Cable insulation resistance monitoring circuit in direct current power supply system

Abstract

The utility model relates to a cable insulation resistance monitoring circuit in a direct current power supply system, which comprises a first constant current source, a second constant current source, an isolation diode D1, an isolation diode D2, a monitoring device, a resistor Rx + to be measured and a resistor Rx-to be measured, the voltage is transmitted to a resistor Rx + to be detected and then to the negative electrode of the first constant current source, and the monitoring device is connected into a current path to detect the voltage U1; the constant current generated by the second constant current source is transmitted to the negative electrode of the transmission cable of the direct current power supply system from the positive electrode of the second constant current source, then transmitted to the resistor Rx-to be detected and then transmitted to the negative electrode of the second constant current source, the monitoring device accesses a detection voltage U2 in a current path, and the isolation diode D1 and the isolation diode D2 are respectively used for isolating the influence of the transmission voltage on the detection voltages U1 and U2. The utility model has the advantages of strong electrical interference resistance, and is suitable for various occasions with high electrical interference.

Description

Technical Field

[0001] This utility model relates to the field of power supply system technology, specifically to a cable insulation resistance monitoring circuit in a DC power supply system. Background Technology

[0002] In a floating DC power supply system, neither the positive nor negative terminals are connected to ground. While grounding one terminal generally does not affect system operation, failure to quickly detect and resolve the fault, followed by grounding of the other terminal, can lead to a serious safety accident. Therefore, existing DC power supply systems are typically equipped with insulation monitoring circuits to monitor the resistance between the positive and negative terminals and ground in real time. This provides early warning of a decrease in insulation resistance between the positive and negative terminals, preventing potential safety incidents.

[0003] Traditional insulation monitoring circuits generally employ three detection methods: the bridge method, the DC voltage injection method, and the AC voltage injection method. However, current insulation monitoring circuits all use voltage as the test source, resulting in poor anti-interference performance in high-electrical-interference environments such as DC power transmission, electric vehicles, and power operating lights, leading to low monitoring accuracy. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a cable insulation resistance monitoring circuit in a DC power supply system, using a current source as the detection source for the insulation monitoring circuit, thereby improving the insulation monitoring circuit's ability to resist electrical interference.

[0005] The objective of this utility model is achieved through the following technical solution:

[0006] A cable insulation resistance monitoring circuit in a DC power supply system, characterized in that it includes a first constant current source, a second constant current source, an isolation diode D1, an isolation diode D2, a monitoring device, and resistors Rx+ and Rx- to be measured, wherein:

[0007] The constant current generated by the first constant current source is transmitted from its positive terminal to the positive terminal of the transmission cable of the DC power supply system, then to the resistor under test Rx+, and then to the negative terminal of the first constant current source. The monitoring device is connected to the current path to detect the voltage U1. The isolation diode D1 is set in the current path of the constant current generated by the first constant current source to isolate the influence of the transmission voltage on the detection voltage U1.

[0008] The constant current generated by the second constant current source is transmitted from its positive terminal to the negative terminal of the transmission cable of the DC power supply system, then to the resistor under test Rx-, and then to the negative terminal of the second constant current source. The monitoring device is connected to the current path to detect the voltage U2. The isolation diode D2 is set in the current path of the constant current generated by the second constant current source to isolate the influence of the transmission voltage on the detection voltage U2.

[0009] The first constant current source and the second constant current source are either DC current sources or AC current sources.

[0010] The monitoring device employs one of the following: MCU, DSP, logic circuit, FPGA, or CPLD.

[0011] The isolation diode D1 is disposed on the positive or negative side of the first constant current source, and the isolation diode D2 is disposed on the positive or negative side of the second constant current source.

[0012] The advantages of this utility model are: strong anti-electrical interference capability, suitable for various high electrical interference occasions; simple principle, multiple replacement schemes, strong adaptability, and suitable for promotion. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the principle of this utility model;

[0014] Figure 2 This is a schematic diagram of a modified alternative to the present invention. Detailed Implementation

[0015] The features and other related features of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments, so as to facilitate the understanding of those skilled in the art:

[0016] Example 1: As Figure 1 As shown, the cable insulation resistance monitoring circuit in the DC power supply system in this embodiment includes a constant current source 1, a constant current source 2, an isolation diode D1, an isolation diode D2, an MCU for detecting voltages U1 and U2, and Rx+ and Rx- for the resistors to be measured.

