An inverter and a protection method for insulation failure of a direct current side of the inverter, and a photovoltaic system

Abstract

The application provides an inverter, a protection method for insulation failure of a direct current side of the inverter, and a photovoltaic system. The protection method comprises the following steps: determining whether an insulation failure communication fault exists in the direct current side of the inverter; if yes, controlling corresponding switch tubes in the inverter to be in a normal-on state, so that a failure fault current loop generated due to the insulation failure communication fault bypasses a direct current bus, and further avoiding the failure fault current loop generated due to the insulation failure communication fault from charging the voltage of the direct current bus to be too high to be damaged. That is, when the insulation failure communication fault occurs in the inverter, the voltage of the direct current bus is still relatively small, the problem that the inverter is damaged due to overvoltage of the direct current bus is avoided, and the service life of the inverter is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inverters, and more particularly relates to an inverter and a protection method for insulation failure of a direct current side of the inverter, and a photovoltaic system. BACKGROUND

[0002] In a photovoltaic 1500V system, an inverter is generally connected to an inverter unit after being collected by a plurality of MPPT systems. Due to the role of the middle wire of the bus in the symmetrical boost circuit three-level topology, related power devices can be widely applied by being selected according to the half-bus voltage level.

[0003] With the increasing of photovoltaic application scenarios, construction quality and aging, the insulation of the cable from the photovoltaic module to the inverter is easily damaged. In the plurality of MPPT systems, when the negative electrode of one circuit and the positive electrode of another circuit are directly connected or connected through the ground, metal support and the like due to insulation failure, the positive half-bus capacitor of the first circuit is charged by the PV1, and the negative half-bus capacitor of the second circuit is charged by the PV2, so that the direct current bus bears two PV series voltages, resulting in serious overvoltage, and the inverter is seriously damaged. Figure 1 To illustrate the loop at this time, the positive half-bus capacitor is charged by PV1, and the negative half-bus capacitor is charged by PV2, so that the direct current bus bears two PV series voltages, resulting in serious overvoltage, and the inverter is seriously damaged. SUMMARY

[0004] Therefore, the purpose of the present application is to provide an inverter and a protection method for insulation failure of a direct current side of the inverter, and a photovoltaic system, to avoid the failure fault current loop caused by the insulation failure connection fault from charging the voltage of the direct current bus to a high level to damage, and to improve the safety of the inverter.

[0005] The first aspect of the present application discloses a protection method for insulation failure of a direct current side of an inverter, comprising:

[0006] determining whether there is an insulation failure connection fault in the direct current side of the inverter;

[0007] if yes, controlling the corresponding switch tube in the inverter to be in a constant-on state, so that the failure fault current loop in the inverter caused by the insulation failure connection fault bypasses the direct current bus.

[0008] Optionally, in the protection method for insulation failure of a direct current side of an inverter, determining whether there is an insulation failure connection fault in the direct current side of the inverter comprises:

[0009] determining whether there are at least two boost circuit direct current side insulation failures and connections in the inverter.

[0010] Optionally, in the protection method for insulation failure of a direct current side of an inverter, the insulation failure connection fault comprises: insulation failure of the positive electrode of at least one boost circuit, and insulation failure of the negative electrode of at least one boost circuit.

[0011] Optionally, in the method for protecting the DC side insulation failure of the inverter, the corresponding switch tube in the inverter is controlled to be in the always-on state, so that the failure fault current loop caused by the insulation failure interconnection fault in the inverter bypasses the DC bus, comprising:

[0012] The switch tube in the boost circuit where the insulation failure interconnection fault occurs and which has the opposite polarity to the insulation failure is controlled to be in the always-on state, so that the failure fault current loop bypasses the DC bus.

[0013] Optionally, in the method for protecting the DC side insulation failure of the inverter, the corresponding switch tube in the inverter is controlled to be in the always-on state, so that the failure fault current loop caused by the insulation failure interconnection fault in the inverter bypasses the DC bus, further comprising:

[0014] The switch tube in the boost circuit where the insulation failure interconnection fault occurs and which has the same polarity as the insulation failure is controlled to be on or off.

[0015] Optionally, in the method for protecting the DC side insulation failure of the inverter, the switch tube with the opposite polarity to the insulation failure is one of the positive and negative switch tubes in the boost circuit where the insulation failure interconnection fault occurs and which has a larger current absolute value.

