Turn-off protection system

Abstract

The invention discloses a turn-off protection system comprising a phase current sensor group which is used for detecting the current of each phase line of a power grid side; the bus current sensor is used for detecting the current ibus of the photovoltaic side negative bus; the protection control module is suitable for respectively comparing the current of each phase line with a preset phase line threshold value Ixref and comparing the current ibus with a preset bus threshold value Ibusref, and the protection control module is used for controlling the current ibus to be smaller than the preset bus threshold value Ibusref under the condition that the current flowing from the photovoltaic side to the power grid side exists in the photovoltaic side negative bus and the current of the phase line is smaller than the preset phase line threshold value Ixref. The protection control module enables the grid-connected switch corresponding to the phase line of which the current is smaller than the preset phase line threshold value Ixref to be switched to an open-circuit state, so that a short-circuit loop can be cut off more safely when the photovoltaic system has a photovoltaic side to-ground short-circuit fault.

Description

Technical Field

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

[0002] The photovoltaic system may have a short-circuit fault on the photovoltaic side to the ground due to reasons such as line aging. Even if the switching devices of the inverter circuit of the photovoltaic system are switched to the open circuit state, a short-circuit loop may be formed by the reverse-parallel diode of the switching device. The large short-circuit current may damage the switching device, causing secondary damage to the photovoltaic system.

[0003] In some related technologies, the short-circuit loop is cut off by directly turning off the grid-connected switch, but arcing may occur and even cause safety accidents. In other related technologies, a shunt circuit is set to increase 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, but the short-circuit loop is not cut off, so a large short-circuit current may still exist, causing damage to the switching devices. Summary of the invention

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

[0005] To achieve the above purpose, the technical solution adopted by the present invention is: a shutdown protection system, comprising: a phase current sensor group, the phase current sensor group is used to detect the current of each phase line on the grid side; a bus current sensor, 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.

[0006] As a preferred embodiment, the protection control module includes a plurality of shut-down 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 value I x_ref The bus current comparator is used to determine the current i busWhether 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 terminals 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, and 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.

[0007] As a preferred embodiment, 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.

[0008] As a preferred embodiment, 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.

[0009] As a preferred embodiment, the shut-off device further comprises an OR gate unit, one of the input ends of the OR gate unit 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_ctlThe 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.

[0010] As a preferred embodiment, the phase current sensor group includes a first phase current sensor, a second phase current sensor and a third phase current sensor, wherein 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 .

[0011] As a preferred embodiment, the plurality of shutoff devices include a first shutoff device, a second shutoff device and a third shutoff device, and 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 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 the 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 the 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.

[0012] As a preferred embodiment, 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 a 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.

[0013] As a preferred embodiment, when a short circuit fault occurs to the ground 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 Ix_ref The grid-connected switches corresponding to the phase lines are switched to the open circuit state one by one.

[0014] As a preferred embodiment, 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.

[0015] Compared with the prior art, the present invention has the following beneficial effects: When a photovoltaic system has a short-circuit fault on the photovoltaic side to the ground, the protection control module can be used to protect the photovoltaic system when the phase line current is less than the preset phase line threshold value I x_ref The grid-connected switch corresponding to the phase line is closed under the condition of being closed, thereby reducing the risk of arcing and improving safety on the basis of cutting off the short-circuit loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The schematic diagram of the photovoltaic system of the related art.

[0017] Figure 2 It is a schematic diagram of a short circuit fault to ground occurring at the positive terminal of a photovoltaic module PV1 of a photovoltaic system in the related art.

[0018] Figure 3 Photovoltaic module PV for photovoltaic system of related art n Schematic diagram of a short-to-ground fault at the negative terminal.

[0019] Figure 4 This is an architecture diagram of a photovoltaic system and a shutdown protection system according to some embodiments of the present application.

[0020] Figure 5 This is an architectural diagram of the protection control module of this application.

[0021] Figure 6 This is a schematic diagram of the shutdown device of the present application.

[0022] Figure 7 Schematic diagram of a photovoltaic system and a shutdown protection system according to other embodiments of the present application.

