Converter and insulation impedance measurement method

Abstract

Disclosed in the present application are a converter and an insulation impedance measurement method. The converter comprises: a controller, a measurement resistor network and a power conversion circuit. The power conversion circuit comprises a first switch tube and a second switch tube, wherein a first end of the first switch tube is connected to a positive electrode of a direct-current power source, a second end of the first switch tube is connected to a first end of the second switch tube, a second end of the second switch tube is connected to a negative electrode of the direct-current power source, and the second end of the first switch tube is grounded by means of the measurement resistor network. The controller is used for obtaining an insulation impedance of the converter according to the voltage between the positive electrode and the negative electrode of the direct-current power source and the voltage to ground of the negative electrode of the direct-current power source before and after the first switch tube or the second switch tube is turned on. By means of controlling the state of a switch, the magnitude of the voltage between a positive electrode and a negative electrode of a direct current of the converter or the magnitude of a voltage to ground of the negative electrode of the direct current is changed, and in combination with an impedance of the measurement resistor network, an insulation impedance of the converter is obtained. The converter only requires the addition of a measurement resistor network, and the switch tubes of the converter are utilized, such that the cost is low.

Description

A converter and insulation impedance detection method

[0001] This application claims priority to the Chinese patent application with application number 202310239127.8 and application name “A converter and insulation impedance detection method” filed with the State Intellectual Property Office of China on March 8, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power electronics technology, and in particular to a converter and an insulation impedance detection method. Background Art

[0003] Clean energy applications, represented by photovoltaic power generation and electrochemical energy storage systems, are becoming increasingly widespread. However, new energy power generation systems are generally placed outdoors and are affected by weather factors such as dust, rain, snow, and fog. This can cause changes in the insulation impedance of subsequent converters (such as inverters) to the ground, i.e., the insulation impedance. If this insulation impedance is too low, the resulting leakage current can pose a risk of electric shock, so real-time monitoring of this insulation impedance is necessary.

[0004] The traditional resistance bridge method requires adding resistance to the ground and its supporting switching circuit, which will reduce equipment reliability and increase costs.

[0005] Summary of the Invention

[0006] In view of this, the present application provides a converter and an impedance detection method, which can accurately detect the insulation impedance of the converter, and has high reliability and low cost.

[0007] The present application provides a converter, comprising: a controller, a detection resistor network, and a power conversion circuit;

[0008] The power conversion circuit includes a first switching tube and a second switching tube;

[0009] A first end of the first switching tube is connected to the positive electrode of the DC power supply, a second end of the first switching tube is connected to the first end of the second switching tube, and a second end of the second switching tube is connected to the negative electrode of the DC power supply; the second end of the first switching tube is grounded through a detection resistor network;

[0010] The controller is used to obtain the insulation impedance of the converter according to the voltage between the positive electrode and the negative electrode of the DC power supply and the voltage between the negative electrode of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed.

[0011] Preferably, the detection resistor network includes a first resistor;

[0012] The second end of the first switch tube is grounded through a first resistor.

[0013] Preferably, the detection resistor network further comprises: a second resistor and a third resistor;

[0014] Two ends of the second resistor are connected to the positive electrode of the DC power supply and the second end of the first switch tube respectively;

[0015] Two ends of the third resistor are connected to the negative electrode of the DC power supply and the second end of the first switch tube respectively.

[0016] Preferably, it further comprises: an inductor;

[0017] The second end of the first switch tube is grounded through an inductor and a first resistor connected in series.

[0018] Preferably, the controller is used to obtain the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and the ground before the first switch tube is closed, and the voltage between the negative pole of the DC power supply and the ground after the first switch tube is closed.

[0019] Preferably, the controller is used to obtain the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and the ground before the second switch tube is closed, and the voltage between the negative pole of the DC power supply and the ground after the second switch tube is closed.

[0020] Preferably, the converter is an isolated DCDC converter or an isolated DCAC converter;

[0021] The first switching tube and the second switching tube are two switching tubes of the first bridge arm of the primary full bridge of the isolated DCDC converter or the isolated DCAC converter; the primary full bridge of the isolated DCDC converter includes the first bridge arm and the second bridge arm.

[0022] Preferably, the converter is a T-type three-level inverter;

[0023] The T-type three-level inverter also includes an inductor;

[0024] The second end of the first switch tube is grounded through an inductor and a detection resistor network connected in series.

[0025] Preferably, the converter includes a three-level Boost circuit and a neutral point clamped inverter circuit; the neutral point clamped inverter circuit includes a first switch module, a second switch module, a third switch module and a fourth switch module connected in series;

[0026] The first switch tube and the second switch tube are respectively the first switch module and the second switch module in the three-level Boost circuit;

[0027] or,

[0028] The first switching tube and the second switching tube are the second switching module and the third switching module of the neutral point clamped inverter circuit.

[0029] Preferably, the converter includes a three-level Boost circuit and an active neutral point clamped inverter circuit;

[0030] The first switching tube and the second switching tube are the first switching tube and the second switching tube in a three-level Boost circuit.

