of the controller 108 of the photovoltaic system, so as to switch the grid-connected switches corresponding to the phases with current less than the preset phase line threshold I x_ref to the open state one by one under the condition that a ground short-circuit fault occurs at the negative terminal of the photovoltaic module PV of the photovoltaic system.

[0063] In some embodiments, as Figure 7 shown, the turn-off protection system further includes a DC switch group 107 and a current sensor CT. The DC switch group 107 is connected between the positive terminal of the photovoltaic module PV and the MPPT circuit 1011, and between the negative terminal of the photovoltaic module PV and the MPPT circuit 1011. The current sensor CT is connected between the negative terminal of the photovoltaic module PV and the MPPT circuit 1011 for detecting the current of the MPPT circuit 1011. Under the condition that there is a current flowing from the negative terminal of the photovoltaic module PV to the grid side in the MPPT circuit 1011, the DC switch group 107 switches to the open state to disconnect the photovoltaic module PV from the MPPT circuit 1011.

[0064] In at least one embodiment, as Figure 7 shown, the DC switch group 107 includes DC switches S pv+ and S pv- . The DC switch S pv+ is connected between the positive terminal of the photovoltaic module PV and the MPPT circuit 1011, and the DC switch S pv- is connected between the negative terminal of the photovoltaic module PV and the MPPT circuit 1011.

[0065] It should be understood that assuming that a ground short-circuit fault occurs at the negative terminal of the photovoltaic module PV n connected to the nth MPPT circuit 1011, the current sensor CT n will detect a current flowing from the negative terminal of the photovoltaic module PV n to the grid side. Then, the controller 108 can make the DC switches S pvn_ctl and S pvn- and S pvn+ switch to the open state to disconnect the photovoltaic module PV n from the nth MPPT circuit 1011.

[0066] It is worth mentioning that after the photovoltaic module PV with a ground short - circuit fault and the corresponding MPPT circuit 1011 are disconnected, the controller 108 of the photovoltaic system can restart the photovoltaic system, enabling the normal photovoltaic modules PV to continue to work properly. That is to say, the photovoltaic module PV with a ground short - circuit fault can be isolated from the photovoltaic system. Furthermore, before the photovoltaic module PV with a ground short - circuit fault is repaired, the photovoltaic system can still work properly, which helps to avoid the photovoltaic system being unable to resume normal operation before manual inspection and fault elimination, thereby improving the reliability and working efficiency of the photovoltaic system.

[0067] In some embodiments, under the condition that a ground short - circuit fault occurs in the photovoltaic system and the switching device of the inverter circuit of the photovoltaic system is in an open - circuit state, the protection control module 104 can make the current of the phase line less than the preset phase - line threshold I x_ref The grid - connected switches corresponding to the phase lines are switched to the open - circuit state one by one.

[0068] Specifically, as Figure 8 shown are the voltage and current waveforms on the grid side when a ground short - circuit fault occurs at the negative terminal of the photovoltaic module PV. Taking phase A as an example, at time a, the grid voltage U a is at zero and about to enter the negative half - cycle. At this time, the body diode of the switching device S4 in the DC / AC unit 102 is reversely cut off, and the current i a of phase A is 0.

[0069] In the time period from a to d, the grid - side voltage is in the negative half - cycle. Under the condition that the voltage difference between the ground and the grid - side voltage is greater than the conduction voltage of the body diode of the switching device S4, a short - circuit loop is formed, and the current i a of phase A gradually increases. At time d, the grid voltage U a is at zero and about to enter the positive half - cycle.

[0070] Among them, at time b, the grid - side voltage U a reaches the maximum value of the negative half - cycle. Due to the ground short - circuit fault at the negative terminal of the photovoltaic module PV, there is an inductive impedance in the short - circuit loop, causing the current to lag behind the voltage. Therefore, the current i a has not yet reached the maximum value. At time c, the current i a reaches the maximum value. In the time period from c to d, the current i a gradually decreases. At time d, the current i a is still negative.

[0071] In the time period from d to f: the grid voltage Ua is in the positive half - cycle.

[0072] Among them, in the time period from d to e, the current i a in the filter inductor L aUnder the action of [something], it maintains its original direction and gradually decreases. At time e, the current i a decreases to 0. In the time period from e to f, the current i a remains 0.

[0073] It should be understood that the factors affecting the lag degree of the current lagging behind the voltage include, but are not limited to, the degree of short - circuit to the ground, the equivalent resistance of the short - circuit loop, and the size of the filtering inductor. The above - mentioned various moments are only examples, and this application does not make specific restrictions on this.

[0074] Such as Figure 9 shown is the turn - off control timing diagram of the grid - connected switches S a , S b and S c when a ground - short - circuit fault occurs at the negative terminal of the photovoltaic module PV. As described above, the control signal K a_ctl is used to control the grid - connected switch S a ; the control signal K b_ctl is used to control the grid - connected switch S b ; the control signal K c_ctl is used to control the grid - connected switch S c .

