Insulation detection circuit of direct current charger

Abstract

The utility model discloses an insulation detection circuit of a direct current charger. The insulation detection circuit comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a first switch, a second switch and a follower, the first end of the first resistor is connected with the direct current output positive port, the second end of the first resistor is connected with the first end of the first switch, and the second end of the first switch is connected with the first end of the second resistor and is connected with the input end of the follower; the second end of the second resistor is connected with the first end of the third resistor and is grounded; the second end of the third resistor is connected with the first end of the second switch, the second end of the second switch is connected with the first end of the fourth resistor, and the second end of the fourth resistor is connected with the direct current output negative port; and the output end of the follower is connected with the micro-control unit. According to the scheme, the sampling voltage has no negative voltage, isolation is not needed, the circuit is simple, precision is high, and cost is low.

Description

Technical Field

[0001] The present application relates to the technical field of electric vehicles, and in particular to an insulation detection circuit of a DC charger. Background Art

[0002] With the popularization of electric vehicles, DC charging piles are being deployed on a large scale. DC charging piles are generally used in harsh environments and have high output voltages. The cables and insulation materials of the piles are prone to aging and damage, affecting the safety of the entire charging system.

[0003] At present, the insulation detection circuit for DC charging piles uses isolation detection due to safety issues. It requires the use of isolated power supplies and isolated operational amplifiers. The circuit is complex, the accuracy is low, and the cost is increased. Utility Model Content

[0004] An embodiment of the present application provides an insulation detection circuit for a DC charger.

[0005] An insulation detection circuit of a DC charger provided by an embodiment of the present application includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a first switch, a second switch, and a follower;

[0006] The first end of the first resistor is connected to the DC output positive port, the second end of the first resistor is connected to the first end of the first switch, the second end of the first switch is connected to the first end of the second resistor, and is connected to the input end of the follower;

[0007] The second end of the second resistor is connected to the first end of the third resistor and is grounded; the second end of the third resistor is connected to the first end of the second switch, the second end of the second switch is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the DC output negative port;

[0008] The output end of the follower is connected to the micro control unit.

[0009] In one embodiment, the insulation detection circuit further includes a filter circuit, and the filter circuit is connected to the output end of the follower and the micro control unit respectively.

[0010] In one embodiment, the filtering circuit includes a fifth resistor and a capacitor;

[0011] A first end of the fifth resistor is connected to the output end of the follower;

[0012] The second end of the fifth resistor is connected to the first end of the capacitor and is also connected to the micro control unit;

[0013] The second terminal of the capacitor is connected to the ground.

[0014] In one embodiment, the output terminal of the follower is connected to an analog-to-digital conversion port of a micro control unit.

[0015] Compared with the prior art, the present application has the following beneficial effects: the sampling voltage does not require negative voltage, only positive voltage is sufficient, that is, the sampling power supply only requires positive power supply, which is simple to implement.

[0016] In addition, the insulation detection circuit of the DC charger provided in the embodiment of the present application can realize insulation detection in the signal conversion part through the first resistor, the second resistor, the third resistor, the fourth resistor, the first switch, the second switch and the follower, that is, the non-isolated detection circuit, and has a simple circuit structure, high precision and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of an insulation detection circuit of a DC charger provided in an embodiment of the present application;

[0019] Figure 2 An equivalent circuit 1 of the insulation detection circuit of the DC charger provided in the embodiment of the present application;

[0020] Figure 3 This is the second equivalent circuit of the insulation detection circuit of the DC charger provided in the embodiment of the present application. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are 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 device or element referred to 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.

[0023] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0024] 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0025] like Figure 1 As shown, it shows a structural schematic diagram of an insulation detection circuit of a DC charger provided in an embodiment of the present application.

[0026] Reference Figure 1 , an insulation detection circuit of a DC charger provided by an embodiment of the present application includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a first switch K1, a second switch K2, and a follower U1;

[0027] A first end of the first resistor R1 is connected to the DC output positive port VOUT+, a second end of the first resistor R1 is connected to a first end of the first switch K1, a second end of the first switch K1 is connected to a first end of the second resistor R2, and is connected to an input end of the follower U1;

[0028] The second end of the second resistor R2 is connected to the first end of the third resistor R3 and is connected to the ground PE; the second end of the third resistor R3 is connected to the first end of the second switch K2, the second end of the second switch K2 is connected to the first end of the fourth resistor R4, and the second end of the fourth resistor R4 is connected to the DC output negative port VOUT-;

[0029] The output end of the follower U1 is connected to the micro control unit MCU.

[0030] In one embodiment, the insulation detection circuit further includes a filter circuit, and the filter circuit is connected to the output end of the follower U1 and the micro control unit MCU respectively.

[0031] In one embodiment, continue to refer to Figure 1 , the filtering circuit includes a fifth resistor R5 and a capacitor C1;

[0032] A first end of the fifth resistor R5 is connected to the output end of the follower U1;

[0033] The second end of the fifth resistor R5 is connected to the first end of the capacitor C1 and is also connected to the micro control unit MCU;

[0034] The second terminal of the capacitor C1 is connected to the ground PE.

[0035] In one embodiment, continue to refer to Figure 1 The output end of the follower U1 is connected to the analog-to-digital conversion port AD (Analog to Digital) of the microcontroller unit MCU.