[0031] Preferably, the converter is a bidirectional DCDC buck-boost converter;

[0032] The bidirectional DCDC buck-boost converter comprises a first switch module, a second switch module, a third switch module and a fourth switch module connected in series in sequence;

[0033] The first switch tube and the second switch tube are respectively the first switch module and the second switch module;

[0034] A common terminal of the first switch module and the second switch module is grounded through a detection resistor network.

[0035] Preferably, the converter is a heric converter;

[0036] The heric converter includes a first bridge arm, a second bridge arm, a fifth switch module, a sixth switch module and an LC filter; the midpoint of the first bridge arm is grounded through a detection resistor network;

[0037] The fifth switch module and the sixth switch module are connected in series and connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm;

[0038] The first end and the second end of the LC filter are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm; the first end and the second end of the LC filter are respectively connected to the two ends of the capacitor through the first inductor and the second inductor.

[0039] Preferably, the converter is a heric converter;

[0040] The heric converter includes a first bridge arm, a second bridge arm, a fifth switch module, a sixth switch module and an LC filter;

[0041] The fifth switch module and the sixth switch module are connected in series and connected between the midpoint of the first bridge arm and the midpoint of the second bridge arm;

[0042] The first end and the second end of the LC filter are connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm respectively; the first end and the second end of the LC filter are connected to the two ends of the capacitor through the first inductor and the second inductor respectively;

[0043] The first end of the LC filter is grounded via a first inductor and a first resistor connected in series;

[0044] The first switching tube and the second switching tube are two switching tubes of the first bridge arm.

[0045] Preferably, it further comprises: a switch;

[0046] The sense resistor network is connected to ground through a switch;

[0047] The controller is also used to control the switch to be closed when the insulation impedance is detected, and to control the switch to be opened otherwise.

[0048] Preferably, the DC power source is a photovoltaic array or a battery.

[0049] The present application also provides a method for detecting insulation impedance of a converter, the converter comprising: a detection resistor network and a power conversion circuit; the power conversion circuit comprising a first switching tube and a second switching tube; a first end of the first switching tube being connected to a positive electrode of a DC power supply, a second end of the first switching tube being connected to a first end of a second switching tube, and a second end of the second switching tube being connected to a negative electrode of the DC power supply; and a second end of the first switching tube being grounded via the detection resistor network;

[0050] The method includes:

[0051] When the first switch tube and the second switch tube are both turned off, a voltage between the positive electrode and the negative electrode of the DC power supply and a voltage between the negative electrode and the ground of the DC power supply are obtained;

[0052] Controlling the first switch tube or the second switch tube to be closed;

[0053] The insulation impedance of the converter is obtained according to the voltage between the positive electrode and the negative electrode of the DC power supply and the voltage between the negative electrode of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed.

[0054] Preferably, the detection resistor network includes a first resistor; the second end of the first switch tube is grounded through the first resistor.

[0055] Preferably, the detection resistor network further comprises: a second resistor and a third resistor;

[0056] Two ends of the second resistor are connected to the positive electrode of the DC power supply and the second end of the first switch tube respectively;

[0057] Two ends of the third resistor are connected to the negative electrode of the DC power supply and the second end of the first switch tube respectively.

[0058] Preferably, obtaining the insulation impedance of the converter according to the voltage between the positive electrode and the negative electrode of the DC power supply and the voltage between the negative electrode of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed specifically includes:

[0059] The insulation impedance of the converter is obtained according to the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and the ground before the first switch tube is closed, and the voltage between the positive and negative poles of the DC power supply after the first switch tube is closed.

[0060] Preferably, obtaining the insulation impedance of the converter according to the voltage between the positive electrode and the negative electrode of the DC power supply and the voltage between the negative electrode of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed specifically includes:

[0061] The insulation impedance of the converter is obtained according to the voltage between the positive and negative electrodes of the DC power supply and the voltage between the negative electrode of the DC power supply and the ground before the second switch tube is closed, and the voltage between the negative electrode of the DC power supply and the ground after the second switch tube is closed.

[0062] It can be seen that this application has the following beneficial effects:

[0063] The converter provided in this application requires only the addition of a detection resistor network. The converter topology already includes a first and second switching transistors connected in series, with the second end of the first switching transistor connected to ground via the detection resistor network. By controlling the switching state of the first or second switching transistor, the voltage between the DC positive and negative electrodes of the converter, or the voltage between the DC negative electrode and ground, can be changed. The insulation impedance of the converter can then be obtained by combining the impedance of the detection resistor network. This converter has a simple structure for detecting insulation impedance, requiring only the addition of a detection resistor network. This utilizes the switching transistors inherent in the converter's power conversion circuit, resulting in low cost and applicability to a variety of converter types. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] FIG1 is a schematic diagram of a converter provided in an embodiment of the present application;

[0065] FIG2 is a schematic diagram of another detection resistor network provided in an embodiment of the present application;

[0066] FIG3 is a schematic diagram of a first resistor grounded according to an embodiment of the present application;

