Protection circuit, control method and photovoltaic system

Abstract

The invention discloses a protection circuit, a control method and a photovoltaic system, and belongs to the technical field of power electronics. The invention provides a protection circuit which is applied to a three-phase inverter circuit, the direct current side of the three-phase inverter circuit is used for being connected with a power supply assembly, the output end of each phase is provided with a relay assembly, and the protection circuit comprises a controllable power device which is connected with a bridge arm in the three-phase inverter circuit in parallel; the fault detection module is electrically connected with the three-phase inverter circuit and is used for generating a fault signal when the fault of short circuit to ground is detected; the current detection circuit is used for detecting the output current of each phase of the three-phase inverter circuit; and the controller is electrically connected with the fault detection module, the current detection circuit and the relay, controls the controllable power device to be switched on after receiving a fault signal, and disconnects the relay assembly of each phase when the output current of each phase meets a zero-crossing condition, so that the relay assembly can be ensured to be switched off safely, and a loop of short-circuit current can be cut off. And the short-circuit current is prevented from damaging components in the circuit.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and in particular, relates to a protection circuit, a control method and a photovoltaic system. Background Art

[0002] Photovoltaic systems usually include photovoltaic modules and inverters. Photovoltaic modules are large-area solar panels formed by encapsulating and protecting solar panels in series. They can convert solar energy into direct current power, and then cooperate with inverters to convert the direct current power of photovoltaic modules into alternating current power, which can be directly connected to the power grid or directly supply electricity.

[0003] In actual projects, the cables of photovoltaic systems are often easily damaged due to construction or harsh environments, which can cause the photovoltaic cables to short-circuit to the ground. When the photovoltaic cables are short-circuited to the ground, the short-circuit current generated will be at the kiloampere level, which makes the risk of damage to the components in the circuit higher. Summary of the invention

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a protection circuit, a control method and a photovoltaic system, which can not only ensure the safe shutdown of the relay, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0005] In a first aspect, the present application provides a protection circuit, which is applied to a three-phase inverter circuit, wherein the DC side of the three-phase inverter circuit is used to connect a power supply component, and each phase output end of the three-phase inverter circuit is provided with a relay component, and the protection circuit includes:

[0006] A controllable power device is connected in parallel with a bridge arm in a three-phase inverter circuit;

[0007] A fault detection module is electrically connected to the three-phase inverter circuit and is configured to generate a fault signal when a short-circuit to ground fault is detected;

[0008] a current detection circuit, electrically connected to the three-phase inverter circuit and configured to detect an output current of each phase of the three-phase inverter circuit;

[0009] The controller is electrically connected to the fault detection module, the current detection circuit and the relay assembly respectively, and is configured to control the controllable power device to conduct after receiving the fault signal, and disconnect the relay assembly of each phase when the output current of each phase meets the zero-crossing condition.

[0010] According to the protection circuit of the present application, when a short-circuit fault to ground occurs between the three-phase inverter circuit and the power supply component, the controller controls the controllable power device to turn on, and the controllable power device shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to prevent excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component of each phase, which can not only ensure the safe shutdown of the relay component, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0011] According to an embodiment of the present application, the bridge arm includes an upper bridge arm and a lower bridge arm, and the fault detection module is configured to generate a first fault signal when a positive electrode of the power supply component is detected to be short-circuited to ground, and / or to generate a second fault signal when a negative electrode of the power supply component is detected to be short-circuited to ground;

[0012] The controller is configured to drive the controllable power device connected in parallel with the upper bridge arm to conduct when receiving the first fault signal; and / or drive the controllable power device connected in parallel with the lower bridge arm to conduct when receiving the second fault signal.

[0013] According to one embodiment of the present application, the fault detection module includes:

[0014] an overcurrent detection module, electrically connected to the current detection circuit, and configured to generate a first overcurrent signal when the negative output current of at least one phase is greater than a first current threshold, and / or to generate a second overcurrent signal when the positive output current of at least one phase is greater than a second current threshold;

[0015] a common-mode current detection module, electrically connected to the DC side of the three-phase inverter circuit, and configured to generate a first common-mode current signal when a negative common-mode current on the DC side of the three-phase inverter circuit is greater than a third current threshold, and / or to generate a second common-mode current signal when a positive common-mode current on the DC side of the three-phase inverter circuit is greater than a fourth current threshold;

[0016] A voltage detection module is electrically connected to the positive electrode of the power supply component, the negative electrode of the power supply component and the ground node, respectively, and is configured to generate a first voltage-to-ground signal when the voltage to ground between the positive electrode of the power supply component and the ground node is less than a first voltage threshold, and / or to generate a second voltage-to-ground signal when the voltage to ground between the negative electrode of the power supply component and the ground node is less than a second voltage threshold;

[0017] a signal conversion module, electrically connected to the overcurrent detection module, the common-mode current detection module and the voltage detection module, respectively, and configured to generate a first fault signal upon receiving at least one of a first overcurrent signal, a first common-mode current signal and a first voltage-to-ground signal; and / or

[0018] The signal conversion module is configured to generate a second fault signal when receiving at least one of the second overcurrent signal, the second common-mode current signal and the second voltage-to-ground signal.

[0019] According to one embodiment of the present application, the signal conversion module includes:

[0020] A first AND gate, wherein the input end of the first AND gate is electrically connected to the output ends of the overcurrent detection module, the common mode current detection module and the voltage detection module respectively, and the output end of the first AND gate is electrically connected to the controller.

[0021] According to one embodiment of the present application, the signal conversion module includes:

[0022] A second AND gate, wherein the input end of the second AND gate is electrically connected to the output end of the overcurrent detection module and the output end of the common mode current detection module respectively;

[0023] A third AND gate, wherein the input end of the third AND gate is electrically connected to the output end of the overcurrent detection module and the output end of the voltage detection module respectively;

[0024] A fourth AND gate, wherein the input end of the fourth AND gate is electrically connected to the output ends of the common-mode current detection module and the voltage detection module respectively;

[0025] An OR gate, an input end of the OR gate is electrically connected to the output ends of the second AND gate, the third AND gate and the fourth AND gate respectively, and an output end of the OR gate is electrically connected to the controller.

[0026] According to one embodiment of the present application, the signal conversion module further includes:

[0027] A data filtering unit, wherein the input end of the data filtering unit is electrically connected to the output ends of the overcurrent detection module, the common-mode current detection module and the voltage detection module respectively, and is configured to filter the first overcurrent signal, the second overcurrent signal, the first common-mode current signal, the second common-mode current signal, the first voltage-to-ground signal and / or the second voltage-to-ground signal.

[0028] According to one embodiment of the present application, the relay assembly includes a plurality of relays connected in series, the controller is electrically connected to each relay, and is configured to use at least two relay shutdown sequences when the relay assembly is controlled to be shut down multiple times.

[0029] According to one embodiment of the present application, the relay assembly includes a first relay and a second relay connected in series, and the controller alternately performs the following operations:

[0030] Control the first relay to be disconnected before the second relay; or,

[0031] The second relay is controlled to be disconnected before the first relay.

[0032] According to one embodiment of the present application, the controllable power device is a fully controlled power device, the output node of the three-phase inverter circuit is also connected to a filter inductor, and one end of the filter inductor away from the output node is electrically connected to the output end of the fully controlled power device.

[0033] According to one embodiment of the present application, the controller includes:

[0034] A pre-breaking module is configured to enter a pre-breaking stage after receiving a fault signal and determine a zero-crossing moment of the output current of each phase of the three-phase inverter circuit for the first time;

[0035] The main disconnecting module is configured to enter the main disconnecting stage after the pre-disconnecting stage ends, and control the relay assembly of the corresponding phase to disconnect when each phase meets at least one of the following conditions:

[0036] The time difference between the current moment and the zero-crossing moment is less than the threshold; or,

[0037] The output current is less than a fifth current threshold.

