Insulation resistance detection device and insulation resistance detection system
By designing an insulation impedance detection device, the voltage divider circuit and detection circuit are used to detect the insulation impedance of the DC circuit, the problem of grounding fault detection of DC circuits is solved, reliable detection of faults is achieved, and the safety of the circuit is improved.
Patent Information
- Application Number
- CN202420513007.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-15
- Publication Date
- 2025-02-25
- Estimated Expiration
- 2034-03-15
AI Technical Summary
A ground fault may occur between the DC circuit and the power converter, resulting in leakage current and the risk of electric shock or fire. How to reliably detect whether the DC circuit has a fault is of great significance.
Design an insulation impedance detection device, including a voltage divider circuit and a detection circuit, one end of the voltage divider circuit is connected to the DC end of the power converter and the other end is connected to the AC end. The detection circuit is used to obtain the target AC voltage of the voltage divider circuit. And determine the insulation impedance based on this voltage to characterize whether the DC circuit has a fault.
Reliable detection of whether a DC circuit fails to the ground is achieved. By detecting the magnitude of the insulation impedance, the fault condition can be accurately judged, and the safety and reliability of the circuit are improved.
Smart Images
Figure CN222529419U_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of power conversion, and in particular to an insulation impedance detection device and an insulation impedance detection system. Background Art
[0002] Affected by various harsh environmental factors, a grounding fault may occur between the ground terminal of the DC circuit and the power converter, resulting in leakage current. Excessive leakage current may cause electric shock to the user or fire.
[0003] In view of this, it is of great significance to reliably detect whether a DC circuit is faulty to ground. Utility Model Content
[0004] Based on this, it is necessary to provide an insulation impedance detection device and an insulation impedance detection system that can reliably detect whether a DC circuit is faulty to the ground in order to solve the above technical problems.
[0005] In a first aspect, the present application provides an insulation impedance detection device. The device comprises:
[0006] A voltage divider circuit, one end of which is used to be connected to a DC terminal of a power converter, and the other end of which is used to be connected to an AC terminal of the power converter;
[0007] A detection circuit, the detection circuit is connected to the voltage divider circuit, and the detection circuit is used to obtain a target AC voltage of the voltage divider circuit and determine the insulation impedance based on the target AC voltage;
[0008] The DC end of the power converter is connected to a DC circuit, the AC end of the power converter is connected to an AC source, and the insulation impedance is used to indicate whether a fault occurs in the DC circuit.
[0009] In one embodiment, the voltage divider circuit includes a first impedance and a second impedance;
[0010] The first end of the first impedance is connected to the DC end of the power converter, the second end of the first impedance is connected to the first end of the second impedance, and the second end of the second impedance is connected to the AC end of the power converter; the detection circuit is connected in parallel with the first impedance.
[0011] In one embodiment, the impedance of the first impedance and the impedance of the second impedance meet a preset condition so that the target AC voltage across the first impedance is within a preset sampling voltage value range.
[0012] In one embodiment, the voltage divider circuit includes a first resistor and a second resistor;
[0013] The first end of the first resistor is connected to the DC end of the power converter, the second end of the first resistor is connected to the first end of the second resistor, and the second end of the second resistor is connected to the AC end of the power converter; the detection circuit is connected in parallel with the first resistor.
[0014] In one embodiment, the ratio of the resistance value of the second resistor to the resistance value of the first resistor is greater than 300 and less than 400.
[0015] In one embodiment, the sum of the resistance of the first resistor and the resistance of the second resistor is greater than or equal to 1 megohm.
[0016] In one embodiment, the device further comprises:
[0017] An operational amplifier circuit, wherein the input end of the operational amplifier circuit is connected to the voltage divider circuit, and the output end of the operational amplifier circuit is connected to the input end of the detection circuit; the operational amplifier circuit is used to perform voltage amplification processing on the target AC voltage of the voltage divider circuit to obtain an amplified target AC voltage;
[0018] The detection circuit is specifically used to determine the insulation resistance based on the amplified target AC voltage.
[0019] In a second aspect, an embodiment of the present application provides an insulation impedance detection system. The system includes a power converter and an insulation impedance detection device as described in any one of the first aspects above;
[0020] The DC end of the power converter is connected to one end of the voltage divider circuit included in the insulation impedance detection device, and the AC end of the power converter is connected to the other end of the voltage divider circuit.