[0067] FIG4 is a schematic diagram of another detection resistor network provided in an embodiment of the present application;

[0068] FIG5 is an equivalent circuit diagram corresponding to when both switches in FIG2 are disconnected;

[0069] FIG6A is an equivalent circuit diagram corresponding to FIG2 when S1 is closed and S2 is open;

[0070] FIG6B is an equivalent circuit diagram corresponding to FIG2 when S1 is open and S2 is closed;

[0071] FIG7 is a flow chart of obtaining insulation impedance of a converter provided by an embodiment of the present application;

[0072] FIG8A is a schematic diagram of an isolated DCDC converter provided in an embodiment of the present application;

[0073] FIG8B is a schematic diagram of another isolated DCDC converter provided in an embodiment of the present application;

[0074] FIG9 is a schematic diagram of an isolated DC-AC converter provided in an embodiment of the present application;

[0075] FIG10 is a schematic diagram of a T-type three-level converter provided in an embodiment of the present application;

[0076] FIG11 is a schematic diagram of a three-level Boost+NPC converter provided in an embodiment of the present application;

[0077] FIG12 is a schematic diagram of another three-level Boost+NPC converter provided in an embodiment of the present application;

[0078] FIG13 is a schematic diagram of a three-level Boost+ANPC converter provided in an embodiment of the present application;

[0079] FIG14 is a schematic diagram of a bidirectional DCDC buck-boost converter provided in an embodiment of the present application;

[0080] FIG15 is a schematic diagram of a heric converter provided in an embodiment of the present application;

[0081] FIG16 is a schematic diagram of another heric converter provided in an embodiment of the present application;

[0082] FIG17 is a schematic diagram of another heric converter provided in an embodiment of the present application;

[0083] FIG18 is a flow chart of a method for detecting insulation impedance of a converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0084] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0085] The converter provided in the embodiment of the present application does not specifically limit the application scenario, and can be photovoltaic power generation, energy storage, or other power electronics fields. In addition, the embodiment of the present application does not specifically limit the specific type of the converter, for example, it can be an isolated converter or a non-isolated converter. In addition, when the converter is an isolated converter, it can be an isolated DCDC converter or an isolated DCAC converter. It should be understood that the insulation impedance obtained by the converter provided in the embodiment of the present application refers to the insulation impedance of the DC side of the converter to the ground.

[0086] For ease of understanding, the following introduction is made using a converter used in a photovoltaic system as an example.

[0087] Refer to Figure 1, which is a schematic diagram of a converter provided in an embodiment of the present application.

[0088] The converter provided in the embodiment of the present application includes: a controller (not shown in the figure), a detection resistor network 100 and a power conversion circuit; the power conversion circuit includes a first switch tube S1 and a second switch tube S2;

[0089] A first end of the first switch tube S1 is connected to the positive electrode PV+ of the DC power supply, a second end of the first switch tube S1 is connected to the first end of the second switch tube S2, and a second end of the second switch tube S2 is connected to the negative electrode PV- of the DC power supply; a second end of the first switch tube S1 is grounded via a detection resistor network 100;

[0090] In this embodiment, a photovoltaic array as a DC power source is used as an example for description.

[0091] The controller is used to obtain the insulation impedance of the converter based on the impedance of the detection resistor network 100, the voltage between the positive and negative poles of the DC power supply before and after the first switch tube or the second switch tube is closed, and the voltage between the negative pole of the DC power supply and the ground.

[0092] The embodiment of the present application does not specifically limit the number of resistors in the detection resistor network 100 . For example, it can be one or more resistors. When there are more than one resistor, it can be three, for example.

[0093] The following describes scenarios where the detection resistor network 100 includes one resistor and three resistors with reference to the accompanying drawings.

[0094] See FIG2 , which is a schematic diagram of a detection resistor network provided in an embodiment of the present application.

[0095] In this embodiment, the detection resistor network includes a first resistor R0 for the purpose of introduction;

[0096] A second terminal of the first switch tube S1 is grounded via a first resistor R0 .

[0097] See Figure 3, which is a schematic diagram of a detection resistor network provided by an embodiment of the present application. S1 and S2 shown in Figure 2 can be multiple switches connected in series. Figure 1 only illustrates part of the converter circuit.

[0098] The source of S1 is connected to the drain of S2. Rm is the inherent impedance of the converter's positive input terminal to ground PE (the chassis), and Rn is the inherent impedance of the converter's negative input terminal to ground PE (the chassis). R0 has a known resistance and is connected in series between PE and the source of S1.

[0099] In addition, the converter may further include: a switch K; for details, please refer to FIG3 , which is a schematic diagram of a detection resistor network grounding provided in an embodiment of the present application.

[0100] One end of the first resistor R0 is connected to the source of S1 through the switch K, and the other end of the first resistor R0 is grounded;

[0101] The controller is also used to control the switch K to be closed when detecting the insulation impedance, and to control the switch K to be open otherwise.