[0038] According to one embodiment of the present application, the three-phase inverter circuit adopts a three-phase four-wire connection method, and the main disconnection module is further configured to enter the main disconnection stage after the pre-disconnection stage ends, and control the relay assembly of the corresponding phase to disconnect when each phase meets at least one of the following conditions:

[0039] The time difference between the current moment and the zero-crossing moment is less than the threshold;

[0040] The output current is less than the fifth current threshold; or,

[0041] The phase angle of the phase voltage is within the target phase angle range;

[0042] Among them, when the positive pole is short-circuited to the ground, the target phase angle range is [180°, 180+θ1°]; when the negative pole is short-circuited to the ground, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

[0043] In a second aspect, the present application provides a control method, which is applied to a three-phase inverter circuit, wherein the DC side of the three-phase inverter circuit is used to connect a power supply component, each phase output end of the three-phase inverter circuit is provided with a relay component, and a bridge arm in the three-phase inverter circuit is connected in parallel with a controllable power device, and the control method includes:

[0044] When a short circuit to ground fault is detected in the power supply component, the controllable power device is controlled to be turned on;

[0045] Detect the output current of each phase of the three-phase inverter circuit;

[0046] After the controllable power device is turned on and the output current of each phase meets the zero-crossing condition, the relay components of each phase are disconnected.

[0047] According to the control method of the present application, when a short-circuit fault to ground occurs between the three-phase inverter circuit and the power supply component, the controller controls the controllable power device to turn on, and the controllable power device shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to prevent excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component of each phase, which can not only ensure the safe shutdown of the relay component, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0048] According to one embodiment of the present application, when the output current of each phase meets the zero-crossing condition, disconnecting the relay assembly of each phase includes:

[0049] In the first stage, the zero-crossing moment of the first zero-crossing point in the output current of each phase of the three-phase inverter circuit is determined;

[0050] In the second stage, when each phase satisfies at least one of the following conditions, the time difference between the current moment and the zero-crossing moment of the relay component of the corresponding phase being disconnected is less than a threshold; or,

[0051] The output current is less than a fifth current threshold.

[0052] According to an embodiment of the present application, the three-phase inverter circuit adopts a three-phase four-wire connection method, and the control method further includes:

[0053] Obtain the phase angle of each phase voltage;

[0054] In the second stage, when each phase meets at least one of the following conditions, the relay assembly of the corresponding phase is controlled to be disconnected:

[0055] The time difference between the current moment and the zero-crossing moment is less than the threshold;

[0056] The output current is less than the fifth current threshold; or,

[0057] The phase angle of the phase voltage is within the target phase angle range;

[0058] Among them, when the positive pole is short-circuited to the ground, the target phase angle range is [180°, 180+θ1°]; when the negative pole is short-circuited to the ground, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

[0059] According to one embodiment of the present application, the bridge arm of the three-phase inverter circuit includes an upper bridge arm, and when a short circuit fault to ground is detected, the controllable power device is controlled to be turned on, including:

[0060] When it is detected that the negative output current of at least one phase of the three-phase inverter circuit is greater than the first current threshold, and / or the negative common mode current on the DC side of the three-phase inverter circuit is greater than the third current threshold, and / or the voltage to ground between the positive electrode of the power supply component and the ground node is less than the first voltage threshold, it is determined that the positive electrode of the power supply component is short-circuited to ground;

[0061] When the positive pole of the power supply component is short-circuited to the ground, the controllable power device connected in parallel with the upper bridge arm is controlled to be turned on.

[0062] According to one embodiment of the present application, the bridge arm of the three-phase inverter circuit includes a lower bridge arm, and when a short circuit fault to ground is detected, the controllable power device is controlled to be turned on, including:

[0063] When it is detected that the positive output current of at least one phase of the three-phase inverter circuit is greater than the second current threshold, and / or the positive common mode current on the DC side of the three-phase inverter circuit is greater than the fourth current threshold, and / or the voltage to ground between the negative electrode of the power supply component and the ground node is less than the voltage threshold, it is determined that the negative electrode of the power supply component is short-circuited to ground;

[0064] When the negative pole of the power supply component is short-circuited to the ground, the controllable power device connected in parallel with the lower bridge arm is controlled to be turned on.

[0065] According to one embodiment of the present application, the relay assembly includes a plurality of relays connected in series, and the control method further includes:

[0066] When the relay assembly is controlled to be turned off multiple times, at least two relay turning-off sequences are used for execution.

[0067] According to one embodiment of the present application, the relay assembly includes a first relay and a second relay connected in series, and the control method further includes:

[0068] Do the following alternately:

[0069] Control the first relay to be disconnected before the second relay; or,

[0070] The second relay is controlled to be disconnected before the first relay.

[0071] In a third aspect, the present application provides a photovoltaic system, which includes a power supply component and an inverter, the DC side of the inverter is used to connect the power supply component, the AC side of the inverter is used to connect to the power grid, and the inverter includes the aforementioned protection circuit, or includes a controller that implements the aforementioned control method.

[0072] According to the photovoltaic system of the present application, when a short-circuit fault to ground occurs between the three-phase inverter circuit and the power supply component, the controller controls the controllable power device to turn on, and the controllable power device shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to prevent excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component of each phase, which can not only ensure the safe shutdown of the relay component, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0073] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0075] Figure 1 is a schematic diagram of the structure of a photovoltaic system provided in an embodiment of the present application;

[0076] Figure 2 is a schematic diagram of the structure of the protection circuit provided in the embodiment of the present application;

[0077] Figure 3 It is one of the structural block diagrams of the signal conversion circuit provided in the embodiment of the present application;

[0078] Figure 4 This is the second structural block diagram of the signal conversion circuit provided in the embodiment of the present application;

[0079] Figure 5 This is the third structural block diagram of the signal conversion circuit provided in the embodiment of the present application;

[0080] Figure 6 It is a schematic diagram of shutting down a relay assembly provided in an embodiment of the present application;

[0081] Figure 7 It is one of the shutdown timing diagrams of the relay components of each phase in the three-phase inverter circuit provided in the embodiment of the present application;

[0082] Figure 8 This is the second shutdown timing diagram of each phase relay component in the three-phase inverter circuit provided in the embodiment of the present application;

[0083] Fig. 9 This is the third of the shutdown timing diagrams of the relay components of each phase in the three-phase inverter circuit provided in the embodiment of the present application;

[0084] Fig.10 is a flow chart of a control method provided by an embodiment of the present application;

[0085] Fig.11 This is the fourth of the shutdown timing diagrams of the relay components of each phase in the three-phase inverter circuit provided in the embodiment of the present application.

[0086] Reference numerals:

[0087] Power supply component 100, boost circuit 200, three-phase inverter circuit 300, overcurrent detection module 410, common-mode current detection module 420, voltage detection module 430, signal latch circuit 441, data filtering unit 442, current detection circuit 500, relay component K, first relay K1, second relay K2, first to fourth AND gates U1~U4, OR gate U5, controllable power device Q, filter inductor L. DETAILED DESCRIPTION

[0088] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0089] In the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "coupled to" or "connected to" another element or an element / circuit is said to be "coupled to" or "connected to" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0090] In the description, the terms "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the numerical descriptors used in this way are interchangeable where appropriate, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0091] In addition, descriptions with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0092] Photovoltaic systems usually include photovoltaic modules and inverters. Photovoltaic modules are large-area solar panels formed by encapsulating and protecting solar panels in series, which can convert solar energy into direct current. The inverter includes a boost circuit 200 and a three-phase inverter circuit 300. The boost circuit 200 can convert the output voltage of the photovoltaic module into a higher and more stable voltage, and the three-phase inverter circuit 300 converts the direct current of the photovoltaic module into alternating current, which can be directly connected to the power grid or directly used for electrical power supply.

[0093] In actual projects, the cables of photovoltaic systems are often easily damaged due to construction or harsh environments, which can cause the photovoltaic cables to short-circuit to the ground. When the photovoltaic cables are short-circuited to the ground, the short-circuit current generated will be at the kiloampere level, which makes the risk of damage to the components in the circuit higher.

