Inverter and insulation detection circuit

Abstract

The present application provides an inverter and an insulation detection circuit. The insulation detection circuit includes: a first circuit and a second circuit, wherein a first end of the first circuit is connected to the positive pole of a busbar, a second end of the first circuit is connected to a first ground line PE, and the first circuit includes at least one detection resistor; a first end of the second circuit is connected to the negative pole of the busbar, a second end of the second circuit is connected to the first ground line PE, and the second circuit includes a sampling resistor and at least one detection resistor, wherein the sampling resistor is connected to a controller; the controller is configured to sample a first DC voltage across the sampling resistor under operating conditions where an input DC bus voltage is established and no AC voltage is output on an output live line L or an output neutral line N, and determine the insulation impedance of the output inverter circuit based on the first DC voltage. The insulation detection circuit proposed in the present application ensures that the insulation impedance of the inverter circuit does not decrease during the insulation detection process.

Description

Technical Field

[0001] The present application relates to the technical field of circuit design, and in particular to an inverter and an insulation detection circuit. Background Art

[0002] Under the dual pressures of energy and the environment, and driven by positive policies, electric vehicles are gaining increasing market share. Onboard chargers are a crucial component of electric vehicles. As user demands grow, onboard chargers are becoming increasingly versatile. Bidirectional onboard chargers are a standard onboard charger with the added functionality of reverse inverters. In addition to a low-voltage system port, a bidirectional charger has an AC port and a high-voltage DC port. When operating as a charger, it charges the power battery from the grid. The AC port serves as the input, connected to an AC source, and the high-voltage DC port serves as the output, connected to a high-voltage DC load. When operating as an inverter, it powers certain onboard or household appliances using AC power from the power battery. The high-voltage DC port serves as the input, connected to a high-voltage DC source, and the AC port serves as the output, connected to an AC load.

[0003] Because power batteries operate at high voltages (typically 300V-700V), when the inverter function is activated (i.e., the power battery starts operating and the vehicle is powered up at high voltage), if the insulation resistance between the output side and the vehicle body drops below a safe value, a large leakage current will occur, posing a direct threat to personal safety. Therefore, it is necessary to promptly shut down the inverter output if leakage current is high.

[0004] Current insulation detection circuits either cause the insulation impedance to drop during insulation detection, making online insulation detection after inverter startup impossible; or they can only implement online insulation detection after inverter startup for specific circuit topologies and are not compatible with other circuit topologies. Summary of the Invention

[0005] The present application provides an inverter and an insulation detection circuit, which can ensure that the insulation impedance does not decrease during the detection process, and can perform online insulation detection, while being compatible with various topological structures of the inverter circuit.

[0006] In a first aspect, an inverter is provided, comprising: a controller, an inverter circuit, and an insulation detection circuit, wherein the inverter circuit is used to convert direct current into alternating current, and the inverter circuit comprises an input end, an output end, and a first ground wire PE, wherein the input end of the inverter circuit comprises an input DC bus, the input DC bus comprises a bus positive pole and a bus negative pole, and the output end of the inverter circuit comprises an output live wire L and an output neutral wire N, and the output live wire L and the output neutral wire N are connected to the first ground wire PE.

[0007] The insulation detection circuit includes: a first circuit and a second circuit, wherein the first end of the first circuit is connected to the first node of the inverter circuit, the second end of the first circuit is connected to the first ground line PE, the first circuit includes at least one detection resistor, the first end of the second circuit is connected to the second node of the inverter circuit, the second end of the second circuit is connected to the first ground line PE, the second circuit includes a sampling resistor and at least one detection resistor, the sampling resistor is connected to the controller, the first node is connected to the positive electrode of the bus, the second node is connected to the negative electrode of the bus, or the first node is connected to the negative electrode of the bus, and the second node is connected to the positive electrode of the bus.

[0008] The controller is used to: control the inverter to be in an offline state, where the offline state means that the input DC bus voltage has been established and no AC voltage is output on the output live wire L and the output neutral wire N; sample the first DC voltage across the sampling resistor, and determine the insulation resistance Rxy of the inverter circuit based on the first DC voltage, where the insulation resistance Rxy is the parallel resistance value of a first insulation resistor Rx and a second insulation resistor Ry, where the first insulation resistor Rx is the insulation resistance of the output live wire L relative to the first ground wire PE, and the second insulation resistor Ry is the insulation resistance of the output neutral wire N relative to the first ground wire PE.

[0009] In this technical solution, the insulation impedance of the inverter circuit can be pre-tested before normal operation to determine whether the insulation impedance meets the requirements, thereby effectively ensuring personal safety. Because the insulation detection circuit determines the insulation resistance value Rxy through the voltage divider across the sampling resistor during offline testing, and does not involve changes in insulation impedance, it can be ensured that the insulation impedance does not decrease during the testing process.

[0010] In combination with the first aspect, in certain implementations of the first aspect, the controller is further used to: control the inverter to be in an online state when the insulation resistance Rxy is not less than a first insulation resistance threshold, the online state means that there is an AC voltage output on the output live wire L and the output neutral wire N, and the first insulation resistance threshold is used to limit the minimum value of the insulation resistance Rxy; short-circuit the detection resistor included in at least one first circuit or the second circuit; sample the second DC voltage across the sampling resistor to obtain a voltage-time change curve of the sampling resistor; determine the capacitance of the Y capacitor based on the voltage-time change curve and the insulation resistance Rxy, the capacitance of the Y capacitor being the capacitance between the first Y capacitor Cx between the output live wire L and the first ground wire PE and the second Y capacitor Cy between the output neutral wire N and the first ground wire PE. and; calculating a first voltage threshold applied across the sampling resistor and a second voltage threshold applied across the sampling resistor based on a second insulation resistance threshold, a first AC voltage, a frequency of the first AC voltage, and the capacitance of the Y capacitor, wherein the second insulation resistance threshold is used to limit a minimum value of the first insulation resistance Rx, the first voltage threshold is used to determine whether the first insulation resistance Rx has an insulation failure, the second voltage threshold is used to determine whether the second insulation resistance Ry has an insulation failure, the second voltage threshold is less than the first voltage threshold, and the first AC voltage is a preset AC safety voltage; sampling the second AC voltage across the sampling resistor to obtain a first sampled voltage value of the sampling resistor; and determining whether the inverter circuit has an insulation failure based on the first voltage threshold, the second voltage threshold, and the first sampled voltage value.

