Current sampling circuit of shunt

Abstract

The invention discloses a shunt current sampling circuit, which comprises a first shunt, a first differential amplification circuit, a capacitor charging circuit connected with a second shunt in series, a voltage drop acquisition circuit and a subtraction circuit, the first differential amplification circuit is used for collecting and outputting a voltage drop on the first shunt as a first voltage output, an output end of the first differential amplification circuit is connected to the capacitor charging circuit, and the voltage drop collection circuit is used for collecting and outputting a voltage drop on the second shunt as a second voltage output. The subtraction circuit receives the first voltage output and the second voltage output and subtracts the second voltage output from the first voltage output as an output of the shunt current sampling circuit. According to the invention, the voltage drop caused by the inductance effect of the shunt can be offset, and the current of an actual main loop is truly restored.

Description

Technical Field

[0001] The present invention relates to a shunt current sampling circuit, belonging to the technical field of current measurement. Background Art

[0002] In the occasion of electrical large current sampling, such as the total current sampling of electric vehicle output, the total current sampling of energy storage cabinet output, etc., it is necessary to accurately collect current data. On the one hand, it is displayed to users to understand the power consumption situation and calculate the remaining battery power. On the second hand and most importantly, it is used for protection. Especially when the output is short-circuited, there may be a huge current. It is necessary to accurately sample and make protection actions in real time. Generally, a shunt with a fixed small resistance value is used to sample such current sampling current. Compared with using Hall or other electromagnetic sensors for sampling, it has the advantages of high reliability, low cost, and no magnetic saturation.

[0003] A typical shunt sampling circuit is as Figure 1 shown. Since the current sampled by such a circuit is very large, generally up to 2000 - 3000A, the resistance value of the shunt 100 is very small. For example, if 0.5V / 1000A (i.e., a resistance value of 0.5mΩ) is adopted, under the action of the main circuit current, a certain voltage drop will be generated on the shunt. Then, a differential amplifier circuit is used to convert the voltage drop value without a common point into voltage data that can be referenced by the subsequent circuit. Among them, the subsequent AD1 data point can be sampled by a single-chip microcomputer or input to a protection circuit for judgment, and then a protection action is generated.

[0004] However, the actual circuit cannot be so ideal. Although the actual shunt 100 is a basically constant resistance device, since the shunt 100 bears the impact of a huge current, especially when the large current is short-circuited, such as when the electric vehicle battery is short-circuited, the current on the shunt 100 may rapidly rise from 0 to several thousand amperes in this process, and this process occurs only within 1ms. Under such a huge current impact, the originally weak inductance effect of the shunt 100 will also generate a voltage drop of the same order of magnitude as the voltage drop caused by the current on it. As Figure 2 shown: when the current suddenly rises from 0 to 3000A within 1ms, the actually sampled voltage value of the sampling circuit = 0.0005 * 3000 + di / dt * L. Although the inductance effect of the shunt 100 is very small, such as only 0.4uH, the current voltage drop contributed by the resistance of the shunt 100 is 1.5V, and the voltage drop value of the shunt 100 contributed by the inductance effect is 1.2V. The total voltage drop is 2.7V. This voltage drop is used to infer the main circuit current without the inductance effect = 2.7 / 0.0005 = 5400A. If the protection circuit is set to act when the current is 5000A, then actually when the current is 3000A, the protection circuit has already malfunctioned. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the object of the present invention is to provide a shunt current sampling circuit, aiming to solve the problem that the additional voltage drop caused by the inductance effect of the shunt itself due to the instantaneous large current impact results in the main circuit current inferred from the measured voltage drop being far greater than the actual current, generating a huge measurement error.

