A power conversion device

Abstract

The application provides a power conversion device, which comprises a breaking circuit and a control unit, the breaking circuit comprising a main circuit and an auxiliary branch. The main circuit is connected in parallel with the auxiliary branch, and the control unit is used for controlling the closing and opening of a switching device in the main circuit and the auxiliary branch. The breaking circuit can be used for the protection of an alternating current circuit comprising a mechanical breaking device, and can quickly cut off a short-circuit fault current when a short-circuit fault occurs in the alternating current circuit, and complete mechanical breaking point isolation of the short-circuit fault. By implementing the application, the cost of a system breaking device can be reduced, the size of the breaking device can be reduced, the amplitude of a fault current can be reduced, the duration of a short-circuit current after a short-circuit fault occurs can be shortened, and the reliability of system fault breaking protection can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power electronics, and particularly relates to a power conversion device. BACKGROUND

[0002] Mechanical breaking devices, such as relays, are common electrical components for controlling the on-off of an alternating current circuit system. When a short circuit fault occurs in the circuit system, the relay cannot break the fault current, and a large short circuit fault current is generated in the circuit. If the alternating current path is not disconnected in time, the temperature of the circuit device will rise rapidly, and a fire or other safety accidents will occur. Therefore, in the prior art, a circuit breaker or a fuse is often connected in series in the alternating current circuit to protect the circuit system. The traditional circuit breaker may cause the misoperation of the circuit breaker around it or cause the burning of the alternating current copper bar around it when breaking action occurs. In addition, the circuit breaker with a large current breaking capacity has a large size and high cost, and the delay time of the breaking action is long, so that the fast shutdown of the fault current cannot be achieved. How to achieve the fast shutdown of the fault current in a simple, convenient and reliable manner has become a problem to be solved by technical personnel. SUMMARY

[0003] The present application provides a power conversion device breaking circuit, which can reduce the amplitude and duration of the fault current after a short circuit occurs in an alternating current circuit system, and has a simple implementation and high reliability.

[0004] In a first aspect, the application provides a disconnection circuit, which comprises a main circuit, an auxiliary branch parallel to the main circuit, the main circuit comprising a first mechanical switch, the auxiliary branch comprising a second mechanical switch, an overcurrent disconnection switch and a current limiting circuit switch, the second mechanical switch, the overcurrent disconnection switch and the current limiting circuit switch being connected in series to form the auxiliary branch. A control unit sends control signals to the first mechanical switch, the second mechanical switch and the current limiting circuit switch in the disconnection circuit according to information about the current or voltage in the main circuit, to control the conduction or turn-off of the first mechanical switch, the second mechanical switch and the current limiting circuit switch. The disconnection circuit can switch the path of short-circuit current between the main circuit and the auxiliary branch when a short-circuit fault occurs in the alternating current circuit system, and finally cut off the fault current to achieve the purpose of mechanical disconnection isolation. Specifically, when the alternating current circuit system is working normally, the control unit sends control signals, the first mechanical switch is in a closed state, and the current limiting circuit switch is in an open state, at which time the current flows only through the main circuit; when a short-circuit fault occurs in the alternating current circuit system, a large short-circuit current is generated in the main circuit, the control unit sends control signals accordingly to control the current limiting circuit switch, the second mechanical switch and the first mechanical switch to be in a closed state, at which time the current flows through the main circuit and the auxiliary branch, which is equivalent to part of the short-circuit current in the main circuit being shared by the auxiliary branch, and the main circuit current is reduced, then the control unit sends control signals to control the first mechanical switch to be open, at which time the short-circuit current flows through the auxiliary branch, due to the increase of the current in the auxiliary branch, the overcurrent disconnection switch is quickly turned off, the short-circuit current in the auxiliary branch is reduced to zero, and finally the control unit sends control signals again to control the second mechanical switch to be open, to achieve mechanical disconnection isolation of the fault. In the application, the disconnection circuit has a small device size, does not need to be arranged separately like a circuit breaker, can be integrated in an alternating current device, has a simple implementation and saves cost, in addition, due to the parallel circuit design of the main circuit and the auxiliary branch and the fast response speed of the current limiting circuit switch, the mechanical disconnection isolation of the fault of the alternating current circuit system can be quickly achieved, and the reliability is high.

[0005] In combination with the first aspect, in a first possible implementation, the first mechanical switch and the second mechanical switch can be relays, contactors or other similar mechanical elements, for carrying the current of the alternating current circuit and having a disconnection distance meeting the safety regulations of the system. The mechanical elements are controlled by the control unit, and can perform the actions of closing or opening when a short-circuit fault occurs, to achieve mechanical disconnection isolation of the alternating current circuit.