[0023] Figure 8 The voltage and current waveforms on the grid side when a short circuit to ground occurs at the negative end of the photovoltaic module PV of the present application.

[0024] Fig. 9 This is a shutdown control timing diagram of the grid-connected switch when a short-circuit fault occurs to the ground at the negative end of the photovoltaic module PV of the present application.

[0025] Fig.10 This is a restart control timing diagram when a short circuit to ground occurs at the negative end of the photovoltaic module PV of the present application.

[0026] In the figure: 101, DC / DC unit; 1011, MPPT circuit; 102, DC / AC unit; 103, grid-connected switch group; 104, protection control module; 1041, shutdown 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. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0028] 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 are not necessarily used to describe a specific order or sequence.

[0029] The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0030] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" 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 a direct connection, a contact connection, or an indirect connection through an intermediate medium, and it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] In order to facilitate the understanding of the following method, this application will be described by a photovoltaic system. Figure 1As shown, a three-phase grid-connected photovoltaic system with n MPPTs in the related art mainly includes n photovoltaic modules PV, a DC / DC unit 101, a DC / AC unit 102 and a grid-connected switch group 103, wherein 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 the bus capacitor, the DC / AC unit 102, the filter inductor and the grid-connected switch group 103. Specifically, the DC / DC unit 101 is composed of n MPPT circuits 1011 connected in parallel, and each MPPT circuit 1011 is 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 Furthermore, the DC / AC unit 102 is composed of switch devices S1 to S6, and the switch devices S1 to S6 are controlled by the controller 108 of the photovoltaic system to switch between an open state and a closed state, so as to convert the direct current on the photovoltaic side into the alternating current on the grid side. It should be understood that Figure 1 The photovoltaic system circuit structure shown is only for the convenience of explaining the subsequent solutions. The DC / AC unit 102 may also be a unidirectional inverter circuit or a three-level three-phase inverter circuit, etc., and this application does not impose any specific restrictions on this.

[0032] Taking photovoltaic module PV1 as an example, it should be understood that the same is applicable to other photovoltaic modules PV. Figure 2 As shown, when the positive terminal of the photovoltaic module PV1 is short-circuited to the ground, due to the action of the diode D1 in the first MPPT circuit 1011, the loop flowing from the grid side to the photovoltaic side is blocked, which is helpful to avoid the generation of short-circuit current.

[0033] Furthermore, photovoltaic modules PV n As an example, it should be understood that the same is applicable to other photovoltaic modules PV. Figure 3 As shown, in the photovoltaic module PV n When the negative terminal is short-circuited to ground, taking phase A as an example, even if the switching devices S1 to S6 are in an open circuit state, a short circuit may occur from the photovoltaic module PV. n The negative end of the switch device S4, the filter inductor L a , Grid-connected switch S a , the short-circuit loop between the power grid and the ground. It is worth mentioning that the current I in the short-circuit loop is V ga / Z eq , where V ga is the grid voltage of phase A, Z eqis the equivalent impedance of the short-circuit loop, that is, a large current exists in the short-circuit loop, which may damage the switch device S4 and cause secondary damage to the photovoltaic system. It should be understood that the above short-circuit loop is also applicable to phase B and phase C, and will not be elaborated in detail here.

[0034] 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, or even cause a safety accident. If a shunt circuit is set to increase the current carrying capacity of the photovoltaic system, since the short-circuit loop is not cut off, a large short-circuit current may still exist, thereby damaging the switch devices S1 to S6.

[0035] Based on the above content, in order to more safely cut off the short circuit when a photovoltaic side short circuit fault occurs in a photovoltaic system, one aspect of the present application provides a shutdown protection system, such as Figure 4 As shown, it includes: 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 current of each phase line on the grid side; the bus current sensor 106 is used to detect the current i of the negative bus on the photovoltaic side. bus The protection control module 104 is adapted to compare the current of each phase line with the 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 that the protection control module 104 can make the current less than the preset phase line threshold I x_ref The grid-connected switch corresponding to the phase line is switched to an open circuit state. It should be understood that the protection control module 104 can be used to control the phase line current to be less than the preset phase line threshold value I x_ref The grid-connected switch corresponding to the phase line is closed under the condition of being closed, thereby reducing the risk of arcing and improving safety on the basis of cutting off the short-circuit loop.