[0006] The technical solution of the present invention is as follows: A shunt current sampling circuit includes a first shunt, a first differential amplifier circuit, a capacitor charging circuit in series with a second shunt, a voltage drop acquisition circuit, and a subtraction circuit. The first shunt is connected in series to the main circuit to be sampled. The first differential amplifier circuit is used to collect and output the voltage drop on the first shunt as a first voltage output. The output end of the first differential amplifier circuit is connected to the capacitor charging circuit. The voltage drop acquisition circuit is used to collect and output the voltage drop on the second shunt as a second voltage output. The subtraction circuit receives the first voltage output and the second voltage output and subtracts the second voltage output from the first voltage output as the output of the shunt current sampling circuit.

[0007] Further, an operational amplifier follower circuit is provided between the output end of the first differential amplifier circuit and the capacitor charging circuit.

[0008] Further, the voltage drop acquisition circuit is a second differential amplifier circuit.

[0009] Further, the subtraction circuit is a third differential amplifier circuit.

[0010] Further, the first differential amplifier circuit includes a first operational amplifier. The “+” input terminal of the first operational amplifier is grounded through a first resistor and connected to the first end of the first shunt through a second resistor as the first input terminal of the first differential amplifier circuit. The “-” input terminal of the first operational amplifier is connected to the second end of the first shunt through a fifth resistor as the second input terminal of the first differential amplifier circuit. The “-” input terminal of the first operational amplifier is connected to the output end of the first operational amplifier through a sixth resistor. The output end of the first operational amplifier serves as the output of the first differential amplifier circuit.

[0011] Further, a first capacitor is connected between the first input terminal and the second input terminal of the first differential amplifier circuit, and a series circuit of a third resistor and a fourth resistor is connected. The connection point of the third resistor and the fourth resistor is grounded.

[0012] Further, the second differential amplifier circuit includes a second operational amplifier. The "+" input terminal of the second operational amplifier is grounded through a tenth resistor and connected to the first end of a second shunt resistor through an eleventh resistor as the first input terminal of the second differential amplifier circuit. The "-" input terminal of the second operational amplifier is connected to the second end of the second shunt resistor through a seventeenth resistor as the second input terminal of the second differential amplifier circuit. The "-" input terminal of the second operational amplifier is connected to the output terminal of the second operational amplifier through an eighteenth resistor, and the output terminal of the second operational amplifier serves as the output of the second differential amplifier circuit.

[0013] Further, a fourth capacitor is connected between the first input terminal and the second input terminal of the second differential amplifier circuit, and a series circuit of a thirteenth resistor and a sixteenth resistor is connected, and the connection point of the thirteenth resistor and the sixteenth resistor is grounded.

[0014] Further, the third differential amplifier circuit includes a third operational amplifier. The "+" input terminal of the third operational amplifier is grounded through a seventh resistor and connected to the output terminal of the first differential amplifier circuit through an eighth resistor as the first input terminal of the third differential amplifier circuit. The "-" input terminal of the third operational amplifier is connected to the output terminal of the voltage drop acquisition circuit through a fourteenth resistor as the second input terminal of the third differential amplifier circuit. The "-" input terminal of the third operational amplifier is connected to the output terminal of the third operational amplifier through a fifteenth resistor, and the output terminal of the third operational amplifier serves as the output of the third differential amplifier circuit.

[0015] Further, a third capacitor is connected between the first input terminal and the second input terminal of the third differential amplifier circuit, and a series circuit of a ninth resistor and a twelfth resistor is connected, and the connection point of the ninth resistor and the twelfth resistor is grounded.

[0016] The advantages of the present invention compared with the prior art are as follows:

[0017] The present invention can cancel out the voltage contribution of di / di*L caused by the inductance effect of the shunt resistor from the final output when the large current on the shunt resistor rises rapidly, so as to truly restore the current of the actual main circuit. When applied to the protection circuit, it can accurately cancel out the voltage drop caused by the inductance effect of the shunt resistor in the main circuit, avoid unnecessary misprotection actions, and ensure the safety and reliability of the equipment. At the same time, the circuit structure is simple and reasonable, easy to implement, and the cost is very low. Description of the Drawings

[0018] Figure 1 It is a shunt resistor current sampling circuit diagram of the prior art.