[0006] In combination with the first possible implementation manner of the first aspect, in a second possible implementation manner, the over-current breaking switch can be a fuse with a large current breaking capacity, or can be a PCB trace with a proper length and width, which is used to be fused when a short-circuit fault occurs in the AC circuit system and the current of the auxiliary branch suddenly becomes large, thereby playing a role of quickly cutting off the short-circuit current.

[0007] In combination with the second possible implementation manner of the first aspect, in a third possible implementation manner, the current-limiting circuit switch can be a semiconductor device with a switching function, which is used to control the on-off of the auxiliary branch.

[0008] Optionally, the semiconductor device can be an insulated gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). The semiconductor device can be made of silicon semiconductor material Si, or third-generation wide-bandgap semiconductor material such as silicon carbide SiC, gallium nitride GaN, diamond, zinc oxide ZnO, or other materials.

[0009] In combination with the third possible implementation manner of the first aspect, in a fourth possible implementation manner, the breaking circuit can be arranged on an output AC path of an inverter. When a short-circuit fault occurs in an internal part such as an inverter bridge of the inverter, the control unit detects the occurrence of the fault, and then controls the breaking circuit to perform a short-circuit current breaking function, thereby completing mechanical isolation of the short-circuit fault and ensuring safe disconnection of the inverter.

[0010] In combination with the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner, the breaking circuit can be arranged on two output AC paths of a single-phase inverter. Specifically, in the single-phase inverter, at least one relay is included on each output AC path. Optionally, in one of the two output AC paths of the single-phase inverter, a relay in the selected output AC path is connected in parallel with an auxiliary branch of the breaking circuit. Thus, a breaking circuit is formed, which includes a main breaking circuit and an auxiliary breaking branch. The main breaking circuit includes a main relay, and the auxiliary breaking branch includes a sub-relay, an over-current breaking switch, and a current-limiting circuit switch connected in series, and the auxiliary breaking branch is connected in parallel across the main breaking circuit. Since short-circuit currents occur on both output AC paths of the single-phase inverter when a short-circuit fault occurs, the breaking circuit of the single-phase inverter can always perform a breaking action to complete mechanical isolation of the short-circuit fault.

[0011] With reference to the fourth possible implementation manner of the first aspect, in a sixth possible implementation manner, the breaking circuit can be arranged on an output AC path of a single-phase inverter in a two-path interleaved parallel mode. The two-path interleaved parallel mode specifically refers to that the single-phase inverter includes two output phases, and each output phase includes two parallel output AC paths. The breaking circuit of the single-phase inverter specifically refers to that, in the two parallel output AC paths of the same phase of the single-phase inverter, at least one relay is included on any output AC path, and an auxiliary branch of the breaking circuit is connected in parallel across the two relays of the two parallel output AC paths of the same phase. In this way, two breaking circuits are formed, but the overcurrent breaking switch and the current limiting circuit switch of the auxiliary branches of the two breaking circuits are shared. That is, the two breaking circuits include a first breaking circuit and a second breaking circuit, the first breaking circuit includes a first breaking main circuit and a first breaking auxiliary branch, the first breaking main circuit includes a first main relay, the first breaking auxiliary branch includes a first auxiliary relay, a first overcurrent breaking switch and a first current limiting circuit switch connected in series, and the first breaking auxiliary branch is connected in parallel across the first breaking main circuit; the second breaking circuit includes a second breaking main circuit and a second breaking auxiliary branch, the second breaking main circuit includes a second main relay, the second breaking auxiliary branch includes a second auxiliary relay, the first overcurrent breaking switch and the first current limiting circuit switch connected in series, and the second breaking auxiliary branch is connected in parallel across the second breaking main circuit. When a short-circuit fault occurs, a short-circuit current is generated on at least one output AC path of the two output AC paths of the same phase of the single-phase inverter arranged with the breaking circuit, and thus the breaking circuit on the output AC path generating the short-circuit current performs a breaking action to complete mechanical breaking isolation of the short-circuit fault of the output AC path.

[0012] In a seventh possible implementation manner of the fourth possible implementation manner of the first aspect, the breaking circuit can be arranged on three-phase output AC paths of the three-phase inverter. The breaking circuit of the three-phase inverter specifically includes at least one relay on each output AC path of the three-phase inverter, and optionally, two of the three-phase output AC paths of the three-phase inverter, and a second auxiliary branch of the breaking circuit is connected in parallel across the two relays on the selected two output AC paths. Thus, two breaking circuits are formed, including a third breaking circuit and a fourth breaking circuit. The third breaking circuit includes a third main breaking circuit and a third auxiliary branch, the third main breaking circuit includes a third main relay, the third auxiliary branch includes a third auxiliary relay, a third overcurrent breaking switch and a third current limiting circuit switch connected in series, and the third auxiliary branch is connected in parallel across the third main breaking circuit. The fourth breaking circuit includes a fourth main breaking circuit and a fourth auxiliary branch, the fourth main breaking circuit includes a fourth main relay, and the fourth auxiliary branch includes a fourth auxiliary relay, a fourth overcurrent breaking switch and a fourth current limiting circuit switch connected in series, and the fourth auxiliary branch is connected in parallel across the fourth main breaking circuit. Since at least two of the three-phase output AC paths of the three-phase inverter have short-circuit currents when a short circuit occurs, one of the third breaking circuit and the fourth breaking circuit of the three-phase inverter can perform a breaking action to complete mechanical breaking and isolation of the short-circuit fault.