[0016] Optionally, in the method for protecting the DC side insulation failure of the inverter, when the DC bus of the inverter is provided with a switch tube in parallel with the full bus or the positive and negative half buses, the corresponding switch tube in the inverter is controlled to be in the always-on state, so that the failure fault current loop caused by the insulation failure interconnection fault in the inverter bypasses the DC bus, comprising:

[0017] The switch tube in parallel with the full bus or the positive and negative half buses is controlled to be in the always-on state, so that the DC bus is short-circuited, and the switch tube in parallel with the full bus or the positive and negative half buses and the corresponding boost circuit form the failure fault current loop.

[0018] Optionally, in the method for protecting the DC side insulation failure of the inverter, the corresponding switch tube in the inverter is controlled to be in the always-on state, comprising:

[0019] The duty cycle of the corresponding switch tube is directly or gradually controlled to 1, so that the corresponding switch tube is in the always-on state.

[0020] Optionally, in the method for protecting insulation failure of the DC side of the inverter, the insulation failure communication fault includes at least one of the following: the DC bus voltage of the inverter triggers protection, the difference between the positive input current and the negative input current of at least one boost circuit of the inverter is greater than a preset value, and the voltage of at least one boost circuit of the inverter is equal to the corresponding half bus voltage.

[0021] The second aspect of the present application discloses an inverter, comprising: a controller, an inverter circuit and at least two boost circuits;

[0022] The input end of each boost circuit is the DC side of the inverter;

[0023] The output end of each boost circuit is connected, and the connection point is connected to the DC bus;

[0024] The DC side of the inverter circuit is connected to the DC bus;

[0025] The AC side of the inverter circuit is the AC side of the inverter;

[0026] The boost circuit and the inverter circuit are controlled by the controller;

[0027] The controller is used to execute the protection method for insulation failure of the DC side as described in any one of the first aspect of the present application.

[0028] Optionally, in the inverter, the DC bus includes a positive half bus and a negative half bus connected in series;

[0029] The positive output end of each boost circuit is connected to the positive pole of the positive half bus; the zero output end of each boost circuit is connected to the negative pole of the positive half bus and the positive pole of the negative half bus, respectively; and the negative output end of each boost circuit is connected to the negative pole of the negative half bus.

[0030] The positive DC side of the inverter circuit is connected to the positive pole of the positive half bus; the zero DC side of the inverter circuit is connected to the negative pole of the positive half bus and the positive pole of the negative half bus, respectively; and the negative DC side of the inverter circuit is connected to the negative pole of the negative half bus.

[0031] Optionally, in the inverter, an inductor is arranged on the positive pole branch and / or the negative pole branch of the boost circuit.

[0032] Optionally, in the inverter, a bypass diode is arranged on the positive pole branch and / or the negative pole branch of the boost circuit; or the boost circuit is not provided with a bypass diode.

[0033] Optionally, in the above-mentioned inverter, the inductance in the boost circuit is a coupling inductance.

[0034] The third aspect of the present application discloses a photovoltaic system, comprising at least one photovoltaic string and at least one inverter as claimed in any one of the second aspect of the present application;

[0035] The output end of each photovoltaic string is connected to the DC side of the corresponding inverter;

[0036] The AC side of the inverter serves as the output end of the photovoltaic system.

[0037] From the above technical solution, the present application provides a protection method for DC side insulation failure of an inverter, comprising: judging whether there is an insulation failure connection fault in the DC side of the inverter; if yes, controlling the corresponding switch tube in the inverter to be in a constant-on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter bypasses the DC bus, thereby avoiding the failure fault current loop generated by the insulation failure connection fault from charging the voltage of the DC bus to be too high to be damaged, i.e., when the inverter has the insulation failure connection fault, the DC bus voltage is still relatively small, avoiding the problem of damage to the inverter due to overvoltage of the DC bus, and improving the service life of the inverter. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0039] Figure 1 is a schematic diagram of an inverter caused by insulation failure leading to direct connection or connection through the ground, metal support, etc. provided by the prior art;

[0040] Figure 2 is a flowchart of a protection method for DC side insulation failure of an inverter provided by an embodiment of the present application;

[0041] Figure 3 is a flowchart of another protection method for DC side insulation failure of an inverter provided by an embodiment of the present application;

[0042] Figure 4 is a flowchart of another protection method for DC side insulation failure of an inverter provided by an embodiment of the present application;

[0043] Figure 5 is a flowchart of another protection method for DC side insulation failure of an inverter provided by an embodiment of the present application;

[0044] Figure 6 is a flow chart of another method for protecting insulation failure of a DC side of an inverter provided by an embodiment of the present application;

[0045] Figure 7 is a schematic diagram of a current loop in a method for protecting insulation failure of a DC side of an inverter provided by an embodiment of the present application;

[0046] Figure 8 is another schematic diagram of a current loop in a method for protecting insulation failure of a DC side of an inverter provided by an embodiment of the present application;