[0036] Specifically, the bus current sensor 106 can detect the current i of the negative bus on the photovoltaic side. bus , and the protection control module 104 is used to determine whether there is a current i flowing from the photovoltaic side to the grid side. bus , that is, it is possible to detect whether the negative terminal of the photovoltaic module PV is short-circuited to the ground. It should be understood that when the negative terminal of the photovoltaic module PV is short-circuited to the ground, when the voltage of one phase of the grid side is in the negative half cycle, the bus current sensor 106 is able to detect the current i flowing from the photovoltaic side to the grid side. busFurthermore, the current of each phase line on the grid side can be detected by the phase current sensor group 105, and the protection control module 104 can determine whether the current of the phase line is less than the preset phase line threshold value I x_ref , and then the current of one of the phase lines on the grid side is less than the preset phase line threshold I x_ref Under the condition, the protection control module 104 can switch the grid-connected switch corresponding to the phase line to the open circuit state.

[0037] For example, when the current of phase A is less than the preset phase line threshold I x_ref Under the condition of a Switch to open circuit state, and the grid-connected switches S of phases B and C are b and S c Maintain in the closed state; further, the current in the B phase line is also less than the preset phase line threshold I x_ref Under the condition of b The grid-connected switch S of phase C is also switched to the open circuit state. c Furthermore, the current in the C phase line is also less than the preset phase line threshold I x_ref Under the condition of c The protection control module 104 is also switched to an open circuit state to cut off the short circuit. In other words, the protection control module 104 is able to 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. It is understood that the order in which the grid-connected switches in the above-mentioned grid-connected switch group 103 are switched to the open circuit state is only an example, and the present application does not make any specific limitation on this.

[0038] In some embodiments, Figure 5 and Figure 6 As shown, the protection control module 104 includes a plurality of shut-off devices 1041, each of which 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 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 value I x_ref ; Bus current comparator 1043 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 terminals of the AND gate unit 1044 is used to receive the output signal of the phase current comparator 1042, and 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 suitable for outputting the intermediate signal Dx_ctl , 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_re f, the grid-connected switch is switched to the open circuit state.

[0039] It should be understood that the phase current comparator 1042 is capable of comparing the phase current measured by the phase current sensor group 105 with the preset phase line threshold value I x_ref The bus current comparator 1043 compares the current i of the negative bus on the photovoltaic side bus and preset bus threshold I bus_ref Furthermore, the output signal of the phase current comparator 1042 and the output signal of the bus current comparator 1043 act together on the AND gate unit 1044, so that there is a current flowing from the photovoltaic side to the grid side in 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 Under the condition of x_ctl The grid-connected switch can be switched to an open circuit state to cut off the short-circuit loop.

[0040] 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 high level.

[0041] In some embodiments, Figure 5 and Figure 6 As shown, the shut-off device 1041 further includes an OR gate unit 1045, one of the input ends of the OR gate unit 1045 is used to receive the intermediate signal D output by the AND gate unit 1044. x_ctl The other input end 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 , the OR gate unit 1045 is adapted to output a control signal K x_ctl , 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.

[0042] It should be understood that, under the condition that the photovoltaic system does not have a photovoltaic side short-circuit fault, the grid-connected switch is controlled by the switch signal S output by the controller 108. x_ctlThe switch devices S1 to S6 are controlled by the controller 108 to switch between the open circuit state and the closed state, respectively, so that the DC power on the photovoltaic side is converted into the AC power on the grid side. Further, under the condition that the negative terminal of the photovoltaic module PV of the photovoltaic system is short-circuited to the ground, the switch devices S1 to S6 are controlled by the controller 108 to remain in the open circuit state, and the grid-connected switch is protected by the intermediate signal D of the control module 104. x_ctl The function is to achieve a current 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 to cut off the short-circuit loop.