[0021] In one embodiment, the power converter includes a DC to AC conversion circuit, and the DC to AC conversion circuit is a resonant circuit.
[0022] In one embodiment, the DC to AC conversion circuit includes a resonant capacitor, and the capacitance of the resonant capacitor is greater than 15 nanofarads.
[0023] In one embodiment, the DC-AC conversion circuit includes: a primary circuit, a primary winding of a transformer, a secondary circuit, a secondary winding of a transformer and two secondary capacitors, wherein:
[0024] The primary winding of the transformer is connected to the primary circuit;
[0025] The secondary winding of the transformer is connected to the secondary circuit;
[0026] The two secondary capacitors correspond to the two bridge arms of the secondary circuit respectively, one end of the voltage divider circuit is connected to the primary circuit, and the other end of the voltage divider circuit is connected to a bridge arm connection point between the two bridge arms.
[0027] In one of the embodiments, the DC-AC conversion circuit of the power converter and the insulation impedance detection device are arranged in the same housing, and the housing is made of insulating material.
[0028] The above-mentioned insulation impedance detection device includes a voltage divider circuit and a detection circuit, one end of the voltage divider circuit is used to be connected to the DC end of the power converter, and the other end of the voltage divider circuit is used to be connected to the AC end of the power converter. The detection circuit is connected to the voltage divider circuit, and the detection circuit is used to obtain the target AC voltage of the voltage divider circuit and determine the insulation impedance based on the target AC voltage. The insulation impedance is used to characterize whether a fault occurs in the DC circuit. In this way, the embodiment of the present application designs an insulation impedance detection device, and the voltage divider circuit in the insulation impedance detection device is connected between the DC end of the power converter and the AC end of the power converter. The DC end of the power converter is connected to the DC circuit, and the AC end of the power converter is connected to the AC source. By using the AC source as an excitation source, the detection circuit samples the target AC voltage of the voltage divider circuit, and determines the insulation impedance of the DC circuit to the ground according to the target AC voltage. According to the size of the insulation impedance, it is possible to accurately determine whether the DC circuit has a fault, thereby achieving reliable detection of whether a fault occurs in the DC circuit to the ground. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG1 is a circuit diagram of an insulation impedance detection device in one embodiment;
[0030] FIG2 is an equivalent circuit diagram formed by a DC circuit, a power converter, a voltage divider circuit and an AC source in another embodiment;
[0031] FIG3 is a circuit diagram of an insulation impedance detection device in another embodiment;
[0032] FIG4 is an equivalent circuit diagram formed by a DC circuit, a power converter, a voltage divider circuit and an AC source in another embodiment;
[0033] FIG5 is a circuit diagram of an insulation impedance detection device in another embodiment;
[0034] FIG6 is a circuit diagram of an insulation impedance detection device in another embodiment;
[0035] FIG7 is a circuit diagram of an insulation impedance detection system in one embodiment;
[0036] FIG. 8 is a circuit diagram of an insulation impedance detection system in another embodiment.
[0037] Description of reference numerals:
[0038] Insulation impedance detection device-100; voltage divider circuit-101; first impedance-101a; second impedance-101b; detection circuit-102; operational amplifier circuit-103; power converter-200; resonant capacitor-201; DC circuit-300; AC source-400. DETAILED DESCRIPTION
[0039] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present application, so the present application is not limited by the specific embodiments disclosed below.
[0040] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.
[0041] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.
[0042] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.
[0043] In the present application, unless otherwise clearly specified and limited, a first feature being “above” or “below” a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being “above”, “above”, and “above” a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being “below”, “below”, and “below” a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.
[0044] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.
[0045] Power converters are power conversion devices used to convert electrical energy from one form to another to achieve energy transmission and control under different power requirements. Power converters can be micro inverters, energy storage converters, etc., one end of which is connected to a DC circuit, which can include photovoltaic modules, batteries, etc. For example, the DC end of a micro inverter is connected to a photovoltaic module, and the DC end of an energy storage converter is connected to a battery. The AC end of a power converter can be connected to an AC source, such as an AC power grid. Power converters can achieve bidirectional transmission of DC and AC.