[0047] Figure 9 is a schematic diagram of a failure fault current loop in a method for protecting insulation failure of a DC side of an inverter provided by an embodiment of the present application;

[0048] Figure 10 is a schematic diagram of a boost circuit in an inverter provided by an embodiment of the present application;

[0049] Figure 11 is a schematic diagram of a boost circuit in an inverter provided by an embodiment of the present application;

[0050] Figure 12 is a schematic diagram of a boost circuit in an inverter provided by an embodiment of the present application;

[0051] Figure 13 is a schematic diagram of a boost circuit in an inverter provided by an embodiment of the present application;

[0052] Figure 14 is a schematic diagram of a photovoltaic system and an inverter provided by an embodiment of the present application. DETAILED DESCRIPTION

[0053] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, 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 some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0054] In this application, the terms "comprise", "contain", or any other variant thereof, are intended to cover non-exclusive inclusions, so that a process, method, article, or device that includes a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, method, article, or device. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of other identical elements in the process, method, article, or device that includes the element.

[0055] It should be noted that, taking the 1500V assembly system as an example, the maximum voltage of the normal working condition assembly is 1500V, the maximum voltage of the DC bus is also 1500V, and the maximum voltage of the corresponding half bus is 750V.

[0056] Figure 1 The switch S1n is closed to simulate the negative electrode of the PV1 assembly to ground insulation failure, and S2p is closed to simulate the positive electrode of the PV2 assembly to ground insulation failure. When the two switches S1n and S2p are simultaneously in the closed state, due to the large capacitance value of the DC bus, the half bus voltage cannot be suddenly changed, and the PV1 assembly voltage is clamped to the positive half bus voltage through the solid line circuit in Figure 1 The PV2 voltage is clamped to the negative half bus voltage through the dashed line circuit in Figure 1 .

[0057] Then, the PV1 assembly charges the positive half bus through the solid line circuit, and the PV2 assembly charges the negative half bus through the dashed line circuit in Figure 1 The half bus voltage will be charged to the open circuit voltage of the assembly, resulting in serious overvoltage of the bus, causing the capacitor of the DC bus to explode.

[0058] Based on this, the embodiments of the present application provide a protection method for DC side insulation failure of an inverter, to solve the problem in the prior art that as the number of photovoltaic application scenarios increases, construction quality and aging can easily cause insulation damage of the cable from the photovoltaic assembly to the inverter, so that the DC bus bears two PV series voltages, resulting in serious overvoltage, and causing serious damage to the inverter.

[0059] It should be noted that, as Figure 14 shown, the inverter 100 includes at least two boost circuits 10 and an inverter circuit 20, one side of each boost circuit 10 as the DC side of the inverter 100, and the other side of each boost circuit 10 connected to the DC side of the inverter circuit 20 through a DC bus 30; the AC side of the inverter circuit 20 as the AC side of the inverter 100.

[0060] Referring to Figure 2 , the protection method for DC side insulation failure of the inverter includes:

[0061] S101, determining whether an insulation failure communication fault exists in the DC side of the inverter.

[0062] It should be noted that the plurality of DC sides of the inverter can be connected to the corresponding photovoltaic modules respectively; of course, it is not excluded that the plurality of DC sides of the inverter are connected to other devices, which will not be described one by one here, and are all within the protection scope of the present application.

[0063] The insulation failure communication fault is that there are at least two DC sides of the inverter with insulation failure, causing direct communication between the corresponding DC sides or communication through the ground, metal support, etc.

[0064] When the inverter has an insulation failure communication fault, the photovoltaic modules connected to each DC side with insulation failure charge the corresponding half bus, so that the DC bus bears the series voltage of the photovoltaic modules connected to each DC side, resulting in serious overvoltage, which causes serious damage to the inverter.

[0065] Therefore, the present application needs to determine whether an insulation failure communication fault exists in the DC side of the inverter, and perform subsequent steps to avoid the harm caused by the insulation failure communication fault.

[0066] If the inverter has an insulation failure communication fault, step S102 is performed.

[0067] S102, controlling the corresponding switch tube in the inverter to be in a normal on state, so that the failure fault current loop caused by the insulation failure communication fault in the inverter bypasses the DC bus.

[0068] That is, the inverter includes a boost circuit, an inverter circuit and a DC bus. The boost circuit is connected to the inverter circuit through the DC bus. The DC bus can be taken as a boundary line to divide into a DC part and an AC part.