[0036] like Figure 1 As shown, Rx is the equivalent insulation resistance of the DC output positive port VOUT+ to the earth PE; Ry is the equivalent insulation resistance of the DC output negative port VOUT- to the earth PE. The voltage between the DC output positive port VOUT+ and the DC output negative port VOUT- is Vout; the input voltage of the follower U1 is Vin, and the output voltage is Vo. First close the first switch K1, and the second switch K2 is disconnected. The impedance of VOUT+ to the earth PE is Rx / / (R1+R2), and the impedance of VOUT- to the earth PE is still Ry. The voltage Vin on the sampling resistor R2 is sent to the AD port of the MCU after passing through the follower U1 and the RC filter circuit. At this time, the sampled voltage is Vin1. Then close the second switch K2, and the first switch K1 continues to remain closed. The impedance of VOUT+ to the earth PE is still Rx / / (R1+R2), and the impedance of VOUT- to the earth PE is Ry / / (R3+R4). The voltage Vin on the resistor R2 is sampled again, and after being filtered by the follower and RC, it is sent to the AD of the MCU. The sampled voltage at this time is Vin2. The resistance values ​​of Rx and Ry can be derived by sampling the voltage twice.

[0037] The specific steps to derive the resistance values ​​of Rx and Ry are as follows:

[0038] To simplify the derivation, R1=R4, R2=R3, and other values ​​are similar.

[0039] When the first switch K1 is closed and the second switch K2 is open, the equivalent circuit is as follows: Figure 2 shown.

[0040] The voltage of VOUT+ to the ground PE is Vp1:

[0041] Vp1=Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+Ry} (1)

[0042] The voltage across the second resistor R2 is now Vin1:

[0043] Vin1=Vp1×R2 / (R1+R2)

[0044] =Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+Ry}×R2 / (R1+R2)Vo1=Vin1=Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+Ry}×R2 / (R1+R2) (2)

[0046] When the second switch K2 is closed and the first switch K1 is still closed, the equivalent circuit is as follows: Figure 3 shown.

[0047] The voltage of VOUT+ to the ground PE is Vp2:

[0048] Vp2=Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+[Ry / / (R1+R2)]}(3)

[0049] The voltage across the second resistor R2 is now Vin2:

[0050] Vin2=Vp2×R2 / (R1+R2)

[0051] =Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+[Ry / / (R1+R2)]}×R2 / (R1+R2)

[0052] Vo2=Vin2

[0053] =Vout×[Rx / / (R1+R2)] / {[Rx / / (R1+R2)]+[Ry / / (R1+R2)]}×R2 / (R1+R2)(4)

[0054] In the above formula, Vout is the voltage between VOUT+ and VOUT-, which has been sampled by the system and is a known condition; R1 and R2 are known parameters of the circuit, and R1=kR2 is set, where k is the proportional coefficient of R1 / R2; Vo1 and Vo2 are AD sampling values, which are known conditions; only Rx and Ry are unknown.

[0055] Substituting the above known conditions into formulas (2) and (4), Rx and Ry can be derived.

[0056] The derivation results are as follows:

[0057] Rx=Vout×(1+k) 2 ×R2×(Vo1-Vo2) / [Vout 2 -2VoutVo1(1+k)+Vo1Vo2(1+k) 2 ]

[0058] Ry=Vout×[(1+k)×R2×(Vo1-Vo2)] / {Vo1×[Vout-Vo2(1+k)]}

[0059] By using the insulation detection circuit of the DC charger provided in the embodiment of the present application, the sampling voltage Vin does not need a negative voltage, but only a positive voltage, that is, the sampling power supply only needs a positive power supply, which is simple to implement.

[0060] In addition, the insulation detection circuit of the DC charger provided in the embodiment of the present application can realize insulation detection in the signal conversion part through the first resistor, the second resistor, the third resistor, the fourth resistor, the first switch, the second switch and the follower, that is, the non-isolated detection circuit, and has a simple circuit structure, high precision and low cost.

[0061] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An insulation detection circuit for a DC charger, characterized in that: The insulation detection circuit comprises: a first resistor, a second resistor, a third resistor, a fourth resistor, a first switch, a second switch, and a follower; The first end of the first resistor is connected to the DC output positive port, the second end of the first resistor is connected to the first end of the first switch, the second end of the first switch is connected to the first end of the second resistor and is connected to the input end of the follower; The second end of the second resistor is connected to the first end of the third resistor and is grounded; the second end of the third resistor is connected to the first end of the second switch, the second end of the second switch is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the DC output negative port; The output end of the follower is connected to the micro control unit.

2. The insulation detection circuit according to claim 1, characterized in that: The insulation detection circuit also includes a filter circuit, and the filter circuit is connected to the output end of the follower and the micro control unit respectively.

3. The insulation detection circuit according to claim 2, characterized in that: The filtering circuit includes a fifth resistor and a capacitor; The first end of the fifth resistor is connected to the output end of the follower; The second end of the fifth resistor is connected to the first end of the capacitor and is also connected to the micro control unit; The second terminal of the capacitor is connected to the ground.

4. The insulation detection circuit according to claim 1, characterized in that: The output end of the follower is connected to the analog-to-digital conversion port of the micro control unit.

Images