[0011] In the above technical solution, the insulation detection circuit can realize online insulation detection after the inverter is started, and can monitor in real time whether the insulation resistance of the inverter output terminal to the ground is insulation failure, thereby ensuring the safety of the inverter circuit.

[0012] In combination with the first aspect, in certain implementations of the first aspect, the controller is specifically used to: determine that the insulation of the output live wire L of the inverter circuit has failed when the first sampling voltage value is greater than the first voltage threshold; and determine that the insulation of the output neutral wire N of the inverter circuit has failed when the first sampling voltage value is less than the second voltage threshold.

[0013] In combination with the first aspect, in certain implementations of the first aspect, the first circuit includes: a first detection resistor R1 and a second detection resistor R2; one end of the first detection resistor R1 is connected to the positive electrode of the bus, the other end of the first detection resistor R1 is connected to one end of the second detection resistor R2, and the other end of the second detection resistor R2 is connected to the first ground line PE.

[0014] In combination with the first aspect, in some implementations of the first aspect, the first circuit further includes: a first switch S1 , the first switch S1 is connected in parallel with the first detection resistor R1 , and the first switch S1 is in a normally open state.

[0015] In combination with the first aspect, in certain implementations of the first aspect, the second circuit includes: a third detection resistor R3 and a sampling resistor Rs; one end of the third detection resistor R3 is connected to the first ground line PE, the other end of the third detection resistor R3 is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is connected to the negative electrode of the bus, and the sampling port of the controller is connected to both ends of the sampling resistor Rs.

[0016] In combination with the first aspect, in some implementations of the first aspect, the second circuit further includes: a second switch K1 , the second switch K1 is connected in parallel with the third detection resistor R3 , and the second switch K1 is in a normally open state.

[0017] The first circuit and the second circuit in the insulation detection circuit given above have simple structures, which can ensure insulation detection of the inverter circuit while reducing space occupation, thereby realizing miniaturization of the inverter where the inverter circuit is located. In addition, the manufacturing cost of the insulation detection circuit is low, which can effectively save costs.

[0018] In a second aspect, an insulation detection circuit is provided, which is used to perform insulation detection on an inverter circuit, wherein the inverter circuit is used to convert direct current into alternating current, and the inverter circuit includes an input end, an output end and a first ground wire PE, wherein the input end of the inverter circuit includes an input DC bus, and the input DC bus includes a bus positive pole and a bus negative pole, and the output end of the inverter circuit includes an output live wire L and an output neutral wire N, and the output live wire L and the output neutral wire N are connected to the first ground wire PE.

[0019] The insulation detection circuit includes: a first circuit and a second circuit, wherein the first end of the first circuit is connected to the positive electrode of the busbar, the second end of the first circuit is connected to the first ground line PE, and the first circuit includes at least one detection resistor; the first end of the second circuit is connected to the negative electrode of the busbar, the second end of the second circuit is connected to the first ground line PE, and the second circuit includes a sampling resistor and at least one detection resistor.

[0020] In combination with the second aspect, in certain implementations of the second aspect, the first circuit includes: a first detection resistor R1 and a second detection resistor R2; one end of the first detection resistor R1 is connected to the positive pole of the bus, the other end of the first detection resistor R1 is connected to one end of the second detection resistor R2, and the other end of the second detection resistor R2 is connected to the first ground line PE.

[0021] In combination with the second aspect, in some implementations of the second aspect, the first circuit further includes: a first switch S1 , the first switch S1 is connected in parallel with the first detection resistor R1 , and the first switch S1 is in a normally open state.

[0022] In combination with the second aspect, in certain implementations of the second aspect, the second circuit includes: a third detection resistor R3 and a sampling resistor Rs; one end of the third detection resistor R3 is connected to the first ground line PE, the other end of the third detection resistor R3 is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is connected to the negative electrode of the bus, and the sampling port of the controller is connected to both ends of the sampling resistor Rs.

[0023] In combination with the second aspect, in some implementations of the second aspect, the second circuit further includes: a second switch K1 , the second switch K1 is connected in parallel with the third detection resistor R3 , and the second switch K1 is in a normally open state.

[0024] In a third aspect, a charger is provided, comprising a rectifier and the inverter as described in the first aspect.

[0025] In a fourth aspect, a vehicle is provided, comprising a vehicle body and the charger described in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a simplified circuit diagram of the bidirectional charger inverter circuit.

[0027] Figure 2 This is a structural diagram of an application circuit of an insulation detection circuit proposed in this application.

[0028] Figure 3 This is a schematic diagram of the specific structure of an application circuit of an insulation detection circuit proposed in this application.

[0029] Figure 4 Offline detection Figure 3 Simplified equivalent circuit diagram of .

[0030] Figure 5 During online detection Figure 3 Simplified equivalent circuit diagram of .

[0031] Figure 6 This is a schematic diagram of the specific structure of an application circuit of another insulation detection circuit proposed in this application.