[0019] Figure 2 It is a circuit schematic diagram of the shunt resistor current sampling circuit of the prior art considering the inductance effect.

[0020] Figure 3 It is a shunt resistor current sampling circuit diagram of the embodiment. Detailed implementation manners

[0021] The present invention will be further described below in conjunction with embodiments, but it is not intended to limit the present invention.

[0022] Please refer to Figure 3 As shown, the shunt current sampling circuit of this embodiment includes a first shunt 1, a first differential amplification circuit, an operational amplifier follower circuit, a capacitor charging circuit 3 in series with a second shunt 2, a voltage drop acquisition circuit, and a subtraction circuit. Among them, the first shunt 1 is connected in series in the main circuit to be sampled, and two input terminals of the first differential amplification circuit are connected to both ends of the first shunt 1 for collecting the voltage drop formed by the large current in the main circuit on the first shunt 1.

[0023] The specific structure of the first differential amplification circuit includes an operational amplifier U1. The “+” input terminal of the operational amplifier U1 is grounded through a resistor R1 and connected to the first end of the first shunt 1 through a resistor R2 as the first input terminal of the first differential amplification circuit. The “-” input terminal of the operational amplifier U1 is connected to the second end of the first shunt 1 through a resistor R5 as the second input terminal of the first differential amplification circuit. The main circuit current flows from the first end of the first shunt 1 to the second end of the first shunt 1. A capacitor C1 is connected between the first end and the second end of the first shunt 1, and a series circuit of a resistor R3 and a resistor R4 is connected. The connection point of the resistor R3 and the resistor R4 is grounded. The “-” input terminal of the operational amplifier U1 is connected to the output terminal of the operational amplifier U1 through a resistor R6, and the output voltage AD1 of the operational amplifier U1 is output as the output of the first differential amplification circuit. When the main circuit receives an instantaneous large current impact, the output voltage AD1 includes the voltage drop caused by the inductance effect of the first shunt 1.

[0024] The output terminal of the first differential amplification circuit is first connected to the operational amplifier follower circuit. The operational amplifier follower circuit is connected to the capacitor charging circuit 3 in series with the second shunt 2. The operational amplifier follower circuit includes an operational amplifier U2. The “+” input terminal of the operational amplifier U2 is connected to the output terminal of the first differential amplification circuit, and the “-” input terminal of the operational amplifier U2 is connected to the output terminal of the operational amplifier U2. The output terminal of the operational amplifier U2 is connected to the second shunt 2, and the second shunt 2 is then grounded through a capacitor C2.

[0025] The voltage drop acquisition circuit is used to acquire the voltage drop across the second shunt 2, that is, the two input terminals of the voltage drop acquisition circuit are connected to both ends of the second shunt 2. In this embodiment, the voltage drop acquisition circuit is the second differential amplifier circuit 4. The second differential amplifier circuit 4 is similar in structure to the first differential amplifier circuit. Specifically, it includes an operational amplifier U4. The "+" input terminal of the operational amplifier U4 is grounded through a resistor R10 and connected to the connection point between the second shunt 2 and the output terminal of the operational amplifier U2 through a resistor R11 as the first input terminal of the second differential amplifier circuit. The "-" input terminal of the operational amplifier U4 is connected to the connection point between the second shunt 2 and the capacitor C2 through a resistor R17 as the second input terminal of the second differential amplifier circuit. A capacitor C4 is connected between both ends of the second shunt 2, and a series circuit of a resistor R13 and a resistor R16 is connected. The connection point of the resistor R13 and the resistor R16 is grounded. The "-" input terminal of the operational amplifier U4 is connected to the output terminal of the operational amplifier U4 through a resistor R18, and the output terminal of the operational amplifier U4 outputs a voltage DIR.