[0046] Affected by various harsh environmental factors, the insulation impedance of the positive and negative poles of the photovoltaic modules or batteries in the DC circuit to the ground (insulation impedance can also be understood as the total equivalent impedance of the DC side of the power converter to the ground) may change, which not only affects the safe operation of the power converter, but also threatens personal safety. For example, due to damage to the photovoltaic module or bad weather, the photovoltaic module and PE (Protecting Earthing) are short-circuited, resulting in a ground fault.
[0047] In the case of a ground fault, leakage current will be generated between the DC circuit and the power converter due to the potential difference, and excessive leakage current may cause electric shock to the user or cause a fire.
[0048] In view of this, it is of great significance to reliably detect whether a DC circuit is faulty to ground.
[0049] The embodiment of the present application provides an insulation impedance detection device, which is used to detect the insulation impedance to ground of the DC circuit at the DC end of the power converter. The power converters involved in the present application include: photovoltaic inverters, energy storage converters, optimizers, micro inverters, uninterruptible power supplies, etc. Any device and equipment containing the protection circuit requested by the present application should be included in the scope of protection requested by the present application.
[0050] Exemplarily, referring to FIG1 , the insulation impedance detection device 100 includes a voltage divider circuit 101 and a detection circuit 102, one end of the voltage divider circuit 101 is used to be connected to the DC end of the power converter 200, and the other end of the voltage divider circuit 101 is used to be connected to the AC end of the power converter 200, the DC end of the power converter 200 is connected to the DC circuit 300, and the AC end of the power converter 200 is connected to the AC source 400, and the AC voltage of the AC source 400 is used as an excitation source. The voltage divider voltage can be detected on the voltage divider circuit 101, and the voltage divider voltage is an AC voltage. In a possible implementation, the voltage divider circuit 101 can be a capacitor voltage divider circuit. Exemplarily, the voltage divider circuit 101 includes a first capacitor and a second capacitor, the first end of the first capacitor is connected to the DC end of the power converter 200, the second end of the first capacitor is connected to the first end of the second capacitor, and the second end of the second capacitor is connected to the AC end of the power converter 200.
[0051] In another possible implementation, the voltage divider circuit 101 may also be a voltage divider circuit in other forms. Possible implementations of voltage divider circuits in other forms will be described in the following embodiments.
[0052] Please continue to refer to Figure 1. The detection circuit 102 is connected to the voltage divider circuit 101 (when the above-mentioned voltage divider circuit 101 is a capacitor voltage divider circuit, the detection circuit 102 can be connected in parallel with the first capacitor). The detection circuit 102 is used to obtain the target AC voltage of the voltage divider circuit 101. The target AC voltage is the voltage divider voltage detected on the voltage divider circuit 101. The detection circuit 102 determines the insulation impedance based on the target AC voltage. The insulation impedance is used to characterize whether a fault occurs in the DC circuit 300. Exemplarily, referring to FIG. 2 , FIG. 2 is an equivalent circuit diagram formed by the DC circuit 300, the power converter 200, the voltage divider circuit 101 and the AC source 400 in FIG. 1 , wherein Zcr is a fixed impedance network parameter inside the power converter 200, Zpv is a fixed impedance network parameter inside the DC circuit 300, and Riso is the insulation impedance of the DC circuit 300 to the ground. Thus, by combining the target AC voltage of the voltage divider circuit 101, the sampled value of the AC voltage, Zcr, Zpv and the resistance of the components in the voltage divider circuit 101, the specific value of Riso can be calculated, that is, the above-mentioned insulation impedance is obtained.
[0053] Under normal circumstances, the impedance Riso of the DC circuit 300 to the ground is usually large enough, such as 10Mohm, 50Mohm, etc., assuming that the target AC voltage measured at this time is V1; when the DC circuit 300 is short-circuited or fails to the ground, the impedance Riso of the DC circuit 300 to the ground changes significantly, for example, from 10Mohm to 1kohm, or even to 50ohm, and the target AC voltage measured at this time will also change significantly. Assuming that the target AC voltage measured at this time is V2, the insulation impedance can be calculated based on the target AC voltage V2, and whether an insulation fault occurs can be determined by the absolute value of the insulation impedance. For example, when the insulation impedance is less than a preset impedance threshold (such as 2kohm), it is regarded as a fault condition, that is, it is determined that the DC circuit 300 has a fault.