[0043] In at least one embodiment, when the photovoltaic system does not have a photovoltaic side short-circuit fault, the intermediate signal D output by the AND gate unit 1044 is x_ctl Keep 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 Keep consistent, so that the grid-connected switch can receive the switching signal S output by the controller 108 x_ctl The controller 108 switches between the open state and the closed state to realize the normal grid-connected operation of the photovoltaic system. Further, when the negative terminal of the photovoltaic module PV of the photovoltaic system is short-circuited to the ground, the switch signal S output by the controller 108 is x_ctl Keep low level, so that the control signal K output by the OR gate unit 1045 x_ctl The intermediate signal D output by AND gate unit 1044 x_ctl The grid-connected switch is controlled by the protection control module 104 to achieve a current 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.

[0044] 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 to output a low level when all input terminals are at a low level.

[0045] In some embodiments, Figure 5 and Figure 6 As shown, 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 The positive input terminal of the phase current comparator 1042 is used to receive the 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_refUnder the condition of , 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 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 1042 is set to a low level, so as to make the grid-connected switch in an open circuit state.

[0046] 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, takes the current flowing from the photovoltaic side to the grid side as the reverse current, and the phase line current detection value I x That is to say, under the condition that the current in the phase line flows from the grid side to the photovoltaic side, the phase line current detection value I output by the phase current sensor group 105 is x is a positive number. Under the condition that the current in the phase line flows from the photovoltaic side to the grid side, the phase line current detection value I output by the phase current sensor group 105 is x It should be understood that the larger the reverse current is, the larger the phase line current detection value I x The larger the absolute value of the phase current detection value I x With the phase current detection value I x The absolute value of the phase current detection value I x The smaller.

[0047] In at least one embodiment, in order to switch the grid-connected switch to an open circuit state when the reverse current is small, the phase line threshold I is preset. x_ref Set to 0 or a negative number. It is worth mentioning that when the preset phase line threshold I x_ref If set to a negative number, the above-mentioned "when the current in the phase line is greater than the preset phase line threshold I x_ref "Under the condition" means that the current of the phase line is greater than the preset phase line threshold I x_ref The absolute value of the preset phase line threshold I x_ref It can be adjusted according to actual working conditions, and this application does not impose any specific restrictions on this.

[0048] Further, under the condition that the input value of the negative input terminal of the phase current comparator 1042 is less than the input value of 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 of the negative input terminal of the phase current comparator 1042 is greater than the input value of 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, the reverse current is greater than the preset phase line threshold value I x_ref When the absolute value of the phase current sensor outputs the phase line current detection value I x The smaller the phase current detection value I x 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 preset phase line threshold I x_ref When the absolute value of the phase current sensor outputs the phase line current detection value I x The larger the phase current detection value I x 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.

[0049] In some embodiments, Figure 5 and Figure 6 As shown, the negative input terminal of the bus current comparator 1043 is used to receive the bus current detection value I output by the bus current sensor 106. bus The positive input terminal of the bus current comparator 1043 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 current i, 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; bus Less than the preset bus threshold I bus_ref Under the condition of, 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 at least one embodiment, the bus current sensor 106 group takes the current flowing from the grid side to the photovoltaic side as the forward current, takes the current flowing from the photovoltaic side to the grid side as the reverse current, and the bus current detection value I bus As the reverse current increases, it decreases. That is, the current i in the negative bus bus Under the condition that the current flows from the grid side to the photovoltaic side, the bus current detection value I output by the bus current sensor 106 group bus is a positive number, the current i in the negative bus bus Under the condition that the current flows from the photovoltaic side to the grid side, the bus current detection value I output by the bus current sensor 106 group bus Is a negative number.

[0051] In at least one embodiment, in order to switch the grid-connected switch to an open circuit state when a short-circuit fault occurs to the ground at the negative end of the photovoltaic module PV, the current i bus When the flow from the photovoltaic side to the grid side, switch the grid-connected switch to the open circuit state, and preset the bus threshold I bus_ref Set to 0. It is worth mentioning that the preset bus threshold I bus_ref It can be adjusted according to actual working conditions, and this application does not impose any specific restrictions on this.