[0102] It should be understood that the converter provided in the embodiment of the present application utilizes the first switching tube and the second switching tube already included in the power conversion circuit, and only adds an external detection resistor network. It has low cost and simple structure. By controlling the switching state of the first switching tube or the second switching tube, the voltage between the DC positive pole and the negative pole of the converter or the DC negative pole to the ground voltage can be changed, and then the insulation impedance of the converter can be obtained in combination with the resistance value of the first resistor.

[0103] Since the first resistor is connected to the positive electrode of the DC power supply through the first switching tube and is connected to the negative electrode of the DC power supply through the second switching tube, when the switching state of the first switching tube or the second switching tube changes, the positive half-bus common-mode voltage or the negative half-bus common-mode voltage can be disturbed, that is, the disturbed voltage range is relatively large, which can make the insulation impedance detection more sensitive.

[0104] Referring to FIG. 4 , this figure is a schematic diagram of another detection resistor network provided in an embodiment of the present application.

[0105] The converter provided in this embodiment will be described by taking its application in the photovoltaic field as an example.

[0106] The detection resistor network further includes: a second resistor R1 and a third resistor R2;

[0107] It should be noted that the advantage of the multiple resistors in FIG. 4 over the single resistor in FIG. 3 is that it facilitates the voltage withstand test.

[0108] Two ends of the second resistor R1 are connected to the positive electrode PV+ of the DC power supply and the second end of the first switch tube S1 respectively;

[0109] Two ends of the third resistor R2 are connected to the negative electrode PV- of the DC power supply and the second end of the first switch tube S1 respectively.

[0110] Similar to the switch K in FIG3 , the corresponding detection resistor network in FIG4 may also correspond to the switch K, that is, one end of the first resistor R0 is connected to the source of S1 through the switch K, and the other end of the first resistor R0 is grounded to PE.

[0111] FIG2 shows that the first resistor is directly grounded. Another implementation is that the common end of the two switching tubes is grounded through the inductor in the filter circuit and the first resistor.

[0112] The following describes in detail the insulation impedance detection principle provided by the embodiments of the present application with reference to the accompanying drawings.

[0113] The embodiment of the present application does not specifically limit whether the first switch tube is closed or the second switch tube is closed to disturb the voltage. The first switch tube can be closed or the second switch tube can be closed. The following description takes the closing of the first switch tube as an example.

[0114] Option 1:

[0115] Refer to FIG5 , which is an equivalent circuit diagram corresponding to the case where both S1 and S2 in FIG2 are disconnected.

[0116] In Figure 2, the source of S1 is connected to the drain of S2. The drain of S1 is connected to one end of resistor Rm and PV+. The other end of Rm is connected to the chassis PE and one end of Rn. The other end of Rn is connected to PV-. R0 is connected to the chassis PE and the other end to the source of S1. Rm is the equivalent impedance between PV+ and PE, and Rn is the equivalent impedance between PV- and PE. The voltage between PV+ and PV- is represented by V1, and the voltage between PV- and ground is represented by V-.

[0117] Refer to FIG6A , which is an equivalent circuit diagram corresponding to S1 being closed and S2 being open in FIG2 .

[0118] When S1 is closed and S2 is open, R0 and Rn are connected in parallel. At this time, the voltage between PV1+ and PV- is V1', and the voltage between PV- and PE is V-';

[0119] It is assumed that the voltage between PV+ and PV- remains unchanged before and after S1 is turned on, that is, V1 = V1'.

[0120] The node current equations for Figures 5 and 6A are listed respectively, and the following formulas (1) and (2) are obtained:

[0121] Subtract formula (1) from formula (2) and sort it out to get formula (3);

[0122] Further optimization, the machine to PE impedance is Riso, Substituting into formula (3), we can solve:

[0123] Option 2:

[0124] This solution is described by taking the control of closing the second switch tube S2 as an example. The equivalent diagram before both switch tubes are opened is shown in FIG5 , and the diagram after S2 is closed is shown in FIG6B .

[0125] When S1 is open and S2 is closed, the equivalent circuit of Figure 2 is shown in Figure 6B. R0 and Rn are connected in parallel. At this time, the impedance between PV1+ and PV- is V1', and the voltage between PV- and PE is V-'.

[0126] Assume that the voltage between PV+ and PV- remains unchanged before and after the tube is turned on, that is, V1 = V1'; list the node current equations for Figure 5 and Figure 6B respectively, and obtain the following formulas (1) and (2):

[0127] Subtract formula (4) from formula (5) and sort it out to get the following formula (6);

[0128] Further optimization, the insulation resistance is Riso, Substituting into formula (6), we can solve:

[0129] It should be understood that for the detection circuit network shown in FIG. 4 , the above method can also be used to control the S1 or S2 state to establish a corresponding formula, thereby obtaining the insulation resistance.

[0130] It should be understood that after obtaining the insulation impedance of the converter, it is possible to determine whether the converter has an insulation fault to ground based on the size of the insulation impedance. For example, the insulation impedance can be compared with a preset value. If the insulation impedance is less than the preset value, it indicates that an insulation fault has occurred. The number of insulation abnormalities is recorded. When the number of insulation abnormalities exceeds the preset number, an alarm is issued to shut down the converter.