[0054] In a specific embodiment, the detection circuit 102 may include a root mean square (RMS) circuit module. The RMS circuit module can continuously collect target AC voltage values of multiple power frequency cycles and obtain the root mean square value of the target AC voltage. Converting the vector voltage into an absolute value output can reduce sampling errors and improve detection accuracy.
[0055] As an embodiment, when the insulation impedance determined based on the target AC voltage of the voltage divider circuit 101 is less than a preset impedance threshold, the detection circuit 102 outputs an indication signal, which is used to indicate that a fault has occurred in the DC circuit 300. At this time, the power converter 200 can be prohibited from generating electricity to avoid damage to the entire photovoltaic system due to excessively low insulation impedance.
[0056] Before and after the power converter 200 is connected to the grid, it is necessary to detect the insulation impedance of the DC side of the power converter 200 (i.e., the insulation impedance of the photovoltaic unit on the DC side of the power converter 200 to the ground) in order to promptly discover and eliminate potential safety hazards. In the embodiment of the present application, before the power converter 200 works, the insulation impedance detection device 100 of the embodiment of the present application can be used to detect the insulation impedance. Exemplarily, the detection time can last for a preset number (e.g., 5-10) of power frequency cycles. For a 50Hz AC source 400, only 100ms-200ms of detection time is required. It can be seen that the insulation impedance detection device of the embodiment of the present application has a short detection time and high detection efficiency, and can better meet the actual detection needs.
[0057] During the normal operation of the power converter 200, the insulation impedance can also be detected. In the actual implementation process, according to the implementation requirements, the insulation impedance can be detected in real time, so as to continuously and accurately monitor whether the DC circuit 300 has a fault.
[0058] In the related art, there are also some ways of insulation impedance detection, for example, setting a switch in the power converter, controlling the on and off of the switch, performing voltage detection under different conditions, and then calculating the insulation impedance detection value, for example, by switching the switch state, to detect the change in the measured value between the DC terminal of the power converter and the grounding point, so as to determine whether the DC terminal of the power converter is short-circuited to the ground or has low impedance. However, the problem with this method is that since the switch (relay) needs to meet the safety requirements of basic insulation and needs to consider certain voltage stress and current stress, the selection requirements of the relay and the circuit cost are high.
[0059] The insulation impedance detection device 100 provided in the present application does not require additional relays, which solves the problems of high requirements for relay selection and high circuit costs. At the same time, it can also avoid the repeated closing and disconnection of isolating switches such as relays in traditional technologies, thereby increasing the reliability of the system. The embodiments of the present application have the effects of using fewer components, simple insulation impedance detection, and accurate insulation impedance detection results.
[0060] In some related technologies, there is also a method of calculating the insulation impedance by controlling the on and off of the switch tube in the power converter, performing at least two measurements, and using the voltage difference of the two measurements. The calculation method of this method is complicated, resulting in low efficiency of insulation impedance detection. In the embodiment of the present application, there is no need to calculate the insulation impedance by the voltage difference measured multiple times, and the insulation impedance can be determined directly based on the target AC voltage of the voltage divider circuit 101, and the insulation impedance detection efficiency is higher.
[0061] Based on the embodiment shown in FIG. 1 , other possible implementations of the voltage divider circuit 101 are exemplarily introduced below.
[0062] Referring to FIG. 3 , the voltage divider circuit 101 includes a first impedance 101a and a second impedance 101b, wherein a first end of the first impedance 101a is connected to a DC end of the power converter 200, a second end of the first impedance 101a is connected to a first end of the second impedance 101b, a second end of the second impedance 101b is connected to an AC end of the power converter 200, and a detection circuit 102 is connected in parallel to the first impedance 101a.
[0063] The first impedance 101a may include a corresponding resistor, inductor and / or capacitor, and the second impedance 101b may also include a corresponding resistor, inductor and / or capacitor. The present application does not limit the number of voltage-dividing resistors. The first impedance 101a / the second impedance 101b may be one or more. For example, the voltage-dividing resistor may be formed by at least one resistor connected in series. During the insulation impedance detection process, the detection circuit 102 samples the voltage across the first impedance 101a to obtain a target AC voltage, and determines the insulation impedance based on the target AC voltage.