[0052] Further, under the condition that the input value of the negative input terminal of the bus current comparator 1043 is less than the input value of 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 of the negative input terminal of the bus current comparator 1043 is greater than the input value of 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 bus current detection value I bus 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 make the intermediate signal D output by the AND gate unit 1044 x_ctl The output signal of the phase current comparator 1042 is used to achieve a 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; when there is a positive current in the negative bus, that is, the bus current detection value I bus 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 make the intermediate signal D output by the AND gate unit 1044 x_ctl Keep it 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 To keep consistent, the grid-connected switch receives the switch signal S output by the controller 108 x_ctl It plays the role of switching between open and closed states to achieve normal grid-connected operation of the photovoltaic system.

[0053] 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 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 phase C on the grid side. c It should be understood that providing current sensors on each phase line on the grid side is beneficial to provide electrical isolation, so as to improve the safety and reliability of the photovoltaic system.

[0054] In some embodiments, the plurality of shutoff devices 1041 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 a Less than the preset phase line threshold I a_ref Under the condition of aSwitch to the 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 b_ref Under the condition of b Switch to the 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 c_ref Under the condition of c Switch to open circuit state.

[0055] It should be understood that the first shutoff device, the second shutoff device and the third shutoff device are respectively used to shut off the grid-connected switch S a , S b and S c Control is beneficial to improve the reliability of the shutdown protection system. It is worth mentioning that the preset phase line threshold I x_ref Including 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 threshold I a_ref ,I b_ref and I c_ref They may be the same or different, and this application does not impose any specific limitation on this.

[0056] Take the first shut-off device as an example, and assume that the preset bus threshold I bus_ref is 0, the preset phase line threshold I of phase A a_ref When the photovoltaic system does not have a short-circuit fault to ground and the photovoltaic system is shut down, the bus current comparator 1043 and the phase current comparator 1042 both output a low level, and the intermediate signal D output by the AND gate unit 1044 is x_ctl Keep it at low level, or the control signal K output by gate unit 1045 x_ctl and the switch signal S output by the controller 108 a_ctl To keep consistent, the grid-connected switch Sa receives the switching signal S output by the controller 108 a_ctl role.

[0057] When the photovoltaic system does not have a short-circuit fault to the ground and the photovoltaic system is operating normally, there is a positive current in the negative bus, that is, the current flows from the grid side to the photovoltaic side. The bus current detection value I busis positive, greater than 0, and the output signal of the bus current comparator 1043 is set to a low level. Further, the magnitude and direction of the current in the phase line of phase A are constantly changing, and the output signal of the phase current comparator 1042 alternates between a low level and a high level. It should be understood that since the output signal of the bus current comparator 1043 is set to a low level, the intermediate signal D output by the AND gate unit 1044 is x_ctl Keep it at low level, or the control signal K output by gate unit 1045 x_ctl and the switch signal S output by the controller 108 a_ctl Keep consistent, grid-connected switch S a The switch signal S output by the controller 108 a_ctl role.

[0058] When a short-circuit fault occurs to the ground at the negative terminal of the photovoltaic module PV of the photovoltaic system, the switch signal S output by the controller 108 a_ctl Keep low level, so that the control signal K output by the OR gate unit 1045 x_ctl The intermediate signal D output by AND gate unit 1044 x_ctl Furthermore, there is a reverse current in the negative bus, that is, the current flows from the grid side to the photovoltaic side, and the bus current detection value I bus is negative, less than 0, and the output signal of the bus current comparator 1043 is set to a high level. Furthermore, the current in the phase line of phase A is a reverse current, and its magnitude is constantly changing. When the reverse current is greater than the preset phase line threshold I a_ref When the absolute value of the phase current detection value I a Less than the preset phase line threshold I a_ref , and then the output signal of the phase current comparator 1042 is set to a high level. At this time, the intermediate signal D output by the AND gate unit 1044 is x_ctl is high level, the control signal K output by the OR gate unit 1045 x_ctl Also high level, grid-connected switch S a In the closed state. When the reverse current is less than the preset phase line threshold I a_ref When the absolute value of the phase current detection value I a Greater than the preset phase line threshold I a_ref , and then the output signal of the phase current comparator 1042 is set to a low level. At this time, the intermediate signal D output by the AND gate unit 1044 is x_ctl is low level, the control signal K output by the OR gate unit 1045 x_ctl Also low level, grid-connected switch S a Switch to the open circuit state to reduce the risk of arcing and improve safety on the basis of cutting off the short circuit.