[0131] The following is a detailed description of the specific process of obtaining insulation impedance of the converter provided in the embodiment of the present application. As shown in Figure 7:

[0132] S1: Start.

[0133] S2: Close switch K and delay for T1 (including switch K shown in Figure 2), and then open S1 and S2.

[0134] S3: Close S1 or S2, open the other switch and delay for T3, detect the voltage between PV+ and PV-, and the voltage between PV- and PE, and calculate the insulation impedance of the system.

[0135] S4: Determine whether the insulation resistance exceeds the set value.

[0136] S5: If S4 is not established, the next step of the boot process is executed.

[0137] S6: If S4 is established, the number of insulation abnormalities is recorded.

[0138] S7: Determine whether the number of insulation abnormalities exceeds the set value.

[0139] S8: If S7 is established, the insulation is determined to be abnormal and the machine will be shut down to alarm.

[0140] The following describes how to obtain insulation impedance using several specific converters.

[0141] See FIG8A , which is a schematic diagram of an isolated DCDC converter provided in an embodiment of the present application.

[0142] In this embodiment, an LLC resonant isolated DC-DC converter is used as an example for description, without limiting the application scenario. For example, the input is the high-voltage side, where HVBUS+ is the positive electrode of the high-voltage side and HVBUS- is the negative electrode of the high-voltage side; the output is the low-voltage side, where LVBAT+ is the positive electrode of the low-voltage side and LVBAT- is the negative electrode of the low-voltage side; the DC power supply connected to the high-voltage side can be a battery.

[0143] The primary high-voltage full-bridge consists of two parallel arms. The left arm includes series-connected switches S1 and S3, and the right arm includes series-connected switches S2 and S4. The first end of the primary side of transformer T is connected to the midpoint of the left arm (i.e., the common terminal of S1 and S3) via inductor L2. The second end of the primary side of transformer T is connected to the midpoint of the right arm (i.e., the common terminal of S2 and S4) via capacitor C.

[0144] The first resistor R0 is directly connected between the midpoint of the left arm of the primary high-voltage full-bridge (i.e., the common terminal of S1 and S3) and the ground PE. By adjusting the conduction and shutdown of the upper tube S1 and the lower tube S3, R0 can be flexibly incorporated into Rm or Rn, thereby obtaining the insulation impedance of the DC side of the converter to the ground.

[0145] In FIG8A , the first resistor is connected between the common terminal of the two switching tubes and the ground. In addition, the first resistor can also be connected between the inductor and the ground. This is described in detail below with reference to the accompanying drawings.

[0146] See FIG8B , which is a schematic diagram of another isolated DCDC converter provided in an embodiment of the present application.

[0147] The first resistor R0 is connected between the inductor L2 of the primary LLC resonant network and the ground PE. By adjusting the on and off states of the upper tube S1 and the lower tube S3 (the same principle applies to adjusting S2 and S4), R0 can be flexibly incorporated into Rm or Rn, thereby obtaining the insulation impedance using the insulation impedance method described above.

[0148] See FIG. 9 , which is a schematic diagram of an isolated DC-AC converter provided in an embodiment of the present application.

[0149] The inverter shown in Figure 9 is a micro inverter, with a full-bridge converter on the primary side and an AC-AC converter on the secondary side. The full-bridge converter on the primary side includes two bridge arms connected in parallel, the left bridge arm includes switching tubes S1 and S3 connected in series, and the right bridge arm includes switching tubes S2 and S4 connected in series.

[0150] The present embodiment does not specifically limit the number of primary paths in the microinverter; it can be one or multiple. For example, when there are multiple paths, each path can be connected to a corresponding photovoltaic array. Figure 9 illustrates an example in which the primary side includes multiple full-bridge converters, which can correspond to multiple transformers, with the output terminals of the secondary sides connected in parallel.

[0151] The first resistor R0 is directly connected between the midpoint of the left arm of the primary full bridge (the common end of S1 and S3) and the ground PE. By adjusting the on and off of the upper tube S1 or the lower tube S3, R0 can be flexibly incorporated into Rm or Rn, thereby obtaining the insulation impedance using the method described above.

[0152] See FIG. 10 , which is a schematic diagram of a T-type three-level converter provided in an embodiment of the present application.

[0153] In this embodiment, the converter is described as an inverter as an example.

[0154] Only one phase of the T-type three-level inverter is shown in Figure 10. The output end of the T-type three-level inverter is connected to an LC filter circuit, which includes an inductor L and a capacitor C.

[0155] The first resistor R0 is connected between the inductor L and ground in the filter circuit of the T-type three-level inverter. The horizontal tubes of the T-type three-level inverter include T2 and T3, and the vertical tubes include T1 and T4. T1 and T4 are respectively analogous to S1 and S2 in Figure 2. By closing T1 or T4, the corresponding formula can be derived to obtain the insulation resistance.