[0094] Reference Figure 1 One embodiment of the present application proposes a protection circuit, which is applied to a three-phase inverter circuit 300. The DC side of the three-phase inverter circuit 300 is used to connect the power supply component 100. The output end of each phase of the three-phase inverter circuit 300 is provided with a relay component K. The protection circuit includes: a controllable power device Q, a fault detection module, a current detection circuit 500 and a controller. The controllable power device Q is connected in parallel with the bridge arm in the three-phase inverter circuit 300; the fault detection module is electrically connected to the three-phase inverter circuit 300, and is configured to generate a fault signal when a short circuit to ground fault is detected; the current detection circuit 500 is electrically connected to the three-phase inverter circuit 300, and is configured to detect the output current of each phase of the three-phase inverter circuit 300; the controller is electrically connected to the fault detection module, the current detection circuit 500 and the relay component K respectively, and is configured to control the controllable power device Q to conduct after receiving the fault signal, and disconnect the relay component K of each phase when the output current of each phase meets the zero-crossing condition.

[0095] The power supply assembly 100 may be a photovoltaic assembly, which transmits electric energy to the three-phase inverter circuit 300 through a photovoltaic cable. The short circuit to ground fault may be caused by a short circuit to ground in the cable connected to the positive pole of the photovoltaic assembly, or by a short circuit to ground in the cable connected to the positive pole of the photovoltaic assembly.

[0096] The bridge arm in the three-phase inverter circuit 300 includes an upper bridge arm and a lower bridge arm, and each of the upper bridge arm and the lower bridge arm includes at least one switch tube. The switch tube can be a MOSFET (Metal-Oxide-Semiconductor Field-EffectTransistor) or an IGBT (Insulated Gate Bipolar Transistor), etc., and a freewheeling diode is provided inside the switch tube.

[0097] The controllable power device Q is connected in parallel with the bridge arm in the three-phase inverter circuit 300. When the circuit is working normally, the controllable power device Q is in the off state, which does not affect the normal operation of the three-phase inverter circuit 300 and does not generate excess heat. When a short-circuit fault to ground is detected, the controllable power device Q is turned on to shunt the short-circuit current flowing through the freewheeling diode in the bridge arm to prevent the short-circuit current from damaging other devices in the circuit.

[0098] The controllable power device Q may be a fully controlled power device or a half-controlled power device. The specific type of the controllable power device Q may be selected according to the actual application scenario and is not limited here. For example, the controllable power device Q may be a thyristor, a MOSFET, or an IGBT.

[0099] The fault detection module is electrically connected to the three-phase inverter circuit 300. The fault detection module can monitor the operating status of the three-phase inverter circuit 300 in real time. When a short circuit to ground fault is detected, a fault signal is generated and sent to the controller.

[0100] The current detection circuit 500 is electrically connected to the output end of the three-phase inverter circuit 300, and can detect the output current of each phase of the three-phase inverter circuit 300, and send the detected current value to the controller. The specific structure of the current detection circuit 500 can be selected according to the actual application scenario, and is not limited here. For example, the current detection circuit 500 may include a current sensor.

[0101] The controller is electrically connected to the fault detection module. After receiving the fault signal, the controller controls the controllable power device Q to turn on. The controllable power device Q shunts the short-circuit current flowing through the freewheeling diode in the bridge arm to prevent the short-circuit current from damaging other devices in the circuit.

[0102] The controller is also electrically connected to the current detection circuit 500 and the relay assembly K. After receiving the fault signal, the controller determines whether the output current of each phase meets the zero-crossing condition according to the output current value of each phase sent by the current detection circuit 500. When the output current of each phase meets the zero-crossing condition, the controller disconnects the relay assembly K of each phase to achieve automatic isolation of the fault.

[0103] According to the protection circuit of the present application, when a short circuit to ground occurs between the three-phase inverter circuit 300 and the power supply component 100, the controller controls the controllable power device Q to turn on, and the controllable power device Q shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to prevent excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component K of each phase, which can not only ensure that the relay component K is safely shut down, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0104] Reference Figure 2 , Figure 2 A schematic diagram of a protection circuit in a one-phase inverter circuit is shown. In some embodiments, the bridge arm includes an upper bridge arm and a lower bridge arm, and the fault detection module is configured to generate a first fault signal when a positive electrode short-circuit fault to ground of the power supply component 100 is detected, and / or to generate a second fault signal when a negative electrode short-circuit fault to ground of the power supply component 100 is detected; the controller is configured to drive the controllable power device Q connected in parallel with the upper bridge arm to conduct when receiving the first fault signal; and / or drive the controllable power device Q connected in parallel with the lower bridge arm to conduct when receiving the second fault signal.

[0105] When a short circuit occurs to the ground in the cable connected to the positive pole of the photovoltaic module, the short-circuit current will flow through the upper bridge arm. When a short circuit occurs to the ground in the cable connected to the negative pole of the photovoltaic module, the short-circuit current will flow through the lower bridge arm.

[0106] When the fault detection module detects a short-circuit fault between the positive pole of the power supply component 100 and the ground, the fault detection module transmits a first fault signal to the controller, and the controller drives the controllable power device Q connected in parallel with the upper bridge arm to turn on. That is, when the positive pole of the power supply component 100 is short-circuited to the ground, the controllable power device Q connected in parallel with the upper bridge arm is used to shunt the short-circuit current.

[0107] When the fault detection module detects a short-circuit fault between the negative pole of the power supply component 100 and the ground, the second fault signal is transmitted to the controller, and the controller drives the controllable power device Q connected in parallel with the lower bridge arm to turn on. That is, when the negative pole of the power supply component 100 is short-circuited to the ground, the controllable power device Q connected in parallel with the lower bridge arm is used to shunt the short-circuit current.

[0108] In some embodiments, the fault detection module includes: an overcurrent detection module 410, a common-mode current detection module 420, a voltage detection module 430 and a signal conversion module. The overcurrent detection module 410 is electrically connected to the current detection circuit 500, and is configured to generate a first overcurrent signal when the negative output current of at least one phase is greater than the first current threshold, and / or to generate a second overcurrent signal when the positive output current of at least one phase is greater than the second current threshold; the common-mode current detection module 420 is electrically connected to the DC side of the three-phase inverter circuit 300, and is configured to generate a first common-mode current signal when the negative common-mode current on the DC side of the three-phase inverter circuit 300 is greater than the third current threshold, and / or to generate a second common-mode current signal when the positive common-mode current on the DC side of the three-phase inverter circuit 300 is greater than the fourth current threshold; the voltage detection module 430 is respectively connected to the positive pole of the power supply component 100, the negative pole of the power supply component 100 and the ground node The power supply assembly 100 is electrically connected to a point, and is configured to generate a first voltage signal to the ground when the voltage to the ground between the positive electrode of the power supply assembly 100 and the ground node is less than a voltage threshold, and / or to generate a second voltage signal to the ground when the voltage to the ground between the negative electrode of the power supply assembly 100 and the ground node is less than a second voltage threshold; the signal conversion module is electrically connected to the overcurrent detection module 410, the common-mode current detection module 420 and the voltage detection module 430, respectively, and is configured to generate a first fault signal when receiving a first overcurrent signal, a first common-mode current signal and / or a first voltage signal to the ground; and / or the signal conversion module is configured to generate a second fault signal when receiving at least one of a second overcurrent signal, a second common-mode current signal and a second voltage signal to the ground.

[0109] The overcurrent detection module 410 is electrically connected to the current detection circuit 500, and is mainly used to compare the current value detected by the current detection circuit 500. The current detection circuit 500 is electrically connected to the output end of the three-phase inverter circuit 300, and the current detected by it is AC. The overcurrent detection module 410 can judge the positive output current and the negative output current in the output current respectively.