[0059] It should be understood that the above content is applicable to the second shutoff device of phase B and the third shutoff device of phase C, and will not be elaborated here in detail.

[0060] 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 the resources of the controller 108 of the photovoltaic system.

[0061] It should be understood that the above logic can also be implemented by the algorithm of the controller 108 of the photovoltaic system to achieve a current less than the preset phase line threshold I under the condition that a short-circuit fault occurs to the ground at the negative end of the photovoltaic module PV of the photovoltaic system. x_ref The grid-connected switches corresponding to the phase lines are switched to the open circuit state one by one.

[0062] In some embodiments, Figure 7 As shown, the shutdown protection system also includes a DC switch group 107 and a current sensor CT. The DC switch group 107 is connected between the positive end of the photovoltaic module PV and the MPPT circuit 1011, and between the negative end of the photovoltaic module PV and the MPPT circuit 1011. The current sensor CT is connected between the negative end of the photovoltaic module PV and the MPPT circuit 1011, and is used to detect the current of the MPPT circuit 1011. When there is a current flowing from the negative end of the photovoltaic module PV to the grid side in the MPPT circuit 1011, the DC switch group 107 is switched to an open circuit state to disconnect the photovoltaic module PV from the MPPT circuit 1011.

[0063] In at least one embodiment, Figure 7 As shown, the DC switch group 107 includes a DC switch S pv+ and S pv- , DC switch S pv+ Connected between the positive terminal of the photovoltaic module PV and the MPPT circuit 1011, the DC switch S pv- Connected between the negative terminal of the photovoltaic module PV and the MPPT circuit 1011 .

[0064] It should be understood that, assuming that the photovoltaic module PV connected to the nth MPPT circuit 1011 n The negative terminal is short-circuited to ground, and the current sensor CT n The photovoltaic module PV n The negative end of the current flows to the grid side, and the controller 108 is able to pass the module signal S pvn_ctl The DC switch S pvn- and S pvn+ Switch to open circuit to enable the photovoltaic module PV n Disconnected from the nth MPPT circuit 1011.

[0065] It is worth mentioning that after the photovoltaic module PV with a short-circuit fault to the ground and the corresponding MPPT circuit 1011 are disconnected, the controller 108 of the photovoltaic system is able to restart the photovoltaic system so that the normal photovoltaic module PV continues to work normally. In other words, the photovoltaic module PV with a short-circuit fault to the ground is isolated from the photovoltaic system, and then the photovoltaic system can still work normally before the photovoltaic module PV with a short-circuit fault to the ground is repaired, which is conducive to avoiding the photovoltaic system from being unable to resume normal operation before the fault is eliminated by human maintenance, thereby improving the reliability and working efficiency of the photovoltaic system.

[0066] In some embodiments, 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 104 is able to 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.

[0067] Specifically, Figure 8 The following figure shows the voltage and current waveforms on the grid side when a short-circuit fault occurs at the negative end of the photovoltaic module PV. Taking phase A as an example, at time a, the grid voltage U a At this time, the body diode of the switch device S4 in the DC / AC unit 102 is reversely cut off, and the current i of phase A is a is 0.

[0068] In the ad time period, the grid-side voltage is in the negative half cycle. When the voltage difference between the ground and grid-side voltages is greater than the conduction voltage of the body diode of the switch device S4, a short circuit is formed, and the current i of phase A a At time d, the grid voltage U a At zero, about to enter the positive half cycle.

[0069] Among them, at time b, the grid side voltage U a The negative half-cycle reaches its maximum value. Due to the short-circuit fault of the negative terminal of the photovoltaic module PV to the ground, there is an inductive impedance in the short-circuit loop, causing the current to lag behind the voltage. Therefore, the current i a It has not yet reached its maximum value. At time c, the current i a reaches its maximum value. In the cd time period, the current i a At time d, the current i a Still negative.

[0070] In the df time period: the grid voltage Ua is in the positive half cycle.

[0071] Among them, in the time period de, the current i a The filter inductor L aUnder the action of , the current i keeps its original direction and gradually decreases. At time e, the current i a Reduced to 0. In the ef period, the current i a Keep it at 0.