[0013] In an eighth possible implementation manner of the seventh possible implementation manner of the first aspect, the third auxiliary relay in the third auxiliary branch and the fourth auxiliary relay in the fourth auxiliary branch can share a coil, thereby saving cost and reducing the size of the breaking circuit.

[0014] In a second aspect, a control method of a breaking circuit is provided. In a first possible implementation manner of the control method, the control method is applied to the first possible implementation manner to the eighth possible implementation manner of the first aspect, and the control method includes the following steps.

[0015] Obtaining the current size in the main circuit of the breaking circuit; when the current is less than a first preset value, i.e. the AC circuit system is in a normal working state, controlling the first mechanical switch to be closed, controlling the second mechanical switch to be closed, and controlling the current limiting circuit switch to be opened, at this time the normal current only flows through the main circuit; when the current is equal to or greater than the first preset value, i.e. the AC circuit system is in a short-circuit fault state, controlling the current limiting circuit switch to be closed, at this time due to the auxiliary branch forming a path, a part of the fault current flowing through the main circuit flows through the auxiliary branch, so that the amplitude of the fault current flowing through the main circuit is reduced, and then controlling the first mechanical switch to be opened, at this time the main circuit forms an open circuit, and the fault current flows through the auxiliary branch, so that the amplitude of the fault current flowing through the auxiliary branch is increased, the over-current breaking switch is over-current fused, and the fault current is cut off, and then controlling the second mechanical switch to be opened, after that the main circuit and the auxiliary branch are both mechanically disconnected, thereby completing the fault mechanical breaking point isolation. In the application, due to the short response time of the current limiting circuit switch, the breaking circuit can rapidly reduce the amplitude of the fault current on the main circuit, and due to the fact that the first mechanical switch and the second mechanical switch both perform the closing action under small current and voltage, the breaking circuit can also quickly extinguish the arc, in addition, due to the fact that the first mechanical switch and the second mechanical switch are both in the open state after performing the fault processing action, the breaking circuit realizes the fault mechanical breaking point isolation. By implementing the application, the fault mechanical disconnection can be quickly and safely realized.

[0016] In a second possible implementation manner of the second aspect, the control method is applied to the first aspect first possible implementation manner to the first aspect eighth possible implementation manner, and the control method comprises:

[0017] Obtain the current size in the main circuit of the breaking circuit; when the current is less than a first preset value, that is, the AC circuit system is in a normal working state, control the first mechanical switch to close, control the second mechanical switch to open, and control the current limiting circuit switch to open. At this time, the normal current only flows through the main circuit; when the current is equal to or greater than the first preset value, that is, the AC circuit system is in a short-circuit fault state, control the second mechanical switch to close, and then control the current limiting circuit switch to close. At this time, due to the formation of a path in the auxiliary branch, a part of the fault current flowing through the main circuit flows through the auxiliary branch, so that the amplitude of the fault current flowing through the main circuit decreases. Then, control the first mechanical switch to open. At this time, the main circuit forms an open circuit, and the fault current flows through the auxiliary branch, so that the amplitude of the fault current flowing through the auxiliary branch increases. The overcurrent breaking switch is overcurrent fused, and the fault current is cut off. Then, control the second mechanical switch to open. After that, the main circuit and the auxiliary branch are mechanically disconnected, thereby completing the fault mechanical disconnection and isolation. In this application, similar to the first possible implementation manner of the second aspect, the breaking circuit can reduce the amplitude of the fault current on the main circuit, and quickly and safely realize the fault mechanical disconnection.

[0018] In combination with the first possible implementation manner of the second aspect or the second possible implementation manner of the second aspect, in a third possible implementation manner, the application provides a relay over-zero shutdown method of the main circuit. The specific implementation manner of the relay over-zero shutdown method is: obtaining the current waveform of the output end or the input end of the breaking circuit; when the current waveform is a normal working current waveform, controlling the relay of the main circuit to close; when a short-circuit fault occurs, the current waveform is a short-circuit fault current waveform, the period of the short-circuit fault current is the same as that of the normal working current, and according to the period of the short-circuit fault current and the mechanical delay time of the main circuit relay disconnection, the control unit sends a control signal in advance to control the main circuit relay to disconnect, so as to realize the disconnection of the main circuit relay near the time when the current reaches zero. Since the main circuit relay is disconnected near the current zero point, the overcurrent breaking switch in the auxiliary branch will be fused with a smaller current, thereby improving the safety of the AC circuit system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A breaking circuit with AC circuit protection function is provided for the application.