[0069] Under normal circumstances, the electric energy of the DC part is transmitted to the AC part through the DC bus. When the inverter has an insulation failure communication fault, if no corresponding control is performed on the inverter, the DC part will continue to charge the DC bus, and thus the DC bus voltage is too high. Therefore, the present application controls the corresponding switch tube in the inverter to be in a normal on state, so that the failure fault current loop bypasses the DC bus. At this time, the path of the failure fault current loop does not pass through the DC bus, that is, the DC part no longer continuously charges the DC bus.

[0070] It should be noted that the switch tube in the corresponding boost circuit can be controlled to be always on, so that the corresponding boost circuit is short-circuited, and the failure fault current loop formed bypasses the DC bus, avoiding the boost circuit continuously charging the DC bus. If the inverter is provided with a corresponding equivalent switch tube, the equivalent switch tube can also be controlled to be always on, and the failure fault current loop formed bypasses the DC bus, avoiding the boost circuit continuously charging the DC bus. Of course, the corresponding switch tube in the inverter can also be controlled to be always on in other ways, which will not be described here one by one, and can be determined according to the actual situation, which is within the protection scope of the present application.

[0071] That is, the energy transmission path between the boost circuit with insulation failure and the DC bus is disconnected, and the energy transmission path between the boost circuit without insulation failure and the DC bus can be always on or disconnected, which is not limited here and can be determined according to the actual situation, which is within the protection scope of the present application.

[0072] In the embodiment, the corresponding switch tube in the inverter is controlled to be always on, so that the failure fault current loop caused by the insulation failure in the inverter bypasses the DC bus, thereby avoiding the failure fault current loop caused by the insulation failure from charging the DC bus to a high voltage that damages the DC bus. That is, when the inverter has an insulation failure, the voltage of the DC bus is still relatively low, avoiding the problem of damage to the inverter due to overvoltage of the DC bus, and improving the service life of the inverter.

[0073] In actual application, referring to Figure 3 , the specific process of step S101, judging whether the DC side of the inverter has an insulation failure and connection fault, is as follows:

[0074] S201, judging whether at least two boost circuits have insulation failure and connection on the DC side.

[0075] It should be noted that after the insulation failure and connection of the DC side of at least two boost circuits, a failure fault current loop is generated. If no control is performed, the failure fault current loop passes through the DC bus, thereby charging the DC bus to a high voltage. In the embodiment, the corresponding switch tube is controlled to be always on to change the path of the failure fault current loop, avoiding the failure fault current loop passing through the DC bus.

[0076] That is, if the inverter has insulation failure and connection of the DC side of at least two boost circuits, it is determined that the inverter has an insulation failure and connection fault, and step S102 is performed. If the inverter does not have insulation failure and connection of the DC side of at least two boost circuits, it is determined that the inverter does not have an insulation failure and connection fault.

[0077] In practical applications, the insulation failure connection fault includes: positive electrode insulation failure of at least one of the boost circuits, and negative electrode insulation failure of at least one of the boost circuits.

[0078] As shown in S2p closing, the boost circuit connected with the switch S2p has positive electrode insulation failure, as shown in S1n closing, the boost circuit connected with the switch S1n has negative electrode insulation failure. Figure 1 Figure 1

[0079] If the direct current side positive electrode insulation failure exists in at least one of the boost circuits, and the direct current side negative electrode insulation failure exists in at least one of the boost circuits, the boost circuit with the direct current side positive electrode insulation failure and the boost circuit with the direct current side negative electrode insulation failure form a loop for charging the positive half bus and the negative half bus, that is, the failure fault current loop passes through the direct current bus, thereby damaging the direct current bus voltage due to overvoltage.

[0080] It should be noted that if the direct current side positive electrode insulation failure exists in at least one of the boost circuits, and the direct current side negative electrode insulation failure exists in at least one of the boost circuits, these boost circuits will be directly connected or connected through the ground or metal frame, thereby generating the failure fault current loop, at this time, the path of the failure fault current loop can be changed by controlling the corresponding switch tube to be always on, so as to avoid the failure fault current loop passing through the direct current bus.

[0081] It should be noted that if the insulation failure connection fault exists in the inverter, the direct current bus voltage in the inverter is charged high, thereby the insulation failure connection fault of the direct current side of the inverter can be judged by judging whether the direct current bus voltage triggers the voltage protection.

[0082] If the insulation failure connection fault exists in the inverter, that is, the positive electrode and / or the negative electrode of the corresponding boost circuit is insulated, a large impact current will appear in the boost circuit; and the current flowing into the positive electrode of the input end of the corresponding boost circuit is not equal to the current flowing out of the negative electrode of the input end; that is, the difference between the positive input current and the negative input current of the boost circuit becomes large, thereby the insulation failure connection fault of the direct current side of the inverter can be judged by judging whether the difference between the positive input current and the negative input current of at least one boost circuit is greater than a preset value.