[0075] At time t0, the switching devices S1 to S6 of the DC / AC unit 102 of the photovoltaic system are switched to the open state.

[0076] At time t1, the current i a of phase A drops to the preset phase - line threshold I a_ref , the control signal K a_ctl is set to a low level, the grid - connected switch S a is switched to the open state, and the grid - connected switches S b and S c remain in the closed state.

[0077] At time t2, the current i b of phase B drops to the preset phase - line threshold I b_ref , the control signal K b_ctl is set to a low level, the grid - connected switch S b is switched to the open state, and the grid - connected switch S c remains in the closed state.

[0078] At time t3, the current i c of phase B drops to the preset phase - line threshold I c_ref , the control signal K c_ctl is set to a low level, the grid - connected switch S c is switched to the open state to cut off the short - circuit loop.

[0079] Regarding the application understanding, the sequence in which each grid-connected switch in the above grid-connected switch group 103 switches to the open state is only an example, and this application does not make specific restrictions on this.

[0080] In some embodiments, under the condition that all grid-connected switches corresponding to the phase lines are in the open state, the controller 108 of the photovoltaic system can disconnect the photovoltaic module PV with a current flowing from the negative terminal of the photovoltaic module PV to the grid side from the MPPT circuit 1011, and restart the photovoltaic system.

[0081] Taking the photovoltaic module PV connected to the nth MPPT circuit 1011 n as an example where a ground short-circuit fault occurs at the negative terminal, it should be understood that at this time, the current sensor CT n connected to the photovoltaic module PV n will detect the current i n flowing from the negative terminal of the photovoltaic module PV to the grid side. Further, the sampled value of the current sensor CT PVN is returned to the control of the photovoltaic system. n Specifically, as

[0082] shown in the restart control timing diagram when a ground short-circuit fault occurs at the negative terminal of the photovoltaic module PV. As described above, the module signal S Figure 10 is used to control the DC switches S pvn_ctl and S pvn- and S pvn+ .

[0083] In the time period from t0 to t3, it is the same as the above-mentioned turn-off control timing, and no detailed description will be given here.

[0084] At the moment of t3, the grid-connected switches S a , S b and S c all switch to the open state.

[0085] At the moment of t4, the controller 108, according to the current sampled value I n returned by the current sensor CT before, makes the module signal S PVN set to the low level, the DC switches S pvn_ctl and S pvn- and S pvn+ switch to the open state, the photovoltaic module PV n is isolated from the photovoltaic system, and the photovoltaic inverter starts to restart.

[0086] At the moment of t5, the output voltage waveform phase-locking is completed, and the grid-connected switches S a , S b and S c switch to the closed state, and the photovoltaic system resumes grid-connected operation.

[0087] Furthermore, before the photovoltaic module PV with a ground short - circuit fault is repaired, the photovoltaic system can still operate normally, which helps to avoid the situation that the photovoltaic system cannot resume normal operation before the fault is eliminated through manual inspection and repair, thereby improving the reliability of the photovoltaic system. n Before the photovoltaic module PV with a ground short - circuit fault is repaired, the photovoltaic system can still operate normally, which helps to avoid the situation that the photovoltaic system cannot resume normal operation before the fault is eliminated through manual inspection and repair, thereby improving the reliability of the photovoltaic system.

[0088] The above describes the basic principle, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above - mentioned embodiments. What is described in the above - mentioned embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A shutdown protection system, characterized in that: include: A phase current sensor group, wherein the phase current sensor group is used to respectively detect the current of each phase line on the power grid side; The bus current sensor is used to detect the current i of the negative bus on the photovoltaic side. bus ; A protection control module, wherein the protection control module is adapted to compare the current of each phase line with a preset phase line threshold I x_ref , and the comparison current i bus and preset bus threshold I bus_ref , there is a current flowing from the PV side to the grid side on the negative busbar on the PV side, and the current of the phase line is less than the preset phase line threshold I x_ref Under the condition of x_ref The grid-connected switch corresponding to the phase line is switched to the open circuit state; The protection control module includes a plurality of shutoff devices, each of which is provided with a phase current comparator, a bus current comparator and an AND gate unit; The phase current comparator is used to determine whether the current of the phase line flows from the photovoltaic side to the grid side, and whether the current of the phase line is less than a preset phase line threshold I x_ref ; The bus current comparator is used to determine the current i bus Whether it flows from the photovoltaic side to the grid side, and whether the current i bus Is it greater than the preset bus threshold I bus_ref ; One of the input ends of the AND gate unit is used to receive the output signal of the phase current comparator, and the other input end of the AND gate unit is used to receive the output signal of the bus current comparator. The AND gate unit is suitable for outputting the intermediate signal D x_ctl , the intermediate signal D x_ctl Act on the grid-connected switch so that there is a current flowing from the photovoltaic side to the grid side on the negative busbar of the photovoltaic side, and the current of the phase line is less than the preset phase line threshold I x_ref Under the condition of , the grid-connected switch is switched to the open circuit state.