[0026] The subtraction circuit is used to subtract the output voltage AD1 and the output voltage DIR to obtain a signal without the voltage drop caused by the inductance effect of the first shunt 1. In this embodiment, the subtraction circuit is the third differential amplifier circuit 5. The third differential amplifier circuit 5 is similar in structure to the first differential amplifier circuit. Specifically, it includes an operational amplifier U3. The "+" input terminal of the operational amplifier U3 is grounded through a resistor R7 and connected to the output terminal of the operational amplifier U1 through a resistor R8 as the first input terminal of the third differential amplifier circuit to receive the output voltage AD1. The "-" input terminal of the operational amplifier U3 is connected to the output terminal of the operational amplifier U4 through a resistor R14 as the second input terminal of the third differential amplifier circuit to receive the output voltage DIR. A capacitor C3 is connected between the output terminal of the operational amplifier U1 and the output terminal of the operational amplifier U4, and a series circuit of a resistor R9 and a resistor R12 is connected. The connection point of the resistor R9 and the resistor R12 is grounded. The "-" input terminal of the operational amplifier U3 is connected to the output terminal of the operational amplifier U3 through a resistor R15, and the output terminal of the operational amplifier U3 outputs a voltage AD2 as the final current sampling output supply.

[0027] The working principle of the present invention is as follows: First, the operational amplifier U2 is used as a follower for impedance matching, and the output of the operational amplifier U2 is given to a capacitor charging circuit 3, in which a second shunt 2 is connected in series to sample the charging current. The charging current value of this circuit is equal to du / dt*C, and du / dt is the part caused by di / dt*L in the front-end main circuit. Therefore, the voltage value on the second shunt 2 is proportional to the voltage drop caused by the inductance effect of the first shunt 1 in the front-end main circuit. This voltage value passes through a voltage drop acquisition circuit (the second differential amplification circuit 4) to obtain a voltage value DIR proportional to di / dt*L. The subtraction circuit (the third differential amplification circuit 5) is an amplification circuit of AD1 - DIR, that is, subtracting DIR (the voltage value proportional to di / dt*L) from the total voltage value of the first shunt 1 sampled originally (including the current voltage drop of the resistor and the voltage drop of the inductance effect). As long as the resistance value of the second shunt 2, the capacitance value of the capacitor C2, and the amplification factors of the second differential amplification circuit 4 and the third differential amplification circuit 5 are adjusted, the voltage drop caused by the inductance effect of the first shunt 1 in the main circuit can always be accurately deducted, and the real current situation can be accurately restored.

[0028] Taking the example that the first shunt 1 in the background technology has an inductance effect of 0.4uH, if the main circuit current rises from 0 to 3000A within 1ms at the moment of 1ms, the voltage increment d AD1 / dt on AD1 is the increment of the resistance voltage drop + inductance voltage drop of the first shunt 1 in the main circuit, and this increment is also the increment of the voltage on the capacitor C2; so:

[0029]

[0030] Since the main circuit current I1 is rising rapidly at the moment of 1ms and is considered to be linearly rising (slope) within a very short time, so I1 "" = 0. Then And the current on the second shunt 2 is the change rate of the voltage across the capacitor C2 multiplied by So

[0031]

[0032] Another

[0033] is the resistance of the second shunt 2. The right side of the equal sign is exactly the voltage drop caused by the inductance of the first shunt 1. Later, the third differential amplification circuit 5 can subtract that is, equal to subtracting the voltage drop caused by the inductance,

[0034] In the above formula, as long as Therefore, by setting the resistance value of the second shunt 2 to 2 kΩ, the capacitance value C2 to 0.4 μF, and the amplification factors of the first differential amplifier circuit, the second differential amplifier circuit 4, and the first differential amplifier circuit 5 all to 1, this function can be achieved.