[0020] Figure 2 A schematic diagram of the over-zero control switch on-off of the breaking circuit is provided for the application.

[0021] Figure 3 Embodiment one of the application of the breaking circuit is provided for the application.

[0022] Figure 4 Embodiment two of the application of the disconnection circuit.

[0023] Figure 5 Embodiment three of the application of the disconnection circuit.

[0024] Figure 6 Embodiment four of the application of the disconnection circuit.

[0025] Figure 7 Embodiment five of the application of the disconnection circuit. DETAILED DESCRIPTION

[0026] The disconnection circuit provided by the present application is a protection circuit of an alternating current circuit system, which can quickly realize mechanical disconnection isolation when a short circuit fault occurs in the circuit system. The present application can be applied to the protection of alternating current circuits of devices with mechanical relays and other mechanical disconnection devices, such as photovoltaic power generation devices, wind power generation devices, electric vehicle devices, etc.

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0029] Please refer to Figure 1 , Figure 1 The disconnection circuit with alternating current protection function provided by the present application is shown in the figure. The disconnection circuit provided by the present application includes a main circuit 04, an auxiliary branch 05 and a control unit 03, and the main circuit 04 and the auxiliary branch 05 are connected in parallel. Among them, the main circuit 04 includes a first mechanical switch K 01 , the auxiliary branch 05 includes a second mechanical switch K 02 , an overcurrent disconnection switch F 01 and a current limiting circuit switch Q 01 in series. The control unit 03 can send control signals to control the conduction or shutdown of the first mechanical switch K 01 , the second mechanical switch K 02 and the current limiting circuit switch Q 01 . The first mechanical switch K 01 and the second mechanical switch K 02It can be a relay, contactor, or other type of mechanical breaking element that carries current during normal operation and breaks current during a fault. The overcurrent breaking switch can be a fuse with high current breaking capacity or a PCB trace of suitable length and width, used to melt and disconnect the circuit when the current suddenly increases. The current limiting circuit switch can be a semiconductor device with switching function, used to control the on / off state of the auxiliary branch. The specific operating modes of the breaking circuit provided in this application to achieve the breaking function include the following two. In the first implementation mode, when the AC circuit system is operating normally, that is, when the normal operating current flows through the breaking circuit, the control unit 03 controls the first mechanical switch K. 01 Close, controlling the second mechanical switch K 02 Close, controlling the current limiting circuit switch Q 01 When the circuit is disconnected, current flows only through the main circuit 04. When a short circuit fault occurs in the AC circuit system, i.e., when the short circuit fault current flows through the disconnecting circuit, the control unit 03 controls the current limiting circuit switch Q. 01 When the circuit is closed, the auxiliary branch 05 forms a closed circuit. At this time, a portion of the short-circuit current in the main circuit 04 is shared by the auxiliary branch 04, reducing the current in the main circuit 04. Then, the control unit 03 controls the first mechanical switch K. 01 When the circuit is disconnected, the main circuit 04 becomes an open circuit. At this time, all the short-circuit current flows in the auxiliary branch 05 and through the overcurrent disconnector F. 01 The current increases rapidly, therefore the overcurrent disconnect switch F 01 A rapid melting and other processes occur, the auxiliary branch 05 becomes an open circuit, the short-circuit current in the disconnecting circuit is reduced to zero, and then the control unit 03 controls the second mechanical switch K. 02 The circuit is disconnected, achieving mechanical isolation of the short-circuit fault. In the second implementation, when the AC circuit system is operating normally, i.e., when the normal operating current flows through the disconnecting circuit, the control unit 03 controls the first mechanical switch K. 01 Close, controlling the second mechanical switch K 02 Disconnect and control the current limiting circuit switch Q. 01 When the circuit is disconnected, current flows only through the main circuit 04. When a short circuit fault occurs in the AC circuit system, i.e., when the short circuit fault current flows through the disconnecting circuit, the control unit 03 first controls the second mechanical switch K. 02 Close, then control the current limiting circuit switch Q. 01When the circuit is closed, the auxiliary branch 05 forms a closed circuit. At this time, a portion of the short-circuit current in the main circuit 04 is shared by the auxiliary branch 04, reducing the current in the main circuit 04. Then, the control unit 03 controls the first mechanical switch K. 01 When the circuit is disconnected, the main circuit 04 becomes an open circuit. At this time, all the short-circuit current flows in the auxiliary branch 05 and through the overcurrent disconnector F. 01 The current increases rapidly, therefore the overcurrent disconnect switch F 01 A rapid melting and other processes occur, the auxiliary branch 05 becomes an open circuit, the short-circuit current in the disconnecting circuit is reduced to zero, and then the control unit 03 controls the second mechanical switch K. 02 The disconnection circuit achieves mechanical isolation of the short-circuit fault. The disconnection circuit provided in this application can effectively reduce the impact on the first mechanical switch K in the main circuit 04. 01 The short-circuit amplitude during disconnection improves system safety, and the disconnection circuit provided in this application has a fast response speed and a simple solution.