[0156] See FIG11 , which is a schematic diagram of a three-level Boost+NPC converter provided in an embodiment of the present application.

[0157] The converter in this embodiment is also introduced by taking an inverter as an example.

[0158] In a three-level floating BOOST+NPC inverter topology, R0 is connected directly between the midpoint of the upper transistor T1 and the lower transistor T2 (i.e., the source of T1) and ground PE. T1 and T2 can be analogized to S1 and S2 in Figure 2, respectively. By controlling the on / off state of the upper transistor T1 or the lower transistor T2, R0 can be flexibly incorporated into Rm or Rn, thereby obtaining the insulation impedance using the method described above.

[0159] In addition, the converter provided in the embodiment of the present application may also connect the first resistor R0 between the inductor L and the ground PE, as shown in FIG12 . Referring to FIG12 , this figure is a schematic diagram of another three-level Boost+NPC converter provided in the embodiment of the present application.

[0160] The on and off states of S1 , S2 , S3 and S4 are controlled separately, so as to obtain the insulation impedance using the above-described method of obtaining the insulation impedance.

[0161] See FIG. 13 , which is a schematic diagram of a three-level Boost+ANPC converter provided in an embodiment of the present application.

[0162] The difference between Figure 13 and Figure 11 is that the clamping tubes in Figure 11 are diodes, namely D1 and S2, and the clamping tubes in Figure 13 are controllable switch tubes, namely S5 and S6. For the converter of Figure 13, the setting method of the first resistor can be referred to Figures 11 and 12, and will not be repeated here.

[0163] See FIG14 , which is a schematic diagram of a bidirectional DCDC buck-boost converter provided in an embodiment of the present application.

[0164] The bidirectional DCDC buck-boost converter provided in this embodiment includes a first switch module S1, a second switch module S2, a third switch module S3 and a fourth switch module S4 connected in series. In this embodiment, each switch module includes a switch tube.

[0165] The first switch tube and the second switch tube in FIG1 are respectively the first switch module and the second switch module in FIG14 ;

[0166] As shown in FIG14 , a common terminal of the first switch module S1 and the second switch module S2 is grounded via a first resistor R0 .

[0167] In the bidirectional DCDC buck-boost converter provided in this embodiment, the first resistor R0 is connected between the midpoint of transistors S1 and S2 (the source of transistor S1) and PE, that is, between point S12 and PE. By independently controlling the on and off of transistors S1 and S2, the system-to-ground impedance loop can be reconstructed, thereby calculating the system-to-ground insulation impedance value. The first resistor R0 can also be connected between the midpoint of transistors S3 and S4 and PE, that is, between point S34 and PE; or between the midpoint of transistors S5 and S6 and PE, that is, between point S56 and PE; or between the midpoint of transistors S7 and S8 and PE, that is, between point S78 and PE.

[0168] The following introduces several implementation methods of the heric converter.

[0169] See Figure 15, which is a schematic diagram of a heric converter provided in an embodiment of the present application.

[0170] In FIG15 , the first resistor R0 is connected between the common terminal of S1 and S3 and the ground.

[0171] See Figure 16, which is a schematic diagram of another heric converter provided in an embodiment of the present application.

[0172] In FIG16 , the first resistor R0 is connected between the inductor L and the ground.

[0173] 15 and 16 , the insulation impedance can be obtained by the following operations: S1 is closed and the other switches are opened; and S3 is closed and the other switches are opened.

[0174] See Figure 17, which is a schematic diagram of another heric converter provided in an embodiment of the present application.

[0175] Assume that the insulation resistance of the PV positive pole to ground is Rm, the insulation resistance of the PV negative pole to ground is Rn, and R1, R2, and R3 are external resistors.

[0176] Connect R1, R2, and R3 across the busbar. Connect one end of R1 to BUS+ and the other to point N. Connect one end of R2 to BUS- and the other to point N. Connect the other end of R3 to PE and the other to point N. Connect the source of switch S1 to point N and the drain of S3.

[0177] The converter provided in the embodiment of the present application can simply obtain the DC side impedance to ground. The converter can be of various types, and the type of converter is not specifically limited. For example, it can be a micro inverter, a string inverter, a DCDC converter, an energy storage converter, or a centralized inverter, etc.

[0178] Based on the converter provided in the above embodiment, an embodiment of the present application further provides a method for detecting insulation impedance of the converter, which is described in detail below with reference to the accompanying drawings.

[0179] See Figure 18, which is a flow chart of a method for detecting insulation impedance of a converter provided in an embodiment of the present application.

[0180] This embodiment provides a method for detecting insulation impedance of a converter, the converter comprising: a detection resistor network and a power conversion circuit; the power conversion circuit comprising a first switching transistor and a second switching transistor; a first end of the first switching transistor being connected to a positive electrode of a DC power supply, a second end of the first switching transistor being connected to a first end of a second switching transistor, and a second end of the second switching transistor being connected to a negative electrode of the DC power supply; and a second end of the first switching transistor being grounded via the detection resistor network;

[0181] The method includes:

[0182] S201: When the first switch tube and the second switch tube are both turned off, obtaining a voltage between the positive electrode and the negative electrode of the DC power supply and a voltage between the negative electrode of the DC power supply and the ground;

[0183] S202: Control the first switch or the second switch to be closed;

[0184] S203: Obtaining the insulation impedance of the converter according to the voltage between the positive electrode and the negative electrode of the DC power supply or the voltage between the negative electrode of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed.