[0083] Specifically, Figure 9 As shown in the capacitor voltage before insulation failure, when S1n and S2p are closed, capacitors Cbst1 and Cbst2 form a series connection, and pass through a bypass diode (such as Figure 9 ​​The Dby1p shown is a boost diode (such as...). Figure 9 The Dbst1p shown rapidly charges the bus capacitor, forming... Figure 9 The circuit shows an inrush current that makes Ibst1p much larger than Ibst1n, and Ibst2n much larger than Ibst2p. Here, Ibst1p, Ibst1n, Ibst2p, and Ibst2n are all currents.

[0084] If the inverter experiences an insulation failure fault, i.e., the positive and / or negative insulation of the corresponding boost circuit fails, the voltage of that boost circuit is clamped to the corresponding half-bus voltage. Therefore, the presence of an insulation failure fault on the DC side of the inverter can be determined by checking whether the voltage of at least one boost circuit is equal to the corresponding half-bus voltage. Specifically, the input voltage of each boost circuit is compared to see if it is near the half-bus voltage. A threshold can be set, such as 30V, but this is not the only possible setting; all are within the scope of protection of this application.

[0085] In other words, insulation failure connection faults can include at least one of the following three: DC bus voltage triggering protection in the inverter, the difference between the positive input current and the negative input current of at least one boost circuit in the inverter being greater than a preset value, and the voltage of at least one boost circuit in the inverter being equal to the corresponding half bus voltage.

[0086] Of course, the insulation failure and connection faults are not limited to the examples mentioned above, and will not be elaborated on here, but are all within the scope of protection of this application.

[0087] The above description can indicate the circuit number of the boost circuit where insulation failure occurred, as well as the corresponding polarity, to help maintenance personnel quickly locate the insulation failure. The specific indication process will not be detailed here; it depends on the actual situation and is all within the scope of protection of this application.

[0088] In this embodiment, the above method is used to identify insulation failure and connection faults and implement protective actions, which not only prevents the inverter from causing bus overvoltage due to insulation failure, but also identifies the positive and negative polarities of the insulation failure, making it easier for maintenance personnel to find the insulation failure point.

[0089] In practical applications, see Figure 4 Step S102: Controlling the corresponding switching transistor in the inverter to be in the normally on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter will bypass the DC bus, including:

[0090] S301. In the boost circuit where an insulation failure occurs and the circuit connection is interrupted, the switching transistor with the opposite polarity to the insulation failure is kept in the normally on state so that the failure fault current loop bypasses the DC bus.

[0091] In other words, if the positive insulation of at least one boost circuit fails, then the switch transistor with the opposite polarity of the insulation failure in that boost circuit becomes the negative switch transistor. If the negative insulation of at least one boost circuit fails, then the switch transistor with the opposite polarity of the insulation failure in that boost circuit becomes the positive switch transistor.

[0092] The positive switch is located between the neutral line and the positive branch of the boost circuit, and the negative switch is located between the neutral line and the negative branch of the boost circuit.

[0093] Specifically, such as Figure 7 As shown, taking the first boost circuit as an example, switch T1P is the positive switch of the first boost circuit, and switch T1n is the negative switch of the first boost circuit. The first boost circuit experiences a DC-side negative insulation failure, meaning that switch T1P is normally on at this time. Simultaneously, the second boost circuit experiences a DC-side positive insulation failure, meaning that switch T2n is normally on at this time. That is, the components connected to the boost circuit with the insulation failure are short-circuited by switch T1p or T2n, thereby preventing the component voltage from charging the DC bus through the boost circuit with the insulation failure, thus protecting the inverter's DC bus from overvoltage risk.

[0094] Specifically, the failure fault current loop is as follows: Figure 7 The solid-line circuit shown has a small current flowing through the dashed section. When a switch with the same polarity as the insulation fails and is turned on, current will flow through that switch (e.g., ...). Figure 7 As shown in T1n and T2p, since a diode is connected in parallel with the switching transistor, according to the conduction performance of the diode (such as...), the diode... Figure 7 Current will also flow through Dinv1n and Dinv1p as shown.

[0095] In practical applications, the switching transistors with opposite polarity in insulation failure are: the one with the larger absolute value of current among the positive and negative switching transistors in the boost circuit where insulation failure occurs and connection fault occurs.

[0096] In other words, the switching transistor with the opposite polarity of insulation failure can be determined by determining the absolute value of the current.

[0097] Specifically, such as Figure 7As shown, taking the first boost circuit as an example, the corresponding switching transistors with larger absolute values ​​of currents Ibst1p and Ibst1n are used as switching transistors with opposite polarity of insulation failure.