[0032] Figure 7 Offline detection Figure 6 Simplified equivalent circuit diagram of . DETAILED DESCRIPTION

[0033] The technical solution in this application will be described below with reference to the accompanying drawings.

[0034] See also Figure 1 , Figure 1 This is a structural diagram of an inverter circuit provided in an embodiment of the present application.

[0035] The inverter circuit is a circuit that converts direct current into alternating current. Figure 1 As shown, the inverter circuit primarily comprises the following structures: an input DC bus, an output live line L, an output neutral line N, a conversion unit, and a first ground line PE. The input DC bus includes a positive bus electrode (Bus+) and a negative bus electrode (Bus-). The output live line L and the output neutral line N are each connected to the first ground line PE. The input DC bus, the output live line L, and the output neutral line N are each connected to the conversion unit, which converts the DC signal input from the input DC bus into an AC signal and outputs it through the output live line L and the output neutral line N.

[0036] When the inverter circuit is working normally, the voltage loaded between the positive bus Bus+ and the negative bus Bus- is the DC input voltage V bus The voltage loaded between the output live wire L and the output neutral wire N is the AC output voltage V ac For example, the DC input voltage V bus Usually it is necessary to ensure that it is greater than or equal to the peak value of the output AC voltage. For example, if the output AC voltage is 220V and its peak value is 311V, then the DC input voltage V bus A fixed voltage of 311V or more, for example, 400V. When the insulation of the inverter circuit is not broken, the AC output voltage V ac The voltage value is 220V (volts), the frequency is 50Hz (hertz) AC voltage, you can use 220V ac / 50Hz indicated.

[0037] After the load is connected to the inverter circuit, the first ground wire PE and the second ground wire of the load of the inverter circuit ( Figure 1(not shown). Typically, the first ground wire PE is grounded (e.g., through a second ground wire). The insulation resistance of the output live wire L relative to the first ground wire PE is a first insulation resistance Rx, and the insulation resistance of the output neutral wire N relative to the first ground wire PE is a second insulation resistance Ry. The parallel resistance value of the first insulation resistance Rx and the second insulation resistance Ry is an insulation resistance Rxy. The Y capacitor between the output live wire L and the first ground wire PE in the inverter circuit is a first Y capacitor Cx, and the Y capacitor between the output neutral wire N and the first ground wire PE in the inverter circuit is a second Y capacitor Cy. It should be understood that a Y capacitor is a capacitor connected across the output live wire L and the first ground wire PE, or between the output neutral wire N and the first ground wire PE, and Y capacitors generally appear in pairs. A Y capacitor is a safety capacitor, which refers to a safety capacitor that will not cause electric shock or endanger personal safety after the capacitor fails. Y capacitors are generally used to suppress common-mode interference in circuits. In this inverter circuit, the insulation impedance may include a first insulation resistor Rx and a second insulation resistor Ry. A circuit consisting of the first insulation resistor Rx, the second insulation resistor Ry, the first Y capacitor Cx, and the second Y capacitor Cy may be referred to as an insulation impedance circuit.

[0038] It should be understood that for different inverter circuits, the structures of the conversion units are different.

[0039] For ease of understanding, Figure 1 A possible structure of a conversion unit is given in the figure, and the embodiment of the present application is specifically described by taking the conversion unit as an example. The conversion unit of the inverter circuit includes: three inductors L1, L2, L3, a capacitor C2, three high-frequency bridge arms Q1Q2, Q3Q4, Q5Q6 and a working bridge arm Q7Q8. Among them, one side of the inductors L1, L2, and L3 is connected to the output live wire L, and the other side is connected to the midpoints of the three high-frequency bridge arms respectively. Among them, the high-frequency bridge arm Q1Q2 includes a switching device S ah S al The high-frequency bridge arm Q3Q4 includes a switching device S bh S bl The high-frequency bridge arm Q5Q6 includes a switching device S ch S cl , power frequency bridge arm S nh S nl The midpoint is connected to N, and the capacitor C2 is connected between the output live wire L and the output neutral wire N. By adjusting the on-off state of the 8 switching devices, the DC input voltage V loaded on the DC input bus can be adjusted. bus , converted into the AC output voltage V loaded between the output live wire L and the output neutral wire N ac .

[0040] The aforementioned conversion unit mainly includes a plurality of switching devices, and is therefore also called a switching circuit. In the embodiment of the present application, the inverter circuit may also include other structures, as long as its inverter function is guaranteed. For example, other switching devices, capacitors, resistors and / or inductors may also be provided in the inverter circuit. For example, when the inverter circuit in the aforementioned 1 is applied to a vehicle charger, the inverter circuit can be reused with a power factor correction (PFC) circuit, and the PFC circuit has a rectifier mode and an inverter mode. When the PFC circuit is in the inverter mode, it realizes the function of the aforementioned inverter circuit, and when the PFC circuit is in the rectifier mode, it realizes the function of the rectifier circuit. The aforementioned Figure 1 The inverter circuit may further include capacitor C1, which is a bus capacitor connected between the positive bus Bus+ and the negative bus Bus-. When the PFC circuit is in rectification mode, capacitor C1 is used to filter the voltage output from the positive bus Bus+ and the negative bus Bus-.

[0041] As mentioned above Figure 1 As shown, in the process of the inverter circuit outputting AC power through the output live wire L and the output neutral wire N, the insulation impedance of the output end to the ground can ensure personal safety, but the insulation impedance may fail due to contamination or other reasons (that is, the insulation impedance decreases). Once the insulation impedance fails, it may cause the first ground wire PE to be energized, which will seriously threaten personal safety. Therefore, the present application proposes a circuit that can perform insulation detection on the inverter circuit.