[0185] The embodiment of the present application does not specifically limit the order of S201 and S202.

[0186] The insulation impedance detection method for a converter provided herein requires only the addition of a detection resistor network to the converter. The converter includes a first switching transistor and a second switching transistor connected in series, with the second end of the first switching transistor connected through the detection resistor network. By controlling the switching state of the first switching transistor or the second switching transistor, the voltage between the DC positive and negative electrodes of the converter, as well as the voltage between the DC negative electrode and ground, can be changed. The insulation impedance of the converter can then be determined by combining the impedance of the detection resistor network. This method for detecting insulation impedance of a converter has a simple structure, low cost, and is applicable to a variety of converter types.

[0187] The detection resistor network can include one resistor or multiple resistors, which are introduced below.

[0188] The first one:

[0189] The detection resistor network includes a first resistor; the second end of the first switch tube is grounded through the first resistor.

[0190] The second type includes a detection resistor network including, in addition to the first resistor, a second resistor and a third resistor;

[0191] Two ends of the second resistor are connected to the positive electrode of the DC power supply and the second end of the first switch tube respectively;

[0192] Two ends of the third resistor are connected to the negative electrode of the DC power supply and the second end of the first switch tube respectively.

[0193] Either the first switch tube or the second switch tube can be controlled to be closed, and the implementation methods are respectively introduced below.

[0194] The first option:

[0195] Obtaining the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and ground before and after the first switching tube or the second switching tube is closed, specifically including: obtaining the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and ground before the first switching tube is closed, and the voltage between the positive and negative poles of the DC power supply after the first switching tube is closed.

[0196] Second option:

[0197] Obtaining the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and the ground before and after the first switching tube or the second switching tube is closed, specifically including: obtaining the insulation impedance of the converter based on the voltage between the positive and negative poles of the DC power supply and the voltage between the negative pole of the DC power supply and the ground before the second switching tube is closed, and the voltage between the negative pole of the DC power supply and the ground after the second switching tube is closed.

[0198] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0199] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one 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 present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A converter, characterized in that, Comprising: A controller, a detection resistor network, and a power conversion circuit; The power conversion circuit includes a first switching tube and a second switching tube; A first end of the first switching tube is connected to the positive pole of a DC power supply, a second end of the first switching tube is connected to a first end of the second switching tube, and a second end of the second switching tube is connected to the negative pole of the DC power supply; the second end of the first switching tube is grounded through the detection resistor network; The controller is configured to obtain the insulation impedance of the converter according to the voltage between the positive and negative poles of the DC power supply and the voltage of the negative pole of the DC power supply with respect to ground before and after the first switching tube or the second switching tube is closed.

2. The converter according to claim 1, wherein The detection resistor network includes a first resistor; The second end of the first switching tube is grounded through the first resistor.

3. The converter according to claim 2, characterized in that, The detection resistor network further includes: a second resistor and a third resistor; Two ends of the second resistor are respectively connected to the positive pole of the DC power supply and the second end of the first switching tube; Two ends of the third resistor are respectively connected to the negative pole of the DC power supply and the second end of the first switching tube.

4. The converter according to claim 2 or 3, characterized in that, Further comprising: An inductor; The second end of the first switching tube is grounded through the inductor and the first resistor connected in series.

5. The converter according to any one of claims 1-4, characterized in that The controller is configured to obtain the insulation impedance of the converter according to the voltage between the positive and negative poles of the DC power supply before the first switching tube is closed and the voltage of the negative pole of the DC power supply with respect to ground, and the voltage of the negative pole of the DC power supply with respect to ground after the first switching tube is closed.

6. The converter according to any one of claims 1-4, characterized in that, The controller is configured to obtain the insulation impedance of the converter according to the voltage between the positive and negative poles of the DC power supply before the second switching tube is closed and the voltage of the negative pole of the DC power supply with respect to ground, and the voltage of the negative pole of the DC power supply with respect to ground after the second switching tube is closed.

7. The converter according to any one of claims 1-6, characterized in that, The converter is an isolated DCDC converter or an isolated DCAC converter; The first switching tube and the second switching tube are two switching tubes of the first bridge arm of the primary full bridge of the isolated DCDC converter or the isolated DCAC converter; the primary full bridge of the isolated DCDC converter includes a first bridge arm and a second bridge arm.

8. The converter according to any one of claims 1-6, characterized in that The converter is a T-type three-level inverter; The T-type three-level inverter further includes an inductor; The second end of the first switching tube is grounded through the inductor and the detection resistor network connected in series.