[0110] The overcurrent detection module 410 generates a first overcurrent signal when the negative output current of at least one phase is greater than the first current threshold; the overcurrent detection module 410 generates a second overcurrent signal when the positive output current of at least one phase is greater than the second current threshold. The specific value of the first current threshold can be selected according to the actual application scenario and is not limited here. For example, the first current threshold can be 13A, 15A or 20A, etc. The absolute value of the specific value of the second current threshold can be equal to the first current threshold.

[0111] The specific structure of the overcurrent detection module 410 can be selected according to the actual application scenario and is not limited here. For example, the overcurrent detection module 410 may include a comparator, the positive input terminal of the comparator is electrically connected to the output terminal of the current detection circuit 500, and the negative input terminal of the comparator is used to access the first current threshold.

[0112] The common-mode current detection module 420 is arranged at the input end of the three-phase inverter circuit 300, and can determine whether there is an abnormally large current in the three-phase inverter circuit 300 by detecting whether there is a common-mode current on the positive and negative busbars. Under normal circumstances, the currents on the positive and negative busbars flow in opposite directions and are the same in magnitude. Therefore, under normal circumstances, the common-mode current on the positive and negative busbars is zero. When the common-mode current detection module 420 detects that the negative common-mode current on the positive and negative busbars is greater than the third current threshold, it indicates that the cable connected to the positive pole of the photovoltaic module may have a short-circuit fault to the ground, and a first common-mode current signal is generated; when the common-mode current detection module 420 detects that the positive common-mode current on the positive and negative busbars is greater than the fourth current threshold, it indicates that the cable connected to the negative pole of the photovoltaic module may have a short-circuit fault to the ground, and a second common-mode current signal is generated.

[0113] The specific value of the third current threshold can be selected according to the actual application scenario and is not limited here. For example, the first current threshold can be 1A or 2A, etc. The absolute value of the specific value of the fourth current threshold can be equal to the third current threshold.

[0114] When the negative pole of the photovoltaic module is short-circuited to the ground, the potential difference between the negative pole of the photovoltaic module and the ground node will decrease rapidly due to the existence of the short-circuit current. Therefore, when the voltage detection module 430 detects that the voltage to the ground between the negative pole and the ground node is less than the voltage threshold, it indicates that the cable connected to the negative pole of the photovoltaic module may have a short-circuit fault to the ground; similarly, when the positive pole of the photovoltaic module is short-circuited to the ground, the potential difference between the positive pole of the photovoltaic module and the ground node will decrease rapidly due to the existence of the short-circuit current. Therefore, when the voltage detection module 430 detects that the voltage to the ground between the positive pole and the ground node is less than the voltage threshold, it indicates that the cable connected to the positive pole of the photovoltaic module may have a short-circuit fault to the ground.

[0115] The specific values ​​of the first voltage threshold and the second voltage threshold can be selected according to the actual application scenario, and are not limited here. The specific values ​​of the first voltage threshold and the second voltage threshold can be the same or different. For example, the first voltage threshold can be 100V or 150V, and the second voltage threshold can be 100V or 130V, etc.

[0116] When the signal conversion module receives at least one of the first overcurrent signal, the first common-mode current signal and the first voltage-to-ground signal, it indicates that the cable connected to the positive pole of the photovoltaic component may have a short-circuit fault to the ground, and generates a first fault signal; when the signal conversion module receives at least one of the second overcurrent signal, the second common-mode current signal and the second voltage-to-ground signal, it indicates that the cable connected to the negative pole of the photovoltaic component may have a short-circuit fault to the ground, and generates a second fault signal.

[0117] Reference Figure 3 In some embodiments, the signal conversion module includes a first AND gate U1, the input end of the first AND gate U1 is electrically connected to the output ends of the overcurrent detection module 410, the common mode current detection module 420 and the voltage detection module 430, and the output end of the AND gate is electrically connected to the controller.

[0118] When the first AND gate U1 receives the first overcurrent signal, the first common-mode current signal and the first voltage signal to ground, it indicates that the cable connected to the positive pole of the photovoltaic component has a short-circuit fault to ground, and a first fault signal is generated; when the first AND gate U1 receives the second overcurrent signal, the second common-mode current signal and the voltage signal to ground, it indicates that the cable connected to the negative pole of the photovoltaic component has a short-circuit fault to ground, and a second fault signal is generated.

[0119] By using the first AND gate U1 to generate a fault signal, the accuracy of the fault signal can be ensured, false triggering due to the presence of interference signals can be avoided, and the accuracy of the protection circuit action can be improved.

[0120] Reference Figure 4 and Figure 5 In some embodiments, the signal conversion module includes: a second AND gate U2, a third AND gate U3, a fourth AND gate U4 and an OR gate U5. The input end of the second AND gate U2 is electrically connected to the output ends of the overcurrent detection module 410 and the common mode current detection module 420 respectively; the third AND gate U3, the input end of the third AND gate U3 is electrically connected to the output ends of the overcurrent detection module 410 and the voltage detection module 430 respectively; the fourth AND gate U4, the input end of the fourth AND gate U4 is electrically connected to the output ends of the common mode current detection module 420 and the voltage detection module 430 respectively; the OR gate U5, the input end of the OR gate U5 is electrically connected to the output ends of the second AND gate U2, the third AND gate U3 and the fourth AND gate U4 respectively, and the output end of the OR gate U5 is electrically connected to the controller.

[0121] Reference Figure 4 When the second AND gate U2 receives the first overcurrent signal and the first common-mode current signal at the same time, it outputs a high-level signal. When the third AND gate U3 receives the first overcurrent signal and the first ground voltage signal at the same time, it outputs a high-level signal. When the fourth AND gate U4 receives the first common-mode current signal and the first ground voltage signal at the same time, it outputs a high-level signal.

[0122] The input end of the OR gate U5 is electrically connected to the output ends of the second AND gate U2, the third AND gate U3 and the fourth AND gate U4 respectively, that is, the signal conversion module generates a first fault signal when receiving any two of the first overcurrent signal, the first common-mode current signal and the first ground voltage signal.

[0123] Reference Figure 5 When the second AND gate U2 receives the second overcurrent signal and the second common-mode current signal at the same time, it outputs a high-level signal; when the third AND gate U3 receives the second overcurrent signal and the second ground voltage signal at the same time, it outputs a high-level signal; when the fourth AND gate U4 receives the second common-mode current signal and the second ground voltage signal at the same time, it outputs a high-level signal.

[0124] The input end of the OR gate U5 is electrically connected to the output ends of the second AND gate U2, the third AND gate U3 and the fourth AND gate U4 respectively, that is, the signal conversion module generates a second fault signal when receiving any two of the second overcurrent signal, the second common-mode current signal and the second ground voltage signal.

[0125] The signal conversion module adopts a logical combination of an AND gate and an OR gate U5 to generate a fault signal when any two modules among the overcurrent detection module 410, the common-mode current detection module 420 and the voltage detection module 430 generate corresponding signals. This can ensure the accuracy of the fault signal and avoid false triggering due to the presence of interference signals, and can also reduce the judgment steps, making the fault signal generation process simpler.

[0126] Continue to refer to Figures 3 to 5 In some embodiments, the signal conversion module further includes a signal latch circuit 441. The signal latch circuit 441 is electrically connected to the output end of the voltage detection module 430, and is mainly used to maintain the level of the ground voltage signal when the voltage detection module 430 generates the first ground voltage signal or the second ground voltage signal, so as to provide a judgment time for the logic judgment of the AND gate.

[0127] In some embodiments, the signal conversion module also includes a data filtering unit 442, the input end of the data filtering unit 442 is electrically connected to the output end of the overcurrent detection module 410, the common mode current detection module 420 and the voltage detection module 430, respectively, and is configured to filter the first overcurrent signal, the second overcurrent signal, the first common mode current signal, the second common mode current signal, the first ground voltage signal and / or the second ground voltage signal.