[0042] The insulation detection circuit provided in the embodiment of the present application can perform insulation detection on the inverter circuit. Figure 2 As shown, Figure 2 This is a schematic diagram of the structure of an insulation detection circuit proposed in this application. The insulation detection circuit is used to detect the inverter circuit (such as Figure 1 Detection is performed as shown).

[0043] The insulation detection circuit includes: a first circuit and a second circuit, wherein the first end of the first circuit is connected to the first node P1 of the inverter circuit, the second end of the first circuit is connected to the first ground line PE, the first circuit includes at least one detection resistor, the first end of the second circuit is connected to the second node P2 of the inverter circuit, the second end of the second circuit is connected to the first ground line PE, the second circuit includes a sampling resistor and at least one detection resistor, the sampling resistor is connected to the controller, the first node P1 is connected to the positive electrode of the bus, the second node P2 is connected to the negative electrode of the bus, or the first node P1 is connected to the negative electrode of the bus, and the second node P2 is connected to the positive electrode of the bus. For ease of understanding, Figure 2 In the figure, the first node P1 is connected to the positive electrode of the bus bar, and the second node P2 is connected to the negative electrode of the bus bar.

[0044] The controller is used for: (1) offline detection. Offline detection means: before the inverter circuit operates, that is, after the input DC bus voltage is established and before the first AC voltage is output on the output live wire L and the output neutral wire N, the insulation test of the inverter circuit is performed, wherein the first AC voltage is the AC voltage output when the inverter circuit operates.

[0045] A first DC voltage across the sampling resistor is sampled, and an insulation resistance Rxy of the inverter circuit is determined based on the first DC voltage. The insulation resistance Rxy is the parallel resistance of a first insulation resistor Rx and a second insulation resistor Ry, where the first insulation resistor Rx is the insulation resistance of the output live wire L relative to the first ground wire PE, and the second insulation resistor Ry is the insulation resistance of the output neutral wire N relative to the first ground wire PE.

[0046] Optionally, a detection resistor included in at least one of the first circuit or the second circuit is short-circuited, and then a second DC voltage across the sampling resistor is sampled to obtain a voltage-time variation curve of the sampling resistor; and the capacitance of the Y capacitor is determined based on the sampled voltage-time variation curve of the sampling resistor and the insulation resistance Rxy, where the capacitance of the Y capacitor is the sum of the capacitances of a first Y capacitor Cx between the output live wire L and the first ground wire PE and a second Y capacitor Cy between the output neutral wire N and the first ground wire PE.

[0047] During offline detection, the insulation detection circuit confirms the insulation resistance Rxy through the voltage divider at both ends of the sampling resistor, and confirms the Y capacitance through the voltage change curve at both ends of the sampling resistor. No impedance change is involved. Therefore, compared with the current technology, the insulation impedance of the inverter in this application will not decrease.

[0048] Optionally, the controller can also be used for: (2) online detection. Online detection means: after the inverter circuit is in operation, that is, after the first AC voltage is output on the output live wire L and the output neutral wire N, an online insulation detection is performed on the inverter circuit.

[0049] It should be understood that online detection can only be performed when the insulation resistance Rxy and the capacitance of the Y capacitor are normal. As long as the resistance value of any one of the first insulation resistor Rx and the second insulation resistor Ry decreases, it can be reflected by the insulation resistance Rxy. Therefore, it is possible to detect whether the insulation impedance has decreased by the insulation resistance Rxy. For example, the calculated insulation resistance Rxy can be compared with the first insulation resistance threshold. When the insulation resistance Rxy is greater than the first insulation resistance threshold, insulation failure is determined, wherein the first insulation resistance threshold is used to limit the minimum value of the insulation resistance Rxy. Under normal circumstances, the insulation resistance Rxy is large, for example, above 100 megohms (Mohms, MΩ). If it decreases, it may drop to the kiloohm (kohms, kΩ) level.

[0050] Similarly, if the capacitance of either the first Y capacitor Cx or the second Y capacitor Cy is too large, it can easily cause a discharge risk during the operation of the inverter circuit, affecting personal safety. When the Y capacitor is too large, it indicates that the capacitance of either the first Y capacitor Cx or the second Y capacitor Cy is too large, and therefore it can be roughly determined that insulation failure has occurred.

[0051] The online detection is described in detail below.

[0052] ① The controller is based on the second insulation resistance threshold and the first AC voltage V ac1 , the frequency of the first AC voltage and the capacitance of the Y capacitor, calculate a first voltage threshold V1 loaded across the sampling resistor and a second voltage threshold V2 loaded across the sampling resistor, wherein the first voltage threshold is used to determine whether the first insulation resistor Rx has an insulation failure, the second voltage threshold is used to determine whether the second insulation resistor Ry has an insulation failure, the second insulation resistance threshold is used to limit the minimum value of the first insulation resistor Rx, and the second voltage threshold V2 is less than the first voltage threshold V1, and the first AC voltage is a preset AC safety voltage loaded between the output live wire L and the output neutral wire N.

[0053] For example, when the insulation of the inverter circuit is not failed, the first AC voltage V ac1 It can be an AC voltage with a voltage value of 220V (volts) and a frequency of 50Hz (hertz). The first AC voltage V ac1 It can be expressed as 220Vac / 50Hz.

[0054] It should be understood that the parameters used to calculate the first voltage threshold and the second voltage threshold do not depend on the inverter circuit being in actual working state. Therefore, the two voltage thresholds can be calculated as long as the capacitance of the Y capacitor in the inverter circuit is determined.

[0055] ② Sample the second AC voltage across the sampling resistor to obtain the first sampling voltage value V of the sampling resistor. ac2 .

