Isolated insulation monitoring circuit

Abstract

The utility model provides an isolation type insulation monitoring circuit comprising a bridge switch circuit located at a high voltage side, a first differential conversion circuit and a control unit which are located at a low voltage side, and a first isolation type amplifier which is coupled with the bridge switch circuit and the differential conversion circuit. Wherein the bridge switch circuit comprises a high-resistance voltage divider and a high-voltage relay, a first input end of the first isolation amplifier is coupled with a high-voltage direct-current voltage to be monitored through the high-voltage relay and the high-resistance voltage divider, and a second input end of the first isolation amplifier is coupled with protective grounding; a first voltage detection resistor is arranged between the first input end and the second input end to obtain an insulation sampling voltage, the output end is coupled with the control unit through the first differential conversion circuit and used for outputting an insulation sampling signal to the control unit, and the control unit is further used for outputting a control signal to control the on-off of the high-voltage relay. The high-voltage relay is only switched on during measurement. The isolation type insulation monitoring circuit can realize low-cost convenient insulation monitoring of the charging pile power distribution system.

Description

Technical Field

[0001] The utility model relates to the technical field of circuit monitoring, in particular to an isolated insulation monitoring circuit. Background Art

[0002] The rapid adoption of electric vehicles has driven a rapid increase in the number of charging stations installed, raising the bar for safe energy transmission in power distribution systems. Currently, electric vehicles utilize high-voltage (HV) batteries around 400V and 800V for energy storage, with a strong trend toward higher voltage batteries to shorten charging times. International standards require that HVDC distribution systems provide user protection mechanisms. All high-voltage components in the system must be isolated to protective ground via a high-resistance path. This insulation limits the maximum leakage current, which international standards require to be below 10mA to prevent personal injury from contact with the system. High-voltage insulation monitoring devices monitor this insulation resistance and initiate shutdown if it is insufficient. Furthermore, IEC 61851-23 further specifies requirements for DC fast-charging stations, requiring regular monitoring of the system's insulation during energy transfer. Furthermore, charging station standards and charging protocols also mandate insulation monitoring and testing before charging.

[0003] There are several insulation monitoring technologies available on the market, the most commonly used being AC current injection. This method generates a square wave signal and injects it into the RC circuit between the high-voltage line and the protective earth (PE) via an RC filter or transformer. The main drawbacks of this method are the difficulty in achieving a reliable and accurate design, as well as the need for a bulky transformer to isolate the injection circuit from the HV line. Summary of the Invention

[0004] Based on the above background, the utility model provides an isolated insulation monitoring circuit to achieve low-cost and convenient insulation monitoring of the charging pile distribution system.

[0005] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0006] An isolated insulation monitoring circuit includes a bridge switching circuit located on the high-voltage side, a first differential conversion circuit and a control unit located on the low-voltage side, and a first isolated amplifier coupled to the bridge switching circuit and the differential conversion circuit; wherein the bridge switching circuit includes a high-resistance voltage divider and a high-voltage relay, a first input end of the first isolated amplifier is coupled to the high-voltage DC voltage to be monitored via the high-voltage relay and the high-resistance voltage divider, a second input end is coupled to protective grounding, and a first voltage detection resistor is provided between the first input end and the second input end to obtain an insulation sampling voltage, an output end is coupled to the control unit via the first differential conversion circuit, and is used to output an insulation sampling signal to the control unit, and the control unit is further used to output a control signal to control the on and off of the high-voltage relay, and the high-voltage relay is only turned on during measurement.

[0007] Furthermore, the bridge switching circuit includes two high-resistance voltage dividers and two high-voltage relays, wherein the first high-resistance voltage divider and the first high-voltage relay constitute a first branch connecting the high-voltage DC positive voltage to be monitored and the first isolation amplifier, and the second high-resistance voltage divider and the second high-voltage relay constitute a second branch connecting the high-voltage DC negative voltage to be monitored and the first isolation amplifier; during measurement, the two branches are connected at different times.

[0008] Furthermore, the isolated insulation monitoring circuit also includes a bus detection circuit, which includes a third high-resistance voltage divider, a second isolated amplifier and a second differential conversion circuit, wherein the first input end of the second isolated amplifier is coupled to the high-voltage DC positive voltage to be monitored via the third high-resistance voltage divider, and the second input end is coupled to the high-voltage DC negative voltage to be monitored, and a second voltage detection resistor is provided between the first input end and the second input end to obtain a bus sampling voltage, and the output end is coupled to the control unit via the second differential conversion circuit for outputting a bus sampling signal to the control unit.

[0009] Furthermore, the first isolation amplifier and the second isolation amplifier are both isolation amplifiers with a fixed gain of 1.

[0010] Furthermore, the control unit is a single chip microcomputer.

[0011] Furthermore, the first differential conversion circuit includes a first operational amplifier and a peripheral resistor coupled to the first operational amplifier, and its input end is coupled to the output end of the first isolation amplifier, and is used to convert the fully differential analog signal output by the first isolation amplifier into a 3.3V internally isolated sampling signal suitable for the ADC pin of the microcontroller.