[0128] The data filtering unit 442 is mainly used to eliminate noise and interference in the first overcurrent signal, the second overcurrent signal, the first common mode current signal, the second common mode current signal, the first voltage to ground signal and the second voltage to ground signal. Data filtering can be implemented by software filtering, which converts the first overcurrent signal, the second overcurrent signal, the first common mode current signal, the second common mode current signal, the first voltage to ground signal and the second voltage to ground signal generated by the fault detection module into digital signals through analog-to-digital conversion, and implements filtering through a filtering algorithm. It has high flexibility and adjustability.

[0129] In some embodiments, the relay assembly K includes a plurality of relays connected in series, the controller is electrically connected to each relay, and is configured to use at least two relay shutoff sequences when the relay assembly K is shut off multiple times.

[0130] Each time the relay assembly K is controlled to be turned off, the relays are turned off in a certain order. The small current in the process of turning off will cause wear to the relay that is turned off first. When the relay assembly K is controlled to be turned off multiple times, at least two relay turn-off sequences are used to balance the wear of the relays and extend the life of the relays.

[0131] As an example, the relay component K includes a first relay K1, a second relay K2, and a third relay connected in series. When the relay component K is turned off for the first time, the first relay K1, the second relay K2, and the third relay are turned off in sequence. When the relay component K is turned off for the second time, the second relay K2 is turned off first, and then the first relay K1 and the third relay are turned off in sequence. When the relay component K is turned off for the third time, the third relay is turned off first, and then the first relay K1 and the second relay K2 are turned off in sequence.

[0132] Reference Figure 6 In some embodiments, the relay assembly K includes a first relay K1 and a second relay K2 connected in series, and the controller alternately performs the following operations: controlling the first relay K1 to be disconnected before the second relay K2; or controlling the second relay K2 to be disconnected before the first relay K1.

[0133] When the controller controls the relay component K to be turned off for the first time, the controller controls the first relay K1 to be disconnected before the second relay K2. When the controller controls the relay component K to be turned off for the second time, the controller controls the second relay K2 to be disconnected before the first relay K1. Repeating the above operations can balance the wear of the first relay K1 and the second relay K2 and extend the life of the first relay K1 and the second relay K2.

[0134] In some embodiments, the controllable power device Q is a fully controlled power device, and the output node of the three-phase inverter circuit 300 is also connected to a filter inductor L, and one end of the filter inductor L away from the output node is electrically connected to the output end of the fully controlled power device.

[0135] Fully controlled power devices have higher control accuracy and faster response speed. They can be turned on in time when a short circuit to ground occurs to avoid damage to other devices caused by short-circuit current.

[0136] The filter inductor L is arranged between the output node of the three-phase inverter circuit 300 and the output end of the fully controlled power device, and can protect the safety of the power supply and the circuit through reverse current when a short circuit to ground occurs.

[0137] In other embodiments, the first end of the filter inductor L is electrically connected to the output end of the fully-controlled power device, and the second end of the filter inductor L is electrically connected to the first end of the relay assembly K, so as to achieve electrical isolation between the three-phase inverter circuit 300 and the power grid.

[0138] In some embodiments, the controller includes: a pre-breaking module and a main breaking module. The pre-breaking module is configured to enter the pre-breaking stage after receiving the fault signal, and determine the zero-crossing moment of the output current of each phase of the three-phase inverter circuit 300 for the first time; the main breaking module is configured to enter the main breaking stage after the pre-breaking stage ends, and control the relay component K of the corresponding phase to disconnect when each phase meets at least one of the following conditions: the time difference between the current moment and the zero-crossing moment is less than the threshold; or the output current is less than the fifth current threshold.

[0139] After receiving the fault signal from the fault detection module, the pre-breaking module determines the zero-crossing moment of the first zero-crossing point in each phase output current according to the detection result of the current detection module. The zero-crossing moment refers to the time point when the current changes from the positive direction to the negative direction or from the negative direction to the positive direction.

[0140] The main disconnecting module disconnects the relay assembly K of the corresponding phase at the target time. The target time is a time point determined according to the zero-crossing time, and the time difference between the time point and the zero-crossing time is less than the preset threshold. This ensures that the relay assembly K is disconnected when the current crosses zero or is close to zero, so as to reduce the generation of arcs and the impact of current on the relay assembly K. The design of the threshold can be selected according to the actual application scenario and is not limited here. For example, the threshold can be 0.5ms.

[0141] When the output current of the main disconnecting module is less than the fifth current threshold, the relay component K of the corresponding phase is disconnected. It can be ensured that the relay component K is disconnected when the current is close to zero. The specific value of the fifth current threshold can be selected according to the actual application scenario and is not limited here. For example, the fifth current threshold can be 0.5A or 0.8A, etc.

[0142] The main disconnect module disconnects the relay assembly K of the corresponding phase at the target time or when the output current is less than the fifth current threshold, which can ensure that the current is small when the relay assembly K is disconnected, and avoid damage to the relay assembly K by the impact current when the relay assembly K is disconnected.

[0143] Reference Figure 7 As an example, the three-phase inverter includes phase A, phase B and phase C respectively. At time t1, it is detected that the negative pole of the photovoltaic component in phase A is short-circuited to the ground. The pre-breaking module determines the zero-crossing time of the first zero-crossing point in the output current of each phase, that is, the zero-crossing time t2 of the zero-crossing point of phase A. The main breaking module controls the relay component K at the output end of phase A at the target time t3. The time difference between the target time t3 and the zero-crossing time t2 is less than the threshold, so that the relay component K of phase A is turned off when the output current meets the zero-crossing condition. At time t5 shown in the figure, the current of phase C is less than the fifth current threshold, so the relay component K of phase C is turned off at time t5 shown in the figure. At time t4 shown in the figure, the current of phase B is less than the fifth current threshold, so the relay component K of phase B is turned off at time t4 shown in the figure.

[0144] In some embodiments, the three-phase inverter circuit 300 adopts a three-phase four-wire connection method, and the main disconnecting module is also configured to enter the main disconnecting stage after the pre-disconnecting stage ends, and control the relay component K of the corresponding phase to disconnect when each phase meets at least one of the following conditions: the time difference between the current moment and the zero-crossing moment is less than the threshold; the output current is less than the fifth current threshold; or, the phase angle of the phase voltage is within the target phase angle range; wherein, in the case of a positive pole to ground short circuit fault, the target phase angle range is [180°, 180+θ1°]; in the case of a negative pole to ground short circuit fault, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

[0145] When the positive pole is short-circuited to the ground and the phase angle of the phase voltage is at [180°, 180+θ1°], there is no current output in the corresponding phase. At this time, turning off the relay component K of the corresponding phase can avoid the impact current from damaging the relay component K. Similarly, when the negative pole is short-circuited to the ground and the phase angle of the phase voltage is at [0°, θ2°], there is no current output in the corresponding phase. At this time, turning off the relay component K of the corresponding phase can avoid the impact current from damaging the relay component K.

[0146] The values ​​of θ1 and θ2 can be selected according to the actual application scenario and are not limited here. For example, θ1 and θ2 can be 90°.

[0147] The principle of controlling the relay component K of the corresponding phase to disconnect when the time difference between the current moment and the zero-crossing moment is less than the threshold or the output current is less than the fifth current threshold can be referred to the aforementioned embodiment and will not be repeated here.

[0148] The main disconnecting module disconnects the relay component K of the corresponding phase at the target time or when the output current is less than the fifth current threshold, or when the phase angle of the phase voltage is within the target phase angle range, thereby ensuring that the current is small when the relay component K is disconnected, thereby avoiding damage to the relay component K due to the impact current when the relay component K is disconnected.