[0064] Exemplarily, referring to FIG. 4 , FIG. 4 is an equivalent circuit diagram formed by the DC circuit 300, the power converter 200, the voltage divider circuit 101 (the first impedance 101a and the second impedance 101b) and the AC source 400 in FIG. 3 , wherein the meanings of the parameters of Zcr, Zpv and Riso can be referred to the above embodiment, and the specific value of Riso can be calculated by combining the target AC voltage at both ends of the first impedance 101a, the sampled value of the AC voltage, Zcr, Zpv and the impedance values of the first impedance 101a and the second impedance 101b, that is, the above-mentioned insulation resistance is obtained.
[0065] As an implementation mode, the detection circuit 102 includes an MCU (Micro controller Unit). In order to ensure the normal operation of the MCU, the operating voltage of the MCU needs to be lower than the power supply voltage (3.3V). Therefore, the target AC voltage at both ends of the voltage divider circuit 101 needs to be within a suitable sampling voltage value range, for example, within a range of 0-3V, thereby ensuring that the operating voltage of the MCU is lower than the power supply voltage.
[0066] In view of this, in the embodiment of the present application, the impedance of the first impedance 101a and the impedance of the second impedance 101b are set to meet the preset condition so that the magnitude of the target AC voltage is within the preset sampling voltage value range. Optionally, the preset condition may be that the ratio of the impedance of the first impedance 101a to the impedance of the second impedance 101b is within a certain ratio range or equal to a certain ratio; optionally, the preset condition may also be that the impedance of the first impedance 101a is determined to be a preset first value and the impedance of the second impedance 101b is determined to be a preset second value.
[0067] In an embodiment of the present application, the first impedance 101a can also be replaced by a first resistor, and the second impedance 101b can be replaced by a second resistor, that is, the voltage divider circuit 101 includes a first resistor and a second resistor, wherein the first end of the first resistor is connected to the DC end of the power converter 200, the second end of the first resistor is connected to the first end of the second resistor, and the second end of the second resistor is connected to the AC end of the power converter 200; the detection circuit 102 is connected in parallel with the first resistor.
[0068] Regarding the connection relationship between the first resistor and the second resistor in the insulation impedance detection device 100, reference may be made to the connection relationship between the first impedance 101a and the second impedance 101b in the insulation impedance detection device 100 in FIG. 3, which will not be described in detail herein.
[0069] Similarly, in the embodiment of the present application, the resistance value of the first resistor and the resistance value of the second resistor are set to meet the preset condition so that the magnitude of the target AC voltage is within the preset sampling voltage value range. Optionally, the preset condition may be that the ratio of the resistance value of the first resistor to the resistance value of the second resistor is within a certain ratio range or equal to a certain ratio; optionally, the preset condition may also be that the resistance value of the first resistor is determined to be a preset first value and the resistance value of the second resistor is determined to be a preset second value.
[0070] In one embodiment, the voltage divider circuit 101 can select a resistor with a larger resistance value to avoid damaging the function of the power converter 200. For example, the value of the sum of the resistance value of the first resistor and the resistance value of the second resistor can be greater than or equal to 1 megohm, so that the leakage current between the primary circuit and the secondary circuit in the power converter 200 is lower than the limited current value, avoiding damaging the insulation function of the primary and secondary circuits of the power converter 200; in addition, the larger resistance value of the voltage divider resistor can ensure that the insulation impedance detection device 100 does not affect the normal operation of the power converter 200, and the insulation impedance detection device 100 can be connected to the system circuit all the time, and it does not need to be disconnected from the main circuit when the insulation impedance detection device 100 is not detecting. Preferably, the value of the sum of the resistance value of the first resistor and the resistance value of the second resistor can be greater than or equal to 3 megohms.