Claims

1. A shunt current sampling circuit, characterized in that, It includes a first shunt, a first differential amplifier circuit, a capacitor charging circuit in series with a second shunt, a voltage drop acquisition circuit, and a subtraction circuit. The first shunt is connected in series to the main circuit to be sampled. The first differential amplifier circuit is used to collect and output the voltage drop on the first shunt as a first voltage output. The output terminal of the first differential amplifier circuit is connected to the capacitor charging circuit. The voltage drop acquisition circuit is used to collect and output the voltage drop on the second shunt as a second voltage output. The subtraction circuit receives the first voltage output and the second voltage output and subtracts the second voltage output from the first voltage output as the output of the shunt current sampling circuit.

2. The shunt current sampling circuit according to claim 1, wherein An operational amplifier follower circuit is provided between the output terminal of the first differential amplifier circuit and the capacitor charging circuit.

3. The shunt current sampling circuit according to claim 1, wherein The voltage drop acquisition circuit is a second differential amplifier circuit.

4. The shunt current sampling circuit according to claim 1, wherein The subtraction circuit is a third differential amplifier circuit.

5. The shunt current sampling circuit according to claim 1, wherein The first differential amplifier circuit includes a first operational amplifier. The "+" input terminal of the first operational amplifier is grounded through a first resistor and connected to the first end of the first shunt through a second resistor as the first input terminal of the first differential amplifier circuit. The "-" input terminal of the first operational amplifier is connected to the second end of the first shunt through a fifth resistor as the second input terminal of the first differential amplifier circuit. The "-" input terminal of the first operational amplifier is connected to the output terminal of the first operational amplifier through a sixth resistor. The output terminal of the first operational amplifier serves as the output of the first differential amplifier circuit.

6. The shunt current sampling circuit according to claim 5, wherein A first capacitor is connected between the first input terminal and the second input terminal of the first differential amplifier circuit, and a series circuit of a third resistor and a fourth resistor is connected, and the connection point of the third resistor and the fourth resistor is grounded.

7. The shunt current sampling circuit according to claim 3, wherein The second differential amplifier circuit includes a second operational amplifier. The "+" input terminal of the second operational amplifier is grounded through a tenth resistor and connected to the first end of the second shunt through an eleventh resistor as the first input terminal of the second differential amplifier circuit. The "-" input terminal of the second operational amplifier is connected to the second end of the second shunt through a seventeenth resistor as the second input terminal of the second differential amplifier circuit. The "-" input terminal of the second operational amplifier is connected to the output terminal of the second operational amplifier through an eighteenth resistor. The output terminal of the second operational amplifier serves as the output of the second differential amplifier circuit.

8. The shunt current sampling circuit according to claim 7, wherein A fourth capacitor is connected between the first input terminal and the second input terminal of the second differential amplifier circuit, and a series circuit of a thirteenth resistor and a sixteenth resistor is connected, and the connection point of the thirteenth resistor and the sixteenth resistor is grounded.

9. The shunt current sampling circuit according to claim 4, wherein The third differential amplifier circuit includes a third operational amplifier. The "+" input terminal of the third operational amplifier is grounded through a seventh resistor and connected to the output terminal of the first differential amplifier circuit through an eighth resistor as the first input terminal of the third differential amplifier circuit. The "-" input terminal of the third operational amplifier is connected to the output terminal of the voltage drop acquisition circuit through a fourteenth resistor as the second input terminal of the third differential amplifier circuit. The "-" input terminal of the third operational amplifier is connected to the output terminal of the third operational amplifier through a fifteenth resistor. The output terminal of the third operational amplifier serves as the output of the third differential amplifier circuit.

10. The shunt current sampling circuit according to claim 9, wherein, A third capacitor is connected between the first input terminal and the second input terminal of the third differential amplifier circuit, and a series circuit connecting a ninth resistor and a twelfth resistor is connected, and the connection point of the ninth resistor and the twelfth resistor is grounded.

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