[0056] ③ According to the first voltage threshold V1, the second voltage threshold V2 and the first sampling voltage value V ac2 , determine whether the insulation of the inverter circuit fails.

[0057] It should be understood that since the first AC voltage V ac1 , the frequency of the first AC output voltage, the capacitance of the first Y capacitor Cx, and the capacitance of the second Y capacitor Cy are usually unchanged. Therefore, when the first insulation impedance Rx of the output live wire L to the first ground wire PE decreases, the voltage value V ac2It has a linear relationship with the resistance value of the first insulation resistor Rx, and the linear relationship is a negative correlation linear relationship, that is, the smaller the resistance value of the first insulation resistor Rx is, the higher the voltage value V sampled by the controller is. ac2 When the second insulation resistance Ry of the output neutral line N to the first ground line PE decreases, the voltage value V obtained by the controller in real time sampling ac2 There is a linear relationship between the resistance value of the second insulation resistor Ry and the linear relationship is a positive correlation linear relationship, that is, the smaller the resistance value of the second insulation resistor Ry is, the higher the voltage value V sampled by the controller is. ac2 The smaller.

[0058] In one implementation, the controller may ac2 When the voltage is greater than the first voltage threshold V1, it is determined that the insulation failure of the output live wire L of the inverter circuit occurs; ac2 When the voltage is less than the second voltage threshold V2, it is determined that the insulation of the output neutral line N of the inverter circuit fails.

[0059] In another implementation, the controller may not need to determine which insulation resistance has insulation failure, but only determine whether insulation failure has occurred. ac2 When the voltage is greater than the first voltage threshold V1, or when the first sampling voltage value V ac2 When the voltage is less than the second voltage threshold V2, it is determined that the insulation of the inverter circuit has failed.

[0060] In another optional manner, the controller may detect the first sampled voltage value V ac2 Whether it falls within the voltage range [V2, V1], when the first sampling voltage value V ac2 If the voltage does not fall within the voltage range [V2, V1], it is determined that the insulation of the inverter circuit fails; when the first sampling voltage value V ac2 If the voltage falls within the range [V2, V1], it is determined that the insulation resistance of the inverter circuit is normal.

[0061] To sum up, the insulation detection circuit provided in the embodiment of the present application can realize online insulation detection. At the same time, since the insulation detection circuit only involves the input DC bus, the output live wire L, the output neutral wire N and the first ground wire, it can be applied to various inverter circuit topologies.

[0062] Below, in Figure 1 Based on this, the present application provides a schematic diagram of a possible specific insulation detection circuit.

[0063] For example, Figure 3As shown, the first circuit includes: a first detection resistor R1 and a second detection resistor R2, wherein one end of the first detection resistor R1 is connected to the positive electrode of the bus, the other end of the first detection resistor R1 is connected to one end of the second detection resistor R2, and the other end of the second detection resistor R2 is connected to the first ground line PE. As an example, the resistance value of R1 can be 6.5MΩ, and the resistance value of R2 can be 19.5MΩ.

[0064] Optionally, Figure 3 The first circuit shown further includes a first switch S1 , which is connected in parallel with the first detection resistor R1 , and is in a normally open state.

[0065] For example, Figure 3 As shown, the second circuit includes: a third detection resistor R3 and a sampling resistor Rs, wherein one end of the third detection resistor R3 is connected to the first ground line PE, the other end of the third detection resistor R3 is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is connected to the negative electrode of the bus, and the sampling port of the controller is connected to both ends of the sampling resistor Rs. Figure 3 In the circuit shown, the controller samples the voltage value of the output voltage of the second circuit by sampling the voltage value of the sampling resistor Rs. As an example, the resistance value of R3 can be 26MΩ, and the resistance value of Rs can be 0.116MΩ.

[0066] based on Figure 3 The insulation detection circuit shown performs offline detection on the inverter circuit, calculates the insulation resistance Rxy of the inverter circuit and the capacitance of the Y capacitor, and thus determines whether there is a problem with the insulation impedance based on the calculation results. During offline detection, since the voltage between the output live wire L and the output neutral wire N is 0V, the output live wire L and the output neutral wire N can be equivalent to a short circuit. In addition, when the steady-state DC voltage is supplied, the capacitor does not participate in the voltage division, so the capacitance of the first Y capacitor Cx and the second Y capacitor Cy can be ignored. The first insulation resistor Rx and the second insulation resistor Ry are equivalent to being connected in parallel. Under this working condition, Figure 3 The circuit is simplified to Figure 4 shown.

[0067] In one implementation, based on Figure 4 In the structure shown, the controller can perform offline detection on the inverter circuit through S410 and S420.

[0068] S410, when the first switch S1 is in the off state, based on the V across the sampling resistor Rs ad (ie the first DC voltage) to calculate the circuit insulation resistance Rxy.

[0069] Since the DC input voltage V bus, the resistance of the first detection resistor R1, the resistance of the second detection resistor R2, the resistance of the third detection resistor R3, and the resistance of the sampling resistor Rs are known, so we can Figure 4 The circuit relationship shown results in an insulation resistance value Rxy, which satisfies formula (1).

[0070]

[0071] Depend on Figure 4 As can be seen from the circuit relationship shown, the voltage V across Rs ad Affected by the first insulation resistor Rx and the second insulation resistor Ry, when the resistance value of any one of the resistors Rx and Ry decreases, the Rs voltage divider will also decrease accordingly.

[0072] S420, close the first switch S1. Figure 4 From the circuit relationship shown, it can be seen that the voltage across Rs will rise. By recording the rising curve of the voltage across Rs, the change of voltage over time can be obtained according to the voltage curve, and the capacitance value of the y capacitor Cx+Cy can be inferred. Cx+Cy satisfies formula (2).