2. The shutdown protection system according to claim 1, characterized in that: The negative input terminal of the phase current comparator is used to receive the phase line current detection value I output by the phase current sensor group. x The positive input terminal of the phase current comparator is used to receive a preset phase line threshold value I x_ref , when the current in the phase line is greater than the preset phase line threshold I x_ref Under the condition that the output signal of the phase current comparator is set to a high level; when the current of the phase line is less than the preset phase line threshold I x_ref Under the condition of, the output signal of the phase current comparator is set to a low level.

3. The shutdown protection system according to claim 1, characterized in that: The negative input terminal of the bus current comparator is used to receive the bus current detection value I output by the bus current sensor. bus The positive input terminal of the bus current comparator is used to receive the preset bus threshold value I bus_ref , at current i bus Greater than the preset bus threshold I bus_ref Under the condition of , the output signal of the phase current comparator is set to high level; when the current i bus Less than the preset bus threshold I bus_ref Under the condition of, the output signal of the phase current comparator is set to a low level.

4. The shutdown protection system according to claim 1, characterized in that: The shut-off device further comprises an OR gate unit, one of the input terminals of which is used to receive the intermediate signal D output by the AND gate unit. x_ctl The other input end of the OR gate unit is used to receive the switch signal S output by the controller of the photovoltaic system. x_ctl , the OR gate unit is suitable for outputting a control signal K x_ctl , the control signal K x_ctl Acting on the grid-connected switch, so that when there is no photovoltaic side short-circuit fault to the ground in the photovoltaic system, the switch signal S x_ctl The grid-connected switch is controlled to remain in a closed state; there is a current flowing from the photovoltaic side to the grid side on the negative busbar on the photovoltaic side, and the current of the phase line is less than the preset phase line threshold I x_ref Under the condition of x_ctl The grid-connected switch can be switched to the open circuit state.

5. The shutdown protection system according to any one of claims 1 to 4, characterized in that: The phase current sensor group includes a first phase current sensor, a second phase current sensor and a third phase current sensor. The first phase current sensor is used to detect the current i of the A phase on the grid side. a The second phase current sensor is used to detect the current i of phase B on the grid side. b The third phase current sensor is used to detect the current i of the C phase on the grid side. c .

6. The shutdown protection system according to any one of claims 1 to 4, characterized in that: The plurality of shutoff devices include a first shutoff device, a second shutoff device and a third shutoff device. There is a current flowing from the photovoltaic side to the grid side on the negative busbar of the photovoltaic side, and the current i of the A phase is a Less than the preset phase line threshold I x_ref Under the condition that the first disconnecting device enables the grid-connected switch S of phase A a Switch to open circuit state; There is a current flowing from the photovoltaic side to the grid side on the negative busbar of the photovoltaic side, and the current i of phase B b Less than the preset phase line threshold I x_ref Under the condition of b Switch to open circuit state; There is a current flowing from the photovoltaic side to the grid side on the negative busbar of the photovoltaic side, and the current i of phase C c Less than the preset phase line threshold I x_ref Under the condition of c Switch to open circuit state.

7. The shutdown protection system according to any one of claims 1 to 4, characterized in that: The shutdown protection system also includes a DC switch group and a current sensor CT. The DC switch group is connected between the positive end of the photovoltaic module PV and the MPPT circuit, and between the negative end of the photovoltaic module PV and the MPPT circuit. The current sensor CT is connected between the negative end of the photovoltaic module PV and the MPPT circuit, and is used to detect the current of the MPPT circuit. When there is current flowing from the negative end of the photovoltaic module PV to the grid side in the MPPT circuit, the DC switch group switches to an open circuit state to disconnect the photovoltaic module PV from the MPPT circuit.

8. The shutdown protection system according to any one of claims 1 to 4, characterized in that: When a short-circuit fault occurs in the photovoltaic system and the switch device of the inverter circuit of the photovoltaic system is in an open circuit state, the protection control module can make the current less than the preset phase line threshold value I x_ref The grid-connected switches corresponding to the phase lines are switched to the open circuit state one by one.

9. The shutdown protection system according to claim 8, characterized in that: Under the condition that the grid-connected switches corresponding to all phase lines are in an open circuit state, the controller of the photovoltaic system can disconnect the photovoltaic module PV where current flows from the negative end of the photovoltaic module PV to the grid side from the MPPT circuit and restart the photovoltaic system.

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