[0030] Please see also Figure 2 , Figure 2 This is a schematic diagram illustrating the on / off state of the zero-crossing control switch for the disconnecting circuit provided in this application. Figure 2 The control methods in [the text] can also be applied to [the text]. Figure 1 In the control process. For example... Figure 2 As shown, the horizontal axis represents time t, and the vertical axis represents the terminal current I of the disconnecting circuit. The terminal current is the sum of the main circuit current and the auxiliary branch current of the disconnecting circuit. During the time period t0 to t1, the terminal current I is the normal operating current, which has a small current amplitude and a fixed current frequency. At time t1, a short circuit fault occurs in the system where the disconnecting circuit is located, and the terminal current I is the short circuit fault current. At this time, the current amplitude is large, but the current frequency of the short circuit fault current is the same as that of the normal operating current. After time δt1, that is, after a delay of δt1 after the short circuit occurs, the AC system sends a control signal to control the mechanical switch of the main circuit to turn off. At time t2, the mechanical switch of the main circuit receives the control signal and performs the turn-off action. After time δt2, the mechanical switch is completely turned off, where δt2 is the mechanical delay required for the mechanical switch to achieve complete turn-off from receiving the turn-off control signal. At time t3, the mechanical switch of the main circuit is completely open.

[0031] After a short circuit occurs, the control unit sends a signal to control the mechanical switch to turn off in advance based on the time of the short circuit fault, the frequency of the normal operating current, and the mechanical delay time of the mechanical switch turning off. This achieves the effect that the current at the endpoint is 0 when the mechanical switch is completely turned off, thereby reducing the current when the fuse of the auxiliary branch blows and improving the safety of the AC system.

[0032] The breaking circuit and its working principle provided by the present application will be further described below by specific embodiments. Figures 3 to 7 The breaking circuit and its working principle provided by the present application will be further described below by specific embodiments.

[0033] Please refer to Figure 3 , Figure 3 Embodiment one is an application example of the breaking circuit provided by the present application in a photovoltaic power generation system, which comprises a photovoltaic power generation assembly S1, a photovoltaic inverter S2, a circuit breaker S3, a transformer S4 and an alternating current power grid S5, the photovoltaic inverter S2 is connected between the photovoltaic power generation assembly S1 and the circuit breaker S3, and the transformer S4 is connected between the circuit breaker S3 and the alternating current power grid S5. Among them, the photovoltaic inverter S2 comprises a DC / DC conversion unit S21, a DC / AC inverter circuit S22 and a breaking circuit S23, and the DC / AC inverter circuit S22 is connected between the DC / DC conversion unit S21 and the breaking circuit S23. When the photovoltaic power generation system is in normal operation, the photovoltaic power generation assembly S1 converts solar energy into direct current, the DC / DC conversion unit S21 further converts the direct current, and sends the converted direct current to the DC / AC inverter circuit S22, and the DC / AC inverter circuit S22 converts the direct current into alternating current. Since the system is in normal operation, the breaking circuit S23 and the circuit breaker S3 do not start the breaking action and are in the normal state of carrying alternating current, and send the alternating current to the transformer S4 for voltage conversion, and finally the alternating current is sent to the alternating current power grid S5. When a short circuit fault occurs in the alternating current path in the photovoltaic power generation system, the breaking circuit S23 starts the breaking action, rapidly cuts off the alternating current path, realizes mechanical isolation of the short circuit fault point, and ensures the safety of the photovoltaic power generation system. In embodiment one, after the breaking circuit S23 is included in the photovoltaic inverter S2, the circuit breaker S3 can be selected to be retained or removed according to the cost and safety of the photovoltaic power generation system, without affecting the fault breaking function of the photovoltaic power generation system when a short circuit occurs.