[0073]

[0074] Among them, T c is the target charge and discharge time, T c It can be determined by the controller. According to the relationship between the charge and discharge time of the capacitor (that is, the charging process corresponds to the charging time, and the discharging process corresponds to the discharging time) and the charging voltage, the target charging time when the charging voltage reaches a stable state can be determined. When the charging voltage reaches a stable state, it can be considered that the capacitor is basically full; the target discharge time when the discharge voltage reaches a stable state can also be determined. When the discharge voltage reaches a stable state, it can be considered that the capacitor is basically discharged. Among them, the target charge and discharge time includes the target charging time or the target discharge time. The target charging time and the target discharge time are usually equal. For example, after the charging voltage reaches a stable state, the charging time corresponding to 0.95 times the full-rated voltage when the capacitor is full is equal to 3 times the charging time constant. Similarly, the discharge time corresponding to 0.95 times the full-rated voltage is equal to 3 times the charging time constant.

[0075] In the embodiment of the present application, since the sampling voltage read by the controller is also stable when the charging voltage is stable, that is, the change states of the two are consistent, the target charge and discharge time T is c It can be determined by the sampled voltage value read by the controller.

[0076] based on Figure 3 The structure shown in the figure is used to perform online detection on the inverter circuit. During online detection, an AC voltage is output between the output live wire L and the output neutral wire N. Under this working condition, the Figure 3The circuit is simplified to Figure 5 shown.

[0077] In one implementation, based on Figure 5 In the structure shown, the controller can perform online detection on the inverter circuit through S510 to S530.

[0078] S510: Calculate a first voltage threshold and a second voltage threshold applied across Rs, wherein the first voltage threshold V1 is used to determine whether the first insulation resistor Rx has failed, and the second voltage threshold V2 is used to determine whether the second insulation resistor Ry has failed, and the first voltage threshold V1 is greater than the second voltage threshold V2.

[0079] In one implementation, the first voltage threshold V1 satisfies formula (3):

[0080]

[0081] Among them, V acpeak The safe AC voltage V is preset on the output live wire L and output neutral wire N of the inverter circuit during operation. ac1 The positive peak value, Rx1 is the second insulation resistance threshold, which is used to limit the minimum value of the first insulation resistance Rx, ω = 2*π*f, f is the AC output voltage V ac1 frequency.

[0082] It should be understood that for AC voltage, the corresponding voltage value is usually different at different times. In this application, a representative voltage value needs to be screened out for subsequent voltage comparison. For example: the first AC voltage V ac1 The waveform is usually a sine wave. In the above formula (3), the first AC voltage value V ac1 It can be the maximum value of the positive half cycle of the sine wave, that is, the positive half cycle peak value; V in formula (3) acpeak It can also be the minimum value of the negative half cycle of the sine wave, that is, the absolute value of the peak value of the negative half cycle. It is worth noting that the first AC voltage V ac1 In addition to screening by peak value, other methods can also be used to screen. It should be understood that V in formula (3) acpeak The voltage threshold value may be replaced by the maximum value in a specified sampling period, or a voltage value that meets specified conditions in a specified sampling period, for example, the average of multiple voltage values ​​sampled at multiple specified sampling times in the specified sampling period, etc., and the present embodiment does not limit this. For ease of understanding, the positive half-cycle peak voltage is used for illustration in the voltage threshold calculation of the present application.

[0083] It should also be understood that in practice, the relationship between Cx and Cy is known, so the capacitance value of Cx can be determined based on the relationship between Cx and Cy. For example, if Cx and Cy satisfy a 1:3 ratio, the capacitance value of Cx can be calculated based on this ratio and formula (2).

[0084] The second voltage threshold V2 satisfies formula (4):

[0085]

[0086] in, The remaining parameters are described in formula (3) and will not be repeated here.

[0087] S520, disconnect the first switch S1, sample the voltage across Rs (i.e., the second AC voltage), and determine a first sampled voltage value V from the multiple voltage values ​​obtained by sampling. ac2 .

[0088] As can be seen from the above, for AC voltage, at different sampling times, the voltage values ​​sampled by the controller are usually different. The controller needs to screen out a representative voltage value (referred to as the first sampled voltage value V in this embodiment of the application) ac2 ).

[0089] It should be understood that since the subsequent first sampling voltage value V ac2 It needs to be compared with the first voltage threshold and the second voltage threshold, so V ac2 and V acpeak The same comparison criteria are required. For example: V acpeak is the maximum value of the positive half cycle of the sine wave corresponding to the AC voltage, then V ac2 It is also the maximum value of the positive half cycle of the sine wave corresponding to the AC voltage.

[0090] S530, according to the first voltage threshold V1, the second voltage threshold V2 and the first sampling voltage value V ac2 , determine whether the insulation of the inverter circuit fails.

[0091] To determine whether the inverter circuit has insulation failure, refer to Figure 2 The description in , will not be repeated here.

[0092] Below, in Figure 1 Based on this application Figure 6 A schematic diagram of another possible specific insulation detection circuit is given.

[0093] For example, Figure 6 As shown, the first circuit includes: a first detection resistor R1, a second detection resistor R2, and the connection relationship between the first detection resistor R1 and the second detection resistor R2 is as follows: Figure 3 The same, no further details here.

[0094] For example, Figure 6 As shown, the second circuit includes: a third detection resistor R3 and a sampling resistor Rs. The connection relationship between the third detection resistor R3 and the sampling resistor Rs is the same as Figure 3 The same is true and will not be repeated here.

[0095] Optionally, Figure 6 The second circuit shown further includes: a second switch K1, wherein the second switch K1 is connected in parallel with the third detection resistor R3, and the second switch K1 is in a normally open state. Figure 3 The difference is that Figure 6 The switch in the first circuit is connected in parallel to R3 in the second circuit.