[0098] In practical applications, see Figure 5 Step S102, controlling the corresponding switching transistor in the inverter to be in the normally on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter will bypass the DC bus, also includes:

[0099] S401 controls the switching transistor in the boost circuit with the same polarity as the insulation failure to turn on or off when an insulation failure occurs.

[0100] In other words, the state of the switching transistor with the same polarity as the insulation failure in the boost circuit where an insulation failure occurs is not specifically limited; it can be either on or off, depending on the actual situation, and all are within the protection scope of this application.

[0101] Specifically, such as Figure 7 As shown, taking the DC-side negative electrode insulation failure of the first boost circuit and the DC-side positive electrode failure of the second boost circuit as examples, the control switch T1p is in a normally on state, and the switch T1n is either on or off. At the same time, the control switch T2n is in a normally on state, and the switch T2p is either on or off.

[0102] It should be noted that, Figure 7 This example demonstrates the situation using the DC-side insulation failure of two boost circuits. Figure 8 As shown, it illustrates a schematic diagram of DC-side insulation failure in three boost circuits. Specifically, as... Figure 8 As shown, when switch S2p is closed, the positive insulation of the second boost circuit connected to switch S2p fails; when switch S1n is closed, the negative insulation of the first boost circuit connected to switch S1n fails; when switch S3p is closed, the positive insulation of the third boost circuit connected to switch S3p fails. At this time, control switches T1p, T2n, and T3n are normally on, and control switches T1n, T2p, and T3p are either on or off. That is, there is no specific limitation on switches T1n, T2p, and T3p.

[0103] like Figure 8 As shown, V PV1 V PV2 For component voltage; C bst1 C bst2 C bst3Dby1p, Dby1n, Dby2p, Dby2n, Dby3p, and Dby3n are the bypass diodes of the corresponding boost circuits; T1p, T1n, T2p, T2n, T3p, and T3n are the switching transistors of the corresponding boost circuits; PE is ground; Dinv1p, Dinv1n, Dinv2p, Dinv2n, Dinv3p, and Dinv3n are the parallel diodes of the corresponding boost circuits; Dbst1p, Dbst1n, Dbst2p, Dbst2n, Dbst3p, and Dbst3n are the boost circuit diodes of the corresponding boost circuits; Vbusp is the positive half-bus voltage; Vbusn is the negative half-bus voltage; BusM is the connection point between the positive and negative half-buses.

[0104] Specifically, the states of each switch are shown in Table 1 and Table 2. Table 1 is... Figure 7 The corresponding switching states are shown in Table 2. Figure 8 The corresponding switching state of the transistor.

[0105] Table 1: Figure 7 Corresponding switching state

[0106] T1p 1 T1n x T2p x T2n 1

[0107] Table 2: Figure 8 Corresponding switching state

[0108] T1p 1 T1n x T2p x T2n 1 T3p x T3n 1

[0109] Where 1 represents conduction, that is, in the normally on state; x represents conduction or deactivation.

[0110] In other words, in the boost circuit, the switching transistors with opposite polarity due to insulation failure are in the on state, and all logic in the boost circuit with the same polarity due to insulation failure is not required to be protected by this solution.

[0111] In practical applications, when the inverter's DC bus is equipped with switching transistors connected in parallel with the full bus or positive and negative half buses, see [reference needed]. Figure 6 Step S102: Controlling the corresponding switching transistor in the inverter to be in the normally on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter will bypass the DC bus, including:

[0112] S501 controls the switching transistor connected in parallel with the full bus or positive and negative half bus to be in a normally on state so that the DC bus is short-circuited, and the switching transistor connected in parallel with the full bus or positive and negative half bus and the corresponding boost circuit form a failure fault current loop.

[0113] In other words, with Figure 7 ,Figure 8 Switches with opposite polarity due to insulation failure, as well as full or half busbar switches connected in parallel at the same position, are also within the protection range.

[0114] In practical applications, controlling the corresponding switching transistors in the inverter to be in a normally-on state includes:

[0115] Control the duty cycle of the corresponding switch transistor directly or gradually to 1, so that the corresponding switch transistor is in the normally on state.

[0116] In this embodiment, faulty boost circuits are quickly identified by electrical characteristics, and the duty cycle of the corresponding switching transistor is controlled directly or gradually to 1, so that the corresponding faulty component is in a short-circuit state to prevent the bus from having excessively high voltage.

[0117] Another embodiment of this application provides an inverter.

[0118] See Figure 14 The inverter 100 includes: a controller, an inverter circuit 20, and at least two boost circuits 10.