[0034] For the convenience of description, in the following embodiments, the mechanical switch is taken as an example of a relay, the overcurrent breaking switch is taken as an example of a fuse, the current limiting breaking unit is taken as an example of an IGBT (insulated gate bipolar transistor, which can be referred to as IGBT for short), and the working mode of the breaking circuit is taken as an example of the first implementation mode described in the description. Figure 1

[0035] Please refer to Figure 4 , Figure 4 ​Embodiment two of the application of the disconnecting circuit provided in this application. Embodiment two is based on this application. Figure 3 The photovoltaic inverter S2 described herein is an application case when it is a conventional single-phase inverter. The output terminal of the single-phase inverter includes two AC output paths: an L-phase AC output path and an N-phase AC output path. A relay K is connected in series in both the L-phase and N-phase AC output paths. L2 and relay K N2 The relay K L2 The AC path is the main circuit, with an auxiliary branch connected in parallel at both ends. The auxiliary branch includes relays K connected in series. L3 Fuse F1 and IGBT Q L1 The main circuit and the auxiliary branch constitute the disconnect circuit. When the single-phase inverter is working normally, the relay K... L2 and the relay K L3 Close, the IGBT tube Q L1 When disconnected, the current in the L-phase output AC path flows only through the main circuit, that is, the current passes through the relay K. L2 Flow; when a short circuit fault occurs in the L-phase output AC path and the N-phase output AC path, the IGBT tube Q L1 When the circuit is closed, the auxiliary branch becomes a closed circuit, and part of the current flowing through the main circuit flows through the auxiliary branch. Therefore, the current in the main circuit decreases, and then the relay K... L2 When the circuit is safely disconnected, the main circuit becomes open, and the short-circuit current flows only through the auxiliary branch. Therefore, the current in the auxiliary branch increases rapidly, causing fuse F1 to blow quickly. The auxiliary branch becomes open, and the L-phase AC output path is disconnected from the N-phase AC output path. Finally, relay K... L3 The circuit is safely disconnected, achieving mechanical isolation of the short-circuit fault between the L-phase output AC path and the N-phase output AC path. The time from detecting the short-circuit fault to disconnecting the circuit during the process from the occurrence of the short-circuit fault to the achievement of mechanical isolation is the time required to control the IGBT transistor Q. L1 The closing time is the sum of the time it takes for the fuse F1 to blow, therefore the disconnecting circuit has a fast shut-off function. In addition, the relay K... L2 The short-circuit current amplitude is significantly reduced upon disconnection, therefore the disconnecting circuit also features safe shutdown. In this embodiment, the disconnecting circuit can also be connected in parallel to the N-phase output AC path.

[0036] Please see also Figure 5 , Figure 5 Embodiment three illustrates the application of the disconnecting circuit provided in this application. Embodiment three is based on this application. Figure 3The photovoltaic inverter S2 described herein refers to an application scenario where a single-phase inverter with dual-path interleaved parallel inverter circuits is included. This single-phase inverter with dual-path interleaved parallel inverter circuits includes an L-phase output AC path and an N-phase output AC path. The L-phase output AC path comprises two parallel, in-phase output AC paths: a first L-phase output AC path and a second L-phase output AC path. Similarly, the N-phase output AC path comprises two parallel, in-phase output AC paths: a first N-phase output AC path and a second N-phase output AC path. In this embodiment, each of the four output AC paths is connected in series with a relay, and the four relays are designated as relay K. L12 Relay K L22 Relay K N12 and relay K N22 In the relay K L12 and relay K L22 A common fuse F1 and an IGBT Q are connected in parallel at both ends. L1 The auxiliary branch, the fuse F1 and the IGBT Q L1 The auxiliary branch is connected in series and also includes a relay K. L13 and relay K L23 That is to say, the relay K L12 The relay K L13 The fuse F1 and the IGBT Q L1 The relay K forms a disconnecting circuit. L22 The relay K L23 The fuse F1 and the IGBT Q L1 This forms another disconnect circuit. When the single-phase inverter, including the dual-channel interleaved parallel inverter circuit, is operating normally, the relay K... L12 The relay K L13 The relay K L22 and the relay K L23 Close, the IGBT tube Q L1 When disconnected, the current in the first L-phase output AC path only flows through the first main circuit, that is, the current passes through the relay K. L12 The current flows through the second L-phase output AC path only through the second main circuit, that is, the current passes through the relay K. L22 Flow; for example, when a short circuit fault occurs between the first L-phase output AC path and any one of the first N-phase output AC path and the second N-phase output AC path, the IGBT transistor Q... L1 Closed, flowing through the relay K L12 Part of the short-circuit current is shared by the auxiliary branch, and then the relay K is disconnected. L12, the current flowing through the fuse F1 increases rapidly, the fuse F1 is fused rapidly, the auxiliary branch forms an open circuit, the first L-phase output AC path is disconnected from the N-phase output AC path, and finally, the relay K L13 is disconnected safely, the mechanical disconnection of the short-circuit fault of the first L-phase output AC path and the N-phase output AC path is achieved, the second L-phase output AC path is not affected, and the current flows normally. Similarly, when the short-circuit fault occurs in the second L-phase output AC path and any one of the first N-phase output AC path and the second N-phase output AC path, the disconnection circuit works similarly. In this embodiment, the disconnection circuit can also be connected in parallel on the N-phase output AC path. Figure 4 Like the previous embodiment, this embodiment also has the feature of rapid and safe shutdown, which will not be described here. The disconnection circuit in this embodiment can also be connected in parallel on the N-phase output AC path.