[0149] Reference Figure 8 As an example, the three-phase inverter includes phase A, phase B and phase C. At time t1, a short circuit fault of the negative pole of the photovoltaic module to the ground is detected in phase A. The pre-breaking module determines the zero-crossing time of the first zero-crossing point in the output current of each phase, and enters the main breaking stage at time t2. At time t2, the voltage phase angle of phase A satisfies 0<θ A <θ2, therefore, the relay component K at the output end of phase A is controlled at time t2, the phase C current at time t3 shown in the figure is less than the fifth current threshold, therefore, the phase C relay component K is turned off at time t3 shown in the figure, the phase B current at time t4 shown in the figure is less than the fifth current threshold, therefore, the phase B relay component K is turned off at time t4 shown in the figure.

[0150] Reference Fig. 9 In other embodiments, a positive-to-ground short circuit fault of the photovoltaic module in phase A is detected at time t1, and the pre-breaking module determines the zero-crossing time of the first zero-crossing point in the output current of each phase, and enters the main breaking stage at time t2. At time t2, the voltage phase angle of phase B satisfies 0<θ B <180+θ1°, therefore the relay component K at the B phase output end is controlled at time t2, the A phase current is less than the fifth current threshold at time t3 shown in the figure, therefore the A phase relay component K is turned off at time t3 shown in the figure, the C phase current is less than the fifth current threshold at time t4 shown in the figure, therefore the C phase relay component K is turned off at time t4 shown in the figure.

[0151] Reference Fig.10 An embodiment of the present application proposes a control method, which is applied to a three-phase inverter circuit 300. The DC side of the three-phase inverter circuit 300 is used to connect the power supply component 100. Each phase output end of the three-phase inverter circuit 300 is provided with a relay component K. The bridge arm in the three-phase inverter circuit 300 is connected in parallel with a controllable power device Q. The control method includes: step 10, step 20 and step 30.

[0152] Step 10: When a short circuit to ground fault is detected in the power supply assembly 100, the controllable power device Q is controlled to be turned on;

[0153] Step 20, detecting the output current of each phase of the three-phase inverter circuit 300;

[0154] Step 30: After the controllable power device Q is turned on and the output current of each phase meets the zero-crossing condition, the relay assembly K of each phase is disconnected.

[0155] An embodiment of the present application provides a control method, and the executor of the control method may be the aforementioned controller or a functional module or functional entity in the controller that can implement the control method. The control method provided in the embodiment of the present application is described below using the controller as an example of the executor.

[0156] The power supply assembly 100 may be a photovoltaic assembly, which transmits electric energy to the three-phase inverter circuit 300 through a photovoltaic cable. The short circuit to ground fault may be caused by a short circuit to ground in the cable connected to the positive pole of the photovoltaic assembly, or by a short circuit to ground in the cable connected to the positive pole of the photovoltaic assembly.

[0157] When the circuit is working normally, the controllable power device Q is in the off state, which does not affect the normal operation of the three-phase inverter circuit 300 and does not generate excess heat. When a short circuit to ground occurs in the power supply component 100, the controller controls the controllable power device Q to turn on, and the controllable power device Q shunts the short-circuit current flowing through the freewheeling diode in the bridge arm to prevent the short-circuit current from damaging other devices in the circuit.

[0158] The controller monitors the output current of each phase of the three-phase inverter circuit 300 in real time. When the output current of each phase meets the zero-crossing condition, the controller disconnects the relay assembly K of each phase to achieve automatic isolation of the fault.

[0159] When the output current of each phase meets the zero-crossing condition, the relay assembly K of each phase is disconnected, which means that the relay assembly K of each phase is disconnected when the output current of the corresponding phase is equal to zero or close to zero, so as to achieve safe shutdown of the relay assembly K.

[0160] When the output current of each phase meets the zero-crossing condition, the controller disconnects the relay assembly K of each phase, which can reduce the generation of arc and the impact of current on the relay assembly K, and achieve safe shutdown of the relay assembly K. Disconnecting the relay assembly K of each phase can cut off the short-circuit current loop and prevent the short-circuit current from damaging the components in the circuit.

[0161] According to the control method of the present application, when a short circuit to ground occurs between the three-phase inverter circuit 300 and the power supply component 100, the controller controls the controllable power device Q to turn on, and the controllable power device Q shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to avoid excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component K of each phase, which can not only ensure that the relay component K is safely shut down, but also cut off the short-circuit current loop to avoid the short-circuit current from damaging the components in the circuit.

[0162] In some embodiments, when the output current of each phase meets the zero-crossing condition, the relay component K of each phase is disconnected, including: in the first stage, determining the zero-crossing moment of the first zero-crossing point in the output current of each phase of the three-phase inverter circuit 300; in the second stage, when each phase meets at least one of the following conditions, controlling the relay component K of the corresponding phase to disconnect when the time difference between the current moment and the zero-crossing moment is less than a threshold; or, the output current is less than the fifth current threshold.

[0163] In the first stage, the controller determines the zero-crossing moment of the output current of each phase of the three-phase inverter circuit 300 for the first time and records the zero-crossing moment. The zero-crossing point refers to the point where the current changes from a positive direction to a negative direction or from a negative direction to a positive direction.

[0164] In the second stage, at the target time or when the output current is less than the fifth current threshold, the relay component K of the corresponding phase is disconnected, which can ensure that the current is small when the relay component K is disconnected, and avoid the impact current when the relay component K is disconnected from damaging the relay component K.

[0165] Reference Fig.11 As an example, the three-phase inverter includes phase A, phase B and phase C respectively. At time t1, it is detected that the positive pole of the photovoltaic component in phase A is short-circuited to the ground. The pre-breaking module determines the zero-crossing time of the first zero-crossing point in the output current of each phase, that is, the zero-crossing time t2 of the zero-crossing point of phase B. The main breaking module controls the relay component K at the output end of phase B at the target time t3. The time difference between the target time t3 and the zero-crossing time t2 is less than the threshold, so that the relay component K of phase B is turned off when the output current meets the zero-crossing condition. At time t4 shown in the figure, the current of phase A is less than the fifth current threshold, so the relay component K of phase A is turned off at time t4 shown in the figure. At time t5 shown in the figure, the current of phase C is less than the fifth current threshold, so the relay component K of phase C is turned off at time t5 shown in the figure.

[0166] In some embodiments, the three-phase inverter circuit 300 adopts a three-phase four-wire connection method, and the control method also includes: obtaining the phase angle of each phase voltage; in the second stage, when each phase meets at least one of the following conditions, controlling the relay component K of the corresponding phase to disconnect: the time difference between the current moment and the zero-crossing moment is less than the threshold; the output current is less than the fifth current threshold; or, the phase angle of the phase voltage is within the target phase angle range; wherein, in the case of a positive pole to ground short circuit fault, the target phase angle range is [180°, 180+θ1°]; in the case of a negative pole to ground short circuit fault, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

[0167] When the positive pole is short-circuited to the ground and the phase angle of the phase voltage is at [180°, 180+θ1°], there is no current output in the corresponding phase. At this time, turning off the relay component K of the corresponding phase can avoid the impact current from damaging the relay component K. Similarly, when the negative pole is short-circuited to the ground and the phase angle of the phase voltage is at [0°, θ2°], there is no current output in the corresponding phase. At this time, turning off the relay component K of the corresponding phase can avoid the impact current from damaging the relay component K.

[0168] In the second stage, at the target time or when the output current is less than the fifth current threshold, or when the phase angle of the phase voltage is within the target phase angle range, the relay component K of the corresponding phase is disconnected, which can ensure that the current is small when the relay component K is disconnected, thereby avoiding damage to the relay component K by the impact current when the relay component K is disconnected.

[0169] In some embodiments, the bridge arm of the three-phase inverter circuit 300 includes an upper bridge arm, and when a short-circuit fault to ground is detected, the controllable power device Q is controlled to be turned on, including: when it is detected that the negative output current of at least one phase of the three-phase inverter circuit 300 is greater than the first current threshold, and / or the negative common-mode current on the DC side of the three-phase inverter circuit 300 is greater than the third current threshold, and / or the ground voltage between the positive pole of the power supply component and the ground node is less than the first voltage threshold, it is determined that the positive pole of the power supply component 100 is short-circuited to the ground; when the positive pole of the power supply component 100 is short-circuited to the ground, the controllable power device Q connected in parallel with the upper bridge arm is controlled to be turned on.