[0071] Exemplarily, the resistance of the first resistor may be 22 kilo-ohms, and the ratio of the resistance of the second resistor to the resistance of the first resistor is greater than 300 and less than 400. For example, the second resistor may be obtained by connecting eight resistors in series, and the resistance of each resistor is 910 kilo-ohms, then the resistance of the second resistor is 910*8 kilo-ohms. In the embodiment of the present application, the first impedance 101a and the second impedance 101b (or the first resistor and the second resistor) are used to implement the resistor voltage divider circuit 101. Compared with the implementation method of the capacitor voltage divider circuit 101, the components in the resistor voltage divider circuit 101 are small in size, occupy a small area of the PCB (Printed Circuit Board), and are more likely to achieve high power density while having a lower cost.
[0072] Based on the embodiment shown in FIG. 1 , referring to FIG. 5 , in this embodiment, the insulation impedance detection device 100 further includes an operational amplifier circuit 103, the input end of the operational amplifier circuit 103 is connected to the voltage divider circuit 101, the output end of the operational amplifier circuit 103 is connected to the input end of the detection circuit 102, and the operational amplifier circuit 103 can amplify the voltage.
[0073] In the embodiment of the present application, the operational amplifier circuit 103 is used to perform voltage amplification processing on the target AC voltage of the voltage divider circuit 101 to obtain an amplified target AC voltage, and the detection circuit 102 is specifically used to determine the insulation impedance based on the amplified target AC voltage.
[0074] In this way, the target AC voltage of the voltage divider circuit 101 is amplified by the operational amplifier circuit 103, and the insulation impedance is determined based on the amplified target AC voltage, so that the accuracy of insulation impedance detection can be improved.
[0075] Taking the voltage divider circuit 101 as the resistance voltage divider circuit 101 shown in Figure 3 as an example, see Figure 6, the input end of the operational amplifier circuit 103 is connected to the two ends of the first impedance 101a, and the output end of the operational amplifier circuit 103 is connected to the input end of the detection circuit 102. The operational amplifier circuit 103 can perform voltage amplification processing on the target AC voltage at the two ends of the first impedance 101a to obtain the amplified target AC voltage.
[0076] In this embodiment, when a resistor is used to implement the voltage divider circuit 101, since the DC side and the AC side of the power conversion circuit need to meet the reinforced insulation requirements, the impedance values used on the DC side and the AC side of the power conversion circuit are large, resulting in a relatively weak target AC voltage across the first impedance 101a. The operational amplifier circuit 103 is used to amplify the target AC voltage, thereby improving the accuracy and detection precision of the insulation impedance detection.
[0077] In general, the above-mentioned insulation impedance detection device 100 uses the AC source 400 as an excitation source, and the detection circuit 102 samples the target AC voltage of the voltage divider circuit 101, and determines the insulation impedance of the DC circuit 300 to the ground according to the target AC voltage. According to the size of the insulation impedance, it can be accurately determined whether the DC circuit 300 has a fault, thereby realizing reliable detection of whether the DC circuit 300 has a fault to the ground.
[0078] In one embodiment, based on the insulation impedance detection device 100 shown in the above embodiments, this embodiment provides an insulation impedance detection system, which includes a power converter 200 and the insulation impedance detection device 100 shown in any of the above embodiments.
[0079] For example, referring to FIG7 , FIG7 is a schematic diagram of an insulation impedance detection system, with the position of the insulation impedance detection device 100 shown in FIG3 . The insulation detection system includes: an insulation impedance detection device 100 and a power converter 200 . Referring to FIG7 , in one embodiment, the DC end of the power converter 200 is connected to a DC circuit 300 , and the DC circuit 300 includes at least one photovoltaic module; the AC end of the power converter 200 is connected to an AC source 400 .
[0080] The DC end of the power converter 200 is connected to one end of the voltage divider circuit 101 included in the insulation impedance detection device 100 , and the AC end of the power converter 200 is connected to the other end of the voltage divider circuit 101 .
[0081] Regarding the implementation of the power converter 200 and the insulation impedance detection device 100 shown in FIG. 7 , reference may be made to the relevant description of the above embodiments, which will not be repeated here.
[0082] Hereinafter, the circuit structure of the power converter 200 will be described by way of example.
[0083] In one embodiment of the present application, the power converter 200 includes a DC-AC conversion circuit, which is used to convert the DC power transmitted by the DC circuit 300 into AC power.