[0037] Please refer to Figure 6 , Figure 6 Embodiment Four of the disconnection circuit provided in this application. Embodiment Four is the application of the disconnection circuit in the photovoltaic inverter S2 described in this application Figure 3 . The output end of the three-phase inverter includes three output AC paths, namely the A-phase output AC path, the B-phase output AC path, and the C-phase output AC path. Among them, the relay K A2 is connected in series on the A-phase output AC path, the relay K B2 is connected in series on the B-phase output AC path, and the relay K C2 is connected in series on the C-phase output AC path. In any two of the three output AC paths, an auxiliary branch is connected in parallel across the two ends of the relay. For example, the A-phase output AC path and the B-phase output AC path are selected, a first auxiliary branch is connected in parallel across the two ends of the relay K A2 , the first auxiliary branch includes the relay K A3 , the fuse F1, and the IGBT tube Q1 connected in series, and the relay K A2 and the first auxiliary branch form a first disconnection circuit; a second auxiliary branch is connected in parallel across the two ends of the relay K B2 , the second auxiliary branch includes the relay K B3 , the fuse F2, and the IGBT tube Q2 connected in series, and the relay K B2 and the second auxiliary branch form a second disconnection circuit. When the three-phase inverter works normally, the relay K A2 , the relay K B2 , the relay K C2 , the relay K A3 , and the relay K B3When closed, IGBTs Q1 and Q2 are disconnected, and at this time, the current in the A-phase output AC path flows only through the relay K. A2 The current in the B-phase output AC path flows only through the relay K. B2 When a short circuit fault occurs in either the C-phase output AC path or any of the other two phase output AC paths, for example, when a short circuit fault occurs in the C-phase output AC path and the B-phase output AC path, the IGBT Q2 closes. At this time, the second auxiliary branch forms a path, flowing through the relay K. B2 The current decreases, then the relay K... B2 Safety disconnection occurs. At this time, the current in the second auxiliary branch increases rapidly, the fuse F2 blows quickly, the second auxiliary branch becomes an open circuit, and the AC output paths of phase C and phase B are disconnected. Finally, the relay K... B3 The system safely disconnects, mechanically isolating the short-circuit fault points of the C-phase and B-phase AC output paths. When a short-circuit fault occurs in either the C-phase or A-phase AC output path, the disconnection principle is similar. When a short-circuit fault occurs in either the A-phase or B-phase AC output path, the control unit can selectively close either IGBT Q1 or IGBT Q2. For example, it can control IGBT Q1 to close. At this time, the first auxiliary branch forms a path, flowing through the relay K. A2 The current decreases, then the relay K... A2 Safety disconnection occurs. At this time, the current in the first auxiliary branch increases rapidly, the fuse F1 blows quickly, the first auxiliary branch becomes an open circuit, and the AC output paths of phase A and phase B are disconnected. Finally, the relay K... A3 The safety disconnection achieves mechanical isolation of the short-circuit fault point between the A-phase output AC path and the B-phase output AC path. The ordinary three-phase inverter in this embodiment can also be a three-phase inverter including a dual-path interleaved parallel inverter circuit; its disconnection circuit working principle is the same as... Figure 5 The working principle of the disconnecting circuit of the single-phase inverter, which includes a dual-path interleaved parallel inverter circuit in the Chinese embodiment, is similar and will not be described in detail here.

[0038] Please see also Figure 7 , Figure 7 Embodiment five illustrates the application of the disconnecting circuit provided in this application. Embodiment five is based on this application. Figure 6 The application of the relay in the auxiliary branch is based on the improved design. In Example 5, the relay K... A3 and the relay K B3 Sharing a single coil winding, they are integrated into a single relay. The working principle of the disconnecting circuit is the same as...Figure 6 The working principle of the disconnection circuit in the fourth embodiment is similar, and thus is not described herein again. By using the scheme of the fourth embodiment, the device size and cost can be saved.

[0039] It should be noted that the above terms "first", "second" are only used for description purpose, and cannot be understood as indicating or implying relative importance.