[0096] based on Figure 6 The structure shown in the figure is used to perform offline detection on the inverter circuit. Figure 6 The circuit is simplified to Figure 7 shown.

[0097] In one implementation, based on Figure 7 In the structure shown, the controller can perform offline detection on the inverter circuit through S710 and S720.

[0098] S710: When the second switch K1 is in the off state, the circuit insulation resistance Rxy is calculated according to the circuit relationship. The calculation of the insulation resistance Rxy can refer to the description in S310 and will not be repeated here.

[0099] S720, close the second switch K1. Figure 7 From the circuit relationship shown, it can be seen that the voltage across Rs will drop. By recording the curve of the voltage change across Rs over time, the capacitance value of the y capacitor Cx+Cy can be inferred.

[0100] based on Figure 6 The structure shown in the figure is used to perform online detection on the inverter circuit. In this working condition, the second switch K1 is disconnected. Figure 6 The circuit simplification and Figure 5 same.

[0101] In one implementation, based on Figure 5 In the structure shown, the controller can perform online detection on the inverter circuit through S810 to S830.

[0102] S810: For details, please refer to the description in S510, which will not be repeated here.

[0103] S820, disconnect the second switch K1, sample the voltage across Rs (i.e., the second AC voltage), and determine a first sampled voltage value V from the multiple voltage values ​​obtained by sampling. ac2For other descriptions, please refer to S520, which will not be repeated here.

[0104] S830: For details, please refer to the description in S530, which will not be repeated here.

[0105] In summary, the insulation detection circuit provided by the present application is configured by setting a first circuit between the positive pole of the busbar and the first ground wire PE, and a second circuit between the negative pole of the busbar and the first ground wire PE. During the offline detection process, the insulation detection circuit confirms the insulation resistance Rxy by sampling the voltage divided across the sampling resistor in the second circuit. The above process does not involve impedance changes. Therefore, the present application does not cause the insulation impedance itself to decrease when performing insulation detection. At the same time, the insulation detection circuit provided by the present application can also realize online insulation detection. The controller samples the voltage value of the sampling resistor in the second circuit, and determines whether the circuit after the inverter is started has insulation failure based on the relationship between the sampled voltage and the voltage threshold corresponding to the sampling resistor, thereby effectively ensuring personal safety. In addition, the insulation detection circuit provided by the present application only involves the input DC busbar, the output live wire L, the output neutral wire N and the first ground wire PE. Therefore, the insulation detection circuit provided by the present application can also be applied to various inverter circuit topologies.

[0106] An embodiment of the present application provides an inverter, including: an inverter circuit, and the insulation detection circuit provided in the above embodiment.

[0107] An embodiment of the present application provides a charger comprising a rectifier and the aforementioned inverter. The rectifier and inverter can be integrated with a PFC circuit to achieve miniaturization of the charger. Optionally, the charger can be used in electric vehicles or other power-driven devices, such as a robot vacuum.

[0108] An embodiment of the present application provides a vehicle comprising a vehicle body and the aforementioned charger. The vehicle comprises: a vehicle body and a charger disposed within the vehicle body. Optionally, the vehicle may also include other onboard equipment, such as an onboard power distribution unit, a motor controller, or a battery pack.

[0109] For example, the vehicle may be an electric vehicle. Alternatively, the electric vehicle may be an electric car, an electric motorcycle, or an electric bicycle.

[0110] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. An inverter, characterized in that: include: A controller, an inverter circuit, and an insulation detection circuit. The inverter circuit is used to convert direct current into alternating current. The inverter circuit includes an input terminal, an output terminal, and a first ground wire PE. The input terminal of the inverter circuit includes an input DC bus, and the input DC bus includes a bus positive electrode and a bus negative electrode. The output terminal of the inverter circuit includes an output live wire L and an output neutral wire N. The output live wire L and the output neutral wire N are connected to the first ground wire PE. The insulation detection circuit comprises: A first circuit and a second circuit, wherein The first end of the first circuit is connected to the first node of the inverter circuit, the second end of the first circuit is connected to the first ground line PE, and the first circuit includes at least one detection resistor. The first end of the second circuit is connected to the second node of the inverter circuit, the second end of the second circuit is connected to the first ground line PE, the second circuit includes a sampling resistor and at least one detection resistor, the sampling resistor is connected to the controller, The first node is connected to the positive electrode of the bus bar, and the second node is connected to the negative electrode of the bus bar, or the first node is connected to the negative electrode of the bus bar, and the second node is connected to the positive electrode of the bus bar; The controller is used to: Controlling the inverter to be in an offline state, wherein the offline state means that the input DC bus voltage has been established and there is no AC voltage output on the output live wire L and the output neutral wire N; sampling a first DC voltage across the sampling resistor, and determining an insulation resistance Rxy of the inverter circuit based on the first DC voltage, wherein the insulation resistance Rxy is a parallel resistance value of a first insulation resistor Rx and a second insulation resistor Ry, the first insulation resistor Rx is an insulation resistance of the output live wire L relative to the first ground wire PE, and the second insulation resistance Ry is an insulation resistance of the output neutral wire N relative to the first ground wire PE; short-circuiting at least one detection resistor included in the first circuit or the second circuit; Sampling a second DC voltage across the sampling resistor to obtain a voltage-time variation curve of the sampling resistor; The capacitance of the Y capacitor is determined according to the voltage-time variation curve and the insulation resistance Rxy, and the capacitance of the Y capacitor is the sum of the capacitances of the first Y capacitor Cx between the output live wire L and the first ground wire PE and the second Y capacitor Cy between the output neutral wire N and the first ground wire PE.