[0084] The embodiments of the present application do not specifically limit the specific circuit structure of the primary circuit, nor do they specifically limit the specific circuit structure of the secondary circuit. The following is an introduction using the example that the primary circuit is an H-bridge circuit and the secondary circuit is a frequency conversion circuit. On the basis of the embodiment shown in FIG7 , referring to FIG8 , the DC-AC conversion circuit is a resonant circuit. The DC-AC conversion circuit includes: a primary circuit, a primary winding of a transformer, a secondary circuit, a primary winding of a transformer, and two secondary capacitors (Cp and Cn as shown in FIG8 ), wherein the primary winding of the transformer is connected to the primary circuit, and the primary winding of the transformer is connected to the secondary circuit.
[0085] The primary circuit may include the switch tubes Q1-Q4 shown in FIG8, and the secondary circuit may include the switch tubes Q5-Q8 shown in FIG8. The two secondary capacitors correspond to the two bridge arms of the secondary circuit respectively. As shown in FIG8, the secondary capacitor Cp corresponds to the bridge arm composed of the switch tubes Q5 and Q6, and the secondary capacitor Cn corresponds to the bridge arm composed of the switch tubes Q7 and Q8.
[0086] One end of the voltage divider circuit 101 is connected to the primary circuit. Optionally, one end of the voltage divider circuit 101 can be connected to the positive electrode of the primary circuit, or can be connected to the negative electrode of the primary circuit. Preferably, the voltage divider circuit 101 of the insulation detection circuit is connected to the negative electrode of the primary circuit, and the negative electrode of the primary circuit can be used as a reference potential, thereby simplifying the control circuit of the entire insulation impedance detection system, wherein the control circuit of the insulation impedance detection system includes a circuit of the insulation impedance detection device.
[0087] The other end of the voltage divider circuit 101 is connected to the bridge arm connection point between the two bridge arms (connection point D as shown in FIG8 ). In this way, the AC source 400 can be used as a stable excitation source for the insulation impedance detection device 100, without worrying about the reverse connection of the L line and the N line of the AC end of the power converter 200 connected to the AC source 400.
[0088] In this embodiment, the DC-AC conversion circuit includes a resonant capacitor 201, and the resonant capacitor 201 is a secondary capacitor (such as Cp and Cn shown in FIG8 ). It can be seen from the calculation method of the fixed impedance network parameters inside the power converter 200 that the size of the fixed impedance network parameters inside the power converter 200 is negatively correlated with the capacitance of the resonant capacitor 201. If the capacitance of the resonant capacitor 201 is too small, the fixed impedance network parameters inside the power converter 200 tend to positive infinity, and then the target AC voltage on the voltage divider circuit 101 is too small, that is, no significant measurement signal can be generated on the voltage divider circuit 101. Therefore, in the embodiment of the present application, the capacitance of the resonant capacitor 201 is greater than a preset capacitance threshold, for example, the capacitance of the resonant capacitor 201 is greater than 15 nanofarads, so that the fixed impedance network parameters inside the power converter can be controlled within a reasonable parameter range, so that the AC voltage generates a significant excitation signal on the voltage divider circuit 101 (specifically, the first impedance 101a in the voltage divider circuit 101), and a significant measurement of the insulation impedance is achieved.
[0089] In one embodiment of the present application, the DC-AC conversion circuit of the power converter 200 is disposed in a housing, and optionally, the DC-AC conversion circuit of the power converter 200 and the insulation impedance detection device 100 are disposed in the same housing. The housing is made of an insulating material, such as plastic, which can reduce the overall cost; in addition, the housing made of insulating material does not need to be grounded, thereby simplifying the system, for example, the power converter 200 can achieve enhanced insulation without a grounding wire; the insulation impedance detection device 100 does not need to determine whether there is a ground fault when the power converter 200 is grounded.
[0090] In an embodiment of the present application, the insulation impedance detection device 100 may also be disposed inside the shell included in the power converter 200 and integrated with the DC-AC conversion circuit on the same circuit board; optionally, the insulation impedance detection device 100 may also be disposed outside the power converter 200.