[0170] The negative output current of at least one phase of the three-phase inverter circuit 300 is greater than the first current threshold, or the negative common-mode current on the positive and negative busbars is greater than the third current threshold, or the voltage to ground between the positive pole of the power supply component and the ground node is less than the first voltage threshold, or when the above three situations occur at the same time, indicating that the cable connected to the positive pole of the photovoltaic component has a short-circuit fault to the ground, the short-circuit current will flow through the upper bridge arm. The specific principle can be referred to the aforementioned embodiment and will not be repeated here.

[0171] When a short circuit occurs to the ground in the cable connected to the positive pole of the photovoltaic module, the controllable power device Q connected in parallel with the upper bridge arm is controlled to be turned on, so as to shunt the short-circuit current flowing through the upper bridge arm and prevent the short-circuit current from damaging other devices.

[0172] In some embodiments, the bridge arm of the three-phase inverter circuit 300 includes a lower bridge arm, and when a short-circuit fault to ground is detected, the controllable power device Q is controlled to be turned on, including: when it is detected that the positive output current of at least one phase of the three-phase inverter circuit 300 is greater than the second current threshold, and / or the positive common-mode current on the DC side of the three-phase inverter circuit 300 is greater than the fourth current threshold, and / or the ground voltage between the negative pole of the power supply component 100 and the ground node is less than the second voltage threshold, it is determined that the negative pole of the power supply component 100 is short-circuited to the ground; when the negative pole of the power supply component 100 is short-circuited to the ground, the controllable power device Q connected in parallel with the lower bridge arm is controlled to be turned on.

[0173] When at least one of the following three situations occurs: the positive output current of at least one phase of the three-phase inverter circuit 300 is greater than the second current threshold, or the positive common-mode current on the DC side of the three-phase inverter circuit 300 is greater than the fourth current threshold, or the voltage to ground between the negative pole of the power supply component 100 and the ground node is less than the voltage threshold, it indicates that a short-circuit fault has occurred to the ground in the cable connected to the negative pole of the photovoltaic component, and the short-circuit current will flow through the lower bridge arm. The specific principle can be referred to the aforementioned embodiment and will not be repeated here.

[0174] When a short circuit occurs to the ground in the cable connected to the negative pole of the photovoltaic module, the controllable power device Q connected in parallel with the lower bridge arm is controlled to be turned on, so as to shunt the short-circuit current flowing through the lower bridge arm and prevent the short-circuit current from damaging other devices.

[0175] In some embodiments, the relay assembly K includes a plurality of relays connected in series, and the control method further includes: when the relay assembly K is controlled to be turned off multiple times, at least two relay turning-off sequences are used for execution.

[0176] Each time the relay assembly K is controlled to be turned off, the relays are turned off in a certain order. The small current in the process of turning off will cause wear to the relay that is turned off first. When the relay assembly K is controlled to be turned off multiple times, at least two relay turn-off sequences are used to balance the wear of the relays and extend the life of the relays.

[0177] In some embodiments, the relay assembly K includes a first relay K1 and a second relay K2 connected in series, and the control method further includes: alternately performing the following operations: controlling the first relay K1 to be disconnected before the second relay K2; or controlling the second relay K2 to be disconnected before the first relay K1.

[0178] When the controller controls the relay component K to be turned off for the first time, the controller controls the first relay K1 to be disconnected before the second relay K2, and when the controller controls the relay component K to be turned off for the second time, the controller controls the second relay K2 to be disconnected before the first relay K1. Alternatively, when the controller controls the relay component K to be turned off for the first time, the controller controls the second relay K2 to be disconnected before the first relay K1, and when the controller controls the relay component K to be turned off for the second time, the controller controls the first relay K1 to be disconnected before the second relay K2, and repeats the above operations, so that the wear of the first relay K1 and the second relay K2 can be balanced, and the life of the first relay K1 and the second relay K2 can be extended.

[0179] An embodiment of the present application proposes a photovoltaic system, which includes a power supply component 100 and an inverter, wherein the DC side of the inverter is used to connect the power supply component 100, and the AC side of the inverter is used to connect to a power grid, and the inverter includes the aforementioned protection circuit, or includes a controller that implements the aforementioned control method.

[0180] The inverter includes a three-phase inverter circuit 300 and the aforementioned protection circuit. The DC side of the three-phase inverter circuit 300 is used to connect to the power supply component 100, and the AC side of the three-phase inverter circuit 300 is used to connect to the power grid. The protection circuit is electrically connected to the three-phase inverter circuit 300. When a short circuit to ground occurs between the three-phase inverter circuit 300 and the power supply component 100, the controller controls the controllable power device Q in the protection circuit to turn on, and disconnects the relay component K of each phase when the output current of each phase meets the zero-crossing condition.

[0181] The specific structure and function of the protection circuit can refer to the above embodiments and will not be described in detail here.

[0182] According to the photovoltaic system of the present application, when a short circuit to ground occurs between the three-phase inverter circuit 300 and the power supply component 100, the controller controls the controllable power device Q to turn on, and the controllable power device Q shunts the short-circuit current flowing through the freewheeling diode in the lower bridge arm to prevent excessive short-circuit current from damaging the freewheeling diode in the bridge arm. In addition, when the output current of each phase meets the zero-crossing condition, the controller disconnects the relay component K of each phase, which can not only ensure that the relay component K is safely shut down, but also cut off the short-circuit current loop to prevent the short-circuit current from damaging the components in the circuit.

[0183] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A protection circuit, characterized in that: Applied to a three-phase inverter circuit, the DC side of the three-phase inverter circuit is used to connect a power supply component, each phase output end of the three-phase inverter circuit is provided with a relay component, and the protection circuit includes: A controllable power device connected in parallel with the bridge arm in the three-phase inverter circuit; a fault detection module, electrically connected to the three-phase inverter circuit and configured to generate a fault signal when a short-circuit to ground fault is detected; a current detection circuit, electrically connected to the three-phase inverter circuit and configured to detect an output current of each phase of the three-phase inverter circuit; The controller is electrically connected to the fault detection module, the current detection circuit and the relay respectively, and is configured to control the controllable power device to be turned on after receiving the fault signal, and to disconnect the relay components of each phase when the output current of each phase meets the zero-crossing condition.

2. The protection circuit according to claim 1, characterized in that: The bridge arm comprises an upper bridge arm and a lower bridge arm, and the fault detection module is configured to generate a first fault signal when a positive electrode of the power supply component is detected to be short-circuited to ground, and / or to generate a second fault signal when a negative electrode of the power supply component is detected to be short-circuited to ground; The controller is configured to drive the controllable power device connected in parallel with the upper bridge arm to conduct when the first fault signal is received; and / or drive the controllable power device connected in parallel with the lower bridge arm to conduct when the second fault signal is received.

3. The protection circuit according to claim 2, characterized in that: The fault detection module comprises: an overcurrent detection module, electrically connected to the current detection circuit, and configured to generate a first overcurrent signal when the negative output current of at least one phase is greater than a first current threshold, and / or to generate a second overcurrent signal when the positive output current of at least one phase is greater than a second current threshold; a common-mode current detection module, electrically connected to the DC side of the three-phase inverter circuit, and configured to generate a first common-mode current signal when a negative common-mode current on the DC side of the three-phase inverter circuit is greater than a third current threshold, and / or to generate a second common-mode current signal when a positive common-mode current on the DC side of the three-phase inverter circuit is greater than a fourth current threshold; a voltage detection module, electrically connected to the positive electrode of the power supply component, the negative electrode of the power supply component and the ground node, respectively, and configured to generate a first voltage-to-ground signal when the voltage to ground between the positive electrode of the power supply component and the ground node is less than a first voltage threshold, and / or to generate a second voltage-to-ground signal when the voltage to ground between the negative electrode of the power supply component and the ground node is less than a second voltage threshold; a signal conversion module, electrically connected to the overcurrent detection module, the common-mode current detection module and the voltage detection module, respectively, and configured to generate a first fault signal upon receiving at least one of the first overcurrent signal, the first common-mode current signal and the first voltage-to-ground signal; and / or The signal conversion module is configured to generate a second fault signal when receiving at least one of the second overcurrent signal, the second common-mode current signal, and the second voltage-to-ground signal.