[0119] The input terminals of each boost circuit 10 serve as the DC side of the inverter 100.

[0120] The output terminals of each boost circuit 10 are connected, and the connection point is connected to the DC bus 30.

[0121] like Figure 14 As shown, the input terminal of each boost circuit 10 is connected to its corresponding photovoltaic module, so that the output power of each photovoltaic module is transmitted to the DC bus 30 through its corresponding boost circuit 10.

[0122] The DC side of the inverter circuit 20 is connected to the DC bus 30.

[0123] In other words, each boost circuit 10 is connected to the inverter circuit 20 via the DC bus 30.

[0124] The AC side of the inverter circuit 20 serves as the AC side of the inverter 100.

[0125] The AC side of the inverter circuit 20 can be connected to the power grid or a load. No specific limitation is made here, and it can be determined according to the actual situation. All of these are within the protection scope of this application.

[0126] The boost circuit 10 and the inverter circuit 20 are controlled by the controller. That is, the controller can control the operating state of the boost circuit 10 and the inverter circuit 20. The specific control process will not be described in detail here, but is within the scope of protection of this application.

[0127] The controller is used to implement protection methods against DC-side insulation failure.

[0128] For details on the specific working process and principle of the controller, please refer to the DC side insulation failure protection method provided in the above embodiments. It will not be repeated here, and all of them are within the protection scope of this application.

[0129] In this embodiment, no additional hardware is required. For example, for an aging power station that is already in operation, only a software upgrade is needed to solve the loss caused by insulation failure.

[0130] In practical applications, the DC bus 30 includes a positive half-bus 31 and a negative half-bus 32 connected in series.

[0131] Specifically, the DC bus 30 may include two bus capacitors, with the bus capacitor located at the positive terminal of the DC bus 30 being the positive half-bus 31 and the bus capacitor located at the negative terminal of the DC bus 30 being the negative half-bus 32.

[0132] The positive terminal of each boost circuit 10 is connected to the positive terminal of the positive half bus 31; the zero point of each boost circuit 10 is connected to the negative terminal of the positive half bus 31 and the positive terminal of the negative half bus 32, respectively; the negative terminal of each boost circuit 10 is connected to the negative terminal of the negative half bus 32.

[0133] The positive terminal of the DC side of the inverter circuit 20 is connected to the positive terminal of the positive half-bus 31; the zero point of the DC side of the inverter circuit 20 is connected to the negative terminal of the positive half-bus 31 and the positive terminal of the negative half-bus 32, respectively; the negative terminal of the DC side of the inverter circuit 20 is connected to the negative terminal of the negative half-bus 32.

[0134] In practical applications, inductors are provided on the positive and / or negative branches of the boost circuit 10.

[0135] Specifically, such as Figure 10 As shown, inductors are provided on both the positive and negative branches of the boost circuit 10; for example... Figure 11 As shown, an inductor is provided on the positive branch of the boost circuit 10; as Figure 12 As shown, an inductor is provided on the negative branch of the boost circuit 10.

[0136] It should be noted that the inductor in the boost circuit 10 can be a coupled inductor, but other cases are not excluded. These will not be elaborated here, and can be determined according to the actual situation. All of these are within the protection scope of this application.

[0137] In practical applications, a bypass diode is provided on the positive branch and / or negative branch of the boost circuit 10; or, the boost circuit 10 is not provided with a bypass diode.

[0138] Specifically, such as Figure 13As shown, bypass diodes are installed on both the positive and negative branches of the boost circuit 10. Alternatively, bypass diodes could be installed on either the positive or negative branch of the boost circuit 10 (not shown in the diagram), as... Figure 10- Figure 12 As shown, no bypass diode is installed on the boost circuit 10.

[0139] In practical applications, the switching transistors in the inverter 100 can be switching devices, or controllable devices such as IGBTs and MOSFETs. Of course, other situations are not excluded, and will not be elaborated here. It depends on the actual situation, and all of them are within the protection scope of this application.

[0140] Another embodiment of this application provides a photovoltaic system.

[0141] See Figure 14 The photovoltaic system includes at least one photovoltaic string 200 and at least one inverter 100.

[0142] The output terminal of each photovoltaic string 200 is connected to the DC side of the corresponding inverter 100.

[0143] The AC side of inverter 100 serves as the output terminal of the photovoltaic system.

[0144] For details on the specific structure and working principle of the inverter 100, please refer to the inverter provided in the above embodiments. They will not be repeated here, and are all within the protection scope of this application.