[0012] Furthermore, the second differential conversion circuit includes a second op amp and a peripheral resistor coupled to the second op amp, and its input end is coupled to the output end of the second isolation amplifier, and is used to convert the fully differential analog signal output by the second isolation amplifier into a 3.3V internal bus sampling signal suitable for the ADC pin of the microcontroller.

[0013] The beneficial effects of the utility model are as follows:

[0014] 1) Using an isolated amplifier circuit to sample the monitored voltage, isolated measurement is achieved without the need for an additional isolated power supply on the high-voltage side. The peripheral circuitry is simple, requiring only a few voltage-divider resistors, an isolation amplifier, and an op amp for accurate insulation monitoring.

[0015] 2) The isolation amplifier can provide an insulation voltage of up to 5000Vrms, which is better than the ordinary optocoupler isolation effect.

[0016] 3) The circuit has low offset error and drift, and adopts 1:1 data acquisition after voltage division, with high sampling accuracy.

[0017] 4) While performing insulation monitoring, the DC bus voltage can also be monitored simultaneously to obtain loop compensation characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the circuit principle of an isolated insulation monitoring circuit embodiment of the present utility model. DETAILED DESCRIPTION

[0019] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0020] The single resistor in the circuit diagram can be replaced by multiple resistors in series or in parallel in the actual circuit, but the present invention is not limited thereto. The high-voltage capacitor can also be replaced by multiple high-voltage capacitors in series or in parallel.

[0021] In addition, the terms "first," "second," and so on, used in this utility model are for descriptive purposes only and do not specifically refer to an order or sequence, nor are they intended to limit this utility model. They are merely used to distinguish components or operations described with the same technical terms, and should not be understood as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one of such features.

[0022] See also Figure 1 An embodiment of the present invention provides an isolated insulation monitoring circuit, comprising a bridge switch circuit located on the high-voltage side, a first differential conversion circuit and a control unit located on the low-voltage side, and an isolated amplifier (I) coupled to the bridge switch circuit and the differential conversion circuit. In this embodiment, the control unit (MCU) is preferably a single-chip microcomputer. The bridge switch circuit includes two high-resistance voltage dividers and two high-voltage relays. The first high-resistance voltage divider RstP and the first high-voltage relay SP form a first branch connecting the high-voltage DC positive voltage (HV DC+) to be monitored with the first input terminal of the isolated amplifier (I). The second high-resistance voltage divider RstN and the second high-voltage relay SN form a second branch connecting the high-voltage DC negative voltage (HV DC-) to be monitored with the first input terminal of the isolated amplifier (I). During measurement, the first high-voltage relay SP and the second high-voltage relay SN of the two branches are turned on at different times in response to an enable signal from the control unit. The second input terminal of the isolated amplifier (I) is coupled to the protective ground (PE). A first voltage detection resistor RinAMC1 is provided between the first and second input terminals to obtain an insulation sampling voltage. The obtained insulation sampling voltage is output through the output end to the first differential conversion circuit composed of operational amplifier 1 and peripheral resistors. The first differential conversion circuit converts the fully differential analog signal output by the isolation amplifier 1 into a 3.3V internal insulation sampling signal suitable for the ADC pin of the microcontroller.

[0023] As a further preferred embodiment, the isolated insulation monitoring circuit in this embodiment also includes a bus detection circuit, specifically comprising a third high-resistance voltage divider RstDC, an isolated amplifier 2, and a second differential conversion circuit. The first input of the isolated amplifier 2 is coupled to the monitored high-voltage DC positive voltage HV DC+ via the third high-resistance voltage divider RstDC, and the second input is coupled to the monitored high-voltage DC negative voltage HV DC-. A second voltage detection resistor RinAMC2 is provided between the first and second inputs to obtain a bus sampling voltage. The output of the isolated amplifier 2 is coupled to a control unit via the second differential conversion circuit for outputting a bus sampling signal to the control unit. The second differential conversion circuit includes an op amp 2 and a peripheral resistor coupled to the op amp 2, and is configured to convert the fully differential analog signal output by the isolated amplifier 2 into a 3.3V internal bus sampling signal suitable for the ADC pin of the microcontroller.

[0024] As a preferred implementation scheme, in this embodiment, the first isolation amplifier and the second isolation amplifier are both isolation amplifiers with a fixed gain of 1, which can restore the sampled voltage to the secondary in a 1:1 ratio.

[0025] The following combination Figure 1 The working principle of the isolated insulation monitoring circuit of the present invention is further explained.