4. The protection circuit according to claim 3, characterized in that: The signal conversion module comprises: A first AND gate, wherein the input end of the first AND gate is electrically connected to the output ends of the overcurrent detection module, the common-mode current detection module and the voltage detection module respectively, and the output end of the first AND gate is electrically connected to the controller.

5. The protection circuit according to claim 3, characterized in that: The signal conversion module comprises: A second AND gate, wherein the input end of the second AND gate is electrically connected to the output end of the overcurrent detection module and the output end of the common mode current detection module respectively; a third AND gate, wherein the input end of the third AND gate is electrically connected to the output end of the overcurrent detection module and the output end of the voltage detection module respectively; a fourth AND gate, wherein input terminals of the fourth AND gate are electrically connected to output terminals of the common-mode current detection module and the voltage detection module respectively; An OR gate, wherein the input end of the OR gate is electrically connected to the output ends of the second AND gate, the third AND gate and the fourth AND gate respectively, and the output end of the OR gate is electrically connected to the controller.

6. The protection circuit according to claim 3, characterized in that: The signal conversion module also includes: A data filtering unit, wherein the input end of the data filtering unit is electrically connected to the output ends of the overcurrent detection module, the common-mode current detection module and the voltage detection module respectively, and is configured to filter the first overcurrent signal, the second overcurrent signal, the first common-mode current signal, the second common-mode current signal, the first voltage-to-ground signal and / or the second voltage-to-ground signal.

7. The protection circuit according to any one of claims 1 to 6, characterized in that: The relay assembly includes a plurality of relays connected in series, the controller is electrically connected to each of the relays, and is configured to use at least two relay shutoff sequences when controlling the relay assembly to shut off multiple times.

8. The protection circuit according to claim 7, characterized in that: The relay assembly includes a first relay and a second relay connected in series, and the controller alternately performs the following operations: Control the first relay to be disconnected before the second relay; or, The second relay is controlled to be opened before the first relay.

9. The protection circuit according to any one of claims 1 to 6, characterized in that: The controllable power device is a fully controlled power device. The output node of the three-phase inverter circuit is also connected to a filter inductor. One end of the filter inductor away from the output node is electrically connected to the output end of the fully controlled power device.

10. The protection circuit according to any one of claims 1 to 6, characterized in that: The controller comprises: A pre-breaking module is configured to enter a pre-breaking phase after receiving the fault signal, and determine the zero-crossing moment of the first zero-crossing point in the output current of each phase of the three-phase inverter circuit; The main disconnecting module is configured to enter the main disconnecting stage after the pre-disconnecting stage is completed, and control the relay assembly of the corresponding phase to disconnect when each phase meets at least one of the following conditions: The time difference between the current moment and the zero-crossing moment is less than a threshold; or, The output current is less than a fifth current threshold.

11. The protection circuit according to claim 10, characterized in that: The three-phase inverter circuit adopts a three-phase four-wire connection method, and the main disconnection module is further configured to enter the main disconnection stage after the pre-disconnection stage ends, and control the relay assembly of the corresponding phase to disconnect when each phase meets at least one of the following conditions: The time difference between the current moment and the zero-crossing moment is less than a threshold; The output current is less than a fifth current threshold; or, The phase angle of the phase voltage is within the target phase angle range; Among them, when the positive pole is short-circuited to the ground, the target phase angle range is [180°, 180+θ1°]; when the negative pole is short-circuited to the ground, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

12. A control method, characterized in that: Applied to a three-phase inverter circuit, the DC side of the three-phase inverter circuit is used to connect a power supply component, each phase output end of the three-phase inverter circuit is provided with a relay component, and a bridge arm in the three-phase inverter circuit is connected in parallel with a controllable power device, and the control method includes: When a short circuit to ground fault is detected in the power supply component, controlling the controllable power device to be turned on; Detecting the output current of each phase of the three-phase inverter circuit; After the controllable power device is turned on and the output current of each phase meets the zero-crossing condition, the relay components of each phase are disconnected.

13. The control method according to claim 12, characterized in that: When the output current of each phase meets the zero-crossing condition, disconnecting the relay components of each phase includes: In the first stage, determining the zero-crossing moment of the first zero-crossing point in the output current of each phase of the three-phase inverter circuit; In the second stage, when each phase satisfies at least one of the following conditions, the relay component of the corresponding phase is controlled to disconnect when the time difference between the current moment and the zero-crossing moment is less than a threshold; or, The output current is less than a fifth current threshold.

14. The control method according to claim 13, characterized in that: The three-phase inverter circuit adopts a three-phase four-wire connection method, and the control method also includes: Obtain the phase angle of each phase voltage; In the second stage, when each phase meets at least one of the following conditions, the relay assembly of the corresponding phase is controlled to be disconnected: The time difference between the current moment and the zero-crossing moment is less than a threshold; The output current is less than a fifth current threshold; or, The phase angle of the phase voltage is within the target phase angle range; Among them, when the positive pole is short-circuited to the ground, the target phase angle range is [180°, 180+θ1°]; when the negative pole is short-circuited to the ground, the target phase angle range is [0°, θ2°], θ1 is the first phase angle threshold, and θ2 is the second phase angle threshold.

15. The control method according to claim 12, characterized in that: The bridge arm of the three-phase inverter circuit includes an upper bridge arm, and when a short circuit to ground fault is detected, the controllable power device is controlled to be turned on, including: When it is detected that the negative output current of at least one phase of the three-phase inverter circuit is greater than the first current threshold, and / or the negative common-mode current on the DC side of the three-phase inverter circuit is greater than the third current threshold, and / or the voltage to ground between the positive electrode and the ground node of the power supply component is less than the first voltage threshold, it is determined that the positive electrode of the power supply component is short-circuited to ground; When the positive electrode of the power supply assembly is short-circuited to the ground, the controllable power device connected in parallel with the upper bridge arm is controlled to be turned on.

16. The control method according to claim 12, characterized in that: The bridge arm of the three-phase inverter circuit includes a lower bridge arm, and when a short circuit to ground fault is detected, the controllable power device is controlled to be turned on, including: When it is detected that the positive output current of at least one phase of the three-phase inverter circuit is greater than the second current threshold, and / or the positive common-mode current on the DC side of the three-phase inverter circuit is greater than the fourth current threshold, and / or the voltage to ground between the negative electrode of the power supply component and the ground node is less than the second voltage threshold, it is determined that the negative electrode of the power supply component is short-circuited to ground; When the negative electrode of the power supply assembly is short-circuited to the ground, the controllable power device connected in parallel with the lower bridge arm is controlled to be turned on.

17. The control method according to any one of claims 12 to 16, characterized in that: The relay assembly includes a plurality of relays connected in series, and the control method further includes: When the relay assembly is controlled to be turned off multiple times, at least two relay turning-off sequences are used for execution.

18. The control method according to claim 17, characterized in that: The relay assembly includes a first relay and a second relay connected in series, and the control method further includes: Do the following alternately: Control the first relay to be disconnected before the second relay; or, The second relay is controlled to be opened before the first relay.

19. A photovoltaic system, characterized in that: It includes a power supply component and an inverter, wherein the DC side of the inverter is used to connect the power supply component, and the AC side of the inverter is used to connect to a power grid, and the inverter includes a protection circuit according to any one of claims 1-11, or includes a controller that implements the control method according to any one of claims 12-17.

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