[0040] The division of the units described above is only a logical function division, and another division mode can be used in actual implementation, for example, multiple units or components can be combined, or can be integrated into another system, or some features can be ignored or not executed. In addition, the connection between each component part shown or discussed can be indirectly coupled or communicatively connected through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0041] The above describes only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A power conversion device, characterized by, The power conversion device comprises a DC / AC inverter circuit, a breaking circuit and a control unit, and the breaking circuit is connected to the output end of the DC / AC inverter circuit; The input end of the DC / AC inverter circuit is used for DC input, the output end of the DC / AC inverter circuit is used for AC output, and the output end is connected to the power grid or AC load through the breaking circuit; The breaking circuit comprises a main circuit and an auxiliary branch, the main circuit and the auxiliary branch are connected in parallel between the output end of the DC / AC inverter circuit and the power grid or load, the main circuit comprises a first mechanical switch, the auxiliary branch comprises a second mechanical switch, an over-current breaking switch and a current limiting circuit switch connected in series, and the breaking circuit is used for protecting the power conversion device when a short circuit fault occurs; The first / second mechanical switch comprises a relay and a contactor; The over-current breaking switch comprises a fuse or a PCB trace; The current limiting circuit switch comprises a thyristor and an IGBT tube; The control unit is used for: obtaining the main circuit current of the breaking circuit; when the main circuit current is less than a first preset value, controlling the first mechanical switch to be closed and the second mechanical switch and the current limiting circuit switch to be opened; when the main circuit current is greater than or equal to the first preset value, controlling the second mechanical switch to be closed, the current limiting circuit switch to be closed, the first mechanical switch to be opened and the second mechanical switch to be opened in sequence.

2. The power conversion device of claim 1, wherein, The breaking circuit is arranged at the output end of a single-phase power conversion device, wherein an auxiliary branch of the breaking circuit is connected in parallel to any phase output circuit of the single-phase power conversion device; or The breaking circuit is arranged at the output end of a three-phase power conversion device, wherein two auxiliary branches of the breaking circuit are connected in parallel to any two phase output circuits of the three-phase power conversion device. The control unit controls the first mechanical switch to be turned off at zero crossing, and the zero-crossing turn-off comprises:

3. The power conversion device of claim 1, further characterized by obtaining the current / voltage at the output end of the power conversion device; obtaining the time when the short circuit fault occurs in the power conversion device; obtaining the time difference between half of the period of the current / voltage and the mechanical delay of the first mechanical switch, and the time difference is denoted as δt; at δt after the short circuit fault occurs in the power conversion device, a turn-off signal is sent to the first mechanical switch, so that the first mechanical switch is turned off when the current / voltage at the output end of the power conversion device is 0; The zero-crossing turn-off is used for reducing the current when the fuse is blown and improving the safety of the power conversion device. The power conversion circuit of the single-phase power conversion device adopts a double-path interleaved parallel mode, and comprises 4. The power conversion device of claim 2, further characterized by any phase output of the single-phase power conversion device is two same-phase and parallel-connected output circuits; one phase of the two-phase output of the single-phase power conversion device has two output circuits, and each output circuit is connected in parallel with an auxiliary branch; the auxiliary branches connected in parallel with the two output circuits share the same over-current breaking switch and the same current limiting circuit switch. The power conversion circuit of the three-phase power conversion device adopts a double-path interleaved parallel mode, and comprises 5. The power conversion device of claim 2, further characterized by ​ Any phase output of the three-phase power conversion device is two same-phase and parallel connected output circuits; Two phases of the three-phase output of the three-phase power conversion device share four output circuits, and each auxiliary branch is connected in parallel; The two auxiliary branches of the same phase in the auxiliary branches connected in parallel in the four output circuits share the same over-current breaking switch and the same current limiting circuit.

6. The power conversion device of claim 2, further characterized by The two second mechanical switches of the two auxiliary branches of the breaking circuit share a coil.

7. A breaking method of a power conversion device, characterized by, The breaking method applied to the breaking circuit of any one of claims 1-6, the breaking method comprising, obtaining the main circuit current of the breaking circuit; when the main circuit current is less than a first preset value, controlling the first mechanical switch to be closed and the second mechanical switch and the current limiting circuit switch to be opened; when the main circuit current is greater than or equal to the first preset value, sequentially controlling the second mechanical switch to be closed, the current limiting circuit switch to be closed, the first mechanical switch to be opened, and the second mechanical switch to be opened.

8. A method of zero-crossing turn-off of mechanical switches of power conversion devices, characterized in that, The zero-crossing breaking method applied to the mechanical switch of any one of claims 1-6, the zero-crossing breaking method comprising, obtaining the current / voltage of the output end of the power conversion device; obtaining the time when the short-circuit fault of the power conversion device occurs; obtaining the time difference between half of the period of the current / voltage and the mechanical delay of the first mechanical switch, and the time difference is denoted as δt; at δt after the short-circuit fault of the power conversion device occurs, sending a breaking signal to the first mechanical switch, so that the first mechanical switch is broken when the current / voltage of the output end of the power conversion device is 0.

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