2. The inverter according to claim 1, characterized in that The controller is also used to: When the insulation resistance Rxy is not less than a first insulation resistance threshold, controlling the inverter to be in an online state, wherein the online state means that an AC voltage is output on the output live wire L and the output neutral wire N, and the first insulation resistance threshold is used to limit a minimum value of the insulation resistance Rxy; Calculating a first voltage threshold applied across the sampling resistor and a second voltage threshold applied across the sampling resistor based on a second insulation resistance threshold, a first AC voltage, a frequency of the first AC voltage, and the capacitance of the Y capacitor, wherein the second insulation resistance threshold is used to define a minimum value of the first insulation resistance Rx, the first voltage threshold is used to determine whether the first insulation resistance Rx has an insulation failure, and the second voltage threshold is used to determine whether the second insulation resistance Ry has an insulation failure, the second voltage threshold is less than the first voltage threshold, and the first AC voltage is a preset AC safety voltage applied between the output live wire L and the output neutral wire N; sampling a second AC voltage across the sampling resistor to obtain a first sampled voltage value of the sampling resistor; It is determined whether the inverter circuit has insulation failure according to the first voltage threshold, the second voltage threshold, and the first sampled voltage value.

3. The inverter according to claim 2, characterized in that: The controller is specifically used for: When the first sampled voltage value is greater than the first voltage threshold, determining that the insulation of the output live wire L of the inverter circuit fails; When the first sampling voltage value is less than the second voltage threshold, it is determined that insulation failure occurs in the output neutral line N of the inverter circuit.

4. The inverter according to any one of claims 1 to 3, characterized in that: The first circuit includes: A first detection resistor R1 and a second detection resistor R2; One end of the first detection resistor R1 is connected to the positive electrode of the busbar, the other end of the first detection resistor R1 is connected to one end of the second detection resistor R2, and the other end of the second detection resistor R2 is connected to the first ground line PE.

5. The inverter according to claim 4, characterized in that: The first circuit further includes: The first switch S1 is connected in parallel with the first detection resistor R1 and is in a normally open state.

6. The inverter according to any one of claims 1 to 3, characterized in that: The second circuit includes: A third detection resistor R3 and a sampling resistor Rs; One end of the third detection resistor R3 is connected to the first ground line PE, the other end of the third detection resistor R3 is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is connected to the negative electrode of the bus, and the sampling port of the controller is connected to both ends of the sampling resistor Rs.

7. The inverter according to claim 6, characterized in that: The second circuit further includes: The second switch K1 is connected in parallel with the third detection resistor R3 , and the second switch K1 is in a normally open state.

8. An insulation detection circuit, characterized in that: The insulation detection circuit is used to perform insulation detection on the inverter circuit, and the inverter circuit is used to convert direct current into alternating current. The inverter circuit includes an input end, an output end, and a first ground wire PE, wherein the input end of the inverter circuit includes an input DC bus, and the input DC bus includes a bus positive pole and a bus negative pole. The output end of the inverter circuit includes an output live wire L and an output neutral wire N, and the output live wire L and the output neutral wire N are connected to the first ground wire PE. The insulation detection circuit comprises: A first circuit and a second circuit, wherein The first end of the first circuit is connected to the positive electrode of the busbar, the second end of the first circuit is connected to the first ground line PE, and the first circuit includes at least one detection resistor; A first end of the second circuit is connected to the negative electrode of the busbar, a second end of the second circuit is connected to the first ground line PE, and the second circuit includes a sampling resistor and at least one detection resistor; Wherein, the first DC voltage of the sampling resistor is used to determine the insulation resistance Rxy of the inverter circuit; The first DC voltage is the voltage across the sampling resistor when the input DC bus voltage is established and there is no AC voltage output on the output live wire L and the output neutral wire N; The second DC voltage of the sampling resistor is used to determine a voltage-time variation curve of the sampling resistor. The voltage-time variation curve and the insulation resistance Rxy are used to determine the capacitance of a Y capacitor. The capacitance of the Y capacitor is the sum of the capacitances of a first Y capacitor Cx between the output live wire L and the first ground wire PE and a second Y capacitor Cy between the output neutral wire N and the first ground wire PE. The second DC voltage is the voltage across the sampling resistor when the input DC bus voltage is established, no AC voltage is output on the output live line L and the output neutral line N, and at least one detection resistor included in the first circuit or the second circuit is short-circuited.

9. The insulation detection circuit according to claim 8, characterized in that: The first circuit includes: A first detection resistor R1 and a second detection resistor R2; One end of the first detection resistor R1 is connected to the positive electrode of the busbar, the other end of the first detection resistor R1 is connected to one end of the second detection resistor R2, and the other end of the second detection resistor R2 is connected to the first ground line PE.

10. The insulation detection circuit according to claim 9, characterized in that: The first circuit further includes: The first switch S1 is connected in parallel with the first detection resistor R1 and is in a normally open state.

11. The insulation detection circuit according to any one of claims 8 to 10, characterized in that: The second circuit includes: A third detection resistor R3 and a sampling resistor Rs; One end of the third detection resistor R3 is connected to the first ground line PE, the other end of the third detection resistor R3 is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is connected to the negative electrode of the bus, and the sampling port of the controller is connected to both ends of the sampling resistor Rs.

12. The insulation detection circuit according to claim 11, characterized in that: The second circuit further includes: The second switch K1 is connected in parallel with the third detection resistor R3 , and the second switch K1 is in a normally open state.

13. A charger, characterized in that: include: A rectifier and an inverter according to any one of claims 1 to 7.

14. A vehicle, characterized in that: include: A vehicle body and a charger as claimed in claim 13.

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