[0091] In conventional technology, the detection circuit in the string inverter usually uses the DC circuit voltage as an excitation source, and usually uses the instantaneous voltage or the average voltage as a judgment means. However, in the embodiment of the present application, since there is no grounding cable in the power converter 200 and the power converter 200 is an insulating shell, it is impossible to directly measure the DC side voltage of the power converter 200 to the ground for impedance judgment. In view of this, the embodiment of the present application uses AC voltage as an excitation source, and the detection circuit 102 samples the target AC voltage of the voltage divider circuit 101. Since the AC voltage is an AC source, the effective value is calculated (that is, the insulation impedance of the DC circuit 300 to the ground is determined based on the target AC voltage) to achieve reliable detection of whether a fault occurs in the DC circuit 300 to the ground.
[0092] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0093] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.
Claims
1. An insulation impedance detection device, characterized in that: The device comprises: A voltage divider circuit, one end of which is used to be connected to a DC terminal of a power converter, and the other end of which is used to be connected to an AC terminal of the power converter; a detection circuit, the detection circuit being connected to the voltage divider circuit, the detection circuit being used to obtain a target AC voltage of the voltage divider circuit and determine insulation impedance based on the target AC voltage; The DC end of the power converter is connected to a DC circuit, the AC end of the power converter is connected to an AC source, and the insulation impedance is used to indicate whether a fault occurs in the DC circuit.
2. The device according to claim 1, characterized in that The voltage divider circuit includes a first impedance and a second impedance; Among them, the first end of the first impedance is connected to the DC end of the power converter, the second end of the first impedance is connected to the first end of the second impedance, and the second end of the second impedance is connected to the AC end of the power converter; the detection circuit is connected in parallel with the first impedance.
3. The device according to claim 2, characterized in that The impedance of the first impedance and the impedance of the second impedance meet a preset condition, so that the target AC voltage across the first impedance is within a preset sampling voltage value range.
4. The device according to claim 1, characterized in that The voltage divider circuit includes a first resistor and a second resistor; Among them, the first end of the first resistor is connected to the DC end of the power converter, the second end of the first resistor is connected to the first end of the second resistor, and the second end of the second resistor is connected to the AC end of the power converter; the detection circuit is connected in parallel with the first resistor.
5. The device according to claim 4, characterized in that A ratio of a resistance value of the second resistor to a resistance value of the first resistor is greater than 300 and less than 400.
6. The device according to claim 4, characterized in that The sum of the resistance of the first resistor and the resistance of the second resistor is greater than or equal to 1 megohm.
7. The device according to any one of claims 1 to 6, characterized in that: The device also includes: an operational amplifier circuit, wherein the input end of the operational amplifier circuit is connected to the voltage divider circuit, and the output end of the operational amplifier circuit is connected to the input end of the detection circuit; the operational amplifier circuit is used to perform voltage amplification processing on the target AC voltage of the voltage divider circuit to obtain an amplified target AC voltage; The detection circuit is specifically configured to determine the insulation impedance based on the amplified target AC voltage.
8. An insulation impedance detection system, characterized in that: The system comprises a power converter and an insulation impedance detection device according to any one of claims 1 to 7; Wherein, the DC end of the power converter is connected to one end of the voltage divider circuit included in the insulation impedance detection device, and the AC end of the power converter is connected to the other end of the voltage divider circuit.
9. The system according to claim 8, characterized in that The power converter comprises a DC-AC conversion circuit, and the DC-AC conversion circuit is a resonant circuit.
10. The system according to claim 9, characterized in that The DC-AC conversion circuit includes a resonant capacitor, and the capacitance of the resonant capacitor is greater than 15 nanofarads.
11. The system according to claim 9, characterized in that The DC-AC conversion circuit comprises: a primary circuit, a primary winding of a transformer, a secondary circuit, a secondary winding of a transformer and two secondary capacitors, wherein: The primary winding of the transformer is connected to the primary circuit; The secondary winding of the transformer is connected to the secondary circuit; The two secondary capacitors correspond to the two bridge arms of the secondary circuit respectively, one end of the voltage divider circuit is connected to the primary circuit, and the other end of the voltage divider circuit is connected to a bridge arm connection point between the two bridge arms.
12. The system according to any one of claims 8 to 11, characterized in that: The DC-AC conversion circuit of the power converter and the insulation impedance detection device are arranged in the same shell, and the shell is made of insulating material.