[0145] The features described in the various embodiments of this specification can be substituted for or combined with each other. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0146] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0147] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for protecting against DC-side insulation failure in an inverter, characterized in that, include: Determine whether there is an insulation failure or continuity fault on the DC side of the inverter; If so, the corresponding switch in the inverter is controlled to be in the normally on state so that the failure fault current loop generated by the insulation failure connection fault in the inverter will bypass the DC bus. Specifically, controlling the corresponding switching transistors in the inverter to be in a normally-on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter bypasses the DC bus, includes: The switch transistor with the opposite polarity to the insulation failure in the boost circuit is kept in a normally-on state so that the failure fault current loop bypasses the DC bus; the switch transistor with the opposite polarity to the insulation failure is the one with the larger absolute value of the current among the positive and negative switches in the boost circuit where the insulation failure connection fault occurs.

2. The protection method for DC-side insulation failure of an inverter according to claim 1, characterized in that, Determining whether there is an insulation failure or continuity fault on the DC side of the inverter includes: Determine whether the inverter has at least two DC-side insulation failures and connections in the corresponding boost circuits.

3. The method for protecting the DC-side insulation of an inverter according to claim 2, characterized in that, The insulation failure connectivity fault includes: at least one positive insulation failure of the boost circuit, and at least one negative insulation failure of the boost circuit.

4. The protection method for DC-side insulation failure of an inverter according to claim 1, characterized in that, Controlling the corresponding switching transistors in the inverter to be in a normally-on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter bypasses the DC bus, further includes: The switch transistor with the same polarity as the insulation failure in the boost circuit is turned on or off when the insulation failure occurs.

5. The protection method for DC-side insulation failure of an inverter according to claim 1, characterized in that, When a switching transistor connected in parallel with the full bus or positive and negative half bus is installed on the DC bus of the inverter, the corresponding switching transistor in the inverter is controlled to be in a normally on state, so that the failure fault current loop generated by the insulation failure connection fault in the inverter will bypass the DC bus, including: The switching transistor connected in parallel with the full bus or positive and negative half bus is kept in a normally on state so that the DC bus is short-circuited, and the switching transistor connected in parallel with the full bus or positive and negative half bus and the corresponding boost circuit form a failure fault current loop.

6. The method for protecting against DC-side insulation failure of an inverter according to any one of claims 1-5, characterized in that, Controlling the corresponding switching transistors in the inverter to be in a normally-on state includes: Control the duty cycle of the corresponding switch transistor directly or gradually to 1, so that the corresponding switch transistor is in the normally on state.

7. The method for protecting against DC-side insulation failure of an inverter according to any one of claims 1-5, characterized in that, The insulation failure connection fault includes at least one of the following three: DC bus voltage triggered protection in the inverter, the difference between the positive input current and the negative input current of at least one boost circuit in the inverter is greater than a preset value, and the voltage of at least one boost circuit in the inverter is equal to the corresponding half bus voltage.

8. An inverter, characterized in that, include: The system includes a controller, an inverter circuit, and at least two boost circuits. The input terminal of each of the boost circuits serves as the DC side of the inverter; The output terminals of each of the aforementioned boost circuits are connected together, and the connection point is connected to the DC bus. The DC side of the inverter circuit is connected to the DC bus; The AC side of the inverter circuit serves as the AC side of the inverter. Both the boost circuit and the inverter circuit are controlled by the controller. The controller is used to perform the protection method for DC side insulation failure as described in any one of claims 1-7.

9. The inverter according to claim 8, characterized in that, The DC bus includes a positive half-bus and a negative half-bus connected in series; The positive terminal of each boost circuit is connected to the positive terminal of the positive half-bus; the zero point of each boost circuit is connected to the negative terminal of the positive half-bus and the positive terminal of the negative half-bus, respectively; the negative terminal of each boost circuit is connected to the negative terminal of the negative half-bus. The positive terminal of the DC side of the inverter circuit is connected to the positive terminal of the positive half-bus; the zero point of the DC side of the inverter circuit is connected to the negative terminal of the positive half-bus and the positive terminal of the negative half-bus, respectively; the negative terminal of the DC side of the inverter circuit is connected to the negative terminal of the negative half-bus.

10. The inverter according to claim 8, characterized in that, The boost circuit has an inductor on its positive and / or negative branches.

11. The inverter according to claim 8, characterized in that, The boost circuit has a bypass diode on its positive and / or negative branches; or, the boost circuit does not have a bypass diode.

12. The inverter according to claim 10, characterized in that, The inductor in the boost circuit is a coupled inductor.

13. A photovoltaic system, characterized in that, include: At least one photovoltaic string and at least one inverter as described in any one of claims 8-12; The output terminal of each photovoltaic string is connected to the DC side of the corresponding inverter; The AC side of the inverter serves as the output terminal of the photovoltaic system.

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