9. The converter according to any one of claims 1-6, characterized in that, The converter includes a three-level Boost circuit and a neutral point clamped inverter circuit; the neutral point clamped inverter circuit includes a first switching module, a second switching module, a third switching module, and a fourth switching module connected in series; The first switching tube and the second switching tube are respectively the first switching module and the second switching module in the three-level Boost circuit; Or, The first switching tube and the second switching tube are the second switching module and the third switching module of the neutral point clamped inverter circuit.

10. The converter according to any one of claims 1-6, characterized in that, The converter includes a three-level Boost circuit and an active neutral point clamped inverter circuit; The first switching tube and the second switching tube are the first switching tube and the second switching tube in the three-level Boost circuit.

11. The converter according to any one of claims 1-6, characterized in that, The converter is a bidirectional DCDC buck-boost converter; The bidirectional DCDC buck-boost converter includes a first switch module, a second switch module, a third switch module, and a fourth switch module connected in series in sequence; The first switch tube and the second switch tube are respectively the first switch module and the second switch module; The common terminal of the first switch module and the second switch module is grounded through the detection resistor network.

12. The converter according to any one of claims 1-6, characterized in that, The converter is a heric converter; The heric converter includes a first arm, a second arm, a fifth switch module, a sixth switch module, and an LC filter; the midpoint of the first arm is grounded through the detection resistor network; The fifth switch module and the sixth switch module are connected in series between the midpoint of the first arm and the midpoint of the second arm; The first end and the second end of the LC filter are respectively connected to the midpoint of the first arm and the midpoint of the second arm; the first end and the second end of the LC filter are respectively connected to both ends of the capacitor through a first inductor and a second inductor.

13. The converter according to any one of claims 1-6, characterized in that, The converter is a heric converter; The heric converter includes a first arm, a second arm, a fifth switch module, a sixth switch module, and an LC filter; The fifth switch module and the sixth switch module are connected in series between the midpoint of the first arm and the midpoint of the second arm; The first end and the second end of the LC filter are respectively connected to the midpoint of the first arm and the midpoint of the second arm; the first end and the second end of the LC filter are respectively connected to both ends of the capacitor through a first inductor and a second inductor; The first end of the LC filter is grounded through the series-connected first inductor and the first resistor; The first switch tube and the second switch tube are two switch tubes of the first arm.

14. The converter according to any one of claims 1-13, characterized in that, Further included: A switch; The detection resistor network is grounded through the switch; The controller is further configured to control the switch to close when detecting the insulation impedance, and vice versa to control the switch to open.

15. The converter according to any one of claims 1-14, characterized in that, The DC power supply is a photovoltaic array or a battery.

16. A method for detecting the insulation impedance of a converter, characterized in that, The converter includes: a detection resistor network and a power conversion circuit; the power conversion circuit includes a first switch tube and a second switch tube; the first end of the first switch tube is connected to the positive pole of the DC power supply, the second end of the first switch tube is connected to the first end of the second switch tube, the second end of the second switch tube is connected to the negative pole of the DC power supply; the second end of the first switch tube is grounded through the detection resistor network; This method includes: When both the first switch tube and the second switch tube are off, obtaining the voltage between the positive and negative poles of the DC power supply and the voltage of the negative pole of the DC power supply to the ground; Controlling the first switch tube or the second switch tube to close; Obtaining the insulation impedance of the converter according to the voltage between the positive and negative poles of the DC power supply and the voltage of the negative pole of the DC power supply to the ground before and after the first switch tube or the second switch tube is closed.

17. The method according to claim 16, wherein The detection resistor network includes a first resistor; the second end of the first switch tube is grounded through the first resistor.

18. The method according to claim 16, wherein The detection resistor network further includes: a second resistor and a third resistor; Both ends of the second resistor are respectively connected to the positive electrode of the DC power supply and the second end of the first switching tube; Both ends of the third resistor are respectively connected to the negative electrode of the DC power supply and the second end of the first switching tube.

19. The method according to claim 17 or 18, characterized in that, Obtaining the insulation impedance of the converter according to the voltage between the positive and negative electrodes of the DC power supply and the voltage of the negative electrode of the DC power supply to the ground before and after the first switching tube or the second switching tube is closed, specifically includes: Obtaining the insulation impedance of the converter according to the voltage between the positive and negative electrodes of the DC power supply before the first switching tube is closed, the voltage of the negative electrode of the DC power supply to the ground, and the voltage between the positive and negative electrodes of the DC power supply after the first switching tube is closed.

20. The method according to claim 17 or 18, characterized in that, Obtaining the insulation impedance of the converter according to the voltage between the positive and negative electrodes of the DC power supply and the voltage of the negative electrode of the DC power supply to the ground before and after the first switching tube or the second switching tube is closed, specifically includes: Obtaining the insulation impedance of the converter according to the voltage between the positive and negative electrodes of the DC power supply before the second switching tube is closed, the voltage of the negative electrode of the DC power supply to the ground, and the voltage of the negative electrode of the DC power supply to the ground after the second switching tube is closed.

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