[0026] The first high-voltage relay SP and the second high-voltage relay SN act as isolation switches, temporarily opening the isolation barrier via a known resistor divider path. The first high-resistance voltage divider RstP and the second high-resistance voltage divider RstN are high-resistance voltage dividers with an accuracy of at least ±1%, switching between the monitored high-voltage DC positive voltage HV DC+ and protective earth ground (PE), and the monitored high-voltage DC negative voltage HV DC– and protective earth ground (PE), respectively. RinAMC1 and RinAMC2 are voltage sense resistors that provide scaled-down voltage inputs to the reinforced isolation amplifier. During measurement, the two resistor branches are connected at different times. The current across the isolation barrier is proportional to the bus voltage, the isolation resistance, and the connected resistor branch.

[0027] Under normal conditions, the isolation barrier is intact, and the high-resistance voltage dividers RstP and RstN between the monitored HVDC+ and HVDC– voltages and the protective earth (PE) are in the megaohm range. Therefore, only a small current flows through these high-resistance voltage dividers, resulting in a very low input voltage signal for the isolation amplifier. The control unit (MCU) controls the closing and opening of relays SP and SN by enabling relays SP and SN, sequentially connecting relays RstP and RstN to determine the voltage between the monitored HVDC+ and HVDC– voltages and the protective earth (PE). This voltage is then fed to the MCU's analog-to-digital sampling port via an isolated amplifier circuit and a differential-to-single-ended converter. This voltage is then used to calculate the system's isolation resistance and, therefore, to determine the system's insulation condition. If the insulation performance of the isolation barrier degrades during insulation testing, the current through the voltage detection resistor RinAMC1 will increase, causing the input voltage signal of the isolation amplifier to increase, which in turn causes the insulation sampling signal to become abnormal, and the control unit (MCU) will output an alarm signal.

[0028] On the other hand, the MCU can also perform real-time sampling and monitoring of the bus voltage through the bus detection circuit.

[0029] The isolated insulation monitoring circuit of the utility model does not require a bulky transformer, and during normal operation, only a small amount of power is consumed by the relay.

[0030] The embodiments of the present invention are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An isolated insulation monitoring circuit, characterized in that: It includes a bridge switching circuit located on the high-voltage side, a first differential conversion circuit and a control unit located on the low-voltage side, and a first isolation amplifier coupled to the bridge switching circuit and the differential conversion circuit; wherein the bridge switching circuit includes a high-resistance voltage divider and a high-voltage relay, the first input end of the first isolation amplifier is coupled to the monitored high-voltage DC voltage via the high-voltage relay and the high-resistance voltage divider, the second input end is coupled to protective grounding, and a first voltage detection resistor is provided between the first input end and the second input end to obtain an insulation sampling voltage, the output end is coupled to the control unit via the first differential conversion circuit, and is used to output an insulation sampling signal to the control unit, and the control unit is also used to output a control signal to control the on and off of the high-voltage relay, and the high-voltage relay is only turned on during measurement.

2. The isolated insulation monitoring circuit according to claim 1, wherein: The bridge switching circuit includes two high-resistance voltage dividers and two high-voltage relays, wherein the first high-resistance voltage divider and the first high-voltage relay constitute a first branch connecting the high-voltage DC positive voltage to be monitored and the first isolation amplifier, and the second high-resistance voltage divider and the second high-voltage relay constitute a second branch connecting the high-voltage DC negative voltage to be monitored and the first isolation amplifier; during measurement, the two branches are connected at different times.

3. The isolated insulation monitoring circuit according to claim 2, wherein: It also includes a bus detection circuit, which includes a third high-resistance voltage divider, a second isolation amplifier and a second differential conversion circuit, wherein the first input terminal of the second isolation amplifier is coupled to the high-voltage DC positive voltage to be monitored via the third high-resistance voltage divider, and the second input terminal is coupled to the high-voltage DC negative voltage to be monitored, and a second voltage detection resistor is provided between the first input terminal and the second input terminal to obtain a bus sampling voltage, and the output terminal is coupled to the control unit via the second differential conversion circuit for outputting a bus sampling signal to the control unit.

4. The isolated insulation monitoring circuit according to claim 3, wherein: The first isolation amplifier and the second isolation amplifier are both isolation amplifiers with a fixed gain of 1.

5. The isolated insulation monitoring circuit according to any one of claims 3 or 4, characterized in that: The control unit is a single chip microcomputer.

6. The isolated insulation monitoring circuit according to claim 5, characterized in that: The first differential conversion circuit includes a first operational amplifier and a peripheral resistor coupled to the first operational amplifier, and its input end is coupled to the output end of the first isolation amplifier, and is used to convert the fully differential analog signal output by the first isolation amplifier into a 3.3V internally isolated sampling signal suitable for the ADC pin of the microcontroller.

7. The isolated insulation monitoring circuit according to claim 5, wherein: The second differential conversion circuit includes a second operational amplifier and a peripheral resistor coupled to the second operational amplifier, and its input end is coupled to the output end of the second isolation amplifier, and is used to convert the fully differential analog signal output by the second isolation amplifier into a 3.3V internal bus sampling signal suitable for the ADC pin of the microcontroller.

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