[0017] Among them: constant current source 1: generates a constant DC current and injects it between the positive terminal of the transmission cable and ground; constant current source 2: generates a constant DC current and injects it between the negative terminal of the transmission cable and ground.

[0018] Isolation diode D1: Isolates the transmission voltage from affecting U1; Isolation diode D2: Isolates the transmission voltage from affecting U2.

[0019] Rx+: Resistance of the positive terminal to ground; Rx-: Resistance of the negative terminal to ground.

[0020] In operation, the current generated by constant current source 1 is injected into the transmission cable between the positive terminal and ground through isolation diode D1. The current path is: constant current source 1+ to D1, D1 to the positive terminal of the transmission cable, the positive terminal of the transmission cable to Rx+, and Rx+ to constant current source 1-. The rated current of the constant current source is I1, and the forward voltage drop of D1 is Vd1. Therefore, Rx+ is:

[0021] Rx+=(U1-Vd1) / I1.

[0022] The current source generated by constant current source 2 is injected into the space between the negative terminal of the transmission cable and ground through isolation diode D2. The current path is constant current source 2+ —— Rx- —— negative terminal of transmission cable —— D2 —— constant current source 2-. The rated current of the constant current source is I2, and the forward voltage drop of D1 is Vd2. Then Rx1 is:

[0023] Rx2 = (|U2| - Vd2) / I2.

[0024] By using the MCU to detect U1 and U2 and then calculate the resistance values ​​of Rx+ and Rx-, an early warning can be given in the DC power supply system when the insulation resistance of the positive and negative terminals decreases, so as to prevent safety accidents from occurring.

[0025] Example 2: Figure 2 As shown, the difference between this embodiment and embodiment one is that the isolation diodes D1 and D2 in this embodiment are located at the lower end of the constant current source.

[0026] In specific implementation of this embodiment: besides the monitoring circuit designed in the above embodiment, based on the same working principle, various alternative solutions can also be adopted, including:

[0027] 1) The DC current source generated by the constant current source is modified to an AC current source;

[0028] 2) The positions of the components in the circuit are changed. For example, in Embodiment 2, compared with Embodiment 1, the isolation diode is moved to the lower end of the constant current source;

[0029] 3) The microcontroller (MCU) is replaced with DSP, logic circuit, FPGA, CPLD, etc.

[0030] Although the above embodiments have described the concept and embodiments of the present invention in detail with reference to the accompanying drawings, those skilled in the art will recognize that various improvements and modifications can still be made to the present invention without departing from the scope of the claims, and therefore will not be elaborated here.

Claims

1. A cable insulation resistance monitoring circuit in a DC power supply system, characterized in that: It includes a first constant current source, a second constant current source, isolation diode D1, isolation diode D2, a monitoring device, and resistors under test Rx+ and Rx-, wherein: The constant current generated by the first constant current source is transmitted from its positive terminal to the positive terminal of the transmission cable of the DC power supply system, then to the resistor under test Rx+, and then to the negative terminal of the first constant current source. The monitoring device is connected to the current path to detect the voltage U1. The isolation diode D1 is set in the current path of the constant current generated by the first constant current source to isolate the influence of the transmission voltage on the detection voltage U1. The constant current generated by the second constant current source is transmitted from its positive terminal to the negative terminal of the transmission cable of the DC power supply system, then to the resistor under test Rx-, and then to the negative terminal of the second constant current source. The monitoring device is connected to the current path to detect the voltage U2. The isolation diode D2 is set in the current path of the constant current generated by the second constant current source to isolate the influence of the transmission voltage on the detection voltage U2.

2. The cable insulation resistance monitoring circuit in a DC power supply system according to claim 1, characterized in that: The first constant current source and the second constant current source are either DC current sources or AC current sources.

3. The cable insulation resistance monitoring circuit in a DC power supply system according to claim 1, characterized in that: The monitoring device employs one of the following: MCU, DSP, logic circuit, FPGA, or CPLD.

4. The cable insulation resistance monitoring circuit in a DC power supply system according to claim 1, characterized in that: The isolation diode D1 is disposed on the positive or negative side of the first constant current source, and the isolation diode D2 is disposed on the positive or negative side of the second constant current source.

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