[0072] It should be understood that factors that affect the degree to which current lags behind voltage include but are not limited to the degree of short-circuit to ground, the equivalent resistance of the short-circuit loop, and the size of the filter inductance. The above-mentioned moments are only examples and this application does not impose specific restrictions on this.

[0073] like Fig. 9 The figure shows the grid-connected switch S when a short-circuit fault occurs at the negative end of the photovoltaic module PV. a , S b and S c As mentioned above, the control signal K a_ctl Used to control the grid-connected switch S a ; Control signal K b_ctl Used to control the grid-connected switch S b ; Control signal K c_ctl Used to control the grid-connected switch S c .

[0074] At time t0 , the switching devices S1 to S6 of the DC / AC unit 102 of the photovoltaic system are switched to an open circuit state.

[0075] At time t1, the current i of phase A is a Drop to the preset phase line threshold I a_ref , control signal K a_ctl Set to low level, the grid switch S a Switch to open circuit state, grid-connected switch S b and S c Keep in closed position.

[0076] At time t2, the current i of phase B is b Drop to the preset phase line threshold I b_ref , control signal K b_ctl Set to low level, the grid switch S b Switch to open circuit state, grid-connected switch S c Keep in closed position.

[0077] At t3, the current i of phase B is c Drop to the preset phase line threshold I c_ref , control signal K c_ctl Set to low level, the grid switch S c Switch to open state to cut off the short circuit.

[0078] It is understood that the order in which the various grid-connected switches in the above-mentioned grid-connected switch group 103 are switched to the open circuit state is only an example, and the present application does not impose any specific limitation on this.

[0079] In some embodiments, when the grid-connected switches corresponding to all phase lines are in an open circuit state, the controller 108 of the photovoltaic system is able to 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 1011 and restart the photovoltaic system.

[0080] The photovoltaic module PV connected to the nth MPPT circuit 1011 n Take the negative terminal short-circuited to ground as an example, it should be understandable that at this time, the PV module connected n Current sensor CT n The photovoltaic module PV n The current i flowing from the negative end to the grid side PVN , further, the current sensor CT n The sampled values ​​are returned to the control of the photovoltaic system.

[0081] Specifically, Fig.10 The figure shows the restart control timing diagram when a short-circuit fault occurs at the negative terminal of the photovoltaic module PV. As mentioned above, the module signal S pvn_ctl Used to control the DC switch S pvn- and S pvn+ .

[0082] During the time period t0-t3, the shutdown control timing is the same as the above-mentioned timing, which will not be elaborated here in detail.

[0083] At time t3, the grid-connected switch S a , S b and S c are switched to open circuit state.

[0084] At time t4, the controller 108 generates a current according to the current sensor CT n The returned current sampling value I PVN , so that the module signal S pvn_ctl Set to low level, the DC switch S pvn- and S pvn+ Switch to open circuit state, photovoltaic module PV n The PV system is isolated and the PV inverter starts to restart.

[0085] At t5, the output voltage waveform is phase-locked and the grid-connected switch S a , S b and S c Switch to the closed state and the photovoltaic system is connected to the grid again.

[0086] Then, when a photovoltaic module PV short-circuit fault occurs, n Before being repaired, the photovoltaic system can still work normally, which helps to avoid the photovoltaic system being unable to resume normal operation before the fault is eliminated by human maintenance, thereby improving the reliability of the photovoltaic system.

[0087] The above describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention to be protected. The scope of protection claimed by the present invention is defined by the attached 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.

2. The shutdown protection system according to claim 1, characterized in that: 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.

3. The shutdown protection system according to claim 2, 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.

4. The shutdown protection system according to claim 2, 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.

5. The shutdown protection system according to claim 2, 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.

6. The shutdown protection system according to any one of claims 1 to 5, 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 .

7. The shutdown protection system according to any one of claims 2 to 5, 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.

8. The shutdown protection system according to any one of claims 1 to 5, 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.

9. The shutdown protection system according to any one of claims 1 to 5, 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.

10. The shutdown protection system according to claim 9, 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.

Images